Synthesis of theoretical and empirical experiences from nutrient and cyprinid reductions in Lake Ringsjön

Reduction of nutrient loading and biomanipulation as tools in water quality management: Long-term observations on Bautzen Reservoir and Feldberger Haussee (Germany)

“…Nevertheless, as has been found in BR, clear water periods (Secchi transparency 2.0-4.5 m) occurred in FH during May and June in a number of years as a result of high Daphnia biomass after biomanipulation became effective. Again, these results are in agreement with observations found during biomanipulation of other deep thermally stratifying lakes suffering from high external or internal nutrient loading (Kubečka et al 1998, Bergmann et al 1999, Dawidowicz et al 2002, Lathrop et al 2002.…”

“…Biomanipulation based exclusively on manual planktivore removal might depend on drastic and fast reduction of their biomass within 2-3 years (Carpenter 1989, Perrow et al 1997, Meijer et al 1999. Nevertheless, as a result of selective fishing and lowered biomass, decreased food competition may finally boost both planktivore reproduction and stocks (Romare and Bergmann 1999). Therefore, a piscivore community consisting of different size classes of several species is essential for long-term success of biomanipulation.…”

Exotic fish introductions and the decline of water clarity in small North Island, New Zealand lakes: a multi-species problem

“…In particular, a number of biomanipulation studies have indicated that the 'top-down' effects of planktivorous fish on zoo-and phytoplankton concentrations and hence on lake water clarity can be reduced in some lakes by stocking piscivores (e.g., Carpenter et al, 1985;McQueen et al, 1986;Shapiro, 1990;Grimm & Backx, 1990;Sondergaard et al, 1997;Bergman et al, 1999). Similarly, a number of studies have indicated that changes in food webs that result in more benthic feeding fish can increase the re-suspension of silt, induce more phosphorus cycling and reduce water clarity through 'bottom-up' effects (e.g., Meijer et al, 1990;Breukelaar et al, 1994;Tatrai et al, 1997; Handling editor J. Cambray D. K. Rowe Thibodeaux & Bierman, 2003).…”

Rehabilitation and management of a moderately deep-stratifying reservoir by the use of nutrient reduction and food-web management

“…Although the water renewal rate is high in Lingese Reservoir, the water quality did not respond as expected to the major reductions of external nutrient loads in 1993, at least in the short term (Scharf, 1999). Particularly, water transparency, as, for example, in Lake Ringsjön (Bergman et al, 1999), did not reflect the decrease of algal biomass corresponding to nutrient load abatement. Thus, the result of the massive investments did not immediately become visible.…”

“…As both of these large-scale restoration attempts were carried out simultaneously, evaluation as to which of them actually caused the observed improvements in water quality is difficult, but this article aims to disentangle the effects caused by the different measures applied-questions of major relevance not only to lake management but also to science for understanding the mechanisms involved. In contrast to most other biomanipulation studies (Bergman et al, 1999;Cooke et al, 2005), there was no need to reduce the abundance and biomass of zooplanktivorous fishes as the reservoir was refilled in 1999. Hence, we relied upon stocking with piscivores only, in combination with catch restrictions for the recreational fisheries to build-up a 'new' fish stock with a high proportion of predators, as e.g.…”