CHARACTERIZING BIOGEOCHEMICAL VARIABILITY ABOVE AND BELOW LARGE WOODY DEBRIS ACCUMULATIONS IN RACCOON CREEK, OH

Large woody debris (LWD) acts as a fluvial sieve, changing flow dynamics and altering the chemistry of transient river water. Quantifying the biogeochemical impact of these organic accumulations on local processes, e.g., ecosystem metabolism, may offer insight into larger themes of fluvial carbon dynamics and overall ecosystem health. Here, we monitored a four-mile stretch of Raccoon Creek (Licking County, Ohio) between May and July, 2022. Three significant LWD accumulations were observed using multiparameter submersible sondes (YSI EXO2, Pro-Oceanus Mini CO₂, and PME miniPAR). Sondes were deployed between 5-10 days above and below each LWD site. Measured parameters showed strong diel variability during background flow conditions, and photosynthetically active radiation (PAR) was significantly reduced by elevated turbidity following precipitation events. Our observations suggest dissolved oxygen (DO), specific conductivity (SC) and pH were lower below LWD (DO: 3.6-5.5%; SC: 9.1-117.9 μS/cm; pH: 0.03-0.08). In contrast, aqueous CO₂ concentrations were between 35 and 430 ppm higher downstream from LWD. Taken together, these data suggest enhanced ecosystem respiration below LWD accumulations in Raccoon Creek. To evaluate this hypothesis, we calculated net ecosystem production (NEP) using water temperature, DO, and several known site parameters such as water depth and barometric pressure. NEP is defined as gross primary productivity plus ecosystem respiration (NEP=GPP+ER): Calculating GPP and ER suggested that areas directly downstream of LWD were largely heterotrophic, with net ecosystem productivity reaching an average low of -6.24 g/m²·day at downstream sites and -2.38 g/m²·day at upstream sites. Our results suggest that LWD promotes enhanced ecosystem respiration, contributes to longitudinal ecosystem heterogeneity, and should be considered when evaluating ecosystem metabolism and designing stream restoration strategies.