Effects of Biomanipulation on Fish and Plankton Communities in Ten Eutrophic Lakes of Southern Finland

Abstract

The effects of biomanipulation were studied in ten Finnish lakes to determine responses in fish and plankton communities and water quality after mass removal of cyprinids. From 1997 to 2001, the fish communities shifted from the dominance of large cyprinids to an explosion of small cyprinids and a higher proportion of piscivores in effectively biomanipulated lakes (>200 kg ha )1 3 yr )1 ). The biomass of cyanobacteria decreased, and the duration of the blooms shortened and shifted towards the autumn. Decreased concentrations and slower cycling of nutrients and increased grazing by cladocerans probably affected the declined biomass of cyanobacteria. Less intensive sediment disturbance and increased phosphorus-retention in fast growing fish biomass may have turned the role of the fish assemblage from 'nutrient recycler' to 'nutrient storage'. Increased potential grazing pressure, higher proportion of edible algae, and lower chlorophyll a:total phosphorus ratio indicated strengthened herbivore control. A high mass removal catch in relation to trophic state, low background turbidity, and bearable external loading favoured the successful biomanipulation, whereas intensive cyprinid reproduction, high nutrient loading and non-algal turbidity hindered the recovery. Three important issues should be noticed before biomanipulation in Finland: (1) careful selection of target lake, (2) well-planned, effective and long-lasting biomanipulation and (3) sustainable management of piscivores.

Shallow lake restoration by nutrient loading reduction—some recent findings and challenges ahead

“…4b) and to reduced internal P loading, having thus reinforced the recovery, at least in the short term. So far, the long-term perspectives are less promising when based on a single event to change the system from turbid to clear (Meijer et al, 1999;Olin et al, 2005;authors' unpublished results). More focus should be on how to stabilise the lake ecosystem to get long term success of biomanipulation (Mehner et al, 2002), perhaps by less intensive but more frequent manipulation of the fish stock.…”

Nutrient removal from polluted stream water by artificial aquatic food web system

“…For this purpose, ecotechnologies, such as constructed wetland (Braskerud, 2003), artificial floating islands (Somodi & Botta-Dukát, 2004), floating mats (Azza et al, 2006), and biomanipulation (Olin et al, 2006), were developed. Among them, the constructed wetland system is one of the typical ecotechnologies for the removal of nutrients, and its usefulness has been proven by several studies (Greenway & Simpson, 1996;Shutes, 2001;Coveney et al, 2002).…”

Sustainable Management of Eutrophic Lakes and Reservoirs

“…When making mass balances on nitrogen and phosphorus, it is important to know the N and P content of the fish that are harvested. Olin et al have used 0.8% P when working with fish fresh weight (FW) [75]. Sterner and George reported a mean value of 1.5% P dry weight for cyprinids [102].…”

“…This harvest removes phosphorus from the lake and allows an effective zooplankton: phytoplankton ratio to be maintained [42]. Table 3 shows fish harvests for several years for several lakes in Finland [75].…”