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Geologic Nitrogen: A Potential Geochemical Hazard in the San Joaquin Valley, California
Author(s) -
Strathouse Scott M.,
Sposito Garrison,
Sullivan P. J.,
Lund L. J.
Publication year - 1980
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1980.00472425000900010014x
Subject(s) - san joaquin , geology , alluvium , cretaceous , clastic rock , nitrate , geochemistry , structural basin , total organic carbon , sedimentary rock , hydrology (agriculture) , environmental chemistry , geomorphology , paleontology , chemistry , soil science , geotechnical engineering , organic chemistry
Nitrogen geochemistry was studied in two selected drainage basins of the Diablo Range, which is adjacent to the San Joaquin Valley in California. Cantua Creek Basin drains into alluvial soils which contain up to 2,000 mg/liter indigenous nitrate N in the soil solution. It represents a fairly complete stratigraphic section of Upper Cretaceous to Tertiary geologic sediments, dominated by fine‐grained mudrocks and shales. The Ortigalita Creek Basin drains into alluvial soils with low levels of indigenous nitrate. It contains an incomplete stratigraphic section dominated by Upper Cretaceous coarse‐clastic rocks with subordinate amounts of mudrocks, capped by Tertiary gravels and marls. Total N concentrations in the Cantua Creek Basin geologic sediments ranged from a few µ g/g to nearly 4,800 µ g/g. Organic N was the major species in the Cretaceous sediments, reaching a maximum concentration approaching 1,200 µ g/g. Nitrate N concentrations were always < 100 µ g/g in the Cretaceous sediments, but approached 4,800 µ g/g in a rock sample from a recent Tertiary unit. The total N and nitrate N concentrations increased from older to younger geologic sediments, while ammonium N concentrations varied from a few µ g/g to 360 µ g/g. Organic N concentrations in the Ortigalita Creek Basin geologic sediments attained a maximum value of 500 µ g/g and nitrate N concentrations there reached a maximum of 600 µ g/g. However, the highest total N concentration of 2,000 µ g/g occurred as 75% fixed and soluble‐exchangeable ammonium. The contrast in concentrations and chemical species of nitrogen between the two basins was explained partially by sediment type. Organic matter is associated with fine‐grained sediments and, consequently, Cantua Creek sediments contain a higher portion of organic matter and a more available geologic source of nitrogen. On the other hand, the presence of high ammonium concentrations and a corresponding high‐charge smectite in the Ortigalita Creek Basin suggested that one of the principal sources of nitrogen in rocks from that basin was fixed ammonium bound to layer silicates.