Subsidising land ecosystems

Posted on December 9, 2010

Although energy and nutrients are involved in continual two-way exchange between freshwater and terrestrial ecosystems, most research has  focussed on transfers from the land to the water, and conceptual models of the transfer of aquatic production to terrestrial habitats have been lacking.  In this connection, insect species are of particular interest because many insects have aquatic larval stages but switch to terrestrial habitats when they become adult.  An ecosystem transfer model has been constructed which incorporates (a) measurements of insect production in lakes and streams, (b) estimates of insect flux between water and land (expressed as the amount of annual production leaving the water per metre of shoreline), and (c) equations that describe a rapid decline in density as insects disperse away from the water.  The model indicates that average-sized (10 ha) lakes contribute levels of secondary production that approach those typical of tundra and desert ecosystems, while larger (1300 ha) lakes and large (16 m wide) streams make contributions at rates similar to those of more productive terrestrial ecosystems such as grasslands.  These estimates indicate  that the transfer of production from water to land is high enough to have a significant influence on terrestrial ecosystem processes. 

Reference:  Gratton, C. & Vanderzanden, J.  2009.  Flux of aquatic insect productivity to land:  comparison of lentic and lotic ecosystems.  Ecology, 90(10), 2689–2699.