Lake IJsselmeer Research Articles

Trends in water quality and algal growth in shallow Frisian lakes, The Netherlands

About 20 shallow lakes form, together with interconnected canals, one hydrological water system in the province of Friesland. Total water surface area meets 14,000 ha, of which the lakes cover 10,000 ha. The regional catchment area is about 305,000 ha. In summer periods inflow of water from Lake IJsselmeer keeps the system on a constant water table of 0.52 m below sea level. At the end of the sixties the lakes became hypertrophic. Algae were dominating the biocenoses and submerged water plants disappeared. Systematic investigations started in 1970, and biological data were included from 1976 on. During twenty years a stable, but highly eutrophic situation, passed. Blue-green algae, especially Oscillatoria agardhii, were dominating the phytoplankton. Submerged vegetation was absent and bream dominated the fish-stock. From 1991 onwards there is a slight improvement in water quality. Transparency increased, phosphorus concentration and algal biomass decreased. Also a shift in phytoplankton species occurred. Dominance of O. agardhii decreased and species diversity increased. First submerged water plants recovered in 1994. Improvements are induced by a combination of measures and a culmination of small effects. Results of 14 years of water quality research are presented. Results are given as trends in time. Attention is paid to the spatial gradient in the province as well. From south to north the chain-arranged lakes represent a remarkable pattern of increasing trophic state, caused by regional loading of nutrients.

Modelling sediment accumulation and dispersion of contaminants in Lake Ijsselmeer (The Netherlands)

In this study two models are integrated for the simulation of sediment distribution and quality in the Lake Ijsselmeer area. STRESS-2d, a two dimensional dynamic model for simulation of sediment transport due to resuspension, erosion, sedimentation and horizontal advection and dispersion is used to simulate the sediment transport dynamics for a period of one year. The model is calibrated on water level, suspended solids concentration and sedimentation flux measurements. The model has a high spatial and temporal resolution. The model DIASPORA, which is based on STRESS-2d results, simulates the effects of sediment transport on morphology and contaminant concentrations in the sediment for a period of decades. DIASPORA also simulates dilution by internally produced CaCO3 and consolidation of sediment layers. The models produce a reasonable reconstruction of suspended solids concentrations and long term accumulation of sediments in deep areas within the lake. Also the temporal and spatial variability in the contaminant concentration in sediments in Lake Ijsselmeer is reconstructed with sufficient quality. Model simulations show that internal redistribution of old deposits in the Usselmeer area and internal production of CaCO3 are diluting the contaminated solids supplied by the river Ijssel.

Trends in water quality and algal growth in shallow Frisian lakes, The Netherlands

About 20 shallow lakes form, together with interconnected canals, one hydrological water system in the province of Friesland. Total water surface area meets 14,000 ha, of which the lakes cover 10,000 ha. The regional catchment area is about 305,000 ha. In summer periods inflow of water from Lake IJsselmeer keeps the system on a constant water table of 0.52 m below sea level. At the end of the sixties the lakes became hypertrophic. Algae were dominating the biocenoses and submerged water plants disappeared. Systematic investigations started in 1970, and biological data were included from 1976 on. During twenty years a stable, but highly eutrophic situation, passed. Blue-green algae, especially Oscillatoria agardhii , were dominating the phytoplankton. Submerged vegetation was absent and bream dominated the fish-stock. From 1991 onwards there is a slight improvement in water quality. Transparency increased, phosphorus concentration and algal biomass decreased. Also a shift in phytoplankton species occurred. Dominance of O. agardhii decreased and species diversity increased. First submerged water plants recovered in 1994. Improvements are induced by a combination of measures and a culmination of small effects. Results of 14 years of water quality research are presented. Results are given as trends in time. Attention is paid to the spatial gradient in the province as well. From south to north the chain-arranged lakes represent a remarkable pattern of increasing trophic state, caused by regional loading of nutrients.

Subsurface irradiance reflectance spectra of inland waters differing in morphometry and hydrology

A database has been established for relating subsurface irradiance reflectance, i.e. water ‘colour’, to the optical properties and water quality parameters of more than 120 Dutch inland water bodies. The concentrations of total chlorophyll-a (TChl-a = chlorophyll-a plus phaeopigment), total suspended matter and the Secchi-disc depth varied between 0.6 and 468 mg m 3 , 0.8 and 98 g m 3 , and 0.15 and 5.50 m, respectively. The water bodies represented very different water types based on morphometry and hydrology. The depth ranged from 0.4 to 40 m, and the surface area from 0.25 ha (fens in the moorland Peel) to 1200 km 2 (Lake IJsselmeer). The mean specific phytoplankton absorption coefficient at 676 nm was 0.013 0.003 m 2 (mg TChl-a) 1 . The absorption by tripton and dissolved humic substances at 440 nm varied between 0.1 and 16.4 m 1 , and 0.1 and 65.5 m 1 , respectively. By using the spectral position and magnitude of the subsurface irradiance reflectance peak alone, it was possible to distinguish groups of water bodies according to a classical typology based on morphometry and hydrology.

Levels of rare earth elements in Dutch drinking water and its sources. Determination by inductively coupled plasma mass spectrometry and toxicological implications. A pilot study

The determination of rare earth elements (REE) in water samples using inductively coupled plasma mass spectrometry was evaluated with respect to selection of isotopes, detection limits, precision, matrix effects, and spectral interferences. The method was applied to raw and drinking water samples of 18 groundwater stations and two surface water stations, and to samples taken from the rivers Rhine and Meuse and from Lake IJsselmeer. Significant amounts of REE were found in the raw water samples of 8 locations and in the drinking water of 3 locations. Of the groundwater stations high concentrations of REE were only found for phreatic winnings of moderate depths having low carbonate contents. From general literature information indicative admissible drinking water concentrations were derived and compared with the found concentrations. For two of the three locations mentioned the indicative admissible concentrations were exceeded for a number of REE elements and possible health risks for humans could not be excluded.

Competitive food exploitation of smelt Osmerus eperlanus by great crested grebes Podiceps cristatus and perch Perca fluviatilis at Lake IJsselmeer, The Netherlands.

The impact of predation by an avian predator (great crested grebe Podiceps cristatus) and a predatory fish (perch Perca fluviatilis) on a common resource, the small planktivorous fish smelt (Osmerus eperlanus) was studied in Lake IJsselmeer, The Netherlands, in July-October 1985-1988. At this time of the year the grebes are in simultaneous wing-moult and therefore temporarily flightless. Four factors limit the predation pressure by grebes: (1) an underwater visibility threshold of c. 40 cm Secchi depth is the lower limit at which large numbers attend the moulting site, (2) a lower density threshold of exploitable smelt biomass of c. 30 kg/ha determines the actual fishing areas, (3) a fish size threshold of 6.5 cm total length further limits prey availability, and (4) the vertical movements of the prey impose a strong (diel) time constraint on the birds, allowing only crepuscular foraging. Perch, the other main predator in this system, is less restricted in its foraging. Perch were found to be in direct competition with the grebes, preying heavily on the juvenile smelt. Over the 4 years of study 90% of all predation from 15 July to 15 October (72-233 kg/ha) was due to perch. The high level of predation by birds and fish was only possible due to a continuous immigration of smelt into the area (1.45 kg/ha per day). In three of the four years, however, the combined predation by fish and birds surpassed the immigration rate of the prey, which led to a strong reduction in smelt stocks in the study area. A conceptual model is developed to describe the different sets of constraints on the grebes' foraging. First, the state of eutrophication in relation to the weather condition determines the degree of algal blooms, and thus underwater visibility, in late summer. This is the major factor governing the numbers of grebes on the moulting area. Second, the size of the population of predatory fish determines the overall food availability (biomass and size distribution of smelt). These factors are partly interconnected and related to human action (pollution, fisheries). It is suggested that, despite deteriorating visibility conditions, the largest moulting site for grebes in Europe at Lake IJsselmeer exists because the stocks of predatory fish are kept low by overfishing.

Distribution and geochronology of priority pollutants in a large sedimentation area, River Rhine, The Netherlands

The concentrations of heavy metals, As, polychlorinated biphenyl (PCB) congeners, poly-nuclear aromatic hydrocarbons (PAH) and various sediment characteristics were determined in 77 samples of the surficial sediments and one 3 m core of Lake Ketelmeer and Lake IJsselmeer in The Netherlands. Absolute contents of these polluting compounds were corrected according to a Dutch normalization procedure. In Lake IJsselmeer the youngest geological layer (Um-deposit) is mainly found in deep sedimentation areas (25%). This deposit is severely polluted in Lake Ketelmeer. Contents of all polluting compounds in this IJm-deposit of Lake Ketelmeer proved to be 1.6–9 times higher than in Lake IJsselmeer. These contents in this deposit in Lake IJsselmeer are 2–4 times higher than those in the older sandy sediments in this lake. Concentrations of heavy metals, As and PCBs increase with depth to a maximum and then decrease to lower levels or background, corresponding to the historic inputs of the river during the past five decades. With increasing distance from the river mouth (Lake Ketelmeer) to Lake IJsselmeer a decrease of the degree of pollution for this young layer is found. Internal carbonate production and the mixing with eroded sediment from other areas seem responsible for the dilution of this deposit.

Distribution and aspects of population dynamics of the zebra mussel, Dreissena polymorpha (Pallas, 1771), in the lake IJsselmeer area (The Netherlands).

The distribution, settling and growth of the zebra mussel, Dreissena polymorpha Pallas, in Lake IJsselmeer and Lake Markermeer in The Netherlands were studied from 1980 to 1985. In these lakes D. polymorpha is the most important food source for wintering diving ducks. The study was part of an investigation into the carrying capacity of the lakes for these birds.

Inlet of alkaline river water into peaty lowlands: effects on water quality and Stratiotes aloides L. stands

As a result of changed land use and concomitantly increased drainage, in combination with increased use of water for industrial, agricultural and other human purposes, there is an increasing shortage of “natural” water in many areas of The Netherlands in summer. To compensate for this shortage, increasing amounts of hard water from the Rivers Rhine and Meuse are diverted to these lowlands. It is commonly assumed that the disappearance of Stratiotes aloides L. in peaty lowlands is caused by a decline of the water quality, owing to high concentrations of nutrients in the incoming water. However, field observations in “de Weerribben”, a large mire complex in The Netherlands, indicated that the decline of the water quality in this area is caused by an altered ion composition of the water. The incoming Rhine-type water from Lake IJsselmeer is very alkaline, rich in HCO 3 − and SO 4 2−. These anions appear to be responsible for a change in the decomposition processes. Consequently, the peat becomes very fine and soft, and because of increased bioturbation the water becomes turbid. As a result of increased reduction processes in the soil there is an increased mobility of phosphorus, leading to internal eutrophication and greatly increased levels of reduced compounds such as S 2−, CH 4 and NH 4 + in the soft, upper layer of the bottom. Transplantation experiments with Stratiotes aloides plants showed that the plants started to decay in winter, after migration to the soft, upper sapropel layer. Culture experiments proved that the S 2− and NH 4 + levels in this layer are lethal to Stratiotes plants.

Diurnal changes in buoyancy and vertical distribution in populations of Microcystisin two shallow lakes

Changes in the buoyancy of Microcystis populations were followed over 24 h periods in two shallow well-mixed lakes, Lake Vinkeveen (area 0.6 km2) and Lake IJsselmeer (1190 km-2), in the Netherlands. The Microcystis colonies collected from the surface layers in both lakes showed a buoyancy decrease during the day and an increase at night. The buoyant colonies, and especially the faster-moving large ones, became concentrated by flotation into the surface mixed layers. As a result the mean position of the cyanobacterial population became located nearer the surface than that of other non-buoyant phytoplankton, such as Scenedesmus. The cyanobacteria would, therefore, have received a higher average irradiance. The Microcystis in these shallow lakes had weaker gas vesicles than those found previously in deeper lakes but it was demonstrated that the loss of buoyancy, which occurred at high irradiances, resulted from an increase in carbohydrate ballast rather than through turgor-driven gas vesicle collapse.

Trace metal chemistry of a Dutch reservoir, the Tjeukemeer

SUMMARY. The concentrations of total and dissolved (<0.2 μm) Fe, Mn, Cu, Co, Zn and Al in the Dutch reservoir, the Tjeukemeer, were recorded fortnightly between 1984 and 1986. Due to its reservoir function, the Tjeukemeer receives water that is relatively rich in Fe and Mn from its peaty drainage area in winter. In summer, water that is relatively rich in Cu and Zn from lake IJsselmeer, which is flushed by a tributary of the River Rhine, flows into the lake. Therefore trace metal loads, as estimated from annual mean concentrations and hydraulic data, are climate‐dependent. In wet years, such as 1985, the annual Fe, Mn, Cu and Zn loads may be 3.1,0.2,0.001 and 0.009 gm−2, respectively. In dry years, such as 1984 and 1986, the Fe and Mn loads may be less than one quarter while the Cu and Zn loads may double. Especially in wet years comparable Cu and Zn inputs occur by deposition. Despite the dependence of trace metal loads on the climate‐dependent water regime. Principal Component Analysis indicated no strong relation between the total Cu, Co, Zn and Al concentrations in lake water and hydrological tracers such as Cl− and UV absorbance. Instead, wind speed appeared to be more strongly connected with the dynamics of these metals. Thus in the shallow Tjeukemeer, internal trace metal loading due to wind‐induced resuspension starts to dominate the contributions of external loads to the total metal concentrations at wind speeds exceeding 3ms−1.

Feather eating in Great Crested Grebes Podiceps cristatus: a unique solution to the problems of debris and gastric parasites in fish‐eating birds

The occurrence of feathers in stomachs of 407 Great Crested Grebes Podiceps cristatus from Lake IJsselmeer, The Netherlands, is described. Only four of the 8718 identified stomach feathers originated from a species other than Great Crested Grebes. In all, 68% were breast and belly feathers and 19% were flank feathers. Flank feathers were positively selected from those becoming available during moult, and also occurred more in the ejected feather pellets than expected from the intake. This suggests that flank feathers, which are long and curved and have a black tip, may be especially suited for the formation of pellets. Feather ingestion was more than balanced by feather production. Feathers were most abundant in stomachs in autumn and were least numerous in winter. Most of this variation can be explained by seasonal differences in the intensity of body moult. In addition, the type of prey was related to the number of ingested feathers. When the diet consisted of smelt, which leave little indigestible matter, more feathers were eaten than with a diet of perch and pikeperch, which leave more fish debris. We suggest the hypothesis that ingested feathers, in the absence of other indigestible matter, contribute substance to the stomach content, enabling the formation of pellets that can be ejected. The habit of regularly ejecting the stomach contents minimizes the chance that any serious population of gastric parasites will build up in the upper part of the alimentary tract.

Foraging rhythm of great crested grebes Podiceps cristatus adjusted to diel variations in the vertical distribution of their prey Osmerus eperlanus in a shallow eutrophic lake in The Netherlands.

Great crested grebes Podiceps cristatus only foraged for an hour or two during dawn and again during dusk on Lake IJsselmeer in August-September. During this time of the year the adult birds are in wing moult and temporarily unable to fly. The food of grebes consisted almost exclusively of smelt Osmerus eperlanus, the most numberous pelagic fish. Simultaneous sonar registrations and trawl net fishing showed that smelt moved to the water surface during the twilight periods. During day and night they were concentrated near the bottom. We argue that grebes have the best foraging opportunities during twilight when much of their prey is near the surface, where light intensities allow the fish to be detected and captured. When the smelt are in the upper water layers the distance to the covered to get the prey (i.e. diving time and cost) is also least.

Morphologische Variation einer europäischen Population des HaubentauchersPodiceps cristatus in Beziehung zu Alter, Geschlecht und Jahreszeit

A sample of 1450 Great Crested Grebes from the non-breeding season (August–March) which had accidentally drowned in fishing nets in Lake IJsselmeer, The Netherlands, was examined for age and sex differences in linear measurements, body mass, plumage, leg colour and gonad condition. During skinning and drying, wings of non-moulting birds decreased 2.41 mm in length, and wings of wing-moulting birds significantly more: 4.72 mm. The shrinkage is due to changes in the feather follicles and wing elements and not to changes in the actual feather length. Measurements of body, wing, bill, tarsus and keel lengths showed that males are larger than females. The sexual dimorphism is most pronounced in bill length (11 % difference). Differences between juvenile (first winter) and adult birds are small or non-existent. A discriminant function incorporating wing and bill length (age groups lumped), correctly classified the sex of 89 % of the original sample, and 85 % of an independent sample of starved beached birds. The presence (in juveniles) or absence (in adults) of brown lesser upper wing-coverts is a reliable ageing criterion during the whole non-breeding season: only 2 % juvenile females are misidentified. The striped head plumage of juveniles disappears during winter, but there is a large variation between individuals. Adults tend to have one or more greater upper wing-coverts with white inner vanes. Adults often have a wider white stripe between eye and crest than juveniles. Adult males in summer plumage have longer crests and tippets than females. The colour and barring patterns of the inner tarsi vary greatly. Adults generally have a higher density of black bars than juveniles. Adult males appear to have two peaks in testis size: one in spring and a second one in autumn. The grebes weigh least during the wing moult period in August–September. Average body masses of all age and sex groups increase from September to November and then remain essentially stable until April. This pattern is very different from the peaked body mass pattern, described for dabbling ducks and waders wintering at the same latitudes, but resembles the body mass patterns of two sawbill species which also feed on fish in Lake IJsselmeer.

Body size, nutrient reserves and diet of Red-necked and Slavonian GrebesPodiceps grisegenaandP. aurituson Lake IJsselmeer, The Netherlands

Samples of Red-necked and Slavonian Grebes that had drowned in gill nets while foraging in winter were analysed for body size, nutrient reserve levels and food content. Measurements of Slavonian Grebes indicated that they may originate from the Icelandic and Norwegian breeding grounds, not from the Baltic area as is suggested in the literature. The mass of the bird after its nutrient reserves have been totally depleted, its ‘structural size’, is best predicted by different body measurements in each of the 2 species and in the Great Crested Grebe, even though they are closely related. Total fat mass was best estimated from fresh abdominal fat mass in both species. An average Red-necked Grebe in midwinter is estimated to have enough nutrient reserves to survive 11 days starvation. The diet of both species consisted exclusively of fish, mainly Smelt, followed by Perch and Ruffe. Both species took more, smaller Smelt than expected from the food supply that is present in the habitat. This suggests that swimming speeds of the fish may be important in determining whether grebes can catch them, so that food selection may be determined more by the agility of the bird than by its bill dimensions.