Accumulation of nutrients in soils affected by perennial colonies of piscivorous birds with reference to biogeochemical cycles of elements

The accumulation of selected N, K, and P forms in soils within three perennial colonies of black cormorant (Phalacrocorax carbo sinensis) and grey heron (Ardea cinerea) located in northern and eastern Poland were investigated. Soil samples were collected beneath the nests from the most representative for each colony plots. Control samples were taken outside the colonies within sites adjacent to the nesting areas but not affected by bird excrement. From each genetic horizon (20 horizons) in soil profiles, a cumulative sample of about 25–30 kg of soil was taken for analysis. Nitrogen by Kjeldahl, ammonium ions (NNH4), nitrates (NNO3), exchangeable potassium (Kex), available potassium (Kav), and available phosphorus (Pav) were determined. The soils affected by birds demonstrated a very strong enrichment with N, K, and P in comparison to the control sites, especially in the topsoil horizons. The content of NNH4 in individual soil horizons from the colonies was from 1.7 to 10.1 times higher than the respective control, NNO3 from 2.9 to 215.7, Kex from 2.0 to 35.1, Kav from 1.1 to 48.1, and Pav in the range from 2.4 to 53.0 times. The highest increment of chemical elements was noticeable in the soils of territories inhabited by cormorants and the least in forest occupied by herons. Some relationships between soil texture and accumulation of biogenic nutrients were determined. Clay loam soil showed the greatest enrichment with analysed forms of elements with the exception of NNH4.