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[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.

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.

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.”

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 ...

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).

[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.

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).

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.

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.

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

In wetlands it is still usual to use the same indicators of eutrophication which were developed to study the effects of nutrient enrichment in lakes; however, since hydroecology and biogeochemistry of wetlands is significantly different from lakes, monitoring of these indicators does not allow a good diagnosis of the changes undergone by the wetland ecosystem under nutrient enrichment scenarios. Microbial activities and their respective community responses have been considered as a measure of ecosystem stability and an indicator of ecosystem perturbation through changes on functional properties associated with nutrient cycling. As in most aquatic ecosystems, the addition of a limiting nutrient to wetland ecosystems promotes primary productivity and stimulates microbial processes. As nutrient loading increase, biogeochemical processes in wetlands are altered, changing their concentrations in water and soil, and therefore, nutrient fluxes and cycling. Nutrient enrichment induces changes in soil physicochemical and microbiological characteristics that may then serve as indicators of nutrient enrichment. In this review, a set of microbial community measurements known to be sensitive to nutrient enrichment in aquatic systems, such as extracellular enzyme activities, respiratory activities, microbial biomass C, N, and P, and microbially mediated N and P turnover rates have been used to characterize physiological response of the microbial community to wetland eutrophication. Some indicators as metabolic efficiency and phosphatase activity clearly reflect the main shifts on wetland ecosystem processes induced by nutrient enrichment and may be considered better than those that are currently used to assess the effects of eutrophication. Moreover, the combined use of different ecophysiological measurements such as extracellular enzymatic ratios and microbial biomass under resource allocation models and ecological stoichiometry demonstrates that ecophysiological measures are sensitive indicators of wetland eutrophication. Further studies are needed refining this approach to get the complex biogeochemical variability of the different wetland types, and to move from a site-based heuristic model to a holistic approach, describing eutrophication patterns in wetlands.

Growing interest in the effects of global change on the metabolism, stoichiometry and cycling of carbon in aquatic ecosystems has motivated research on the export of organic carbon (OCE) from catchments. In this article, quantitative and functional features of the annual export rates of total, particulate and dissolved organic carbon (TOC, POC and DOC) were reviewed, and the stoichiometry of export (OC:N, OC:P and N:P) from 550 catchments worldwide was reported. TOC export ranged 2.1-92,474 kg C km-2 year-1, POC export ranged 0. 4-73,979 kg C km-2 year-1 and DOC export ranged 1.2-56,946 kg C km-2 year-1. Exports of TOC and DOC were strongly linked, but POC export was unrelated to DOC. The DOC fraction comprised on average 73 ± 21% of TOC export. The export rates of organic carbon were poorly related to those of total nitrogen and total phosphorus. Discrete and continuous environmental variables failed to predict TOC export, but DOC export was influenced by discharge and catchment area worldwide. Models of OCE in different catchment types were controlled by different environmental variables; hydrological variables were generally better predictors of OCE than anthropogenic and soil variables. Elemental ratios of carbon export in most catchments were above the Redfield ratio, suggesting that phosphorus may become the limiting nutrient for downstream plant growth. These ratios were marginally related to environmental data. More detailed hydrological data, consideration of in-stream processes and the use of quasi-empirical dynamical models are advocated to improve our knowledge of OCE rates and those of other nutrients. © 2010 Springer Science+Business Media B.V., This article is funded by Projects 81/2005 and 001/2008 of the National Parks’ Network of the Spanish Ministry of the Environment.

Some freshwater ecosystems have received waste water for many centuries (AlvarezCobelas & Verdugo, 1995), i.e. the Latium wetlands close to Rome or the Thames and the Spree rivers downstream London and Berlin, respectively. The strong development experienced in many areas of the world in the 20th century has resulted in increasing waste water disposal almost everywhere that has increasingly threatened freshwater ecosystems receiving these loadings. The concern of human health and, later, ecosystem health resulted in the implementation of waste water treatment facilities in many developed countries, such as those of Northern and Central Europe, USA, Canada and Japan (Tchobanoglous et al., 2003), which diminished wastewater inputs to freshwater environments. Unfortunately, this has not been the case in many semiarid countries whose economy or, more often, some lack of concern for environmental quality does not enable funding enough for these otherwise expensive facilities. While waste water pollution cannot always be abated, its effects are likely to be diminished if enough water is available to produce both dilution and wash out, as often occurs in cold temperate and tropical environments. Unfortunately, this is not the case in semiarid areas where rainfall is unevenly distributed throughout the year, also showing a strong interannual variability. For example, Fig. 1 depicts the long-term (19452006) annual precipitation falling on a semiarid central Spanish area, which results in an average of 418 ± 128 mm/year, ranging 189-857 mm/year. In fact, traditional approaches to water management in semiarid regions have been based more on the increase of water availability rather than improving the water quality of waste waters to make them feasible for future use. In water shortage scenarios, domestic lifestyle adaptations and optimization of water consumption by both agriculture and industry have been managed to maintain the balance between water supply and demand. However, although this balance could be achieved and the amount of waste water reduced, the characteristic low water flow of semiarid rivers makes impact of waste water discharge in freshwater ecosystems stronger. Streamwater discharge to wetlands and lakes is highly variable over time in semiarid areas. Fig. 2 shows an example of these fluctuating water flows of a semiarid river that drains to a central Spanish wetland (Las Tablas de Daimiel National Park). Semiarid regions of the world are confronted with a largely unpredictable

The traditional perception of wetlands as nutrient sinks has led them to be used as wastewater disposal areas for a long-time, resulting in a severe alteration of the structure and function by eutrophication. Nutrient loading is usually linked to hydrological alterations which encompasses shifts in vegetation patterns and nutrient cycling. The eutrophication process in wetlands accelerates primary productivity and increases net accumulation of organic matter and nutrients but also enhances organic matter decomposition, microbial activity and soluble nutrients in sediments. Internal loading becomes the main nutrient source to the wetland, even in the years of low external inputs, controlling the nutrient dynamics. Since soil phosphorus microbial biomass responds positively to phosphorus enrichment in wetlands, mineralized phosphorus in wetland soils appear as the most responsive microbial indicator to nutrient enrichment in wetlands. Therefore, phosphorus internal loading is the critical factor in regulating eutrophication status of wetlands. N2O and N2 emissions by wetlands can be enhanced in the future as nitrate availability in wetlands continues to be high due to increased pollution

13 pages, figures, and tables statistics., Thirty five catchments in semiarid Central Spain were monitored monthly in late winter and spring to search for relationships between environmental variables (sedimentary nutrients and hydrological topographical, geological, pedological, land use factors) and nutrient concentrations and exports. Results enabled to outline differences between semiarid and moist catchments, the latter drawn from other studies. While land use, topography and ecotone features explained an important fraction of overall variance of nutrients in moist areas, geological and pedological features were much better descriptors in semiarid catchments. Runoff explained most variability of total carbon, organic carbon and nitrogen export, and soil types and carbon and phosphorus contents stored in stream sediments best explained total phosphorus, dissolved- and particulate organic carbon export in semiarid catchments. In moist catchments geology, climate, pedology and land use were shown to influence nutrient export. Hydrology potentially swamped effects related to land use and landscape structure (i.e. topographical, geological and soil factors). Thus nutrient concentration and export in semiarid catchments deviate from those in moist catchments which is due to the overriding effects of hydrological features, geology and pedology. Further research, including the application of combined GIS techniques and modeling approaches, is needed to generalize our findings over other semiarid areas.

Wetland loss is common worldwide. In Spain, around 90% of the surface covered by floodplain wetlands has disappeared during the last century, and only 32 km2 remain as of today. Las Tablas de Daimiel National Park (20 km2) is unique in Mediterranean Europe. It is the most representative Spanish floodplain wetland nowadays and depicts the core area of La Mancha Humeda Biosphere Reserve (8,000 km2), one of the main wetland district occurring in the semi-arid Mediterranean Europe. Despite the ecological richness supported by this wetland, a controversial history of desiccation, groundwater overexploitation and water quality deterioration threatens this wetland since the 1950s. This chapter describes the main features of the wetland as well as of its basin, revising all impacts received and their environmental consequences. Groundwater overexploitation by irrigation farming is discussed as the main cause of wetland degradation in the socioeconomic framework of the Upper Guadiana River Basin.

Water quality has historically relied upon wetland openness and water availability. For many years until 1986, Las Tablas de Daimiel wetland was enabled to export water and materials downstream, thus diminishing the impairing effects of pollutant storage. Since 1987, when the wetland was dammed, good-quality inputs of low-salinity groundwater were discontinued, streams directed urban and agricultural wastewater towards the wetland, discharge inputs were rather low, due to groundwater exhaustion in the catchment and, hence, its internal loading had greatly increased. As a result, wetland salinization, pollution and eutrophication increased both in water and sediments, and siltation appeared as a severe threat. This chapter will review long-term patterns (1945–2007) of these processes, paying special attention to wetland connectivity and water export downstream.

16 pages, figures, and tables statistics., We reviewed global P export and its controlling factors from 685 world rivers. We used available continuous (runoff, rainfall, catchment area, % land use, and population density) and discrete (runoff type, soil type, biome, dominant land use, dominant type of forest, occurrence of stagnant water bodies in catchment, and Gross Product per Capita [GPC]) variables to predict export of P fractions. P export (kg P km22 y21) spanned 6 orders of magnitude worldwide. The distribution of all fractions of P export (total P [TP], soluble reactive P [SRP], and nonSRP [dissolved organic and particle-bound P]) was right skewed. Export of nonSRP had the highest coefficient of variability, and nonSRP was the dominant part of export. The available environmental variables predicted global P export fairly well (R2 = 0.73) if total N export was included in calculations. The unexplained variance in P export might be attributed to noise in the data set, inaccuracy of measurements of environmental variables at fine scales, lack of quantitative data on anthropogenic P sources, insufficient knowledge of P behavior in catchment soils, and nonlinearity of controlling processes. P exports were highly variable among catchment types, and runoff and population density were the predictors shared by most models. P export appeared to be controlled by different sets of environmental variables in different types of catchments. Quasi-empirical, mechanistic models of P export performed better than did empirical models. Our mechanistic understanding of P export could be improved by refining current analytical methods to obtain fast and reliable values of all P fractions in aquatic ecosystems and by incorporating better and more detailed data on catchment features, anthropogenic sources of P, and instream variables in a mechanistic modelling framework.

9 pages, 6 figures, 3 tables, Nutrient (C, N and P) fluxes were monitored in a microtidal semi-arid mangrove system, which links a semi-enclosed shallow coastal lagoon with the Gulf of California. We assessed the role of the mangrove ecosystem as a nutrient sink/source and determined how mangrove litterfall rates, tidal regime and climate factors influence these fluxes. Despite high seasonal differences in DOC, POC, N-NO3 and TP levels, nutrient concentrations were only marginally influenced by either hydrological variables or the concentration of these fractions in the adjacent lagoon. The carbon budget appeared to be balanced throughout the study. Retention rates in the mangrove system were related to litterfall rates. Export of DIN was observed mainly in the wet season due to the low nitrogen assimilation efficiency of the system. Import of organic nitrogen was related to the high retention efficiency of particulate organic nitrogen. Phosphorus fractions were imported and retained in the mangrove supporting previous findings that mangroves are phosphorus sinks. Finally, through a simple meta-analysis we tested the quantitative importance of main variables (tidal flow, tidal elevation, tidal range, rainfall, mangrove catchment area, litterfall) controlling mangrove nutrient dynamics. Although results suggest that generalizations can be made about factors regulating nutrient export from mangroves, the lack of statistical significance highlights the relative importance of the local environment for the magnitude of nutrient exchange in mangroves. Future research should focus on finding mechanistic models to explain these general patterns, taking into account the main biogeochemical processes and their roles in coastal ecosystem ecology., This research was supported by the Mexican Secretary of Natural Resources and Environment (SEMARNAT-CONACYT; contract SEMARNAT-2002-C01-0147).

14 pages, and tables statistics., This study describes the long-term changes of spatial patterns of cut-sedge (Cladium mariscus) and common reed (Phragmites australis) in the Spanish floodplain wetland Las Tablas de Daimiel. Using seven sets of aerial photographs, we determined changes in their spatial patterns (size of patches) between 1945 and 2001 that resulted from combinations of natural change and anthropogenic stress (irrigated agriculture, waste water discharge, fire, ploughing). Our approach consisted in using 1 ha cells as units of spatial resolution in principal coordinates of neighbour matrices and spatial correlograms to assess the spatial scale of interest and spatial patterns at (1) the whole wetland and (2) two areas of the wetland with locally contrasting biophysical settings and anthropogenic stress history. Results showed that vegetation spatial patterns were influenced by natural variability until the 1970s. Thereafter, anthropogenic perturbation became the main driver of vegetation change, especially in the lower part of the wetland where local impacts were stronger. Natural variability did not fragment cut-sedge patches, and the effects of biological traits were less important for its spatial pattern. By contrast, man-made change resulted in a marked cut-sedge cover decrease and patch fragmentation, and the importance of its biological traits on spatial patterns increased. The trends of reed spatial patterns were generally opposite to, but not as clear as those for, cut-sedge. The trends of spatial patterns were especially evident at very broad (3,500–10,000 m) and broad (1,000–3,400 m) spatial scales. Competition for space and abiotic factors (water quality and water depth) were not strong predictors of cover variability at the 1-ha scale, particularly in the lower area of the wetland. This suggests that other environmental variables need to be considered in spatially explicit modelling of vegetation spatial patterns in wetlands. Consideration of spatial hierarchies and species-specific ecological traits is paramount to the conservation of degraded wetlands.

9 pages, and tables statistics, and figures Man-made change in wetland ecosystems is mainly a 20th century process. Here, we report the changes over the last 55 years in the hydrology and botany of a Spanish semi-arid wetland, Las Tablas de Daimiel, a Ramsar site and a National Park. The land- scape is valuable because of interesting waterfowl and plant species (particularly, Netta ru na and Cladium mariscus) brought about by the ¯uctuations in water table arising from the interaction of surface ¯ooding due to stream- and groundwater discharges and water retention by watermill dams. However, drainage reduced the wetland area to one seventh of its original value in 8 years between 1965 and 1973, and watermills were destroyed in the 1960s. Water pollution, mainly organic matter, nitrogen and phos- phorus, coming from point (towns and agroindustry) and non-point sources (agricultural practices in the watershed) started in the late 1970s and peaked by the middle of next decade, decreasing later as a result of newly-implemented, water treatment plants in the catchment area. Water availability was reduced greatly between the late 1970s and the 1990s because of irrigation programs in the catchment area, which exhausted the groundwater aquifer, and their e ects on plants were mediated by decreasing yearly average ¯ooding and its variability. The combined e ect of increased eutrophication and decreased water inputs reduced the Cladium cover 10-fold, reduced the extent of Charophyte meadows and three quarters of hydrophyte species were lost. The reed (Phragmites communis) cover increased 22-fold. Later, a sudden increase in water inputs coming from a nearby aquifer raised the number of hydrophytes and the Cladium cover, and reduced the reed cover. Thus, decreases in water quantity and quality have acted together on wetlands over the last 35 years a ecting plant species richness and cover. Wetland survival is endangered if no remedial actions, such as those we propose, are implemented.

Ecological systems may occur in alternative states that differ in ecological structures, functions and processes. Resilience is the measure of disturbance an ecological system can absorb before changing states. However, how the intrinsic structures and processes of systems that characterize their states affects their resilience remains unclear. We analyzed time series of phytoplankton communities at three sites in a floodplain in central Spain to assess the dominant frequencies or "temporal scales" in community dynamics and compared the patterns between a wet and a dry alternative state. The identified frequencies and cross-scale structures are expected to arise from positive feedbacks that are thought to reinforce processes in alternative states of ecological systems and regulate emergent phenomena such as resilience. Our analyses show a higher species richness and diversity but lower evenness in the dry state. Time series modeling revealed a decrease in the importance of short-term variability in the communities, suggesting that community dynamics slowed down in the dry relative to the wet state. The number of temporal scales at which community dynamics manifested, and the explanatory power of time series models, was lower in the dry state. The higher diversity, reduced number of temporal scales and the lower explanatory power of time series models suggest that species dynamics tended to be more stochastic in the dry state. From a resilience perspective our results highlight a paradox: increasing species richness may not necessarily enhance resilience. The loss of cross-scale structure (i.e. the lower number of temporal scales) in community dynamics across sites suggests that resilience erodes during drought. Phytoplankton communities in the dry state are therefore likely less resilient than in the wet state. Our case study demonstrates the potential of time series modeling to assess attributes that mediate resilience. The approach is useful for assessing resilience of alternative states across ecological and other complex systems., This study was also funded by the projects CGL 2009 10292 (Spanish Ministry of Economy and Competitiveness) and 001/2008 (Spanish Ministry of Environment and National Parks Authority).

This study attempts to describe changes in plankton biomass (including bacteria, phyto- plankton, ciliates, rotifers, and crustaceans) in the semi-arid, hypertrophic, freshwater wetland, Las Tablas de Daimiel National Park (central Spain), in relation to water inflow. An inter-annual compari- son of 1996 and 1997, with contrasting rainfall, reveals that inflows in the form of flooding act as a bottom-up structuring force on total plankton biomass. However, the responses of plankton biomass to flooding were different in strength between the two years, which can be attributed to shifts in plankton community structure. Crustacean zooplankton conditioned total plankton biomass in 1996, based on the relationship between the high individual biomass and community development. Crust- aceans decreased in 1997, while bacteria, phytoplankton and rotifers increased. The quantitative increase of the latter groups resulted in a higher total plankton biomass in 1997. The key position of crustaceans in the wetland plankton is also reflected in their capability for exerting significant top- down control, which was clearly evident in 1996 but weaker in 1997, based on their numerical reduction. Statistical analyses provide evidence that the decline of trophic interactions in 1997 is related to the strength of flooding in that year, thereby highlighting the significance of the disruptive action of physical disturbance on biotic interactions in the plankton. Flooding and areal inundation were also shown to be significant for spatial heterogeneity. In 1996, site-specific development took place in the absence of prolonged flooding effects, resulting in high spatial heterogeneity. In 1997, however, remarkable homogenization of plankton biomass occurred along the major water flow path. Thus, wetland landscape heterogeneity depends on inflows which condition areal inundation. This, in turn, influences plankton dynamics.