The Norwegian reference lake ecosystem, Øvre Heimdalsvatn

The subalpine lake, Øvre Heimdalsvatn and its catchment, situated in the mountains of southern Norway, has been the subject of extensive ecosystem studies over the last 50 years covering a wide range of disciplines. The lake is located at 1,088 m a.s.l., has an area of 0.78 km², a maximum depth of 13 m, and a catchment area of 23.6 km². It lies more or less on the limit of the birch forest, while the catchment extends up over 1,800 m a.s.l. and into the high alpine zone. The valley is little influenced by human activity and there is no permanent habitation, although the area is used for grazing of domestic livestock during summer. Otherwise the lake and its catchment have always been important for fish and game. The catchment also received major radionuclide fallout from the Chernobyl accident in 1986. The studies include Quaternary history, the development of algorithms for remote sensing of snow conditions, long-term changes in lake ice cover and temperature, the zooplankton and benthic communities, as well as the uptake of Chernobyl radionuclides and mercury by the biota. The consequences of the introduction of the European minnow (Phoxinus phoxinus) on the benthos, zooplankton and the brown trout (Salmo trutta) have also been investigated. The lake and its catchment are widely used in university teaching and thesis work. On account of the substantial knowledge base, Øvre Heimdalsvatn is well suited to long-term monitoring.     

Heavy metals (Cu and Zn) in recent sediments of Llangorse Lake,Wales: non-ferrous smelting,Napoleon and the price of wheat — a palaeoecological study

Elevated concentrations of Cu and Zn have been found in the upper part of three sediment cores collected from Llangorse Lake, in south Wales. Palaeomagnetic evidence from one of the cores and ²¹⁰Pb analysis of another, suggests that the increase in sediment Cu and Zn concentrations began during the eighteenth century. A sharp increase in the concentrations of these metals in the sediment profile appears to have occurred during the latter part of the eighteenth century and these concentrations remained high until the mid to late nineteenth century.The absence of known ore deposits and industry around the lake suggests that the lake and catchment soils were increasingly contaminated by long-range aerial transport of emissions from the expanding activity of Cu and Zn smelters located some 80 km upwind in the Swansea area during the Industrial Revolution. Evidence from agricultural crop returns indicates a significant increase in the amount of land devoted to tillage in the catchment, particularly to cereal production, during the late eighteenth and the first half of the nineteenth century which included the Napoleonic Wars. This agricultural shift appears to coincide with increased concentrations of Cu and Zn in the lake sediments. It is suggested that newly ploughed soils, contaminated with metals for many years by long-range aerial transport from the Swansea area, eroded, and were carried into the lake by catchment run-off and added to the sediment burden of Cu and Zn. A subsequent decline of Cu and Zn emissions due to the collapse of the non-ferrous smelting industry and reduced soil erosion because of a 50% reduction of tillage due to an agricultural depression in the second half of the 19th century may explain the fall in Cu and Zn concentrations in the upper part of the sediment profile. The most recent sediments (20th century) show the increase in heavy metals characteristic of many lakes around the world.     

Sediment supply and accumulation in a small Moroccan lake: an historical perspective

Dayat-er-Roumi is a small lake (73 ha) located in the sub-humid region of NE Morocco. Lake sediment and catchment soils are examined to identify areas of sediment supply to the lake. Magnetic measurements and clay mineralogy are used to show that recent lake sediment is derived predominantly from eroded topsoil. ²¹⁰Pb dating of one sediment core provided a chronology for the calculation of sediment accumulation rates. The rate of sediment accumulation increased slowly throughout the earlier part of the 20th century and then rapidly in the mid-1970's. These increases are attributed to human disturbances in the catchment, initially by olive planting and then by drainage of a wetland area.     

A Multiscale Framework for Deconstructing the Ecosystem Physical Template of High-Altitude Lakes

An ecosystem is generally sustained by a set of integrated physical elements forming a functional landscape unit—ecotope, which supplies nutrients, microclimate, and exchanges matter and energy with the wider environment. To better predict environmental change effects on ecosystems, particularly in critically sensitive regions such as high altitudes, it is imperative to recognise how their natural landscape heterogeneity works at different scales to shape habitats and sustain biotic communities prior to major changes. We conducted a comprehensive survey of catchment physical, geological and ecological properties of 380 high-altitude lakes and ponds in the axial Pyrenees at a variety of scales, to formulate and test an integrated model encompassing major flows and interactions that drive lake ecosystems. Three composite drivers encompassed most of the variability in lake catchment characteristics. In order of total percentage of variance explained, they were (i) hydrology/hydrodynamics—responsible for type and discharge of inlets/outlets, and for waterbody size; (ii) bedrock geomorphology, summarising geology, slope and fractal order—all dictating vegetation cover of catchment slope and lake shore, and the presence of aquatic vegetation; and (iii) topography, that is, catchment formation type—driving lakes connectivity, and the presence of summer snow deposits. Although driver (i) appeared to be local, (ii) and (iii) showed gradient changes along altitude and latitude. These three drivers differentiated several lake ecotopes based on their landscape similarities. The three-driver model was successfully tested on a riparian vegetation composition dataset, further illustrating the validity and fundamental nature of the concept. The findings inform on the relative contribution of scale-dependent catchment physical elements to lake ecotope and ecosystem formation in high-altitude lakes, which should be considered in any assessment of potentially major deleterious effects due to environmental/climate change.     

The effect of agriculture on the primary production in Lake Beskie (Poland) as recorded in the stratigraphy of fossil pigments

Analysis of fossil pigments deposited in the bottom sediments of Lake Beskie, was used to assess changes in the primary productivity during the past years. Three characteristic periods of lake development were distinguished. These periods correspond with a transformation in the lake's catchment area induced by the development of agriculture. A first period was characterized by intensive inflow of allochthonous matter into the lake, due to agriculture in the catchment area, favouring soil erosion. This erosion and the subsequent increase in mineral fertilization resulted in decrease of sorption ability of the soil. This in turn led to increased leaching of nutrients into the lake which resulted in increased primary production and hypolimnetic anoxia. These high oxygen deficits were characterized by a development of photosynthetic bacteria of the genus Chlorobium, and an intensification of the lake's enrichment, mainly with phosphorus. In a final period organic fertilizers (manure) were used in the catchment area. A noticeable improvement of sorption ability of the soil occurred, migration of nutrients to the lake was inhibited, and primary productivity decreased.     

Relationships between morphometry,geographic location and water quality parameters of European lakes

I addressed the question how lake and catchment morphometry influences water chemistry and water quality over a large scale of European lakes, and developed the regression equations between most closely related morphometric and water quality indices. I analysed the data of 1,337 lakes included in the European Environment Agency (EEA) database, carrying out separate analyses for three basic lake types: large lakes (area ≥100 km², 138 lakes), shallow lakes (mean depth ≤3 m, 153 lakes) and large and shallow lakes (area ≥100 km² and mean depth ≤8 m, 35 lakes). The study revealed that in Europe, the lakes towards North are larger but shallower and have smaller catchment areas than the southern lakes; lakes at higher altitudes are deeper and smaller and have smaller catchment areas than the lowland lakes. Larger lakes have generally larger catchment areas and bigger volumes, and they are deeper than smaller lakes, but the relative depth decreases with increasing surface area. The lakes at higher latitudes have lower alkalinity, pH and conductivity, and also lower concentrations of nitrogen and phosphorus while the concentration of organic matter is higher. In the lakes at higher altitudes, the concentration of organic matter and nutrient contents are lower and water is more transparent than in lowland lakes. In larger lakes with larger catchment area, the alkalinity, pH, conductivity and the concentrations of nutrients and organic matter are generally higher than in smaller lakes with smaller catchments. If the lake is deep and/or its residence time is long, the water is more transparent and the concentrations of chlorophyll a, organic matter and nutrients are lower than in shallower lakes with shorter residence times. The larger the catchment area is with respect to lake depth, area and volume, the lower is the water transparency and the higher are the concentrations of the nutrients, organic matter and chlorophyll as well as pH, alkalinity and conductivity. The links between lake water quality and morphometry become stronger towards large and shallow lakes. Along the decreasing gradients of latitude, altitude and relative depth, the present phosphorus concentration and its deviation from the reference concentration increases.     

Climatic changes in northwestern Ontario have had a greater effect on erosion and sediment accumulation than logging and fire: Evidence from 210Pb chronology in lake sediments

Sedimentation patterns in nine lake basins were examined where catchments were either clearcut, burned in recent history, or where there has been no recorded disturbance and the catchments consist of mature forests. Pronounced declines in sedimentation rates were observed in eight of eleven cores after 1980, in reference, clearcut, and burn lakes. The degree of change was positively correlated with the drainage ratio (catchment area: lake area), but was unrelated to land use history. The decline in sedimentation rates after 1980 coincide with a 60% decrease in catchment runoff and precipitation measured over the same time interval at the nearby Experimental Lakes Area. These results indicate that climatic changes over the past 20 years have had a greater effect on catchment erosion than either clearcutting or fire.     

Byglandsfjorden. Primary production and other limnological features in an oligotrophic Norwegian lake

Byglandsfjorden is a lake situated in southern Norway, about 80 km north of Kristiansand. The catchment area consists of archean rocks. The river Otra flows through the lake. Water samples were taken from the lake 4 times during the summer of 1971, and primary production was measured three times. The chemical analyses show an oligotrophic lake. The lake is acid and poor in electrolytes. pH-values vary between 5.3 and 6.0, and the specific conductivity lies at about 10. Primary production is rather high, and per m² lake surface the values are found to be about the same as in Svinsjøen, a rather eutrophic lake near Oslo. However, an index used by Rodhe (1965) shows that the lake is of a more oligotrophic type.     

Cyanophytes and chlorophytes versus raphidophytes in humic lakes with different catchment basins

The aim of the study was to evaluate the effects of coniferous forest cover in the catchment basin and relative catchment area (catchment area to lake volume ratio) on phytoplankton composition in humic lakes. The study was carried out in 11 small and shallow lakes situated in the West Polesie region (Eastern Poland). The lakes were divided with respect to forest cover in their catchment basins into two groups: high forest cover — HFC (more than 60%) and low forest cover — LFC (less than 60%). The study showed that both, land use in the catchments (proportion of forests) and the relative catchment area determined physicochemical and biological parameters in the lakes. The high relative catchment area affects their high productivity expressed by high chlorophyll a concentration and low water visibility. The lakes of the LFC group had low water colour as well as high concentration of total phosphorus (P_tot), reaction (pH), and conductivity of water and a large number of cyanophytes and chlorophytes. The dominant species, e.g., Planktolyngbya limnetica, Limnothrix planctonica, Planktothrix agardhii, Coenococcus planctonicus, were characteristic of high trophic status. In the lakes of the HFC group, P_tot, pH, conductivity of water and the contribution of cyanophytes and chlorophytes was considerably lower, whereas the water colour and the number of raphidophytes represented by Gonyostomum semen was high. The large number of raphidophytes and the small amount of chlorophytes and cyanophytes in the lakes of the HFC group indicated the lake naturalness.     

Burial rates and stoichiometry of sedimentary carbon,nitrogen and phosphorus in Midwestern US reservoirs

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The importance of lake morphometry and catchment characteristics in limnology – ranking based on statistical analyses

This work introduces an interpretational key to quantify and understand how much of variations among lakes in fundamental ecosystem characteristics that may be related to lake morphometry, catchment area features, measurement uncertainties and other factors (mostly climate). The size and form of lakes regulate many general transport processes, such as sedimentation, internal loading and outflow, which in turn regulate many abiotic state variables, such as concentrations of phosphorus, colour, water chemical variables and water clarity, which regulate primary production, which regulate secondary production. This paper discusses relationships between key abiotic state variables, lake morphometry and catchment area characteristics using empirical/statistical analyses based on data from 95 lakes. It has been shown that of the studied variables Secchi depth depends most on morphometry (34%); 31% of the variations among the lakes in Secchi depth may be related to catchment area characteristics, 1% to uncertainties in empirical data and 34% to other (climatological) factors. The corresponding figures for alkalinity, which depends least on lake morphometry are, 0% related to morphometry, 34% to catchment conditions, 1% to empirical uncertainty and 58% to other causes. For all other studied variables, i.e., conductivity, hardness (CaMg), calcium, iron, colour, pH and phosphorus the corresponding figures vary between these values. The interpretational key helps to explain the mechanistic reasons for these statistical/empirical results.     

Climate-lake interactions recorded in varved sediments from a Swedish boreal forest lake

A 1100-year long record of lake ecosystem response to climate and catchment change with precise chronological control is reported. Diatom and pollen assemblages of an annually laminated (varved) sediment from a northern Swedish lake (Kassjön, Våsterbotten) were used as records of lake diatom communities and catchment vegetation. These data were compared with summer temperature estimates based on tree-ring records of the same geographical area to identify the effects of climate change and catchment disturbance on diatom assemblages in the lake. In a canonical ordination, 23% of the variability in the total diatom assemblages for the period AD1040–1804 was accounted for by changes in pollen data which reflect agricultural development in the catchment. Diatom species richness, however, exhibited a stronger relationship with summer temperature and, significantly, declined with the lower temperatures associated with the Little Ice Age minimum (early 17th century). Summer temperature accounted for 23% of the variability in diatom species richness 20 years later. The mechanism behind this time-lag is unclear, but may be related to catchment-mediated effects, given recent evidence for lags in the response of boreal-forest vegetation regeneration cycles to climatic variability. These results suggest that climate-related effects on lakes occurring over medium timescales can be resolved in lake sediments. Moreover, it is possible to identify these effects despite cultural-related signals, but as the latter become more extreme in the late 20th century the climate signal is obscured.     

Macrozoobenthos of two different catchment areas of the tatra mountain lakes with a special reference on the effects of acidification

The structure of macrozoobenthos of two different high-mountain Tatra lakes, namely Starolesnianske pleso (strongly acidified) and Ni?né Terianske pleso (reference site) is described. The latter is characterised by a large catchment and total area, and is relatively deep with strong inlet and outlet. It is not affected by acidification. Univoltine species of mayflies, stoneflies and caddisflies dominate in the littoral, mainly scrapers. Predators are represented by stoneflies. Shredders dominate in the lake outlet. From the zoogeographic point of view, Carpathian endemites and Central European species prevail. Forty percent of species are sensitive to acidification. The former has a smaller catchment and total area, and is relatively shallow, without inlet. It is strongly affected by acidification. Semivoltine species, mainly predators (beetles) and shredders prevail. From the zoogeographic point of view Palaearctic species dominate. Species sensitive to acidification are missing. Emergence of water insects has two peaks during spring and fall circulation.     

Planning for the recovery of Lake Toolibin,Western Australia

Lake Toolibin, an intermittently flooded freshwater wetland in the southwest of Western Australia, is threatened by salinization due to extensive clearing within its catchment. The lake is a Wetland of International Importance under the Ramsar Convention because of the extensive stands of trees on the lake bed and its significance as a waterbird breeding site. Past research and monitoring have identified the causes of wetland vegetation and water quality decline and this information has been used to design a Recovery Plan for the lake. The plan is currently in the early stages of implementation and includes both short-term engineering measures to reduce salinity within the lake and long-term rehabilitation measures within the catchment. Community involvement in the recovery process is an integral part of the plan and ensures that recovery of the lake remains as the focus for ongoing catchment rehabilitation.     

Climate-related challenges in long-term management of Säkylän Pyhäjärvi (SW Finland)

Säkylän Pyhäjärvi (SW Finland) is an example of a large and shallow lake suffering from eutrophication. During the last 20 years, the quality and general usability of water in Pyhäjärvi have shown considerable variation driven by both a variety of human activities and climate-related factors such as wet and dry years. The lake has been thoroughly studied for decades and has been the object of comprehensive restoration activities both in the catchment and in the lake since the 1990s. Large variety of water protection measures like wetlands, sedimentation ponds and filtering systems have been implemented in the catchment area to reduce external nutrient load. Another important tool for Pyhäjärvi restoration is biomanipulation, done by local commercial fishermen in winter. Twenty-five percent of the annual phosphorus input is removed with fish catch. Currently, restoration work is facing new challenges: short or even nearly missing ice cover period and increased winter time nutrient load from the catchment. In the 2000s, there were 3 years with exceptionally short ice period, allowing only brief winter seining periods. Consequently, the biomanipulation catch was very low in 2007 and 2008 leading to observable food web effects. Phosphorus load was especially high in winters 2006/2007 and 2008/2009. On the basis of the data of 1987–2008, we have tested the hypothesis if climate-related winter time variables like phosphorus load, air temperature and precipitation would affect the water quality of the lake in following summer, here measured as chlorophyll a concentration in the lake water. A linear model has been used and a validation procedure has been performed to select the best variables. Our results indicate some of the linkages between climate-related catchment processes and the ecological status of the lake.     

MANAGEMENT OPTIONS FOR SHALLOW HYPERTROPHIC LAKES,WITH PARTICULAR REFERENCE TO ZEEKOEVLEI,CAPE TOWN

Summary

Zeekocvlei, a freshwater coastal lake, is an important regional recreation area in the south-western Cape, South Africa. The lake is hypertrophic, experiences perenially dense populations of cyanobacteria (Microcystis), invasive bulrush and reed encroachment, and has a thick benthic layer of sediments rich in organic matter. User and scientific surveys have indicated that management problems centre around the dense phytoplankton population and the nutrient loading of the lake. Both in-lake and catchment-based management options for improving the water quality of the lake were evaluated. Given the present socio-economic constraints in South Africa, only catchment-based management can be recommended before any rehabilitation measures are undertaken in the lake itself. This would entail the investigation and implementation of measures to reduce levels of catchment-derived nutrient loading by managing the water quality of agricultural (predominantly horticulture) and urban catchment runoff.     

Relationships between lake macrophyte cover and lake and landscape features

We examined the ability of lake and landscape features to predict a variety of macrophyte cover metrics using 54 north temperate lakes. We quantified submersed cover, emergent cover, floating leaf cover, Eurasian watermilfoil cover and total macrophyte cover. Measured lake features included lake physio-chemical and morphometric variables and landscape features included hydrologic, catchment and land use/cover variables. Univariate regression analyses demonstrated that these macrophyte cover metrics are predicted by a wide range of predictor variables, most commonly by: Secchi disk depth, maximum or mean depth, catchment morphometry, road density and the proportion of urban or agricultural land use/cover in the riparian zone or catchment (r² = 0.06–0.46). Using a combination of lake and landscape features in multiple regressions, we were able to explain 29–55% of the variation in macrophyte cover metrics. Total macrophyte cover and submersed cover were related to Secchi disk depth and mean depth, whereas the remaining metrics were best predicted by including at least one land use/cover variable (road density, proportion local catchment agriculture land use/cover, proportion cumulative catchment urban land use/cover, or proportion riparian agriculture land use/cover). The two main conclusions from our research are: (1) that different macrophyte growth forms and species are predicted by a different suite of variables and thus should be examined separately, and (2) that anthropogenic landscape features may override patterns in natural landscape or local features and are important in predicting present-day macrophytes in lakes.