Plant diversity and water quality of grassland ponds under different agri-environment schemes

anglais. peer reviewed

anglais. Ponds are declining ecosystems of high importance for freshwater biodiversity. Promoting less intensive agricultural practices in pond catchments may be particularly effective at enhancing their biodiversity and is more feasible compared to larger freshwater habitats. This study aimed to determine whether ponds located in grasslands with lower management intensity, under agri-environment schemes (AES), exhibit better water quality, including lower nutrient content, and harbor specific plant communities that are richer in species compared to more intensively managed grasslands. A vegetation survey was conducted, and abiotic parameters were measured in 38 ponds located in grasslands under AES in Wallonia, southern Belgium. Four management intensities were considered, including three AES categories: ‘MC4—Grassland with High Biological Value’ (n = 10), ‘MB2—Natural Grassland’ (n = 7), ‘MB9—Grassland in Forage Autonomy’ (n = 10), and grasslands without AES (none of these AES, n = 11), representing the most intensive management. There was evidence that vegetation on pond banks in grasslands under MC4 or MB2 were richer in species and supported different plant communities compared to those under MB9 or without AES. Ponds exhibited variations in conductivity and dissolved oxygen concentration according to the type of AES. Additionally, high nitrate concentrations in water were more common under MB9 or in ponds without AES. However, the diversity of hydrophytes was not correlated with grassland management practices. The results suggest that AES promoting lower management intensity in surrounding grasslands, such as MC4 and MB2, may improve water quality and increase plant species richness in ponds. These AES also influenced the composition of plant species on pond banks, although they did not significantly affect hydrophyte species. While a pluriannual survey would be necessary to confirm these hypotheses, our findings support the promotion of grassland deintensification around ponds, particularly through AES.