THE EFFECTS OF TRADITIONAL AND CAFO AGRICULTURE ON SUMMER NITRATE LEVELS IN STREAM WATER

Agricultural land use can add significant amounts of nutrients, including nitrates, to adjacent streams. Spruce Creek (central Pennsylvania) is a spring-fed stream with traditional livestock farms and the state's largest Concentrated Animal Feeding Operation (CAFO) along its banks. Warrior’s Mark Run is a major tributary to Spruce Creek and also runs through traditional agricultural land. To evaluate geographic sources of nutrients and analyze the impact of different scales of farming upon nitrate loading, we monitored a variety of physical and chemical parameters in these streams during the summer of 2003.

Both CAFO and traditional agriculture contribute significant amount of nitrates to Spruce Creek. The highest observed concentrations of nitrates were from immediately downstream of the CAFO on 44% of the days we sampled. Although the overall trend was for nitrate values to decrease further downstream on these days, the pattern was complex. The overall volume of nitrates increased between each sample location, but increases in discharge also impacted nitrate concentration. On 56% of the days that we sampled, nitrate concentrations reached peak values in areas of traditional farming, not at the CAFO. Clearly, the impact of traditional agriculture—as well as the CAFO—upon nitrate loading is significant for this stream.

Along Warrior’s Mark Run, the location of highest nitrate concentration was also variable, with highest values occurring evenly among three different locations at which there is significant streamside grazing. However, downstream of areas with significant streamside grazing, nitrate concentration decreased due to dilution. Although there is no CAFO along this stream, nitrate concentrations on Warrior’s Mark Run was comparable with those on Spruce Creek.

There were a number of watershed-wide increases in nitrate concentrations typically associated with watershed-wide decreases in discharge. There were also increases in nitrate concentrations that occur only along Spruce Creek but not Warrior’s Mark Run and vice versa. Each of these increases in nitrate concentration is associated with a stream-specific decrease in discharge. However, decrease in discharge alone (i.e. concentration) cannot explain the magnitude of nitrate increases.