Man\u27s Physical Effects on the Elizabeth RIver

Man\u27s ever increasing activities in the Elizabeth River, i.e. dredging, disposal of dredged material and waterfront development, have drastically altered the river floor, reshaped the shoreline and changed the circulation. Long-continued dredging of shipping channels, which is fostered by coal export, larger ships, and military needs, has moved 220 million cu yds of sediment since 1870. As a result channel depth has increased 1.8 fold, and maintenance dredging rates have doubled about every 35 years. Open water disposal released 40 million cu yds into Hampton Roads and lower Chesapeake Bay. Landfill buried tributary creeks, moved the waterfront into the river and reduced the river area by 27%. As a consequence of reduced area and greater channel depth, current velocity has diminished and near-bottom salinity likely increased. These conditions induce faster sedimentation that in turn, creates a need for greater maintenance dredging and hence, greater disposal. The dredge and fill cycle, therefore, is self-perpetuating. The long-term trends of channel deepening, enlargement, and landfill, are expected to continue in response to larger ships, military needs and projected sea-level rise.https://scholarworks.wm.edu/vimsbooks/1155/thumbnail.jp

Estimates of new and total productivity in central Long Island Sound from in situ measurements of nitrate and dissolved oxygen

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 36 (2013): 74-97, doi:10.1007/s12237-012-9560-5.Biogeochemical cycles in estuaries are regulated by a diverse set of physical and biological variables that operate over a variety of time scales. Using in situ optical sensors, we conducted a high-frequency time-series study of several biogeochemical parameters at a mooring in central Long Island Sound from May to August 2010. During this period, we documented well-defined diel cycles in nitrate concentration that were correlated to dissolved oxygen, wind stress, tidal mixing, and irradiance. By filtering the data to separate the nitrate time series into various signal components, we estimated the amount of variation that could be ascribed to each process. Primary production and surface wind stress explained 59% and 19%, respectively, of the variation in nitrate concentrations. Less frequent physical forcings, including large-magnitude wind events and spring tides, served to decouple the relationship between oxygen, nitrate, and sunlight on about one-quarter of study days. Daytime nitrate minima and dissolved oxygen maxima occurred nearly simultaneously on the majority (> 80%) of days during the study period; both were strongly correlated with the daily peak in irradiance. Nighttime nitrate maxima reflected a pattern in which surface-layer stocks were depleted each afternoon and recharged the following night. Changes in nitrate concentrations were used to generate daily estimates of new primary production (182 ± 37 mg C m-2 d-1) and the f-ratio (0.25), i.e., the ratio of production based on nitrate to total production. These estimates, the first of their kind in Long Island Sound, were compared to values of community respiration, primary productivity, and net ecosystem metabolism, which were derived from in situ measurements of oxygen concentration. Daily averages of the three metabolic parameters were 1660 ± 431, 2080 ± 419, and 429 ± 203 mg C m-2 d-1, respectively. While the system remained weakly autotrophic over the duration of the study period, we observed very large day-to-day differences in the f-ratio and in the various metabolic parameters.This work was supported by the Yale Institute for Biospheric Studies, the Sounds Conservancy of the Quebec-Labrador Foundation, and the Yale School of Forestry and Environmental Studies Carpenter-Sperry Fund.2014-01-0