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- Milbrink, Göran
(författare)
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Composition and abundance of oligochaetes in Scandinavian lakes in the 1970s in full compatibility with the "morpho-edaphic index" : Do these relationships still hold 40 years later?
- 2020
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Ingår i: Proceedings Of The 14th International Symposium On Aquatic Oligochaeta. - : MAGNOLIA PRESS. - 9781776708697 - 9781776708703 ; , s. 77-88
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Konferensbidrag (refereegranskat)abstract
- In the 1960s it became fairly well-known that biological indices through their supposedly integrative power could be more robust measures of the water quality than separate chemical data. Oligochaetes and chironomid larvae in the bottom fauna hereby played an important role. Precision, however, increased dramatically if the relationship between oligochaetes and the so-called morpho-edaphic index, i.e. the average total phosphorus content in mu g/l divided by the mean depth (in meters) of the lake (Ryder et al., 1974), was used in stead (Milbrink, 1978). The percentage composition and total abundance of oligochaetes in a number of lakes or selected basins of large lakes in southern Sweden and Norway were thus tested against this index in the 1970s. In logarithmic scales these relationships turned out to be more or less linear. The immediate conclusions were then that this method of classifying lakes could be of considerable scientific as well as practical value. Today we know a lot more about the ecological preferences of oligochaete species and characteristic species associations. The oligochaete fauna of the large lakes of southern Sweden, Malaren, Vattern, Vanern and Hjalmaren, have been studied in detail over many years- over 100 years in the first three of these lakes and in the last lake for over 50-years. Effects of generally applied advanced sewage treatment in Sweden since the late 1960s are easily recognizable in the material. We have a situation of oligotrophication. With our new knowledge it comes natural today to study changes in species composition after trophic change and to investigate if the above close relationships in abundance are still largely linear.
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- Milbrink, Göran, et al.
(författare)
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Large-scale and long-term decrease in fish growth following the construction of hydroelectric reservoirs
- 2011
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 68:12, s. 2167-2173
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Tidskriftsartikel (refereegranskat)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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- Milbrink, Göran, et al.
(författare)
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Long-term effects of nutrient enrichment on the condition and size-structure of an alpine brown trout population
- 2008
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Ingår i: Environmental Biology of Fishes. - : Springer Science and Business Media LLC. - 0378-1909 .- 1573-5133. ; 81:2, s. 157-170
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Tidskriftsartikel (refereegranskat)abstract
- Long-term effects of nutrient enrichment on a population of brown trout inhabiting a small, alpine lake in north-central Sweden have been studied for nearly 20 years. The study took place between 1981 and 1999 starting up between 1982 and 1987 with full nutrient enrichment of phosphorus and nitrogen in a ratio by weight of 1:8, followed by a period of reduction by half between 1988 and 1994, and thereafter no enrichment at all. Growth of the brown trout population was low before the application of nutrients. Fertilization promoted the development of zooplankton in great abundance, which gave rise to abundant food for the trout. Already during the first year of nutrient addition the average 4+ and 5+ fish had increased in weight by nearly 50% and in length by about 30%. Maximum growth was reached 5-6 years later-weight by about 175% and length by about 50% higher than before application. The slope of the growth curves for fish of ages 2+ to 5+ increased significantly from 1981 to 1987, and so did the size-variation with a high proportion of the fish reaching larger size. After each change in nutrient treatment the mean weights of 5-6-year-old trout were maintained for about 3 years. Five years after termination of fertilization growth was nearly back to the original state. Although badly needed, long-term studies of fish populations like this are few in the literature.
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- Milbrink, Göran, et al.
(författare)
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Rapid growth response of the Arctic charr to changing environmental conditions is not the result of a population bottleneck
- 2013
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Ingår i: Annales Zoologici Fennici. - 0003-455X .- 1797-2450. ; 50:6, s. 385-389
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Tidskriftsartikel (refereegranskat)abstract
- We tested if within-lake differences in individual growth in an Arctic charr population before and after nutrient enrichment was due to a population bottleneck, for example as a result of strong selection for growth in a limited part of the population. The positive change in growth pattern after treatment was not coincident with a reduction in microsatellite variability, and various genetic estimators of demographic change did not indicate changes in population size. This suggests that the change in growth was not a result of only a limited part of the population responding, but an overall response.
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- Milbrink, Göran
(författare)
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Where have all the "vejdovskies" gone (Potamothrix vejdovskyi Hrabe)? : Ponto-Caspian tubificid oligochaete species in Lake Malaren, south-central Sweden, in a 100 year perspective
- 2014
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Ingår i: Proceedings of the 12th International Symposium on Aquatic Oligachaeta. ; , s. 95-102
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Konferensbidrag (refereegranskat)abstract
- Potamothrix vejdovskyi is one of several alien Ponto-Caspian species presently invading Europe and the New World. Its invasive success has been suggested to be dependent upon the trophic degree of the water, and this species is considered to be particularly indicative of mesotrophy (Lang & Reymond 1996). Bottom fauna surveys performed by the Swedish Fisheries Board in 1915 and 1916 and in 1933-1935 did not reveal the existence of P. vejdovskyi in Lake Malaren, whereas extensive bottom fauna programs in the lake in 1967-1976 demonstrated a wide distribution of the species in the central, least polluted basins. Strict quantifications of the distribution of oligochaetes in those basins in 1974 showed that P. vejdovskyi then made up on average 28 % of the total abundance of oligochaetes. However, in later bottom fauna surveys in Lake Malaren, performed by the Swedish Environment Protection Agency in 1981 and in 2009-2011), P. vejdovskyi could not be found at all. Sewage treatment around Lake Malaren accelerated in the late 60's and the phosphorus load is nowadays considerably lower than before treatment (about 30 % less in terms of total-P concentrations in the water). The question of why this species seems to have more or less disappeared from the lake remains unsolved.
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