Variation in fecal pollution indicators through tidal cycles in the Fraser River estuary

Abstract

Daily fluctuations in fecal pollution indicators in the Fraser River estuary were examined by sampling through 24 h at four sites; water levels, currents, and salinities were observed simultaneously. Fecal coliforms were measured on shipboard using the membrane filter technique, and coprostanol and cholesterol were extracted using hexane and analyzed by gas chromatography. Maximum concentrations of fecal sterols and coliforms occurred after high tide at the station upstream of major sewage outfalls and on the ebb or at low tide at the stations downstream of major sewage outfalls. Fecal coliform counts were highly correlated with coprostanol and cholesterol levels at sites near sewage treatment plants. Coprostanol was highly correlated with cholesterol except where concentrations approached detection limits. In receiving waters, fecal coliform counts but not sterol concentrations were reduced by chlorination of sewage treatment plant effluents during the summer months. We concluded that, dependent on the objectives of a future monitoring program, samples should be collected either randomly in time such that the seasonal or annual mean includes tidal variability or systematically during the ebb tide to assess contributions to bathing beaches and shellfish harvesting areas. Fecal sterols deserve consideration as potential indicators of fecal contamination from chlorinated sewage effluents.