Watershed-scale controls outweigh local crossing effects on sediment loss from unpaved roads

In rural areas, unpaved roads can drive water quality degradation via sediment inputs. Excess sediment loss from poorly maintained unpaved roads to adjacent waterways blocks sunlight, decreasing primary productivity and increasing nutrient concentrations. This is particularly relevant to Arkansas, where 85% of county roads are unpaved; however, few studies have explored the impacts of unpaved roads in rural watersheds dominated by pasture. We sampled Brush Creek (Arkansas) to understand local (i.e., road crossing type) and watershed-scale (e.g., land cover/use) controls on sediment loss. We collected monthly baseflow and four opportunistic storm flow samples for total suspended solids (TSS) upstream and downstream at bridge, culvert, and direct stream crossings. Mean TSS yields downstream versus upstream of road crossings were comparable, especially at bridge and culvert sites, indicating these road crossings may not be critical TSS sources. At the watershed scale, TSS load showed increasing trends as both total length of unpaved roads and area of pastureland in a subwatershed increased (linear mixed effects; β = 0.03, R² = 0.41, p > 0.1; β = 0.67, R² = 0.42, p = 0.07, respectively). Moreover, TSS yields were higher during stormflow than baseflow (26.87 ± 6.82 vs. 0.38 ± 0.04 kg km^-2 day^-1; unpaired t-test, p < 0.01). Finally, seasonality influenced local and watershed patterns of TSS loss via variation in transport controls, including wet season conditions, discharge rates, and overland flow. Our findings indicate watershed-scale characteristics are key contributors to sediment loss in rural watersheds. Targeted best management practice implementation should focus on unpaved roads and pasturelands during key transport periods to effectively protect downstream water quality.