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.
Bibliographical noteFunding Information:
The authors acknowledge the City of Phoenix for their financial sponsorship of this research with assistance from the Salt River Project and the Central Arizona Project for continued strategic and administrative support. Milton Sommerfeld contributed by leading parallel algae-studies along with the reported DOM work. Supporting research was provided by Mario Esparza, Kirsten Hintze, Tom Dempster, Mari Rodriguez, Michelle Cummings and Samanth Dawson. 13 C NMR studies were performed at the ASU Nuclear Magnetic Facility (CHE-92-14799, CHE-9808678). The authors also acknowledge the valuable insight provided by the anonymous reviewers for this manuscript.
- Dissolved organic matter
- organic nitrogen