Leaf Decomposition in a 6th Order Blackwater River in the Southeastern Coastal Plain: A 2-Year Study Over Differing Hydrologic Regimes

Leaf decomposition and colonizing invertebrates were examined in a 6th order reach of the Ogeechee River in southeast Georgia from 2012-2013. Litterbags filled with oak (Quercus sp.) or maple (Acer sp.) leaves were placed in the stream and retrieved after 56d. Leaf decomposition was measured using an exponential decay model and colonizing macroinvertebrates were enumerated, identified, and categorized into functional feeding groups. Differences in hydrology were observed with noticeably higher discharge rates during 2013. Leaf decomposition rates for Quercus and Acer ranged between -0.021 to -0.041 during 2012 and -0.012 to -0.044 during 2013, respectively, suggesting that both litter types breakdown quickly. Total macroinvertebrate abundance in litterbags was similar for both leaf types and increased slightly after the initial stages of leaf decay. Colonizing macroinvertebrate communities were dominated by scrapers (snails; Pleurocera) in 2012 and collector-gatherers (Chironomidae larvae) in 2013. The differences observed in macroinvertebrate taxonomic composition could be attributed to differences in hydrology and water quality from year to year at the site. Results suggest that leaf detritus can represent an important energetic source in large blackwater rivers.