Data from: Projected land use changes will cause water quality degradation at drinking water intakes across a regional watershed

Forest conversion to development threatens the ability of watersheds to
provide stable and clean water supplies. Water managers are targeting
forest conservation as a source water protection strategy to maintain
healthy watershed function in developing areas, especially upstream of
drinking water treatment facilities. Understanding the role of current
forest cover in safeguarding these facilities is therefore crucial. We
used the Soil and Water Assessment Tool (SWAT) to examine the relationship
between upstream forest cover and downstream water resources under both
current (2020) conditions and multiple projected land use scenarios for
2070 in the Middle Chattahoochee watershed, USA. We investigated the
extent to which existing forest cover benefits water quality at 15
drinking water intake facilities within the watershed. Our analysis of
four land use change scenarios revealed that forest conversion and
increased development resulted in higher average annual concentrations of
total suspended sediment (TSS) and total nitrogen (TN) at 13 out of 15
intake facilities, with potential increases of up to 318% for sediment and
220% for nitrogen. Conversely, concentrations decreased relative to the
baseline when upstream agricultural land was converted to forest cover or
new, low-intensity development, suggesting that certain types of
development may improve water quality compared to maintaining agricultural
land. Our results also indicated that extreme nitrogen and sediment
concentration events – defined as days exceeding the highest 10th
percentile of baseline concentrations – could become 3.6 to 6.6 times more
frequent in the future, respectively. Notably, forest conversion to new
development upstream of intakes with smaller subwatersheds could reduce
water quality for utilities serving smaller towns and rural areas, which
may have limited resources for managing this challenge. Our findings
highlight vulnerable intake locations and underscore the benefit of forest
conservation for source water protection under future land use change.