Diurnal variations in water quality at surface-water-quality stations
Two primary causes of diurnal variations in dissolved-oxygen concentration (DO), pH, and specific conductance are photosynthesis and aerobic respiration. Photosynthesis is driven by sunlight and produces free oxygen, which causes an increase in DO during the day. Algal, microbial, and plant respiration consumes free oxygen, which causes a decrease in DO, and releases carbon dioxide during the night. Because visits to surface-water-quality stations typically take place between 8 a.m. and 2 p.m., these variations generally are not observed.
In an effort to document the occurrence and magnitude of these diurnal variations when stream-flow was at base-flow levels, water temperature (degrees Celsius), DO (milligrams per liter), percent of dissolved-oxygen saturation (percent), specific conductance (micro-Siemens per centimeter), and pH (units) were monitored continuously and recorded hourly at 94 stations during water years 2000-03, and 2005-10. The continuous measurements were made by using multi-constituent sensors, or monitors, deployed for 3 to 6 days at U.S. Geological Survey surface-water-quality stations during June, July, August, and September. The stations were selected on the basis of previous occurrences of DO supersaturation (greater than 120 percent of saturation) or undersaturation (less than 60 percent of saturation) during routine station visits.
In water year 2002, water temperature, DO, percent of dissolved-oxygen saturation, specific conductance, and pH were monitored continuously at three stations in the Passaic River Basin: Pompton Plains (01388500), Passaic River at Little Falls (01389500), and Saddle River at Lodi (01391500). The monitors were deployed for five 1-week periods during the summer months of a State-declared drought emergency with modified allowable passing flows in the basin (William Honachefsky, N. J. Department of Environmental Protection, written commun., April 2003). Although the intent was to obtain measurements under base-flow conditions, about 1 inch of rain fell during June 10-14.
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Two primary causes of diurnal variations in dissolved-oxygen concentration (DO), pH, and specific conductance are photosynthesis and aerobic respiration. Photosynthesis is driven by sunlight and produces free oxygen, which causes an increase in DO during the day. Algal, microbial, and plant respiration consumes free oxygen, which causes a decrease in DO, and releases carbon dioxide during the night. Because visits to surface-water-quality stations typically take place between 8 a.m. and 2 p.m., these variations generally are not observed.
In an effort to document the occurrence and magnitude of these diurnal variations when stream-flow was at base-flow levels, water temperature (degrees Celsius), DO (milligrams per liter), percent of dissolved-oxygen saturation (percent), specific conductance (micro-Siemens per centimeter), and pH (units) were monitored continuously and recorded hourly at 94 stations during water years 2000-03, and 2005-10. The continuous measurements were made by using multi-constituent sensors, or monitors, deployed for 3 to 6 days at U.S. Geological Survey surface-water-quality stations during June, July, August, and September. The stations were selected on the basis of previous occurrences of DO supersaturation (greater than 120 percent of saturation) or undersaturation (less than 60 percent of saturation) during routine station visits.
In water year 2002, water temperature, DO, percent of dissolved-oxygen saturation, specific conductance, and pH were monitored continuously at three stations in the Passaic River Basin: Pompton Plains (01388500), Passaic River at Little Falls (01389500), and Saddle River at Lodi (01391500). The monitors were deployed for five 1-week periods during the summer months of a State-declared drought emergency with modified allowable passing flows in the basin (William Honachefsky, N. J. Department of Environmental Protection, written commun., April 2003). Although the intent was to obtain measurements under base-flow conditions, about 1 inch of rain fell during June 10-14.
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