August 19, 2020
A New Approach for Identifying Water Quality Hot Spots in Watersheds
Differential concentration-discharge (C-Q) analysis tool holds promise for helping water quality managers pinpoint critical stream reaches for monitoring.
Concentration–discharge (C-Q) relationships reflect sources, storage, reactions, and transport of solutes in watersheds. Compared to traditional C-Q approaches, a new “differential C-Q” approach performed well and enabled researchers to identify critical stream segments that assimilate harmful chemicals such as nitrate and phosphate. The new, easy-to-use approach can account for gains, losses, and/or fractional solute turnover over each stream segment. It also yielded a better accounting than traditional approaches of the specific sources, hillslope contributions, and critical stream segments that can adversely impact river water quality.
The differential C-Q analysis is a valuable tool for assessing differences across stream reaches, comparing accumulation and mobilization of harmful chemicals within and across reaches, and monitoring solute behavior in the face of hydrologic and climatic perturbations. This approach can therefore aid watershed and land managers in identifying the stream segments that are essential to monitor and in designing pollution prevention or intervention strategies.
Concentration-discharge (C-Q) relationships are often used to describe how water moves through streams and the chemicals that are transported with it. These relationships are typically examined at individual sampling stations, which do not provide sufficient information about accumulation or mobilization of harmful chemicals, pesticides, or other solutes. In this study, the researchers present a new differential C-Q approach that can capture the increase, decrease, and/or the fractional solute turnover over each stream segment. To evaluate and compare this differential approach with traditionally used approaches, the team used water quality data collected at the East River, Colorado, watershed. The traditional C-Q patterns showed a consistent “L” shape for nitrate across three stations of the East River watershed. In comparison, differential C-Q approach showed gains in nitrate in the upstream reach and losses in the downstream reach during high gains in discharge. In contrast to nitrate, gains in phosphate, organic carbon, molybdenum, and several other solutes were observed in the downstream reach due to its low-relief, meandering terrain. In this manner, the new C-Q approach clearly indicated when and where small increases in nutrients like phosphorus and nitrate can be particularly concerning, given the potential for algal growth and eutrophication. Overall, the differential C-Q approach holds potential for aiding water quality managers in the identification of critical stream reaches that assimilate harmful chemicals.
Lawrence Berkeley National Laboratory
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
This material is based on work supported as part of the Aggregated Watershed Component of the Watershed Function Scientific Focus Area funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award no. DE-AC02-05CH11231.
Arora, B., et al. "Differential C-Q Analysis: A New Approach to Inferring Lateral Transport and Hydrologic Transients within Multiple Reaches of a Mountainous Headwater Catchment." Frontiers in Water 2 (24), (2020). https://doi.org/10.3389/frwa.2020.00024.