Landscape pollution source dynamics highlight priority locations for
basin-scale interventions to protect water quality under extreme events
Abstract
Extreme weather conditions are associated with a variety of water
quality issues that can pose harm to humans and aquatic ecosystems.
Under dry extremes, contaminants become more concentrated in streams
with a greater potential for harmful algal blooms, while wet extremes
can cause flooding and broadcast pollution. Developing appropriate
interventions to improve water quality in a changing climate requires a
better understanding of how extremes affect watershed processes, and
which places are most vulnerable. We developed a Soil and Water
Assessment Tool model of the Cape Fear River Basin (CFRB) in North
Carolina, USA, representing contemporary land use, point and non-point
sources, and weather conditions from 1979 to 2019. The CFRB is a large
and complex river basin undergoing urbanization and agricultural
intensification, with a history of extreme droughts and floods, making
it an excellent case study. To identify intervention priorities, we
developed a Water Quality Risk Index (WQRI) using the load average and
load variability across normal conditions, dry extremes, and wet
extremes. We found that the landscape generated the majority of
contaminants, including 90.1% of sediment, 85.4% of total nitrogen,
and 52.6% of total phosphorus at the City of Wilmington’s drinking
water intake. Approximately 16% of the watershed contributed most of
the pollutants across conditions—these represent high priority
locations for interventions. The WQRI approach considering risks to
water quality across different weather conditions can help identify
locations where interventions are more likely to improve water quality
under climate change.