Impact of Riparian Zone Protection from Cattle on Nutrient, Bacteria, F‐coliphage, Cryptosporidium, and Giardia Loading of an Intermittent Stream

This 5‐yr study compared, via an upstream–downstream experimental design, nutrient and microbial water quality of an intermittent stream running through a small pasture (∼2.5 animals ha−1) where cattle are restricted from the riparian zone (restricted cattle access [RCA]) and where cattle have unrestricted access to the stream (unrestricted cattle access [URCA]). Fencing in the RCA excluded pasturing cattle to within ∼3 to 5 m of the stream. Approximately 88% (26/32) of all comparisons of mean contaminant load reduction for lower, higher, and all stream flow conditions during the 5‐yr study indicated net contaminant load reductions in the RCA; for the URCA, this percentage was 38% (12/32). For all flow conditions, mean percent load reductions in the RCA for nutrients and bacteria plus F‐coliphage were 24 and 23%, respectively. These respective percentages for the URCA were −9 and −57% (positive values are reductions; negative values are increases). However, potentially as a result of protected wildlife habitat in the RCA, the mean percent load reduction for Cryptosporidium for “all flow” was −321% for the RCA and 60% for the URCA; for Giardia, these respective percentages were −209% (RCA) and 73% (URCA). For “all flow” situations, mean load reductions for the RCA were significantly greater (p < 0.1) than those from the URCA for NH4+–N, dissolved reactive phosphorus (DRP), total coliform, Escherichia coli, and Enterococcus. For “high flow” situations, mean load reductions were significantly greater for the RCA for DRP, total coliform, and Enterococcus. For “low flow” conditions, significantly greater mean load reductions were in favor of the RCA for DRP, total P, total coliforms, fecal coliforms, E. coli, and Enterococcus. In no case were mean pollutant loads in the URCA significantly higher than RCA pollutant loads. Restricting pasturing livestock to within 3 to 5 m of intermittent streams can improve water quality; however, water quality impairment can occur if livestock have unrestricted access to a stream.