Author(s): Carla Van Wijck, CornelisJan De Groot
Many temporary marshes in the Camargue (Southern France) are managed as permanent marshes to create habitats attractive to waterfowl.Potamogeton pectinatus, a common food for waterfowl, is in a bad condition in several of these marshes. This might be due to the accumulation of toxic compounds such as ferrous iron and sulphide in the anoxic, organic rich sediment. We examined whether desiccation of the sediment of such a permanent marsh leads to a better growth ofP. pectinatus. Field observations showed that a summer drawdown of the permanent marsh Garcines led to a considerable abundance of annual plants and a decrease in the biomass production ofP. pectinatus in the following spring. We investigated the difference in growth ofP. pectinatus when growing on sediment that dried (border) and sediment that did not dry (centre). However, the border sediment did not dry long enough to oxidize all the reduced constituents and ferrous iron remained present in the interstitial water. No difference in biomass production was found in plants growing on the border or on the centre sediment. The plants from the centre sediments had very low root to shoot ratios, which might be caused by sulphide. Many tubers were formed; the tuber production was probably enhanced by stress due to the presence of toxic compounds in the sediment. Repeated short winter drawdowns might be the best management to increaseP. pectinatus production.