SEASONAL VARIATION OF NITRATES IN A KARST SPRING, NOLTE, PENNSYLVANIA

Bimonthly samples were collected over 18 months (Sept 2002 – present) from the Nolte spring in southeastern PA. In addition, sensors recorded the stage, conductivity and temperature to analyze the relationship of nitrate to storm events. The changes in conductivity, calcium concentration, suspended sediment, and stage of the Nolte spring in response to the storm were examined in a previous study. The response of the above characteristics depended on the storm water pathways through the karst network and antecedent conditions. The recharge area for the spring is mainly pasture and cropland.

Unlike the above parameters, the nitrate concentration has a seasonal rather than a storm trend. The elevated values occurred between the middle of autumn and beginning of winter. The minimum nitrate concentrations, 6.87 – 9.40 mg/l, were recorded between February and September, which spans the entire growing season. Elevated nitrate values, 15.26 -19.69 mg/l, were measured between October and January. The concentration rose again in October of the second year. The increase in nitrate is attributed to the release of nitrate from the soil at the end of the growing season. It is unlikely that nitrates are retained in the karst drainage system, suggesting that the appearance of nitrate at the spring is due to sequestration then recharge through the soil and epikarst.