Lakes In Finland Research Articles

Probabilistic Evaluation of Ecological and Economic Objectives of River Basin Management Reveals a Potential Flaw in the Goal Setting of the EU Water Framework Directive.

The biological status of European lakes has not improved as expected despite up-to-date legislation and ecological standards. As a result, the realism of objectives and the attainment of related ecological standards are under doubt. This paper gets to the bottom of a river basin management plan of a eutrophic lake in Finland and presents the ecological and economic impacts of environmental and societal drivers and planned management measures. For these purposes, we performed a Monte Carlo simulation of a diffuse nutrient load, lake water quality and cost-benefit models. Simulations were integrated into a Bayesian influence diagram that revealed the basic uncertainties. It turned out that the attainment of good ecological status as qualified in the Water Framework Directive of the European Union is unlikely within given socio-economic constraints. Therefore, management objectives and ecological and economic standards need to be reassessed and reset to provide a realistic goal setting for management. More effort should be put into the evaluation of the total monetary benefits and on the monitoring of lake phosphorus balances to reduce the uncertainties, and the resulting margin of safety and costs and risks of planned management measures.

Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake.

Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s) obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes.

Importance of spatial scale in structuring emergent lake vegetation across environmental gradients and scales: GIS-based approach

Geographical information systems (GIS)-based approaches support the traditional empirical assessment and monitoring measures to indicate large-scale environmental alterations caused by global change. We examined the relationship between cover patterns of emergent aquatic plants derived from the CORINE land cover database, and environmental gradients (i.e. lake, climate and land cover and soil variables) at four different buffer scales (50m, 100m, 300m and 500m) in 408 boreal lakes in Finland. Our main statistical methods were hierarchical partitioning (HP), generalized linear models (GLM) and variation partitioning (VP).Based on correlations and HP, the importance of different buffer zones varied between environmental variables in explaining the vegetation cover. Our study also demonstrated that landscape productivity variables (i.e. Normalized Difference Vegetation Index and Tasseled Cap Greenness) strongly structured the vegetation cover. These productivity variables proved to be proxies for agricultural land and nutrient leaching from terrestrial areas to water, but they were also associated with shading of riparian vegetation. In the VP, land cover and soil variable groups influenced emergent vegetation cover the most, followed by lake and, lastly, by climate variables.Our work emphasized the importance of spatial scale in structuring freshwater assemblages that should be taken into account in ecological research and bioassessment. The use of a single spatial scale may lead to flawed results on the relevance of various environmental gradients on freshwater assemblages. Moreover, our study showed that satellite-based productivity variables can be powerful proxies for the amount of nutrients eventually entering aquatic ecosystems from adjacent terrestrial areas. The GIS-based approach used here provided an ecologically sound and cost-efficient early-warning estimation of vegetation overgrowth in boreal lakes. This approach is applicable to other regions with similar land cover data sets.

Role of terrestrial carbon in aquatic UV exposure and photoprotective pigmentation of meiofauna in subarctic lakes

Summary Aquatic organisms are adversely influenced by ultraviolet radiation (UV) and utilise photoprotective strategies, including pigmentation. We examined UV‐protective melanin pigmentation of aquatic meiofauna (Cladocera) in relation to the UV exposure across 25 tree line lakes in Finland to address the potential effects of increased UV and altered input of UV‐screening terrestrial dissolved organic carbon (DOC) on aquatic organisms. Bio‐optical parameters, including concentration of DOC, the coloured dissolved organic matter (CDOM) fraction, a suite of carbon quality indices and chlorophyll a, were analysed from lake water, and their role in controlling underwater UV environment (measured as diffuse UV attenuation coefficient Kd at 305 and 340 nm) was examined. Cladoceran (Alona affinis) carapaces were extracted from the surface sediments, and their melanisation was assessed with spectroscopic UV‐visible light absorbance measurements. DOC, CDOM and specific UV absorbance (SUVA) had strong positive relationships with the attenuation of UV in the lakes, suggesting that terrestrial organic carbon controls underwater UV exposure in the examined lakes. The absorbance measurements indicated the presence of melanin in the cladoceran carapaces, the degree of melanisation varying strongly among the lakes. Melanisation had significant relationships with SUVA and fluorescence index (FI). It was higher in lakes with low SUVA and high FI, indicating that cladocerans exhibit strong melanisation in lakes with low contribution of UV‐attenuating allochthonous DOC (i.e. high UV exposure). The results suggest that cladoceran meiofauna respond to UV by utilising photoprotective pigmentation and that the degree of pigmentation is affected by site‐specific underwater UV exposure, which is ultimately controlled by UV‐attenuating DOC of terrestrial origin. Although cladoceran meiobenthos are able to adapt to varying underwater UV doses, climate change with its multiple consequences on hydrology, limnology and catchment vegetation in the tree line zone may cause major changes in underwater UV environment for the organisms to adapt.

Morphometrics, body condition, and growth of the ringed seal (Pusa hispida saimensis) in Lake Saimaa: Implications for conservation

AbstractMorphometrics and growth of the critically endangered Saimaa ringed seal (Pusa hispida saimensis), which inhabits a freshwater lake in Finland were studied using data from 344 carcasses. This study presents the first detailed information on ringed seal pup growth and body condition from birth to the age of one year. Newborn pups were on average 68 cm long and weighed 5 kg. Pups attained the majority of their first year growth during the nursing period. Body condition and growth declined after weaning, but pups recovered from postweaning nutritional deprivation at the age of 8 mo. The seals achieved their maximum body length, girth, and mandible size around the age of 4 yr, and asymptotic body mass two years later. Baculum growth indicated that males reached sexual maturity at age 5–6 yr. The Saimaa ringed seals' asymptotic body length and mass were 132 cm and 59 kg, respectively, which is similar to medium sized marine ringed seals. Saimaa ringed seals' survival to adulthood is extremely low due to high bycatch mortality; furthermore climate change may hamper pup growth and elevate mortality. Therefore we recommend continuation of fishing closures to improve pup survival.

Assimilation of lake water surface temperature observations using an extended Kalman filter

A new extended Kalman filter (EKF)-based algorithm to assimilate lake water surface temperature (LWST) observations into the lake model/parameterisation scheme Freshwater Lake (FLake) has been developed. The data assimilation algorithm has been implemented into the stand-alone offline version of FLake. The mixed and non-mixed regimes in lakes are treated separately by the EKF algorithm. The timing of the ice period is indicated implicitly: no ice if water surface temperature is measured. Numerical experiments are performed using operational in-situ observations for 27 lakes and merged observations (in-situ plus satellite) for 4 lakes in Finland. Experiments are analysed, potential problems are discussed, and the role of early spring observations is studied. In general, results of experiments are promising: (1) the impact of observations (calculated as the normalised reduction of the LWST root mean square error comparing to the free model run) is more than 90% and (2) in cross-validation (when observations are partly assimilated, partly used for validation) the normalised reduction of the LWST error standard deviation is more than 65%. The new data assimilation algorithm will allow prognostic variables in the lake parameterisation scheme to be initialised in operational numerical weather prediction models and the effects of model errors to be corrected by using LWST observations.

Variable Effects of Iron (Fe (III)) Additions on Potential Methane Production in Boreal Lake Littoral Sediments

We studied potential methane (CH4) production and Fe (III) oxide reduction activity in sediments sampled from 12 vegetated littoral sites at eight lakes in Finland. The effects of added amorphous Fe (III) oxyhydroxide and organic substrate (acetate) on methanogenic and Fe (III) reduction activities were studied in anaerobic laboratory incubations (in vitro). The concentration of total iron in the sediments varied between 0.3 and 7.7 % (DW) and their organic matter content (loss of ignition) varied between 1 and 64 % (DW). The potential methane production at vegetated littoral sites varied greatly and was between 0.4 and 312 μmol CH4 kg−1d−1. Fe (III) addition suppressed methane production by over 50 % if the total iron content in the studied littoral sediment was ≥3 % (DW). Our results show that Fe (III) reduction is an important factor for organic matter decomposition in boreal freshwater littoral sediments. In addition to affecting methanogenesis, iron may also play a role in suppressing other microbial activities in anaerobic soils and sediments.

Diet‐specific biomarkers show that high‐quality phytoplankton fuels herbivorous zooplankton in large boreal lakes

Summary The zooplankton is a key link in the transfer of energy from primary producers up through aquatic food webs. Previous efforts to quantify the importance of basal resources to aquatic consumers have used stable isotopes (SI) and simple ternary models, including only ‘bulk’ phytoplankton, bacteria or terrestrial particulate organic matter (t‐POM). We used a novel Bayesian mixing model based on fatty acids (FA) to quantify the dietary assimilation of seven basal resources, including five phytoplankton groups, pelagic bacteria and t‐POM, to Cladocera in large boreal lakes in Finland. To account for trophic enrichment of FA from the diet to consumers, we parameterised the model with a resource library, from many feeding trials, consisting of Daphnia magna fed 22 diverse basal taxa. The results of the feeding trials show that the distinctive FA profiles of algal groups are transferred to consumers. Moreover, the large number of FA variables (n = 22) used in the model avoids the limitations of underdetermined mixing problems, common to SI modelling, in cases when the number of resources outnumbers the tracer variables. We show that cladocerans were generally supported by phytoplankton (86–94%), with little use of t‐POM (1–9%) and bacteria (1–3%). Cladocerans used primarily high‐quality phytoplankton (cryptophytes, diatoms and dinoflagellates) in both summer (51 ± 22%) and autumn (79 ± 12%), and the relative importance of medium‐quality resources (cyanobacteria, chlorophytes and chrysophytes) declined from 37 ± 23% in the summer to 8 ± 2% in the autumn. High‐quality resources, rich in essential biochemical compounds, are critical in fuelling food webs in large lakes, even those with high concentrations of allochthonous organic matter.

Strong dependence between phytoplankton and water chemistry in a large temperate lake: spatial and temporal perspective

In lakes, spatial and temporal variability of water chemistry and phytoplankton are characteristic phenomena although often difficult to link together. This motivated us to study their interplay in Lake Vanajanselka, a eutrophic lake in Finland. We hypothesized that in summer spatial and temporal differences in phytoplankton and water chemistry can be extended in comparison to spring and autumn. Therefore, chlorophyll a and water chemistry was examined by six sampling campaigns with 15 sampling sites over the lake in May–October 2009–2010. In summer, chlorophyll, pH, and oxygen were horizontally and vertically unevenly distributed in the lake, and in the epilimnion pH and oxygen showed a distinct diurnal variability suggesting high photosynthesis during the day. Daily >1 pH unit difference between the sites and 2.5 pH unit difference between the epi- and hypolimnion were found. In agreement with pH and oxygen, NO3-N and NH4-N could be unevenly distributed in the epilimnion. In autumn no spatial differences were found, however. The results emphasized that algae and cyanobacteria were responsible, at least partly, for the variability in water chemistry in the surface layer, and short- and long-term gradients in space and time need to be considered when productive lakes are studied.

<p class="HeadingRunIn"><strong>A new species of <em>Chrysosphaerella </em>(Chrysophyceae: Chromulinales), <em>Chrysosphaerella rotundata sp. nov.</em>, from Finland</strong></p>

Chrysosphaerella rotundata sp. nov. is described from a small lake in Finland. Ultrastructural morphology of C. rotundata scales is similar, even identical, to the morphology of C. brevispina scales. However, C. rotundata possesses three types of scales: scales characterized by a circular or almost circular outline were found in addition to the larger and smaller oval scales. Significant genetic differences were recognized in ITS rDNA sequences between C. rotundata and C. brevispina. Results of the molecular analyses and the observed morphological variation of scales have been discussed, clearly showing the existence of a hidden diversity within the genus Chrysosphaerella.

A new species of Chrysosphaerella (Chrysophyceae: Chromulinales), Chrysosphaerella rotundata sp. nov., from Finland

Chrysosphaerella rotundata sp. nov. is described from a small lake in Finland. Ultrastructural morphology of C. rotundata scales is similar, even identical, to the morphology of C. brevispina scales. However, C. rotundata possesses three types of scales: scales characterized by a circular or almost circular outline were found in addition to the larger and smaller oval scales. Significant genetic differences were recognized in ITS rDNA sequences between C. rotundata and C. brevispina. Results of the molecular analyses and the observed morphological variation of scales have been discussed, clearly showing the existence of a hidden diversity within the genus Chrysosphaerella.

Willingness to pay for water level regulation in Lake Pielinen, Finland

Water environments provide many benefits for humans. In Finland, thousands of inland lakes serve a very rich and important environment for many activities and a number of ecosystem services. These services can be threatened due to other human activities but also for natural reasons. The natural fluctuation of water level in Lake Pielinen, the largest non-regulated lake in Finland, damages occupational, recreational and housing possibilities. This paper focuses on the examination of the local households’ attitudes, opinions and willingness to pay (WTP) for water level regulation at optimum level for recreational purposes in the summertime. The related economic benefits are analysed by applying the contingent valuation (CV) method. The logistic regression model and a variant of the Tobit model are used in the econometric analyses. The results show that WTP increases with higher income, youth, living near the shore, having a boat, being aware of the regulation plans and having no difficulties with the questions. The aggregate WTP of the local population is approximately EUR 0.24–0.44 million. The attitudinal results reveal a strong local interest in the regulation of Lake Pielinen.

Indirect effects of invasive crayfish on native fish parasites

Interactions between invasive and native species are often modified by parasites. One little‐studied scenario is that invasive species affect parasite transmission to native hosts by altering the relative abundance of hosts needed in parasite life cycles, for example by predation on these hosts. Here we show that presence of an invasive crayfish species, Pacifastacus leniusculus, decreases the mean abundance of native parasites transmitted from snails and aquatic isopods to perch, Perca fluviatilis, in two large boreal lakes in Finland. In contrast, parasites transmitted to the fish from planktonic copepods or mussels, hosts not readily preyed on by crayfish, were not affected by crayfish presence. We suggest that the effect of crayfish on native parasite fauna of fish is mediated via complex effects on invertebrate populations. Hence, our study provides an example of how the indirect ecological effects of species introductions can extend beyond the generally anticipated direct effects, predation and competition.

Zooplankton (Cladocera) in assessments of biologic integrity and reference conditions: application of sedimentary assemblages from shallow boreal lakes

Zooplankton are potentially powerful proxies for the assessments of biologic integrity. The paleolimnological perspective and use of fossil Cladocera also provide the means to reconstruct reference conditions and natural long-term community dynamics. Unfortunately, the use of zooplankton in lake quality assessments is currently underexploited. We studied a surface sediment dataset of 41 lakes in Finland to examine the relationship between Cladocera remains and environmental variables. Of the examined environmental variables, total phosphorus availability was found to be the most important variable in explaining the Cladocera community composition. Following the tests on species environment relations, we selected a lake trophic typology as the most suitable environmental variable for developing a new tool for limnoecological quality assessments. A test of the model on a modern and historic sample from a eutrophied lake showed that the test lake has proceeded from “mesotrophic/poor” to “eutrophic/bad” limnoecological state in agreement with previous independent evidence. The model developed here showed favorable performance that can be used to provide reliable estimates of ecological and environmental state of lakes.

Response of macrophyte communities and status metrics to natural gradients and land use in boreal lakes

We studied the relations of aquatic macrophyte communities, ecological quality metrics and water quality to lake characteristics and to land use defined at multiple spatial scales (three lake marginal zones (LMZs) of contrasting width and the whole topographic catchment) in 110 boreal lakes in Finland using ordination and generalised additive modelling. Variation in macrophyte community composition of our lakes was related to water quality, land use, latitude and lake morphology. Relationships of macrophyte status metrics – the proportion of type-specific species (TT50), Percent Model Affinity (PMA) and Trophic Index (TI) – to land use were scale dependent. The proportion of agricultural and urban land use adjacent to the lake shoreline (LMZs of 300m and 500m) had a more significant effect on the metrics compared to land use at the catchment scale. The scale-related pattern in the effect of land use was not congruent among metrics and the metrics also showed different indications of deterioration. Lower sensitivity to the measured disturbance of the pressure sensitive metric TI compared to the other metrics (TT50 and PMA) based on general type-specific species composition was presumably due to a lack of helophytes in the species pool used, and due to invariable indicator values across lake types. Moreover, TI varied more with hydromorphology related natural gradients than TT50 and PMA. This could be due to lack of habitat for eutrophication sensitive submerged indicator species in shallow lakes. Our study demonstrates that choosing the most influential catchment scale for the evaluation and mitigation of anthropogenic impacts on lacustrine biota, may be significant in conserving and restoring the ecological quality of freshwaters, as required by, e.g., the European Water Framework Directive.

Assessing ecological status of regulated lakes with littoral macrophyte, macroinvertebrate and fish assemblages

Anthropogenic alterations of hydrologic regime are a major stressor for aquatic ecosystems. In boreal lakes water levels are often drawn down several meters for hydropower production in winter, which may have negative impacts particularly on littoral biota. We examined macrophyte, macroinvertebrate, and fish assemblages in littoral zone of 30 regulated and non-regulated reference lakes in Finland. We applied community metrics which correspond to demands of EU Water Framework Directive (WFD) to (i) assess and classify ecological status of the lakes, and to (ii) estimate critical water level drawdown in winter that would allow for acceptable status (“Good” ecological quality class in WFD). All three organism groups indicated strong response to winter drawdown, but with rather high mutual variation. Macroinvertebrates showed the strongest response (r2=0.73 between Ecological Quality Ratio (EQR) and winter drawdown), followed by macrophytes (r2=0.43) and fish (r2=0.40). Mean-EQR over the three organism groups indicated that Good ecological status class was usually not attained if winter drawdown exceeded 3.46m, whereas minimum-EQR (lowest of the three groups, i.e. one-out, all-out principle) indicated a critical threshold of 1.76m. Generally, our results suggest that monitoring and ecological status assessment of regulated lakes should focus on littoral biota which is most vulnerable to water level fluctuations.

Stratification of selected hydrolytic enzyme activities in the sediment in two lakes in Finland

To investigate the stratification of hydrolytic enzyme activities and importance of subsurface layers in depolymerization of detritus biopolymers, nine hydrolytic enzyme activities involved in the cycling of carbon, phosphorus, nitrogen and sulphur were measured in various sediment layers and their extracts at Kyläniemi in Lake Saimaa in southern Finland and in Lake Ahvenjärvi in northern Finland. The results show that for each lake all nine hydrolytic enzyme activities were higher in all sediment layers than in comparable sediment extracts indicating that the major part of enzymes was bound to the sediment particles in all layers in both lakes. Carbohydratase, β-cellobiosidase, activities did not show any gradient with sediment depth at Kyläniemi in Lake Saimaa indicating that there was rapid turnover of carbohydrates in the entire sediment column. The activities of acetate esterase, butyrate esterase, phosphomonoesterase, aminopeptidase, N-acetyl glucosaminidase, sulphatase and β-glucosidase in the deepest layers were 19–53% of those in the surface sediment indicating that depolymerization of biopolymers involved in the cycling of carbon, nitrogen, phosphorus and sulphur was substantial in subsurface sediment.

Fish–duck interactions in boreal lakes in Finland as reflected by abundance correlations

We studied the hypothesis that fish play an important role in lake use by ducks (pairs and broods) in boreal lakes. The study was based on densities of different duck and fish species in 28 boreal lakes in southern Finland. We focused on the three most common duck species (mallard Anas platyrhynchos, green-winged teal A. crecca and common goldeneye Bucephala clangula) and on the three most common fish species (perch Perca fluviatilis, roach Rutilus rutilus and pike Esox lucius) in the region. We considered both competitive and predatory interactions between ducks and fish, the perch and roach being potential competitors with ducks and the pike a potential predator of ducks. We found a negative association between green-winged teal brood density and total fish density, the other duck species having only a weak association with total fish density. When the three fish species were considered separately, a negative association, suggesting food competition, was found between perch, green-winged teal and goldeneye, whereas the role of roach as a food competitor seemed to be of minor importance. We did not find any clear signs of predatory effects of pike on ducks. Our results suggest that food competition is a more important factor than pike predation in affecting lake use by ducks in oligotrophic boreal environments in southern Finland.

Is catchment productivity a useful predictor of taxa richness in lake plankton communities?

The influence of catchment variables on lake organisms is understudied. The terrestrial zone in the vicinity of lakes is, however, probably highly important for biota due to the effects on water chemistry and to various processes operating across ecosystem boundaries. We examined the relative importance of lake and catchment variables, as well as large-scale geographical factors, on the taxa richness of phyto- and zooplankton in 100 small lakes in Finland. In variation partitioning, the variability of phytoplankton richness was most strongly related to the effects of lake variables, the joint effects of lake and catchment variables, and the joint effects of all three groups of variables. Zooplankton richness, in turn, was most strongly related to the effects of lake and catchment variables and the joint effect of lake and catchment variables. The exact results of the variation partitioning depended on the catchment sizes considered in the regression models. Among lake variables, planktonic richness was strongly related to variables indicating productivity. Among catchment variables, the normalized difference vegetation index (NDVI), indicating catchment productivity, showed a relatively strong association with planktonic richness. These results provide evidence that catchment variables such as the NDVI may be efficient predictors of planktonic richness in small lakes. It is possible that individual lakes embedded in a highly productive landscape have higher taxa richness than solitary, potentially productive lakes because of the high influx of dispersing propagules from the regional pool. We also suggest that catchment variables may respond to environmental changes at different scales than the lake variables, and explicit consideration of catchment productivity would therefore be useful when planning research and monitoring programs for freshwater organisms.

Subfossil chydorid (Cladocera, Chydoridae) ephippia as paleoenvironmental proxies: evidence from boreal and subarctic lakes in Finland

Chydorids (Cladocera, Chydoridae) have two reproductive strategies: asexual reproduction that prevails during favorable environmental conditions and sexual reproduction that is induced by environmental stimuli associated with seasonal or aperiodic environmental stresses. These modes of reproduction can be recognized in the subfossil sedimentary records as parthenogenetic shells of females (asexual reproduction) and by ephippia (sexual reproduction). We studied the interrelations between subfossil chydorid ephippia and environmental variables by analyzing surface sediment samples obtained from 76 Finnish lakes across a latitudinal gradient (60–70°N). The results showed that the total chydorid ephippia (TCE) increases along the climate gradient from ~2 to 3% in the south to ~25% in the north and suggested a significant dependence (r ~ −0.8, P < 0.001) with several climate factors, especially that of mean July air temperature. We used this relationship to create a model for reconstructing past mean July air temperatures. A linear regression of the log10 transformed TCE as a single independent variable explained 76% (SE ± 0.76°C) of the variance of the observed mean July air temperatures. Accordingly, we propose that this novel tool may be highly suitable for reconstructing paleotemperatures in cold-temperate environments.