Factors Governing Macrophyte Status in Hampshire Chalk Streams: Implications for Catchment Management

Abstract Severe droughts in the late 1980s and 1990s have highlighted the fragility of many aquatic environments in southern England; in particular, declining river flows may be having an adverse affect on macrophytes in the chalk‐fed streams of the Rivers Test and Itchen. Detailed macrophyte survey data which were collected from representative sites in both rivers during 1991–1995 are interpreted in the context of changing hydroclimatic, water quality and in‐stream channel conditions. Multivariate statistical analyses support the assertion that river flow is the most significant parameter governing observed changes in macrophyte cover. During low flow years, filamentous algae have increased at most sites to the detriment of Ranunculus spp. These findings have catchment‐management implications which should be addressed if the long‐term integrity of such aquatic ecosystems is to be safeguarded.