ABSTRACT:

Water quality modeling tools such as Qual2K (Q2K) will be key to understanding future nutrient fluxes as western U.S. rivers experience urban development and changes to migratory fish populations. The Q2K model does not include macrophytes, which may influence nutrient flux and are common in some western rivers such as the Henry’s Fork of the Snake river in east Idaho. My objective was to evaluate the effectiveness of Q2K in the Henry’s Fork. I struggled to model total phosphorus (TP) and soluble reactive phosphorus (SRP) flux in the Henry’s Fork. Q2K over-predicted for both. SRP was sensitive to phosphorylation rates in sediments, flow rate, and periphyton coverage; processes influenced by macrophyte growth. Future use of Q2K to model P load from wastewater and kokanee in the Henry’s Fork will require an accurate understanding of feedbacks between SRP and macrophytes. My study results will enhance efforts to link nutrient flux and ecosystem change in the Henry’s Fork and in stream ecosystems in general.