Tom Blom

The Relationship between Diatoms and Water Temperature in Thirty Subarctic Fennoscandian Lakes

The relationship between surface sediment diatom (Division: Bacillariophyta) assemblages and measured water chemical and environmental variables in 30 lakes from northern Fennoscandia were examined...

Diatoms as quantitative indicators of pH and water temperature in subarctic Fennoscandian lakes

Weighted averaging (WA) regression and calibrationbased optima and tolerances of lakewater pH andtemperature are presented for diatoms in ecologicallysensitive, subarctic Fennoscandian lakes. The studysites are mostly small, simple, oligotrophic,low-conductivity lakes with a pH range from 5.0 to7.7 and a temperature range (after data screening)from 9.3 to 15.0 °C. Experiments with inverse andclassical deshrinking, with or without tolerancedownweighting, were used to identify the bestcalibration functions. The model estimates wereadjusted by jackknifing procedures. WA by inversedeshrinking and with tolerance downweighting performedbest for pH prediction, whereas simple WA wasmarginally superior for predicting water temperature.The established pH model is accurate to within± 0.39 H units, and the temperature model towithin ± 0.88 degrees Celcius. Fifteen diatom taxawere identified as potential indicator species for pHand three for temperature.

Paleohydrology inferred from diatoms in northern latitude regions

Several recent studies have successfully applied diatom-based paleolimnological techniques to infer past hydrological changes in arctic and subarctic regions. For example, we summarize arctic studies that attempt to determine changes in peat water content, flood frequency, river discharge, effective moisture and ice cover in northern regions. Some of the investigations are still in preliminary stages, but represent innovative approaches to study arctic and subarctic paleohydrology. New data demonstrate that lake depth, which may be related to changing hydrological conditions, is a significant variable influencing the distributions of diatom taxa in lake surface sediment calibration sets from Wood Buffalo National Park (WBNP), on the border of Alberta and the Northwest Territories, Canada, and from Fennoscandia (mainly northwest Finland). Weighted averaging regression and calibration methods were used to develop quantitative inference models for lake depth using diatom assemblages preserved in surface sediments. The predictive abilities of the transfer functions were relatively high (for WBNP r2 = 0.70 and RMSE = 2.6 m, and for Fennoscandia r2 = 0.88 and RMSE = 1.8 m). However, evaluating the transfer functions using jack-knifing procedures indicated lower predictive abilities, possibly reflecting the relatively small sample size and/or short gradients used in these calibration sets. Such transfer functions can be used to track overall trends in lake levels, and provide an objective assessment as to directions of changing lake levels. Any interpretations of inferred lake levels, especially those related to climate change, must be made cautiously and must include some understanding of the local, present-day hydrological system.

Recent environmental changes in a naturally acidic rocky lake in southern Finland, as reflected in its sediment geochemistry and biostratigraphy

Paleolimnological methods are combined with statistical multivariate analyses (PCA and CCA) to study the effects of local environmental disturbances and changes in loading of atmospheric origin on water acidity and the physiochemical properties of the sediment in a small, naturally acidic rocky lake in southern Finland. The pH of the lake as calculated from the diatom flora increased by 0.9 pH units as a consequence of a forest fire in the catchment area at the turn of the last century, and the changes in the diatom assemblages point to an increase in dys(eu)trophy and turbulence. In terms of element influx (in µg cm-2 yr-1), the effects of the fire are seen in a slight increase in the accumulation of lithophilous elements. Diatom-inferred pH values decline upwards in the sediment, but do not regain the level recorded before the fire. This is attributed to reactions between Fe3+ and S, which has partly accumulated from the air as SO2-, producing internal alkalinity. Accumulation rates of many elements increase markedly after the 1960s, an effect for Al, Mg, Na, P and Zn may be connected mainly with the enhanced accumulation of dry matter, whereas the accumulation of K, Ni, Pb, Ti and V in surface sediment are obviously related to atmospheric loading. Measured accumulation rates of Cd and Cu are lower than the calculated values especially in the surface sediment, possibly because of diagenetic changes. Accumulation of Ca and Mn decreases towards the surface on account of acidification of anthropogenic origin.

Marked early 20th century pollution and the subsequent recovery of Töölö Bay, central Helsinki, as indicated by subfossil diatom assemblage changes

Diatoms were used to infer the trophic status history of a Baltic Sea inlet, Töölö Bay, located in central Helsinki. The waterbody received partially treated sewage effluent from the local sewage works and from a sugar factory from ca. 1890 until ca. 1960 when primary sewage treatment and the diversion of the effluent began. The increased nutrient input is shown in the diatom stratigraphy in the form of a rapid increase in planktonic eutrophic forms particularly Cyclotella cf. meneghiniana, and a reciprocal destruction of the periphytic flora. The overall diversity decreased markedly at this time. There is a gradual recovery of the system to the predisturbance conditions from 1960 onwards, as indicated by the re-emergence of the mesotrophic periphytic diatoms. Detrended correspondence analysis (DCA) is used to summarize the responses of the diatom assemblages to changing nutrient concentrations.

Physical and chemical characterisation of small subarctic headwater lakes in Finnish Lapland and the Kola Peninsula

High !atitude regions are important reference sites for the study of global environmental change. Freshwater ecosystems are essential features of the nonhern environment. They are sensitive to changes in external conditions, and often are rhe first to show signs of environmental shifts (KoRHOIA 1996, RousE et al. 1997, BLOM er al. 1998). However, litde is known of the chemical and limnological properties of these ecosystems, which markedly impedes the use of northern lakes as sensors of environmental change. To explore these properties, a total of 129 lakes located in NW Finnish Lapland, NE Lapland and in the Kola Península was surveyed. This paper mainly focuses on a subset of NW Finnish Lapland lakes (n= 50) which were used to investigate the effects of catchment factors on lake water and sediment properties.

Chironomids, temperature and numerical models: a reply to Seppälä

We reply to comments by Seppälä (2001) concerning the suitability of the surface-water temperature measurements and mean July air temperature estimates used by Olanderet al. (1999) to derive quantitative chironomid-temperature transfer functions. We use new data for water temperatures based on two-hourly recordings from thermistors installed in 32 lakes and air-temperature data from an automatic weather station at one lake to refute Seppälä’s accusations that our field data are unsatisfactory. We also respond to Seppälä’s suggestions about factors influencing chironomid distribution and abundance and suggest that there is a serious confusion of temporal and spatial scales between Seppälä’s ideas and the Olanderet al. study. We attempt to explain the underlying logic behind empirical transfer functions that form a major part of Holocene quantitative environmental reconstructions and the major assumptions behind such transfer functions as Seppälä appears not to understand the basis or the assumptions of such widely used numerical models in palaeolimnology. We respond to Seppälä’s comments that lakewater pH and distance beyond tree-line have been inadequately measured and answer his erroneous understanding that a helicopter was used to facilitate lake sampling. We briefly consider Seppälä’s suggestion that a helicopter can totally mix the surface water of a lake for many hours.