Urban Stream Restorations Increase Floodplain Soil Carbon and Nutrient Retention along a Chronosequence


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Stream restoration is a common management practice to meet regulatory or voluntary efforts to improve water quality via carbon and nutrient retention, including in the Chesapeake Bay watershed. However, restoration projects have few quantifiable measures of project success, no standard metrics, and rarely collect pre-restoration data. Storage of nutrients, such as phosphorus (P), and carbon (C), in floodplain soils of restored streams can act as an easily quantifiable indicator of restoration success, particularly when the project goals include improved water quality. To determine how floodplains of restored streams change in their phosphorus and carbon storage as time since restoration increases, floodplain surficial soil samples (10 cm depth) were collected from 18 streams in the urbanized Piedmont region of northern Virginia, representing a chronosequence of time (1-10+ yrs.) since restoration as well as unrestored and reference streams. The samples were analyzed for total carbon (TC), total nitrogen (TN) and total phosphorus (TP) storage, whereas CO2 mineralization potential and equilibrium phosphorus concentration (EPC0) were measured as metrics of nutrient and carbon loss. These metrics were compared to time since restoration and potential environmental drivers, including soil moisture, pH, particle size, organic matter content, and degree of phosphorus saturation. These stream restorations demonstrated increasing nutrient storage for TC, TN, and TP along the chronosequence to values greater than both unrestored or reference streams, as well as decreasing C mineralization turnover and no significant changes in EPC0. Soil wetness and organic matter, key drivers in nutrient retention, also increased as restoration projects aged increasing nutrient and C storage. Overall, stream restoration did improve carbon and nutrient retention in floodplains as compared to unrestored sites and exceeded those of low urbanization 'reference' sites.