Influence of bedrock geology on dissolved organic matter quality in stream water

A field study was conducted to determine the linkage between dissolved organic matter (DOM) quality and bedrock geology. Sediment and water samples were collected from six streams, three flowing over sandstone and three flowing over limestone bedrock in the Bankhead National Forest, Alabama. Various stream water and sediment characteristics were determined by standard limnological methods and DOM quality was determined by Fourier transform ion cyclotron resonance mass spectrometry with sample introduction by electrospray ionization (ESI FT-ICR MS). Stream waters from limestone streams showed higher concentrations of calcium, magnesium, sodium, sulfate and dissolved inorganic carbon, as well as higher pH and acid neutralizing capacity, and were enriched in condensed hydrocarbons. In contrast, stream waters from sandstone streams showed higher concentrations of aluminum and iron and were enriched in tannin-like compounds. ESI FT-ICR MS analysis indicated that stream water DOM consisted of between 2950 and 3700 individual compounds ranging from 250 to 1000 Dalton. DOM compounds were grouped into 35 heteroatom (NnOoSs) classes based on molecular formula assignments and multivariate statistical analysis was applied to reveal the patterns of variation of the DOM quality and identify environmental parameters associated with the variation. Partial redundancy analysis indicated that the variation in stream water DOM quality correlated with stream location and water chemistry parameters associated with bedrock type. A similar analysis including three previously published ESI FT-ICR MS analyses of stream water DOM showed similar correlations with location and stream water chemistry, indicating that bedrock geology via stream water chemistry influences DOM quality.