Determining Sources of Dissolved Organic Carbon and Disinfection Byproduct Precursors to the McKenzie River, Oregon

Abstract

This study was conducted to determine the main sources of dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors to the McKenzie River, Oregon (USA). Water samples collected from the mainstem, tributaries, and reservoir outflows were analyzed for DOC concentration and DBP formation potentials (trihalomethanes [THMFPs] and haloacetic acids [HAAFPs]). In addition, optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) were measured to provide insight into DOM composition and assess whether optical properties are useful proxies for DOC and DBP precursor concentrations. Optical properties indicative of composition suggest that DOM in the McKenzie River mainstem was primarily allochthonous--derived from soils and plant material in the upstream watershed. Downstream tributaries had higher DOC concentrations than mainstem sites (1.6 +/- 0.4 vs. 0.7 +/- 0.3 mg L(-1)) but comprised < 5% ofmainstem flows and had minimal effect on overall DBP precursor loads. Water exiting two large upstream reservoirs also had higher DOC concentrations than the mainstem site upstream of the reservoirs, but optical data did not support in situ algal production as a source of the added DOC during the study. Results suggest that the first major rain event in the fall contributes DOM with high DBP precursor content. Although there was interference in the absorbance spectra in downstream tributary samples, fluorescence data were strongly correlated to DOC concentration (R2 = 0.98), THMFP (R2 = 0.98), and HAAFP (R2 = 0.96). These results highlight the value of using optical measurements for identifying the concentration and sources of DBP precursors in watersheds, which will help drinking water utilities improve source water monitoring and management programs.

Concurrent photolytic degradation of aqueous methylmercury and dissolved organic matter

“…To examine which part of the absorbance and fluorescence spectra were most strongly related to MeHg concentration and percent MeHg loss, we calculated the correlation coefficients between MeHg concentration and percent loss and each individual absorbance wavelength and fluorescence wavelength pair over the course of the light exposure incubation. This graphical approach has been used to identify regions within optical spectra related to reactivity of DOM and the production of disinfection byproducts (Kraus et al, 2010). Correlation coefficients (R) were calculated using the Pearson Product Moment function in Excel and confirmed with Sigmaplot® (v.11).…”

Influence of habitat on the quantity and composition of leachable carbon in the O2 horizon: Potential implications for potable water treatment

“…Future work should also consider the seasonality of DOC production and flux, which will necessarily vary between species. It should also be noted that seasonal changes in flow paths will affect Implications of habitat coverage for water treatment downstream DOC composition and quantity (Kraus et al 2010).…”

Seeing the light: The effects of particles, dissolved materials, and temperature on in situ measurements of DOM fluorescence in rivers and streams

“…Continuous in situ measurements of the fraction of CDOM that fluoresces (hereafter referred to as FDOM) in freshwaters provide new opportunities for assessing constituent loads, drinking water quality, terrestrial carbon budgets, and changes in ecosystem food webs (Cole et al 2007;Findlay and Sinsabaugh 2003;Kraus et al 2010). However, measuring fluorescence in situ in inland water bodies, which are often highly colored or turbid, can require corrections and accommodating procedures not usually needed for optically clearer coastal waters.…”