Polyhumic Lake Research Articles

Temporal coherence in water temperature and chemistry under the ice of boreal lakes (Finland)

Temporal coherence was assessed for 11 limnological variables—water temperature, oxygen, conductivity, alkalinity, pH, colour, calcium (Ca), iron, aluminium, total phosphorus and total nitrogen—between 28 boreal lakes in southern Finland for the winter ice-covered period. The lakes were mainly small (<0.2 km 2) and brown-coloured, and located within a circle of 10-km radius. A mean Pearson correlation coefficient for all lake pairs and variables averaged 0.37. Temporal coherence of variables across lake pairs was highest for conductivity, Ca, water temperature and alkalinity. The lake pairs with a direct surface water channel connection had a higher coherence than the lake pairs not connected by a stream. The size of the lake or catchment area had little effect on the coherence between the lakes. Temporal coherence was not strongly related to the difference in water colour (dystrophy) between the lakes. However, between polyhumic lakes (colour >100 g Pt m −3) the coherence was generally higher than between less coloured lakes. Year-to-year variation in limnological characteristics could be partly explained by the variation in local weather. In March, water temperature and chemistry were infrequently related to winter weather, rather they correlated with the weather conditions of the previous autumn, while the ambient late winter weather seemed to have a stronger influence on lake conditions in April. Temporal variation in some variables was related to the atmospheric pressure changes over the North Atlantic (the North Atlantic Oscillation, NAO). Our results suggest that the potential effects of climatic change on lakes can be generalised regionally for brown-coloured dystrophic lakes.

Plankton community of a polyhumic lake with and without Daphnia longispina (Cladocera)

The impact of Daphnia longispina (Cladocera) on the plankton food web was studied in a polyhumic lake where this species comprised almost all zooplankton biomass. Plastic enclosures (volume 7 m3) were inserted into the lake retaining the initial water stratification except that in one enclosure zooplankton was removed. After the removal of Daphniaa rotifer, Keratella cochlearis, ciliates and heterotrophic nanoflagellates increased markedly and the density and biomass of bacteria decreased. Edible algal species, Cryptomonas rostratiformisand three small chrysophytes,Ochromonas, Pedinella and Spinifermonas, took advantage of the removal of Daphnia, while more grazing-resistant species declined. In spite of the changes in the species composition of phytoplankton, the removal of Daphnia did not affect the biomass, primary production or respiration of plankton. The results implied that the density of heterotrophic flagellates and ciliates was controlled by Daphnia, but in its absence the former took its role as the bacterial grazers.

&lt;i&gt;Acamptocladius reissi&lt;/i&gt; Cranston &amp; Saether, 1982 (Diptera, Chironomidae): first record to Spain

This note represents the first record of the species Acamptocladius reissi Cranston & Saether, 1982 to Spain and the Pyrenees —Zone 2 in the Limnofauna Europaea (Fittkau & Reiss, 1978)—. The genus had not been found before in the area (Soriano et al., 1997). Until now three species of the genus Acamptocladius have been described, two in Europe and one in Canada, always from relatively cold sites. Both European species —A. reissi and A. submontanus (Edwards, 1932)— are found in mountain peat pools and polyhumic lake shores where mosses are important. A. reissi has only been found to our knowledge, at the site of its first description, in Oberbayern, Murnauer Moos (West Germany) (Cranston & Saether, 1982), in a couple of sites in Norway (Schnell & Aagaard, 1996) and in Finland (Lindegaard, 1997).

The effects of forest fertilization on a small polyhumic lake

The effects of forest fertilization on a small polyhumic lake

Influence of changing food web structure on nutrient limitation of phytoplankton in a highly humic lake

We determined the potential nutrient limitation of summer phytoplankton production using 2 × 2 × 2 factorial design of enrichment bioassays both before and after the introduction of planktivorous whitefish (Coregonus lavaretus) in a polyhumic lake with an abundant population of the large cladoceran Daphnia longispina. After the fish introduction, Daphnia disappeared and was substituted by the rotifer Keratella cochlearis. During the dominance of Daphnia, additions of nutrients had little or no effect on primary production of phytoplankton in short-term (1-day) incubations. However, 5-day incubations suggested that P most likely was the limiting nutrient. After the fish introduction, both 1- and 5-day enrichment bioassays indicated potential N limitation of phytoplankton production. The strong response of phytoplankton production to combined enrichments with P and N also suggested colimitation by P and N, but this was probably forced by the relatively high additions of nutrients. Consistently low primary production after the combined addition of P and glucose suggests that in the presence of a labile organic C source, epilimnetic bacteria were superior to algae in the uptake of P. Our results suggest that changes in the food web structure may determine the limiting nutrient also in a highly humic lake.

Tracing of Peroxidase Activity in Humic Lake Water

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Growth of Daphnia longispina L. in a polyhumic lake under various availabilities of algal, bacterial and detrital food

The availability and importance of food sources for growth of Daphnia longispina L. from a highly coloured fishless lake with anoxic hypolimnion were assessed by combining in situ and laboratory experiments. In in situ experiments populations were enclosed in tubes with natural temperature stratification and with or without anoxic hypolimnion. In the laboratory experiments the importance of food source (littoral zone vs pelagic epilimnion) was assessed by enclosing moss thalli and a natural zooplankton population in a large-scale flow-through system supplying food for experimental Daphnia. Growth of juveniles of Daphnia in epilimnetic water was determined in batch culture experiments and the importance of increasing concentrations of bacteria and algae for their growth and development was investigated with a small-scale flow-through system. Access to the anoxic hypolimnion enhanced the growth of Daphnia by 23–24%. Growth rates in the tubes with anoxic hypolimnion were 0.36 and 0.16 d−1 in July and August respectively. In tubes without anoxia the corresponding values were 0.29 and 0.13. In batch-cultures the highest growth rate determined was 0.16 and the overall rates were lower than in in situ experiments. In batch culture Daphnia was able to grow in darkness for 10 days with a rate of 0.16. In the large-scale flow-through system Daphnia population fed with littoral water reproduced well despite the low concentration of algae and increased its number by a factor of c. 32 in 10 days. However, the animals were small and net production of Daphnia population thus lower under the littoral influence than in the control treatment. Population could survive and grew slowly on pelagial water processed by a natural zooplankton community and with very little algae left. It is thus possible that bacteria serve as a ‘life-support system’ enabling the population survival over periods of algal shortage. Small-scale flow-through experiments revealed that Daphnia longispina is able to mature and reproduce on a bacterial diet if the food concentration is high enough and Daphnia on bacterial food could achieve growth rates similar to those on an algal diet. The threshold food level for Daphnia longispina was estimated to be c. 18.5 μg C 1−1. Detrital material is of limited value in nutrition of Daphnia even in a lake where more than 75% of carbon is bound in particulate detritus.

Extracellular enzymes in a small polyhumic lake: origin, distribution and activities

Extracellular enzymes in a small polyhumic lake: origin, distribution and activities

Littoral-pelagial interchange and the decomposition of dissolved organic matter in a polyhumic lake

Littoral-pelagial interchange and the decomposition of dissolved organic matter in a polyhumic lake

Extracellular enzymes in a polyhumic lake: important regulators in detritus processing

Extracellular enzymes in a polyhumic lake: important regulators in detritus processing

Bacterioplankton in a small polyhumic lake with an anoxic hypolimnion

Bacterioplankton in a small polyhumic lake with an anoxic hypolimnion

Zooplankton-phytoplankton interactions and their importance in the phosphorus cycle of a polyhumic lake

Zooplankton-phytoplankton interactions and their importance in the phosphorus cycle of a polyhumic lake

Extracellular proteolytic activity and its relation to dissolved amino acid composition in the DOM of a polyhumic lake

(1990). Extracellular proteolytic activity and its relation to dissolved amino acid composition in the DOM of a polyhumic lake. SIL Proceedings, 1922-2010: Vol. 24, No. 1, pp. 293-293.

Changes in Fish Mercury Concentrations in an Intensively Fished Lake

A small polyhumic lake inhabited by northern pike (Esox lucius), burbot (Lota lota), perch (Perca fluviatilis), roach (Rutilus rutilus), and eel (Anguilla anguilla) was fished intensively during spring 1984 and 1985 to lower the high mercury levels in the top predator, northern pike. A total catch of 29.5 kg∙ha−1 (74% roach) was removed which represented about 50% of the total fish biomass. Mercury concentrations in burbot, large pike, and small roach had decreased by 1987 and 1988, but increased in young pike and some perch. Northern pike had the clearest increase in growth rate, while that of perch and roach levelled off within 3 yr at the prefishing level. Only a small increase in growth rate of burbot occurred. The yearly accumulation of mercury in northern pike remained constant, and the decrease in [Hg] was apparently due to growth dilution. The decrease in [Hg] of burbot and roach is explained by a switch to a diet with lower [Hg] or a decrease in water methylmercury concentrations. The amount of methylmercury removed from the lake by fishing was equivalent to several years of calculated mercury methylation and accumulation in the fish. Overfishing may be a feasible means of lowering methylmercury levels in this type of oligotrophic lake.

Evaluation of the measurements of extracellular enzyme activities in a polyhumic lake by means of studies with 4-methylumbelliferyl-substrates

Evaluation of the measurements of extracellular enzyme activities in a polyhumic lake by means of studies with 4-methylumbelliferyl-substrates

The relative importance of algae and bacteria as food for Daphnia longispina (Cladocera) in a polyhumic lake

SUMMARY. 1. Grazing on algae and bacteria by the planktonic cladoceran, Daphnia longispina, was studied in a small polyhumic lake with low phytoplankton primary production in southern Finland.2. D. longispina filtered algae at average rates of 0.09‐0.82 ml ind−1 h−1. The filtering rates on bacteria were 26‐92% of those on algae in parallel experiments.3. From June to August algae, including mixotrophic and heterotrophic forms, comprised 56‐93% of the food ingested by D. longispina. In mid‐September and early October, when the Daphnia population was declining and the algal biomass was low, bacteria comprised 73% and 55% respectively of the food of Daphnia.4. For D. longispina, an energy pathway via bacteria and bactivorous flagellates is probably a more important link to allochthonous organic matter than direct utilization of epilimnetic bacteria.

Emergence phenology and ecology of aquatic and semi‐terrestrial insects on a boreal raised bog in Central Finland

Emergence of peatland insects was studied in Central Finland by sampling insects on a raised bog with tent traps from five different surfaces: muddy hollow without vegetation; hollow covered with Sphagnum; deep (0.7–0.9 m) open‐water pool; shallow (about 0.3 m) pool with bottom covered by Carex vegetation; shallow (about 0.3 m) pool with bare muddy bottom. The material was collected at two‐days intervals from 13 May until 31 August in 1981.Biomass emerging from the sites varied considerably. In general, aquatic sites were clearly more productive than semi‐terrestrial sites. Corrected total biomass values for deep pools, shallow Carex pools, and shallow mud pools were 2.471, 1.066, and 0 514 g m−2, respectively. The corresponding values for muddy and Sphagnum hollows were 0.208 and 0.236 g m−2, respectively.All chironomids, chaoborids and trichopterans from the aquatic sites were identified to species, and their emergence phenology and habitat preferences are discussed. 14 species were considered as eurytopic littoral species, 9 species showed strong preference for the bog pools or polyhumic lakes, and 8 species were of diverse origin. Differences in emergence patterns and habitat preferences are probably connected with species‐specific resistances to freezing and oxygen and nutrient requirements. The role of emerging insects in the peatland food webs, especially as food for breeding birds, is briefly discussed.

Phyloflagellates and their ecology in Tasmanian polyhumic lakes

Phyloflagellates and their ecology in Tasmanian polyhumic lakes

Acidity and humic matter in small forest lakes

The ion balances of 73 small lakes with forested catchments were calculated using the main cations and the inorganic anions. A clear cation excess was observed in polyhumic lakes. However, taking into account the estimated acidic organic anion concentrations the ion ratios appeared to be balanced. In addition, strong and weak acids were analyzed in 26 of the lakes using the coulometric Gran titration.

Epizooic ciliates (Vorticella sp.) compete for food with their host Daphnia longispina in a small polyhumic lake.

Clearance rates of epizooic ciliates (Vorticella sp.) were measured together with their host, a planktonic cladoceran Daphnia longispina by using fluorescent latex beads as tracers of food. Vorticellans and their host graze on food of same size range (nanoplanktonic algae and bacteria). Individual clearance rates of Vorticella averaged 6.9 and 7.0 μl ind-1 h-1 and those of Daphnia 463 and 708 μl ind-1 h-1 for beads with diameter 2.00 and 3.92 μm. On the average, epizooic vorticellans together on the carapace of Daphnia cleared particles with rates representing 25-33% of that the host cleared, the maximum rates being 50-80%. In a steeply stratified polyhumic lake vorticellans take advantage of following Daphnia to food patches and they can severely compete for food with their host.