Application of Nitrogen Stable Isotopes to Identify Sources of Nutrient Pollution PDF Download

Author: Elizabeth A. Redon
Publisher:
ISBN:
Category : Nitrogen
Languages : en
Pages : 196

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Book Description
Nutrient pollution may perhaps be one of the oldest water quality problems and has recently been considered as one of the greatest threats to estuarine and coastal waters. Excessive nutrient loads have had a vast array of impacts on estuarine and coastal ecosystems globally. Direct negative effects include: shading out of benthic plant communities, hypoxia and anoxia due to increased biological oxygen demand, compositional change in plant and fauna! community structure and increased occurrences of harmful algal blooms. This has lead to decreased biodiversity, habitat, fisheries, tourism and aesthetics. So far environmental managers have had to rely on a posteriori assessments of the status of nutrient pollution, using indicators such as taxonomic shifts and changes in biological abundance, which have already occurred. By the time nutrient pollution is detected, restoration of habitats is costly and sometimes no longer an option. Therefore, there is a need for management tools to assess sources of nutrient loads before damage to estuarine and coastal ecosystems progresses beyond recovery. Early work using stable isotopes of dissolved inorganic nitrogen in groundwater samples demonstrated the potential for using stable isotopes to identify anthropogenic sources of nitrogen. These studies revealed that nitrogen sources such as fertilizers, soil organic nitrogen and wastewater nitrogen have isotopically distinct signatures that could be used to assess anthropogenic nitrogen contributions. Therefore, application of nitrogen stable isotope methods could potentially provide information on the anthropogenic nitrogen sources stimulating nutrient pollution in estuarine and coastal waters. However, when I assessed this approach for application, two sources of errors became apparent. First, laboratory isolation of dissolved inorganic nitrate from seawater delivered results depleted in 15N relative to the standard used to assess the method. Second, isotopic fractionation associated with nitrogen cycle processes complicates usage of an isotopic mass balance to solve for the nitrogen source and its fractional contribution based on isotopic data alone. As a result, isotopic analysis alone of dissolved inorganic nitrogen to determine anthropogenic sources of nutrient loads to estuarine and coastal waters is not a practical approach to obtain management information concerning nutrient pollution.