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Impacts of eelgrass (Zostera marina) on pore-water sulfide concentrations in intertidal sediments of Casco Bay, Maine

Date: 2016-05-01

Creator: Sabine Y Berzins

Access: Open access

Eelgrass (Zostera marina) is a perennial seagrass that provides many vital ecosystem services including stabilizing sediments, maintaining water clarity, and providing complex habitat in the intertidal and shallow subtidal coastline. Historically, Maine supported dense eelgrass beds in shallow waters surrounding islands and along the coastal mainland. However, in 2012, high population densities of European green crabs (Carcinus maenas), which physically disturb and remove eelgrass as they forage, were correlated with widespread eelgrass declines. Over 55% of the area of eelgrass in Casco Bay was lost, mainly between 2012 and 2014. Eelgrass typically grows in low-oxygen sediments that produce a chemically reducing environment. Sulfate-reducing bacteria in these reduced sediments produce hydrogen sulfide, a toxin that can intrude into eelgrass tissues and impair the plants’ ability to photosynthesize. When eelgrass is not present, sulfide can build up in the pore-water. When eelgrass is present, it can oxygenate the sediments through its roots, thereby preventing the intrusion and buildup of toxic hydrogen sulfide. However, if the substrate is de-vegetated, oxygen levels drop as sedimentary organic matter is decomposed, and the accumulation of sulfides to harmful concentrations in the pore-water may make recolonization of eelgrass difficult or perhaps impossible even in the absence of green crabs. In an effort to monitor characteristics of Casco Bay eelgrass beds and determine spatially where eelgrass may be more likely to recover, four Casco Bay sites with varying degrees of vegetation loss were sampled in 2015 for pore-water sulfide concentration, sediment carbon and nitrogen content, and sediment grain size analysis. Measurements of sulfide concentrations showed correlations with the timing of eelgrass loss, such that vegetated sites had low pore-water sulfide concentrations and sites that had been de-vegetated for longer periods of time had high sulfide concentrations. Carbon and nitrogen content in the sediment was higher at de-vegetated sites, likely due to a higher percentage of finer sediments at those locations. Coarser sediments were more highly vegetated than finer sediments, perhaps displaying a preference of green crabs to forage in finer sediments. Catastrophic loss of eelgrass in Casco Bay has likely led to differences in sulfide levels, carbon and nitrogen content in the sediment, and grain size distribution, depending on degree of vegetation. Eelgrass restoration in Casco Bay will likely be limited by high pore-water sulfide concentrations.

Peace Be Dammed? Water Power and Water Politics in the Tigris-Euphrates Basin

Date: 2015-05-01

Creator: Camille E. Wasinger

Access: Open access

The Price of Carbon: Politics and Equity of Carbon Taxes in the Middle Income Countries of South Africa and Mexico

Date: 2015-05-01

Creator: Bridgett C McCoy

Access: Open access

This study provides the first analysis of the politics and ethics behind carbon taxation in South Africa and Mexico. Using the preexisting scholarly frameworks of climate change policy, tax policy, and Robert Putnam’s two level games, I determine that in both cases, international pressures from multilateral negotiations and international development funding sources initiated the carbon tax policymaking process within the environment and treasury ministries of both countries. Once environment ministry bureaucrats initiated the carbon tax a lack of politicization of climate change (both countries) and an additional gain of raising revenue (Mexico) allowed the taxes to become law. I then turn to the laws themselves, analyzing their implications for climate justice. In both cases, the government did not adopt any proposals made interest groups representing environmental concerns and poverty groups, and instead shaped the bills so as to tailor to the interests of heavy manufacturing. This policy decision had the main effect of weakening the climate change mitigation impact of the carbon tax, and exacerbating issues of regressivity by not recycling revenues towards projects aimed at poverty reductions. I conclude this paper with an analysis of the ethics of such a carbon tax in developing countries. The carbon taxes, as they currently exist, sacrifice the rights and needs of the present poor for those of the future generation while an ideal policy that addresses poverty betters the condition of both groups. In order to ensure climate justice and for all groups and prevent political backlash, policy makers in middle-income countries must make carbon reduction policies with the unique challenges of poverty and climate change mitigation in mind.