Improving water quality through cost-effective marsh restoration

Author(s): Sparks, E.; Cebrian, J.

Marshes provide many ecosystem functions and services that are integral for coastal health. One of the most valuable ecosystem services provided by coastal marshes is the removal excess nutrients prior to entering coastal waters. Unfortunately, marsh degradation has led to drastic reductions in the capacity of marshes to provide this nutrient buffering service. As an attempt to mitigate for this reduced nutrient removal capacity, many restoration projects have been and will continue to be conducted. However, the majority of these projects are limited in evaluation of the ecosystem services they provide, cost-effectiveness, and how climate change will affect them. Given the high cost associated with these projects, evaluating the cost-effectiveness and resilience of different designs is necessary for making restoration a more ubiquitous and effective practice. We constructed and evaluated experimental marshes at the Grand Bay and Weeks Bay National Estuarine Research Reserves to test the effectiveness of different initial planting densities at removing nutrient pollution. At the Grand Bay site, we had initial planting densities of 0%, 50%, and 100% of Juncus roemerianus (black needlerush). At the Weeks Bay site, we created marshes in abandoned canals and, within them, planted black needlerush at 5 different densities (0%, 25%, 50%, 75%, and 100%). In half of the Weeks Bay plots, we simulated short term sea-level rise to approximate levels projected at 2030. At both sites we compared porewater concentrations of dissolved inorganic nitrogen (DIN) and used this measurement as a proxy for nutrient removal across all plots. Our findings indicate the 50%, 75%, and 100% planting densities suppress porewater DIN concentrations to similar levels and at significantly greater levels than the 0% and 25% planting densities. Therefore, the 50% planting density is suggested as the most cost-effective design for nutrient removal. Effects of short term sea-level rise on DIN concentrations varied by marsh location, but, in general, did not have a large effect. This information can be used by managers to design more cost-effective restoration projects that take into account the potential effects of sea-level rise.

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