Periodic Reporting for period 1 - FLAMMINGGOS (Functional Links in Avian, Microbial, Macrophyte, and INvertebrate Greenhouse Gas Output Stimulation)
Reporting period: 2018-09-01 to 2020-08-31
Wetlands are globally important hotspots for atmospheric carbon (C) storage and greenhouse gas (GHG) emissions. Their roles as sinks or sources of GHGs are affected by environmental drivers such as nitrogen (N) and phosphorus (P) availability, which stimulate emission of GHGs such as nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2 ).
Biotic communities in wetlands also play an important - but not yet well understood - role in GHG fluxes. Mounting evidence suggests that aquatic invertebrate activity enhances GHG emissions (e.g. burrows of fly larvae emit high concentrations of N2O). Considering that invertebrates can reach high densities in wetlands (>100,000 per square meter), they may be substantial drivers of wetland chemical processes.
The roles that larger animals play in modifying GHG emissions have received less attention, and yet their potentially large effects via predation, nutrient subsidies, sediment disturbance, and herbivory may be critical to our understanding of the forces controlling wetland contributions to global GHG emissions. To successfully predict and model GHG fluxes to the atmosphere, a thorough understanding of the factors influencing these processes is crucial. But how do higher trophic levels play a role in these processes? Waterbirds, for instance, have been shown to reduce densities of aquatic invertebrates, which could potentially moderate GHG flux. But on the other hand, C, N, and P subsidies in waterbird guano may stimulate microbial activity. These bottom-up forces could then enhance GHG flux and dampen the top-down effects of predation.
Our FLAMMINGGOS (Functional Links in Avian, Microbial, Macrophyte, and INvertebrate Greenhouse Gas Output Stimulation) project was created to test the relative strength of top-down and bottom-up effects of predatory waterbirds on wetland GHG flux by examining these and other interactions through controlled field and laboratory experiments. This represents a new and potentially transformative line of inquiry into the roles of multiple trophic levels in regulating global wetland GHG flux.
Our objectives were:
1. To test for top-down control, via a trophic cascade, of waterbirds, benthic invertebrates, and microbes on wetland GHG flux.
2. To test for bottom-up effects on GHG flux, via C, N, P subsidies (guano) and sediment disturbance by waterbirds.
Biotic communities in wetlands also play an important - but not yet well understood - role in GHG fluxes. Mounting evidence suggests that aquatic invertebrate activity enhances GHG emissions (e.g. burrows of fly larvae emit high concentrations of N2O). Considering that invertebrates can reach high densities in wetlands (>100,000 per square meter), they may be substantial drivers of wetland chemical processes.
The roles that larger animals play in modifying GHG emissions have received less attention, and yet their potentially large effects via predation, nutrient subsidies, sediment disturbance, and herbivory may be critical to our understanding of the forces controlling wetland contributions to global GHG emissions. To successfully predict and model GHG fluxes to the atmosphere, a thorough understanding of the factors influencing these processes is crucial. But how do higher trophic levels play a role in these processes? Waterbirds, for instance, have been shown to reduce densities of aquatic invertebrates, which could potentially moderate GHG flux. But on the other hand, C, N, and P subsidies in waterbird guano may stimulate microbial activity. These bottom-up forces could then enhance GHG flux and dampen the top-down effects of predation.
Our FLAMMINGGOS (Functional Links in Avian, Microbial, Macrophyte, and INvertebrate Greenhouse Gas Output Stimulation) project was created to test the relative strength of top-down and bottom-up effects of predatory waterbirds on wetland GHG flux by examining these and other interactions through controlled field and laboratory experiments. This represents a new and potentially transformative line of inquiry into the roles of multiple trophic levels in regulating global wetland GHG flux.
Our objectives were:
1. To test for top-down control, via a trophic cascade, of waterbirds, benthic invertebrates, and microbes on wetland GHG flux.
2. To test for bottom-up effects on GHG flux, via C, N, P subsidies (guano) and sediment disturbance by waterbirds.
Our study investigated both top-down and bottom-up effects of waterbirds that may modify wetland greenhouse gas (GHG) emissions. The FLAMMINGGOS project aimed to used paired field and laboratory studies to investigate the combined effects of waterbirds, plants, invertebrates, and microbes on GHG flux in Mediterranean wetlands.
As one of the largest remaining networks of wetlands in Europe, Doñana National Park provides critical habitat to an abundant and diverse array of waterbirds, and is a potential sink for CO2. Our study sites were selected to represent a wide-range of wetland types. i.e. nearly fresh to hypersaline, seasonally inundated sites to permanent ones, and natural to reconstructed to heavily managed resource harvesting sites (i.e. aquaculture and salt production). This allowed us to investigate the roles these factors have in mitigating or enhancing GHG production as well.
With different types of bird exclosures we manipulated predation pressure on sediment invertebrate communities. In total, 126 waterbird exclosure plots were established in eleven coastal wetlands in three provinces of Andalucía: Sevilla, Huelva, and Cádiz province. These exclosures were maintained and sampled over the course of ~2.5 years, and sampled periodically for GHG emissions, sediment and water chemistry, and invertebrate densities. GHGs were measured on site with portable analyzers, and sediment cores were brought from field locations to climate-controlled chambers in the Doñana Biological Station. In a closed-loop system, GHG analyzers measured emissions of CO2, CH4, and N2O, and then invertebrates in the cores were counted and identified.
Throughout the project, six erasmus interns from Third Sector International were mentored, and the thesis of one masters student from Kristianstad University was supervised by the fellow. All interns and mentees were trained in the measurement of wetland GHG emissions, identification of aquatic invertebrates, and design and implementation of a large-scale research project.
In conjunction with field studies, laboratory mesocosms allowed us to manipulate invertebrate densities and nutrient concentrations under controlled conditions. We mimicked predation pressure by manipulating invertebrate densities in different treatments. We also controlled the supply of C, N and P to sediments by adding freeze-dried algae at rates reflecting conditions in wetlands receiving low or high levels of fertilizer pollution. Similarly, in another experiment we added waterbird guano at levels representing high or low waterbird population densities. When we measured GHG emissions from these mesocosms we were able to estimate the effects of predation, waterbird defecation, and algal blooms on sediment GHG flux.
In laboratory studies, significant stimulatory effects of sinking algal cells and aquatic worm densities on CO2 and CH4 flux were observed, as well as small but statistically significant inhibitory effects of waterbird guano on CH4. The exclusion of predatory waterbirds from wetlands resulted in significant enhancement of benthic GHG flux. Enhanced CO2 flux may have been due to significantly increased densities and body sizes of benthic invertebrates in the absence of waterbirds. However, reduced disturbance of sediments within waterbird exclosures may also have allowed the development of more stable biofilms and higher biofilm community respiration. Sediment samples collected within exclosures were sent to collaborators at the University of Valencia and University of Granada for molecular analysis that may elucidate the mechanisms responsible for enhanced GHG flux.
As one of the largest remaining networks of wetlands in Europe, Doñana National Park provides critical habitat to an abundant and diverse array of waterbirds, and is a potential sink for CO2. Our study sites were selected to represent a wide-range of wetland types. i.e. nearly fresh to hypersaline, seasonally inundated sites to permanent ones, and natural to reconstructed to heavily managed resource harvesting sites (i.e. aquaculture and salt production). This allowed us to investigate the roles these factors have in mitigating or enhancing GHG production as well.
With different types of bird exclosures we manipulated predation pressure on sediment invertebrate communities. In total, 126 waterbird exclosure plots were established in eleven coastal wetlands in three provinces of Andalucía: Sevilla, Huelva, and Cádiz province. These exclosures were maintained and sampled over the course of ~2.5 years, and sampled periodically for GHG emissions, sediment and water chemistry, and invertebrate densities. GHGs were measured on site with portable analyzers, and sediment cores were brought from field locations to climate-controlled chambers in the Doñana Biological Station. In a closed-loop system, GHG analyzers measured emissions of CO2, CH4, and N2O, and then invertebrates in the cores were counted and identified.
Throughout the project, six erasmus interns from Third Sector International were mentored, and the thesis of one masters student from Kristianstad University was supervised by the fellow. All interns and mentees were trained in the measurement of wetland GHG emissions, identification of aquatic invertebrates, and design and implementation of a large-scale research project.
In conjunction with field studies, laboratory mesocosms allowed us to manipulate invertebrate densities and nutrient concentrations under controlled conditions. We mimicked predation pressure by manipulating invertebrate densities in different treatments. We also controlled the supply of C, N and P to sediments by adding freeze-dried algae at rates reflecting conditions in wetlands receiving low or high levels of fertilizer pollution. Similarly, in another experiment we added waterbird guano at levels representing high or low waterbird population densities. When we measured GHG emissions from these mesocosms we were able to estimate the effects of predation, waterbird defecation, and algal blooms on sediment GHG flux.
In laboratory studies, significant stimulatory effects of sinking algal cells and aquatic worm densities on CO2 and CH4 flux were observed, as well as small but statistically significant inhibitory effects of waterbird guano on CH4. The exclusion of predatory waterbirds from wetlands resulted in significant enhancement of benthic GHG flux. Enhanced CO2 flux may have been due to significantly increased densities and body sizes of benthic invertebrates in the absence of waterbirds. However, reduced disturbance of sediments within waterbird exclosures may also have allowed the development of more stable biofilms and higher biofilm community respiration. Sediment samples collected within exclosures were sent to collaborators at the University of Valencia and University of Granada for molecular analysis that may elucidate the mechanisms responsible for enhanced GHG flux.
By manipulating waterbird and invertebrate densities, this was one of the first long-term field studies to test the hypothesis that predatory waterbirds alter wetland GHG emissions both through predation and the excretion and egestion of guano. The exclusion of predatory waterbirds resulted not only in significant increases in numbers of sediment-dwelling invertebrates, but also in the enhancement of CO2 flux, which to our knowledge has not previously been demonstrated in a long-term ecosystem-scale manipulative experiment. This new and transformative line of inquiry would not have been possible without the generous support of the European Commission's Horizon 2020 Program, as well as the support and facilitation of research by researchers and staff at the Doñana Biological Station, the University of Granada, Wageningen University, the Institute of Marine Sciences of Andalucía, the University of Cadiz, the University of Seville, Kristianstad University, the University of Valencia, the erasmus internship exchange managed by Third Sector International, and staff and land managers at the Finca Veta la Palma, Doñana National Park, Marismas del Odiel Natural Park, and two Salinas in the Bay of Cádiz. For all this exceptional support, the fellow will forever be grateful.