Date of Award

Winter 2008

Project Type


Program or Major

Natural Resources: Water Resources

First Advisor

William H McDowell


Dissolved organic nitrogen (DON) is an important bioavailable source of nitrogen in terrestrial and aquatic systems. However, few studies quantify DON constituents such as dissolved free amino acids (DFAA) and investigate their concentrations along a hydrologic flowpath. Dissolved free amino acids and other water chemistry parameters were measured at different sites along the Lamprey River from September, 2006 to September 2007. The same analyses were performed on wet precipitation and throughfall samples within the Lamprey River watershed to represent a flowpath from atmosphere to surface waters to better understand nitrogen cycling within the watershed and speculate on possible influences. Ions and nutrients, as well as amino acid concentrations, increased from wet precipitation to throughfall and decreased in stream water. The amino acid contribution to DON increased slightly from wet precipitation to stream water. High concentrations of amino acids asscociated with microbes were present in throughfall and stream samples. A principal components analysis showed that amino acids, especially those of peptidoglycans, explained more within group variance, in throughfall and stream water. Discriminant analysis showed that specific amino acids differed significantly and were used to discriminate between water types. Amino acid concentrations correlated well with dissolved inorganic nitrogen in wet precipitation and throughfall. Amino acids were better correlated with NH4+ than all other solutes in stream water. Amino acids did not appear to correlate with a runoff index in stream sub-basins. The percent of wetlands within sub-basins was significantly correlated with amino acid concentrations. More DON in streams existed in aromatic forms than in rainfall or throughfall, which suggests that soils are a major source of complex organic molecules found in streams and a major sink for dissolved free amino acids.