IMPACT OF ALL-TERRAIN-VEHICLE (ATV) TRAIL CROSSINGS ON STREAM QUALITY, LITTLE SEQUATCHIE RIVER, TN

A popular ATV trail crosses the Little Sequatchie River (LSR) increasing sediment delivery from exposed collovium. Multiple groundwater inputs from karst topography increases event-driven high-flow, leading to increased sediment entrainment from the trail surface during flooding. Stream-center water grab samples were collected over 10 weeks at 7 sites (LSR1-LSR7) and analyzed to determine water chemistry changes with flow velocity fluctuations. Field analyses show mean pH values for all sites ranged from 7.2 to 7.7. Alkalinity titration data relates these pH values with basin geology. Samples at LSR 1 are more influenced by carbonate (Alkalinity = 78.9 mg/L) than the upstream samples (LSR 2-7) where alkalinity ranged from 56.1-57.7 mg/L. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was utilized to identify the presence of trace metals; concentrations were well within the range of natural waters. Spectrophotometer analysis found high SiO₂ values (5.07 – 6.00 mg/L) correlating to X-Ray diffraction (XRD) analysis of substrate specimens (sandstone). Hardness revealed higher concentrations of Mg than Ca; characteristic of local dolomite aquifers. Colluvium particle distribution by sieve and hydrometer show fines (<2mm) composed the majority of sediment. Stream geometry was quantified at 2 sites; LSR 5 (trail crossing) and LSR 2 (downstream pool) to determine boundary layer shear stresses. LSR 2 shear stress was calculated as 0.264 N/m², less than the critical value of 0.837 N/m² to initiate movement of particles 0.5mm (the most abundant size from sieve and hydrometer analysis). LSR 5 shear stress was calculated as 1.27 N/m², greater than the calculated critical shear stress of 0.838 N/m², needed to transport colluvium of 0.5mm. This indicates transport of sediments from LSR 5 and deposition at LSR 2 during low-flow events.