1. Introduction
Livestock farming has been suggested to be one of the major causes of deterioration of riparian areas and water quality. Hafez and Bouissou (1975) found that grazing cattle defecate between 12 to 18 times in 24 hours. Most bacterial water quality criteria are based on the concentrations of faecal coliforms and faecal streptococci. The ratio of faecal coliforms to faecal streptococci can be used to identify particular animal sources of faecal contamination (Geldreich, 1976 in Baxter-Potter & Gilliland, 1988). Cow faeces have been found to be a reservoir for Escherichia coli (E. coli) (Hussein, 2000) and other pathogens.
Thelin & Gifford (1983) found that 100 ml of bovine faeces contained 107 coliforms. Not surprisingly, perhaps, with figures like these, bacterial densities in run-off from agricultural lands often exceed water quality standards (Baxter-Potter & Gilliland, 1988). Microbes and nutrients from manure enter streams by several potential pathways. One is direct deposition from the animals as they drink, graze, or otherwise spend time in and along the stream (Tiedemann et al., 1988).
The second pathway is via runoff or overland flow, where deposits of manure along with organisms and nutrients in the manure are transported to the stream (Gary et al., 1983; Larsen et al., 1994). Other pathways include subsurface transport and filtration, and artificial drainage. The extent or severity of elevated bacterial indicator organisms in grazed streams in the US is proportional to the increase in cattle numbers, and inversely related to size of pasture (Darling & Coltharp, 1973; Gary et al., 1983; Larsen et al., 1994). In addition, bacterial concentrations in stream water from grazed pastures are directly related to the availability of meadows near the water (Tiedemann et al., 1988).
It has been suggested that the impact of defecation on aquatic ecosystems, may be resolved by excluding stock from streams by fences, and by providing alternative water in troughs. However, fencing would be economically prohibitive in the United States (Platts & Wagstaff, 1984) and in New Zealand (Bettjeman, 1997). There have been few studies on the effect of cattle defecation in streams under New Zealand farming conditions.
In a study examining factors influencing the use of streams by cattle (Bagshaw, 2001), three experiments were carried out. During the course of these experiments the location and timing of defecation for each animal was recorded.
The aims of this study were to establish; (1) both the distribution and frequency of cattle defecation in the riparian zone and remainder of the grazing area; (2) the seasonal pattern of cattle defecation in the riparian zone and the remainder of the grazing area; (3) the effectiveness of locating a water trough distant from a stream on discouraging defecation in the riparian area; (4) the effectiveness of other resources (e.g. shade) on discouraging defecation in the riparian area. All experiments in this study were carried out under normal farm management practices on hill country in New Zealand.
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