Tuesday, May 27, 2008
202

Variation in macrophyte nutrient content and biomass across a range of nutrient enrichment in the portneuf river

Flint A. Raben, Dept. of Biological Sciences, Idaho State University, 921 S. 8th Ave, Pocatello, ID 83202-8007, Andrew M. Ray, Idaho Department of Environmental Quality, 444 Hospital Way #300, Pocatello, ID 83201, and Amy M. Marcarelli, Center for Ecological Research and Education, Department of Biological Sciences, Idaho State University, 921 S. 8th Ave, Pocatello, ID 83202-8007.

We used the submerged macrophyte Potamogeton pectinatus to test whether variation in nitrogen (N) and phosphorus (P) content of macrophytes reflected differences in nutrient concentrations of the Portneuf River, Idaho. Tissue N and P increased with N and P concentrations in surface water; however, tissue N plateaued when water NO2 + NO3-N was ≥ 0.7 mg/L.  Similarly, a non-linear relationship between tissue and water P concentrations suggested P saturation. We conducted a laboratory bioassay with source water from reaches with a range of N and P concentrations (0.88 – 2.30 mg/L NO2 + NO3-N; 0.01 – 1.1 mg/L ortho-P) and wild-harvested floating macrophytes (Lemna minor). Lemna abundance and biomass increased only 1.5 – 4X across treatments (largely as increased root mass), while N and P concentrations were 230 and 110X greater than controls, respectively. Epiphytes introduced with macrophytes and growing attached to aquaria glass responded more strongly than Lemna to nutrient concentrations. Chlorophyll a concentrations from nutrient-rich reaches were 250 – 360X greater than the controls and 50X greater than less nutrient-rich reaches. Macrophyte bioassays may be an effective way to infer nutrient enrichment of river producers, but must consider both the tissue nutrient status and abundance of macrophytes along with associated epiphytes.


Web Page: Lemna minor, nutrient

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