Abstract. Myriad studies have shown the extent of human alteration to global biogeochemical cycles. Yet, there is only a limited understanding of the influence that humans have over silicate weathering fluxes; fluxes that have regulated atmospheric carbon dioxide concentrations and global climate over geologic timescales. Natural landscapes have been reshaped into agricultural ones to meet food needs for growing world populations. These processes modify soil properties, alter hydrology, affect erosion, and consequently impact water-soil-rock interactions such as chemical weathering. Dissolved silica (DSi), Ca2+, Mg2+, NO3−, and total alkalinity were measured in water samples collected from five small (0.65 to 38.3 ha) gauged watersheds at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio, USA. The sampled watersheds in this unglaciated region include: a forested site (70+ yr stand), mixed agricultural use (corn, forest, pasture), an unimproved pasture, tilled corn, and a recently (<3 yr) converted no-till corn field. The first three watersheds had perennial streams, but the two corn watersheds only produced runoff during storms and snowmelt. For the perennial streams, total discharge was an important control of dissolved silicate transport. Median DSi yields (22.1–30.8 kg ha−1 a−1) were similar to the median of annual averages between 1979–2009 for the much larger Ohio-Tennessee River Basin (25.6 kg ha−1 a−1). Corn watersheds, which only had surface runoff, had substantially lower DSi yields (<5.3 kg ha−1 a−1) than the perennial-flow watersheds. The lack of contributions from Si-enriched groundwater largely explained their much lower DSi yields with respect to sites having baseflow. A significant positive correlation between the molar ratio of (Ca2+ + Mg2)/alkalinity to DSi in the tilled corn and the forested site suggested, however, that silicate minerals weathered as alkalinity was lost via enhanced nitrification resulting from fertilizer additions to the corn watershed and from leaf litter decomposition in the forest. This same relation was observed in the Ohio-Tennessee River Basin where dominant landuse types include both agricultural lands receiving nitrogenous fertilizers and forests. Greater gains in DSi with respect to alkalinity losses in the Ohio-Tennessee River Basin than in the NAEW sites suggested that soils derived from younger Pleistocene glacial-till may yield more DSi relative to nitrogenous fertilizer applications than the older NAEW soils. Because silicate weathering occurs via acids released from nitrification, CO2 consumption estimates based on the assumption that silicate weathers via carbonic-acid alone may be especially over-estimated in fertilized agricultural watersheds with little baseflow (i.e. 67% overestimated in the corn till watershed). CO2 consumption estimates based on silicate weathering may be as much as an average of 8% lower than estimates derived from carbonic acid weathering alone for the Ohio-Tennessee River Basin between 1979–2009.
view Abstract Citations (13) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrogen-deficient atmospheres for cool carbon stars. Johnson, H. R. ; Alexander, D. R. ; Bower, C. D. ; Lemke, D. A. ; Luttermoser, D. G. ; Petrakis, J. P. ; Reinhart, M. D. ; Welch, K. A. ; Goebel, J. H. Abstract Motivated by recent work which hints at a possible deficiency of hydrogen in non-Mira N-type carbon stars and to further explore the parameter space of chemical composition, computations have been made of a series of hydrogen-deficient models for carbon stars. For these models Teff = 3000 K, and log g = 0.0. Solar abundances are used for all elements except for carbon (which is enhanced to give C/O = 1.05), hydrogen, and helium. As the fractional abundance of hydrogen is decreased, being replaced by helium, the temperature-optical depth relation is affected only slightly, but the temperature-pressure relation is changed. The most striking change in the emergent flux is the decrease of the H(-) peak at 1.65 micron compared with the blackbody peak at 1.00 micron. Publication: The Astrophysical Journal Pub Date: May 1985 DOI: 10.1086/163151 Bibcode: 1985ApJ...292..228J Keywords: Carbon Stars; Cool Stars; Hydrogen; Stellar Atmospheres; Stellar Composition; Abundance; Atmospheric Composition; Atmospheric Models; Stellar Spectrophotometry; Astrophysics full text sources ADS | data products SIMBAD (1)
Mercury (Hg) can be emitted to the air from Hg-enriched and unenriched substrates, as well as deposited to terrestrial surfaces from the air as wet and dry deposition and subsequently re-emitted. The relative magnitude of these processes is important to understand for developing regional and global biogeochemical mass balances, and assessing the effectiveness of regulatory controls. Mercury emissons often follow a diel pattern with emissions highest during midday. Light is thought to be a dominant parameter driving emissions with temperature, atmospheric turbulence and precipitation all demonstrated to exert some control. This paper presents new insights into other parameters important in controlling Hg air- substrate exchange. Recent work has shown that soil moisture content and atmospheric ozone signficantly enhance Hg emissions from enriched and unenriched substrates. Evaporation of moisture from soils is also thought to be an important process whereby Hg within the soil column is transported by mass flow to the soil-air interface. It has been suggested that with increasing anthropogenically derived atmospheric oxidants in the air Hg emission from soils may increase. Little work has been done to investigate the potential for dry deposition of elemental Hg to soils and the potential for re-emission of Hg deposited by dry or wet processes. Field and laboratory studies have shown that elemental Hg is dry deposited to substrate. Laboratory experiments have shown that factors controlling deposition include air Hg concentrations, dark versus light conditions, soil pH, and atmospheric chemistry. Data from a field experiment using stable Hg isotopes amended in a simulated light rain event to desert soils indicated that HgCl2 is not rapidly re-emitted.
Issyk‐Kul Lake is one of the largest brackish water lakes in the world. Being a closed‐basin lake, it is susceptible to volume changes caused by natural climatic variability, as well as human‐induced water diversion from the basin. Long‐term lake level records indicate that lake levels are declining and that salinity is increasing because of evapoconcentration. We present the first trace element data for this important lacustrine system and, using both ours and previously published data, investigate the geochemical dynamics within the watershed.
