You are here:
Spatial Variability of Nitrogen Isotope Ratios of Particulate Material from Northwest Atlantic Continental Shelf Waters
Citation:
MCKINNEY, R. A., A. J. Oczkowski, J. Prezioso, AND K. J. Hyde. Spatial Variability of Nitrogen Isotope Ratios of Particulate Material from Northwest Atlantic Continental Shelf Waters. ESTUARINE, COASTAL AND SHELF SCIENCE. Elsevier Science Ltd, New York, NY, 89(4):287-293, (2010).
Impact/Purpose:
This manuscript describes results of a long-term monitoring partnership between the US EPA Atlantic Ecology Division and NOAA / NMFS Northeast Fisheries Science Center to track changes in stable nitrogen isotope ratios (δ15N) in particulate material along the east coast US continental shelf. The objective of the monitoring was to examine whether anthropogenic nitrogen exported from estuaries may be reaching shelf waters. Particulate matter has been collected seasonally from surface waters off the US east coast starting in 2000 from near-shore sample sites proximal to the mouth of six estuaries and sites farther offshore. In samples collected from 2000 – 20005, near-shore (mean 33.7 km from estuary mouth) δ15N values ranged from 5.5 – 7.7 ‰ and increased from north to south. Offshore values (mean 92.4 km from estuary mouth) were consistently lower than near-shore sites (average 4.7 ± 1.0 ‰ versus 6.8 ± 1.1 ‰). In addition, mean monthly chlorophyll a concentrations from the sea-viewing wide field-of-view sensor (SeaWiFS) were significantly higher at near-shore sites near the mouth of three of the six estuaries. Our results supports the hypothesis that terrigenous runoff may be a source of nitrogen to continental shelf waters and provides evidence suggesting the spatial extent of the influence of terrestrial nitrogen in the vicinity of larger estuaries. This is potentially important information for the management of nitrogen inputs from coastal watersheds because of the projected increase in human-derived nitrogen inputs to estuaries, and the potential for estuarine export to become a significant source of nitrogen to continental shelf waters.
Description:
Human encroachment on the coastal zone has led to a rise in the delivery of nitrogen (N) to estuarine and near-shore waters. Potential routes of anthropogenic N inputs include export from estuaries, atmospheric deposition, and dissolved N inputs from groundwater outflow. Stable N isotope ratios provide a means to assess the source of N to shelf waters, particularly since dissolved anthropogenic N has elevated δ15N values (range: 7 – 30 ‰). We collected particulate matter from surface waters off the US east coast during spring, summer, and fall from 2000 – 2005. Near-shore sample sites proximal to the mouth of six estuaries were paired with sites farther offshore. Near-shore (mean 33.7 km from estuary mouth) δ15N values ranged from 5.5 – 7.7 ‰ and increased from north to south. Offshore values (mean 92.4 km from estuary mouth) were consistently lower than near-shore sites (average 4.7 ± 1.0 ‰ versus 6.8 ± 1.1 ‰). In addition, mean monthly chlorophyll a concentrations from the sea-viewing wide field-of-view sensor (SeaWiFS) were significantly higher at near-shore sites near the mouth of three of the six estuaries. Our results support the hypothesis that estuarine nitrogen is influencing continental shelf ecosystems, and provide evidence of the spatial extent of its influence. However, these results need to be considered in the context of a shelf nitrogen budget that includes inputs from lateral along-shelf transport and upwelling from slope water.
URLs/Downloads:
Spatial Variability of Nitrogen Isotope Ratios of Particulate Material from Northwest Atlantic Continental Shelf Waters