Meeting the moment: leveraging temporal inequality for temporal targeting to achieve water quality load reduction goals

Authors: OPALINSKI, NICOLE - Pennsylvania State University; SCHULTZ, DANIEL - Pennsylvania State University; Veith, Tameria - Tamie; ROYER, MATT - Pennsylvania State University; PREISENDANZ, HEATHER - Pennsylvania State University

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2022
Publication Date: 3/22/2022
Citation: Opalinski, N., Schultz, D., Veith, T.L., Royer, M., Preisendanz, H. 2022. Meeting the moment: leveraging temporal inequality for temporal targeting to achieve water quality load reduction goals. Water. 14:1003. https://doi.org/10.3390/w14071003.
DOI: https://doi.org/10.3390/w14071003

Interpretive Summary: To improve water quality in our streams, the typical method for reducing pollution has been to target the placement of control strategies in places with the largest pollution sources (also called “hot spots”). However, there is currently no common way to design conservation strategies so that they treat the “hot moments” in time, when most pollutant loads are transported through the watershed. This study evaluates daily flow and pollutant loading from eight catchments in the Chesapeake Bay watershed to determine the periods of time during which loads are transported that are equal to the amounts that need to be reduced to be in compliance with load reduction goals. The targeting framework identifies the times that could be targeted to achieve these load reduction goals under low-flow or high-flow conditions to provide flexibility in the design of the control strategies. These results are critical in guiding development of site-specific, cost-effective tools to meet load reduction goals and water quality restoration goals for individual catchments.

Technical Abstract: Inequality is an emergent property of complex systems. In catchments, variation in hydroclimatic conditions and biogeochemistry cause streamflow and constituent loads to exhibit strong temporal inequality, with most loads exported during “hot moments”. Achieving water quality restoration goals in a cost-effective manner requires targeted implementation of conservation practices in “hot spots” in the landscape and “hot moments” in time. While spatial targeting is commonly included in development of watershed management plans, the need for temporal targeting is often acknowledged, but no common way to address it has been established. Here, we implement a Lorenz Inequality decision-making framework that uses Lorenz Curves and Gini Coefficients to quantify the degree of temporal inequality exhibited by contaminant loads and demonstrate its utility for eight impaired catchments in the Chesapeake Bay watershed. The framework requires a load reduction goal be set, and then links the degree of temporal inequality in annual nutrient loads to the periods of time during which those loads could be targeted. These results are critical in guiding development of site-specific, cost-effective tools that facilitate load reduction and water quality goal attainment for individual catchments. The framework provides valuable insight into site-specific potentials for meeting load reduction goals.