Effects of Fish and Nutrient Additions on Food Web Stability in a Charophyte-Dominated lake.

Abstract not availableJRC.H-Institute for environment and sustainability (Ispra

Short-term and long-term effects of zooplanktivorous fish removal in a shallow lake: a synthesis of 15 years of data from Lake Zwemlust

1. Removal of zooplanktivorous fish (mainly bream) in 1987 from a shallow eutrophic lake in the Netherlands, Lake Zwemlust, resulted in a quick switch from a turbid state with cyanobacteria blooms to a clear state dominated by macrophytes. 2. The clear state was not stable in the long term, however, because of high nutrient loadings. 3. In 1999, another removal of zooplanktivorous fish (mainly rudd) had similar effects as in 1987, although macrophytes returned more slowly. 4. In the years directly following both interventions there was a 'transition period' of very clear water with high densities of zooplanktonic grazers in the absence of macrophytes; low oxygen concentrations indicate that during those years primary production was low relative to heterotrophic activity. 5. The transition period appears to provide the light climate necessary for the return of macrophytes. 6. Reduction of nutrient loading is necessary to improve water quality in Lake Zwemlust in the long term. In the short term, repeated fish stock reduction is a reasonable management strategy to keep Lake Zwemlust clear

Impact of submerged macrophytes including charophytes on phyto- and zooplankton communities: allelopathy versus other mechanisms

Submerged macrophytes are crucial for the stabilization of the clear water state in shallow, mesotrophic and eutrophic lakes. Especially, charophytes often play an important role because they are typically rapid colonizers and because charophyte meadows are believed to have a particularly strong positive effect on water transparency compared to other macrophytes. Several mechanisms may contribute to the impact of submerged macrophytes on the planktonic food web. In this paper, the available literature on these mechanisms is briefly reviewed and special attention is paid to the impact of charophytes on the structure and dynamics of phyto- and zooplankton communities. The paper focuses on allelopathy, and possible differences between charophytes and other macrophytes, as well as gaps in our knowledge are discussed. [KEYWORDS: Macrophyte; Charophyte; Allelopathy; Zooplankton and phytoplankton]