The field campaign
Within ALFAwetlands, we measure and evaluate wetland restorations, impacts and possible strategies, trying to answer multiple specific research questions. The variety of wetland living labs across Europe allows partner-wise harmonized methodologies for continuous monitoring. Furthermore, individual experiments may be conducted. In this context, the CNRS team from Toulouse, in collaboration with the team from the University of Barcelona and with the involvement of every ALFAwetlands partner, prepared and led (and finally carried out) a field campaign during the summer of 2024, visiting 20 sites across the 5 ALFAwetlands living labs of Finland, Estonia, Belgium, France, and Spain. The field campaign had several objectives declined in multiple experiments that contributed to multiple tasks of the WP3 (T3.3, T3.4, T3.5).
Experiment part 1: Effect of nutrient amendment on GHG production rate
As the CNRS Toulouse team, we aimed to understand better what controls greenhouse gas production (e.g., carbon dioxide, methane, nitrous oxide) in natural wetlands ecosystems and restored sites. Here, we focus mainly on nitrous oxide (N₂O), produced during the natural removal of nitrate pollution in wetlands ecosystems and which fluxes remain challenging to predict. On each wetlands site visited, we evaluated the gas exchange using Licor’s mobile analysers and our home-made measurement chambers following three treatments: the addition of nitrate, the combined addition of nitrate and acetate (a carbon source widely used by bacteria), and a control with only water addition. The “Licors”, used in several ALFAwetland Living labs, are high-precision and high-frequency portable devices that detect changes of less than 1% in atmospheric GHG concentration. This approach produces N2O.
To link the gas exchange measurements recorded in the field, we collected samples to measure soil physical properties, bulk and water chemistry, as well as enzymatic activities related to N2O emission. Special probes were also left at each site to follow the change in soil water saturation and temperature continuously during a whole year, and two additional experimental designs were set up to assess the biological activity of macro and micro-organisms and their contribution to soil turnover and carbon availability.
Experiment part 2: Macro- and micro-organisms’ contribution to soil turnover using Bait lamina and cotton strips
Invertebrates, such as earthworms and insects, are great indicators of biodiversity and contribute to organic matter degradation. Nevertheless, the determination and evaluation of species is time-consuming and requires further experience. Alternatively, to measure the rate of organic matter decomposition in wetland soils, so-called bait-lamina strips can be used. The advantages are obvious: it is specific to macro- and meso fauna, further complementary to microbial degradation, and provides activity information in different soil depths. Furthermore, bait lamina is very cost- and time-efficient and does not require specific invertebrate taxonomy knowledge.
Another method to determine the decomposition in organic matter and the activity of microorganisms in soils is cotton strips. Cotton fibres, or better to say, cellulose, are important parts of fresh organic matter. Consequently, cotton decay, expressed by a loss of tensile strength, is strongly related to fungal activity in the soil. The cotton strips are buried into the soil over a certain period, retrieved, and the loss of tensile strength of the cotton fibres, a proxy of its level of degradation, is determined in the laboratory using a tensiometer.
These two methods provided valuable insights into the biological and microbial processes occurring within the top 10 cm of soil and will help us to explain the greenhouse gas production recorded on the field and the response to nutrient addition.
Experiment part 3: GHG production dynamics and maximum rate in controlled conditions
From each site, the CNRS team also brought back some souvenirs: three soil cores of 12cm diameter and 10 cm deep (called monolith) that we will use in simulated flooding experiments back in our lab at Toulouse, using a custom-designed system under controlled condition. Our “Aquacosm” design allows us to simulate a rise in the water table and to investigate the dynamic of GHG production over several days following changes in hydrological conditions, effectively mimicking the effect of some restoration strategies such as rewetting. It further allows us to evaluate the maximal production rate for each wetland type to help calibrate a new model for N2O emissions.
We are carefully optimistic to say that all these data collected in the field and in controlled experiments will help us to provide new insights into the mechanism that controls GHG production, as well as to extend existing models for GHG production to the European Wetlands.
This field campaign was a unique opportunity for the CNRS team to experience first-hand the diversity of wetland sites included in the ALFAwetlands Project, from the high-altitude Pyrenean fen peatland in France and Spain, the Belgian meadows, boreal forests from Finland, the restored peat extraction site from Estonia, to the Spanish and French flood forests. With all these sites characterized by unique species composition and different climates, it will certainly influence biological and microbiological activity. Hence, witnessing these differences will also help better understand European wetlands. It was also another good opportunity for the ALFAwetland partners to meet in person (and not through a screen).
Long days, short nights, promising (preliminary) results – we dare to say this campaign to the ALFAwetlands from European South to North was a success story. A few good ideas, great team spirit, and awesome motivation, what else is needed.