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Nutrient Chemistry and Microbial Activity in the Upper Mississippi River Basin: Stoichiometry and Downstream Patterns
Citation:
HILL, B. H., C. M. ELONEN, T. M. JICHA, AND D. W. BOLGRIEN. Nutrient Chemistry and Microbial Activity in the Upper Mississippi River Basin: Stoichiometry and Downstream Patterns . Presented at American Water Resources Association Annual Meeting, New Orleans, LA, November 17 - 20, 2008.
Impact/Purpose:
Studies on the Mississippi River have concluded that N enrichment and stable or declining Si concentrations have disrupted algal ecology and food-webs of the Gulf of Mexico.
Description:
Nutrients, carbon, and silica have been used to track changes in water quality in the major rivers of the world. Most studies focus on the mouths of rivers and adjacent coastal waters. Studies on the Mississippi River have concluded that N enrichment and stable or declining Si concentrations have disrupted algal ecology and food-webs of the Gulf of Mexico. We present data from a synoptic survey of rivers of the major sub-basins within the Upper Mississippi River basin. These data were collected as a part of the US EPA's EMAP assessment of the Great Rivers of the Central United States. Water and sediment chemistry, and sediment microbial respiration and extracellular enzymes activity (EEA), were collected from 447 sites between 2004 and 2006. The waters of the Upper Mississippi River had the highest N, P and Si concentrations; the Missouri had the lowest N concentrations; and the Ohio had the lowest C and P concentrations. Sediment chemistry was less predictable, with the Mississippi having the highest P concentrations, while the Missouri and the Ohio had the highest N and C concentrations, respectively. Concentrations of water column and sediment nutrients generally increased with downstream distance, with the notable exceptions of a lack of downstream trend for most chemical constituents in the Upper Mississippi. Canonical correlation revealed significant relationships between water chemistry and watershed land use and atmospheric deposition. No significant correlations were found for sediment chemistry. Microbial respiration and EEA were higher in the Mississippi and Missouri Rivers than in the Ohio, with the exception of phosphatase activity, which was higher in the Ohio. Canonical correlation also revealed significant relationships between EEA and water and sediment chemistry. Nutrient stoichiometry (C:N, C:P, N:P, Si:N. Si:P) showed significant inter-river patterns, and significant downstream decreases in all rivers. Stoichiometry suggests the Mississippi is both N- and Si-enriched; the Missouri is N-limited and Si-enriched; and the Ohio is P-limited. Stoichiometry based on microbial EEA weakly reflected these nutrient limitations and/or enrichments.