A nutrient’s downstream fate: Assessing nutrient transport using TASCC

Session: Physical Ecology in Large Lakes and Their Watersheds

Terri Jicha, USEPA, [email protected]
Brian Hill, Retired USEPA, [email protected]
Ken Fritz, USEPA, [email protected]
Frank McCormick, USFS, [email protected]
Phil Kaufman, USEPA, [email protected]
Dustin Woodruff, USEPA/ORD Mid-Continent Ecology Division, [email protected]
Tammy Newcomer-Johnson, USEPA, [email protected]

Abstract

Streams hydrologically connect watersheds to their respective Great Lake, playing a central role in the load and form of nutrients downstream waters receive.  We used the Tracer Additions for Spiraling Curve Characterization (TASCC) to measure uptake length, velocity and areal rate over a range of phosphate, nitrate, and ammonium concentrations.  Our findings indicate that nutrient concentrations alone do not characterize how in-stream nutrient uptake responds to changes in watershed or habitat conditions (no significant correlations).  Stream uptake lengths generally decreased with increasing nutrient concentrations from increased disturbance. Mean uptake length for phosphate (242.6 ± 25.1) was shorter than for nitrate (420.6 ± 45.3) or Ammonium (522.9 ± 72.6). In urban streams this uptake length decrease was a result of higher areal uptake likely from physical retention.  Streams with relatively complex in-channel and riparian habitats and slow flows may have more capacity to remove nutrients than flashy streams with hardened banks.  As streams widen, shallow, and increase velocity uptake lengths increase for phosphates (R²= 0.28 p=0.03) and nitrates (R²= 0.21 p=0.04), respectively. Effective management of eutrophication requires an understanding of how streams transport and transform nutrients, such that watersheds can be prioritized, and in-stream habitat features can be restored or protected.