CORRELATIONS BETWEEN LAND USE AND THE ABILITY OF DOM FRACTIONS TO COMPLEX COPPER AND ZINC

Dissolved organic matter (DOM) characteristics are known to vary depending on their source. It is reasonable to suggest that land use plays a significant role in the type of DOM found in surface water systems. Metals, as well as organic pollutants, are known to complex readily with DOM present in natural systems. For instance, in surface waters, copper-DOM and zinc-DOM complexes are known to be the dominant species for these metals. It is hypothesized that DOM from different land uses varies in their ability to complex copper and zinc.

In order to test this hypothesis, four surface water bodies located within distinct land use areas were selected for sampling. These areas represent varying degrees of anthropogenic influence. Samples were collected from agricultural runoff, a golf course pond, a parking lot stormwater detention basin, and a forested swamp. A fractionation scheme utilizing different solid phase extraction cartridges conducted in parallel was used to isolate DOM based on hydrophobic, hydrophobic/hydrophilic, anionic, and cationic interactions; and quantified by the amount of dissolved organic carbon (DOC). The bulk molecular weight and the extent of aromatic structure were also used to characterize DOM. Inductively coupled plasma mass spectrometry was used to analyze copper and zinc concentrations within each fraction.

All four land uses produced DOC isolated by anion exchange (>80%), while no DOC was retained by cation exchange. The amount of DOC that could be retained by hydrophobic mechanisms ranged from 6% to 43%, with DOM from the parking lot stormwater detention basin showing the greatest hydrophobic interaction. The aromatic composition of DOM appears to increase with the bulk molecular weight, however, neither characteristic correlated with metal complexation. Strong linear correlations (R² > 95%) for binding constants (mg metal/mg DOC) were observed when data was grouped by land use in all cases except one (i.e., forested swamp). Complexation with DOM from golf courses did not fully explain metal concentrations. No correlations were observed when land use was not taken into account. These preliminary results suggest that land use influences the ability of DOM to complex metals.