Lake Hiidenvesi Research Articles

Stratification controls the magnitude of in-lake phosphorus cycling: insights from a morphologically complex eutrophic lake

Using a combination of sediment trap experiments, sedimentary biogeochemical analyses and mass balance calculations, we conducted a comprehensive quantitative evaluation of the in-lake phosphorus (P) cycles including in both the water and sediment phases for Lake Hiidenvesi, a dimictic eutrophic lake in southern Finland. We explicitly demonstrated the heterogeneity of the in-lake P cycles between basins with distinct morphological features. Enhanced interactions between waters and sediments occur in shallow and non-stratified areas, as evidenced by the magnitudes of gross sedimentation and total internal P loading. In such shallow areas, sediment resuspension contributes over 60% of the total internal P loading throughout the entire open water season. In contrast, sedimentary P cycling is less intensive in deep and stratified areas, where diffusive fluxes account for an average of 70% of total internal P loading. We show that sedimentary P burial plays a key role in controlling the in-lake P cycle. Permanent burial of P showing higher rates and efficiencies tends to occur in deeper areas. Overall, sediments in Lake Hiidenvesi act as a net P sink under modern biogeochemical settings; the lake is in the process of long-term recovery from eutrophication due to the larger annual P output than external loading.

Elevated internal phosphorus loading from shallow areas of eutrophic boreal lakes: Insights from porewater geochemistry

Internal phosphorus (P) loading is widely recognized as a major cause of lake eutrophication. One conventional paradigm states that the magnitude of internal loading through P diffusion is constrained by the presence of iron (Fe) oxides in surface sediments under oxic conditions near the sediment-water interface (SWI). However, biogeochemical P dynamics in Fe-rich sedimentary systems are still not fully understood, especially in eutrophic lakes where intensively coupled organic matter (OM) remineralization and reductive dissolution of Fe-bound P (Fe-P) exist concurrently. Here, we assess the diagenetic processes that govern sedimentary P cycling in two eutrophic Fe-rich lakes in southern Finland, Lake Hiidenvesi and Lake Kytäjärvi, using a combination of porewater and solid-phase analyses. Coupled reductive dissolution of Fe-P and OM remineralization controlled P regeneration in both lakes, with Fe-P acting as the dominant source for porewater P. Vivianite formation likely immobilized sedimentary P in the deepest basin of Hiidenvesi. Elevated P diffusion rates were observed at shallow sites under oxic bottom water conditions in summer in both lakes, stimulated by enhanced remineralization of both freshly- (mostly phytoplankton-origin) and earlier-deposited OM under elevated temperatures. Areas overlain by oxic bottom water contributed more benthic P fluxes to the water column compared to anoxic/hypoxic areas in both lakes during all sampling seasons. Our study suggests that in shallow eutrophic settings with high OM deposition and elevated temperatures, remineralization in upper sediments regenerates P efficiently enough to support a significant amount of P release to the water column even under sedimentary molar Fe/P ratios >20. We also discuss the implication of our findings for lake restoration strategies.

Correction to: Tracking the Limnoecological History of Lake Hiidenvesi (Southern Finland) Using the Paleolimnological Approach

Erroneous information considering Chironomidae and Chaoboridae accumulation was given in Figure 4 published in Luoto et al. (2017).

VARIABILITY OF REMOTE SENSING SPECTRAL INDICES IN BOREAL LAKE BASINS

Abstract. Remotely sensed hyperspectral data has widely been used to determine water quality parameters in oceanic waters. However in freshwater basins the dependence between the hyperspectral data and the parameters is more complicated. In this work some ideas are presented concerning the study of this dependence. The data used in this study were collected from the lake Hiidenvesi in southern Finland. The hyperspectral data consists of reflectances in 36 bands in the wavelength area 508…878 nm and the separately measured water quality parameters are turbidity, blue-green algae, chlorophyll, pH and dissolved oxygen. Hyperspectral data was used as bare band reflectances, but also in the form of two simple spectral indices: ratio A / B and difference A − B, where A and B go through all the bands. The correlations of the indices with the parameters were presented visually as 1- or 2-dimensional arrays. To examine the significance on the results of different variables, the data was classified in two different ways: the natural basins and the values of the water quality parameters. It was noticed that the variability of the correlation arrays was particularly strong among different basins in both the magnitude of correlation and the best performing indices. Further studies are needed to clarify which features of the basins are of most importance in predicting the shapes of the correlation arrays.

Tracking the Limnoecological History of Lake Hiidenvesi (Southern Finland) Using the Paleolimnological Approach

We examined a sediment record from Lake Hiidenvesi in southern Finland using paleolimnological methods to trace its limnoecological history. In our record, beginning from the 1940s, chironomid (Diptera) assemblages shifted from typical boreal taxa towards mesotrophic community assemblages at ~ 1960–1980 CE being finally replaced by eutrophic taxa from the 1990s onward. The diatom (Bacillariophyceae) assemblages reflected relatively nutrient rich conditions throughout the record showing a further increase in eutrophic taxa from the 1970s onward. A chironomid-based reconstruction of late-winter hypolimnetic dissolved oxygen (DO) conditions suggested anoxic conditions already in the 1950s, probably reflecting increased inlake production due to allochthonous nutrient inputs and related increase in biological oxygen consumption. However, the reconstruction also indicated large variability in long-term oxygen conditions that appear typical for the basin. With regard to nutrient status, chironomid- and diatom-based reconstructions of total phosphorus (TP) showed a similar trend throughout the record, although, chironomids indicated a more straightforward eutrophication process in the benthic habitat and seemed to reflect the intensified human activities in the catchment more strongly than diatoms. The DO and TP reconstructions were mostly similar in trends compared to the measured data available since the 1970s/1980s. However, the increase in TP during the most recent years in both reconstructions was not visible in the monitored data. The results of our multiproxy study emphasize the significance of including both epilimnetic and hypolimnetic systems in water quality assessments and provide important long-term limnoecological information that will be useful in the future when setting targets for restoration.

Water pH and sediment resuspension regulating internal phosphorus loading in a shallow lake – field experiment on diurnal variation

Resuspension-mediated aerobic release of P can be crucial to the phosphorus cycling of a shallow lake. The effect of resuspension on the aerobic release of phosphorus was studied in the field with experimental water columns. The study included four experiments that were conducted in May and August during the day and following night in the shallow Kirkkojarvi basin of Lake Hiidenvesi. In all the experiments, the concentrations of suspended solids (SS) and total phosphorus (TP) increased substantially, due to the 10-min resuspension treatment. However, the concentration of soluble reactive phosphorus (SRP) was strongly affected only at night in August, when high pH levels promoted SRP release by ligand-exchange reactions. During the day experiment in August, no SRP release was detected, due to high assimilation by phytoplankton. The results pointed out that coupling of resuspension and high algal blooms induced pH in the water column can liberate significant amounts of soluble P into the water column. The importance of this phenomenon for the lake studied was emphasized by the fact that the P pools susceptible to pHdependent P release (Al-P and Fe-P) formed a large part of the total extractable P of the surface sediment. Additionally, the conditions of high pH are common from early July to late September and the water pH can stay at a high level also at night during strong phytoplankton blooms.

Food niche segregation between two herbivorous cyprinid species in a turbid lake

The diet and growth of two cyprinids, roach Rutilus rutilus and rudd Scardinius erythrophthalmus, in the clay-turbid Kirkkojärvi basin in Lake Hiidenvesi (Finland) were studied. Young R. rutilus fed mainly on detritus, molluscs, chironomids and zooplankton, while older individuals consumed mostly detritus, molluscs and filamentous algae. In the food of S. erythrophthalmus, detritus was less prevalent and animal food and plants contributed to most of the diets. The animal food of S. erythrophthalmus consisted mostly of surface insects. Of the plant food, the macrophytes Potamogeton obtusifolius and Ranunculus circinatus had the highest representation, while the proportion of filamentous algae was low. The growth rate of S. erythrophthalmus was significantly higher than that of R. rutilus. The results suggested that the species composition of vascular macrophytes was not favourable for R. rutilus. Small submerged species suitable for R. rutilus were absent and they fed on filamentous algae and detritus, which resulted in a slow growth rate. The results suggested that in a clay-turbid lake the food spectrum is more suitable for S. erythrophthalmus than for R. rutilus. In such conditions, R. rutilus may have no benefit from its generalistic feeding abilities.

Spatial variability in the abundance of pelagic invertebrate predators in relation to depth and turbidity

The abundance of pelagic invertebrate predators in relation to turbidity and depth gradients in Lake Hiidenvesi (southern Finland) were studied. In the shallow ( 500 μg dw l−1) and Leptodora kindtiii (Focke) (17 μg dw l−1), while in the less turbid (10–40 NTU) stratifying area Chaoborus flavicans (Meigen) dominated (max 146 μg dw l−1). In the temporarily stratifying and moderately turbid basin Chaoborus and small-bodied invertebrate predators co-existed. Mysis relicta (Loven) occurred only in the stratifying area (max 15 μg dw l−1). The results suggested that both water depth and turbidity contributed to the community structure of Chaoborus flavicans. Depth great enough for stratification was of special importance and its effect was amplified by elevated turbidity, while high turbidity alone could not maintain chaoborid populations. Mysis relicta also requires a hypolimnetic refuge but is more sensitive to low oxygen concentrations and may therefore be forced to the epilimnion where it is vulnerable to fish predation. Cyclopoids as rapid swimmers can take advantage at elevated turbidity levels and coexist in high biomass with fish even in shallow water. Leptodora kindtii can form high biomass despite planktivorous fish providing that turbidity exceeds 20 NTU. The results demonstrated that depth and water turbidity can strongly regulate the abundance and species composition of invertebrate predators. These factors must thus be taken into account when applying food web management, which aims to reduce phytoplankton biomass by depressing planktivorous fish.

Hydroacoustic in situ target strength of smelt ( Osmerus eperlanus (L.))

Dependence of the in situ acoustic target strength (TS) of smelt ( Osmerus eperlanus (L.)) on the total fish length ( L) was estimated from TS measurements made with a split-beam 120 kHz echo sounder with reference to fish length–frequency distributions in trawl catches. The studies were conducted in the eutrophic and turbid Lake Hiidenvesi in southern Finland. Smelt dominated the catches-in-number with proportions at different sampling stations ranging from 91.8 to 100%. A TS–length equation of the form TS = alog L − b was fitted through the modes in the TS-distributions and in the respective fish length distributions. The estimated model (±parameter standard error) was TS = 23.4 (±2.24)log 10 L − 68.7 (±1.82). With a pre-defined slope of 20, the fitted equation was TS = 20 log 10 L − 65.9 (±0.23). The estimated day–night difference in TS–length relationship was not significant ( t-test, p = 0.37).

Phytoplankton community assembly in a large boreal lake – deterministic pathways or chaotic fluctuations?

Summary1. The concepts of community assembly and succession are closely related, yet their foci differ slightly. Succession describes the trajectory of species replacements during the temporal development of the community, while assembly also allows that a locality can harbour different communities depending on the events in the near past of community development.2. The aims of this study were (i) to examine the year‐to‐year variation in phytoplankton community assembly among basins of different trophy and disturbance in the large boreal Lake Hiidenvesi and (ii) to assess community persistence and diversity among basins in relation to prevailing environmental factors.3. The results showed that the assembly did not follow similar trajectories each year. According to mean similarity analyses, there was a large degree of variability especially among the groups of samples collected in the same months of different years. Similarity between pairs of consecutive samples was highest in a cold year (1998) in all basins. Community assembly was most unpredictable in the basin of highest productivity, perhaps implying that the number of alternative stable states increased towards higher productivity. Our data also showed a strong unimodal relationship between phytoplankton species richness and grazing by cladoceran zooplankton in the basin of highest trophy.4. This study showed that phytoplankton community assembly exhibited large variability among the years. This implies that different environmental conditions might be the strongest mechanism behind this pattern, given that the degree of community similarity paralleled the year‐to‐year variation in mean temperature. Unravelling the patterns in community assembly has a number of important implications, especially for the monitoring of ecological impacts based only on snapshots of biological assemblages.

Clay‐Turbid Interactions May Not Cascade—A Reminder for Lake Managers

Abstract Food web management is a frequently used lake restoration method, which aims to reduce phytoplankton biomass by strengthening herbivorous zooplankton through reduction of planktivorous fish. However, in clay‐turbid lakes several factors may reduce the effectivity of food web management. Increasing turbidity reduces the effectivity of fish predation and weakens the link between zooplankton and phytoplankton. Therefore, the effects of fish stock manipulations may not cascade to lower trophic levels as expected. Additionally, in clay‐turbid conditions invertebrate predators may coexist in high densities with planktivorous fish and negate the effects of fish reductions. For instance, in the stratifying regions of the clay‐turbid Lake Hiidenvesi, Chaoborus flavicans is the main regulator of cladocerans and occupies the water column throughout the day, although planktivorous Osmerus eperlanus is very abundant. The coexistence of chaoborids and fish is facilitated by a metalimnetic turbidity peak, which prevents efficient predation by fish. In the shallow parts of the lake, chaoborids are absent despite high water turbidity. We suggest that, generally, the importance of invertebrate predators in relation to vertebrate predators may change along turbidity and depth gradients. The importance of fish predation is highest in shallow waters with low turbidity. When water depth increases, the importance of fish in the top‐down regulation of zooplankton declines, whereas that of chaoborids increases, the change along the depth gradient being moderate in clear‐water lakes and steep in highly turbid lakes. Thus, especially deep clay‐turbid lakes may be problematic for implementing food web management as a restoration tool.

Diel Variations in the Vertical Distribution of Crustacean Zooplankton and Food Selection by Planktivorous Fish in a Shallow Turbid Lake

AbstractThe variations in the vertical migrations by zooplankton and food composition of fish in the shallow, clay‐turbid Mustionselkä basin of Lake Hiidenvesi were studied (water depth 3 m). Daphnids showed signs of reverse migration, their density in the surface layer being highest during the day. The reverse migration was probably due to predation threat by the predatory cladoceran Leptodora kindtii. Chydorus sphaericus, which was consumed especially by the day active bleak (Alburnus alburnus), showed normal vertical migration. Copepods showed no clear vertical movements. Leptodora kindtii, as well as the large herbivore Limnosida frontosa, showed no vertical migrations, but their overall abundance increased considerably during the night, indicating horizontal movement towards the open water at night. Due to the shallowness of the water, vertical migrations may not be a good predator‐avoidance strategy for the largest cladocerans, which may be able to perform horizontal migrations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Seasonal bottlenecks in diet shifts and growth of smelt in a large eutrophic lake

Seasonal growth of smelt Osmerus eperlanus was studied in the Kiihkelyksenselkä basin in the eutrophic Lake Hiidenvesi, southern Finland. The growth of age 1+ and 2+ year smelts was very low probably due to the discontinuous supply of large invertebrates Chaoborus flavicans and Mysis relicta. Diet shift back to zooplankton in autumn, suggested the existence of a bottleneck in the growth of these age groups. Slow growth rate was further intensified by the onset of maturity at age 2 years, combined with the high diet and habitat overlaps between similar‐sized 1+ and 2+ year smelts. Older 3+ and 4+ year smelts shifted to piscivory, i.e. cannibalism, during the growing season, which was seen as rapid increases in their growth rates.

The supremacy of invertebrate predators over fish - factors behind the unconventional seasonal dynamics of cladocerans in Lake Hiidenvesi

In the eutrophic Lake Hiidenvesi (30.3 km 2 ), the early summer biomass maximum of cladoceran zooplankton is missing and the highest biomass is found unusually in mid summer. The contribution of the phantom midge Chaoborus flavicans to the unconventional seasonal dynamics of cladocerans was studied. The seasonal development of the C. flavicans population and the zooplankton community was studied together with food consumption by chaoborids and the most common vertebrate predator, smelt. The population density of Chaoborus peaked in June and collapsed in mid summer. Thereafter, another peak occurred at the end of August. The maximum density of chaoborids in the water column varied between 5,500 and 8.700 inc./m 2 . In early summer, the most common food items of Chaoborus were bosminids while later in summer the share of daphnids increased. Food consumption by the Chaoborus population peaked at 26-46 μg Cl -1 d -1 in June and clearly exceeded the production rate of cladocerans. Cladoceran consumption by smelt population reached its maximum, 1.13 μg Cl -1 d -1 , in early July. Cladocerans showed a 20-40 μg C/l biomass peak in July-August, coincidently with the minimum density of chaoborids. When predation pressure decreased, the mean size of cladocerans increased at 10-15 m, the depth occupied by chaoborids during daytime. The results suggest that in early summer the high predation pressure prevents cladocerans from reaching a sufficient body length to defend them against Chaoborus and that the timing of the cladoceran biomass peak is determined by the relaxation of chaoborid predation.

Effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in Lake Hiidenvesi (southern Finland)

The effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in the shallow Kirkkojärvi basin of Lake Hiidenvesi were studied by sedimentation traps and sediment and water samples. During the 83 d study period, 793 g DW m −2 of sediment was resuspended within the stand formed by Ranunculus circinatus, Ceratophyllum demersum and Potamogeton obtusifolius. Outside the stand, 1701 g DW m −2 sediment resuspension was measured during the same period. Water turbidity and concentration of suspended solids (SS) were significantly lower within the plant bed compared with the surrounding water area. Despite the higher concentration of inorganic suspendoids, the concentration of chlorophyll a was higher in the open water than within the submerged plant bed, owing to the enhanced nutrient recycling rate in the absence of submerged plants. With the resuspended sediment, 11.8 mg P m −2 d −1 was brought into the water column within the stand and 24.5 mg P m −2 d −1 outside the stand. Within the macrophyte stand, resuspended particles absorbed phosphorus from the water (indicated by the inverse relationship between SS and soluble reactive phosphorus), which was probably connected to the lowered phosphorus concentration of surface sediment due to uptake by macrophytes.

Photoreceptors and cone patterns in the retina of the smelt Osmerus eperlanus (L.) (Osmeridae: Teleostei)

AbstractThe outer retina of the smelt Osmerus eperlanus, a visually orientated plankton feeder, of Lake Hiidenvesi (Finland), was examined using both light and transmission electron microscopy. Apart from rods, six morphologically different cone photoreceptor types were identified: short single cones, long single cones, unequal/equal double cones and triple cones (triangular and linear variety). Additionally, in the dorsal region, multiple cone arrangements consisting of up to five members occur. Long single cones and triple cones were observed only sporadically throughout the retina. The incidence of short single cones as a regular element of the cone mosaic is restricted to the ventrotemporal area. The dominant pattern in the Osmerus retina is a pure or a twisted row pattern occurring in all regions. Ventrotemporally, however, square patterns were found as well. The highest cone densities occur in the peripheral ventrotemporal retina. These results indicate that the ventrotemporal region plays an important role in the vision of the smelt. The findings are discussed with respect to the photic habitat conditions and behavioural ecology of the smelt in Lake Hiidenvesi.

Mysis relicta in a eutrophic lake: Consequences of obligatory habitat shifts

Low numbers of mysids in eutrophic lakes have usually been related to their poor tolerance to low oxygen. In eutrophic Lake Hiidenvesi, we studied the possibility that water quality indirectly affects mysids by forcing them to habitats where they are vulnerable to fish predation. Mysis relicta was absent from basins that did not stratify (water depth< 10 m). In the deep basin, as the summer progressed, M. relicta was concentrated in the deepest areas and moved upward in the water column as water temperature increased and dissolved oxygen decreased. Between mid‐August and mid‐September, only a thin water layer was habitable; the rest had either intolerably low oxygen concentration or too high of a temperature. M. relicta abundance decreased from 2.72 X 108 individuals on 3 June to 3.72 × 106 individuals on 19 October, with the sharpest decrease taking place in August. At the same time, the vertical distribution of smelts shifted downward and the percentage of mysids in the stomach contents of smelts increased steeply. The consumption rate by smelts was high enough to explain the collapse of the M. relicta population; during 18 August–2 September, smelts consumed 5.6 times the mysid production. The results suggested that unfavorable physicochemical conditions did not directly cause the drastic reduction of the population abundance of M. relicta but indirectly facilitated predation by smelts, which was the final cause of the collapse. The high predation rate by smelts was probably accelerated by the emergence of chaoborid larvae, which were important food items for smelts in early summer.

Feasibility of airborne imaging spectrometry for lake monitoring—a case study of spatial chlorophyll a distribution in two meso-eutrophic lakes

The spatial distribution of the sum of chlorophyll a and phaeophytin a concentrations (chl-a) under light wind (0–2 m s−1) conditions was studied in two lakes with an AISA airborne imaging spectrometer. Chl-a was interpreted from AISA radiance data using an algorithm based on the near-infrared (700–710 nm) to red (660–665 nm) ratio. The results of Lake Lohjanjärvi demonstrate that the use of one monitoring station can result in over- or underestimation by 29–34% of the overall chl-a compared with an AISA-based estimation. In Lake Hiidenvesi, the AISA-based estimation for the mean chl-a with 95% confidence limits was 25.19±2.18 µg l−1. The use of AISA data together with chl-a measured at 15 in situ sampling stations decreased the relative standard error of the mean chl-a estimation from 20.2% to 4.0% compared with the use of 15 discrete samples only. The relative standard error of the mean chl-a using concentrations at the three routine monitoring stations was 15.9 µg l−1 (63.1%). The minimum and maximum chl-a in Lake Hiidenvesi were 2 and 101 µg l−1, 6 and 70 µg l−1 and 11 and 66 µmg l−1, estimated using AISA data, data from 15 in situ stations and data from three routine in situ stations, respectively.

Leptodora kindti and Flexible Foraging Behaviour of Fish – Factors behind the Delayed Biomass Peak of Cladocerans in Lake Hiidenvesi

AbstractIn the eutrophic L. Hiidenvesi, the spring biomass maximum of cladoceran zooplankton is missing and the highest biomass takes place in July–August. The factors behind the delayed biomass peak were studied in four different basins of the lake with concomitant data on cladocerans assemblages, density of the predatory cladoceran Leptodora kindti and food composition of fish. In all the basins, the abundance of Leptodora peaked in June, being highest (up to 800 ind. m–3) in the two most shallow basins (max depth < 4 m). The duration of the high population density was short and in July‐August Leptodora density stayed below 200 ind. m–3, although the water temperature was still favourable. The collapse of the Leptodora population coincided with the change in the feeding habits of fish. In early summer, fish predation was targeted mainly on copepods and zoobenthos, while in high summer Leptodora was one of the main preys of perch, white bream and bleak. The biomass of herbivorous cladocerans was below 10 μg C l–1 in June, and climbed to a maximum in August in the two most shallow basins (34 and 76 μg C l–1), in July in the deepest basin (27 μg C l–1), and in September in the intermediate basin (55 μg C l–1). In the two most shallow basins, the death rate of the dominating cladoceran, Daphnia cristata, closely followed the food consumption rate by the Leptodora population. In the deeper basins, the agreement was not so close, smelts (Osmerus eperlanus) and chaoborids being important predators of herbivores. The duration of the period of high Leptodora density thus depended on the predation pressure by fish, while the increased fish predation on Leptodora in July–August allowed the elevation of the biomass of herbivorous cladocerans.

Implications of rudd (Scardinius erythrophthalmus) herbivory on submerged macrophytes in a shallow eutrophic lake

The role of rudd (Scardinius erythrophthalmus) herbivory was studied in Kirkkojarvi, a shallow and turbid basin in Lake Hiidenvesi, Finland. The submerged species dominating in the rudd diets were Potamogeton obtusifolius, Ranunculus circinatus, Sparganium emersum, bryophytes, and filamentous algae. Plant consumption estimated with bioenergetics modelling increased with fish age, being highest in late summer concomitant with the macrophyte biomass peak. Depending on the age structure, a rudd biomass of 20 kg ha−1 consumes 18–23 kg of macrophytes ha−1 a−1, while a rudd biomass of 100 kg ha−1 results in plant consumption of 92–115 kg ha−1 a−1. Although, rudd seemed to feed rather unselectively on suitable-sized and edible plants, some species abundant in the littoral, such as Myriophyllum verticillatum and pleustophytic Ceratophyllum demersum, were not found in rudd guts, indicating selective plant consumption. In Kirkkojarvi, selective grazing by rudd and increased turbidity and high nutrient levels partly caused by bottom dwelling cyprinid fish, may promote the inedible and pleustophytic macrophytes, which have increased in Kirkkojarvi during the past decades.