Dissolved organic matter in Arizona reservoirs: assessment of carbonaceous sources

Most studies of freshwater dissolved organic matter (DOM) have been conducted in temperate climates where allochthonous organic material is abundant. Because climatic conditions of the Southwestern USA are different than temperate environments, DOM from three freshwater reservoirs (Saguaro Lake, Bartlett Lake and Lake Pleasant) was investigated to determine the importance of allochthonous and autochthonous organic material. Results from the study show hydrophobic acids constitute a small percentage of the DOM, while the neutral and hydrophilic fractions are more prevalent. C/N ratios are comparatively low relative to other freshwater systems, ranging between 28 and 35 for the hydrophobic acid fractions, while DOC/DON ratios are seasonally influenced by epilimnionic algal growth. The isolated organic fractions were low in aromatic content measured by solid-state 13C NMR resulting in low aromatic to aliphatic carbon ratios. Organic material recovered from Saguaro Lake and Lake Pleasant display traits that suggest most allochthonous contributions are highly attenuated favoring organic material from autochthonous sources (low C/N and aromatic/aliphatic carbon ratios), whereas organic material from Bartlett Lake demonstrated a greater seasonal perturbation in source influence.