HR: 0800h
AN: B31A-0979    [Abstracts]
TI: Rivers and Stable Isotopes as Indicators of Biogeochemical Gradients
AU: * Barth, J A
EM: johannes.barth@uni-tuebingen.de
AF: University of Tuebingen, Center for Applied Geoscience / Sigwartstr. 10 , Tuebingen, D 72076 Germany
AB: Consideration of processes on very small (microbe) to large (catchment) scales become increasingly important in biogeochemical gradient work. In this context, rivers are ideal indicators of biogeochemical gradients for large continental scales when geochemical- and discharge data are combined for flux evaluations. If these are further combined with isotope measurements, sources and turnover of water and dissolved constituents can be quantified. An example study is the combination of GIS-, discharge- and water stable isotope data on the in Clyde River basin in Scotland. Here we determined transpiration with an annual average of 0.489 km³ a^-1. When combining this rate with the water use efficiency, the CO₂ uptake of the entire basin yielded an annual net primary production (NPP) of 185.2 g C m^-2. Compared to other temperate areas this is about half the NPP than expected, which is most likely caused by the predominant cover of grasslands. Therefore, agricultural and forest vegetation schemes could influence continental water balances on time scales of years to decades. In another study on the Lagan River in N. Ireland, stable isotope methods were applied to evaluate the role of carbonate versus silicate dissolution. Of these two types of weathering only silicate dissolution withdraws atmospheric CO₂ to be stored in the continental crust over long time periods. A downstream evolution with increasing pH- and δ¹³C_DIC values revealed carbonate dissolution despite their minor abundance in the catchment of less than 5 %. This dominant carbonate signal on the riverine carbon cycle outlines the capacity of buffering anthropogenic influences and CO₂ turnover. It should be even more pronounced in other rivers where carbonates usually occupy a larger proportion of the basin geology. Future biogeochemical gradient work on rivers should apply particulate and dissolved organic constituent fluxes. This includes more refined compound specific isotope work on selected pollutants such as TCE, PAH, PCB as well as riverine microbiological considerations. Such expansions meet the challenge of measuring much smaller concentrations compared to groundwater contaminant plumes. Further combinations of stable N, H, O, and S isotope systems would also help to resolve overlapping trends when only carbon isotopes are measured. Apart from combining traditional light stable isotope systems, addition of newly accessible isotope groups by multicollector ICP-MS (i.e. Fe, Cr, Zn) and radioisotope techniques can provide innovative tools for resolving gradients and their biogeochemical cycling within rivers.
DE: 0400 BIOGEOSCIENCES
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
SC: Biogeosciences [B]
MN: Fall Meeting 2005