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.
