The Fate of Nitrogen in Dredged Material Used for Tidal Marsh Restoration

Lorie W Staver,Kenneth W Staver,Michael Owens,Leysa Lopez-Gonzalez,Jeffrey C Cornwell,Walter Boynton,J Court Stevenson,Nicholas J Nidzieko

doi:10.3390/jmse9080849

Abstract

Tidal marsh restoration using dredged material is being undertaken in many coastal areas to replace lost habitat and ecosystem services due to tidal marsh loss. The fate of high levels of nitrogen (N) in fine-grained dredged material used as a substrate for marsh restoration is uncertain, but if exported tidally may cause subtidal habitat degradation. In this study, a mass balance was developed to characterize N fluxes in a two-year-old restored tidal marsh constructed with fine-grained dredged material at Poplar Island, MD, in Chesapeake Bay, and to evaluate the potential impact on the adjacent submersed aquatic vegetation (SAV) habitat. Denitrification and N accumulation in Spartina organic matter were identified as the major sinks (21.31 and 28.5 mg N m−2 d−1, respectively), while tidal export of TN was more modest (9.4 mg N m−2 d−1) and inorganic N export was low (1.59 mg N m−2 d−1). Internal cycling helped retain N within the marsh. Mineralization of N associated with labile organic matter in the dredged material was likely a large, but unquantified, source of N supporting robust plant growth and N exports. Exceedances of SAV water quality habitat requirements in the subtidal region adjacent to the marsh were driven by elevated Chesapeake Bay concentrations rather than enrichment by the marsh.

Highlights

Global wetland losses during the last century are estimated to be in excess of 50% [1], with losses of many valuable ecosystem services such as provision of habitat, protection of coastal infrastructure, and nutrient and carbon transformation and sequestration [2]
As part of the ongoing assessment of the suitability of this material for tidal marsh restoration, we examined the wetland N balance through estimation of the soil N reservoir, standing stocks, and key Nfluxes
The sediment below the root zone contains >90% of total N (TN) in the marsh (441,880 kg), while the sediment within the root zone accounts for 8% of the TN stock (Table 2)

Summary

Introduction

Global wetland losses during the last century are estimated to be in excess of 50% [1], with losses of many valuable ecosystem services such as provision of habitat, protection of coastal infrastructure, and nutrient and carbon transformation and sequestration [2]. Replacing lost habitats and associated ecosystem services is the goal of several current and planned projects utilizing material dredged from navigation channels in the upper Chesapeake. Eutrophication from anthropogenic inputs of nitrogen (N) and phosphorus (P) has caused profound changes in coastal ecosystems globally [5] and has been identified as the driver behind losses of submersed aquatic vegetation (SAV) [6], often an important ecosystem component of shallow subtidal areas. Efforts to reduce nutrient inputs have become the centerpiece of restoration efforts in many impaired coastal systems, including

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