SOIL FINGERPRINTING IN THE PALOUSE BASIN, USA USING STABLE CARBON AND NITROGEN ISOTOPES

1 INTRODUCTION Watershed restoration efforts have been accelerated in recent years by mandates in the Clean Water Act, the Endangered Species Act, and increasing pressure from environmental groups (Wagner and Roberts, 1998). To address these mandates, water-quality management plans and Total Maximum Daily Loads (TMDLs) have been developed for surface waters, such as streams placed on the 303(d) list because of beneficial use impairment. Commonly, much of the degradation of surface…

SOIL FINGERPRINTING IN THE PALOUSE BASIN, USA USING STABLE CARBON AND NITROGEN ISOTOPES

Stable carbon and nitrogen isotopic compositions of soils coupled with mean elemental measurements of carbon/nitrogen (C/N) are potentially powerful tools for identifying soil origin in a watershed. Specifically, stable carbon and nitrogen isotopic compositions of soils reflect the types of plants growing on them and the source of nitrogen, respectively. The C/N ratios reflect the presence of an active biological milieu altering the elemental composition of soils. The objectives of this paper are to use the stable isotope technique to distinguish between forest and agricultural soils found in the Palouse Watershed and examine the predictive ability and rigorousness of this method. The isotopic enrichment of forest and agriculture soil samples is determined via a mass spectrometer by comparing the isotopic ratio of soil samples with those of standard materials. The findings of this study indicate that in monoculture environments stable carbon isotopic compositions do not differ between forest and agricultural soils. Instead, stable nitrogen isotopic compositions along with the C/N measurements could provide a reliable fingerprinting tool.