Grantee Research Project Results

Hydrological and Biogeochemical Interactions Across Scales: Implications for the Sustainability of Intensively-Managed Systems

EPA Grant Number: F6A10018
Title: Hydrological and Biogeochemical Interactions Across Scales: Implications for the Sustainability of Intensively-Managed Systems
Investigators: Hinckley, Eve-Lyn S.
Institution: Stanford University
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2006 through August 1, 2008
Project Amount: $111,344
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Environmental

Objective:

It is well documented that fertilizer nitrogen (N) has contributed to groundwater contamination, changes in sensitive coastal ecosystems, and increased emissions of the greenhouse gas nitrous oxide around the globe. Few studies have addressed how other applied nutrients may affect N losses, or the degree to which hydrologic flow paths control the coupling, transformations, and transfers of N and other nutrients from the soil core to the watershed. My research examines how sulfur (S), used intensively as a fungicide in the vineyard systems of Northern California, interacts with N, a nutrient necessary for vine growth, and the ways in which hydrologic conditions determine their fates. I will place emphasis on investigating both the pattern of solution losses (particularly at the field or management unit scale) and the primary mechanisms controlling transformations and losses of these nutrients.

The objective of this research is three-fold: to provide greater insight into the N and S cycles, to better understand the interactions of hydrology and biogeochemistry, and to provide results that can be used by winegrowers to inform environmentally-sound management practices.

Approach:

This project has three main phases: phase 1 is a field campaign to measure hydrologic losses of N and S species below the rooting zone of the vines during different hydrologic flow conditions, and N and S contents in the soil during the growing and dormant seasons; phase 2 is a set of laboratory experiments to determine (a) the primary mechanisms controlling the fates of N and S in soil cores using ¹⁵N and ³⁴S isotopes, (b) the N and S absorption capacities of soils collected from several locations across the region, and (c) how addition of S affects the transformations of N in soil cores; and phase 3 uses an EM38 to map apparent electrical conductivity at the field scale, which can be used to generate maps of correlating soil properties (e.g. texture, nutrient content, and salinity) that may control biogeochemical transformations and flow path characteristics.

Expected Results:

In the field experiments, I expect that the most influential flow paths in this system will be preferential flow paths formed by the drying of high clay soils during the growing season (coinciding with the dry season) and saturated matrix flow during the dormant season (wet season). N and S species collected in preferential flow will primarily reflect mineral surface interactions, whereas matrix flow will reflect the redox conditions (e.g. oxygen content and microbial community) of the system. In the lab experiments, I expect to see a higher preference for soil retention of sulfate-S versus nitrate-N, inhibition of nitrification (conversion of ammonium to nitrate) due to rapid oxidation of applied S, and conservation of N as ammonium under reducing conditions, due to reduction of sulfate to hydrogen sulfide. I expect to use the maps of soil properties resulting from the EM38 survey to connect the results of the core-scale laboratory experiments to patterns of losses at the field scale, and to guide hypotheses about processes operating at the landscape scale.

Supplemental Keywords:

Nitrogen, sulfur, hydrologic flow paths, biogeochemistry, sustainable agriculture,, RFA, Scientific Discipline, Water, Geographic Area, Water & Watershed, Hydrology, State, Environmental Monitoring, Ecology and Ecosystems, Watersheds, anthropogenic processes, biogeochemical study, nitrogen loading, agricultural watershed, fertilizer, fungicide, coastal ecosystems, ecosystem stress, herbecides, watershed assessment, California (CA)

Progress and Final Reports:

2007

Final