Phosphorus Dynamics in a Karstic Groundwater-Surface Water System in Western New York

The Onondaga limestone in parts of western New York forms a poorly developed karstic terrain with fracture-dominated flow. Much of the land use in the area within Livingston and Genesee Counties and surrounding Oatka Creek is dominated by agriculture. Oatka Creek has experienced degraded water quality conditions due to excess nutrients, in particular phosphorus. In this study, we investigate trends in total P (TP) concentrations within a reach of Oatka Creek and the shallow groundwater system. Water samples were collected along a reach of Oakta Creek, from shallow regional water wells and from fractures within the Onondaga formation exposed in a gorge within the stream reach studied. Results show an increase in TP concentrations moving downstream through the Oatka Creek reach with values ranging from approximately 250 ug/L to 320 ug/L. The maximum increase from the upstream to downstream sampling stations observed to date is 55 ug/L over the approximately 3.6 km reach of stream. Groundwater samples in the region taken from the Onondaga formation show a wide range of values from approximately 60 ug/L to over 350 ug/L TP. Similar to the groundwater samples as expected, samples from the exposed fractures show TP values with a range similar to groundwater samples, and often at a higher concentration that the upstream surface water samples. In particular, high TP values are often seen during and immediately following rain events. These data suggest that the karst topography and fracture dominated flow in the water table aquifer impact local stream water quality rapidly and with little natural attenuation of P.