Influence of perennial colonies of piscivorous birds on soil nutrient contents in a temperate humid climate

Abstract

During the last decades, the number of perennial colonies of piscivorous<br/>birds especially cormorant colonies in North-western Europe<br/>has grown rapidly due to protection. Their impact on vegetation<br/>has been recognized, as many trees containing perennial colonies<br/>of piscivorous birds have collapsed, but the bird’s influence on the<br/>soil conditions has only in few cases been studied in detail. In this<br/>study the influence of perennial colonies of piscivorous birds on soil<br/>nutrient contents and accumulation of carbon, nitrogen and phosphorus<br/>in a humid climate has been determined by measuring pH,<br/>electric conductivity and content of carbon, nitrogen, phosphorus,<br/>calcium and potassium in a reference area and in two cormorant<br/>sub-colonies. In general, the soils exposed to cormorant guano had<br/>lower pH and higher contents of plant available phosphorus, calcium<br/>and potassium compared to the control reference soil, especially in<br/>the top horizons, and the magnitude of increase in nutrient content<br/>varied with the bird-dropping density and the age of the colony. In<br/>addition, soil influenced by cormorants had a higher electric conductivity<br/>compared to the control reference and can be classified as<br/>saline soils. Under influence of the cormorants the herb vegetation<br/>below the nesting areas has been changed.