Milbrink, G. & S. Holmgren. (1981). Addition of Artificial Fertilizers as a Means of Reducing Negative Effects of “Oligotrophication” in Lakes After Impoundment. Reports of the Institute of Freshwater Research, Drottningholm. 59:97-120.

510840

Milbrink, G. & S. Holmgren

1981

59:97-120.

Publication

http:// http://hdl.handle.net/2077/48740

Available for editors   [request]

There have hitherto been few biological methods at hand for compensating the most adverse effects of impoundment. Four seasons of “partial fertilization” in the impounded Lake Anjan have indicated that nutrient enrichment (nitrogen and phosporus in a fixed ratio) is an effective way of locally restoring fish populations in such lakes. Continuous nutrient enrichment of a small stream leading into a half-secluded bay of the lake promoted the development of an exceedingly rich zooplankton fauna in the bay which primarily favoured the char which largely became attracted to the area and rapidly improved in quality. Also the stream bottom fauna improved considerably for the benefit of brown trout, grayling —• and char. The rich availability of prey animals (especially zooplankton) is reflected in a high degree of niche-overlapping in the food of the fish species mentioned. The results of the present study suggest that it is possible to produce and retain positive “damming-up effects” (Nilsson 1973), which generally follow — though for a limited time the damming of water, provided the enrichment is kept under proper control. An obvious case of seasonal feeding migration has simultaneously been studied in a system of small, organically polluted lakes connected with a larger obligotrophic lake via a narrow stream about 5 kilometers long. Balanced nutrient enrichment of ideally shaped bays of oligotrophic lakes is here suggested for the twofold purposes of improving the condition and the stock size of salmonid fish and increasing the buffering capacity against acidification — now rapidly in progress even in northern Scandinavia. The method is partly in controversy with the general policy of indiscriminately purifying sewage water as much as possible.

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