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INLAND DISSOLVED SALT CHEMISTRY: STATISTICAL EVALUATION OF BIVARIATE AND TERNARY DIAGRAM MODELS FOR SURFACE AND SUBSURFACE WATERS
Citation:
Baca, R M. AND S. T. Threlkeld. INLAND DISSOLVED SALT CHEMISTRY: STATISTICAL EVALUATION OF BIVARIATE AND TERNARY DIAGRAM MODELS FOR SURFACE AND SUBSURFACE WATERS. JOURNAL OF LIMNOLOGY 59(2):156-166, (2000).
Impact/Purpose:
This research project sets out to design and conduct an assessment of the long-term ecological consequences of alternative management choices. As the first project to be done at this scale using predictive ecological endpoints, we will seek to identify the appropriate components of such an analysis. We will use experience gained in the conduct of this BASE analysis to identify key research and data needs for address, to estimate timing, resource needs, etc., for future analyses. We will extend this analysis beyond previous and ongoing studies in two ways: by incorporating biological endpoints, primarily properties of fish communities, and by introducing the concept of sustainability of ecological state under future scenarios contrasted with the present state of those same ecological resources. Requirements that are identified during the course of this study will permit the recommendation of specific capabilities that should be incorporated in a general modeling system currently under development to support BASE and other environmental assessments. Finally, the analysis is intended to be of value for establishing environmental management choices that will be beneficial and those that would be detrimental to the sustainability of ecological resources of the Albemarle-Pamlico Basin.
Description:
We compared the use of ternary and bivariate diagrams to distinguish the effects of atmospheric precipitation, rock weathering, and evaporation on inland surface and subsurface water chemistry. The three processes could not be statistically differentiated using bivariate models even if large water bodies were evaluated separatefrom small water bodies. Atmospheric precipitation effects were identified using ternary diagrams in water with total dissolved salts (TDS) <25 mg r' dominated by SO4(-2), Ca(+2) and (Na+ + K), though water whose inorganic chemistry was dominated by atmosfheric precipitation were few. Waters affected by weathering had TDS of 15 to 1, 000 mg and were dominated by (HC03- + CO 3(-2) and Ca(+2). The effects of rock weathering on ion chemistry were the dominant mechanism influencing water chemishy. The contribution ofsilicates, carbonates, and evaporites to ions in weathering were distinguished using ternary diagrams. Weathering of silicates was evident in low TDS waters, while weathering of carbonates and evaporites was evident in moderate and high TDS waters, respectively. Evaporation effects were first obvious in water around 1, 000 mg TDS as a shift towards higher S04(-2), Cl, and (Na+ + K+). At higher TDS, Cl became the dominant anion while (Na+ + K+) remained the dominant cation. The general patterns were consistent in lakes, rivers, and subsurface water bodies, although sub- surface waters did not show an influence due to ionsfrom atmospheric precipitation. While several of the TDS size classes separated statistically into distinct groups, there was wide variation in the pattern of inorganic ions within a TDS size class, especially when TDS > 1000 mg. A principal components analysis showed that the variability in the relative proportions of the major ions was related to atmospheric precipitation, weathering, and evaporation. About half of the variation in the distribution of inorganic ions was related to rock weathering. By considering most of the important inorganic ions, ternary diagrams are able to distinguish the contributions of atmospheric precipitation, rock weathering, and evaporation to inland water chemishy.