Skip to main content

Quantifying the Impacts of Instream Macrophytes on Nutrient Assimilation in a Southern California Stream: Implications for TMDLS

Buy Article:

$17.50 plus tax (Refund Policy)

Or sign up for a free trial


A stream's capacity for assimilating nutrients is often strongly tied to the presence of instream biota. In many small and/or ephemeral streams, emergent macrophytes can dominate nutrient processing. Nutrient uptake by these plants increases seasonal assimilative capacities and can reduce loadings to downstream reaches and receiving water bodies. However, plants must be harvested to achieve complete removal of nutrients from the system. Understanding and quantifying these processes can greatly aid in defining appropriate TMDL methodologies and performing supporting numerical modeling for streams with macrophytes. The study presented here aimed to quantify nitrogen and phosphorus assimilation and downstream delivery rates in a small stream dominated by large wetland emergent macrophytes. The stream is "mowed" annually for flood control purposes. Nutrient addition experiments were performed at two different stages of macophyte growth: late in the growing season, just before the reach was mechanically cleared of macrophytes (September) and then again two months later after re-growth had commenced and new shoots were established. A stream solute transport numerical model was applied that captures both transport processes and biokinetics of the system. Experimental and modeling results show that, in the short-term, mowing created a more nutrient-retentive system, compared to pre-mowing. This appears to be due to increased uptake in the re-growth (compared to old shoots) and decreased downstream solute velocities (as a result of downed vegetation). Whole-stream effective nitrogen uptake rates ranged from 12 to 16 mg-N m-2 d-1 (pre-mowing) and 40 to 57 mg-N m-2 d-1 (postmowing). Effective phosphorus uptake rates ranged from 15 to 17 mg-P m-2 d-1 (premowing) and 32 to 52 mg-P m-2 d-1 (post-mowing). These rates compare well to literature-reported rates for constructed wetlands when transport limitations are accounted for. Stream average solute velocities decreased nearly 3x after mowing (1389 vs. 482 m d-1 ), despite slightly higher flows. Both the uptake rates and solute velocities will be useful for parameterization of future watershed numerical models, including those to be used for TMDL analyses. Implications for future TMDL analyses are demonstrated.


Document Type: Research Article


Publication date: 2007-10-01

More about this publication?
  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

    A subscription to the Proceedings of the Water Environment Federation includes access to most papers presented at the annual WEF Technical Exhibition and Conference (WEFTEC) and other conferences held since 2000. Subscription access begins 12 months after the event and is valid for 12 months from month of purchase. A subscription to the Proceedings of the Water Environment Federation is included in Water Environment Federation (WEF) membership.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access. Access begins 12 months after the conference or event
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • Learn about the many other WEF member benefits and join today
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more