Selected Water Quality Processes in Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 143

FIGURE 5.16 Aftermath of debris low in Jones Gap State Park during the morning of Monday, June 26,
2006 (the large boulder in the middle of the image is several feet in diameter). (From Moore, P.D., Flash lood-
ing along the Blue Ridge, National Weather Service Forecast Ofice, Greenville-Spartanburg, SC, 2006.)
FIGURE 5.17 Mount St. Helens debris low. (From USGS, Available at volcanoes.usgs.gov/hazards/lahar/
rain.php. Photograph by K. Scott on June 24, 1990.)
5.5 DISSOLVED OXYGEN
DO is a fundamental water quality parameter and one that is often used to assess the health of
aquatic systems. While some rivers and streams are naturally low in DO, low DO is most commonly
associated with pollution.
First, a little terminology and background related to oxygen in the environment. Some of the
processes impacting DO are illustrated in Figure 5.18. Autotrophic ( auto or self, trophic food or
nutrition) organisms produce complex organic compounds from inorganic compounds in the pres-
ence of an energy source. Those that do so, such as plants, in the presence of light (photo) are
referred to as phototrophs and the rate of biomass production is referred to as primary production
(and the organisms as primary producers). Heterotrophs ( hetero from different or other) utilize the
organic matter to produce chemical energy, and produce inorganic compounds in the process. Both
heterotrophs and autotrophs respire, during which carbon dioxide is produced. So, during daylight
hours, phototrophs may both respire and produce, and only respire during dark hours, resulting in
diel variations in oxygen and carbon dioxide concentrations.