Temporal Variation Of Sediment Distribution In A Karst Aquifer, Easton, Pennsylvania

Abstract

I studied the amount and type of sediment transport in a karst system as a function of storm events and seasonality. My research area is a karst groundwater system in the vicinity of the Bushkill Creek, north of the City of Easton, Northampton County, Pennsylvania. The karst system developed within the Ordovician Epler Limestone and Rickenbach Dolomite. Groundwater samples were collected from two karst springs identified along the eastern bank of the Bushkill, and a well installed in the Epler Formation, approximately 2,000 feet east of the Bushkill in a local recharge zone. Samples were also collected from a non-karst spring in the red shale of the Triassic Stockton Formation approximately 40 miles south of Easton in the Town of Buckingham, Bucks County, Pennsylvania. Biweekly samples were analyzed for particle size and water chemistry and selected samples for clay mineralogy. In addition, water level was measured in the monitoring well and Spring No. 1. An increased amount of sediment was transported in the monitoring well (approximately 200 to 800 mg/L) during the autumn and early fall compared to a low of 0 mg/L during the spring and summer. The spring discharged a low amount of sediment (a maximum of 9 mg/L) during the autumn of 2000 and three times the amount during the spring and summer. One storm monitored in March, 2000, monitored at the spring only, showed that the sediment load reached the maximum discharge of sediment (13 mg/L) subsequent to the storm peak. Correlation between sediment yield and water level in Spring No. I and the monitoring well.show that the overall sediment load increased during periods of low precipitation. The cumulative effect of karst systems flushed during the spring and summer may be to decrease sediment loading to discharge points, while water chemistry varies with individual precipitation events. The aqueous chemistry of the system shows dilution during wet periods and enriching of ions during dry periods. Storm chemistry shows that both dilution and flushing does occur in karst systems because ion concentration decreased over the course of a storm whereas the sediment yield increased. Sediment transport in karst aquifers varies because of how precipitation infiltrates the complex diffuse-­conduit systems of karst.