Waterbird numbers & fertilizer use

Posted on March 23, 2016

Nutrients applied as fertiliser to farmland leach into rivers and streams and are transported to coastal waters, where concentrations of nitrogen and phosphorus are now respectively ten and three times higher than in pre-industrial times. While moderate rises in nutrient availability can have beneficial impacts on aquatic production, excessive nutrient levels lead to the eutrophication of rivers, lakes and estuaries, with an associated depletion of available oxygen, the proliferation of blue-green algae and microbes, and the loss of animal species. Researchers examined how historical changes in the rate of fertiliser application to farmland have affected populations of aquatic consumers by relating population data from the International Waterbird Census (carried out across Europe in the winters of 1982-2008) to fertiliser use in the European Union over the same period. They found that the effect of fertiliser use on bird abundance varied significantly with species. Populations of most species declined as fertiliser use increased, the species showing the strongest reductions being Eurasian spoonbill, greylag goose, gadwall, golden plover and pink-footed goose. In contrast, fertiliser use led to population growth in species such as scaup, pochard, oystercatcher, Bewick’s swan and purple sandpiper. Species showing a positive relationship with fertiliser use tend to winter in marine habitats more often than those showing a negative relationship, and it’s been suggested that species in the first group have a greater preference for eutrophic water. Rates of fertiliser use on European farms increased steadily through most of the twentieth century, but have been falling since about 1990 due to changes in agricultural policy. However, ecosystem responses to recent declines in fertilizer use have been relatively sluggish, being about three times slower than rates of change in the build-up phase, presumably because of the time required to deplete phosphorus stored in aquatic sediments. Therefore, policies to reduce the impacts of eutrophication on bird populations are unlikely to have significant effects in the short term.

Reference: Moller, A.M. & Laursen, K. 2015. Reversible effects of fertilizer use on population trends of waterbirds in Europe. Biological Conservation 184, 389–395. https://www.researchgate.net/publication/273398363_Reversible_effects_of_fertilizer_use_on_population_trends_of_waterbirds_in_Europe