Status of aquatic macrophytes in an undrained area of fen in the Norfolk broads, England

Abstract

The aquatic macrophyte vegetation of dykes and pools in an area of undrained fen in Broadland, Norfolk, is analysed and described. Three main types of vegetation have been identified, an Elodea-Potamogeton crispus community, a Ceratophyllum-Stratiotes community and a Utricularia vulgaris community. The first two normally occur near the land margins of the fens and the last mainly on deep peat in the central areas. Most luxuriant macrophyte growth was observed at the fen margins where levels of nitrate-nitrogen, derived from land drainage, were higher (both in the water and sediments) than in the central fen areas. Preliminary comparisons are made of some chemical characteristics of the water and sediments of sites with a well developed macrophyte vegetation with others where macrophytes are very poorly developed, or completely absent. Sites poor in macrophytes had higher levels of sodium in the water and sediments and also more strongly reducing sediments than those with a rich macrophyte vegetation. However, measured levels of dissolved inorganic nitrogen and soluble reactive phosphorus were lower, or not significantly different. A recent reduction in the amount of Stratiotes aloides in some dykes may possibly be related to nutrient impoverishment rather than enrichment.