How the Distribution of Anthropogenic Nitrogen Has Changed in Narragansett Bay (RI,USA) Following Major Reductions in Nutrient Loads     

Autumn Oczkowski  Courtney Schmidt  Emily Santos  Kenneth Miller  Alana Hanson  Donald Cobb  Jason Krumholz  Adam Pimenta  Leanna Heffner  Sandra Robinson  Joaquín Chaves  Rick McKinney 《Estuaries and Coasts》2018,41(8):2260-2276

Over the past decade, nitrogen (N) loads to Narragansett Bay have decreased by more than 50%. These reductions were, in large part, the direct result of multiple wastewater treatment facility upgrades to tertiary treatment, a process which employs N removal. Here, we document ecosystem response to the N reductions and assess how the distribution of sewage N in Narragansett Bay has changed from before, during, and shortly after the upgrades. While others have observed clear responses when data were considered annually, our seasonal and regional comparisons of pre- and post-tertiary treatment dissolved inorganic nitrogen (DIN) concentrations and Secchi depth data, from bay-wide surveys conducted periodically from the early 1970s through 2016, resulted in only a few subtle differences. Thus, we sought to use stable isotope data to assess how sewage N is incorporated into the ecology of the Bay and how its distribution may have changed after the upgrades. The nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope measurements of particulate matter served as a proxy for phytoplankton, while macroalgae served as short-term integrators of water column bio-available N, and hard clams (Mercenaria mercenaria) as integrators of water column production. In contrast to other estuarine stable isotope studies that have observed an increased influence of isotopically lower marine N when sewage N is reduced, the opposite has occurred in Narragansett Bay. The tertiary treatment upgrades have increased the effluent δ¹⁵N values by at least 2‰. The plants and animals throughout Narragansett Bay have similarly increased by 1–2‰, on average. In contrast, the δ¹³C values measured in particulate matter and hard clams have declined by about the same amount. The δ¹⁵N results indicated that, even after the N reductions, sewage N still plays an important role in supporting primary and secondary production throughout the bay. However, the δ¹³C suggests that overall net production in Narragansett Bay has decreased. In the 5 years after the major wastewater treatment facilities came on-line for nutrient removal, oligotrophication has begun but sewage remains the dominant source of N to Narragansett Bay.  相似文献   

Erosion and reorientation of the Sapodilla Cays,Mesoamerican Reef Belize from 1960 to 2012   总被引：1，自引：0，他引：1  

Chris Houser  Tiffany D’Ambrosio  Courtney Bouchard  William Heyman  Kellie Darbonne  Samantha Kuykendall 《自然地理学》2014,35(4):335-354

The Sapodilla Cays Marine Reserve in southern Belize includes nine low-relief sand cays that were first surveyed in 1960. The purpose of this study is to reconstruct a 52-year history of the Sapodilla Cays (1960–2012) using a combination of historical topographic surveys, satellite imagery, and additional field data collection. Results suggest that the majority of islands are eroding with some islands having lost over 70% of their area, and many have become swash aligned, which suggests limited sediment availability. The proportion of area lost on each island is related to the width of the reef platform (to the 5?m isobaths) in the direction of the reef edge, while island area is dependent on the width of the reef platform in the direction of the resultant wind. This suggests that the width of the reef platform is a primary determinant of sediment supply between storms that tend to erode the eastern shoreline of the island through refraction along the reef edge. While storm erosion tends to be concentrated along the eastern shoreline through the loss of sediment offshore, alongshore transport to the lagoon shoreline, and the transfer of sediment to the interior of the island, net shoreline retreat is greatest along the lagoon, suggesting that the relatively small winter “northers” and a lack of sediment supply from the reef lagoon are responsible for the observed erosion. Extrapolations based on contemporary loss-rates suggest that the smallest cays will disappear by 2020, while the largest cays will begin to disappear by the end of century.  相似文献   

Changes in bark properties and hydrology following prescribed fire in Pinus taeda and Quercus montana     

Courtney Siegert  Anna Ilek  Adam Wade  Callie Schweitzer 《水文研究》2023,37(1):e14799

In the eastern United States, the use of prescribed fire as a silvicultural technique to manage for desirable upland tree species is increasing in popularity. Bark physical properties such as thickness, density, and porosity have known associations with fire tolerance among species. These physical properties simultaneously influence rainfall interception and canopy storage and thus are of interest across a range of disciplines. Furthermore, while these characteristics are innate to a species, it is unknown whether repeated exposure to fire facilitates physical change in bark structure and whether these changes are consistent among species. To answer these questions, bark samples were collected from mature pine (Pinus taeda L.) and oak (Quercus montana Willd.) trees from sites across the Bankhead National Forest in Alabama, USA under three different burn regimes: 3-year cycle, 9-year cycle, and no fire. Samples were analysed in the laboratory for bulk density, porosity, water storage capacity, and hygroscopicity (the amount of atmospheric water vapour absorbed by bark during non-rainfall conditions). Drying rates of saturated samples under simulated wetting conditions were also assessed. Oak bark had higher bulk density, lower porosity, and dried slower than pine bark. Interestingly, bark from both species had lower bulk density, higher porosity, greater water storage capacity, and dried faster in stands that were burned every 3 years compared to other fire regimes (p < 0.001). In summary, this study demonstrates that prescribed fire regimes in an eastern US forest alter bark structure and thus influence individual tree control on hydrological processes. The increase in bark water storage capacity, coupled with faster bark evaporation times may lead to less water inputs to the forest floor and drier overall conditions. Further investigation of this fire-bark-water feedback loop is necessary to understand the extent of these mechanisms controlling landscape-scale conditions.  相似文献