Water quality effects of stream restoration in the Chesapeake Bay watershed: benefits and unintended consequences
Citation:
Mayer, P. AND S. Kaushal. Water quality effects of stream restoration in the Chesapeake Bay watershed: benefits and unintended consequences. The State of the Science and Practice of Stream Restoration in the Chesapeake: Lessons Learned to Inform Better Implementation, Assessment and Outcomes, Woodbridge, VA, March 21 - 23, 2023.
Impact/Purpose:
Stream restoration is a popular approach for managing nutrients in degraded, flashy urban streams. Despite billions of dollars spent on restoration, questions remain over its efficacy as a nutrient BMP. Our presentation recaps 20 years of research investigating the long-term effects of geomorphic stream restoration in urban streams in the Chesapeake Bay watershed. Overall, we found that the restoration improved nitrogen uptake and that restoration represents a potential BMP for nutrient management depending on restoration features and approach. Our research contributes significantly to the development of revised restoration protocols for nutrient removal credits in the Chesapeake Bay. Our data will help guide practitioners identify the most effective stream restoration approaches for nitrogen management in urban ecosystems. Future efforts must focus on improved monitoring efforts to accurately assess BMP effectiveness, which will be dependent upon long-term studies and properly designed experiments.
Description:
Stream restoration is a popular but expensive approach for managing nutrients (nitrogen and phosphorus) and sediment dynamics in urban watersheds. However, questions about costs and benefits remain. Here, we discuss lessons learned over 20 years of investigating effects of geomorphic stream restoration on riparian and in-stream nitrogen transport and transformation in urban streams in the Chesapeake Bay watershed. We examined relationships between hydrology, chemistry, and biology to determine how flashiness, and nutrient concentrations and flux, changed after restoration. We present data from multiple sites and various restoration approaches including natural channel design, regenerative stormwater conveyance, and removal of legacy sediments. We show that restoration can be an effective nutrient management approach dependent upon re-establishing groundwater-surface water interaction, addressing erosion and shear stress, protecting riparian zones, and ensuring sufficient cycling of organic matter for microbial activity. Benefits observed include: 1) reduced concentration and loads of nitrogen, 2) reduced peak flows, flashiness, and shear stress, and 3) increased denitrification. There are also potential unintended negative consequences including: 1) mobilization of metals and ions after tree removal, 2) erosion and channel degradation from poor channel design and underestimation of peak flows, and 3) low dissolved oxygen from reduced flows. We identify remaining data gaps, critical questions, and monitoring needs for elucidating effective nutrient BMPs.