The Missing Link in Bacteria TMDLs: Natural Growth

Fecal indicator bacteria (FIB), including total coliform, fecal coliform (or E. coli), and Enterococcus, have long been used to indicate the contamination of fecal matters in beaches, streams, and lakes (USEPA, 1986, 2002). When the bacterial concentration in a waterbody exceeds the FIB water quality criteria, the waterbody may be identified on the Clean Water Act Section 303(d) list of impaired waters. Section 303(d) requires the development and implementation of total maximum daily loads (TMDLs) for the impaired waterbody. Bacteria have been listed as number one pollutant with regard to impairments reported for the nation, and a total of 2678 bacterial TMDLs have been developed (USEPA, 2005). In California, 298 waterbodies have been 303(d) listed as impaired by FIB. Among these listed waterbodies, 37 TMDLs for FIB have been developed and approved by USEPA in 2002, which placed FIB TMDLs atop among all TMDLs developed so far in California.

It is challenging and often difficult to address water quality impairment effectively while developing and implementing TMDLs without knowing the source of contamination. The sources of FIB are generally believed from the wastes of humans or animals due to accidental sewage spills/leaking, impropriate disposal of pet/livestock waste, or waste droppings from wildlife (Noblet et al., 2005; Grant et al., 2003). The fact that high FIB levels have been found in areas where there are no apparent external inputs indicates sources other than humans or animals. This implies that a natural entity such as water, soil/sediment, and plant may serve as FIB sources. We present here the field evidence of survival/growth of FIB in fresh water and sediment in San Diego, California.

Samples were collected from various locations in San Diego County during dry weather (May through September). Water samples were taken by standing downstream and submerging the sample bottle below the water surface in the upstream direction. Water samples were also collected at locations where ponded water was present. For shallow water, a sample was taken using a plastic syringe. Sediment samples were taken from sites where water samples were
collected. Samples were placed in an ice chest, stored at 4oC, and delivered to a laboratory within 6 hours. All samples were analyzed for total coliform, fecal coliform, and enterococcus using standard methods. The multiple tube fermentation method was used to enumerate total coliform, fecal coliform, and Enterococcus. Results were expressed as most probable number (MPN) per 100 mL for water samples and MPN per gram of solid (dry weight) for sediment samples.

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