Hydrocarbons of Aquatic and Terrestrial Origin in Mountain Streams of the Marmot Basin

The abundance of n‐alkanes in stream waters of the Marmot Creek drainage basin was studied to develop an understanding of the source of hydrocarbons in a pristine mountain stream. The n‐alkanes varied in concentration from 0.02 µg/liter to 0.06 µg/liter and exhibited a bimodal distribution with one grouping in the range of C15–C23 and the other between C25–C32. Carbon preference indices (1.2 and 4.0, respectively) suggested that the first group was largely produced by nonphotosynthetic aquatic organisms and second was from soil and terrestrial vegetation. The contributions from stream and soil were roughly equal. Hydrocarbons in pristine mountain streams thus appeared to be derived both from autochthonous and allochthonous sources. Isoprenoid hydrocarbons were present in lesser abundance than alkane hydrocarbons. Abundance of the isoprenoids relative to n‐alkanes indicated that little, if any, degradation of n‐alkanes occurs in the stream waters. Aromatic hydrocarbons were not present above detection limits of 1 ng/liter.