Nutrient, Trace Metal and Particle Release from Sediments in the Great Bay Estuary and Riverine System
The goal of this project is to determine the chemical and physical mechanisms that release nutrients and trace-metals from the fine-grained sediments of the rivers and estuary of the Great Bay, and to assess if the sediments are a significant source of these contaminants to the Great Bay aquatic ecosystem. The conditions that lead to the erosion of fine particles from sediments will also be determined and the importance of river sediments as a source of silt to the Great Bay will be established. These questions will be addressed through a series of detailed field and laboratory observations. In the field, the geochemistry will be sampled concomitantly with observations of the fluid stresses, sediment suspension, and bed elevation at three locations within the Great Bay. The laboratory investigations will allow for a more detailed correlation between fluid stresses and nutrient fluxes and trace metal release. This study will provide regional and local resource managers with concrete information on the magnitude of nutrient, metal and particle release from sediments in the estuary and from the sediment pools behind dams.
Geochemical and physical mechanisms that release nutrients and trace-metals from the finegrained sediments of the rivers and estuary of the Great Bay will be examined. The sediments will be examined to determine if they are a significant source of contaminants to the Great Bay aquatic ecosystem. The conditions that lead to the erosion of fine particles from sediments will also be determined and the importance of river sediments as a source of silt to the Great Bay will be established. The magnitude of nutrient, trace-metals and particle release from sediments in the estuary and from the sediment pools behind dams relative to other contributions will be quantified.
Sediments a Significant Source of Nutrient Inputs into Great Bay
Researchers developed an instrumentation deployment method for equipment used to investigate fluid flow and sediment erosion in a water body. This deployment method allows the instruments to be securely mounted in the water column and allows researchers to collect data during storm events when it might not otherwise be possible to physically do so, thus providing more accurate and up-to-date information about changes in a water body during extreme weather conditions.
The fine-grained sediments in coastal areas close to population centers are often large stores of contaminants that have built up over centuries. These sediments do not permanently store contaminants however, and the quantity of trace metals that are released from sediments into the Great Bay was previously unknown. With funding provided by NHSG, researchers conducted erosion chamber experiments and physical field observations in 2012 to produce estimates of fluxes from the sediment in the bay. Based on their experiments, researchers determined that trace metal-enriched particles are eroded into the water column regularly — at least 20% of the time — thus providing an important method of trace metal transport in the bay. These results provide more accurate information for scientists to assess trace metal inputs into the estuary.
Nutrients in Great Bay Estuary come from a variety of sources, but estimating the nutrients that are released due to particle resuspension in the water column can be challenging. In 2012, NHSG-funded researchers used erosion chamber experiments to determine how much ammonium in the estuary is released due to resuspension. Researchers found that the ammonium input due to resuspension in the fall is comparable to the ammonium input from rivers during that same time of year. This indicates that resuspension of ammonium is an important aspect of the nutrient load calculation for the estuary. These results help scientists and resource managers to better understand the controls on coastal water quality.
First Field Verification of Erosion Chamber Gives Confidence to Measurements of Sediment Erosion
The quantity of nutrients and trace metals that are released from sediments during resuspension events in the Great Bay Estuary has not been previously studied. In 2012, researchers combined two different datasets — in situ instrument measurements and erosion chamber experiments — to provide a better understanding of the mechanisms of sediment resuspension operating in coastal waters. This comparison resulted in the first field verification of any erosion chamber, thus giving confidence to geochemical measurements on the impacts of sediment erosion. Results from this research will enable scientists to use this technology for effective and accurate estimates of sediment resuspension in coastal waterways.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Wengrove, M. and D. Foster (2014). Field evidence of the viscous sublayer in a tidally forced developing boundary layer. Geophysical Research Letters 41(14):5084-5090, July 2014.
- Wengrove, M., D. Foster, L. Kalnejais, V. Percuoco and T. Lippmann (2015). Field and laboratory observations of bed stress and associated sediment nutrient release in a tidal estuary. Estuarine, Coastal and Shelf Science 161:11-24, August 2015.
- Percuoco, V., L. Kalnejais and L. Officer (2015). Nutrient release from the sediments of the Great Bay Estuary, N.H. USA. Estuarine, Coastal and Shelf Science 161:76-87, August 2015.
- Wengrove, M. (2012). Observations of a developing boundary layer in a tidally forced estuary. Master's Thesis, University of New Hampshire.
- Percuoco, V. (2012). Geochemistry and release of contaminants from cohesive sediments of the Great Bay Estuary, New Hampshire. Master's Thesis, University of New Hampshire.