Title: Agricultural Irrigation Water Quality In The Lower Boise River Basin: A Quantitative Assessment Of Canal Ecosystem Metabolism And Escherichia Coli Spatiotemporal Variability
Program: Master of Science in Hydrologic Sciences
Advisor: Dr. Kendra Kaiser, Geosciences
Committee Members: Dr. Anna Bergstrom, Geosciences; and Dr. Alejandro Flores, Geosciences
Within agricultural regions irrigation canals are pervasive. Despite their vast spatial extent and significant volumetric impact on the hydrologic cycle, the role of irrigation canals as intermittent channels within a river network, as well as their various functions (e.g.,, supporting aquatic ecosystems, transporting microbial communities, altering the carbon cycle) are not well understood. Microbial water quality and aquatic ecosystem metabolism represent two critical components of stream channel assessments that can provide new insights into the complex roles and spatiotemporal patterns of irrigation canals, both for the human health sector and the field of stream ecology. The goal of this research is to expand our understanding of irrigation canals beyond their primary role as water conveyance systems. To facilitate this understanding, research in an agricultural canal system in the Lower Boise River Basin was conducted to answer the following questions: 1) Does E. coli spatial dependence exist in the canals?; 2) Are there other water quality metrics that predict E. coli spatiotemporal variability?; 3) How do canals function metabolically compared to natural streams?; and 4) What role do canals play in the carbon cycle? To address these research questions the following field methods were conducted: 1) a 2-year sampling design at 60 sites in two canals to determine E. coli levels and three other water quality parameters (TSS, dissolved oxygen, temperature); and 2) a 1-station continuous dissolved oxygen monitoring approach with bayesian inverse modeling to calculate daily metabolic rates in g O2 m-2 d-1. The findings indicate that: 1) there may be a generalized pattern of E. coli spatial dependence across canals and other water quality parameters may help detect changes in E. coli magnitude, and 2) canals have the potential to support increasing levels of primary production throughout the entire growing season and may end up with a net-neutral annual carbon balance due to the period removal of organic matter from the canal limiting heterotrophic respiration.