Phytoplankton Aug 19902000

0 25 50 75 100 125

0 25 50 75 100 125

Figure 4.3. Average biomass of phytoplankton in August in several lakes in the River Dalälven catchment in the period 1990-2000 as a function of the nutrient (phosphorus) status of the lakes. Biomasses expressed in mm3/l. Reprinted with permission from Lindestrom, 2003.

Biomass (irim-71}

Figure 4.3. Average biomass of phytoplankton in August in several lakes in the River Dalälven catchment in the period 1990-2000 as a function of the nutrient (phosphorus) status of the lakes. Biomasses expressed in mm3/l. Reprinted with permission from Lindestrom, 2003.

The fish fauna, finally, in Lake Runn during catches made in the period 1980-2001 was found to consist of at least 12 different species: bleak, bream, burbot, crucian carp, pearch, pike, roach, rudd, ruffe, silver bream, smelt and vendace. There is presumably also at least eel in the lake, but this species in not readily caught in the nets used. The age distribution of perch was normal in the whole lake and that of roach was normal at least in the southern parts of the lake. Also the growth of perch was found to be normal as compared to other lakes in the region. Finally, physiological surveys showed that the health conditions of perch, e.g. the liver size, the blood values, etc., were normal. The only observation of a deviation from the normal status was that small roaches were underrepresented in the northwestern part of the lake, near the city of Falun, as well as in the central lake. In both cases, the lower number of young roach may be due to the lack of convenient spawning areas in these parts of the lake, due to the presence of a dense carpet of fluffy iron precipitates. No deformations of individual fish have been reported from Lake Runn.

Analyses of the content of copper and zinc in the liver of perch have been conducted in many of the lakes in the River Dalalven drainage basin in 1996. The results of these analyses are presented in diagrams together with the concentrations of the same metals in the water of the lakes, see Figure 4.4. Data from Lake Runn are represented by three bars, corresponding to fish from the south (S), central ( C) and north (N) parts of the lake.

Figure 4.4. Concentrations of copper and zinc in water (curve) and in liver tissue of perch (bars) in several lakes in the River Dalälven drainage basin. Concentrations in water are expressed as ^g/l and in liver tissue as ^g/g DM.Reprinted with permission from Lindeström, 2003.
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