The survival of enteric bacteria was measured in bovine feces on pasture. In each season, 11 cow pats were prepared from a mixture of fresh dairy cattle feces and sampled for up to 150 days. Four pats were analyzed for Escherichia coli, fecal streptococci, and enterococci, and four inoculated pats were analyzed for Campylobacter jejuni and Salmonella enterica. Two pats were placed on drainage collectors, and another pat was fitted with a temperature probe. In the first 1 to 3 weeks, there were increases (up to 1.5 orders of magnitude) in the counts of enterococci (in four seasons), E. coli (three seasons), fecal streptococci (three seasons), and S. enterica (two seasons), but there was no increase in the counts of C. jejuni. Thereafter, the counts decreased, giving an average ranking of the times necessary for 90% inactivation of C. jejuni (6.2 days from deposition) < fecal streptococci (35 days) < S. enterica (38 days) < E. coli (48 days) < enterococci (56 days). The pat temperature probably influenced bacterial growth, but the pattern of increases and decreases was primarily determined by desiccation; growth occurred when the water content was greater than 80%, but at a water content of 70 to 75% counts decreased. E. coli and enterococcus regrowth appeared to result from pat rehydration. Of 20 monthly leaching losses of E. coli, 16 were <10% of the total counts in the pat, and 12 were <1%. Drainage losses of C. jejuni (generally <1%) were detected for only 1 to 2 months. Although enterococci exhibited the best survival rate, higher final counts suggested that E. coli is the more practical indicator of bovine fecal pollution.

The inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, was determined in 100 l chambers of seawater and river water located at an outdoor site. The chambers (paired with dark controls) were seeded with waste stabilization pond effluent and laboratory-cultured pathogens, and exposed to sunlight in summer and winter experiments. All sunlight inactivation (k S ) rates, as a function of cumulative global solar radiation (insolation), were far higher than the corresponding dark (k D ) rates, with a ranking (and average k S rates for seawater and river water, respectively) of: C. jejuni (3.23; 2.34) . S. enterica (0.51; 0.37) . E. coli (0.34; 0.26). All the T 90 (time to 90% inactivation) values were higher in winter than in summer, but there was far greater similarity between the summer and winter S 90 (insolation needed for 90% inactivation) values. The rapid inactivation of C. jejuni was attributed to a high susceptibility to photooxidative damage. The results suggest that, in sunlight-exposed waters, E. coli will be a more conservative indicator for C. jejuni than for S. enterica, and C. jejuni transmission as a pathogenic agent is less likely than for S. enterica.

Three microbial tracers -Escherichia coli J6-2, a somatic coliphage (ØESR1) and endospores of Bacillus subtilis var. niger NCIB 8649 tracer strain JHI -were added to effluent flood irrigated onto border dyke strips at a sewage treatment plant near Christchurch, New Zealand. All three tracers, and three effluent indicators -faecal coliforms, F-RNA phages, and chloride -were recovered in a bore, approximately 100 m downstream. A simple spatial model was applied to the breakthrough curves (BTCs) in the bore, using a series of hypothetical "entry points" in the strips. This analysis indicated effluent transport velocities through the 16.8 m deep vadose zone of between 15.7 and 39.2 m hr −1 . The shapes of the BTCs for the microorganisms and chloride were very different, suggesting that they reached the groundwater table via two pathways: -both underwent rapid transport to the groundwater though macropores, but chloride also underwent far slower (matrix) transport though micropores. The BTC shapes also suggested transport velocities in the vadose zone of E. coli J6-2 > B. subtilis JH1 endospores > phage ØESR1, which is consistent with the theory of pore size exclusion, based on particle size. Reductions in microbial concentrations were ≈100 times greater than for chloride, and occurred rapidly, suggesting that up to 99% of the microorganisms underwent early exclusion from macropore flow and were removed during matrix flow. Nevertheless, the results show that substantial numbers of bacteria and viruses will still reach the groundwater through macropores beneath effluent irrigation schemes located on alluvial gravel formations.

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