Henn Timm

Response of macroinvertebrates and water quality to long-term decrease in organic pollution in some Estonian streams during 1990–1998

A survey was started in 1990 of the benthic macroinvertebrate community and water quality in some Estonian streams affected by organic pollution, especially the spreading of slurry on fields. The study was expanded during 1991–1998 to involve 47 sampling sites. Long-term dependence was tested using the SAS/GLM contrast statement. All biological indices used (BMWP-ASPT, number of ASPT scoring families (NASPT), Danish Fauna Index, Belgian Biotic Index, EPT-index) were significantly related to the degree of organic pollution. Compared with the reference sites, the test sites revealed significantly lower water quality: higher BOD7, total P and NH4; lower pH and all hydrobiological indices. Season and stream size at the sampling site (expressed in km from the stream source) had significant effects on both hydrochemical and hydrobiological variables. On the contrary, discharge and precipitation had no significant influence on the studied water quality indicators, with the exception of pH in a few cases. At the same time, all but three variables for the reference and the test sites were different at the beginning of the sampling period; this difference remained only for a few sensitive indices such as ASPT and Danish Fauna Index at the end of the period, indicating general improvement in the environment.

Benthic foodweb structure in a large shallow lake studied by stable isotope analysis

Abstract: The benthic foodweb structure of Lake Võrtsjärv, a large (270 km2), shallow, and turbid Estonian lake, was evaluated based on C and N stable-isotope signatures (&dgr;13C, &dgr;15N). Variation in &dgr;13C between sampling sites was not related to site proximity to the littoral zone or the more vegetated southern part of the lake, but rather appeared to be influenced by in-situ site peculiarities. &dgr;13C was stable temporally and between functional feeding groups, a result implying that the whole benthic food web of the lake relies largely on the same C source admixture, essentially particulate organic matter (POM). Thus, the foodweb composition of Lake Võrtsjärv is remarkably homogeneous given the lakes large surface area. Apparent trophic-level &dgr;15N fractionation between total collectors and total predators (mean 1.7‰) was lower than the value of 3.4‰ generally adopted in foodweb studies, but the higher value was valid for specific prey—predator links. The low &dgr;13C signature of some chironomid samples indicated probable assimilation of methane-oxidizing bacteria (MOB) by these sediment-dwelling invertebrates. However, the lack of similar 13C depletion in benthic filterers (mussels) indicated that the MOB layer is essentially confined to the sediments and does not reach the water column, which probably constrains transfer of methane-derived C through the food web to fish in this lake. Our study demonstrates that the benthic food web of shallow turbid lakes like Võrtsjärv is simplified and is mostly sustained by phytoplanktonic C sources.

Macrozoobenthos of Lake Verevi

An overview on studies of macrozoobenthos in the small, hard-water, stratified and hypertrophic Lake Verevi (South-Eastern Estonia) is given. The list of macroinvertebrates comprises at least 105 taxa. In the open water habitats, the biomass and abundance of macrozoobenthos (except the phantom midge Chaoborus flavicans) was rather constant beginning from the epilimnion up to the upper hypolimnion (depth 2–4 m), but very low in the lower hypolimnion (depth 6 m), which was inhabited mainly by Chaoborus. Comparison with long-term reference data from other Estonian lakes, belonging to similar limnological types, indicated that the total biomass and abundance (without Chaoborus) in the profundal of Verevi were very low.

Baltic and Eastern Continental Rivers

This chapter focuses on the four major rivers that flow into the eastern Baltic Sea. From west to east, these are the Vistula, the Nemunas, the Western Dvina, and the Narva. Other larger rivers in this region are the Pregolja, the Venta, the Lielupe, the Gauja, the Parnu, and the Luga. All these rivers are meandering, lowland rivers fringed by vast floodplains. They drain the eastern continental plains and Baltic area. This area includes eastern Poland, Lithuania, Latvia, Estonia, and western and central Belarus; the Kaliningrad and Pskov regions as well as the western Leningrad region in Russia. The area belongs to the Central European mixed forest and North Atlantic moist mixed forest biomes. It is bordered by the Carpathian montane coniferous forests in the southwest and Scandinavian and Russian taiga in the east. All these rivers are regulated to some extent, modifying flow regimes, and suppressing the migration of fishes. The Upper Vistula has been converted into a chain of dams and the Wloclawek reservoir intersects the lower river. In the middle Nemunas, the Kaunas hydroelectric power station was built. Three major hydropower stations occur along the Western Dvina and a large hydroelectric power plant is near the mouth of the Narva River.

The effect of channelization on the biological quality of lowland streams using macroinvertebrates as proxies

We studied whether and how channelization affects macroinvertebrate communities and biological quality in lowland streams of Estonia (Northern Europe). Two datasets of semi-quantitative samples (collected during 2001–2010) were used: (1) pairwise data (natural sites located upstream of the channelized sites; 22 streams, 24 pairs), and (2) background data (73 natural sites from 62 streams, 73 channelized sites from 62 streams). The mean stream order in both datasets was 3. Channelization had no significant effects on physicochemical parameters or on macroinvertebrates in the pairwise dataset where channelization was done decades earlier. However, it had several negative effects on macroinvertebrates in the background dataset where several areas had probably been maintained more recently. Richness of sensitive data, Shannon diversity, mean sensitivity, organic pollution index, and multimetric quality were significantly lower for the modified sites than for the natural sites. Only total taxon richness and score of hydromorphology were not significantly affected by channelization. Thus, several macroinvertebrate metrics that indicate water pollution, proved to be sensitive to channelization as well. The recovery conditions (such as stream type, channelization season, recovering duration, etc.) have been poorly studied and would deserve further attention.