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Sources: HydroQual, 1991; O'Shea and Brosnan, 1997.

Note: Some municipal dischargers (WPCPs) include industrial discharges.

Sources: HydroQual, 1991; O'Shea and Brosnan, 1997.

Note: Some municipal dischargers (WPCPs) include industrial discharges.

Summer Average---Confidence Interval

Figure 6-17 Long-term trends in summer geometric mean fecal coliform bacteria. Data represents harborwide composite of 40 stations monitored since at least 1970. Source: O'Shea and Brosnan, 1997.

harbor, are attributed to increased surveillance and maintenance of the entire sewage distribution system, including the capture of combined sewage during rain events (Brosnan and O'Shea, 1996b).

Long-term summer DO saturation records, collected almost continuously since 1909, at a station in the Hudson River near 42nd Street on the west side of Manhattan (Figure 6-18) and stations at Baretto Point and 23rd Street in the Upper and Lower East River (Figure 6-19) clearly document the beneficial impact of upgrading water pollution control facilities to full secondary treatment. Over a 40-year period from the 1920s through the 1960s, summer oxygen saturation levels were only about 35 percent to 50 percent at the surface and 25 percent to 40 percent in bottom waters. As a result of significant reductions in biochemical oxygen demand loading (see Figure 6-11), DO saturation levels increased to about 90 percent in the surface and greater than 60 percent in the bottom (Brosnan and O'Shea, 1996a). DO concentrations have increased significantly since the 1980s harborwide (Brosnan and O'Shea, 1996a; Parker and O'Reilly, 1991). In many waterways, the greatest oxygen and BOD5 improvements were recorded between 1968 and 1984, coinciding with the greatest water pollution control plant construction and upgrading activity (O'Shea and Brosnan, 1997). Analysis of data for stations from 1968 to 1995 document reductions in ammonia-nitrogen (Figure 6-20) and decreases in BOD5 (Figure 6-21) throughout New York Harbor; exceptions to these decreasing trends include stations in Jamaica Bay and scattered stations in Lower New York Bay and the Upper East River (O'Shea and Brosnan, 1997).

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