Environmental shaping and carbon cycling in a macrophyte-dominated Mediterranean coastal lagoon

[spa] Las lagunas litorales son sistemas altamente dinámicos en los que la vegetación sumergida juega un papel estructural y funcional fundamental. En esta tesis se ha realizado una aproximación a la ecología funcional de una laguna litoral mediterránea dominada por macrófitos (s'Albufera des Grau, Menorca, Islas Baleares). Se han estudiado los principales procesos determinantes de su funcionamiento ecológico, con aproximaciones a la hidrología, al régimen lumínico subacuático y a la dinámica de las praderas de macrófitos. Finalmente se ha caracterizado el metabolismo y el ciclaje del carbono en el sistema como descriptores del funcionamiento del mismo. Se han utilizado distintas escalas temporales de observación para abarcar la máxima variabilidad posible, desde escalas subdiarias, a análisis interanuales o Incluso decadales. La Albufera des Grau es un sistema dominado por el macrófito Ruppia cirrhosa, que muestra un claro ciclo estacional de producción -descomposición. La elevada producción anual de esta especie sitúa la laguna en el rango superior de producción para este tipo de sistemas. La distribución espacial de las praderas viene determinada por la disponibilidad lumínica y por el efecto perturbador de los intensos vientos de componente norte. Por otro lado, la dinámica interanual de la vegetación sumergida está relacionada con los niveles de salinidad y disponibilidad lumínica en verano y primavera respectivamente. El efecto de la disponibilidad de luz sobre la producción primarla bentónica también se pone de manifiesto al analizar el régimen lumínico subacuático. Una fracción importante del bentos de la laguna está potencialmente limitada por luz durante el periodo de crecimiento macrofítico. En las partes profundas de la laguna, esta limitación vendría dada exclusivamente por cambios en la atenuación de la luz en el agua, mientras que en las zonas someras, donde la limitación es menos probable, el nivel del agua también tendría un papel importante. La atenuación de la luz en la columna de agua está determinada, en este sistema, a partes iguales por el fitoplancton y por el carbono orgánico disuelto, mientras que los sólidos inorgánicos en suspensión juegan un papel muy secundario. La hidrología de la laguna ha sido correctamente descrita por un modelo dinámico simple basado en balances diarios de agua y sal en la laguna y en un balance de agua en la cuenca hidrológica. El modelo, calibrado y validado en series independientes de datos, se ajusta correctamente a la dinámica diaria del nivel del agua y la salinidad del sistema y simulaciones para un periodo histórico de 30 años han permitido caracterizar el balance hídrico de la laguna. A pesar de la enorme variabilidad interanual, se ha observado una clara relación de la salinidad media anual con la precipitación total anual, con la cual se ha definido una salinidad de equilibrio para la laguna. La elevada actividad de las praderas de macrófitos se pone de manifiesto en los descriptores metabólicos a nivel de sistema, estimados a partir de variaciones nictemerales de carbono inorgánico disuelto, DIC, y de oxigeno disuelto, DO, en distintas localidades de la laguna. En la dinámica de estos dos componentes influyen, además de los procesos de metabolismo de las praderas, procesos bacterianos anaeróbicos y reacciones químicas que tienen lugar en la columna de agua y en la interfase entre agua y sedimento. A pesar de la importancia del metabolismo interno en la dinámica nictemeral de DIC, a una escala estacional e interanual este componente se ve afectado también por flujos hidrológicos, por el intercambio atmosférico de Co2, y por la precipitación de carbonato cálcico. A nivel de balance de carbono, la laguna actúa como fuente o sumidero en función de la presencia o ausencia estacional de vegetación sumergida, con perturbaciones de este ciclo básico por parte de crecimiento masivos de fitoplancton. La laguna muestra, además, una clara variabilidad interanual. Por otro lado, la estimación de los distintos flujos de carbono orgánico y la exploración isotópica de la red trófica del sistema sugieren que hay un bajo consumo de la gran producción macrofítica, cuyo destino principal sería la rápida descomposición y secundariamente el enterramiento en el sedimento

Sèiem

Sèiem i ens miràvem de reüll. Jo, al costat dret de l’embarcació, amb els peus damunt la caixa blanca, valuosíssima, que mantenia portàtil, llibretes, xeringues i vials a redossa de la inundació. Tot eren regalim

Sèiem

Sèiem i ens miràvem de reüll. Jo, al costat dret de l’embarcació, amb els peus damunt la caixa blanca, valuosíssima, que mantenia portàtil, llibretes, xeringues i vials a redossa de la inundació. Tot eren regalim

Limnological research in the Iberian Peninsula: a ten-year survey of published literature.

Research on limnology in southern Europe had achieved a notable presence in the international arena before the onset of the current dramatic cuts in public investment in science. We assessed the limnological research published in peer-reviewed journals by Spanish and Portuguese (i.e., Iberian) researchers during the decade prior to the economic recession (2000 to 2009). The Thompson Reuters Web of Knowledge database was used to retrieve all publications on limnology authored by researchers affiliated with Spanish or Portuguese institutions independently of the geographical setting of the study. The publishing pattern was characterised in terms of authors, journals, and citation statistics. In addition, a thematic characterisation of the research was performed by a manual assignation of several categorical descriptors combined with a blind word count analysis. Iberian researchers produced an annual mean of 278 papers on limnology. Papers were published in journals that had impact factors ranging from 0.1 to 31.4, with a mean of 2.0. Based on citations, the impact of the Iberian limnological research was not due to a few highly cited papers but rather to a wide number of publications; each paper received a mean of 8 citations. The Iberian limnological research involved up to 5460 researchers, with a mean of 4.3 authors per paper. The research largely focused on fluvial systems, with 47 % of total publications (2778) devoted to these ecosystems. There was a dominant focus on local, within-system aspects of study sites and the research was mostly restricted to the Iberian Peninsula; larger spatial scales of analysis (i.e., landscape, regional, or global) tended to be overlooked. Iberian research addressed fundamental (75 %) rather than applied (17 %) or methodological (5 %) questions and was vastly dominated by observational approaches (75 %). Interestingly, Iberian limnological research increased its scientific productivity during the analysed decade at a higher rate than its international counterpart (increase of 119 %). Overall, Iberian research on limnology appeared to be in good health during the analysed decade. Certain areas have been more studied than others, which opens opportunities to develop new research

Major effects of alkalinity on the relationship between metabolism and dissolved inorganic carbon dynamics in lakes

Several findings suggest that CO2 emissions in lakes are not always directly linked to changes in metabolism but can be associated with interactions with the dissolved inorganic carbon equilibrium. Alkalinity has been described as a determining factor in regulating the relative contributions of biological and inorganic processes to carbon dynamics in lakes. Here we analyzed the relationship between metabolic changes in dissolved oxygen (DO) and dissolved inorganic carbon (DIC) at different timescales in eight lakes covering a wide range in alkalinity. We used high-frequency data from automatic monitoring stations to explore the sensitivity of DIC to metabolic changes inferred from oxygen. To overcome the problem of noisy data, commonly found in high-frequency measurements datasets, we used Singular Spectrum Analysis to enhance the diel signal-to-noise ratio. Our results suggest that in most of the studied lakes, a large part of the measured variability in DO and DIC reflects non-metabolic processes. Furthermore, at low alkalinity, DIC dynamics appear to be mostly driven by aquatic metabolism, but this relationship weakens with increasing alkalinity. The observed deviations from the metabolic 1:1 stoichiometry between DO and DIC were strongly correlated with the deviations expected to occur from calcite precipitation, with a stronger correlation when accounting also for the benthic contribution of calcite precipitation. This highlights the role of calcite precipitation as an important driver of CO2 supersaturation in lakes with alkalinity above 1 meq L−1, which represents 57% of the global area of lakes and reservoirs around the world

The relevance of pelagic calcification in the global carbon budget of lakes and reservoirs

Calcite precipitation acts as a carbon sink in the sediments and a short-term source of carbon dioxide (CO2) to the atmosphere, as widely acknowledged in marine studies. However, pelagic calcite precipitation has received limited attention in lakes. Here we use the relationship between lake water alkalinity and reported calcification rates to provide the first global estimate of pelagic calcification in lakes. Global gross calcification rates amount to 0.03 Pg C yr-1 (0.01 - 0.07) comparable to rates of or­ganic carbon burial, whereas its related CO2 release is largely buffered by the carbonate equilibria. Calcification occurs at water alkalinity above 1 meq/L corresponding to 57 % of global lake and reservoir surface area. Pelagic calcification therefore is a prevalent process in lakes and reservoirs at the global scale, with a potentially relevant role as a sedimentary inorganic carbon sink, comparable in magnitude to the total calcite accumulation rates in ocean sediments

Eutrophication and geochemistry drive pelagic calcite precipitation in lakes

Pelagic calcification shapes the carbon budget of lakes and the sensitivity of dissolved inorganic carbon (DIC) responses to lake metabolism. This process, being tightly linked to primary production, needs to be understood within the context of summer eutrophication which is increasing due to human stressors and global change. Most lake carbon budget models do not account for calcification because the conditions necessary for its occurrence are not well constrained. This study aims at identifying ratios between calcification and primary production and the drivers that control these ratios in freshwater. Using in situ incubations in several European freshwater lakes, we identify a strong relationship between calcite saturation and the ratio between calcification and net ecosystem production (NEP) (p-value < 0.001, R2 = 0.95). NEP-induced calcification is a short-term process that is potentiated by the increase in calcite saturation occurring at longer time scales, usually reaching the highest levels in summer. The resulting summer calcification event has effects on the DIC equilibria, causing deviations from the metabolic 1:1 stoichiometry between DIC and dissolved oxygen (DO). The strong dependency of the ratio between NEP and calcification on calcite saturation can be used to develop a suitable parameterization to account for calcification in lake carbon budgets

Effect of small water retention structures on diffusive CO2 and CH4 emissions along a highly impounded river

The impoundment of running waters through the construction of large dams is recognised as one of the most important factors determining the transport, transformation, and outgassing of carbon (C) in fluvial networks. However, the effects of small and very small water retention structures (SWRS) on the magnitude and spatiotemporal patterns of C emissions are still unknown, even though SWRS are the most common type of water retention structure causing river fragmentation worldwide. Here we evaluated and compared diffusive carbon dioxide (CO2) and methane (CH4) emissions from river sections impounded by SWRS and from their adjacent free-flowing sections along a highly impounded river. Emissions from impounded river sections (mean [SE] = 17.7 [2.8] and 0.67 [0.14] mmol m−2 d−1, for CO2 and CH4, respectively) never exceeded those from their adjacent free-flowing river sections (230.6 [49.7] and 2.14 [0.54] mmol m−2 d−1). We attribute this finding to the reduced turbulence in impounded river sections induced by SWRS compared to free-flowing river sections (i.e., physical driver). Likewise, the presence of SWRS favoured an increase of the concentration of CH4 in impounded waters, but this increase was not sufficient to cause a significant influence in the CH4 efflux from the downstream free-flowing river sections. By contrast, this influenced the larger-scale longitudinal patterns of dissolved CH4, which exhibited a clear shifting pattern along the study stretch, modulated by variables associated with the presence of SWRS, such as higher water residence times, higher sedimentation rates, and higher temperatures. Overall, our results show that the presence of SWRS can modify the concentrations of C gases in highly impounded rivers but exerts a minor influence on diffusive C emissions

Primer C-Hydrochange workshop sobre métodos y técnicas de medida de flujos de CO2 y CH4 en lagos y embalses

La distribución de la reservas de carbono (C) entre compartimentos del Sistema Tierra constituye uno de los principales temasde estudio de la biogeoquímica moderna. Lagos y embalses des-empeñan un papel importante en los intercambios globales de Cmediante la regulación del transporte de este elemento desde loscontinentes hasta los océanos. [...

Carbon dioxide efflux during the flooding phase of temporary ponds

Small water bodies, such as temporary ponds, have a high carbon processing potential. Nevertheless, despite the global occurrence of these systems, the carbon effluxes from such water bodies have been largely overlooked. In this study, we examined the intra- and intersystem variability of carbon dioxide (CO2) effluxes from a set of Mediterranean temporary ponds during the flooding phase, a hot-spot for biogeochemical cycling in temporary systems. The CO2 effluxes showed higher variability among the various sections of each pond (i.e., inundated, emerged-unvegetated and emerged-vegetated) than among the ponds. The emerged-vegetated sections showed the highest CO2 effluxes per unit area and tended to drive the total effluxes at the whole-ecosystem scale. The mean CO2 efflux (121.3 ± 138.1 mmol m 2 d 1) was in the upper range for freshwater ecosystems. The CO2 effluxes were not related to catchment properties but rather to the organic content of the sediments, especially in the emerged sections of the ponds. Our results indicate that temporary ponds, especially their emerged sections, are important sources of CO2 to the atmosphere, highlighting the need to include the dry phases of these and other temporary aquatic systems in regional carbon budgets