Effects of paper mill effluents on the fish fauna of stony shores of Lake Päijänne

The fish fauna of the stony littoral in the central parts of L. Päijänne was studied by electric fishing on four occasions during 1988–1989. Ten fish species and 1681 individuals (14.5 kg) were caught in the 15 fishing sites (4096 m²) which gives a mean density of 0.41 ind. m^–2 and biomass of 3.5 gm^–2. Effluent from two large paper mills causes a clear zonation of the fish fauna in the area. In the most polluted shores, only burbot and perch occurred regularly and the reproduction of other species was inhibited. In the semipolluted area (5–15 km from the Kaipola paper mill), burbot and stone loach occurred regularly, but owing to low numbers of perch and bullhead the total densities were usually low.The clean shores were characterized by an abundance of stone loach and bullhead and locally also of minnow, which seemed to be very sensitive to pollution. The strong floods during summer 1988 had positive effects on the reproduction of perch and pike, but the densities of other species were highest during the normal water level in autumn 1989.     

Incipient forebrain boundaries traced by differential gene expression and fate mapping in the chick neural plate

We correlated available fate maps for the avian neural plate at stages HH4 and HH8 with the progress of local molecular specification, aiming to determine when the molecular specification maps of the primary longitudinal and transversal domains of the anterior forebrain agree with the fate mapped data. To this end, we examined selected gene expression patterns as they normally evolved in whole mounts and sections between HH4 and HH8 (or HH10/11 in some cases), performed novel fate-mapping experiments within the anterior forebrain at HH4 and examined the results at HH8, and correlated grafts with expression of selected gene markers. The data provided new details to the HH4 fate map, and disclosed some genes (e.g., Six3 and Ganf) whose expression domains initially are very extensive and subsequently retract rostralwards. Apart from anteroposterior dynamics, some genes soon became downregulated at the prospective forebrain floor plate, or allowed to identify an early roof plate domain (dorsoventral pattern). Peculiarities of the telencephalon (initial specification and differentiation of pallium versus subpallium) are contemplated. The basic anterior forebrain subdivisions seem to acquire correlated specification and fate mapping patterns around stage HH8.     

Size-dependent over-winter mortality of young-of-the-year roach, Rutilus rutilus

Over-winter survival of starved and fed young-of-the-year roach from two lakes in central Finland was examined in the laboratory between November 1992 and May 1993. The mortality rate of starving YOY roach (total length 38 ± 2 mm) from small (ca. 0.5 km²), eutrophic Lake Isojärvi was 50%, whilst roach (total length 32 ± 3 mm) from large Lake Päijänne (1106 km²) suffered 42% mortality. Mortality was size-dependent among roach from Lake Isojärvi, smaller individuals being more vulnerable. There was not strict size limit for survival as proposed previously. However, it seems that within populations approximately the same proportion of smallest roach died independent of the absolute lengths of the fish. Mortality of fed roach from both lakes was always < 5%. This good survival indicates indirectly the importance of energy reserves in wintering. Lipid and protein content of fasting roach from lake Isojärvi decreased during the winter. In the group of fasting roach from Lake Päijänne the amount of lipids stored increased between November and March and decreased thereafter. No change in protein content of fasting fish from Lake Päijänne was observed.     

Reproductive success of Coregonus species in areas loaded by effluents from paper mills

The annual reproductive success of Coregonus albula and C. lavaretus in some polluted and clean areas of the central parts of L. Päijänne was estimated in 1981–90 on the basis of occurrence of larvae in shore seine and seine net samples after the ice melted. In polluted areas (0–5 km from Kaipola paper mill) larvae of coregonids were found only occasionally. In semipolluted areas (5–15 km from the paper mill) the densities of larvae were usually less than 0.1 ind m^–2. In clean areas the mean densities of larvae ranged from 0.45 to 5.34 inds m^–2. A relatively high reproductive success of vendace was observed in 1984–85, moderate success in 1982–83 and low success in 1986–90. The larvae of whitefish were scarce in both polluted and semipolluted areas and their density ranged from 0.01 to 0.15 ind m^–2 in clean shores. The highest density was observed in 1989. In spite of the improvement of the quality of water in the area in the 1980s, the reproductive success of coregonids is still low in a great part of the basin which may depend on adverse oxygen conditions of the hypolimnion and sediment and the toxic effects of the effluents.     

Lacustrine profundal meiobenthos as an environmental indicator

Organic loading and eutrophy is indicated at profundal depths by large numbers of resting copepodid stages of cyclopoid copepods, by the occurrence of the naidid oligochaete species, Amphichaeta leydigii and Specaria josinae, and the harpacticoid species Canthocamptus staphylinus, and by a low meiobenthos/macrobenthos biomass ratio. An oligotrophic environment is indicated by the occurrence of the aeolosomatid oligochaetes Aeolosoma quaternarium, A. hemprichi and Rheomorpha neiswestnovae, the naidid oligochaete Chaetogaster langi and the harpacticoid species Attheyella crassa and a high meiobenthos/macrobenthos biomass ratio.     

Changes in water quality in Lake Päijänne following decrease of effluent load from the pulp and paper industry in 1969–1989

Lake Päijänne, the second largest lake in Finland, has been seriously polluted since the 1960s due to the effluents from pulp and paper mills, notably the Äänekoski sulphate and sulphite pulp mills situated about 50 km north of the lake, and the sulphite pulp mill and paper mills of Jämsänkoski and Kaipola on Central Lake Päijänne.A sulphite lye evaporation and combustion plant installed at the Jämsänkoski sulphite pulp mill in 1969 reduced the organic pollution of Central Päijänne. Lignin concentration decreased and the oxygen balance improved. The sulphite pulp mill was closed in 1981 and replaced by a thermo-mechanical pulp mill. Eutrophication is the main threat to water quality in Central Lake Päijänne at present.A significant improvement in the water quality, especially in oxygen balance, was achieved in the watercourse of Äänekoski and in Northern Päijänne after replacement of the old sulphite and sulphate pulp mills at Äänekoski by a large sulphate pulp mill with a biological purification plant employing the activated sludge method. The BOD₇-loading dropped from 46 to 3–4 t d^–1, but the nutrient loading has not decreased sufficiently, and the Äänekoski watercourse and Northern Päijänne are still eutrophic.