Deeper insight from shallow waters?

Posted on March 27, 2012

Although lakes are regularly monitored with the aim of maintaining environmental quality, the fact that standard procedures rely heavily on open-water sampling may render them less than ideal for the early detection of pollution.  In low-nutrient lakes, levels of biological production and community diversity are disproportionately high in shallow near-shore habitats, and it’s possible that in the early stages of pollution, nutrients entering a lake are taken up and concentrated near the lake margins, with little or no detectable impact on the deeper offshore waters. Lake Crescentis a low-nutrient lake, about 18 km long and 190 m deep, in the Olympic National Park inWashington,USA.  Food web analysis using stable isotope techniques showed that the top predators (two species of trout) obtained most of their food inshore, in waters shallower than 30 m, even though this zone accounted for only 2.5% of the lake’s volume.  Although residential development bordering the lake was very sparse, growths of rock algae and accumulations of  organic matter were significantly (3-4 times) higher in residential areas than elsewhere, which suggested a fertilization effect.  However, no corresponding signals of human impact emerged from the offshore nutrient data.  These findings support the case for nearshore monitoring in situations where the shoreline is impacted by even modest levels of human activity.  While some human-induced impacts, such as fertiliser runoff or the release of sewage, reduce water quality, others, such as the clearing of waterline vegetation, can have a direct influence on food web structure by slowing the supply of terrestrial insect prey to the inshore zone.

Reference:  Hampton, S.E., Fradkin, S.C., Leavitt, P.R. & Rosenberger, E.E.  2011.  Disproportionate importance of nearshore habitat for the food web of a deep oligotrophic lake.  Marine and Freshwater Research  62, 350–358.