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Pollution mapping in freshwater systems: using aquatic plants to trace N-Loading
Expanded Title:The global degradation of both marine and freshwater ecosystems is primarily driven by the excessive addition of anthropogenic nutrients to watersheds. Increased nitrogen loading, for example, can result in widespread ecosystem deterioration and may include harmful algal blooms, large scale fish kills, hypoxia, the loss of aquatic vegetation and habitat, loss of biodiversity, disruption of ecosystem functioning and the establishment of invasive species. Reactive nitrogen inputs (N) stem from intensive agricultural land use, resulting in the increased use of N-containing organic and inorganic fertilizers and/or animal manure and their consequent run-off and the discharge of human sewage. In recent years, aquatic ecosystem health has been monitored using a number of techniques, of which the most widely applied in South Africa is the South African Scoring System (SASS5; Dickens and Graham, 2002). Bio-monitoring, however, typically identifies eutrophication problems only after ecosystem-level impacts have already occurred and where ecosystem health has been disrupted, it is often not possible to link biotic changes to identifiable causes (especially in the case of non-point source pollution). Any methods that would allow for the detection of emerging eutrophication which can also trace and identify nutrient sources would greatly improve our ability to effectively manage our aquatic resources. High loads of nitrogen are often associated with enriched δ15N values of aquatic vegetation relative to pristine conditions and consequently may act as early warning indicators of nitrogen pollution in aquatic ecosystems, prior to the onset of system degradation. Using stable isotopic values of indicator plants in a particular catchment, it is often possible to determine both the spatial source and the composition of nitrogen sources. This technique, referred to as sewage plume mapping, has been used in numerous countries to identify and map the sources, dilution and sinks of nutrients in aquatic ecosystems. The baseline work for calibrating isotopic responses for the indicator organism Spirodela sp. in response to nutrient concentrations was completed in WRC Report No. KV 280/11 (Hill et al., 2011) and Hill et al. (2012), during which they identified the need for intensive fields tests of the sewage plume mapping technique in the natural environment. OBJECTIVES The primary aim of this study was to evaluate the potential of sewage plume mapping for the monitoring of water quality in natural systems. Long term field testing on the New Years- Bushmans River in the Eastern Cape of South Africa, allowed the mapping of in-situ N dynamics over a period of 13 months, to assess its applicability for the assessment of ecosystem health, the monitoring of temporal variability in N loading, and the identification of incipient eutrophication.
Date Published:01/04/2015
Document Type:Research Report
Document Subjects:Ecosystem - Invertebrates
Document Keywords:Environment, Water Quality
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:2262/1/15
ISBN No:978-1-4312-0653-7
Authors:Hill JM; Motitsoe SN; Hill MP
Project No:K5/2262
Originator:WRC
Organizations:Rhodes University
Document Size:764 KB
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