Factors Affecting Dissolved Phosphorus and Nitrate Concentrations in Ground and Surface Water for a Valley Dairy Farm in the Northeastern United States

Abstract

Agriculture often is considered to be a contributor of soluble reactive phosphorus (SRP) and nitrate‐N (NO3−‐N) to surface waters. This research analyzed SRP and NO3−‐N concentrations in groundwater and in a creek fed by groundwater on a valley dairy farm in the Cannonsville basin of the New York City (NYC) watershed. A total of 37 groundwater piezometers were installed to depths of 0.3 to 1.5 m. Water‐table depth and concentrations of SRP, NO3−‐N, dissolved organic carbon (DOC), and dissolved oxygen were measured at regular intervals over a three‐year period. A multivariate mixed model analysis of variance indicated that the SRP and NO3−‐N concentrations were controlled primarily by three classes of variables: environmental variables, including precipitation and water table depth; source variables, including manure applied and crop type; and chemical variables, including DOC and dissolved oxygen concentrations in groundwater. The highest groundwater concentrations of NO3−‐N and SRP were found at the shallowest water‐table depths, which has implications for agricultural nutrient management in areas with shallow groundwater.

Factors Affecting Phosphorous in Groundwater in an Alluvial Valley Aquifer: Implications for Best Management Practices

“…Although the largest P losses from manure occur shortly after spreading in liquid manure handling systems [59], this farm applied more solid manure that contains higher amounts of organic material. In fall when manure was applied we noted high concentration in groundwater especially after large storms (such as in [44]) when preferential flow with the SRP from the manure was likely the cause of these high concentrations. After high concentrations occur, the concentrations at the next sampling date decreased [12] because of interactions with the soil matrix.…”

“…Minimum concentrations observed in baseflow during summer and spring, were around 0.01 mg L −1 and less than 0.005 mg L −1 during fall and winter (Table 1). During high flow events maximum concentrations were significantly greater in the baseflow of Creek B and the groundwater because the groundwater came close to the ground surface where P concentrations were greater [44]. In these cases surface water table intersected with the ground likely contributing to the elevated concentrations in Creek B.…”

“…The 19 ha study site is located on a dairy farm in a valley bottom along a tributary of the West Branch of the Delaware River in the Cannonsville Reservoir watershed (1165 km 2 ) that supplies drinking water to New York City [44]. It has a physiography characterized by narrow valleys with steep walls and flat valley bottoms.…”

“…Overland flow is typically absent because of the high infiltration rates of these alluvial soils. Depth to the bedrock is approximately 18 m based on a measurement taken from a nearby well located 1 km to the north [44]. The climate of the study site is humid continental with an average temperature of 8 °C.…”

“…To measure water table heights and facilitate groundwater sampling, 22 subsurface PVC piezometers were installed at depths ranging from 0.3 to 1.5 m in the southern field of the study site ( Figure 1) [44]. The piezometers were 3.5 cm in diameter; with a screened length of 0-0.3 m from the bottom and wrapped with geosynthetic filter cloth.…”