Large Boreal Lake Research Articles

Invasive crayfish increase habitat connectivity: a case study in a large boreal lake

Several studies have shown that distinct compartments of lake ecosystems are coupled via transportation of organic matter, nutrients and energy across habitat boundaries. Here we evaluate the potential of the invasive signal crayfish (Pacifastacus leniusculus (Dana)) to modify energy pathways in large boreal lakes. Using a stable isotope mixing model and calculation of the isotopic niches we estimated the contribution of different food sources to the diets of crayfish captured from different habitats, and from that inferred their potential to transport energy across the littoral-profundal gradient. The crayfish caught from the littoral area utilized mainly littoral food sources, whereas the importance of profundal sources increased consistently with depth. We also found crayfish in deeper habitats with littoral δ13 C label, which indicates significant use of littoral sources. These results presents evidence that invasive signal crayfish create a new link in energy transfer from littoral areas to profundal areas and thereby increase connectivity between these spatially distinct habitats. Our results highlight a need for better understanding of the role of crayfish in lake energy dynamics and habitat connectivity.

Do introduced crayfish affect benthic fish in stony littoral habitats of large boreal lakes?

Invasive crayfish are spreading rapidly across Europe, where they are replacing the native crayfish species and impacting negatively on some other biota. Freshwater crayfish and many benthic fishes share similar habitat and food requirements and hence potentially compete for resources. In this study, we investigated impacts of the introduced signal crayfish (Pacifastacus leniusculus) on fish in stony littoral habitats of two large boreal lakes. We compared the littoral fish community composition and the densities of two common benthic fish species between sites with and without crayfish. To evaluate whether signal crayfish share the same food resources as benthic littoral fish or change their feeding habits, we used mixing models and trophic niche estimates based on analyses of stable isotopes of carbon and nitrogen. Both the community composition of littoral fish and the densities of benthic fish species were similar at sites with and without signal crayfish. Even though stable isotope signatures indicated strong dietary overlap between crayfish and benthic fish, the use of food sources and trophic niche widths of fish were not noticeably different between crayfish sites and non-crayfish sites. Our results suggest that, at current densities, the non-native signal crayfish does not have significant impacts on benthic fish in the stony littoral habitats of large boreal lakes.

Lack of Angling-Sized Yellow Perch in a Canadian Boreal Lake: Potential Influences of Growth Rate, Diet, and Predation by Double-Crested Cormorants

Fisheries for yellow perch Perca flavescens are economically important in North America, but in many lakes this species does not attain sizes desirable to anglers (total length [TL] > 250 mm). We investigated factors potentially contributing to the lack of angling-sized yellow perch in Dore Lake, Saskatchewan. This large boreal lake has a long history of exploitation and is subject to current controversy regarding the impact of double-crested cormorants Phalacrocorax auritus on its fisheries. We found that yellow perch in Dore Lake attained greater maximum ages (mean ± SD = 7.4 ± 1.0 years) but smaller maximum sizes (215 ± 7 mm TL) than other yellow perch populations. Thus, the lack of angling-sized yellow perch in Dore Lake is probably the result of slow growth rates rather than short life spans. Double-crested cormorants preyed heavily on yellow perch, but predation was highly skewed toward much smaller sizes (<100 mm TL) than those preferred by anglers. Stomach contents and stable nitrogen isotopes confirmed that yellow perch in Dore Lake undergo expected ontogenetic diet shifts and become predominantly piscivorous at around age 3. Analysis with stable isotopes also revealed long-term dietary differences between age-2 and age-3 yellow perch captured in littoral versus offshore habitats, suggesting some degree of intrapopulation variability in resource and habitat use among yellow perch in Dore Lake.

Long-term changes in the water quality and fish community of a large boreal lake affected by rising water temperatures and nutrient-rich sewage discharges – with special emphasis on the European perch

In this study, we report the changes in the water quality and fish community of a large boreal lake (Lake Pyhaselka, Finland) in 1975–2005, when the lake was affected first by industrial and municipal sewage discharge and then by rising water temperatures. In the 1980s, the lake’s trophic state proceeded from oligotrophic to mesotrophic, which favoured cyprinids. The increased cyprinid density strengthened the competition pressure on perch (Perca fluviatilis ) reducing the growth rates of young perch. The lake’s trophic state shifted from mesotrophic back to oligotrophic in the 1990s as a result of effective treatment of sewage waters. The water temperature in Lake Pyhaselka rose from the beginning to the end of the monitoring period. The higher temperature favoured perch. In future, the warming may benefit pikeperch (Sander lucioperca ) even more than perch. This will probably affect the perch population, as pikeperch prey effectively on perch.

Habitat level determinants of emergent macrophyte occurrence, extension and change in two large boreal lakes in Finland

Historical (1947–1950) and present day (1998–2000) aerial photograph data of aquatic vegetation were combined with soil, land use and habitat morphology variables in two lakes, oligotrophic L. Näsijärvi (256 km 2) and eutrophic L. Pyhäjärvi (122 km 2), with regulated water levels in southern Finland. Multivariate GLM analyses were used to examine the determining factors of occurrence and horizontal extension of vegetation, occurrence of common reed ( Phragmites australis) and water horsetail ( Equisetum fluviatile) and the vegetation change in 474 sites. Despite differences in geography and water level regulation between the lakes, congruent trends were identified. The vegetation occurrence in both lakes had a positive response to clay soils and incoming nutrients and a negative response to housing and shore slope. Moraine soils, housing and shore slope had a negative effect on horizontal extension of vegetation in both lakes. The occurrence of P. australis was controlled by a negative response to moraine and the occurrence of E. fluviatile to slope in both lakes. The vegetation change in both lakes was characterized by a negative response to housing and slope.

The cultural eutrophication of Lac la Biche, Alberta, Canada: a paleoecological study

A multiproxy paleoecological investigation of Lac la Biche, a large boreal lake in northeastern Alberta, Canada, revealed that the lake was eutrophic before European settlement but has undergone additional cultural eutrophication in the past 30 to 50 years. Annual fluxes to sediments of phosphorus, nitrogen, carbon, and inorganic sediments have increased with time. A declining N–P ratio has increasingly favored nitrogen-fixing cyanobacteria. Increased deposition of microbial pigments and diatom frustules and a recent shift in diatom species also indicate increasing eutrophication. Biogenic silica increased with time, but there is no evidence of a near-surface decline that would indicate silica limitation. Stable isotopes suggest that an increasing proportion of carbon deposited in sediments is of in-lake origin, indicating increased productivity. In the basin nearest the town of Lac La Biche, an increase in δ15N followed the construction of the sewage treatment plant, but more recently, decreased δ15N in both basins suggests that nitrogen fixation has become a more important source of nitrogen. Despite documented damage to the fishery of the lake, zooplankton fossils do not show evidence of a strong trophic cascade. The study illustrates the power of a multiproxy approach in obtaining reliable paleolimnological conclusions.

Autumnal shift from diurnal to nocturnal peaking feeding activity of Rutilus rutilus in boreal lake littoral zones

The possibility that the feeding activity of roach Rutilus rutilus shows an autumnal shift towards hours of lower light intensity in shallow and illuminated habitats in temperate watercourses as a consequence of relatively increasing daytime predation risk was tested in a littoral zone of a large boreal lake using trapping experiments. Autumnal feeding activity of R. rutilus first showed a striking shift from day to twilight when water temperature fell from 20 to 10° C, and a low but steady night activity prevailed in late autumn, when temperature had fallen to 5° C and the length of the night had increased. The size of the captured littoral R. rutilus also increased throughout the autumn. Both shifts may be linked to increasing daytime predation risk and decreasing food demand and availability.

Growth responses of riparian Thuja occidentalis to the damming of a large boreal lake

Growth responses of riparian eastern white cedar trees ( Thuja occidentalis L.) to the double damming of a large lake in the southeastern Canadian boreal forest was analyzed to determine whether the shoreline tree limit is the result of physiological flood stress or mechanical disturbances. The first damming, in 1915, caused a rise in water level of ca. 1.2 m and resulted in the death of the trees that formed the ancient shoreline forest, as well as the wounding and tilting of the surviving trees (by wave action and ice push) that constitute the present forest margin. The second damming, in 1922, did not further affect the water level, but did retard the occurrence of spring high water levels, as well as reduce their magnitude. However, this did not injure or affect the mortality of riparian eastern white cedars. Radial growth was not affected by flooding stress, probably because inundation occurred prior to the start of the growing season (1915–1921) or was of too short duration to adversely affect tree metabolism (after 1921). It follows that (i) the shoreline limit of eastern white cedar is a mechanical rather than a physiological limit, and (ii) disturbance-related growth responses (e.g., ice scars, partial cambium dieback, and compression wood) are better parameters than ring width for the reconstruction of long-term water level increases of natural, unregulated lakes.

Diet of brown trout in relation to variation in abundance and size of pelagic fish prey

The seasonal diet of a predator, brown trout Salmo trutta[total length (LT) 17–69 cm] and simultaneous density and size‐structure of prey populations, vendace Coregonus albula and smelt Osmerus eperlanus(4–16 cm LT), in a large boreal lake were analysed and compared in 2001 and 2002. The upper LT limit for consumed prey was c. 40% of the predator LT. All brown trout, however, preferred small (&lt;10 cm LT) and avoided large (≥10 cm LT) prey. The results also suggested that equal densities of similar‐sized (4–10 cm LT) fish of the two prey species led to random foraging on these species by brown trout, but if either one of the prey species predominated (&gt;50%) in the lake, brown trout shifted to foraging on this species almost exclusively. Brown trout diets thus reflected the density dynamics of the two alternative prey species.

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.

Interannual variation and climatic regulation of the CO2 emission from large boreal lakes

AbstractWe studied the interannual variation of surface water partial pressure of CO2 (pCO2) and the CO2 emissions from the 37 large Finnish lakes linking them to the water quality, catchment and climate attributes in 1996–2001. The lake water CO2 was measured three times a year in the study lakes in 1998 and 1999 and for the rest of the years the CO2 was modeled by measured alkalinity. The median annual CO2 emission to the atmosphere ranged between 1.49 and 2.29 mol m−2 a−1. The annual CO2 emission followed closely the annual precipitation pattern with the highest emission during the years when the precipitation was highest (r2=0.81–0.97, P&lt;0.05). There was a strong negative correlation (r2=0.50–0.82, P&lt;0.001) between O2 and CO2 saturation in the lake water during stratification suggesting effective decomposition of organic matter in the lakes. Furthermore, total phosphorus and the proportion of agricultural land in the catchment had significant positive correlations with CO2 saturation.

Length at Release Affects Movement and Recapture of Lake-Stocked Brown Trout

Abstract The effect of length (total length = 15-50 cm) at release on the yield and recapture of stocked brown trout Salmo trutta was examined by tagging experiments in a large boreal lake, Lake Oulujarvi in Finland (928 km2). The time the fish spent in the lake before harvesting and the size of the area from which they were harvested diminished with increasing length at release. Small brown trout (<40 cm) moved towards a part of the lake where the highest densities of pelagic prey fish are found, whereas large brown trout (≥40 cm) were captured near their release sites. The longer the distance between the release site of the small brown trout and the good foraging area, the lower their recapture rate. Both relative yield and recapture rate (per 1,000 fish released) increased with increasing fish length at release. However, the positive relation between recapture rate and fish length at release disappeared or turned negative (depending on the release site) when the production costs of fish were taken into...

Pulp and paper mill pollution and subsequent ecosystem recovery of a large boreal lake in Finland: a paleolimnological analysis

Sedimentary diatom frustules and chironomid remains, in addition to the chemical stratigraphy of 32 elements and resin acids, were studied from short-core samples taken from two basins and a sheltered bay of Lake Paijanne in southern Finland (about 61 °10′–62 °15′ N, 25 °30′ E). The lake was formerly oligotrophic but has been subject to effluent loading from pulp and paper mills during the past century since the opening of the first pulp mill in the 1880s. Four developmental phases were distinguished and named mainly according to the effects found in the basin close to the pollution source: (1) the pre-industrial phase (from the 1800s to ca. 1920), including the early years of industrialization, with low impacts; (2) the phase of increasing pollution (ca. 1920–1969); (3) the phase of severe pollution (1970–1981); and (4) the water protection phase (1982 onwards). Distinct differences were observed between pelagic (diatoms) and benthic (chironomid) ecosystems in their response to pollution. Effluent loading from the pulp and paper mills had a pronounced impact on chironomid assemblages, but only a slight influence on diatoms in the basin close to the pollution source. In the southern basin, approximately 60 km downstream, an increase in acidophilous species was observed in the diatom assemblages during the early years of pollution, but changes in chironomids in this basin were negligible. The water protection work of the past 30 years, which has led to an improvement in water quality and a marked recovery of the profundal biota, has also resulted in a slight increase in primary production of the lake. The decrease in brown-coloured effluent water has led to an increase in thickness of the lake's photic productive layer, while the toxicity of the water has simultaneously diminished. Rapid changes in chironomid assemblages and sedimentation observed in the sheltered bay highlight the importance of local land-use activities as causes of environmental change in this area, and especially their effects on sedimentation and benthic life.

Zoobenthic communities in relation to the depth zones in a large boreal lake in Finland

Zoobenthic communities in relation to the depth zones in a large boreal lake in Finland

8000-year history of palaeoproductivity in a large boreal lake

An 8000-year record of palaeoproductivity, based on the chemical and chironomid stratigraphies from Lake Paijanne, S. Finland, was assessed with respect to known morphometric, climatic and anthropogenic events. A gradual trend of dystrophication and an associated decrease in aquatic production was detected during the Holocene, with the following exceptions: (1) high diatom and chironomid production around 8000-6000 cal yr BP, (2) eutrophication around 2000 cal yr BP, and (3) an anthropogenic signal during the last few decades. The changes in chironomid assemblages, before the past few decades, have mainly been shifts in concentration, but not in species composition. Variation in chironomid production was mainly explained by the accumulations of biogenic silicon, carbon and organic matter. Nutrient availability seems to be important in controlling biogenic silicon, which we use to infer past diatom production. The high production ca. 8000-6000 cal yr BP and the fluctuation in chironomid influx after ca. 2000 cal yr BP, however, were probably caused by the proposed warm/dry and cold/wet conditions during these times, respectively. These results highlight the sensitivity of boreal shield lake ecosystems to climatic forcing. In contrast, the pronounced change in the morphometry of the basin around 7000 cal yr BP had little effect on the trophic state of the lake. The human-induced trophic change during the past few decades has affected the Lake Paijanne ecosystem to an extent never experienced before during the last 8000-years.