Augtenes hipereitrofikācija jūras kraukļu Phalacrocorax carbo koloniju dzīvotnēs Kaņiera ezera Ābeļu un Egļu salās

English. Nowadays, great cormorants Phalacrocorax carbo are frequently nesting in colonies in trees next to water bodies or on isles in several lakes in Latvia. The first nests of great cormorant appeared in isles of Lake Kaņieris in 2005. Our study shows how the presence of the great cormorant colonies has affected the vegetation and soil chemical composition on the isles of Lake Kaņieris in a long term (2010–2017). To evaluate the impact of great cormorant colonies on soil and vegetation, the study was carried out on two isles (Ābeļu and Egļu) in Lake Kaņieris occupied by the great cormorant in July of 2010 and 2017. All isles are/were predominantly covered by forest vegetation. Two different sampling sites on each isle were set up: one of them representing a site without vegetation, and the other one – a site with vegetation. The Riekstu Isle in the same lake was selected to represent control conditions – natural habitat without the great cormorant colonies. In the sampling plots, the occurrence and cover of plant species in each vegetation layer was determined visually. Soil reaction (pHKCl), electrical conductivity, content of essential plant nutrients (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu), as well as Na in 1 M HCl extraction were determined at two topsoil layers at 1–10 cm and 11–20 cm depth. The results revealed that the forest stands of the Ābeļu and Egļu Isles have totally changed under continuous input of chemical elements from nutrient-rich guano during the last seven years. The forest stands have lost the typical spatial continuity and layering, the plant species composition has fully changed. The deciduous forest stands are totally degraded. The habitats with extremely high concentration of phosphorus, nitrogen, sulphur, zinc and other elements in soils are no longer suitable for growth of plants. In sites with less intensive input and accumulation of guano from the great cormorants in topsoil, development of nitrophilous plant communities, e.g. establishment of Urtica dioca at the herb layer and Sambucus nigra at the shrub layer was observed.

Latvian. Kopš 2005. gada jūras kraukļu kolonizētās Kaņiera ezera Ābeļu un Egļu salu mežaudzes nepārtrauktas ķīmisko elementu ieneses rezultātā 12 gados ir pilnībā pārmainījušās. Tās ir zaudējušas mežaudzēm raksturīgo telpisko kontinuitāti un stāvojumu, kā arī pilnībā nomainījies augu sugu sastāvs. Platlapju mežaudzes ir degradējušās, to vietā veidojas augu augšanai nepiemēroti neauglīgi klājumi, kuru augsne ir pārsātināta ar fosforu, slāpekli, sēru, cinku u. c. elementiem. Vietās, kur nenotiek tik intensīva jūras kraukļu ekskrementu ienese un akumulēšanās augsnes virskārtā, ir izveidojušās pēc platības nelielas nitrofīlas augu sugas – lielās nātres Urtica dioica – saaudzes, bet krūmu stāvā pamazām ieviešas melnais plūškoks Sambucus nigra.