Double-crested Cormorant guano impacts on the nitrogen chemistry and forest composition of two island ecosystems in the Great Lakes.

Abstract

Redistribution of allochthonous nutrients from the aquatic zone to adjacent terrestrial habitats can lead to inputs of limiting nutrients especially nitrogen resulting in a fertilization effect. Currently controversy over the Double-crested Cormorants impacts on fish consumption and terrestrial ecosystem alterations ia a topic of great debate. The data from this research shows that cormorants have increased 15N in the O horizon soil and plant biomass as well as %N in foliage of at two nearby islands in Lake Michigan. Furthermore I found that as a result of increased N inputs C:N ratios were lowered in former and current nesting locations. The opposite trend was observed in an undisturbed region of one of the islands. Recently management implementations have been put into place to reduce potential impacts of cormorants in the Great Lakes region. However, very little is known and even less formal research has been gathered in order to fully understand the more subtle ecosystem interactions and process of this phenomenon.