EVALUATING THE IMPACT OF FLUVIAL WOOD ON ECOSYSTEM METABOLISM IN A LOW-GRADIENT, MID-CONTINENT STREAM, OHIO, USA

Accumulations of fluvial wood (FW) promote heterogeneity in streams, encourage biodiversity, and improve stream health. Previous studies on the impact of FW on biogeochemical dynamics in Raccoon Creek (Licking County, Ohio, USA), found enhanced gross primary production (GPP) above logjams and enhanced ecosystem respiration (ER) below logjams. Infrastructure associated with recent industrial development in Licking County is likely to change ecosystem processes in the Raccoon Creek watershed. To investigate this impact, we synchronously monitored biogeochemical dynamics upstream and downstream of a FW accumulation in the headwater region of Raccoon Creek (40.084667°, -82.596514°). The study site drains 43.6 km² in the headwaters of the broader 264 km² Raccoon Creek watershed. The upstream locality was in the open channel far from any FW. The downstream site was located ~40 m away, in a partially isolated pool immediately below a channel-spanning FW accumulation. At each site, we deployed a YSI EXO multiparameter sonde and a Pro-Oceanus Mini CO₂ Submersible pCO₂ Sensor. The YSI EXO measured depth, temperature, turbidity, dissolved oxygen (DO), pH, and specific conductivity (SC), and the Pro-Oceanus Mini CO₂ sensor measured dissolved carbon dioxide (CO_2(aq)). Photosynthetically active radiation was measured with a PME miniPAR between the upstream and downstream sites. On average, DO and pH were lower in the downstream site (~4%, and ~0.2, respectively), whereas CO_2(aq) concentrations were higher (~770 ppm). These observations suggest increased ecosystem respiration downstream of FW, likely due to increased cellular respiration of the accumulated organic matter in the scour pool. To further test our hypothesis we calculated net ecosystem production (NEP), defined as the sum of GPP and ER, using water temperature, DO, depth, and light. Our results suggest that this reach of Raccoon Creek is heterotrophic. Areas immediately downstream of FW show enhanced ecosystem respiration, suggesting the presence of fluvial wood promotes biogeochemical and environmental heterogeneity and should be considered in the development of stream management strategies.