THE EFFECT OF ANAEROBIC SEDIMENT ON THE GROWTH OF POTAMOGETON-PECTINATUS L - THE ROLE OF ORGANIC-MATTER, SULFIDE AND FERROUS IRON

The influence of sediment organic matter content on biomass production of Potamogeton pectinatus L. was investigated using nine Camargue sediments ranging from 8 to 66 mg C g-1. The biomass production of P. pectinatus was found to increase with increasing sediment organic matter content up to 26 mg C g-1. Biomass production was low on some sediments with a high organic matter content. Further experiments showed that the increase in biomass production was probably owing to increased availability of nitrogen which is released during the mineralization of organic matter. Modification of the water content and/or structure of the sediments by the addition of sand had no influence on biomass production. The relatively low biomass production observed on some sediments rich in organic matter could not be explained by a lack of available nitrogen, but presumably by anoxic conditions caused by the high quantities of organic matter present. The addition of iron and sulphide had a negative effect on biomass production, presumably owing to the presence of Fe2+ and S2- in the interstitial water. Concentrations of Fe2+ and S2- in the interstitial water of the sediments of some marshes in the Camargue were found to be sufficiently high to be of ecological importance to submerged macrophytes.