Animal manure contains many biodegradable organic (carbon-based) compounds. These compounds, once in surface water, tend to be decomposed by bacteria and other microorganisms, with a resulting decrease in aqueous dissolved oxygen concentrations. This in turn can have deleterious effects on aquatic organisms that require oxygen to survive, and severe reductions in surface water dissolved oxygen can results in hypoxic zones and even fish kills. Less severe drops in dissolved oxygen levels can result in decreased biodiversity and a relative increase in species that require lower levels of oxygen (USEPA, 2003a). The degraded organic matter can also potentially react with drinking water disinfectants (e.g., chlorine) to produce potentially harmful disinfection byproducts.
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