Reversible effects of fertilizer use on population trends of waterbirds in Europe

Abstract

Nutrients are often limiting primary productivity, and fertilizer use by agriculture increases primary and secondary productivity in marine environments. High levels of eutrophication due to fertilizer use can have negative effects on the distribution and the abundance of many organisms including waterbirds inhabiting freshwater and marine wetlands. Because nutrients, in particular phosphorus, can be stored in sediment, reversal of effects of eutrophication can take considerably longer time than the period during which effects of eutrophication build up. We quantified the effects of fertilizer use on 50 species of freshwater and coastal waterbirds monitored across Europe during 1982–2008 during the increase and the decrease phase of fertilizer use. More species were negatively affected by fertilizer use, and use of marine habitats during winter was the single-most important predictor of negative trends. The relative effect of fertilizer use on abundance of waterbird species was consistent during the increase and the decrease phase of fertilizer use. The effects of fertilizer use were statistically independent of the effects of climate change. Reversal of the effect of fertilizer use on population trends of waterbirds was almost three times as slow as the build-up of effects of nutrients on population size. These findings have management implications for the extent and the duration of fertilizer policies at local, national and international levels since these policies will partly determine the population trends and the population sizes of waterbirds.