Impacts of land use and water quality on organic matter dynamics and secondary production in floodplain wetlands

"September 2009".

Project Number: Impacts of land use and water quality on organic matter dynamics and secondary production in floodplain wetlands - M/BUS/260.

MDFRC item.

The lower Murrumbidgee (lowbidgee) floodplain is a nationally important floodplain system, recognised for important river red gum and lignum vegetation communities, bird breeding events, and important habitat for the endangered southern bell frog. The floodplain has been extensively modified through past and present land use practises (including grazing, cropping and timber harvesting) which have altered flood regimes and vegetation communities. These land use practices may have altered ecosystem functioning and trophic dynamics in floodplain wetlands through changes to the quality and quantity of the organic matter resources forming the basis of the food web. This project aimed to determine how land use on the lowbidgee floodplain has altered trophic dynamics in wetlands through changes in resource quantity and quality. This was done by determining the type and quality of organic matter being incorporated into the wetland food web, using stable isotope and stoichiometric analysis. The results indicated that: wetland food webs on the lowbidgee appear to be influenced by the presence of vegetation on the adjacent floodplain, which provided a source of energy in some wetlands, and macrophyte biomass which provided a substrate for the development of the major food source - biofilm - in one wetland; contrary to other studies, resource quality was not related to nutrient enrichment, indicating that land use activities which alter nutrient dynamics alone may not impact the nutritional requirements of consumers; and land use intensity appears to impact the nutritional value of food sources for particular invertebrate functional feeding groups – for example, the nutritional value of leaf litter to detritivore shredders increased with increasing land use intensity, whereas for other taxa there was no clear relationship between land use and resource nutritional value. The project has assisted the Department of Environment and Climate Change and Water’s, NSW Rivers Environmental Restoration Program (RERP) in the characterisation of lowbidgee wetlands. This will enable the prioritisation of watering for wetlands which provide high quality resources to aquatic consumers and enable better understanding of the impacts of land use on ecosystem functioning so that decisions about watering events on private properties may be done with more confidence of achieving the desired outcomes.