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- Rydin, E., et al.
(author)
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Compensatory nutrient enrichment in an oligotrophic mountain reservoir : effects and fate of added nutrients
- 2008
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In: Aquatic Sciences. - : Springer Science and Business Media LLC. - 1015-1621 .- 1420-9055. ; 70:3, s. 323-336
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Journal article (peer-reviewed)abstract
- Most Scandinavian rivers are impounded for power production. High altitude reservoirs retain water during summer and fall for power production during winter and spring. The oligotrophic lakes Mjölkvattnet and Burvattnet were impounded in 1942. Annual water level fluctuations caused by regulation have resulted in a loss of littoral habitat, and Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) populations have declined. To assess compensatory nutrient enrichment as a remedy against declining fish populations, we added dissolved phosphate and nitrate to Mjölkvattnet in June and July in 2002 and 2003, and used the upstream lake Burvattnet as a reference system. Nutrient addition doubled water column total phosphorus concentration, from 3 to 6 μg P/L and increased nitrogen concentration by about 20 μg/L. Half of the added phosphorus settled out as organic matter, and about one third was lost downstream. Phytoplankton production and biomass increased, but species composition remained principally unchanged. Rotifers and cladocerans responded rapidly, as did the condition of fish. After two years of nutrient addition, five year old Arctic char had doubled in weight and increased significantly in length, reaching pre-impoundment conditions.
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- Milbrink, Göran, et al.
(author)
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Large-scale and long-term decrease in fish growth following the construction of hydroelectric reservoirs
- 2011
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In: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 68:12, s. 2167-2173
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Journal article (peer-reviewed)abstract
- Hydroelectric reservoirs retain large volumes of water and have a global impact on sea level, elemental cycles, and biodiversity. Using data from a total of 90 historical and recent surveys in nine regulated and eight unregulated alpine and subalpine lakes, we show an additional large effect of reservoirs, i.e., that impoundment causes drastically decreased fish growth and thereby great negative consequences for inland fisheries in Scandinavia. Following a long period (40-65 years) after impoundment, the length and mass of Arctic charr (Salvelinus alpinus) of the single age class 4+ years was, on average, 35% and 72% lower, respectively, in impounded versus natural lakes in northern Scandinavia. The effect was stronger at higher altitudes and can be mitigated by addition of inorganic nutrients. We suggest that the decreased fish growth is a consequence of lowered ecosystem productivity, oligotrophication, caused by impoundment, resulting in erosion and loss of the littoral ecosystem as well as delayed flooding and leakage of nutrients from the riparian zone until after the growing season.
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