EFFECTS OF VARIABLE STREAM DISCHARGE ON TEMPORAL COMPARISON OF WATER QUALITY DATA DUE TO LAND USE

Like all streams passing through transitions of changing land management practices, water quality in the lower Esopus Creek, located in Hurley, New York, is often at risk of contamination. Analyses of stream water chemistry parameters were performed over a span of three growing seasons to evaluate water quality evolution in a selected reach of the drainage basin, with the intention of determining the effectiveness of environmentally friendly growing practices implemented by the Hudson Valley Farm Hub (HVFH), in Hurley NY. However, the comparison of water quality changes over time gets complicated because the stream flow may not remain the same while water samples get collected at different times. If the land use does not change, the dissolved load of constituents should remain the same. In this circumstance, samples collected during high flow condition should show a lower concentration compared to samples collected when the stream discharge is lower.

Water samples were collected from the lower Esopus Creek and its tributaries flowing through the HVFH area at 18 locations. Stream discharge was measured in five selected sample locations using a current flow meter. These samples were analyzed for common cations (Ca, Mg, Na, P, and NH₄) and anions (NO₃, PO₄, Cl, and SO₄). The temperature, pH, dissolved oxygen, and total dissolved solids (TDS) of water samples were measured in the field. The water chemistry data were compared with the stream discharge data.

The result shows that water quality gradually improved over time. The variation in stream discharge affects concentrations but no significant relationship was observed. For example, during early summer, the TDS showed a strong negative correlation with stream discharge, while nitrate concentration did not show any significant relationship with discharge. However, when the TDS and nitrate concentrations were compared using June-October data, no relationship was observed with discharge, but nitrate showed a better relationship with discharge than TDS in this case. This could be attributed to the fact that during low flow condition the baseflow is the dominant contributor of stream discharge and the water quality parameters of baseflow remain relatively constant. Additional temporal data needs to be collected to figure out this complex relationship for better comparison.