Geologic nitrogen and the occurrence of high nitrate soils in the western San Joaquin Valley, California

Abstract

Mudstones of the Tulare Formation, shales and sandstones of the Vaqueros Formation, and the Kreyenhagen Shale are identified as the NO3--rich (≤4758 μg/g) sources of geol. N within the Ortigalita Creek and Cantua Creek drainage basins of the Diablo Range. The distribution of these NO3--rich formations within the drainage basins tributary to the San Joaquin Valley are used to predicted alluvial fan enrichment in groundwater-transported NO3-. The most NO3--rich alluvial fan soils are predicted between Panoche and Cantua creeks; high-moderate soil NO3- can be expected below Arroyo Honda and between Tumey Gulch and Little Panoche creeks. These predicted NO3- distributions show no apparent relation to mapped soil-type patterns, consistent with a soil NO3- enrichment process which is independent of pedogenetic development.