Synchronisms and antagonisms in the relations between agricultural environment, biodiversity, and ecological functions in an agricultural constructed wetland - SynBioTox

Objectives

In this context, the Constructed Wetland of Rampillon (CWR, Seine-et-Marne) intercepts drainage and runoff water from an agricultural basin. The aquatic biocenosis that lives there is potentially exposed to the effects of agricultural pollution. A major challenge is, therefore, to determine whether the wetland is a shelter or, on the contrary, an ecological trap.

To answer this question, the present study aims to evaluate the biological responses to exposure with contaminants through multi-taxa measurement and monitoring campaigns (amphibians, benthic macroinvertebrates) at different levels of organization (cell, individual, community), based on spatiotemporal comparisons. The selected comparison sites follow a gradient of contamination with agricultural pollutants. The following are evaluated: (i) biodiversity indices, (ii) a functional response of the benthic macroinvertebrate community via the study of the litter breakdown process, (iii) the ecotoxicological and functional effects of pesticides on an invertebrate (Gammarus fossarum) monitored in mesocosms, (iv) in situ effects of pesticides on the activity levels of several enzymes (in saliva) involved in neurotransmission (acetylcholinesterase) and enzymes involved in the processes of cellular detoxification or witnesses of cellular stress (peroxidase, glutathione-S-transferase, alkaline phosphatase, etc.) in the Common toad (Bufo bufo) and the Green frog (Pelophylax sp.). Our first results, from a census period from February to July 2023, indicate that the CWR is characterized by a high level of amphibian biodiversity compared to exposed and unexposed control sites. Litter breakdown is similar between the sites subjected to different pesticide pressures and the most contaminated site (upstream of the CWR) seems to be richer in pollution-resistant invertebrate taxa. This result could be linked to the harmful effects of pesticides on populations of sensitive species. The majority of the measured traits of Gammarus fossarum appear to respond to the cocktail of pesticides with a strong influence of environmental conditions. It was difficult to link toads enzymatic activities to the different levels of pesticide contamination, but a partially response was observed, highlighting an intermediate level of stress of toads in the CWR. This work provides a better understanding of the role of agricultural constructed wetlands for conservation of aquatic fauna in agricultural landscapes.