Longitudinal assessment of the effect of concentration on stream N uptake rates in an urbanizing watershed

• Published in: Biogeochemistry Vol. 98; no. 1-3; pp. 63 - 74
• Main Authors: Claessens, Luc, Tague, Christina L, Groffman, Peter M, Melack, John M
• Format: Journal Article
• Language: English
• Published: Dordrecht Dordrecht : Springer Netherlands 01.04.2010; Springer; Springer Netherlands; Springer Nature B.V
• Subjects: Addition; ammonium nitrogen; aquatic organisms; Barns; Biogeochemistry; Biogeosciences; Biological effects; Biological uptake; carbon; Dilution; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecosystems; Environmental Chemistry; Exact sciences and technology; forested watersheds; Geochemistry; Headwaters; hydrochemistry; Hydrology; Hydrology. Hydrogeology; Life Sciences; Lotic systems; Maryland; Mineralogy; nitrate nitrogen; Nitrogen; Nutrient concentrations; Nutrient uptake; Nutrients; Residential development; Rivers; Silicates; Size effects; Solutes; stream channels; Stream water; Streams; suburban areas; summer; Urban development; Water geochemistry; Watershed management; Watersheds; Baltimore County Maryland; United States; Maryland; USA, Maryland; Nutrient additions; Nitrogen; Nutrient saturation; Streams; experimental studies; stream transport; models; nitrogen; river discharge; streams; concentration; drainage patterns; velocity; loading; drainage divide; nitrates; North America; forests; urbanization; ammonium ion; nutrients; saturation; drainage basins; channels; dilution; carbon
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-009-9376-y

We examined the effect of concentration on nitrogen uptake patterns for a suburban stream in Maryland and addressed the question: How does NO₃ ⁻ uptake change as a function of concentration and how do uptake patterns compare with those found for NH₄ ⁺? We applied a longitudinal (stream channel corridor) approach in a forested stream section and conducted short-term nutrient addition experiments in late summer 2004. In the downstream direction, NO₃ ⁻ concentrations decreased because of residential development in headwaters and downstream dilution; NH₄ ⁺ concentrations slightly increased. The uptake patterns for NO₃ ⁻ were very different from NH₄ ⁺. While NH₄ ⁺ had a typical negative relationship between first-order uptake rate constant (K c ) and stream size, NO₃ ⁻ had a reverse pattern. We found differences for other metrics, including uptake velocity (V f ) and areal uptake rate (U). We attributed these differences to a stream size effect, a concentration effect and a biological uptake capacity effect. For NO₃ ⁻ these combined effects produced a downstream increase in K c , V f and U; for NH₄ ⁺ they produced a downstream decrease in K c and V f , and a not well defined pattern for U. We attributed a downstream increase in NO₃ ⁻ uptake capacity to an increase in hyporheic exchange and a likely increase in carbon availability. We also found that K c and V f were indirectly related with concentration. Similar evidence of ‘nutrient saturation' has been reported in other recent studies. Our results suggest that higher-order uptake models might be warranted when scaling NO₃ ⁻ uptake across watersheds that are subject to increased nitrogen loading.