Location: Water Quality and Ecology ResearchTitle: Source, habitat and nutrient enrichment effects on decomposition of detritus in Lower Mississippi River Basin bayous Author
Submitted to: Freshwater Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2017
Publication Date: 9/12/2017
Citation: Taylor, J.M., Lizotte Jr, R.E., Testa Iii, S., Dillard, K.R. 2017. Source, habitat and nutrient enrichment effects on decomposition of detritus in Lower Mississippi River Basin bayous. Freshwater Science. 36(4):000-000 doi:10.1086/694452. Interpretive Summary: Interactions between agricultural runoff and changing inputs of leaf matter to water bodies may significantly alter their ecological function in the Lower Mississippi River Basin (LMRB). This is important because dead leaf material support aquatic food webs from the tiniest microbe all the way up to game fish. This study compared the breakdown of leaves from corn and a common oak species (willow oak) to better understand how leaf matter breakdown from two very different sources occurs in LMRB lakes. Additionally, we measured microbial respiration, a process that consumes dissolved oxygen and is linked to leaf decay. The central findings of this study were: 1) corn residue is highly labile and breaks down rapidly in LMRB lakes; and 2) nutrient enrichment enhances breakdown rates and associated microbial respiration of both corn and oak leaves. These results provide additional support for establishing more extensive forest buffers between agricultural areas and water bodies within the LMRB. Enhanced forested areas intercept and process excess nutrients in agricultural runoff, but can also modulate the timing, quality, and composition of leaf inputs. Our results suggest that reductions in inputs of crop residue coupled with lower nutrient inputs to agricultural water bodies may reduce the magnitude and frequency of depleted oxygen events in aquatic ecosystems surrounded by agricultural landscapes in the LMRB.
Technical Abstract: Potential differences in storage and processing of detritus in agricultural landscapes may alter freshwater ecosystem function. We compared decomposition rates of maize (Zea mays) and willow oak (Quercus phellos) from three bayous located within the Lower Mississippi River Basin of NW Mississippi, and in stream mesocosms enriched to agriculturally relevant concentrations of N, P, and N+P. We hypothesized maize would break down faster than willow oak, and overall bayou nutrient and habitat factors would influence decomposition for each species. Breakdown rates for maize were significantly higher (k = 0.0229- 0.0386) than willow oak (0.0026-0.0240), but we observed significantly lower decomposition in lotic habitats for both species. Mesocosm results confirmed corn residue breakdown rates were significantly higher than willow oak, and decomposition for both species increased significantly in mesocosms enriched with N or N+P. Patterns in field leaf C:N and C:P ratios were overall lower for maize and varied with time differently depending on habitat. Leaf nutrient ratio responses to enrichment in mesocosms varied with time, but lower C:N ratios were observed in streams enriched with N or N+P and C:P ratios decreased in streams enriched with N+P by the end of the experiment. Respiration rates for corn residue were double that of willow oak and enrichment effects varied with time, but there was clear experimental evidence that N+P enrichment increased respiration for both species by the end of the experiment. Our results demonstrate changes in organic matter sources from riparian species to more labile crop residues, combined with nutrient enrichment may impact agricultural water bodies by increasing microbial respiration resulting from faster organic matter breakdown rates.