CONTRIBUTION OF SURFACE TRANSIENT STORAGE TO NITROGEN RETENTION WITHIN WETLAND-DOMINATED STREAM REACHES IN NEW ENGLAND

Nutrient retention is one of the most important ecosystem services provided by river networks, especially in urbanizing regions, and is one of the desired outcomes of many river restoration efforts. Nutrients transported downstream by rivers frequently interact with stationary yet biologically productive regions of surface and groundwater. The functional significance of these transient storage zones depends on their volume, their connectivity with the stream channel, and their reactivity, factors that differ between different hydrogeologic settings and that are sensitive to changes in precipitation regimes and watershed land use. We focused on improving understanding of hydraulic controls and nutrient uptake in eight storage-dominated headwater reaches in coastal New Hampshire and Massachusetts. A series of conservative tracer injections revealed that storage zone volume and access differs depending on wetland geometry and discharge. Net nutrient uptake depends on flow sequencing, and is particularly influenced by intermediate discharges. River restoration for nutrient retention should focus on improving the area and connectivity of transient storage at intermediate discharges.