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Rivers are important sites for carbon (C) transport and critical components of the global C cycle that is currently not well constrained. However, little is known about C species’ longitudinal and temporal changes in large tropical rivers. The Usumacinta River is Mexico’s main lotic system and the tenth largest in North America. Being a tropical river, it has a strong climatic seasonality. This study aims to evaluate how organic (DOC and POC) and inorganic (DIC and PIC) carbon change spatially and seasonally along the Usumacinta River (medium and lower basin) in rainy (RS-2017) and dry (DS-2018) seasons and to estimate C fluxes into the southern Gulf of Mexico. Concentrations of DOC, POC, DIC, and PIC ranged from 0.88 to 7.11 mg L−1, 0.21 to 3.78 mg L−1, 15.59 to 48.27 mg L−1 and 0.05 to 1.51 mg L−1, respectively. DOC was the dominant organic species (DOC/POC > 1). It was ~doubled in RS and showed a longitudinal increase, probably through exchange with wetlands and floodplains. Particulate carbon showed a positive relationship with the total suspended solids, suggesting that in RS, it derived from surface erosion and runoff in the watershed. DIC is reported for the first time as the highest concentration measured in tropical rivers in America. It was higher in the dry season without a longitudinal trend. The C mass inflow–outflow balance in the RS suggested net retention (DOC and POC sink) in floodplains. In contrast, in the DS, the balance suggested that floodplains supply (C source) autochthonous DOC and POC. The lower Usumacinta River basin is a sink for DIC in both seasons. Finally, the estimated annual C export for the Usumacinta-Grijalva River was 2.88 (2.65 to 3.14) Tg yr−1, of which DIC was the largest transported fraction (85%), followed by DOC (10%), POC (4%), and PIC (, This research was funded by the FORDECYT-CONACYT Project 273646 “Fortalecimiento de las capacidades científicas y tecnológicas para la gestión territorial sustentable de la Cuenca del Río Usumacinta y su Zona Marina de Influencia (CRUZMI), así como su adaptación ante el cambio climático”, the UNAM-PAPIIT Project IN216818 “Flujos de carbono, nutrientes y sedimentos en un sistema lótico tropical”, the Programa de Investigación en Cambio Climático, UNAM, Projects PINCC 2020 & PINCC 2021 “Cuerpos acuáticos epicontinentales: papel en la dinámica del carbono y emisiones de gases de efecto invernadero en México”, and the Ministerio de Ciencia e Innovación, Consejo Superior de Investigaciones Científicas de España Project COOPA20433 “Contribución del neotrópico acuático continental a las emisiones de gases de efecto invernadero” and COOPA20472 “Los grandes ríos del neotrópico y su contribución al ciclo de carbono global”.

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but information is needed on the variability of their biogeochemical dynamics, especially for tropical systems. A long-term N and P mass balance (2003-2018) in a small tropical eutrophic reservoir lake, Valle de Bravo (VB), Mexico, showed it is a net sink of N (-41.7 g N m-2 y-1), and P (-2.7 g P m-2 y-1), mainly through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m-2 y-1 and 4.2 g P m-2 y-1). N mass balance showed that VB has a high net N atmospheric influx (31.6 g N m-2 y-1), which was 1.3 times the external load, and likely dominated by N2 fixation. During a period of high water level fluctuations (WLF), the net N atmospheric flux decreased by half compared to high level years. WLF can be a useful management tool to improve the trophic status of water bodies by decreasing anoxic conditions and net atmospheric fluxes, possibly through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load.

[EN] Wetlands act as nutrient sinks or sources playing a key role in downstream water quality and ecosystem productivity. Despite their importance, wetlands are highly threatened ecosystems and biogeochemical processes are changing in response to several external and internal constrains; however, these functional alterations have not been evaluated in the long term. In this paper we assess the nutrient dynamics (TOC, TN and TP) in Las Tablas de Daimiel in the long-term, through an input-output study using nutrient concentrations and flows measured monthly in the wetland from October 1980 to December 2018. Considering the entire period, on an annual basis Las Tablas de Daimiel was a net source of TOC (467 % of TOC inputs were exported) and net sink of TN and TP (83 % of TN and 92 % of phosphorus were retained and transformed in the wetland). For the longer period of records, mean export loading of TOC was 2177 g C/m2/y, while retention of TN and TP were 62.8 g N/m2/y and 5.7 g P/m2/y, respectively. However, since the 1980s nutrient concentration and nutrient import and export trends have changed dramatically as has their seasonality. High TOC export in Las Tablas are probably related to the short circuit existing in the hydrological functioning of the wetland after the 1980s in which outflows are usually disrupted to extend the wetland inundation for longer. TN and TP retentions begin to show signs of exhaustion but currently it is not possible to conclude if the wetland sediments have reached nutrient saturation. During the last 38 years the wetland has undergone similar environmental scenarios several times but the biogeochemical response of the system has never been repeated. This means the time scale of the environmental interactions and the ecosystem responses are unpredictable, and therefore long-term observations are key to understanding how nature will respond to upcoming global change., [ES] Los humedales actúan como sumideros o fuentes de nutrientes y desempeñan un papel clave en la calidad del agua y la produc-tividad de los ecosistemas ubicados aguas abajo. En estos ecosistemas tan amenazados los procesos biogeoquímicos están en continuo cambio como respuesta los impactos externos e internos. Sin embargo, estas alteraciones funcionales no se han evaluado a largo plazo. En este trabajo hemos estudiado la dinámica de los nutrientes (TOC, TN y TP) en Las Tablas Daimiel a largo plazo, mediante un balance de entradas y salidas que utiliza concentraciones de nutrientes y caudales medidos mensualmente en el humedal desde octubre de 1980 hasta diciembre de 2018. Teniendo en cuenta todo el período, a escala anual Las Tablas fueron una fuente neta de TOC (se exportó el 467 % de las entradas) y un sumidero neto de TN y TP (el 83 % del nitrógeno y el 92 % del fósforo). En este período, la carga de exportación media de TOC fue de 2177 g C/m2/año, mientras que la retención de TN y TP fue de 62.8 g N/m2/ año y 5.7 g P/m2/ año, respectivamente. Sin embargo, las tendencias en la concentración de nutrientes y en su importación y exportación cambiaron drásticamente desde 1980, haciéndolo también su estacionalidad. La elevadísima exportación de TOC en Las tablas probablemente esté relacionada con el cortocircuito en el funcionamiento hidrológico que sufre el humedal desde la década de 1980, pues las salidas se han interrumpido para expan-dir la inundación del humedal por más tiempo. Las retenciones de TN y TP comienzan a mostrar signos de agotamiento, pero actualmente no es posible concluir si los sedimentos del humedal están ya saturados de nutrientes. Durante los últimos 38 años, el humedal ha experimentado escenarios ambientales similares varias veces, pero la respuesta biogeoquímica del sistema nunca ha sido la misma. Debido a que la escala temporal de las interacciones ambientales y las respuestas de los ecosistemas son impredecibles aún, las observaciones a largo plazo son claves para comprender cómo la naturaleza responde a las próximas nuevas condiciones globales., Several projects funded by the Agency for National Parks from 1992 supported this study.

Inland aquatic ecosystems are valuable sentinels of anthropic-associated changes (e.g., agriculture and tourism). Eutrophication has become of primary importance in altering aquatic ecosystem functioning. Quantifying the CO2 emissions by inland aquatic ecosystems of different trophic statuses may provide helpful information about the role of eutrophication on greenhouse gas emissions. This study investigated diel and seasonal carbon dioxide (CO2) concentrations and emissions in three tropical karst lakes with different trophic statuses. We measured CO2 emissions using static floating chambers twice daily during the rainy/warm and dry/cold seasons while the lakes were thermally stratified and mixed, respectively. The CO2 concentration was estimated by gas chromatography and photoacoustic spectroscopy. The results showed a significant seasonal variation in the dissolved CO2 concentration (CCO2) and the CO2 flux (FCO2), with the largest values in the rainy/warm season but not along the diel cycle. The CCO2 values ranged from 13.3 to 168.6 µmol L−1 averaging 41.9 ± 35.3 µmol L−1 over the rainy/warm season and from 12.9 to 38.0 µmol L−1 with an average of 21.0 ± 7.2 µmol L−1 over the dry/cold season. The FCO2 values ranged from 0.2 to 12.1 g CO2 m−2 d −1 averaging 4.9 ± 4.0 g CO2 m−2 d −1 over the rainy/warm season and from 0.1 to 1.7 g CO2 m−2 d −1 with an average of 0.8 ± 0.5 g CO2 m−2 d −1 over the dry/cold season. During the rainy/warm season the emission was higher in the eutrophic lake San Lorenzo (9.1 ± 1.2 g CO2 m−2 d−1), and during the dry/cold the highest emission was recorded in the mesotrophic lake San José (1.42 ± 0.2 g CO2 m−2 d−1). Our results indicated that eutrophication in tropical karst lakes increased CO2 evasion rates to the atmosphere mainly due to the persistence of anoxia in most of the lake’s water column, which maintained high rates of anaerobic respiration coupled with the anaerobic oxidation of methane. Contrarily, groundwater inflows that provide richdissolved inorganic carbon waters sustain emissions in meso and oligotrophic karstic tropical lakes., This research was supported with public funds from the National Research Programs of Mexico (DGAPA/UNAM through the Projects PAPIIT-IN219215, PAPIIT-IV200319, and PAPIITIV200122, PINCC/UNAM through Projects PINCC 2020 and PINCC 2021), and Spain (PID2020-116147GB-C21 funded by MCIN/AEI/ 10.13039/501100011033 as well COOPA20433 funded by CSIC within the i-COOP + 2020 Program).

Estimations of gas emissions that impinge on global warming are growing worldwide as concern for this problem widens. Most are devoted to anthropogenic sources, but there is an increasing number dealing with natural sources. We offer here a preliminary assessment of methane and nitrous oxide emissions from Iberian freshwaters, mostly ascertained from reservoir data, which is probably the ecosystem type encompassing the higher fraction of inland aquatic cover in the Iberian Peninsula. Novel linear equations are produced using literature data and relating ecosystem area and annual emissions of CH4 and N2O at the ecosystem level. They enable us to estimate annual Iberian emissions of those gases which may be considered as a high limit because of many still unresolved uncertainties. Such equations could also be helpful to make estimations in other territories worldwide. Annual methane emissions by Iberian reservoirs would attain 19.45 Gg CH4/y as a high extreme, that of nitrous oxide accounting for 0.43 Gg N2O/y. As a result, Iberian reservoirs emit 541 Gg [CO2-equivalent] per year of both gases together. The percentage of their inland water emissions is lower than 1 % of joint Portugal and Spain overall emissions in 2015. Interestingly, these estimations of methane and nitrous oxide emissions from freshwaters represent 71 % and 19 %, respectively, of non-anthropogenic emissions from Iberian Peninsula.The obviously interesting topic of ascertaining CO2 emissions by Iberian freshwaters is impaired by the fact of lacking data on the surface area of streams (which might be the main source on account of their more frequent heterotrophy) for the whole territory. Clearly, simple databases on Iberian inland waters (streams, wetlands, natural and man-made lakes, ponds¿) including surface area, volume, depth and shape must be compiled to enable a more accurate description of their future changes, partly arising from global change. This morphometric database would also be very helpful to improve CH4 and N2O estimations.Non-anthropogenic emissions from the Iberian Peninsula appear to be biased by IPCC estimation procedures, which are employed uncritically by Spanish and Portuguese governments. There is an urgent need to improve them regionally if the share of inland waters in gas emissions is to be accurately assessed.

Spatial variations of denitrification activity and the relative importance of controlling factors were determined using the isotope pairing technique in a seepage chain of Mediterranean flowthrough lakes (Ruidera lakes) and within a given lake in the chain (Colgada lake), all receiving extremely high nitrogen inputs. The range of denitrification rates measured (28-155 ¿mol N m-2 h-1) were comparable with rates measured with isotope pairing in other freshwater systems. While the bulk of total denitrification was mostly based on NO3- from the overlying water, coupled nitrification-denitrification seemed to be lower in all Ruidera lakes. At the regional scale, i.e. lake district, inter-variability in denitrification (CV = 37 %) was lower than the intra-variability observed in a single lake (CV = 54 %). In fact, a preliminary meta-analysis of data from published studies suggested that denitrification rate variabilities did not differ statistically between the environmental and regional scales. Dissolved oxygen concentration, dissolved organic carbon content and nitrate from the overlying water were found to be the most important factors affecting the spatial heterogeneity of denitrification rate in the lake complex. At the single-lake scale, only phosphorus explained the variability of denitrification rates observed along its main axis. Our study emphasizes the significance of hotspots in denitrification processes, but also highlights the need for further studies on spatial denitrification given that fact that conflicting controlling factors have been found at different scales. To spatially measure denitrification is complicated due to the intrinsic difficulties of the incubation process and hotspots, which makes modelling indispensable., [ES] Mediante la técnica del par isotópico, estudiamos las variaciones espaciales de la actividad desnitrificante y la importancia relativa de sus factores de control en una cadena de lagos mediterráneos de tipo fluvial (lagunas de Ruidera) y en un lago concreto dentro de la misma (Laguna Colgada), todos los cuales reciben cargas elevadas de nitrógeno. El rango de las tasas medidas mediante dicha técnica fue comparable (28-155 µmol N m-2 h-1) al registrado en otros ambientes dulceacuícolas. Gran parte de las tasas se debieron al nitrato presente en el agua sobrenadante al sedimento (62-83 %), resultando de menor importancia los procesos acoplados de nitrificación-desnitrificación en todos los lagos estudiados. A escala del conjunto lacustre, la variabilidad del proceso fue inferior (CV = 37 %) a la presente en un único lago (CV = 54 %). En relación con esto, un meta-análisis preliminar de la variabilidad de la desnitrificación en distintos limnoambientes reveló que no había diferencias significativas entre la escala del ecosistema individual y la regional. Las concentraciones de oxígeno disuelto, carbono orgánico disuelto y nitrato en el agua sobrenadante fueron los factores fundamentales que controlaron las tasas de desnitrificación en el conjunto de lagos, mientras que en la laguna Colgada solo el ortofosfato explicó la variabilidad del proceso registrada en su eje principal. Este estudio recalca la importancia de los micrositios más favorables (hotspots) para el proceso de desnitrificación, pero también apoya la necesidad de más estudios sobre el tema porque los factores que lo controlan a distintas escalas espaciales difieren entre estudios. Las dificultades intrínsecas a la incubación y a la existencia dichos micrositios para medir espacialmente este proceso mediante cualquier técnica hacen imprescindible la modelización del mismo, We gratefully acknowledge the technical staff of Lagunas de Ruidera Natural Park for assistance and lake level data. We are also grateful to the Guadiana Water Authority for data on water discharge to Ruidera lakes. Field and lab help provided by Jos? Mar?a Alonso, Eva L?pez-Del-gado and Meritxell Plensa is also acknowledged. Julio Mateo is thanked for constructing the incubators for the isotope pairing technique improving an earlier design by the Swiss EAWAG (Prof. Bernhard Wehrli). This study has been supported by a predoctoral fellowship to E. Piña-Ochoa and the REN-2002-00558 and CGL-2006-2346/HID Projects of the Spanish Ministry of Education and Science.

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but the variability of their biogeochemical dynamics is still poorly documented, particularly in tropical systems. To contribute to the extending of information on tropical reservoirs and to increase the insight on the factors affecting N and P cycling in aquatic ecosystems, we here report on a long-term N and P mass balance (2003–2018) in Valle de Bravo, Mexico, which showed that this tropical eutrophic reservoir lake acts as a net sink of N (−41.7 g N m y) and P (−2.7 g P m y), mainly occurring through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m y and 4.2 g P m y). The N mass balance also showed that the Valle de Bravo reservoir has a high net N atmospheric influx (31.6 g N m y), which was 1.3 times the external load and likely dominated by N fixation. P flux was driven mainly by external load, while in the case of N, net fixation also contributed. During a period of high water level fluctuations, the net N atmospheric flux decreased by 50% compared to high level years. Our results outlining water regulation can be used as a useful management tool of water bodies, by decreasing anoxic conditions and net atmospheric fluxes, either through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load. These findings also sustain the usefulness of long-term mass balances to assess biogeochemical dynamics and its variability., This research was funded by UNAM, PAPIIT-IN207702 and CONACYT-SEMARNAT, C01-1125 projects to M.M-I

Particulate organic carbon (POC) derived from inland water plays an important role in the global carbon (C) cycle; however, the POC dynamic in tropical rivers is poorly known. We assessed the POC concentration, flux, and sources in the Usumacinta, the largest tropical river in North America, to determine the controls on POC export to the Gulf of Mexico. We examined the Mexican middle and lower Usumacinta Basin during the 2017 dry (DS) and rainy (RS) seasons. The POC concentration ranged from 0.48 to 4.7 mg L􀀀1 and was higher in the RS, though only in the middle basin, while remaining similar in both seasons in the lower basin. The POC was predominantly allochthonous (54.7 to 99.6%). However, autochthonous POC (phytoplankton) increased in the DS (from 5.1 to 17.7%) in both basins. The POC mass inflow–outflow balance suggested that floodplains supply (C source) autochthonous POC during the DS while retaining (C sink) allochthonous POC in the RS. Ranging between 109.1 (DS) and 926.1 t POC d􀀀1 (RS), the Usumacinta River POC export to the Gulf of Mexico was similar to that of other tropical rivers with a comparable water discharge. The extensive floodplains and the “Pantanos de Centla” wetlands in the lowlands largely influenced the POC dynamics and export to the southern Gulf of Mexico., This research was financially supported by the FORDECYT-CONACYT project 273646 “Fortalecimiento de las capacidades científicas y tecnológicas para la gestión territorial sustentable de la Cuenca del Río Usumacinta y su Zona Marina de Influencia (CRUZMI), así como su adaptación ante el cambio climático” and UNAM-PAPIIT project IN216818 “Flujos de carbono, nutrientes y sedimentos en un sistema lótico tropical.” This research was also financially supported by the Programa de Investigación en Cambio Climático (PINCC 2020-2021) through project “Cuerpos acuáticos epicontinentales: papel en la dinámica del carbono y emisiones de gases de efecto invernadero en México.”

Considerable variability in methane production and emissions has been reported in mangroves, explained by methane inhibition and oxidation. In this study, soil pore waters were collected from mangrove forests located in the Gulf of California (Mexico) exposed to shrimp farm disturbance. The δ13C of dissolved inorganic carbon (DIC) and CH4 were analyzed along with the δ13C of the soil organic matter to assess the proportion of CO2 derived from methanogenesis, its main pathway, and the fraction of methane oxidized. We performed slurry incubation experiments to fit the isotope–mass balance approach. Very low stoichiometric ratios of CH4/CO2 were measured in pore waters, but isotope mass balances revealed that 30–70% of the total CO2 measured was produced by methanogenesis. Mangrove soils receiving effluent discharges shifted the main methanogenesis pathway to CO2 reduction because of an increase in refractory organic matter. Isotope–mass balances of incubations indicated that methane was mainly oxidized by anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and the increase in recalcitrant organic matter should fuel AOM as humus serves as a terminal electron acceptor. Since methanogenesis in mangrove soils is strongly controlled by the oxygen supply provided by mangrove roots, conservation of the forest plays a crucial role in mitigating greenhouse gas emissions., CONACyT: PROFAPI, Spanish Ministry of Science and Innovation (Grant: CGL2014-54502) and CSIC (Grant: I-COOP+2020–COOPA20433) funded this research.

Miguel-Ruano, M., Sanchez-Carrillo, S. 2020. The decline of aquatic vegetation in wetlands in response to the environmental degradation: the case of the cut-sedge (Cladium mariscus) in Las Tablas de Daimiel and its potential restoration. Ecosistemas 29(3):1963. https://doi.org/10.7818/ECOS.1963 Wetlands disappear at the rate that their biodiversity does. This study evaluates the causes of the serious decline that the cut-sedge (Cladium mariscus) experienced in Las Tablas de Daimiel National Park (PNTD) wetland, where the population has decreased from 1,100 ha in 1956 to 10 ha in 2019. To do this, we have carried out a comparative study in the La Mancha Humeda Biosphere Reserve, using the PNTD's cut-sedge population and the populations of other wetlands where this macrophyte is not in decline (Laguna del Masegar and Lagunas de Ruidera), which were grown in controlled conditions in the laboratory and later transplanted in PNTD wetland. Differences in C and N content, survival and growth rates, and seed viability and germination capacity indicated that the decline in the PNTD cut-sedge population is related to the hydrological degradation of the wetland, which has caused (i) population aging due to long-term use of clonal reproduction, (ii) a very low colonization of environmental-favorable habitats within the wetland due to a limited dispersion of generative propagules by hydrochory and (iii) a genetic isolation of the population due to the lack of hydrological connection with the other wetlands in the Upper Guadiana river basin. Restoration measures must be immediate, to recover stands in key areas of the wetland with specimens from nurseries and in the medium and long-term to promote the expansion of the cut-sedge to other areas of the wetland ecosystem.

The effects of the combined roles of abiotic and biotic factors defining foodweb structure are often ignored. In aquatic systems, abiotic variables can regulate food webs through bottom-up ...

Global change effects, such as warming and increases in nitrogen loading, alter vulnerable Mediterranean aquatic systems, and charophytes can be one of the most affected groups. We addressed the possible interaction between these factors on two populations of the cosmopolitan charophytes Chara hispida and Chara vulgaris. Populations were taken from two different environments, a nitrate-poor mountain lake and a nitrate-rich Mediterranean coastal spring. The laboratory experiment had a 2 × 2 factorial design based on two nitrate levels (similar to and double the local conditions) and two temperatures. Increased temperatures favoured the growth of the four populations, but an increase in nitrate did not have any effect on their growth or architecture. Both species took up and stored more nitrogen (measured as %N in plant tissue) when more nitrate was supplied, and warming favoured this increase in %N and, consequently, in N:P ratio. The effects of both factors depended on the local conditions where the populations originated and on the species. Chara vulgaris, a pioneer species, exhibited more phenotypic plasticity than C. hispida, and its ecotype from the coastal spring was better adapted to changes in temperature and nitrate level. These differential responses to warming conditions and nitrate pollution may modify charophyte diversity, which might be reflected in ecosystem performance, a matter of concern in vulnerable Mediterranean water bodies where these species co-occur., This study was supported by the Spanish Ministry of Economy and Competitiveness for research project CGL2014-54502-C2-1-P (including EC FEDER funding). Eric Puche is the holder of a grant (UV-INV-PREDOC16F1-383810) funded by the University of Valencia.

[EN] Theoretical Limnology is a neglected topic nowadays. Here we make an endeavour to launch and promote theoretical developments in Limnology, dealing with the mechanistic relationships among biogeochemistry, production, species richness and food webs in the most common-sized lakes, i.e. small-to-medium ones. Although few studies are currently underway to support includes such relationships, well-known interactions enable us to place such lakes within a conceptual model bottom-up model, which include water retention, total phosphorus and dissolved organic carbon as the driving variables. All response variables are viewed on the basis of area, which enables circumventing the otherwise important issue of depth (and hence stratification). Seven lake types are considered with unique sets of features concerning species richness, food web connectance, nutrient fluxes and lake metabolism. The extension and tuning of this conceptual model to all stagnant waters (from small to large) can be undertaken when more data on these topics are available, probably taking horizontal transport features into account. We look forward to seeing future developments in theoretical Limnology, also paying special attention to Mediterranean limnological features which differ somewhat from those of cold temperate-and tropical areas., [ES] La Limnología teórica es un tema olvidado en estos tiempos. Por eso, aquí proponemos un intento modesto de iniciar y promover teorías limnológicas, explorando las relaciones mecanicistas entre biogeoquímica, producción, riqueza específica y redes tróficas para los tipos más frecuentes de tamaño de lago, que son los pequeños y medianos. Aunque el número de estudios que ofrece resultados para apoyar dichas relaciones es bastante reducido, algunas bien conocidas de estas facilitan el organizar los lagos dentro de un esquema conceptual que usa la retención del agua, el fósforo total y el carbono orgánico disuelto como variables de control. Considerar todas las variables de respuesta por unidad de superficie permitirá pasar por alto el importante asunto de la profundidad, y el de la estratificación térmica por lo tanto. Nuestro esquema conceptual vislumbra siete tipos de lagos con conjuntos de respuestas únicas relativas a la riqueza de especies, la conectancia de las redes tróficas, los flujos biogeoquímicos y la productividad lacustre. Una mayor concreción de este modelo conceptual y la extensión del mismo a todos los ambientes estancados (de los pequeños a los grandes) podrán llevarse a cabo cuando haya más datos sobre estos temas, probablemente teniendo en cuenta además alguna variable relativa al transporte horizontal. Tras esta contribución, nos gustaría ver nuevos desarrollos teóricos que –además– presten atención a la Limnología mediterránea, la cual difiere un poco de la existente en las zonas templadas frías y tropicales del globo.

In recent years, little scrutiny has been devoted to charophytes with regard to carbon, nitrogen and phosphorus contents, their ratios and the factors controlling them. Data from published literature, and our own unpublished data, will be used along with environmental data to depict overall statistical distributions and controlling factors of charophyte stoichiometry, along with two hypotheses already suggested for plankton. Data on whole and decarbonated plants will be reviewed separately, but the role of the phosphorus-bound, external crust in the charophyte metabolism is still unclear. These algae have an intermediate carbon content, and lower nitrogen and phosphorus contents, among other aquatic plants. Hence their C:N and C:P ratios are usually higher than those of other submerged plants. Phosphorus is the outstanding key factor for charophyte growth and stoichiometry. Charophyte P content appears to be related to C, N and P sedimentary contents; a higher P content will result in increased growth rates. The maximal growth rates recorded occur at charophyte C:N:P ratios of 343-759:18-44:1, higher than the well-known Redfield values for optimal growth in other algae. While PAR irradiance partly controlled charophyte nitrogen content and the C:N ratio, UV-B radiation increased C and N content, albeit not affecting nutrient ratios. We conclude that the light:nutrient and the growth rate hypotheses hold true for charophytes. Increasing temperatures by global warming could decrease charophyte P content, thereby augmenting the C:P ratio. Further studies on charophyte stoichiometry are encouraged, specifically to disentangle the relationship between plant and carbonate crust and the role of stonewort stoichiometry in aquatic system.

Species invasion and habitat degradation very often result in local species loss, which may result in a cascade of secondary extinctions that typically end up disrupting whole ecological netwroks. Herein, we used historical records and the natural abundance of stable isotopes (13C and 15N) of primary producers, aquatic animals and sediment/detritus to derive the past and present structure of food webs from the freshwater wetland “Las Tablas de Daimiel”, in cen-tral Spain. Before the green revolution and agricultural transformation of the area, this wet-land was characterised by a high biodiversity of basal species, including primary consumers such as bivalves and gastropods, which are currently absent or very scarce. Our results demonstrate that the increase of anthropogenic disturbances, exotic species and changes in primary productivity of this wetland is affecting the biodiversity at all trophic levels (mainly herbivorous fish) but not the length of the food chain, which we estimated between 3.9 and 4.4 trophic levels. Using the mixing models, we showed that macrophytes represent an im-portant contribution of matter and energy to higher trophic levels. Our model also suggested that a currently expanding, allochthonous halophytic tree (Tamarix canariensis) may be the main energy source for two species of commonly found butterflies (Pieris rapae and Rho-dometra sacraria) as well as for invertebrates, while the macrophyte Thypa dominguensis was the main diet source for the exotic crayfish Procambarus clarkii, which occupies the niche left by the native crayfish. Our work demonstrates the importance of taking a whole-systems ap-proach to characterize the magnitude of human impacts on the functioning of wetland ecosys-tems.

Approximately 95% of the total carbon (C) in wetlands is typically found as particulate organic matter (POM). In this study, we evaluated the main C sources of a semiarid floodplain wetland in central Spain under disturbance. For this, we used stable isotopes (13C and 15N) and the Bayesian mixing model SISUS. We show that the allochthonous C derived from wastewater discharges have distinctive δ13C values compared to the C of sites that did not receive wastewater discharges. Wastewater discharges affected the isotopic signatures of dissolved organic carbon as well as δ15N values of primary producers (epiphyton, filamentous algae and Scirpus maritimus). δ15N values showed a greater response to the effects of environmental degradation. The salt-tolerant marginal tree Tamarix canariensis was the main autochthonous contributor to POM (69 to 84%), while the main source of energy for the secondary production was the submerged macrophyte Ceratophyllum submersum. Tamarix canariensis was also the main component of the diet for macroinvertebrates, followed by POM. Other species such as Cladium mariscus, an emblematic aquatic plant in the region, showed a very low contribution to POM (less than 20%), although it represented a relatively important energy source for zooplankton (up to 47%). This relatively low contribution is probably due to the drastic reduction in the abundance of this species during the last 50 years. In contrast, Phragmites australis, which has multiplied its abundance by twenty-two since 1950, does not seem to contribute significantly to POM or to the diet of invertebrates (less than 22%), although it can represent up to 54% zooplankton’s diet. Isotopic results confirm that in this eutrophied and disturbed wetland, the contribution of macrophytes to the food web as autochthonous organic sources is lower than expected based on their biomass.

Wetlands provide a great variety of environmental services to society, but they are currently globally threatened by human activities. We evaluated the effects of anthropogenic disturbances on the ecological quality of semiarid wetlands from central Spain (La Mancha Húmeda) through the natural abundance of isotopes (13C and 15N) of aquatic plants. We measured water quality and also compiled historical information about land-use and socioeconomic characteris-tics at local (100 m around the lagoon) and regional (sub-basin) scales. We then related this information to isotopic signatures of three types of aquatic plants: (i) charophytes, (ii) marginal aquatic macrophytes and (iii) vascular plants. Aquatic plants exposed to high levels of nitrogen showed very low δ13C values, consistent with negative physiological effects. Vascular aquatic plants were the group that best reflected the effects of nutrient enrichment in wetlands and la-goons through significant correlations between their δ15N values and total nitrogen and phos-phorus concentrations in water. Demographic factors did not exert a clear influence on aquatic plant isotopic signatures, although we observed inverse correlations between the coverage of natural vegetation at regional scale and δ13C of marginal plants and δ15N of vascular plants. Furthermore, the isotopic signatures of Phragmites australis, present in 96% of the studied la-goons, were not significantly correlated with any of the environmental quality variables evalu-ated. Although δ13C signatures of Typha dominguensis and Cladium mariscus increased signif-icantly due to changes in water quality, their narrow isotopic variability at the regional scale limits their use as a bioindicators of environmental changes in this wetland system. Finally, we propose the use of δ15N measured in the vascular plant Salicornia sp. as the most suitable bio-indicator of anthropogenic impacts in La Mancha Húmeda region, a highly emblematic system of semiarid Mediterranean wetlands that is unique in the Mediterranean region of Europe.

[EN] Most ecological processes can only be understood from a long-time perspective. Ecosystems are changing in such a complex way that we are still trying to identify how and at what rate they are changing according to the complex network of stressors that impinges on them. The existing longterm observations in the LTER-Daimiel node allow us to assess the main causes and effects of major environmental changes in Las Tablas de Daimiel for the past 70 years. We show three examples of the validity of long-term observations as opposed to short-term records to assess the effects of various environmental impacts occurring in the wetland., [ES] La mayor parte de los procesos ecológicos sólo pueden entenderse desde una perspectiva temporal larga. Los ecosistemas están cambiando de un modo tan complejo que todavía estamos intentando detectar cómo lo hacen y a qué ritmo ante la compleja red de estresores a que están sometidos. Las observaciones a largo plazo existentes en el nodo LTER-Daimiel nos permiten evaluar las causas y los efectos de los principales cambios ambientales ocurridos en Las Tablas de Daimiel durante los últimos 70 años. En este trabajo presentamos tres ejemplos que ponen de manifiesto la validez de las observaciones a largo plazo en la interpretación de diversos fenómenos ambientales ocurridos en el humedal, en contraposición a lo que proporcionan registros temporales limitados.

Plant and community traits provide valuable insights in ecosystem functioning. Yet, such traits are costly to sample. Existing trait data bases give access to species-specific traits and help to reduce the sampling effort and costs. However, many traits show a high intra-specific plasticity due to the variability of environmental conditions, which is not fully accounted for in the data bases. As an alternative approach, remote sensing is able to retrieve some traits from the spectral reflectance signal of the canopy. Here we test whether remotely sensed traits provide the level of detail to trace the trait plasticity in response to changing environmental conditions. For this proof of concept study, we selected the example of leaf mass per area (LMA), a key trait for ecosystem functioning and good negative correlate of potential growth rate, in our study site Las Tablas de Daimiel National Park (Spain). This wetland was affected by a long-term drought, which introduced a pronounced trait plasticity as part of the adaptation mechanisms of the vegetation to reduced water availability as well as a decrease in photosynthetic activity. Imaging spectroscopy (HyMap) data of the wetland at peak drought intensity were acquired in 2009 simultaneous to a field campaign. We applied an inversion of the PROSAIL radiative transfer model on these data to map the LMA distribution across the wetland. Further, we quantified trends in photosynthetic activity and changing species composition across the wetland by analyzing time series of the normalized difference vegetation index (NDVI) as calculated for multispectral remote sensing data. The retrieved LMA values were analyzed within and between stands of different species and communities along a gradient of changing photosynthetic activity and species composition. Results show that LMA values retrieved for stands of species with high photosynthetic activity at peak drought intensity closely meet the values reported in data bases. The observed intra-specific LMA variability is in line with the expected plasticity of this trait along a moisture gradient that is reflected in a change in photosynthetic activity and species composition. We thus conclude that LMA values retrieved from imaging spectroscopy data provide sufficient detail to trace the response of wetland vegetation to long-term drought stress., Funding for this study was granted by the German Ministry of Economics and Technology (BMWI) within the framework of the project of the 2009 EnMAP preparation campaign, the DECAMERON project 1/2008 of the Agency for National Parks of the Spanish Ministry of Agriculture, Food and Environment, and by the German Research Foundation (DFG grant FE1331/2-1).

Research has dealt with coupling of chemical element cycles and feedback in recent years. Sometimes, this biogeochemical coupling is reversed through abiotic or biotic (including man-made) processes. It is then called biogeochemical decoupling and is a disconnection between two chemical elements whereby transformations of one affect cycling of the other, and results in asynchronical behavior of chemical elements. It appears to be more important and widespread than earlier reports suggest, and gives rise to important changes in element stoichiometry of resources. These changes in turn modify organismal stoichiometry that, if great enough, can affect biodiversity and food webs, thus altering community structure and function. Biogeochemical decoupling then impinges on ecosystem dynamics and may impair ecosystem services.

[EN]: The addition of stable isotopes (SI) of 13C and 15N has been used to study several aquatic processes, thus avoiding environmental disturbance by the observer. This approach, employed for the last three decades, has contributed to expanding our knowledge of food-web ecology and nutrient dynamics in aquatic systems. Currently, SI addition is considered a powerful complementary tool for studying several ecological and biogeochemical processes at the whole-aquatic-ecosystem scale, which could not be addressed otherwise. However, their contributions have not been considered jointly nor have they been evaluated with a view to assessing the reliability and scope of their results from an ecosystem perspective. We intend to bridge this gap by providing a comprehensive review (78 scientific publications reporting in situ 13C/15N additions at the whole-aquatic-ecosystem scale) addressing the main results arising from their use as tracers. Specifically, we focus on: (i) reasons for SI additions at the whole-ecosystem scale to study ecological processes, (ii) the paradigms resulting from its use and the insights achieved, (iii) uncertainties and drawbacks arising from these SI addition experiments, and (iv) the potential of this approach for tackling new paradigms. SI tracer addition at the ecosystem scale has provided new functional insights into numerous ecological processes in aquatic sciences (importance of subsidies in lakes; heterotrophy dominance in benthic food webs in lakes, wetlands and estuaries; the decrease in N removal efficiency in most aquatic ecosystems due to anthropogenic alteration; the recognition of hyporheic zones and floodplains as hot spots for stream denitrification; and high rates of internal N recycling in tidal freshwater marshes). However, certain constraints such as the high cost of isotopes, the maintenance of the new isotopic steady state, and avoidance of biomass changes in any compartment or pool during tracer addition bear witness to the difficulties of applying this approach to all fields of aquatic ecology and ecosystems. The future development of this approach, rather than expanding to larger and complex aquatic ecosystems, should include other stable isotopes such as phosphorus (P18O4)., [FR]: L’ajout d’isotopes stables (IS) de 13C et 15N est utilisé pour étudier plusieurs processus aquatiques, évitant ainsi la perturbation environnementale par l’observateur. Cette approche, employée depuis les trois dernières décennies, a contribué a`élargir nos connaissances de l’écologie des réseaux trophiques et de la dynamique des substances nutritives au niveau des systèmes aquatiques. Actuellement, l’ajout d’IS est considéré comme un outil complémentaire puissant permettant d’étudier plusieurs processus écologiques et biogéochimiques a` l’échelle de l’écosystème aquatique entier, ce qui ne pourrait pas être abordé autrement. Cependant, leurs contributions n’ont pas été considérées conjointement, ni été évaluées en vue de déterminer la fiabilité et la portée de leurs résultats d’une perspective écosystémique. Nous avons l’intention de combler ces lacunes en présentant une revue complète (de 78 publications scientifiques rapportant des ajouts de 13C/15N in situ a` l’échelle de l’écosystème aquatique entier) se penchant sur les principaux résultats découlant de leur utilisation comme traceurs. Spécifiquement, nous nous concentrons sur: (i) les raisons d’ajouter des IS a` l’échelle de l’écosystème entier afin d’étudier des processus écologiques; (ii) les paradigmes issus de leur utilisation et les connaissances acquises; (iii) les incertitudes et les inconvénients découlant de ces expériences d’ajout d’IS et (iv) la possibilité de dépasser les nouveaux paradigmes par cette approche. L’ajout de traceur isotopiques stables a` l’échelle écosystémique a fourni de nouvelles notions fonctionnelles au sujet des nombreux processus écologiques dans le domaine des sciences aquatiques (l’importance des contributions dans les lacs, la domination hétérotrophique des réseaux trophiques benthiques au niveau des lacs, des terres humides et des estuaires; la perte d’efficacité au niveau de l’élimination de l’azote dans la plupart des écosystèmes aquatiques en raison de changements anthropogéniques; la reconnaissance de zones hyporhéiques et de plaines inondables comme des points chauds susceptibles de dénitrification des cours d’eau et de hauts taux de recyclage interne de l’azote dans les marais d’eau douce a` marée). Cependant, certaines contraintes, telles que le coût élevé des isotopes, le maintien du nouvel état stable isotopique et l’évitement de changements de biomasse dans tout compartiment ou bassin pendant l’ajout de traceur, témoignent des difficultés d’appliquer cette approche a` tous les domaines d’écologie aquatique et a` tous les écosystèmes. Le développement de cette approche a` l’avenir, plutôt que de s’étendre aux écosystèmes aquatiques plus grands et complexes, devrait inclure d’autres isotopes stables, comme le phosphore (P18O4)., The BIOMET project (CGL2009–10408), funded by the Spanish Ministry of Science and Innovation, and the MACROFITOS project (CGL2014–54502-C2–2-P), funded by the Spanish Ministry of Economy and Competitiveness, have supported this publication.

Availability of fixed nitrogen is a pivotal driver on primary productivity in the oceans, thus the identification of key processes triggering nitrogen losses from these ecosystems is of major importance as they affect ecosystems function and consequently global biogeochemical cycles. Denitrification and anaerobic ammonium oxidation coupled to nitrite reduction (Anammox) are the only identified marine sinks for fixed nitrogen. The present study provides evidence indicating that anaerobic ammonium oxidation coupled to the reduction of sulfate, the most abundant electron acceptor present in the oceans, prevails in marine sediments. Tracer analysis with 15N-ammonium revealed that this microbial process, here introduced as Sulfammox, accounts for up to 5 μg 15N2 produced g−1 day−1 in sediments collected from the eastern tropical North Pacific coast. Raman and X-ray diffraction spectroscopies revealed that elemental sulfur and sphalerite (ZnFeS) were produced, besides free sulfide, during the course of Sulfammox. Anaerobic ammonium oxidation linked to Fe(III) reduction (Feammox) was also observed in the same marine sediments accounting for up to 2 μg 15N2 produced g−1 day−1. Taxonomic characterization, based on 16S rRNA gene sequencing, of marine sediments performing the Sulfammox and Feammox processes revealed the microbial members potentially involved. These novel nitrogen sinks may significantly fuel nitrogen loss in marine environments. These findings suggest that the interconnections among the oceanic biogeochemical cycles of N, S and Fe are much more complex than previously considered., This work was financially supported by grants from the Council of Science and Technology of Mexico (Program Frontiers in Science, Grant 1289) and the Marcos Moshinsky Foundation to FJC.

Copyright © 2018 by the author(s)., Art–science approaches are mounting to increase public literacy about sustainability challenges as planet Earth swiftly moves to an uncertain future. We use data sonification, an approach that allows converting scientific data into music, to document the large-scale transformation of the agricultural sector in central Spain during the 1970s. We converted 71-year time series of inundation area and rainfall data from the freshwater marsh Las Tablas de Daimiel into a soprano and bass voice, respectively. We composed “The Lament of Las Tablas de Daimiel,” which sings the biophysical disruption of the wetland due to the agricultural transformation. More generally, the song testifies to the demise of the natural aquatic environment due to unsustainable use of limited water resources in dryland countries and elsewhere. Making the mute voices of ecosystem heard may have potential to increase awareness about the unsustainable use of short water supplies and other social-ecological challenges. In the age of big data in science, data sonification may be a useful tool to represent and communicate such challenges., This research was funded by the Swedish Research Councils Formas (2014-1193) and VR (2014-5828).

9 páginas, 5 figuras, 4 tablas.-- Este artículo está dedicado a nuestro amigo y colega el Prof. Alejandro Javalera, fallecido en el curso de esta investigación., This study shows results on litterfall dynamics and decay in mangrove stands of Avicennia germinans distributed along a latitudinal gradient (three forest sites) in the Gulf of California, in order to assess whether internal sources could support the observed mangrove ecosystem organic deficit in this arid tropic. Total mean annual litterfall production increased southward (712.6 ± 53.3, 1501.3 ± 145.1 and 1506.2 ± 280.5 g DW m−2 y−1, in the Yaqui, Mayo and Fuerte areas respectively), leaves being the main component of litter in all locations during the entire year, followed by fruits. The wet season (June–September) showed the highest litterfall rates through fruits. The temporal trend of litterfall production was significantly explained through mean air temperature (R2 = 68%) whilst total annual litter production in the entire region showed a statistically significant relationship with total soil phosphorus, salinity, total nitrogen, organic matter and tree height (R2 = 0.67). Throughout 117 days of the decomposition experiment, the litter lost 50% of its original dry weight in 5.8 days (average decay rate of 0.032 ± 0.04 g DW d−1) and there were not significant differences in the remaining mass after 6 days. The percentage of both C and P released from the litter correlated significantly with the ratio of tidal inundated days to total experiment days (R2 = 0.62, p = 0.03 and R2 = 0.67, p = 0.02, respectively); however, the frequency of tidal inundation only showed a significant increase in C release from Avicennia litter after 6 and above 48 days of decomposition. Whereas the total C content of litter bags decreased linearly over the decomposition to (% Total C = 5.52 − 0.46 days, R2 = 0.81, p = 0.0005), N content displayed an irregular pattern with a significant increase of decay between 48 and 76 days from the beginning of the experiment. The pattern for relative P content of litter revealed reductions of up to 99% of the original (%tot-P = −9.77 to 1.004 days, R2 = 0.72, p = 0.01) although most of the P reduction occurred between 17 and 34 days after the experiment started. Soil N and P contents, which exhibited significant differences in the course of the decomposition experiment, appeared to show significant differences between sampling sites, although they were not related to tidal influence, nor by leaf and nutrient leaching. In a global basis, C/N litter ratios decreased linearly (C/N = 32.86 − 0.1006 days, R2 = 0.62, p = 0.02), showing a strong and significant correlation with meteorological variables (R2 = 0.99, p = 0.01). C/P ratios of litter increased through an exponential function (C/P = 119.35e0.04 day, R2 = 0.89, p < 0.001). Changes in the remaining percentage of litter mass during the experiment were significantly correlated with soil C/N ratio (R2 = 0.56, p = 0.03) as well as with the soil C/P ratio (R2 = 0.98, p < 0.001). Our results of litter decomposition dynamics in this mangrove support the fact of null net primary productivity of the arid mangrove wetlands: fast litter decomposition compensates the ecosystem organic deficit in order to sustain the mangrove productivity. Litter decomposition plays a key role in the ecosystem metabolism in mangroves of arid tropics., This research was supported by the Mexican Secretary of Natural Resources and Environment (SEMARNAT-CONACYT; contract SEMARNAT-2002-C01-0147) and by the Spanish Ministry of Environment (Organismo Autónomo Parques Nacionales; contract 2008/001 DECAMERON). The first author has been granted a CSIC-JAEDoc contract.

In semi-arid floodplains the average times between floods have been cited to drive metabolic and biogeochemical responses during the subsequent flooding pulse. However, the interaction effects of flood pulse duration and the length of time between floods on the carbon budget are not well understood. Using field experiments, flood pulses—dry cycles were simulated (SF plots—short flood/dry cycles: 15 flood days + 7 dry + 15 flood and LF plots—long flood/dry cycles: 21 flood + 14 dry + 21 flood) in a semi-arid floodplain in Central Spain, in order to study the effects on soil CO2 emissions. Differences on soil water content among SF, LF and control plots were statistically significant throughout the experiment (p

In this study we evaluated the usefulness of rotifer emergence from dry soils to indicate the environmental status of a remnant temporary pond complex in an agricultural area in central Spain. Because the ponds did not flood during our project, emergence was studied in relation to environmental variables in outdoor microcosms. Redundancy analysis and nestedness analysis showed that salinity and total nitrogen concentrations shaped the emerged communities. Depauperate rotifer assemblages from pond microcosms with higher salinity and nitrogen levels were nested subsets of species-rich communities from microcosms of less enriched sites. Rotifer community structure also identified small ponds as reference sites that should receive priority in conservation and degradation mitigation programs. Results suggest that rotifer emergence from rewetted sediments using microcosms can be useful for evaluating the nutrient status during the dry phase of temporary wetlands. While results from this approach are conservative, requiring comparisons with field observations, their tentative value lies in alerting management and providing a basis for future research of poorly studied but threatened temporary habitats. Rotifer emergence could be a useful alternative to traditional biological indicators of nutrient status that depend on the presence of water.

In this study we compare phytoplankton community similarity between sites in a semiarid floodplain wetland over a 6-year period with variable hydroperiod and connectivity regimes. Phytoplankton communities showed a relatively high site idiosyncrasy during most parts of the study; however, during situations of low connectivity when individual sites were highly fragmented, phytoplankton communities occasionally became more similar between sites. This suggests that mass effects related to dispersal-mediated processes could be important. Viewed from a metacommunity perspective, phytoplankton community assembly at the wetland scale involves complex hierarchical processes that can act independently at different spatial extents. The main conclusion of this study is that the well-known effects of environmental variability associated with hydrological disturbance alone may not be sufficient for explaining, and by extension predicting, community assembly in this wetland. Other processes, perhaps involving overland dispersal, may eventually add a new dimension to, and complicate our understanding of, community processes in fluctuating wetlands.

Understanding landscape correlates of local habitat integrity and community structure and the identification of spatial scales at which these associations operate are relevant for management and conservation of unique but globally threatened temporary ponds. We use a multivariate variance decomposition approach to determine taxon-specific associations of zooplankton communities banked in dry pond soils (rotifers, cladocerans, copepods) with local habitat features and landscape characteristics across four spatial scales (100 buffer strip, 1, 5, and 10 km scales). Results show similar degrees of correlation between rotifer and cladoceran communities with local habitat conditions (chiefly water quality). This is interpreted according to life-history traits of component species of wetland propagule banks. Associations with landscape features varied between communities with rotifers correlating with landscape structural features only at the buffer scale while cladocerans showed no significant correlations with landscape characteristics across all scales. Copepods were neither significantly associated with local nor landscape characteristics. The results of this study contrast strikingly with our previous population-based study, where populations of Triops cancriformis and Branchinecta orientales were significantly correlated with landuse features at the broadest scale. The combined results suggest that a three-way management scheme could be useful for conservation of zooplankton resting egg banks in this remnant wetland complex. These schemes could focus on the restoration of wetland water quality, the establishment of vegetated buffer strips around the ponds to counteract degradation resulting from runoff, and reforestation and/or the creation of hedgerows in agricultural catchments to avoid impacts resulting from broad-scale diffuse pollution fluxes.

9 pages, 4 figures.-- PMID: 18374463 [PubMed].-- Printed version published on Nov. 2008.-- Supplementary data available: Tables: Data sources of nitrogen export by world catchments and catchment characterization., This study reviews nitrogen export rates from 946 rivers of the world to determine the influence of quantitative (runoff, rainfall, inhabitant density, catchment area, percentage of land use cover, airborne deposition, fertilizer input) and qualitative (dominant type of forest, occurrence of stagnant waterbodies, dominant land use, occurrence of point sources, runoff type) environmental factors on nitrogen fluxes. All fractions (total, nitrate, ammonia, dissolved organic and particulate organic) of nitrogen export showed a left-skewed distribution, which suggests a relatively pristine condition for most systems. Total nitrogen export showed the highest variability whereas total organic nitrogen export comprised the dominant fraction of export. Nitrogen export rates were only weakly explained by our qualitative and quantitative environmental variables. Our study suggests that the consideration of spatial and temporal scales is important for predicting nitrogen export rates using simple and easy-to-get environmental variables. Regionally based modelling approaches prove more useful than global-scale analyses., Spatial and temporal scales are important determinants for nitrogen export from catchments and emphasis should be put on regional approaches., This is a result of Project CGL2006-2346-HID, funded by the Spanish Ministry of Education.

We assessed the temporal evolution of vegetation activity of mangroves in the Southeastern coastal of the Gulf of California (Mexico) through a multi-temporal analysis of Landsat TM images from 1990 to 2010 where time series of the Normalized Difference Vegetation Index (NDVI) were obtained. A multivariate regression analysis showed the presence of statistically significant negative trends of NDVI (low vegetation activity) in the coverage of mangrove forest, mangrove forest with pickleweed, and pickleweed; however, we did not found any meteorological variable (built time series of average minimum and maximum temperatures, and of accumulated rainfall) that controlled the observed trends. A pixel-by-pixel spatially distributed analysis of the temporal trends of NDVI, complemented by digitalization through photo interpretation of the shrimp farms present in the study area, showed a spatial relationship between the zones of greatest loss of vegetation activity (1990–2010) and the areas with greater proliferation of shrimp farms in the study area. Our study demonstrated the applicability of NDVI for the environmental assessment of mangroves. The relationship between changes in remote sensing indices and environmental variables allows for an efficient evaluation of the main environmental impacts, which can be used for coastal planning and management., The research was supported by the Mexican Secretary of Natural Resources and Environment (SEMARNAT-CONACYT; grant number SEMARNAT-2002-C01-0147). SM-B and RJM are students of Academic Program of Geoinformatics (UACJ).

[EN] Nutrient fluxes take place in lakes through different flow paths, and the importance of their nutrient flux changes depend on the biogeochemical processes involved. In flow-Through lakes, the hydrological control of these flux processes appears to be very important, but the significance of other processes is poorly understood. To test this significance, we analyzed C, N and P fluxes on a weekly scale during mid-stratification in a Spanish calcareous lake fed by agriculturally-drained streams and groundwater. As expected, hydrologic flow paths were more important than those of biogenic fluxes for the nutrient budgets. The organic C (OC hereafter), total N and total P surface inflows and outflows differed. While C and N surface hydrological fluxes covaried, P input or output fluxes were unrelated with those of other nutrients. Net groundwater C and P fluxes covaried, but they were not related with those of N. The accumulations of OC, N and P were also related with each other. All of the biogenic fluxes were highly variable. Primary production by emergent plants (Cladium) were higher than water column photosynthesis, the latter being net autotrophic most of the time. Particulate nutrient settling rates were within the range of those in oligotrophic lakes. Denitrification was not as high as expected in the nitrate-rich water of this lake, which was limited by low levels of soluble reactive phosphorus and dissolved organic carbon. CO degassing from the surface to the atmosphere was always positive, suggesting net heterotrophy, but this was the opposite of previous results. These conflicting results could be reconciled by the high hydrological inputs of inorganic carbon, which yielded more carbon dioxide to be outgassed. Albeit low, the CO production from CaCO formation could sometimes be a source of CO. However, the biogenic fluxes were higher than expected in flow-Through lakes, mostly arising from the role of littoral emergent plants in nutrient fluxes, which was often neglected in biogeochemical budget studies. Furthermore, no relationship was found between water renewal time and accumulation, thus emphasizing the significance of biogenic fluxes on nutrient retention. At the ecosystem level, our study highlighted both the importance of the hydrogeological setting of the basin on nutrient fluxes and the importance of emergent vegetation on lake nutrient budgets., [ES] Los flujos de nutrientes tienen lugar en los lagos siguiendo líneas de flujo diferentes, cuya importancia depende de los procesos biogeoquímicos implicados en ellos. En los lagos fluviales el control hidrológico de estos flujos es muy notable, pero la importancia de otros procesos sobre dicho control aún se conoce mal. Con objeto de mejorar el conocimiento de estos aspectos limnológicos, analizamos aquí los flujos de C, N y P a escala semanal durante el periodo central de la estratificación en un lago calcáreo español (laguna Conceja, Centro de España), alimentado por ríos y agua subterránea que han drenado zonas agrícolas. El transporte hidrológico fue más importante que los flujos biogénicos en los balances de nutrientes. Las entradas de carbono orgánico, nitrógeno y fósforo totales fueron diferentes de las salidas. Aunque los flujos hidrológicos superficiales de C y N covariaron, las entradas y salidas de P no lo hicieron. Los flujos subterráneos de C y P covariaron, pero no se relacionaron con los de N. Las acumulaciones de C orgánico, N y P estuvieron relacionadas entre sí. Todos los flujos biogénicos de nutrientes fueron muy variables. La producción primaria debida a las plantas emergentes (Cladium) fue mayor que la fotosíntesis en la columna de agua, la cual experimentó una autotrofia neta durante la mayor parte del periodo de estudio. La sedimentación de los nutrients particulados estuvo dentro del rango de la observada en otros lagos oligotróficos. La desnitrificación no fue tan alta como la esperada a juzgar por el elevado contenido en nitrato del lago, lo cual se debió a la limitación por las escasas concentraciones de fósforo reactivo soluble y carbono orgánico disuelto. El lago perdió CO2 hacia la atmósfera, lo cual sugiere heterotrofia neta, cosa que contradice el resultado referido más arriba, estos datos contradictorios se explican teniendo en cuenta las elevadas entradas de carbono inorgánico por vía hidrológica, que aportaron más carbono gaseoso para su expulsión por el lago hacia la atmósfera. Aunque baja, la producción de CO2 a partir de la formación de CaCO3 en este lago kárstico pudo ser en ocasiones una fuente significativa de CO2. Sin embargo, los flujos biogénicos fueron mayores de lo esperado en ambientes como los lagos fluviales, y se debieron sobre todo al papel que tienen las plantas emergentes en los flujos nutritivos, el cual se suele pasar por alto en los estudios de balances biogeoquímicos. No encontramos relación entre el tiempo de renovación del agua y la acumulación de nutrientes en el lago, lo cual recalca el peso de los flujos biogénicos en la retención de nutrientes. A nivel del ecosistema, nuestro estudio revela la importancia que tiene el contexto hidrogeológico del agua sobre los flujos de nutrientes y la de la vegetación emergente sobre el balance de nutrientes en el lago., This study was funded by the grant PO7-CVI-02598 of Andalucía County, awarded to P. Carrillo, and by grant CGL2009-10408 of the Spanish Ministry of Economy and Competitiveness, awarded to S. Sánchez-Carrillo.

Nutrient patterns in wetlands are usually studied at a single sampling station and not for more than two or three hydrological years. This makes environmental assessment difficult, particularly when spatial heterogeneity and wetland responses depend upon water availability, as often occurs in Mediterranean wetlands. Furthermore, the spatial scale of environmental control of wetland dynamics is usually hypothesized to change as a result of water connectedness, so the higher the rate of water renewal, the larger the spatial scale of environmental control. To test this idea, we carried out a study of monthly nutrient loadings, organic carbon, total nitrogen, and phosphorus in a Spanish hypertrophic floodplain (Tablas de Daimiel National Park) for six years at three sites to ascertain the significance of both the spatial heterogeneity and the long-term responses of nutrient patterns to water availability. Our study demonstrated that strong site effects prevailed on nutrient chemistry in this wetland, irrespective of the degree of wetland connectivity, since there were very few significant correlations among different sites for a single nutrient and no significant correlations with loadings. Causes for this behavior might be that water inputs to this Mediterranean wetland were highly variable and leveling ecological effects were dampened by site processes. Spatially, an increasing gradient of total organic carbon and nitrogen occurred toward the outlet, but total phosphorus peaked in the middle of the wetland. Such a decoupling was also shown by PCA analysis where three different factors explained 69% of overall variability of nutrient patterns: flooding, both organic carbon and total nitrogen content, and total phosphorus. No temporal trend in nutrient content was observed. No simultaneous seasonal patterns were obvious in nutrient data from the same site or for the same nutrient at different sites. Periodicity analyses did not show overlapping of annual rhythms. That lack of patterns could be evidence of the major importance of site processes. This wetland behaved as a sink for nutrients, a fact also suggested by the increasing carbon and phosphorus content in sediments of all sites over time. Sediment nitrogen dynamics, however, might experience differential among-site processes resulting in no trend in accumulation in some areas. These results challenge current views on the spatial scale of environmental control on wetland performance and suggest that the role of water availability in ecological connectivity may be more complex than previously suspected.

This study describes the changes in height and diameter in Quercus ilex trees grown on agricultural land in a semi-arid Mediterranean climate, in response to different soil management practices: mechanical weeding (MW), chemical weeding (CHW) and no treatment (NT); and compares trees grown from 1-year-old saplings and from acorns. After 6 years, trees that had been mechanically weeded were largest; for trees grown from saplings the average height was 120 cm and diameter was 3.83 cm, for trees grown from acorns average height was 100 cm and diameter was 2.56 cm. Soil organic matter increased in all managed plots while phosphorus, nitrate, and water content oscillated between years. The no treatment plot had the highest values for nitrate and organic matter while the chemical weeding plot had the highest level of phosphorus. Annual mean on C/N ratios were higher in the mechanical weeding (12.6 ± 3.3) followed by the chemical weeding (12.0 ± 1.6). Also mechanical weeding treatment showed the lowest soil water content throughout the study. An old tillage-induced compaction zone appeared in all plots at a depth of 12.5–17.5 cm with mechanical weeding causing the greatest compaction. However, no relationships were found with tree heights, neither with spatial compaction zoning. All trees showed the same growth pattern, whether raised from saplings or acorns and irrespective of soil management system. The height and diameter of trees were linked to the sum of height and diameter ratios from previous years. Our study shows that soil management does influence tree growth rate. Mechanical weeding should be considered for afforestation of agricultural lands with Q. ilex in semiarid Mediterranean lands.

9 pages, and figures, and tables statistics., This study evaluates whether the size structure of seston (the sum of living and nonliving particles in the water column) reflects the effects of fish on wetland water quality. Using enclosures, we measured water quality and zooplankton community structure in the presence and absence of two fish species with distinct foraging strategies [benthivorous carp (Cyprinus carpio) and planktivorous mosquitofish (Gambusia holbrooki)]. Seston collected from the enclosures was counted and sized automatically with a Coulter counter, and the size structure in the range of 1–60μm was modelled using the underlying Pareto distribution of particles. Only Cyprinus contributed to a loss of water quality (increased nutrient levels, algal and non-algal turbidity, hypoxia), while both fish species changed zooplankton community composition compared to fishless controls. However, these changes were not reflected in parameters [goodness of fit (r 2) and parameter c (slopes)] of Pareto models. Multivariate statistics suggest that seston size structure responded more to environmental gradients related to water depth but the relationships were also weak. Our overall result contrasts with the regulation of size spectra constructed from living organisms. Although seston integrates many structural and functional features of the water column, the lack of strong relationships between Pareto model parameters and water quality suggests that a size-based approach to characterise seston structure has a limited potential for assessing biota-mediated effects in wetlands in a straightforward manner.

13 pages, and figures, and tables stadistics., Open water evaporation and macrophyte transpiration rates were analyzed in a semi-arid, freshwater wetland in Central Spain over two meteorological periods between 1993 and 1998. The aim was identifying the importance of these variables in the dynamics of evapotranspiration in different water level scenarios. Throughout the vegetation growth period, transpiration versus evaporation ratios were about 2 for cut-sedge, 1 for reed and 0.5 for cattail, but these values declined significantly when calculated on a yearly basis. Open water area to macrophyte cover ratios showed significant dependence on inundation. Increased vegetation cover did not result in a statistically significant reduction of evapotranspiration, but it did increase the transpiration to evaporation ratio. Increased open water area resulted in increased wetland evapotranspiration. The results indicate that Linacre’s theory needs to be modified to take into account emergent macrophyte strategies to flood tolerance and plant physiological traits. The authors provide a conceptual model to explain wetland evapotranspiration dynamics in relation to vegetation cover, physiological strategies and inundation

Summary 1. Natural wetlands have traditionally been considered as efficient ‘ecological engineers’ for waste water treatment. However, the structure and function of many natural wetlands have been severely altered by the chronic exposure to pollutants, especially nutrients. 2. Despite the similarity of symptoms of eutrophied shallow lakes and wetlands, restoration strategies differ distinctly between these rather similar aquatic systems. Many of the tools applied in shallow lake restoration programs, for example biomanipulation, have received little attention in wetland management and restoration. 3. Although a strong conceptual basis for food web management exists, biotic interactions as influences on wetland communities have been largely neglected by wetland scientists and managers. 4. In this paper we show that biomanipulation may have a strong potential for wetland eutrophication abatement. This potential will be demonstrated by reviewing studies carried out in different wetland types in contrasting climatic regions. 5. We propose four different scenarios for when, where and why biomanipulation may be used to rehabilitate freshwater wetlands. These scenarios reflect different settings of hydrological variability, eutrophication sources and gradients of wind exposure and water colour.

The Free Air CO2 Enrichment (FACE) system has proved suitable for exposing plants to elevated [CO2] with minimal disturbance of their natural environment. Here we describe a FACE facility in a floodplain wetland in detail and, additionally, its performance after the first year of operation (2012). The FACE system consisted of six 3-m diameter emission rings in which Phragmitesaustralis was grown. The target [CO2] was 550 μmol mol−1 and fertilization was carried out continuously. Daily temporal [CO2] performance was adequate with 61 and 83 % of air samples at the ring’s centre having a [CO2] within 10 and 20 % of the target, respectively, with values closest to their target during summer months and daytime. Spatial [CO2] distribution showed no significant gradients across the ring. Increased wind speed improved the system’s spatial performance, as [CO2] was within ±10 % of the target in the whole ring. Across the entire fertilization season, CO2 requirements for maintaining a mean [CO2] of 582 μmol mol−1 in wetland plots averaged 17.4 kg CO2 ring−1 day−1. Our requirements (2.5 kg CO2 m−2 day−1) were very low compared to other FACE systems, demonstrating its high potential to study the effects of elevated CO2 in wetlands at low cost., The DECAMERON project (2008/001) funded by the Agency for National Parks of the Spanish Ministry of Agriculture, Food and Environment, provided financial support for the wetland FACE facility. RMwas a FPI fellowship; LSGand RSAwere supported by JAE-PreDoc and JAE-Doc contracts respectively co-funded by the European Social Funds.

6 páginas, and table stadistic, and figures, An enclosure experiment was conducted to assess the separate effects of exotic benthivorous (Cyprinus carpio L.), planktivorous (Gambusia holbrooki Gir.), and omnivorous (Lepomis gibbosus L.) fish on the dynamics of bacterioplankton (BAC) and autotrophic picoplankton (APP) in a semiarid Spanish marsh. Special emphasis was put on simulating the effect of natural fish density situations occurring under periods of hydrological confinement in the wetland, i.e. during summer draw downs or artificial water-level reductions, when fish biomass can reach high levels. The resulting simulation of such a scenario (C. carpio, 5000 to 6000 kg ha–1; L. gibbosus, 1300 to 1700 kg ha–1, and G. holbrooki, 115 kg ha–1) revealed that C. carpio and L. gibbosus significantly increased the trophic level in the enclosures. This resulted in a significant increase of BAC in the respective treatments. G. holbrooki, on the other hand, failed to fuel BAC growth. Considering APP, composed of phycocyaninrich picocyanobacteria Synechococcus sp., no fish treatment effects were detected, suggesting that the fishes, independent of biomasses used, were not important in driving APP. Results indicate that microbial communities respond in different ways to changes in fish biomass in fluctuating wetlands.

Estimates of transpiration are often needed for hydrological management in wetlands. A new and simple method, using a portable steady-state porometer, is presented for estimating transpiration in three aquatic emergent macrophytes (reed, cut-sedge, and cattail). The method was established on the basis of the relationships between transpiration, solar radiation, relative humidity and air temperature. By assessing relationships between all variables in piecewise linear regressions with breakpoint, water loss by transpiration can be estimated. The regression equations are calculated from direct observations including daily averages of climatic variables. Other data used in the model are area-defined leaf density of macrophytes and yearly macrophyte cover. The results of this method in comparison with literature transpiration data confirm the importance of transpiration in the water balance in aquatic ecosystems. The advantage of this method relies on the possibility to determine the physiological variability of transpiration in relation to climatic variables determined in situ. This permits a closer approximation of processes taking place in nature. Given that the required information is easily obtainable and that good estimates of transpiration in emergent macrophytes are provided, the method serves as a valuable tool for wetland hydrology management.

Despite sedimentation being recognized as a very important process in wetlands, very little is known about its dynamics. This study analyzed sedimentation on a short-term scale in the semiarid floodplain wetland Las Tablas de Daimiel National Park (central Spain). In monthly sampling intervals during 1997 and 1998, we measured seasonal and spatial sedimentation patterns of total solids, organic and mineral matter, nitrogen, and phosphorus using sediment traps. The highest mean mass accumulation rates were obtained at the wetland-input site (135 ± 57 g m−2 d−1), but a decrease in sedimentation rates was noted with increasing distance from the inflow (49 ± 39 g m−2 d−1 in the terminal zone of the wetland). Flow and water level explained only 13% of variance in sedimentation. The sedimentation patterns presented clear seasonality, coinciding with the period of vegetation growth. There existed a marked spatial heterogeneity in sedimentation that can be attributed to differences in vegetative cover. In vegetated areas, sedimentation of solids was related with nutrient deposition coming from detritus. Sedimentation of mineral matter dominated over the organic fraction. Autochthonous material comprised a very important fraction of accumulated sediment (between 31–57% of mineral matter and 45–65% of organic matter). Sedimentation of autochthonous total phosphorus made up about 90% of total settling phosphorus. Reed (Phragmites australis) and sawgrass (Cladium mariscus) plant cover significantly explained sedimentation of organic matter in the wetland (R2= 0.78 and 0.57, respectively). The contribution of phytoplankton primary productivity to total organic carbon sedimentation was negligible and observed only at the deeper sampling stations. The autochthonous mineral matter of the settling seston may originate either from primary precipitation of endogenic calcite and/or rapid mineralization of organic matter on the sediment surface. Accretion rates were very high (1.61–3.87 cm yr−1), suggesting that the wetland will silt up within the next century if present rates are maintained. Thus, sedimentation dynamics must be involved in management strategies in order to conserve important wetlands.

A three-year study was carried out in Las Tablas de Daimiel National Park, a Spanish semi-arid wetland, to describe eutrophication patterns and the responses of the main primaryproducers in contrasting inundation years. Total and dissolved nitrogen and phosphorus, phytoplankton chlorophyll-a(monthly) and emergent macrophyte cover (yearly) were measured together with water levels. Water balances were taken to assessphosphorus and nitrogen annual nutrient budgets. The wetland could be termed hypertrophic. Nutrients displayed distinct seasonality because nitrogen peaked both in winter and summer,whereas phosphorus did so in late spring and early summer. A reduction in both total nitrogen and phosphorus in humid yearsdue to higher water levels was also observed. An important spatial heterogeneity in nutrient content occurred throughout the study, part of which could be ascribed to hydrological fluctuations since the input site showed higher mean values in rainy years. Mass balances suggested that sedimentation played a key role in nutrient dynamics, with macrophyte leaching and waterfowl additions being minor sources. Internalloading was much higher than external loading in this wetland,thereby being responsible for higher sedimentation rates.Phytoplankton chlorophyll-a displayed seasonality, withpeaks in late summer, when macrophyte activity was decreasing.No relationship between either chlorophyll-a and nutrients or hydrological conditions could be ascertained formost sampling stations and years of study. However, the waterlevel-dependent, emergent macrophyte sawgrass (Cladium mariscus) presented a statistically significant relationship with both nitrogen and phosphorus. Our results demonstrate thatmacrophytes must be taken into account in wetland eutrophicationmodels. A conceptual model comparing the responses of primary producers to eutrophication in lakes and wetlands is outlined.

This study describes the effects of the American red swamp crayfish, Procambarus clarkii Girard, on water quality and sediment characteristics in the Spanish floodplain wetland, Las Tablas de Daimiel National Park. Our short term enclosure study during a summer drawdown revealed that crayfish acted as a nutrient pump that transformed and translocated sediment bound nutrients to the water column. Water quality impoverishment was mainly due to the increase of dissolved inorganic nutrients (soluble reactive phosphorus and ammonia), and a significant increase of total suspended solids occurred likely as a result of crayfish associated bioturbation. At the same time, crayfish reduced the content of organic matter in the sediment and we observed a slight increase of total sediment phosphorus and nitrogen content as a result of crayfish benthic activity. P. clarkii effects, in terms of internal nutrient loading (229.91 mg TP m−2 d−1), were shown to be important on a local scale, indicating the significance of internal nutrient supply to water column primary producers particularly under low external supply (summer). Extrapolations to the whole ecosystem, however, revealed a negligible crayfish contribution (0.06%) to total internal nutrient loading (0.035 mg TP m−2 d−1). Hence, crayfish spatial heterogeneity patterns are important in global and local matter fluxes and nutrient cycles in wetlands.

(2000). Rainfall-driven changes in the biomass of a semi-arid wetland. SIL Proceedings, 1922-2010: Vol. 27, No. 3, pp. 1690-1694.