Quantifying the cumulative effects of stream restoration and environmental site design on nitrate loads in nested urban watersheds using a high-frequency sensor network

PI: C. Welty; co-PIs:
A.J. Miller; J. Duncan

Funding Source: Chesapeake Bay Trust (7/1/18 - 3/31/21)

ABSTRACT
This project seeks to address elements of Question 1 on watershed restoration assessment: 
What are the cumulative effects of watershed restoration activities within a watershed? 
We propose to analyze high-frequency nitrate and streamflow data from heavily instrumented watersheds in suburban Baltimore to address this question to address the following hypotheses: (1) Effectiveness of a treatment train on removal of nitrate loads (a wetland pond coupled with stream restoration) will be dependent upon flow regime, where the water quality detention basin is designed to treat storm flows and the stream restoration is expected to be most effective (remove a higher percentage of nitrate) at base flow and small storms.  (2) Stream restoration will enhance connectivity between the stream and riparian zone and reduce stream loads of nitrate at the watershed outlet. (3) Effectiveness of stream restoration in reducing nitrate load is a function of the ratio of the area draining to the restored reach to watershed area. (4) Implementation of stormwater infiltration structures will reduce nitrate loads primarily through reduction of stormflow volumes. This effect will be observable even if only a small fraction of the drainage area is treated.

Review of previous work points to the need for detailed mass balance studies over long periods of time to discern the impacts of stormwater management and stream restoration practices on nutrient export over a complete spectrum of flow regimes and at multiple watershed scales.  We are in a novel position to address this identified research gap, as we have had ongoing high-frequency measurements of nitrate and stream discharge in a set of experimental watersheds in suburban Baltimore, Maryland, at nested watershed scales for over 5 years.  We propose to use this instrumentation, augmented by several new stations, to quantify the effects of a recently installed stream restoration and stormwater quality pond on nitrate loads at nested watershed outlets, and compare to nitrate loads from a similar-sized watershed where such facilities have not been installed. In addition, we propose to conduct a retrospective study in one headwater catchment on temporal changes that have taken place in nitrate load at the watershed outlet as a number of stormwater facilities have been installed since 2012.