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Estimating suspended sediment and trace element fluxes in large river basins: Methodological considerations as applied to the NASQAN programme

Hydrological Processes

By:
, ,
DOI: 10.1002/hyp.206

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Abstract

In 1994, the NASQAN (National Stream Quality Accounting Network) programme was redesigned as a flux-based water-quality monitoring network for the Mississippi, Columbia, Colorado, and Rio Grande Basins. As the new programme represented a departure from the original, new sampling, processing, analytical, and data handling procedures had to be selected/developed to provide data on discharge, suspended sediment concentration, and the concentrations of suspended sediment and dissolved trace elements. Annual suspended sediment fluxes were estimated by summing daily instantaneous fluxes based on predicted suspended sediment concentrations derived from discharge-based log-log regression (rating-curve) models. The models were developed using both historical and current site-specific discharge and suspended sediment concentrations. Errors using this approach typically are less than ?? 10% for the 3-year reporting period; however, the magnitude of the errors increases substantially for temporal spans shorter than 1 year. Total, rather than total-recoverable, suspended sediment-associated trace element concentrations were determined by direct analysis of material dewatered from large-volume whole-water samples. Site-specific intra- and inter-annual suspended sediment-associated chemical variations were less (typically by no more than a factor of two) than those for either discharge or suspended sediment concentrations (usually more than 10-fold). The concentrations, hence the annual fluxes, for suspended sediment-associated phosphorus and organic carbon, determined by direct analyses, were higher than those determined using a more traditional paired, whole-water/filtered-water approach (by factors ranging from 1.5- to 10-fold). This may be important for such issues as eutrophication and coastal productivity. Filtered water-associated (dissolved) trace element concentrations were markedly lower than those determined during the historical NASQAN programme; many were below their respective detection limits. This resulted from the use of clean sampling, processing, and analytical protocols. Hence, the fluxes for filtered water-associated (dissolved) Ag, Pb, Co, V, Be, Sb, and Se, as well as the total (filtered water plus suspended sediment-associated) fluxes for these constituents, could not be estimated.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Estimating suspended sediment and trace element fluxes in large river basins: Methodological considerations as applied to the NASQAN programme
Series title:
Hydrological Processes
DOI:
10.1002/hyp.206
Volume
15
Issue:
7
Year Published:
2001
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Hydrological Processes
First page:
1107
Last page:
1132
Number of Pages:
26