A mechanism to account for macrophyte decline in progressively eutrophicated freshwaters

Abstract

Artificial fertilization of lakes ultimately leads to reduction in submerged macrophyte productivity. This has usually been attributed to shading by increasing populations of phytoplankton. Evidence is given that loss of macrophytes is often due to increased growth of, and shading by, epiphytes and filamentous algae associated with the weed beds, and that phytoplankton development is subsequent rather than causative. A new hypothesis is outlined in Fig. 1 and support for it is drawn from palaeolimnological studies, laboratory experiments and field observations and experiments in the Norfolk Broads, an area of shallow, peat-excavated lakes, and from the literature.