Soluble Phosphorus And Nitrate Transport By Monitoring Ground Water And Stream Flow Discharges In The New York City Source Watersheds

Abstract

Agricultural areas are assumed to contribute excessive nutrients to surface and ground water. However, little research has explored the impact of agricultural activity on alluvial valley soils in mountainous terrain. Soluble reactive phosphorus (SRP) and nitrate-N (NO3--N) concentrations were measured in 37 groundwater sampling wells, and 11 locations in two streams in an alluvial valley farm in the Catskill Mountains of New York State to assess the impact of agricultural activity on stream water quality. During the study period the farm implemented several near stream best management practices (BMPs), which allowed comparative analysis of the impact of BMPs on water quality. Analysis of measured SRP concentrations from shallow wells indicated that groundwater concentrations in the near stream area were not correlated with the instream concentrations. Despite over 100 years of manure application on the study farm stream SRP concentrations were generally below 0.1 mg L-1, with an average of 0.037 mg L-1, significantly less than those reported from surrounding hillside farms. The highest SRP concentrations were consistently measured at the shallowest groundwater depths. The NO3--N concentrations varied from the detection limit of 0.05 to 5 mg L-1 with an average of 2.2 mg L-1 similar to levels reported from other agricultural areas in the Catskills. The implementation of near stream BMPs, consisting of exclusionary fencing and cattle crossings, resulted in a 33% reduction (0.008 mg L-1) in stream SRP concentrations during the growing season. There was no detectable effect of the BMPs during the non-growing season. The NO3--N concentrations did not appear to be influenced by the BMP. The spatial variability of groundwater SRP indicated that SRP concentrations increased as the distance to the streams decreased. There was no a good relationship between concentrations in the groundwater riparian areas near stream and the stream itself where the SRP concentration in the groundwater around the stream was much greater than that in the stream. Temperature throughout the soil profile and depth to the groundwater table played an important role in the temporal availability of SRP in groundwater.