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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.

El tratamiento de aguas residuales por medio de los humedales artificiales se utiliza como una tecnologia verde que surge de la necesidad de replicar los beneficios ecosistemicos de los humedales naturales para tratar diversos afluentes de aguas residuales. Este trabajo presenta una revision bibliografica acerca de los diferentes tipos de humedales artificiales y sus procesos depurativos. Si bien existen muchos estudios sobre humedales artificiales, es necesario realizar una sinergia de dicha informacion. No obstante, aunque los humedales artificiales son una frecuente practica de gestion para la mitigacion de contaminantes provenientes de escorrentia agricola y municipal, en muchos paises faltan estudios comparativos sobre su eficiencia depurativa y el mantenimiento a los mismos, asi como profundizar en la investigacion de sustratos alternativos y detallar medidas preventivas para la evitar la colmatacion del sustrato.

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

Recientemente se ha revalorado la relevancia de los sistemas acuaticos epicontinentales en el ciclo global del carbono, ya que estos tienen una gran capacidad de ser tanto sumideros de carbono, hacia sus sedimentos, como fuentes de carbono atmosferico. Sin embargo, la informacion acerca de los sistemas tropicales es aun heterogenea y escasa, situacion particularmente critica, dado que estos sistemas enfrentan problemas crecientes en el panorama del cambio global, contaminacion y eutrofizacion incluidas, particularmente esta ultima, asi como impactos de las estrategias de manejo (e.g., cambios en el nivel de agua). El estudio de la dinamica del oxigeno, criticado en el pasado, ha sido retomado y hoy es nuevamente utilizado ampliamente para estimar la produccion primaria y la respiracion ecosistemica ante la urgencia por estimar los flujos de carbono asociados a los sistemas acuaticos. Se revisan aqui, por ello, los aspectos metodologico-conceptuales asociados a la implementacion moderna del metodo de evolucion del oxigeno y se discuten las ventajas y los problemas asociados a esta metodologia, para facilitar y extender su aplicacion a los sistemas tropicales, donde su implementacion es muy conveniente. Se propone tambien una secuencia metodologica unificadora para hacer posible la comparacion entre estudios, y el escalamiento de los flujos de carbono, tanto espacial como temporalmente. Los inventarios de carbono en diferentes escalas (espaciales y temporales) son necesarios para entender la participacion y las respuestas de los sistemas acuaticos y regiones tropicales (en particular su papel como fuentes o sumideros de carbono) frente al cambio global.

Long-term and seasonal changes in production and respiration were surveyed in the Valle de Bravo reservoir, Mexico, in a period during which high water-level fluctuations occurred (2006–2015). We assessed the community metabolism through oxygen dynamics in this monomictic water-body affected by strong diurnal winds. The multiple-year data series allowed relationships with some environmental drivers to be identified, revealing that water level-fluctuations strongly influenced gross primary production and respiratory rates. Production and respiration changed mainly vertically, clearly in relation to light availability. Gross primary production ranged from 0.15 to 1.26 gO2 m−2 h−1, respiration rate from −0.13 to −0.83 gO2 m−2 h−1 and net primary production from −0.36 to 0.66 gO2 m−2 h −1 within the production layer, which had a mean depth of 5.9 m during the stratification periods and of 6.8 m during the circulations. The greater depth of the mixing layer allowed the consumption of oxygen below the production layer even during the stratifications, when it averaged 10.1 m. Respiration below the production layer ranged from −0.23 to −1.38 gO2 m−2 h−1. Vertically integrated metabolic rates (per unit area) showed their greatest variations at the intra-annual scale (stratification-circulation). Gross primary production and Secchi depth decreased as the mean water level decreased between stratification periods. VB is a highly productive ecosystem; its gross primary production averaged 3.60 gC m−2 d−1 during the 10 years sampled, a rate similar to that of hypertrophic systems. About 45% of this production, an annual average net carbon production of 599 g C m−2 year−1, was exported to the hypolimnion, but on the average 58% of this net production was recycled through respiration below the production layer. Overall, only 19% of the carbon fixed in VB is buried in the sediments. Total ecosystem respiration rates averaged −6.89 gC m−2 d−1 during 2006–2015, doubling the gross production rates. The reservoir as a whole exhibited a net heterotrophic balance continuously during the decade sampled, which means it has likely been a net carbon source, potentially releasing an average of 3.29 gC m−2 d−1 to the atmosphere. These results are in accordance with recent findings that tropical eutrophic aquatic ecosystems can be stronger carbon sources than would be extrapolated from temperate systems, and can help guide future reassessments on the contribution of tropical lakes and reservoirs to carbon cycles at the global scale. Respiration was positively correlated with temperature both for the stratification periods and among the circulations, suggesting that the contribution of C to the atmosphere may increase as the reservoirs and lakes warm up owing to climate change and as their water level is reduced through intensification of their use as water sources.

Ramirez-Zierold JA, Merino-Ibarra M, Monroy-Rios E, Olson M, Castillo FS, Gallegos ME, Vilaclara G. 2010. 2010. Changing water, phosphorus and nitrogen budgets for Valle de Bravo reservoir, water supply for Mexico City Metropolitan Area. Lake Reserv. Manage. 26:23-34. Valle de Bravo reservoir (VB) provides water supply to the Mexico City Metropolitan Area and other surrounding cities. Nutrient loading to this reservoir increased 276% for phosphorus (P) and 203% for nitrogen (N) in a single decade. During 2002–2005, P and N mean loadings to VB were 120.8 × 103 kg P/y and 591.8 × 103 kg N/y. These loadings were quite variable because of source variations from uncontrolled domestic and agricultural inputs. More than half (56%) of the maximal water storage of the reservoir was withdrawn annually. Water withdrawal removed 22% of the P input. Comparative examination of P and N mass balances showed that most (85%) of the P input to VB accumulates in the sediments. Despite the hypolimnetic anoxia that VB...

Valle de Bravo (VB) is a tropical reservoir located (19°21′30″ N, 100°11′00″ W) in the highlands of Mexico. The reservoir is daily swept by strong (7.4 m s−1 mean speed) diurnal (12:00–19:00 h) winds that blow along its two main arms. As expected from its fetch (6.9 km) and its depth (21.1 m mean), the reservoir behaves as a warm monomictic water body. During 2001, VB was stratified from February to October, and well mixed from November to January. Its mean temperature was 19.9°C; the maximum found was 23.8°C in the epilimnion, while a minimum of 17.8°C was registered during mixing. VB exhibited a thermal regime similar to other water bodies of the Mexican tropical highlands, except for a steady increase of its hypolimnetic temperature during stratification, which is attributed to entrainment of epilimnetic water into the hypolimnion. During stratification, the hypolimnion was anoxic, while the whole water column remained under-saturated (60%) during mixing. The flushing time is 2.2 years. Mineralization and total alkalinity are low, which allows strong changes in pH. Ammonia remained low (2.4 μmol l−1 mean) in the epilimnion, but reached up to 60 μmol l−1 in the hypolimnion. Soluble reactive phosphorous had a mean of 0.28 μmol l−1 in the epilimnion and a mean of 1.25 μmol l−1 in the hypolimnion. Nitrate exhibited maxima (up to 21 μmol l−1) during mixing, and also in the metalimnion (2 μmol l−1) during stratification. Low dissolved inorganic nitrogen indicated nitrogen limitation during stratification. Eutrophication is an emerging problem in VB, where cyanobacteria dominate during stratification. At VB chlorophyll a is low during mixing (mean of 9 μg l−1), and high during stratification (mean 21 μg l−1), when blooms (up to 88 μg l−1) are frequent. This pattern is similar to that found in other eutrophic tropical water bodies. We propose that in VB the wind regime causes vertical displacements of the thermocline (0.58–1.10 m hr−1) and boundary mixing, enhancing the productivity during the stratification period in this tropical reservoir.

Tesis de Maestría

As long as lakes and reservoirs are an important component of the global carbon cycle, monitoring of their metabolism is required, especially in the tropics. In particular, the response of deep reservoirs to water-level fluctuations (WLF) is an understudied field. Here, we study community metabolism through oxygen dynamics in a deep monomictic reservoir where high WLF (~10 m) have recently occurred. Simultaneous monitoring of environmental variables and zooplankton dynamics was used to assess the effects of WLF on the metabolism of the eutrophic Valle de Bravo (VB) reservoir, where cyanobacteria blooms are frequent. Mean gross primary production (P g) was high (2.2 g C m(-2) day(-1)), but temporal variation of P g was low except for a drastic reduction during circulation attributed to zooplankton grazing. The trophogenic layer showed net autotrophy on an annual basis, but turned to net heterotrophy during mixing, and furthermore when the whole water-column oxygen balance was calculated, considering the aphotic respiration (Raphotic). The high total respiration resulting (3.1 g C m(-2) day(-1)) is considered to be partly due to mixing enhanced by WLF. Net ecosystem production was equivalent to a net export of 3.4 mg CO₂ m(-2) day(-1) to the atmosphere. Low water levels are posed to intensify boundary-mixing events driven by the wind during the stratification in VB. Long-term monitoring showed changes in the planktonic community and a strong silicon decrease that matched with low water-level periods. The effects of low water-level on metabolism and planktonic community in VB suggest that water-level manipulation could be a useful management tool to promote phytoplankton groups other than cyanobacteria.