IngentaConnect Terrestrial vegetation and the seasonal cycleof dissolved silica ...

Abstract:

The Pawcatuck river watershed (797 km²) is located in southern Rhode Island and northeastern Connecticut. The predominant lithology of the area is granite, and over 60% of the watershed remains forested with mixed hardwoods (primarily oak) and eastern white pine. As part of a larger study of nutrient and sediment exports from the watershed to Little Narragansett Bay, we measured dissolved silica (SiO₂) (DSi) concentrations at the river mouth over 70 times between January 14, 2002 and November 29, 2002. Annual export of DSi during our study was 40 × 10⁶ mol or 50 kmol km^-2. The United States Geological Survey (USGS) obtained DSi concentrations at this site, at varying frequencies, from 1978 to the present, which allowed for a historical comparison of this study with previous years. River DSi concentrations exhibited a strong seasonal signal that did not vary in a regular way with water discharge or water temperature. DSi and dissolved inorganic nitrogen (DIN) concentrations were significantly related over the annual cycle (p<0.0001) and both decreased substantially during the spring. Dissolved inorganic phosphorus (DIP) did not covary at any time with silica or nitrogen, suggesting that in-stream biological uptake was not responsible for the seasonal decline in silica. The spring decline in river silica concentrations may be due to silica uptake by terrestrial vegetation. We estimate a net forest silica accretion rate of 41 kmol km^-2 y^-1, a value that is stoichiometrically consistent with other measurements of net carbon accretion in nearby forests.

Keywords: Little Narragansett Bay; dissolved silica river fluxes; seasonal cycles; watershed export, forest uptake

Document Type: Research article

DOI: 10.1007/s10533-004-2947-z

Affiliations: 1: Graduate School of Oceanography, University of Rhode Island, Narragansett, 02882-1197, USA, Email: wally@gso.uri.edu 2: Graduate School of Oceanography, University of Rhode Island, Narragansett, 02882, USA,

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Terrestrial vegetation and the seasonal cycleof dissolved silica in a southern New Englandcoastal river