Current & past projects
Macrophytes and global change: horizontal food web and nitrogen cycle (MACROFITOS)
CGL2014-54502 - Ministry of Economy, Industry and Competitiveness, National Plan of Research-Development-and-Innovation. 01/01/2015 - 31/12/2018. Funds: 137,600 €. IP: C. Rojo (C1-1-P; U. Valencia), S. Sánchez-Carrillo (C2-2-P).
This is a coordinate project carried out jointly with the University of Valencia (C. Rojo and M.A. Rodrigo). The main goal of the project is to assess how macrophytes modulate structure and function of freshwater ecosystems under global change. This implies two types of interactions: i) community changes as mediated by macrophytes (mostly charophytes) arising from environmental changes, and ii) enhancing or inhibiting effects of these changes in processes related with N cycle. Our lab is dedicated to this last interaction.
Our hypothesis is that global change stressors impinge on functional groups of horizontal (planktic-benthic) food web through infochemicals by modifying environmental conditions and changing microbial transformations of N and its balance in freshwaters. Chara hispida is the structuring species of the community chosen for experimentation, which interact with the planktic-benthic food web through allelopathy, thus shaping the horizontal food web (HFW). This charophyte is gathered from two distinct environments, namely, one oligotrophic, deeper and cold ecosystem and other eutrophic, shallower and warmer ecosystem. The environmental factors whose changes are suspected to affect charophytes are temperature increase, increasing pulses of the RUV:PAR ratio arising from high frequency, small ozone holes which have already been described for the Mediterranean area. N content increase, which has also considered to be important in eutrophication processes, did not affect significantly the performance of C. hispida. Response variables will concern HFW and both agents and processes of N cycle, such as i) changes in architecture, growth and molecular composition (stoichiometry, N isotopes, infochemicals and pigments) of Charophytes; ii) structural changes (functional diversity, food web architecture, size spectrum) and metabolism (photosynthesis, respiration) of HFW; iii) changes in genetic potential of nitrification and denitrification and its potential rates in environments with and without macrophytes; iv) denitrification, nitrification, anammox and DNRA.
Our approach will be mechanistic and experiments will be carried out at three, increasingly complex spatial scales. Stressors and their synergies on charophytes and the N cycle will be tested in microcosms. The effect of two combinations of stressors, namely those of the strongest and the weakest adverse effect, will be tested on HFW in mesocosms using model environments which encompass water and sediments gathered from their original environment. Finally, we will undertake an experiment with limnocorrals in a shallow environment where the more resistant-to-change charophyte meadows have been grown, hence evaluating community changes and the efficiencies of N cycle.
Our results will prove relevant to several areas of expertise: i) the search for relationships between ecosystem biodiversity and function; ii) the forecast of charophyte meadows changes of our lakes and wetlands, iii) the modeling of N cycle as related with global change stressors; and last but not least iv) the application of these knowledge to environmental management of Mediterranean freshwater ecosystems.
Isotope biogeochemistry applied to lake metabolism (BIOMET)
CGL2009-10408 - Ministry of Science and Innovation, National Plan of Research-Development-and-Innovation. 01/01/2010-31/12/2013. Funds: 120,000 € IP: S. Sánchez-Carrillo.
The in situ addition of stable isotopes of 13C and 15N as large-scale tracers of aquatic ecosystems has significantly improved our knowledge of numerous biogeochemical processes. Its capacity lies in the combination of the theory of isotopic ecology with the enrichment of nutrients without disturbance (i.e. nutrient enrichment). The temporal stability of stable isotopes and the processes governing isotopic fractionation make them useful as tracers, thus allowing measurement of simultaneous ecological and biogeochemical processes at the whole-ecosystem scale. The release of 13C and 15N in aquatic ecosystems has represented an important advance in the study of aquatic metabolism and basal resources, in the understanding of the structure of the food webs or in the processes driving carbon and nitrogen cycles. Currently, the addition can be considered as a powerful complementary tool for the study of ecological and biogeochemical processes at ecosystem scale.
This project has focused on the usefulness of stable isotopes for the study of function and structure of aquatic ecosystems. First, using the natural abundance of 13C and 15N in secondary consumers in 8 lakes located in different parts of the world, we tested the trophic metric based on stable isotopes and constructed from a Bayesian approach to evaluate the effect of the main abiotic variables driving the trophic architecture of lake food-webs. Secondly, in a third order agricultural Mediterranean temporary stream exposed to urban wastewater discharges, the metabolism has been studied, including the hyporheic, and the NH4+ spiralling and the results were compared with those obtained by a continuous injection during 5.5 hours of (15NH4)2SO4. Both approaches give similar results but isotopic allows to quantify not only the NH4+ assimilation but also the transformation by different microbial processes. Finally, in an oligotrophic lake, a study of N metabolism was carried out by adding (15NH4)2SO4 in a 12 h pulse combined with a quantitative analysis (qPCR) of the functional genes of denitrification, nitrification, anammox and DNRA in the lake. Results demonstrated sediments have a greater microbial potential than water, being higher in the fluvial environment than in lacustrine. While streams shown high nitrifier and denitrifier potential , the lake only shown genes associated with denitrification. The isotopic enrichment showed that an important fraction of 15N added in the form of ammonium –which was not assimilated in the lake– was subsequently retained at the outlet stream, where the microbial activity resulted more active. The plants assimilated the added 15N differently depending on their preference for ammonium or nitrate as a nutrient. Finally, the 15N isotopic signal in the gases (N2 and N2O) indicated denitrification was coupled to the nitrification in this oligotrophic lake.
Remote detection of global change effects on ecology and biogeochemistry of Las Tablas de Daimiel National Park (DECAMERON)
001/2008 - Ministry of Environment, National Plan of Environmental Research-Spanish National Park Network. 20/12/2008-30/06/2013. Funds: 125.000 €. IP: S. Sánchez-Carrillo
The Free Air CO2 Enrichment (FACE) system has proved suitable for exposing plants to elevated [CO2] with minimal disturbance of their natural environment. In this project we built a FACE facility in a floodplain wetland located in central Spain (Las Tablas de Daimiel) which was under operation during the 2012 and 2013 in order to test the effects of elevated atmospheric carbon dioxide (eCO2) on reed (Phragmites australis) and in the wetland soil environment. More specifically, we tested the effect of eCO2 on P. australis growth, photosynthesis, transpiration, and biomass, its effect on modifying plant and soil ratios of carbon, nitrogen, and phosphorus, and if the strong environmental variability of this wetland modulates these responses. 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 [average CO2≈ 582 µmol mol-1] . 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.
Previous FACE experiments have indicated that eCO2 stimulates growth in diverse terrestrial ecosystems. Studies of the effects of eCO2 on wetland plants have indicated a similar response, but these studies were mostly performed in growth chambers. Our results of two-year FACE experiment show that effects of eCO2 in this wetland environment are more complex than previously believed, probably due to hydrological effects. The effects of eCO2 on reed plants were cumulative, and manifested at the end of the growing season as increased instantaneous transpiration efficiency (ITE, ratio of net photosynthesis to transpiration), which was dependent on plant age. However, this increase did not result in a significant increase in biomass, because of excessive root exudation of carbon. These observations contrast with previous observations of wetland plants to increased atmospheric CO2 in growth chambers, and shed new light on the role of wetland plants as a carbon sink in the face of global climate change. The combined effects of water stress, eCO2, and soil carbon processes must be considered when assessing the function of wetlands as a carbon sink under global change scenarios. In soil, CO2 enrichment resulted increasing 44% the enzyme activity of protease in reed plots. A parallel tracking using field hyperspectral spectroradiometry displayed that three indexes (NDNI, TVI and CRI2) showed spectral changes in reed plants as related to CO2 enrichment, although any significant interactions between treatment factor and time factor were established. Transpiration was the best ecophysiological variable to be modeled through spectral measurements by means of two indexes which includes plant water contents (NDWI and SIWSI). However, the lack of statistical relationship between this variable and CO2 enrichment limits its applicability to the existence of intermediate relationships with other variables that did respond to CO2 fertilization. Finally, we developed a basic protocol for remote sensing to identification of specific spectral features of the Mediterranean wetland degradation associated with climate change.
Previous FACE experiments have indicated that eCO2 stimulates growth in diverse terrestrial ecosystems. Studies of the effects of eCO2 on wetland plants have indicated a similar response, but these studies were mostly performed in growth chambers. Our results of two-year FACE experiment show that effects of eCO2 in this wetland environment are more complex than previously believed, probably due to hydrological effects. The effects of eCO2 on reed plants were cumulative, and manifested at the end of the growing season as increased instantaneous transpiration efficiency (ITE, ratio of net photosynthesis to transpiration), which was dependent on plant age. However, this increase did not result in a significant increase in biomass, because of excessive root exudation of carbon. These observations contrast with previous observations of wetland plants to increased atmospheric CO2 in growth chambers, and shed new light on the role of wetland plants as a carbon sink in the face of global climate change. The combined effects of water stress, eCO2, and soil carbon processes must be considered when assessing the function of wetlands as a carbon sink under global change scenarios. In soil, CO2 enrichment resulted increasing 44% the enzyme activity of protease in reed plots. A parallel tracking using field hyperspectral spectroradiometry displayed that three indexes (NDNI, TVI and CRI2) showed spectral changes in reed plants as related to CO2 enrichment, although any significant interactions between treatment factor and time factor were established. Transpiration was the best ecophysiological variable to be modeled through spectral measurements by means of two indexes which includes plant water contents (NDWI and SIWSI). However, the lack of statistical relationship between this variable and CO2 enrichment limits its applicability to the existence of intermediate relationships with other variables that did respond to CO2 fertilization. Finally, we developed a basic protocol for remote sensing to identification of specific spectral features of the Mediterranean wetland degradation associated with climate change.
Carbon sources and sinks in the wetland Las Tablas de Daimiel National Park (CARBONDAI)
81/2005 - Ministry of Environment, National Plan of Environmental Research-Spanish National Park Network. 01/01/2006-31/12/2009. Funds: 85.000 €. IP: M. Álvarez-Cobelas
Currently, the primary production in the wetland Las Tablas de Daimiel is very high, according with the elevated biomass of its plant communities. When the plants die, this organic matter accumulates in the wetland, reducing its water storage capacity, damaging the environmental quality for the flora and fauna, contributing to the coloration of the waters and affecting visitors with unpleasant odors. Carbon is involved in all these aspects, but data on sources (inputs from the watershed, methane production and carbon dioxide by primary producers, soil and bacteria) and sinks (mainly photosynthesis of primary producers and sedimentation in the wetland) existed and also lacked updated information on the chemical composition of the carbon stored in their soils, especially after the intense disturbances that have affected the area in recent decades. For all these reasons, in this project was proposed a study to evaluate these sources and sinks and to develop environmental guidelines for the National Park Staff in order to reduce the accumulation of organic matter in the wetland.
During the study period, the wetland was a net carbon sink, storing around a t C per ha per year. This quantity is higher than that of cold temperate wetlands and the Amazon, but it is lower than that of semi-arid pine forest and cold temperate grassland. The processes of carbon accumulation were mainly due to plant photosynthesis because there was no water inflow into the wetland during the study period. The production of emergent macrophytes and terrestrial plants was much higher than that of submerged macrophytes and phytoplankton, but all of them were very variable according to the zone of the wetland. Soil microbial respiration was ever higher than plant respiration, but always very variable, depending on the wetland site. Due to the lack of flooding during the study period, the methane emission rates were practically negligible. Only phytoplankton showed an emission ratio (Respiration: Production) that, at times, could have supposed net emission of carbon to the atmosphere, but this community was almost negligible during this period because the small flooding area. The other communities of primary producers always behaved as net carbon sinks which forced the carbon budget of the wetland ecosystem. Between 6 and 7% of the total dry matter present in the wetland soils is organic carbon with the inorganic carbon reaching around 14%. Zones with permanent flooding and / or periodic flooding are the richest in recalcitrant carbon and they are dominated by carbon compounds rich in methyl, methoxy and alkyl groups.
During the study period, the wetland was a net carbon sink, storing around a t C per ha per year. This quantity is higher than that of cold temperate wetlands and the Amazon, but it is lower than that of semi-arid pine forest and cold temperate grassland. The processes of carbon accumulation were mainly due to plant photosynthesis because there was no water inflow into the wetland during the study period. The production of emergent macrophytes and terrestrial plants was much higher than that of submerged macrophytes and phytoplankton, but all of them were very variable according to the zone of the wetland. Soil microbial respiration was ever higher than plant respiration, but always very variable, depending on the wetland site. Due to the lack of flooding during the study period, the methane emission rates were practically negligible. Only phytoplankton showed an emission ratio (Respiration: Production) that, at times, could have supposed net emission of carbon to the atmosphere, but this community was almost negligible during this period because the small flooding area. The other communities of primary producers always behaved as net carbon sinks which forced the carbon budget of the wetland ecosystem. Between 6 and 7% of the total dry matter present in the wetland soils is organic carbon with the inorganic carbon reaching around 14%. Zones with permanent flooding and / or periodic flooding are the richest in recalcitrant carbon and they are dominated by carbon compounds rich in methyl, methoxy and alkyl groups.
Effects of flood pulses on carbon biogeochemistry of Mediterranean flooplain wetlands (FLOODMED)
Spanish Council for Scientific Research (Proyecto Intramural de Incorporación IE320). 01/09/2007-31/12/2008. Funds: 35.000 €. IP: S. Sánchez-Carrillo
Semi-arid floodplains are important regulating the water quality of rivers and acting as landscape buffers. Flooding plays a significant role on stream biogeochemistry, either as source or sink of carbon, nitrogen and phosphorus, through diverse biogeochemical processes mediated by soil microbial biomass. Flood pulse changes alter subsidies provided by either streams or floodplains, modifying nutrient balances and, hence, ecosystem processes. The impact of these changes on floodplain nutrient inputs –as flood mediated– on floodplain CO2 fluxes was unknown until this project was performed. 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<0.01). Soil CO2 emission rates during drying time were significantly related with the duration of previous flooding and inter-flooding intervals (R2= 0.52-0.64, p=0.03). During the first stage of desiccation, the high soil water content appears to limit aerobic metabolism. Soil respiration rates similar to those of control plots measurements occurred 1-2 weeks later. Then, soil respiration increased to a maximum rate which was delayed 5-8 weeks, as high soil water content limited microbial activity. While more than 7 days of inundation promoted denitrification, organic nutrients supplied by flood water increased 1% soil respiration during drying. Differences between SF and LF plots in soil CO2 emissions only appeared after floodplain soil had been subjected to two consecutive flood-dry cycles. 70 days after the second inundation ended, CO2 fluxes achieved similar values in all treatments. Daily soil CO2 emission rates during the entire study period (117 days) were comparable, independently of the flood duration and the time between floods (75.76±1.59 and 77.94±0.45 mmol CO2 m-2 day-1, in SF and LF respectively). Flood disturbance affects site-specific microbial processes, but only during very short time periods. The mechanism by which soil microbial communities cope or adapt to new conditions needs to be reassessed in future research in order to determine the long-term effects of hydrological changes in the soil carbon balance of semi-arid floodplains.
Hydrogeomorphology and ecology of mangrove wetlands in South Sonora and North Sinaloa (Mexico)
Mexican Secretary of Environment and Natural Resources (SEMARNAT), Fondo de Investigación Ambiental SEMARNAT-CONCACYT 2002-C01-147. 01/09/2002-31/12/2007. Funds: 250.000 €. IP: S. Sánchez-Carrillo
In this project we studied the mangrove wetlands located in the Yaqui, Mayo and Fuerte river deltas which were originated during the Pliocene (5 million years ago) associated with several processes of river avulsion. These mangrove forests are microtidal systems conditioned strongly by exchanges with the adjacent sea instead of those occurring with the continent (river flow). Currently these wetlands extend throughout an area of 46,600 ha. The main impacts they receive are: (i) the drastic reduction of fresh water discharges by the hydraulic regulation of the hydrological basins for irrigation; (ii) shrimp farming, which continues to expand although at a lower rate than in the 1990s, which directly destroys extensions of mangrove forest and discharges the over-fertilized waters into the estuaries; and (iii) agricultural and urban wastewater, which is discharged directly in estuaries and bays with no or insufficient treatment. Other minor problems are overfishing and uncontrolled tourist activities. During the last 35 years, by means of aerial photographs and LANDSAT images, there has been a reduction, albeit fluctuating, in the area covered by mangroves, which might be explained partially by the cited impacts although some intrinsic ecosystem processes may be important.
The mangrove forests are mostly monospecific stands of Avicennia germinans, although close to the coast and to the south they can be mixed with Rizophora mangle. Laguncularia racemosa, Maytenus phyllanthoides and Conocarpus erectus appear as marginal species. There is a zonation in the occurrence of species and in the structure of the mangrove that responds more to competition for space than to environmental constrains. Structurally the mangroves in the Mayo region are the best preserved while those of the Yaqui are the worst. The production of litter in the forests increases towards the south, with a seasonality dependent on the average air temperature. Total annual production throughout the region depends more on intrinsic forest variables (total soil phosphorus, salinity, total nitrogen, organic matter and tree height). During decomposition, litter loses 50% of its initial dry weight in less than 6 days, without negligible subsequent changes. The leaf litter P is rapidly processed in the ecosystem with reductions of up to 99% during decomposition. The amount of C and P that is released during decomposition depends on the frequency of tidal flood. The balance of C in these mangrove systems is balanced throughout the year, in equilibrium with the net primary productivity of mangrove trees. The metabolism of these forests depends on the production of litter, exporting dissolved inorganic nitrogen during the wet season and retaining organic nitrogen. On the contrary, these mangroves are important phosphorus sinks. Estuaries and coastal lagoons, according to the LOICZ biogeochemical model, are nitrogen sinks in summer and in winter and sources of phosphorus in summer and sinks in winter. In summer, the ecosystem net metabolism (ENM) is heterotrophic, dominating the process of denitrification; in winter, ENM is autotrophic and dominates nitrogen fixation.
In the estuaries the microphytoplankton was composed of 122 benthic diatom species, 67 planktonic diatom species, 29 dinoflagellate species, 19 cyanophyte species, 9 chlorophyll species, 3 chrysophyte species and 1 ciliate species. In zooplankton dominates Crustacea (nauplii and copepods) followed by pseudocelomados (rotifers). The degradation and contamination of the estuaries significantly affects the abundance and richness of fish species, crustaceans, mollusks and cnidarians, mainly at higher trophic levels. The Simpson and Shannon diversity indexes for fish showed a much higher value in the pristine estuaries compared with the degraded ones. On the contrary, in crustaceans it is greater in the latter. The effects of the shrimping effluents in the trophic structure of the estuaries in the study area were assessed using stable isotopes (δ13C, δ15N). While δ13C signatures give a very ambiguous signal of degradation, δ15N is a good descriptor of aquaculture impacts with signature enrichments ≈ 5 ‰ in sediments, macroalgae, benthic algae, filter feeders and omnivores which result in qualitative differences in the food-web structure of estuaries receiving aquaculture discharges. Food webs of disturbed estuaries are supported by detritus and dominated by opportunistic species. While alterations in the availability of resources do not directly affect the length of the trophic chain, the trophic connections between the compartments of the food web are reduced as a result of the impacts of the shrimp discharges. Main results obtained in this project were used to elaborate a coastal management plan for this area focused on mangrove conservation to long-term.
The mangrove forests are mostly monospecific stands of Avicennia germinans, although close to the coast and to the south they can be mixed with Rizophora mangle. Laguncularia racemosa, Maytenus phyllanthoides and Conocarpus erectus appear as marginal species. There is a zonation in the occurrence of species and in the structure of the mangrove that responds more to competition for space than to environmental constrains. Structurally the mangroves in the Mayo region are the best preserved while those of the Yaqui are the worst. The production of litter in the forests increases towards the south, with a seasonality dependent on the average air temperature. Total annual production throughout the region depends more on intrinsic forest variables (total soil phosphorus, salinity, total nitrogen, organic matter and tree height). During decomposition, litter loses 50% of its initial dry weight in less than 6 days, without negligible subsequent changes. The leaf litter P is rapidly processed in the ecosystem with reductions of up to 99% during decomposition. The amount of C and P that is released during decomposition depends on the frequency of tidal flood. The balance of C in these mangrove systems is balanced throughout the year, in equilibrium with the net primary productivity of mangrove trees. The metabolism of these forests depends on the production of litter, exporting dissolved inorganic nitrogen during the wet season and retaining organic nitrogen. On the contrary, these mangroves are important phosphorus sinks. Estuaries and coastal lagoons, according to the LOICZ biogeochemical model, are nitrogen sinks in summer and in winter and sources of phosphorus in summer and sinks in winter. In summer, the ecosystem net metabolism (ENM) is heterotrophic, dominating the process of denitrification; in winter, ENM is autotrophic and dominates nitrogen fixation.
In the estuaries the microphytoplankton was composed of 122 benthic diatom species, 67 planktonic diatom species, 29 dinoflagellate species, 19 cyanophyte species, 9 chlorophyll species, 3 chrysophyte species and 1 ciliate species. In zooplankton dominates Crustacea (nauplii and copepods) followed by pseudocelomados (rotifers). The degradation and contamination of the estuaries significantly affects the abundance and richness of fish species, crustaceans, mollusks and cnidarians, mainly at higher trophic levels. The Simpson and Shannon diversity indexes for fish showed a much higher value in the pristine estuaries compared with the degraded ones. On the contrary, in crustaceans it is greater in the latter. The effects of the shrimping effluents in the trophic structure of the estuaries in the study area were assessed using stable isotopes (δ13C, δ15N). While δ13C signatures give a very ambiguous signal of degradation, δ15N is a good descriptor of aquaculture impacts with signature enrichments ≈ 5 ‰ in sediments, macroalgae, benthic algae, filter feeders and omnivores which result in qualitative differences in the food-web structure of estuaries receiving aquaculture discharges. Food webs of disturbed estuaries are supported by detritus and dominated by opportunistic species. While alterations in the availability of resources do not directly affect the length of the trophic chain, the trophic connections between the compartments of the food web are reduced as a result of the impacts of the shrimp discharges. Main results obtained in this project were used to elaborate a coastal management plan for this area focused on mangrove conservation to long-term.