| 1 | Mitigation of atrazine,S-metolachlor,and diazinon using common emergent aquatic vegetation显示文摘By the year 2050, the population of the United States is expected to reach over 418 million,while the global population will reach 9.6 billion. To provide safe food and fiber, agriculture must balance pesticide usage against impacts on natural resources. Challenges arise when storms cause runoff to be transported to aquatic receiving systems. Vegetated systems such as drainage ditches and constructed wetlands have been proposed as management practices to alleviate pesticide runoff. Twelve experimental mesocosms(1.3 × 0.71 × 0.61 m) were filled with sediment and planted with a monoculture of one of three wetland plant species(Typha latifolia, Leersia oryzoides, and Sparganium americanum).Three mesocosms remained unvegetated to serve as controls. All mesocosms were amended with 9.2 ± 0.8 μg/L, 12 ± 0.4 μg/L, and 3.1 ± 0.2 μg/L of atrazine, metolachlor, and diazinon, respectively, over a 4 hr hydraulic retention time to simulate storm runoff.Following the 4 hr amendment, non-amended water was flushed through mesocosms for an additional 4 hr. Outflow water samples were taken hourly from pre-amendment through8 hr, and again at 12, 24, 48, 72, and 168 hr post-amendment. L. oryzoides and T. latifolia had mean atrazine, metolachlor, and diazinon retentions from 51%–55% for the first 4 hr of the experiment. Aside from S. americanum and atrazine(25% retention), unvegetated controls had the lowest pesticide retention(17%–28%) of all compared mesocosms. While native aquatic vegetation shows promise for mitigation of pesticide runoff, further studies increasing the hydraulic retention time for improved efficiency should be examined. | Matthew T.Moore Martin A.Locke Robert Krǒger | 2017 | Journal of Environmental Sciences2017，29，6： | 2 |
| 2 | Dredging effects on selected nutrient concentrations and ecoenzymatic activity in two drainage ditch sediments in the lower Mississippi River Valley显示文摘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. | Matt Moore Martin A.Locke Michael Jenkins Robert W.Steinriede Daniel S.McChesney | 2017 | International Soil and Water Conservation Research2017，5，3： | 1 |
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