6 research outputs found
The Role of Small Reservoirs in Reducing Reactive N Export Via Denitrification
Reactive nitrogen (N), which harms ecosystem health, has been increasing in the biosphere, leading to higher N export to coastal ecosystems. Although man-made reservoirs can be significant sources of greenhouse gases, they can also retain N, thus reducing N export. Because many dams are relics from industrial hydropower, their removal is becoming increasingly common. It is therefore crucial to understand the ecological tradeoffs of man-made reservoirs. While previous studies have examined nutrient budgets and denitrification at inputs and outputs of large reservoirs, small reservoir dynamics remain understudied. In this study, we measured inputs and outputs of NO3 and N2 at two small coastal reservoirs and assessed reasons for changes by sampling internally within the reservoirs. We hypothesized that denitrification is high in small reservoirs due to lower dissolved oxygen. While we found evidence of denitrification in one reservoir the second reservoir showed evidence of N fixation. Fixation was evident within the reservoir where low NO3 concentrations and high algal growth occurred, suggesting that NO3 was being assimilated, limiting algal growth, and allowing the occurrence of N fixing algae. As a result, reservoirs may not always remove N, but may at times be a source of additional N. As dam removal decisions continue, the role of reservoirs in N export should be carefully considered
Contribution of fluvial wetlands to nitrogen retention in urbanizing coastal watersheds in New England across multiple scales
Contribution of fluvial wetlands to nitrogen retention in urbanizing coastal watersheds in New England across multiple scales
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Assessment of Select Climate Change Impacts on U.S. National Security
This report examines climate change impacts to U.S. national security by quantifying select impacts globally at the national level and identifying countries that are both at high risk from projected climate change and possess risk factors associated with political instability. Exposure to global seaâlevel rise risk exposure is quantified by identifying lowâelevation coastal zones (LECZ), at 1, 3, 5, 7, 9, 10 and 12 meters of elevation. Countries with high risk factors for instability that also have the most people exposed to seaâlevel rise include China, Philippines, India, and Indonesia. Those with the greatest percentage of population so exposed include Philippines, Egypt, and Indonesia. Within these countries, Egypt has especially high rates of population growth within the LECZ. Aggregate climate change vulnerability is quantified by using an index that takes into account both projected temperature change and adaptive capacity. For countries with high risk factors for instability, the most vulnerable countries are South Africa, Nepal, Morocco, Bangladesh, Tunisia, Paraguay, Yemen, Sudan and CĂ´te dâIvoire. Water scarcity is examined by comparing numbers of people living under conditions of water in the present with three future scenarios â one in which the climate remains unchanged but population changes; one in which population changes but the climate remains static; and one in which both population and climate change. Countries with high risk factors for instability that are projected to have the biggest increases in water scarcity are Mozambique, CĂ´te dâIvoire, Nigeria, Iraq, Guatemala, Zimbabwe, Ethiopia, Somalia, China, Syria and Algeria