THE INFLUENCE OF LARGE WOODY DEBRIS ON AQUATIC BIOGEOCHEMISTRY IN THE HEADWATERS OF A SMALL MID-CONTINENT STREAM IN OHIO, USA

Large woody debris (LWD) plays an important role in modifying physical and biological dynamics in fluvial ecosystems. Our previous work documented the influence of LWD on geomorphological and biogeochemical patterns in Raccoon Creek (Licking County, Ohio, USA). LWD accumulations enhanced hydraulic complexity and sediment storage capacity through development of backwater pools and depositional bar formation. Biogeochemical measurements indicated enhanced gross primary productivity (GPP) above and ecosystem respiration (ER) below LWD accumulations. The veracity of our biogeochemical conclusions, however, are uncertain because previous observations made above and below LWD were not synchronous. Here we present new data collected at the same time from above and below a single LWD accumulation in Raccoon Creek (42° 4.535’ N, 82° 33.77’ W). The site drains ~215 km² of the headwaters of Raccoon Creek. Most environmental variables (depth; dissolved oxygen, DO; pH, specific conductivity, SC; temperature; and turbidity) were recorded using YSI EXO2 and EXO3 multiparameter sondes. Photosynthetically active radiation (PAR) and aqueous carbon dioxide (CO²) were collected using a PME miniPAR logger and Pro-Oceanus Mini CO² sensor, respectively. Diel air and water temperatures ranged over ~10 and ~4 °C, respectively. PAR values were linked with turbidity and discharge. DO and pH were higher above LWD, suggesting enhanced ecosystem respiration within LWD accumulations in Raccoon Creek. To further evaluate this conclusion, we used water temperature, DO and several known site parameters to calculate net ecosystem respiration (NEP = GPP + ER; Note: ER is defined as a negative number, g O₂/m²⋅ d). GPP and ER values suggest Raccoon Creek is heterotrophic with enhanced ER associated with LWD accumulations. Ongoing environmental monitoring will further characterize shoulder season NEP. Our results suggest that the presence of LWD in Raccoon Creek facilitates elevated ecosystem respiration, promotes physical and biogeochemical fluvial heterogeneity, and should be considered when evaluating ecosystem metabolism and designing stream restoration strategies.