Effects of watershed land use on nitrogen concentrations and δ15 Nitrogen in groundwater

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 77 (2006): 199-215, doi:10.1007/s10533-005-1036-2.Eutrophication is a major agent of change affecting freshwater, estuarine, and marine systems. It is largely driven by transportation of nitrogen from natural and anthropogenic sources. Research is needed to quantify this nitrogen delivery and to link the delivery to specific land-derived sources. In this study we measured nitrogen concentrations and δ15N values in seepage water entering three freshwater ponds and six estuaries on Cape Cod, Massachusetts and assessed how they varied with different types of land use. Nitrate concentrations and δ15N values in groundwater reflected land use in developed and pristine watersheds. In particular, watersheds with larger populations delivered larger nitrate loads with higher δ15N values to receiving waters. The enriched δ15N values confirmed nitrogen loading model results identifying wastewater contributions from septic tanks as the major N source. Furthermore, it was apparent that N coastal sources had a relatively larger impact on the N loads and isotopic signatures than did inland N sources further upstream in the watersheds. This finding suggests that management priorities could focus on coastal sources as a first course of action. This would require management constraints on a much smaller population.This work was supported by funds from the Woods Hole Oceanographic Institution Sea Grant Program, from the Cooperative Institute for Coastal and Estuarine Environmental Technology, from Massachusetts Department of Environmental Protection to Applied Science Associates, Narragansett, RI, as well as from Palmer/McLeod and NOAA National Estuarine Research Reserve Fellowships to Kevin Kroeger. This work is the result of research sponsored by NOAA National Sea Grant College Program Office, Department of Commerce, under Grant No. NA86RG0075, Woods Hole Oceanographic Institution Sea Grant Project No. R/M-40

Effects of Tin on the Physical Properties and Crack Growth in Soda-Lime-Silica Float Glass

The effect of tin on the properties of soda-lime-silica glass was examined with glasses doped with 0.2-3.0-mol % SnO2. Trends in the properties are consistent with an increase in the network connectivity with increasing tin concentration. The difference in the thermo-elastic properties of the tin doped glass suggests the creation of residual stresses in the near surface region of float glass, resulting form the tin concentration gradient during cooling. Two-point fiber bend tests were conducted to determine the effect of tin on the stress corrosion susceptibility of tin doped soda-lime-silica glasses. The results showed the stress corrosion exponent for the tin-doped glasses to be a weak positive function of tin concentration

NMR insights into wasteforms for the vitrification of high-level nuclear waste

Magic-angle spinning nuclear magnetic resonance of B-11, Si-29 and Al-27 has been used to study the distribution of nonbridging oxygen atoms (NBO) in an alkali borosilicate glass to which surrogate oxides for high-level radioactive waste have been added. The properties of such glasses are shown to depend on the fraction N (4) of four-coordinated boron atoms (B4) and on the fraction of silicate tetrahedra possessing one NBO, Q(3). The aqueous corrosion rate increases with Q(3) content, as does weight loss due to evaporation from the melt. The activation energy for direct current conduction scales with N-4. Values of N-4 obtained for these glasses deviate from those predicted by the currently accepted model and are strongly affected by the modifier or intermediate nature of the surrogate oxide and also by its effect on the distribution of NBO between the silicate and borate polyhedra