Lake restoration studies: Failures, bottlenecks and prospects of new ecotechnological measures (original) (raw)
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Lakes in the Netherlands, their origin, eutrophication and restoration: state-of-the-art review
Ecological Restoration of Aquatic and Semi-Aquatic Ecosystems in the Netherlands (NW Europe), 2002
This article starts with a brief description of the origin and eutrophication of shallow Dutch lakes, followed by a review of the various lake restoration techniques in use and the results obtained. Most freshwater lakes in the Netherlands are very shallow (<2 m), and owe their origins to large-scale dredging and removal of peat during the early 17th century. They vary in area from a few hectares to a few thousand hectares, and are generally found in the northern and western part of the country. Most of them lie in the catchment areas of the major rivers: the Rhine, the Meuse and the Schelde. Because of their natural and aesthetic value, these lakes fulfil a recreational function. The lakes are important to the hydrology, water balance and agriculture in the surrounding polder country. The external input to the lakes of phosphorus (P) and nitrogen (N) and of polluted waters from the rivers and canals have been the major cause of eutrophication, which began during the 1950s. In addition, more recently climate changes, habitat fragmentation and biotic exploitation of many of these waters have probably led to loss of resilience and thus to accelerated eutrophication. Lake eutrophication is manifested essentially in the poor under-water light climate with high turbidity (Secchi-disc, 20-40 cm) caused usually by cyanobacterial blooms (e.g. Oscillatoria sp.), and loss of littoral vegetation. Despite recent perceptible reductions in external P inputs, non-point sources, especially of N from agriculture, still remain high and constitute a major challenge to the lake restorers. Lake recovery is also invariably afflicted by in-lake nutrient sources. These include P loading from the P-rich sediments, mineralization in the water and release by the foraging and metabolic activities of the abundant benthivorous and planktivorous fish, mainly bream (Abramis brama).
Water, 2017
Biomanipulation by fish removal has been used in many shallow lakes as a method to improve lake water quality. Here, we present and analyse 30 years of chemical and biological data from the shallow and 16 ha large Lake Vaeng, Denmark, which has been biomanipulated twice with a 20-year interval by removing roach (Rutilus rutilus) and bream (Abramis brama). After both biomanipulations, Lake Vaeng shifted from a turbid, phytoplankton-dominated state to a clear, water macrophyte-dominated state. Chlorophyll a was reduced from 60-80 µg•L −1 to 10-30 µg•L −1 and the coverage of submerged macrophytes, dominated by Elodea canadensis, increased from <0.1% to 70%-80%. Mean summer total phosphorus was reduced from about 0.12 to 0.07 mg•L −1 and total nitrogen decreased from 1.0 to 0.4 mg•L −1. On a seasonal scale, phosphorus and chlorophyll concentrations changed from a summer maximum during turbid conditions to a winter maximum under clear conditions. The future of Lake Vaeng is uncertain and a relatively high phosphorus loading via the groundwater, and the accumulation of a mobile P pool in the sediment make it likely that the lake eventually will return to turbid conditions. Repeated fish removals might be a relevant management strategy to apply in shallow lakes with a relatively high external nutrient loading.
2000
Lake restoration in Denmark has involved the use of several different restoration techniques, all aiming to improve lake water quality and establishing clear-water conditions. The most frequently used method, now used in more than 20 lakes, is the reduction of zooplanktivorous and benthivorous fish (especially roach (Rutilus rutilus) and bream (Abramis brama)) with the objective of improving the growth conditions for piscivores, large-sized zooplankton species, benthic algae and submerged macrophytes. Piscivore stocking (mainly Esox lucius (pike)), aiming especially at reducing the abundance of young-of-theyear fish, has been used in more than 10 lakes and frequently as a supplement to fish removal. Hypolimnetic oxidation, with oxygen and nitrate, has been undertaken in a few stratified lakes and sediment dredging, with the purpose of diminishing the internal phosphorus loading, has been experimented with in one large, shallow lake. Submerged macrophyte implantation has been conducted in some of the biomanipulated lakes to increase macrophyte abundance and distribution. Overall, the results from lake restoration projects, in the mainly shallow Danish lakes, show that external nutrient loading must be reduced to a level below 0.05-0.1 mg P L -1 under equilibrium conditions to gain permanent effects on lake water quality. By using fish removal, at least 80% of the fish stock should be removed over a period of not more than 1-2 years to obtain a substantial effect on lower trophic levels and to avoid regrowth of the remaining fish stock. Stocking of piscivores requires high densities (>0.1 individuals m -2 ) if an impact on the plankton level is to be obtained and stocking should be repeated yearly until a stable clear-water state is reached. The experiments with hypolimnetic oxygenation and sediment dredging confirm that internal phosphorus loading can be reduced. Experience from macrophyte implantation experiments indicates that protection against grazing by herbivorous waterfowl may be useful in the early phase of recolonization.
Eutrophication and restoration in temperate lakes
IOP Conference Series: Earth and Environmental Science, 2020
Eutrophication affects many lakes and reservoirs worldwide. It is caused by excessive amounts of nutrients entering waterbodies from their catchments, mainly due to human activity. The main sources of these nutrients are discharges from industry and wastewater treatment systems, and agricultural runoff. The water quality problems caused by eutrophication, such as harmful algal blooms, affect the sustainable use of lakes for agriculture, fisheries, recreation, tourism and water supply. They also degrade habitat quality and threaten biodiversity. A range of methods for improving lake water quality are explored, including catchment management and in-lake restoration measures. The potential impacts of these on lake biodiversity are explored, including species interactions and ecosystem feedbacks that may confound the recovery process. A particular challenge is the fact that achieving sustainable recovery may take many years, mainly due to the impact of legacy pollution problems. This mu...
Restoration by biomanipulation of lake Bleiswijkse Zoom (The Netherlands): First results
Hydrobiological Bulletin, 1989
In 1987, the Bleiswijkse Zoom, a small, shallow lake in The Netherlands, was divided into two compartments to investigate the possible use of biomanipulation as a tool for restoring the water quality of hypertrophic lakes. The density of the fish stock before restoration was about 650 kg.ha-1, composed mainly of bream, white bream and carp. Pikeperch was the main fish predator in the lake. In April, 1987, in one compartment (Galgje) all planktivorous bream and white bream and about 85% of the benthivorous bream and carp were removed. Advanced pikeperch fry were introduced as predator during the transient period. The other compartment (Zeeltje) was used as a reference. Removal of the fish in Galgje resulted in low concentrations of chlorophyll-a, total phosphorus, nitrogen and suspended solids. The absence of bottom-stirring activity by benthivorous fish and the low chlorophyll-a concentrations led to an increase in the Secchi disk transparency from 20 to 110 cm. Within two months after removal of the fish, macrophytes, mainly Characeae, became abundant. Until July the high density of large zooplankton species caused low algal biomass. From June onwards, the zooplankton densities decreased, but the algal concentrations remained low. This is probably because of nutrient limitation or depression of algal growth by macrophytes or both. Compared with the non-treated compartment the number of fish species in the treated compartment was higher. Perch, rudd and roach, i.e. the species associated with aquatic vegetation, were found in the samples. The survival of the 0 + pikeperch was poor. The pikeperch could not prevent the growth of young cyprinids. Within two months after the removal of the fish a habitat for northern pike was created.
Comparing Grazing on Lake Seston by Dreissena and Daphnia: Lessons for Biomanipulation
Microbial Ecology, 2005
Biomanipulation measures in lakes, taken to diminish algal blooms, have mainly been restricted to the reduction of zooplanktivorous fish with the aim to stimulate the grazing pressure by native filter feeders such as Daphnia. However, larger filter feeders like the exotic zebra mussel, Dreissena polymorpha, have been suggested as an optional tool because of their high filtering capacity. We compared grazing by two filter feeders, D. polymorpha and Daphnia galeata, offered seston from Lake IJsselmeer, the Netherlands in two consecutive years: 2002 and 2003. The seston in both years was dominated by the colony-forming cyanobacterium Microcystis aeruginosa. The grazing studies were performed under controlled conditions in the laboratory and samples were analyzed on a flow cytometer, making it possible to quantify grazing on different seston components and size fractions, including cyanobacteria, other phytoplankton (green algae, diatoms, etc.), and detritus. No differences in clearance rates, on a per weight basis, were found between the two grazer species. The clearance rate on cyanobacteria (especially G20 2m) was lower in 2003 than in 2002. In 2003, the microcystin concentration of cyanobacteria was higher than in 2002, suggesting that the observed lower clearance rate in 2003 was due to the enhanced toxin content of the cyanobacteria. Zebra mussels, although indiscriminately filtering all seston groups out of the water, positively selected for phytoplankton in their mantle cavity, irrespective of its toxicity, and rejected detritus. Since no differences in clearance rates were found between the two grazer species, we conclude that for biomanipulation purposes of shallow lakes, native species like the daphnids should be preferred over exotic species like zebra mussels. When the seston is dominated by phytoplankton that cannot be filtered out of the water column by Daphnia, however, the use of zebra mussels may be considered. Care should be taken, however, in the choice of the lakes since the mussels may have severe ecological and economic impacts.
First attempt to apply whole-lake food-web manipulation on a large scale in The Netherlands
Hydrobiologia, 1990
Lake Breukeleveen (180 ha, mean depth 1.45 m), a compartment of the eutrophic Loosdrecht lakes system, was selected to study the effects of whole-lake foodweb manipulation on a large scale. In Lake Loosdrecht (dominated by filamentous cyanobacteria), due to water management measures taken from 1970-1984 (sewerage systems, dephosphorization) the external P load has been reduced from 1.2 g m-2 y-1 to 0.35 g m-2 y-i. The water transparency (Secchi-depth ca. 30 cm), however, has not improved. The aim of the food-web manipulation in Lake Breukeleveen was not only to improve the light climate of the lake, but also to study if the successfull effects observed in small lakes (a few ha) can be upscaled. In March 1989 the standing crop of planktivorous and bentivorous fish populations was reduced by intensive fishery, from ca. 150 kg ha-1 to ca. 57 kg ha-1. The lake was made unaccessible to fish migrating from the other lakes and it was stocked with large-sized daphnids and 0 ÷ pike. However, water transparency did not increase in the following summer and autumn 1989, which is in contrast with great improvement in the light conditions previously observed in smaller lakes. The main explanations for the negative outcome in Lake Breukeleveen are: 1)the rapid increase of the planktivorous fish biomass and carnivorous cladocerans, predating on the zooplankton community; 2) suppression of the large daphnids by the high concentrations of filamentous cyanobacteria; 3) high turbidity of the lake due to resuspension of bottom material induced by wind, unlike in smaller lakes, and thus inability of submerged macrophytes to develop and to stabilize the ecosystem.
The dynamics and role of limnetic zooplankton in Loosdrecht lakes (The Netherlands)
Hydrobiologia, 1992
The paper summarizes the results of a ten-year (1981-1991) zooplankton research on the Lake Loosdrecht, a highly eutrophic lake. The main cause of the lake's eutrophication and deteriorating water quality was supply up to mid 1984 of water from the River Vecht. This supply was replaced by dephosphorized water from the Amsterdam-Rhine Canal in 1984. The effects of this and other restoration measures on the lake's ecosystem were studied. Despite a reduction in the external P-load from ca. 1.0 g P me2 y-l to ca. 0.35 g rnp2 y-l now, the filamentous prokaryotes, including cyanobacteria and Prochlorothrix, continue to dominate the phytoplankton. Among the crustacean plankton Bosmina spp, Chydorus sp. and three species of cyclopoid copepods and their nauplii are quite common. Though there was no major change in the composition of abundant species, Daphnia cucullata, which is the only daphnid in these lakes, became virtually extinct since 1989. Among about 20 genera and 40 species of rotifers the important ones are: Anuraeopsis j?ssa, Keratella cochlearis, Filinia longiseta and PoZyarthra. The rotifers usually peak in midsummer following the crustacean peak in spring. The mean annual densities of crustaceans decreased during 1988-1991. Whereas seston (< 150 pm) mean mass in the lake increased since 1983 by 20-60%, zooplankton (> 150 pm) mass decreased by 15-35x. The grazing by crustacean community, which was attributable mainly to Bosmina, had mean rates between 10 and 25% d-'. Between 42 and 47% of the food ingested was assimilated. In spring and early summer when both rotifers and crustaceans have their maximal densities the clearance rates of the rotifers were much higher. Based on C/P ratios, the zooplankton (> 150 pm) mass contained 2.5 times more phosphorus than seston (< 150 pm) mass so that the zooplankton comprised 12.5 y0 of the total-P in total particulate matter in the open water, compared with only 4.5% of the total particulate C. The mean excretion rates of P by zooplankton varied narrowly between 1.5 and 1.8 pg P l-' d-', which equalled between 14 and 28% d-' of the P needed for phytoplankton production. The lack of response to restoration measures cannot be ascribed to one single factor. Apparently, the external P-loading is still not low enough and internal P-loading, though low, may be still high enough to sustain high seston levels. Intensive predation by bream is perhaps more important than food quality (high concentrations of filamentous cyanobacteria) in depressing the development of large-bodied zooplankton grazers, e.g. Daphnia. This may also contribute to resistance of the lake's ecosystem to respond to rehabilitation measures.
1994
The effects of fish stock reduction have been studied in 3 Dutch lakes (Lake Zwemlust, Lake Bleiswijkse Zoom and Lake Noorddiep) and 1 Danish lake (Lake Vaeng) during 4-5 years. A general response is described. The fish stock reduction led in general to a low fish stock, low chlorophyll-a, high Secchidisc transparency and high abundance of macrophytes. Large Daphnia became abundant, but their density decreased, due to food limitation and predation by fish. The total nitrogen concentration became low due to N-uptake by macrophytes and enhanced denitrification. In Lake Bleiswijkse Zoom the water transparency deteriorated and the clear water state was not stable. The fish stock increased and the production of young fish in summer was high. Clear water occurred only in spring. Large daphnids were absent in summer and the macrophytes decreased.