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Figure 23.6. Dissolved oxygen trends in the Hudson River in the Albany Pool near Glenmont, NY, ca. 1949-1997. Data represent summer average concentrations and percent saturation of 6-14 samples per summer, except for 1949, 1951, 1961, 1965, 1975, and 1987-97, which represent 1-4 samples per summer, and 1966 which represents 38 samples.

These increases in DO have improved the ability of the Hudson River to sustain life. Biological monitoring using resident benthic macroinvertebrate communities (for example, aquatic insects, worms, clams) as indicators of water quality has documented significant improvements in many sites in watersheds throughout New York State. Of 216 sites monitored periodically statewide from 197292, eighty-three sites improved. Improvements at 53 percent of these eighty-three sites was attributed to improved sewage treatment, 9 percent was due to industry, and 25 percent was due to a combination of improvements in municipal and industrial discharges (Bode, Novak, andAbele, 1993). The Albany Pool was cited as one of the ten greatest success stories, with all biological indices improved since 1972. The replacement of pollution tolerant tubifex worms and midges with pollution sensitive mayflies, stoneflies, and caddisflies is attributed to the completion of secondary WTPs in the Albany and Rensselaer county sewer districts (Bode et al., 1993).

Improvements in New York Harbor, as well as other east and west coast harbors, have resulted in a resurgence of marine borers such as shipworms (Teredo spp.) and gribbles (Limnoria spp.) that devour natural driftwood and manmade wooden structures such as boats and pilings. Previously abundant populations of pollution intolerant borers were decimated as water quality declined well into the twentieth century. Improved water quality conditions in the mid-1980s has coincided with a severe re-infestation of borers and rapid deterioration of wood pilings and other submerged wooden structures in New York Harbor (Abood, Ganas, and Matlin, 1995). Improved benthic communities in Lower New York Bay have also been documented (Steimle and Caracciolo-Ward, 1989; Cerrato, Bokuniewicz, and Wiggins, 1989; Chapter 18, this volume).

Trends in sanitary quality. Fecal coliform bacteria are used by various water quality monitoring programs as indicators of sewage-related pollution. Elevated concentrations in the aquatic environment indicate the presence of fecal contamination and the potential presence of pathogenic bacteria, fungi, and viruses often associated with untreated wastewater pollution. New York State water quality standards use fecal coliform bacteria as indicators of the sanitary quality of area waterways for uses such as shell fishing, swimming, and secondary contact recreation.

Declining concentrations of fecal coliform bacteria indicate that the sanitary quality of both the middle and lower Hudson River has also improved significantly in response to improved capture and treatment of sewage over the last three decades (Fig. 23.7). Undisinfected wastewater contains 107 cells/100 mL of coliform bacteria (Thomann and Mueller, 1987). Seasonal chlorination (May-September) using either sodium hypochlorite or chlorine gas started in the 1940s for the WTPs in Staten Island, and included all fourteen of New

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