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A stable isotope approach for the early detection and identification of N loading in aquatic ecosystems
Expanded Title:Excessive nitrogen loads in aquatic ecosystems are the result of increased urbanization and anthropogenic activity within watersheds and catchment areas. Increased nitrogen loading can result in widespread aquatic ecosystem degradation including: harmful algal blooms, increased turbidity, hypoxia, loss of aquatic vegetation and habitat and fish kills. Nitrogen loading is also one of the mechanisms driving aquatic weed invasions. Understanding the fate and processing of anthropogenic nutrients in natural systems is therefore critical for both preserving the well-being and biotic heritage for future generations as well as providing a tremendous opportunity to improve ecosystem management driven by science. This study set out to evaluate the feasibility of mapping anthropogenic pollution through stable isotopes signatures of aquatic plants and to investigate the potential for identifying different pollution sources, concentrations and distributions in a freshwater environment. Through the use of Spirodella sp. as an indicator species, results indicate that nitrogen mapping, water quality monitoring, and the identification of pollution hotspots can be easily and quickly done. Spirodella sp. clearly differentiated between different nutrient types within four days of exposure and established that, not only do plants demonstrate concentration level isotope relationships, but transplanted individuals will reflect nutrient loading in a natural environment This technique, of placing organisms into the field to monitor changes in nutrient status within a system, has rarely been used in South Africa and has great potential for identifying pollution sources, concentrations and distributions within aquatic ecosystems. However, the application is still in its infancy and will require further fine-tuning. This technique needs to be field tested on a larger scale over a number of well-defined nutrient gradients and further investigation into local/regional variation in nutrient sources needs to be completed. Additional laboratory studies, to disentangle the effects of iron limitation on nutrient uptake with respect to isotope signatures, may also provide insights into nutrient dynamics of eutrophic systems. This technique may address the identification of causes of degrading ecosystems and aquatic weed invasions, to the benefit of water resource managers.
Date Published:01/10/2011
Document Type:Research Report
Document Subjects:Ecosystem - Biodiversity protection
Document Keywords:Water Quality
Document Format:Report
Document File Type:pdf
Research Report Type:Consultant
WRC Report No:KV 280/11
ISBN No:978-1-4312-0163-1
Authors:Hill JM; Kaehler S; Hill MP; Coetzee J
Project No:K8/786
Originator:WRC
Organizations:Department of Zoology and Entomology, Rhodes University; Department of Botany, Rhodes University
Document Size:1 329 KB
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