Pertti Huttunen

Estimation of pH optima and tolerances of diatoms in lake sediments by the methods of weighted averaging, least squares and maximum likelihood, and their use for the prediction of lake acidity

Ecological optima and tolerances with respect to autumn pH were estimated for 63 diatom taxa in 47 Finnish lakes. The methods used were weighted averaging (WA), least squares (LS) and maximum likelihood (ML), the two latter methods assuming the Gaussian response model.WA produces optimum estimates which are necessarily within the observed lake pH range, whereas there is no such restriction in ML and LS. When the most extreme estimates of ML and LS were excluded, a reasonably close agreement among the results of different estimation methods was observed. When the species with unrealistic optima were excluded, the tolerance estimates were also rather similar, although the ML estimates were systematically greater.The parameter estimates were used to predict the autumn pH of 34 other lakes by weighted averaging. The ML and LS estimates including the extreme optima produced inferior predictions. A good prediction was obtained, however, when prediction with these estimates was additionally scaled with inverse squared tolerances, or when the extreme values were removed (censored). Tolerance downweighting was perhaps more efficient, and when it was used, no additional improvement was gained by censoring. The WA estimates produced good predictions without any manipulations, but these predictions tended to be biased towards the centroid of the observed range of pH values.At best, the average bias in prediction, as measured by mean difference between predicted and observed pH, was 0.082 pH units and the standard deviation of the differences, measuring the average random prediction error, was 0.256 pH units.

The use of fallout 137Cs and 239,240Pu for dating of lake sediments

The distribution of 137Cs and 239,240Pu in sediment core samples of the Finnish lakes Laukunlampi, Lovojärvi and Pääjärvi were determined. The sediment samples were collected using dry ice and liquid nitrogen freezing methods. The sediments of these lakes are annually laminated. A clear maximum concentration of 137Cs and 239,240Pu was found in sediment layers formed during 1962–1964, the years of maximum fallout, and the middle of the 1950s can be estimated from the 137Cs and 239,240Pu profiles. The highest concentrations, 11 500 and 820 pCi kg−1 dry wt for 137Cs and 239,240Pu, respectively, were found in the sediment of Laukunlampi. The vertical distribution was similar for 137Cs and 239,240Pu in the lakes investigated. A slight migration of 239,240Pu and 137Cs was found and the migration of 137Cs seems to be higher than that of 239,240Pu. The advantages of 137Cs dating method are rapidity and simplicity. 239,240Pu is preferable when the sample size is small. The agreement found between 137Cs and 239,240Pu dates and the annual laminae show that these fallout radio isotopes can be used for dating sediments formed during the past 25 years.

Long-term fire frequency in the spruce-dominated forests of the Ulvinsalo strict nature reserve, Finland

Abstract The long-term fire history of the spruce-dominated forests of the Ulvinsalo strict nature reserve in Kuhmo, eastern Finland (63°58′N, 30°22′E), was studied by means of charcoal particle layer records and macroscopic charcoal particles in peat and by pollen analysis. The data suggest that spruce forest sites in the area burned at a mean interval of a few centuries over a period of almost 6000 years prior to the beginning of slash-and-burn cultivation in the area. This low forest fire frequency can be attributed to the fragmented landscape pattern, which restricted the spread of fires ignited by lightning. Because a similar landscape pattern predominates over large areas of boreal Fennoscandia, it is possible that natural fire frequencies may also have been considerably lower than expected in these areas. It may well have been the case that, at least in spruce forests located in fragmented landscapes, small-scale disturbances were more important for the forest dynamics than fires.

Interpretation of lake quality from contemporary diatom assemblages

Diatom assemblages from the topmost sediment of 49 lakes were ordinated by means of a program for detrended correspondence analysis and reciprocal averaging (Decorana). Five lake groups were separated, each having more or less characteristic diatom assemblages and water quality. Shifts from one group to another caused by factors such as acidification, artificial drainage, diffuse nutrient loading and sewage are discussed.

Maximum likelihood prediction of lake acidity based on sedimented diatoms

. As an example of ecological gradient analysis, Gaussian response functions, with Poisson or quasi-Poisson error distribution, were fitted for diatom taxa on a pH gradient. It is possible to predict or infer the pH of lake water from the fitted curves using the method of maximum likelihood, which is easily implemented in standard non-linear regressionprograms. Due to overdis-persion with respect to the Poisson distribution, moment estimates forthe negative binomial distribution were also applied, both in estimating the species response curves and in prediction. Simulations indicated that the theoretical maximum precision (measuredby standard deviation of prediction errors) in our data set was 0.17 pH units. The observed errors were much greater (SD 0.35 to 0.43). It seems that roughly equal proportions of the excess error were caused (1) by systematic differences between the training (estimation) data and the validation (prediction) data, and (2) from a misspecified model. It is suggested that the error due to model misspecification consists of inadequacy of the presumed error distribution and of inadequacy of the simple Gaussian response function.

The trophic state of Lake Ladoga as indicated by late summer phytoplankton

As a part of the joint Russian-Finnish evaluation of human impact on Lake Ladoga, we studied the phytoplankton of the lake in order to find biological indicators for eutrophication. A second aim of the investigation was intercalibration of sampling and phytoplankton counting techniques between the Russian and Finnish laboratories. Phytoplankton samples were collected from 27 sampling stations in the lake and from the rivers Volkhov and Neva in 9–13 August 1993. In surface water samples the phytoplankton fresh weight biomass varied in the range 218–3575 mg m−3. Highest biomass values were encountered in Sortavala Bay, and lowest ones in the western central part of the lake. Phytoplankton species composition varied considerably in the lake; blue-green and green algae predominated near-shore areas and Cryptophyceae in the offshore stations. Canonical correspondance analysis revealed close grouping of eutrophy indicating communities, dominated mainly by greens and blue-greens, in the most nutrient-rich parts of Lake Ladoga, the Volkhov and Svir Bays. Samples from the vicinity of the inflows of Vuoksi and Burnaya Rivers and off Pitkaranta formed a separate group, dominated by diatoms, most of which were typical to mesotrophic or eutrophie lakes. As judged by phytoplankton biomass values and chlorophyll a concentrations, Lake Ladoga may generally be classified as mesotrophic. Eutrophicated areas are found in the northern archipelago of the lake and in the areas influenced by large rivers.

Chrysophyte scales recorded in lake sediments from eastern Finland

Chrysophyte (mallomonadacean) scales were examined from the surface sediments of 18 lakes from eastern Finland, representing a wide range of limnological characteristics. Scales were always well preserved and 23 taxa were observed. The relative frequencies of the dominant taxa were plotted relative to the average autumn lakewater pH. The distribution of chrysophyte species in the calibration set was ordinated by means of DECORANA analysis. The occurrence of these species appeared to be closely related to pH, colour and nutrients in the ordinated lake groups. Chrysophyte scales are potentially useful environmental and paleolimnological indicators in eastern Finland.

Paleolimnological reflections of fiber-plant retting in the sediment of a small clear-water lake

Likolampi is a small groundwater kettle-hole lake in Ilomantsi, Eastern Finland. At 11 m water depth the uppermost 51 cm of sediment contains about 390 varves. A thin layer of chrysophyte statospores is the main structural unit in these; in some varves it is followed by a layer of cf. Drepanocladus fluitans moss spores. Below the laminated sequence, two layers of moss detritus (110–87 cm, 81–51 cm) alternate with greyish brown fine detritus. Pollen analysis reveals that the start of the deposition of varved sediment coincides with the beginning of intensive fiber plant retting with large quantities of Cannabis/Humulus -type pollen and even regular occurrence of the insect-pollinated Linum usitatissimum. The cf. Drepanocladus spores are almost absent during the retting period (c. 1590–1900 by the varves), but very common before and after it. Drepanocladus fluitans is capable of assimilating dissolved CO2 in water, so it thrives at low pH and is typical for oligotrophic clear-water lakes. We conclude that the stratigraphy of Drepanocladus fragments and spores is a true negative indicator of cultural influence in Likolampi.

Spatial patterns and relationships between phytoplankton, zooplankton and water quality in the Saimaa lake system, Finland

The interactions between phytoplankton and zooplankton were studied in two large lakes in the Saimaa lake system, Finland. Both are subjected to substantial waste water loading, and exhibit a clear trophic gradient between the loaded and unloaded areas. The phytoplankton and zooplankton were compared in terms of composition, abundance and biomass at 34–39 stations located in different parts of the lakes. At least four mechanisms were thought to affect the composition of plankton communities: (1) the amount of nutrients (trophic gradient), (2) grazing of algae by herbivores, (3) the effect of the algal species composition on feeding by zooplankters (large, colonial algae in the more loaded parts of the lakes) and (4) the regeneration and reorganization of nutrients.

Palaeolimnology of Lake Piene-Kuuppalanlampi (Kurkijoki, Karelian Republic, Russia): isolation history, lake ecosystem development and long-term agricultural impact

The post-glacial history of Lake Pieni-Kuuppalanlampi, western Lake Ladoga region, was studied by means of stratigraphic pollen and diatom analyses. Diatoms were analysed to track the isolation history of the basin and the limnological effects of the early land-use phases indicated by pollen analysis. Chrysophycean stomatocysts and Isoëtes spores were also employed in the limnological reconstructions. Sediment dating was provided by six conventional radiocarbon dates.The lower part of the 370-cm long sediment sequence represents early Holocene, large lake conditions: the (freshwater) Yoldia and Ancylus stages of the Baltic basin, with a short-term lagoonal or isolation phase at the end of Yoldia. The basin was isolated due to Ancylus lake regression at 9785 cal B.P. For the small-lake sequence (0–250 cm) we used diatom inferences (WA-method) for hindcasting water chemistry. The post-isolation limnology of Pieni-Kuuppalanlampi reflects the development of vegetation on its small hill-top catchment. In its early development, the lake was mesotrophic, but became more acidic (pH about 6) and oligotrophic after the decline of temperate hardwood trees and the spread of spruce to the area after around 5000 B.P. The lake ecosystem appears to have reacted sensitively to agricultural land-use in the catchment from AD 400–800 onwards: inferred total phosphorus levels and pH both rise during these periods.