Lake Zwemlust Research Articles

The impact of climate warming on water temperature, timing of hatching and young-of-the-year growth of fish in shallow lakes in the Netherlands

The Intergovernmental Panel on Climate Change (IPCC) predicts increases in global average surface temperature from 1.1 to 6.4 °C for the year 2100. Here, we focus on the impact of climate warming on eutrophic shallow lakes in the Netherlands, using three representative lakes that cover the full range of lake sizes and depths. In these lakes, temperature has been shown to be the main determinant of hatching and growth of young-of-the-year fish. Because records of water temperature of our study lakes are incomplete, we applied an existing model to predict water temperatures from air temperatures for shallow, wind exposed and holomictic water bodies. To evaluate the implications of our results for marine systems, we also analyzed water temperature data of Marsdiep, a tidal inlet to the Waddensea. The lake water temperature model fitted equally well to all four water bodies. Applying the water temperature model to the period 1961–2006 showed an annual increase of 0.042 °C irrespective of lake size and depth. We extrapolated the consequences of lake warming for the onset of growth of larval bream and the size of young-of-the-year bream at the end of the year using an existing fish hatching and growth model. Both models were tested against data from Lake Tjeukemeer, which is intermediate in size compared to Lake Zwemlust and Lake IJsselmeer. The main conclusions of this study are that 1) there is a very tight coupling between air and water temperatures in Dutch shallow lakes, irrespective of their size, resulting in highly similar patterns of lake temperature and a direct translation of climate warming into lake warming; 2) on average water temperature has increased by 2 °C in the period 1961–2006; 3) temperature patterns in the tidal inlet showed a surprising resemblance with the lake temperature patterns, the coastal marine system essentially behaving like an extremely large lake; 4) there are, however, strong seasonal patterns in the extent of warming in a given period of the year; 5) lake warming leads to ca. 3 weeks earlier onset of growth and 20 mm larger sizes in bream during 1971–2006 under the assumption of temperature limited growth in these eutrophic ecosystems.

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

SUMMARY 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.

A multivariate analysis of phytoplankton and food web changes in a shallow biomanipulated lake

1. Phytoplankton dynamics, food chain changes and resilience in Lake Zwemlust, a shallow lake in The Netherlands, are described for the period 1986–94.2. After biomanipulation in 1987, the lake moved through two alternative states, while the external nutrient loadings were maintained. A clear‐water phase, mostly dominated by macrophytes, persisted from 1987 to 1991, and a rather turbid state, dominated by algae, occurred in the summers of 1992–94, after several consecutive and sustained perturbations affecting different parts of the food web in the lake. These two periods were characterized by different community structures.3. The phytoplankton assemblage gradually changed in a pattern that reverted in later years towards that of the pre‐biomanipulation stage, although the same species composition was not regained. This agrees with some mathematical models. During the clear‐water phase, nutrient shortage, light climate and zooplankton feeding selected in favour of small, high surface : volume ratio and rapidly reproducing algae. However, in mid‐summer of 1992–94, nutrient availability and cladoceran grazing on edible algae favoured cyanophytes.4. Nutrients were transferred to higher trophic levels or lost from the system at relatively high rates when the lake was in a piscivore–macrophyte‐dominated state, while they tended to accumulate in the algae in a planktivore‐dominated chain without macrophytes. The role of weed beds was central for nutrient competition (mostly nitrogen) with algae, as well as a refuge and a base for alternative food sources to grazers. Weed beds seemed to have a strong effect in increasing connectedness, resilience and stability of the lake community.5. The complete return of Zwemlust to a turbid state dominated by phytoplankton seems to have depended upon turnover of the limiting nutrient, which was retarded by macrophytes and stimulated by planktivorous fish and waterfowl.

Transition of a lake to turbid state six years after biomanipulation: mechanisms and pathways

Six years after application of biomanipulation in 1987, Lake Zwemlust (The Netherlands) returned during the summer from a clear water state dominated by aquatic vegetation to a turbid state characterized by high algal biomass. Herbivory and growth of epiphytes on macrophytes were the main factors triggering the switch. Selective herbivory by coots (Fulica atra) and rudd (Scardinius erythrophthalmus) caused a change in macrophyte species composition from a dominance of Elodea nuttallii in 1988/1989 to Ceratophyllum demersum in 1990/1991, and finally to Potamogeton berchtholdii in 1992/1993/1994. Observations revealed a general lack of epiphytes associated with Elodea and Ceratophyllum, while Potamogeton showed a progressive coverage with epiphytes, causing Potamogeton to decline markedly during late summer. Phytoplankton blooms, dominated by cyanobacteria, appeared again during three consecutive autumns, 1992, 1993 and 1994, with chlorophyll-α concentrations reaching 60-240 μg 1−1.

Modelling nutrient cycles in relation to food web structure in a biomanipulated shallow lake

The modelPCLAKE describes the phosphorus and nitrogen cycles within a shallow lake ecosystem, including the sediment and a simplified biological food web. All components are modelled in a generalized way rather than a very detailed one. This model has been applied to Lake Zwemlust, a small biomanipulated lake in The Netherlands. Formerly, this highly eutrophic lake was dominated by cyanobacteria and devoid of macrophytes. Biomanipulation was carried out in 1987 by pumping-out of the water, removal of all fish, and refilling of the lake with seepage water. The lake was restocked with some rudd, pike, zooplankton and seedlings of macrophytes, and then monitored up to 1992. Macrophytes developed rather quickly and reached their maximum biomass during the six-years period in 1989. Despite the continuously high nutrient (N and P) loading, algal biomass remained low due to nitrogen limitation, caused by competition with the macrophytes. From 1990 onwards, the macrophytes declined again and a species shift occurred, following an increase of herbivorous birds on the lake and the development of herbivorous fishes. Model simulations grossly reproduced the observed developments in Lake Zwemlust before and after the biomanipulation measures. The existence of multiple steady states at the same trophic state and the possible shift between them could be simulated well. This study also demonstrates the interrelation between system structure and the distribution and cycling of nutrients. It is concluded, that within general boundary conditions set by the trophic state of the system, the food web structure determines the actual nutrient flows and the occurrence of nutrient limitations of the primary producers. It is shown that both aspects can be integrated in one mathematical model. The long-term stability of the macrophyte dominance in the lake is discussed.

Transition of a lake to turbid state six years after biomanipulation: Mechanisms and pathways

Six years after application of biomanipulation in 1987, Lake Zwemlust (The Netherlands) returned during the summer from a clear water state dominated by aquatic vegetation to a turbid state characterized by high algal biomass. Herbivory and growth of epiphytes on macrophytes were the main factors triggering the switch. Selective herbivory by coots (Fulica atra) and rudd (Scardinius erythrophihalmus) caused a change in macrophyte species composition from a dominance of Elodea nuttallii in 1988/1989 to Ceratophyllum demersum in 1990/1991, and finally to Potamogeton berchtholdii in 1992/1993/1994. Observations revealed a general lack of epiphytes associated with Elodea and Ceratophyllum, while Potamogeton showed a progressive coverage with epiphytes, causing Potamogeton to decline markedly during late summer. Phytoplankton blooms, dominated by cyanobacteria. appeared again during three consecutive autumns, 1992, 1993 and 1994, with chlorophyll-a concentrations reaching 60–240 µg 1-1.

Long-term responses to fish-stock reduction in small shallow lakes: interpretation of five-year results of four biomanipulation cases in The Netherlands and Denmark

The effects of fish stock reduction have been studies 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 id described. The fish stock reduction led in general to a low fish stock, low chlorophyii-a, high transparency and high abunuance 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. lear water occurred only in spring. Large daphnids were absent in summer and the macrophytes decreased.

Macrophyte-related shifts in the nitrogen and phosphorus contents of the different trophic levels in a biomanipulated shallow lake

Lake Zwemlust, a small highly eutrophic lake, was biomanipulated without reducing the external nutrient loading, and the effects were studied for four years. In this paper we pay special attention to the shifts in relative distribution of nitrogen and phosphorus in the different trophic levels and to the changes in growth limitation of the autotrophs.Despite of the high external nutrient loads to the lake (ca 2.4 g P m−2 y−1 and 9.6 g N m−2 y−1), the effects of biomanipulation on the lake ecosystem were pronounced. Before biomanipulation no submerged vegetation was present in the lake and P and N were stored in the phytoplankton (44% N, 47% P), fish (33% N, 9% P) and in dissolved forms (23% N, 44% P). P and N contents in sediments were not determined. In the spring and summer following the biomanipulation (1987), zooplankton grazing controlled the phytoplankton biomass and about 90% of N and P were present in dissolved form in the water. From 1988 onwards submerged macrophyte stands continue to thrive, reducing the ammonium and nitrate concentrations in the water below detection levels. In July 1989 storage of N and P in the macrophytes reached 86% and 80%, respectively. Elodea nuttallii (Planchon) St.John, the dominant species in 1988 and 1989, acted as sink both for N and P during spring and early summer, withdrawing up to ca 60% of its N and P content from the sediment. At the end of the year only part of the N and P from the decayed macrophytes (ca 30% of N and 60% of P) was recovered in the water phase of the ecosystem (chiefly in dissolved forms). The rest remained in the sediment, although some N may have been released from the lake by denitrification.In summer 1990 only 30% of the N and P was found in the macrophytes (dominant species Ceratophyllum demersum L.), while ca 30% of N and P was again stored in phytoplankton and fish.

Growth and nutrient uptake by two species of Elodea in experimental conditions and their role in nutrient accumulation in a macrophyte-dominated lake

The capacity of Elodea nuttallii (Planch.) St. John and Elodea canadensis Michx. to remove nitrogen from water was evaluated in laboratory experiment. The growth rate of plants and their effect on the nitrogen level of hypertrophic Lake Zwemlust (the Netherlands) as well as on lake water enriched with nitrogen were investigated. The plants grew best in water enriched with up to 2 mg NH4-Nl−1 and 2 mg NH4-Nl−1 plus 2 mg NO3 Nl−1. During a 14 day experiment, plants absorbed from 75% to 90% of nitrogen. Higher nitrogen concentration than 4 mg l−1 had a negative effect on growth of both species. Elodea nuttallii and E. canadensis prefer NOinf4/p+ over NOinf4/p− when both ions were present in water in equal concentrations.

Macrofauna and its ecology in Lake Zwemlust, after biomanipulation II. Fauna inhabiting hydrophytes

Macrofauna and its ecology in Lake Zwemlust, after biomanipulation II. Fauna inhabiting hydrophytes

Macrofauna and its ecology in Lake Zwemlust, after biomanipulation I. Bottom fauna

Macrofauna and its ecology in Lake Zwemlust, after biomanipulation I. Bottom fauna

Can macrophytes be useful in biomanipulation of lakes? The Lake Zwemlust example

Lake Zwemlust (area 1.5 ha, Zm 1.5 m) has been the object of an extensive limnological study since its biomanipulation involving removal of planktivorous fish (bream) in March 1987 and emptying of the lake. In the subsequent summer period of 1987 the Secchi depth increased to the lake bottom (2.5 m), compared withca 30 cm in the earlier summers. The reaction of submerged macrophytes to improving under-water light climate was rapid. In summer 1987, besides the introducedChara globularis, 5 species of submerged macrophytes occurred and colonized 10% of the lake area. In 1988 and 1989 only quantitative changes were observed; new species did not appear, but the area colonized by macrophytes increased by 7 and 10 times, respectively.Elodea nuttallii was dominant among the macrophytes andMougeotia sp. among the filamentous green algae. Their abundance, contributed to transient N-limination of phytoplankton causing a persistent clear water phase in 1988 and 1989, unlike in 1987 when zooplankton grazing contributed chiefly to the water clarity. Laboratory bioassays on macrophytes confirmed nitrogen limitation.

Restoration by biomanipulation in a small hypertrophic lake: first-year results

Biomanipulation was carried out in order to improve the water quality of the small hypertrophic Lake Zwemlust (1.5 ha; mean depth 1.5 m). In March 1987 the lake was drained to facilitate the elimination of fish. Fish populations were dominated by planktivorous and benthivorous species (total stock c. 1500 kg) and were collected by seine- and electro-fishing. The lake was subsequently re-stocked with 1500 northern pike fingerlings (Esox lucius L.) and a low density of adult rudd (Scardinius erythrophthalmus). The offspring of the rudd served as food for the predator pike. Stacks of Salix twigs, roots of Nuphar lutea and plantlets of Chara globularis were brought in as refuge and spawning grounds for the pike, as well as shelter for the zooplankton. The impact of this biomanipulation on the light penetration, phytoplankton density, macrophytes, zooplankton and fish communities and on nutrient concentrations was monitored from March 1987 onwards. This paper presents the results in the first year after biomanipulation. The abundance of phytoplankton in the first summer (1987) after this biomanipulation was very low, and consequently accompanied by increase of Secchi-disc transparency and drastic decline of chlorophyll a concentration. The submerged vegetation remained scarce, with only 5 % of the bottom covered by macrophytes at the end of the season. Zooplankters became more abundant and there was a shift from rotifers to cladocerans, comprised mainly of Daphnia and Bosmina species, the former including at least 3 species. The offspring of the stocked rudd was present in the lake from the end of August 1987. Only 19% of the stocked pike survived the first year. Bioassays and experiments with zooplankton community grazing showed that the grazing pressure imposed by the zooplankton community was able to keep chlorophyll a concentrations and algal abundance to low levels, even in the presence of very high concentrations of inorganic N and P. The total nutrient level increased after biomanipulation, probably due to increased release from the sediment by bioturbation, the biomass of chironomids being high. At the end of 1987 Lake Zwemlust was still in an unstable stage. A new fish population dominated by piscivores, intended to control the planktivorous and benthivorous fish, and the submerged macrophytes did not yet stabilize.

Structure and feeding activities of zooplankton community in Lake Zwemlust, in the two years after biomanipulation

The biomanipulation study in Lake Zwemlust (area 1.5 ha; mean depth 1.5 m) is among the series of such investigations initiated recently in The Netherlands. The effects of the lake's reffilling (after it was first completely drained empty) almost entirely the nutrient-rich seepage water from the River Vecht flowing nearby and of removal of the planktivorous bream (Abramis brama), on zooplankton community structure and feeding activities of crustaceans were monitored for two successive years (1987, 1988). In these years a classical pattern of succession occurred, with the rotifer spring maximum preceding the crustacean maximum by about 3 weeks. Among the fiveDaphnia species, which appeared in quick succession during May–July, two were large-bodied forms (D. magna; D. pulex). OnlyD. pulex persisted and was the important grazer species in the second year, especially in spring. In the first year the crustacean grazing, with several values >100%.d−1, contributed significantly to the lake's improved water clarity, with Secchi-disc transparencies of 1.5 m and more almost throughout the summer, compared with 0.3 m before the biomanipulation. Even though the water clarity climate in the second year was quite similar to that in the first, the causal factor was high macrophytic vegetation, rather than zooplankton grazing. The lake developed a rich littoral flora and fauna in the second year in response to the optimal light and nutrient conditions. Apparently, the predation by the introduced planktivorous rudd (Scardinius erythrophthalmus) on zooplankton was an important factor in the changes in zooplankton structure, and in the reduced role of zooplankton in seston elimination during the second year. There is some evidence from bioassay work that, simultaneously with the littoral development, nitrogen limitation of the phytoplankton also contributed to the improved light situation in the second year.

Food web manipulation in Lake Zwemlust: Positive and negative effects during the first two years

The hypertrophic Lake Zwemlust, a small water body used as a swimming pool, was characterized by algal blooms in summer, reducing the Secchi disk transparency to less than 0.3 m. Since in The Netherlands a Secchi disk transparency of ≥1 m is obligatory for swimming waters, corrective measures were called for to improve the light climate of the lake. In March, 1987, as an experiment, the lake was drained by pumping out the water to facilitate fish elimination. Planktivorous and benthivorous fish species, which were predominant, were removed by seine- and electro-fishing. After the lake had refilled by seepage it was restocked by a new simple fish community comprising pike (Esox lucius) and rudd (Scardinius erythrophthalmus) only. Stacks of willow twigs (Salix) and macrophytes (roots ofNuphar lutea and ‘seedlings’ ofChara globularis) were introduced into the lake as spawning grounds and refuges for the pike against cannibalism and as shelter for the zooplankton. The effects of this food web manipulation on the light climate, phytoplankton, zooplankton, fish, macrophytes, macrofauna and on the nutrient concentrations were monitored during 1987 and 1988. In summer 1987, despite of high nutrient concentrations, the phytoplankton density was low, due to control by zooplankton, causing a Secchi disk transparency of ≥2.5 m, the maximum depth. Chlorophyll-a concentrations were low (<5 μg Chl.l−1), blooms of cyanobacteria did not occur and a shift from rotifers to cladocerans took place. In 1988, however, also some negative effects were noticed. Macrophytes and filamentous green algae reached a much higher biomass (50–60% cover of the lake bottom) than in 1987; some species, growing through the entire water column, interfered with the lake's recreational use. Associated with the macro-vegetation and possibly with the absence of larger cyprinids, the diet of which also comprises snails, a large scale development of the snail population, among themLymnaea peregra var.ovata took place. This species is known to act as an intermediate host of the bird-parasitizing trematodeTrichobilharzia ocellata, the cercariae of which cause an itching sensation at the spot of penetration of the human skin, accompanied by rash (schistosome dermatitis or swimmers' itch); in July, 1988, about 40% of the bathers complained about this itching. A positive effect of the macrophytes and filamentous green algae was the high uptake of nitrogen, resulting in a low nitrogen concentration in the lake and growth limitation of the phytoplankton population by nitrogen in the summer of 1988. In 1988 the cladocerans were abundant in April only; and unlike in 1987, in the summer of 1988 there was a shift from cladocerans to rotifers. Therefore, only in early spring (April) zooplankton grazing controlled phytoplankton growth and in summer nitrogen limitation was the major controlling factor, keeping chlorophyll-a concentrations low.