SPATIAL AND TEMPORAL VARIABILITY OF ANION CONCENTRATIONS AND SUSPENDED SOLIDS IN THE LITTLE CHAZY RIVER, NORTHEASTERN NEW YORK

The Little Chazy River is a 145 km² rural watershed in northeastern New York. Agriculture comprises about 17% of land use in the watershed; much of which is distributed along the lower reaches of the main channel in the Champlain Valley. In this study we assessed the sources of nitrate-N, total phosphorus, soluble reactive phosphorus, chloride, and sulfate-S in the Little Chazy River and its tributaries at high-resolution spatial and temporal scales.

The spatial distribution of solute concentrations generally reflects land cover and land-use patterns in the watershed. Nutrient concentrations (nitrate-N, TP and SRP) increase downstream, reflecting the cumulative impact of agricultural land use in the Champlain Lowland. Smaller scale variations relate to spatially and temporally variable stream discharge, manure-application rates and distribution, dilution, physical or biological sequestration in small impoundments and variable inputs from small agricultural tributaries drainage ditches, or tile drains. Concentrations of chloride and sulfate-S also increase downstream with secondary variations more closely related to inputs from roads or small communities than agriculture.

We also evaluated solute and suspended solids concentrations in storm runoff for seven runoff events, including two snow melt events in March 2011 and the late summer runoff from Hurricane Irene in August 2011. For all events, stream-water solute concentrations varied closely with rainfall or snowmelt intensity. Most of the solute load was released during the early rising limb of the stormflow hydrograph and fell near background levels shortly after the stormflow peak. Suspended solids concentrations generally were more closely related to stormflow discharges. Bound phosphorus, which represents the difference between TP and SRP, increased along with the solutes during the hydrograph rise but followed TSS, near the stormflow peak. These observations reflect varying sources and runoff pathways during the event, with most of the solutes contributed via surface pathways in the earliest stages and particulate constituents derived from upstream or in-channel sources later. Modest increases in solutes during the later portion of the falling limb were observed during some of the events. These increases probably reflect the cessation of stormflow and return to baseflow.