Browsing by Subject "nitrate"

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A Spatial and Statistical Assessment of the Vulnerability of Texas Groundwater to Nitrate Contamination
(University of Texas at Austin, 1995-11) Evanns, T.A.; Maidment, D.R.
Nitrogen nutrition of Alexandrium tamarense : using δ¹⁵N to track nitrogen source used for growth
(2009-05) Smith, Christa Belle; Erdner, Deana L.; Pease, Tamara Kaye; McClelland, James W.
Alexandrium tamarense is a harmful algal species that can produce saxitoxins, a suite of powerful neurotoxins that bioaccumulate up the food chain and can have severe economic and health impacts. With harmful algal blooms increasing temporally and spatially, it is important for us to understand the relationship between harmful algal blooms and nutrients, particularly nitrogen from anthropogenic sources. To this end, the stable nitrogen isotopic composition (δ¹⁵N) of medium nitrate, algal cells and toxin in both nitrogen-replete and nitrogen-limited batch cultures of A. tamarense were measured in order to assess the potential for using the δ¹⁵N of the toxin as a tracer of the nitrogen source used for growth. A. tamarense cells grown under nitrate-replete conditions were depleted by 1.5‰ relative to the growth medium, and saxitoxin was depleted by 1.5‰ relative to the whole cells. Under nitrate-limiting conditions, the isotopic difference between cells and saxitoxin changed as nitrate in the growth medium was depleted, indicating uncoupling of toxin synthesis and cell growth rates under changing external nutrient conditions. Determination of the absolute magnitude of the isotopic differences between the medium nitrate and either the cells or the saxitoxin was confounded by 1) using two different nitrate sources – one nitrate source was used to grow the inoculum and a different nitrate source was used for the experimental medium - with different ‰ values and 2) the presence of an unidentified, isotopically-light, nitrogen blank in the low-nitrate medium samples. I conclude that STX nitrogen isotope values have the potential to be used as nitrogen source indicators. However, overall fractionation between whole cells and STX is unknown due to the uncoupling between cell growth and STX synthesis observed during my nitrogen-limited experiment. Based on previous research on cell growth and toxin production dynamics under different nutrient regimes, it is also reasonable to assume that the observed results here may differ if a different nitrogen source was utilized by the cells for STX production. Further research could include isotope analysis of cultures grown on different nitrogen sources, such as ammonium and urea; isotopic analysis of additional compounds, such as amino acids; or use of additional stable isotopes, such as C or O.
Options for Community Response to the Safe Drinking Water Act, PRP 35
(LBJ School of Public Affairs, 1979) Eaton, David J.
Water Chemistry of Shoal Creek And Waller Creek, Austin, Texas, and Potential Sources of Nitrate
(U.S Geological Survey, 1996) Ging, Patricia B.; Lee, Roger W.; Silva, Steven R.
Steep limestone slopes, thin soils, sparse vegetation, and impervious cover within the Shoal Creek and Waller Creek watersheds, Austin, Texas, contribute to rapid runoff that can quickly carry contaminants such as nitrate, into the creeks. Land use within the watershed is predominantly residential (single-family and multifamily dwellings). Impervious cover within both watersheds was about 55 percent during 1994 95. Water samples were collected for chemical analysis at seven sites in the Shoal Creek and Waller Creek watersheds from September 1994 to April 1995. Samples were collected during 4 stormflow events and 3 base-flow periods. Water samples were analyzed for major ions and nutrients as well as for nitrogen and oxygen isotopes in the nitrate anion. Concentrations of dissolved constituents, including nitrate, are smaller in stormflow samples than in base-flow samples. Calculated dissolved solids range from 16 to 187 milligrams per liter for stormflow samples and from 213 to 499 milligrams per liter for base-flow samples. Nitrogen and oxygen isotopes in dissolved nitrate in conjunction with water chemistry were used to indicate sources of nitrate in surface water. A combination of atmospheric nitrate, and soil nitrate and ammonium fertilizer is the most likely source of nitrate in stormflow samples (assuming that there is little or no use of synthetic nitrate fertilizers in the watersheds). Nitrogen and oxygen isotopic data in nitrate for stormflow samples are in or near the isotopic composition ranges for atmospheric nitrate, and soil nitrate and ammonium fertilizer sources. Nitrogen and oxygen isotopic data in nitrate for base-flow samples are in or near the isotopic composition ranges for soil nitrate and ammonium fertilizer, and sewage and animal waste sources of nitrate. Sewage is the most likely source of nitrate in base flow because of the potential for older sewer lines to leak, the proximity of sewer lines to creek beds, and an excess of chloride relative to sodium at some sampling sites (an indicator of the presence of sewage) under base-flow conditions. Nitrate in the creeks at any given time is a mixture that results predominantly from surface sources (atmospheric nitrate, soil nitrate and ammonium fertilizer) during stormflow and predominantly from subsurface sources (sewage) during base flow.