The Effects of Off-Highway Vehicle Trails and Use on Stream Water Quality in the North Fork of the Broad River

Managing forests for recreational benefits, such as off-highway vehicle (OHV) use, as well as other ecosystem services, such as clean and abundant water, can often present challenges for land managers when one ecosystem service conflicts with another. We conducted research in the Chattahoochee-Oconee National Forest to determine if the presence and use of OHV trails were associated with greater total suspended solids (TSS) concentrations and turbidity in streams during storm events in 2015-2016. We used a paired-watershed approach, with a treatment watershed containing the Locust Stake OHV trail system on the North Fork of the Broad River, and a reference watershed (Kimbell Creek) similar in all respects except for the presence and use of OHV trails. During the study period, mean streamflow rates across all sampling times were 19% greater, but mean stormflow rates were 29% less, at Locust Stake compared to Kimbell Creek. During storm sampling, the average storm TSS concentration was greater at Locust Stake (101.1 mg L-1) than at Kimbell Creek (65.3 mg L-1). The results indicate that the greater the stormflow, the greater the TSS concentration for each storm event sampled across both watersheds. TSS concentration was linearly and positively related to stormflow, with R2 values ranging from 0.11 to 0.92 for all events in both watersheds. Across all sampling dates, the TSS concentration per unit stormflow was greater at Locust Stake than at Kimbell Creek, and was 7-fold greater at Locust Stake after the OHV trails were opened compared to when they were closed for maintenance and assessment. When the OHV trails were closed, the TSS concentration per unit stormflow was still significantly greater, by 4-fold, at Locust Stake compared to Kimbell Creek. Our results suggest that the presence and use of the Locust Stake OHV trail system are associated with poorer water quality, and with better water quality when the trails are closed. Forest managers face a well-defined set of tradeoffs between providing OHV recreation and water quality benefits that warrants careful planning and monitoring. Keywords: National Forest System, Off-highway vehicles, Recreation, Sedimentation, Streamflow, Turbidity, Water quality.