Contribution of first flush runoff events from intense rainfall to downstream aquatic ecosystems are often reported in terms of sediment and nutrient delivery, with hardly any consideration to the contribution that st...Contribution of first flush runoff events from intense rainfall to downstream aquatic ecosystems are often reported in terms of sediment and nutrient delivery, with hardly any consideration to the contribution that standing, concentrated tailwater in primary aquatic systems makes to downstream nutrient loads. Two geographically distinct studies （Jonesboro Arkansas, and Stoneville Mississippi; 4 studies, n = 30） evaluated the effectiveness of drainage ditch systems to mitigate nutrient concentrations and loads. Within each independent study all experimental ditches had elevated background nutrient concentrations as a result of standing water, prior to the start of each simulated runoff experiment. These concentrations remained elevated 15-30 minutes post the start of each simulation as the concentrated, impounded water was pushed out through each system. In both these systems, it was hypothesized that water had accumulated in the respective drainage ditches and had been concentrated though evaporation and aquatic macrophyte transpiration. It is theorized that additional controlled drainage with improved dilution and hydraulic residence management.展开更多
Agricultural drainage ditches are conduits between production acreage and receiving aquatic systems.Often overlooked for their mitigation capabilities,agricultural drainage ditches provide an important role for nutrie...Agricultural drainage ditches are conduits between production acreage and receiving aquatic systems.Often overlooked for their mitigation capabilities,agricultural drainage ditches provide an important role for nutrient transformation via microbial metabolism.Variations in ecoenzyme activities have been used to elucidate microbial metabolism and resource demand of microbial communities to better understand the relationship between altered nutrient ratios and microbial activity in aquatic ecosystems.Two agricultural drainage ditches,one in the northeast portion of the Arkansas Delta and the other in the lower Mississippi Delta,were monitored for a year.Sediment samples were collected prior to each ditch being dredged(cleaned),and subsequent post-dredging samples occurred as soon as access was available.Seasonal samples were then collected throughout a year to examine effects of dredging on selected nutrient concentrations and ecoenzymatic activity recovery in drainage ditch sediments.Phosphorus concentrations in sediments after dredging decreased 33–66%,depending on ditch and phosphorus extraction methodology.Additionally,ecoenzymatic activity was significantly decreased in most sediment samples after dredging.Fluorescein diacetate hydrolysis activity,an estimate of total microbial activity,decreased 56–67%after dredging in one of the two ditches.Many sample sites also had significant phosphorus and ecoenzymatic activity differences between the post-dredge samples and the year-long follow-up samples.Results indicate microbial metabolism in dredged drainage ditches may take up to a year or more to recover to pre-dredged levels.Likewise,while sediment nutrient concentrations may be decreased through dredging and removal,runoff and erosion events over time tend to quickly replenish nutrient concentrations in replaced sediments.Understanding nutrient dynamics and microbial metabolism within agricultural drainage ditches is a crucial step toward addressing issues of nutrient enrichment in aquatic receiving systems,especially those contributing to the Gulf of Mexico.展开更多
文摘Contribution of first flush runoff events from intense rainfall to downstream aquatic ecosystems are often reported in terms of sediment and nutrient delivery, with hardly any consideration to the contribution that standing, concentrated tailwater in primary aquatic systems makes to downstream nutrient loads. Two geographically distinct studies （Jonesboro Arkansas, and Stoneville Mississippi; 4 studies, n = 30） evaluated the effectiveness of drainage ditch systems to mitigate nutrient concentrations and loads. Within each independent study all experimental ditches had elevated background nutrient concentrations as a result of standing water, prior to the start of each simulated runoff experiment. These concentrations remained elevated 15-30 minutes post the start of each simulation as the concentrated, impounded water was pushed out through each system. In both these systems, it was hypothesized that water had accumulated in the respective drainage ditches and had been concentrated though evaporation and aquatic macrophyte transpiration. It is theorized that additional controlled drainage with improved dilution and hydraulic residence management.
文摘Agricultural drainage ditches are conduits between production acreage and receiving aquatic systems.Often overlooked for their mitigation capabilities,agricultural drainage ditches provide an important role for nutrient transformation via microbial metabolism.Variations in ecoenzyme activities have been used to elucidate microbial metabolism and resource demand of microbial communities to better understand the relationship between altered nutrient ratios and microbial activity in aquatic ecosystems.Two agricultural drainage ditches,one in the northeast portion of the Arkansas Delta and the other in the lower Mississippi Delta,were monitored for a year.Sediment samples were collected prior to each ditch being dredged(cleaned),and subsequent post-dredging samples occurred as soon as access was available.Seasonal samples were then collected throughout a year to examine effects of dredging on selected nutrient concentrations and ecoenzymatic activity recovery in drainage ditch sediments.Phosphorus concentrations in sediments after dredging decreased 33–66%,depending on ditch and phosphorus extraction methodology.Additionally,ecoenzymatic activity was significantly decreased in most sediment samples after dredging.Fluorescein diacetate hydrolysis activity,an estimate of total microbial activity,decreased 56–67%after dredging in one of the two ditches.Many sample sites also had significant phosphorus and ecoenzymatic activity differences between the post-dredge samples and the year-long follow-up samples.Results indicate microbial metabolism in dredged drainage ditches may take up to a year or more to recover to pre-dredged levels.Likewise,while sediment nutrient concentrations may be decreased through dredging and removal,runoff and erosion events over time tend to quickly replenish nutrient concentrations in replaced sediments.Understanding nutrient dynamics and microbial metabolism within agricultural drainage ditches is a crucial step toward addressing issues of nutrient enrichment in aquatic receiving systems,especially those contributing to the Gulf of Mexico.
