Spatial and Temporal Patterns of THM Precursors in a Eutrophic Reservoir

ABSTRACT

Temporal and spatial patterns of trihalomethane (THM) precursors (measured as THM formation potential, THMFP) are described and analyzed for eutrophic Cannonsville Reservoir, NY, based on monitoring conducted weekly over the April to November interval of 1995 at three sites along the main axis of the reservoir. Ninety-eight percent of the precursors formed chloroform, and 94% were in a dissolved (0.45-μm filtrate) form. Distinct seasonal, vertical and longitudinal patterns were observed. Progressive increases in THMFP occurred from spring (~170 μg · L⁻¹) through midsummer (~360 μg·L⁻¹) in the epilimnion of the lacustrine zone of die reservoir, followed by subsequent decreases through early fell. Progressive, but smaller, increases in THMFP occurred in the hypolimnion throughout the period of stratification. Vertical patterns in dissolved THMFP within the hypolimnion indicate the sediments were not an important source of precursors to the water column. Summer epilimnetic concentrations of THMFP were substantially higher than those reported for the inflows (Stepczuk et al. 1998a), establishing the operation of autochtonous sources. Features of the THMFP patterns, including epilimnetic enrichment, the seasonality, and higher concentrations in the more eutrophic riverine zone, and the results of a single laboratory experiment, indicate a linkage between primary production and autochthonous production of precursors. Dissolved organic carbon was not a good surrogate measure of THMFP.

Key Words:

• THM precursors
• allochthonous sources
• autochthonous sources
• eutrophication
• reservoir
• primary productivity