Evaluation of the effects of wetland restoration design on hydraulic residence time and nutrient retention

Abstract

Hydraulic residence time (HRT) is a critical factor that can be integrated into wetland restoration designs to promote nutrient retention, but HRT in the context of wetlands with storm-driven hydrology is not well understood. A model for nutrient retention optimization based on HRT was evaluated using three indicators of HRT and nutrient stocks in above-ground plant biomass. Results indicated that a commonly used indicator of HRT, the ratio of wetland to watershed area, may be insufficient, while nominal HRT provided an overestimate for wetlands receiving storm runoff. While there was little relationship between total nitrogen and HRT, results suggested that HRT may explain some variation in total phosphorus. Results also indicated that the studied wetland restorations were not designed to provide sufficient HRT to promote the retention of dissolved nutrients, and that staged outlets could be used to provide significant HRT's for a range of storm events.