Shifts in water quality in a drinking water reservoir during and after the removal of cyprinids

Abstract

Lake Ü lemiste, the drinking water reservoir of Estonia's capital city Tallinn, was biomanipulated by manual removal of cyprinids in [2004][2005][2006] and its impact on water quality in the vegetation period was studied. A total biomass of 156 tonnes corresponding to 160 kg ha -1 of fish, predominantly cyprinids, were removed. A decline in the unit catches of fishing was observed. The removed fish biomass versus phosphorus concentration of the lake was considered sufficient to reduce the impact of cyprinids on water quality. The phosphorus removed within fish biomass corresponded to 38 lg l -1 and 21% of the external phosphorus load of the fishing period. The mean total phosphorus concentration dropped from [50 to B36 lg l -1 . However, the densities of planktivorous young-of-the-year percids remained high and the role of zooplankton grazing in improving water quality was found non-significant or transient. The cladocerans biomass decreased and the small-sized Daphnia cucullata remained almost the only daphnid in Lake Ü lemiste during and after the manipulation. Predomination of filamentous cyanobacteria was replaced by a more diverse phytoplankton composition and co-domination of micro-and pico-sized colonial cyanobacteria during summer. Mean phytoplankton biomass decreased from 15 to 6 mg l -1 primarily as a result of decreased in-lake TP availability. The Secchi disc transparency increased only in May 2005-2007. The effects of coincidental events, a decline of external loading of phosphorus and a simultaneous flushing induced by heavy rainfall, on lake water quality are discussed with some implications to the future management of the reservoir.

Responses of the fish community in a eutrophicated lake to long-term food web management assessed by multiple sampling methods

“…However, assuming a 0.8% phosphorus proportion from the fresh mass of cyprinid fish (Schreckenbach et al, 2001), 0.2-1.4 kg ha -1 of P was removed annually in the biomanipulation of Lake Tuusulanjärvi (Luodeslampi et al, 2017). This is 3-40% of the annual total P losses from the lake, highest proportions in dry years with low total P load and lowest proportions in rainy years of highest P load to the lake (See also Pedusaar et al, 2010). Together with other restoration activities of the project, this has probably made a beneficial contribution to the general positive development of the lake.…”

Estimating internal P loading in a deep water reservoir of northern China using three different methods

“…In order to quantify P net exchange in the sediment-water interface, a mass balance method was calculated (see supplementary material) (Kelderman et al 2005;Pedusaar et al 2010)…”

Impacts of fish on phosphorus budget dynamics of some SA reservoirs: evaluating prospects of ‘bottom up’ phosphorus reduction in eutrophic systems through fish removal (biomanipulation)

“…The present analysis indicates that complete fish eradication (if possible) would impact only marginally on internal nutrient stocks and nutrient recycling within the study reservoirs -unlike the common reliance on fish removal as an adjunct component of biomanipulation management in many eutrophic temperate lakes and reservoirs (e.g., Bendorff, 1995;Mehner et al, 2002;Kasprzak et al, 2007;Scharf, 2007;Søndergaard et al, 2008;Pedusaar et al, 2010). This difference appears largely attributable to the inordinately high external nutrient loadings impacting our study reservoirs (Table 1) -1 to 2 orders of magnitude higher than a critical 'biomanipulation efficiency threshold of phosphorus loading' limit (0.6 to 0.8 g TP/m2/yr (< 10 kg TP/ha/yr)) suggested by Bendorff (1987-see Bendorff 1990).…”