Natural-born contaminators

Posted on September 26, 2009

By acting as prey for riparian predators such as spiders, birds, bats, reptiles and amphibians, aquatic insects play an important role in the transfer of energy and materials from freshwater to terrestrial food webs.  However, many freshwater streams have a history of pollution: for example, in theU.S.38% of recently surveyed stream sections were listed as ‘‘impaired’’ for fish consumption, mainly due to persistent contaminants such as mercury and polychlorinated biphenyls (PCBs).  Do insects therefore transfer persistent pesticides from impaired streams to the riparian zone?   ASouth Carolinastudy shows that  they do.  Measurements of stable isotope concentrations in fauna from a stream polluted by PCBs were used to clarify feeding pathways, by identifying the prey types taken by different riparian predators.  PCB concentrations were also measured, and were found to be high in several predator species.  Predators that depend heavily on aquatic insects contained the highest PCB levels.  The use of chemical contaminants as tracers of stream-derived energy can help to bridge the gap between reach-scale and landscape-scale studies. 

Reference:   Walters, D.M., Fritz, K.M. & Otter, R.R.  2008.  The dark side of subsidies: adult stream insects export organic contaminants to riparian predators.   Ecological Applications 18(8), 1835–1841.