The synergistic effects of climate variability, streamflow, land cover change, and fertilizer application on long-term stream water quality across scales

Abstract:

Understanding the coupled human-nature system effects on stream water quality is essential for watershed management. Few studies investigated the synergistic effects of a comprehensive set of drives—climate variability, stream flow, land cover change, and fertilizer application—on long-term stream water quality across local and regional scales. To bridge this gap, we collected/generated annual land cover, monthly streamflow, climate normal, climate extremes, and fertilizer application data to determine their individual and combined influence on stream water quality in the Texas Gulf Region from 1985 to 2015. Stream water quality indicators included chlorine, dissolved oxygen, pH, total suspended solid, sulfate, conductivity, total phosphorus, and water temperature. At the subbasin (HUC8) scale, we used time series cross-correlation analysis and Granger’s causality test to investigate how stream water quality responds to changes of different drivers in each subbasin. At the subregional (HUC4) and regional (HUC2) scales, we applied linear mixed models to quantify how much variation in steam water quality is explained by each driven factor as well as their interaction effects. The preliminary results suggested that the major driven factor of stream water quality trend varied according to spatial heterogeneity and seasonality. The synergistic effect of multiple drivers could either mitigate or exacerbate each other in affecting stream water quality. The results of this study can inform efficient water quality management approaches under different land use and climate scenarios by uncovering the potential mechanisms in stream water quality impairment.