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| Content Provider | Springer Nature Link |
|---|---|
| Author | Hagy, James D. Boynton, Walter R. Keefe, Carolyn W. Wood, Kathryn V. |
| Copyright Year | 2004 |
| Abstract | A 52-yr record of dissolved oxygen in Chesapeake Bay (1950–2001) and a record of nitrate (NO$_{3}$ $^{−}$) loading by the Susquehanna River spanning a longer period (1903, 1945–2001) were assembled to describe the long-term pattern of hypoxia and anoxia in Chesapeake Bay and its relationship to NO$_{3}$ $^{−}$ loading. The effect of freshwater inflow on NO$_{3}$ $^{−}$ loading and hypoxia was also examined to characterize its effect at internannual and longer time scales. Year to year variability in river flow accounted for some of the observed changes in hypoxic volume, but the long-term increase was not due to increased river flow. From 1950–2001, the volume of hypoxic water in mid summer increased substantially and at an accelerating rate. Predicted anoxic volume (DO<0.2 mg I$^{−1}$) at average river flow increased from zero in 1950 to 3.6×10$^{9}$ m$^{3}$ in 2001. Severe hypoxia (DO<1.0 mg I$^{−1}$) increased from 1.6×10$^{9}$ to 6.5×10$^{9}$ m$^{3}$ over the same period, while mild hypoxia (DO<2.0 mg I$^{−1}$) increased from 3.4×10$^{9}$ to 9.2×10$^{9}$ m$^{3}$. NO$_{3}$ $^{−}$ concentrations in the Susquehanna River at Harrisburg, Pennsylvania, increased up to 3-fold from 1945 to a 1989 maximum and declined through 2001. On a decadal average basis, the superposition of changes in river flow on the long-term increase in NO$_{3}$ $^{−}$ resulted in a 2-fold increase in NO$_{3}$ $^{−}$ loading from the Susquehanna River during the 1960s to 1970s. Decadal average loads were subsequently stable through the 1990s. Hypoxia was positively correlated with NO$_{3}$ $^{−}$ loading, but more extensive hypoxia was observed in recent years than would be expected from the observed relationship. The results suggested that the Bay may have become more susceptible to NO$_{3}$ $^{−}$ loading. To eliminate or greatly reduce anoxia will require reducing average annual total nitrogen loading to the Maryland mainstem Bay to 50×10$^{6}$ kg yr$^{−1}$, a reduction of 40% from recent levels. |
| Starting Page | 634 |
| Ending Page | 658 |
| Page Count | 25 |
| File Format | |
| ISSN | 01608347 |
| Journal | Estuaries |
| Volume Number | 27 |
| Issue Number | 4 |
| Language | English |
| Publisher | Springer-Verlag |
| Publisher Date | 2004-01-01 |
| Publisher Place | New York |
| Access Restriction | Subscribed |
| Subject Keyword | Environment Ecology Geosciences Freshwater & Marine Ecology Environmental Management Nature Conservation |
| Content Type | Text |
| Resource Type | Article |
| Subject | Environmental Chemistry Aquatic Science Environmental Science |
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