HighlightsOak leached more tannic acid, true color, and chemical oxygen demand (COD) than ash and mixed hardwood chips.The factors became similar (tannic acid, COD) or below stream levels (true color) after flushing.Eleven site-years of field bioreactor data showed decreasing tannic acid and true color over time.Post-startup tannic acid was lower in bioreactor outflow than in area streams.True color did not appear to be a reliable indicator of leachate tannic acid at low concentrations.Abstract. Woodchips have been a preferred denitrifying bioreactor medium to date, but concerns about potential harmful effects of tannins in the leachate have precluded the use of oak chips in many installations. A study was conducted to compare the suitability of oak (genus Quercus) woodchips as a denitrifying bioreactor medium relative to other types of woodchips, both in lab leachate tests and in the context of observed bioreactor leaching in the field. Assessment measures included the content of tannic acid and other compounds in the leachate, as well as leachate color, which can often be high during startup. An 84-day leaching test using rectangular bioreactor cells filled with either oak (Quercus rubra), ash (Fraxinus spp. L.), or a generic hardwood blend showed that oak initially leached higher concentrations of tannic acid, true color, and chemical oxygen demand (COD) than the other two media. The significant differences in leached concentrations among the three wood types were eliminated after a finite leaching period. Tannic acid and true color in 11 site-years of field bioreactor outflow data generally decreased over time, except following a dry period when one of the bioreactors received no drainage inflow for more than two months. The lab and field results indicated the capability of woodchip bioreactors to flush at least these two analytes to ambient stream levels. True color did not appear to be the best parameter for estimating the tannin content of woodchip leachate due to discrepancies at low concentrations. Mass normalized tannic acid leaching ranged from 0.03 to approximately 40 mg tannic acid g-1 woodchip across the lab and field assessments. Oak initially leached more tannic acid, color, and COD than the other wood types, but the eventual similarity among the wood types after flushing with a sufficient number of pore volumes meant that any potentially negative environmental impacts would likely be limited to the startup period or possibly after dry periods. Oak initially eluted higher mean total nitrogen (TN) concentrations than the other wood types, but the treatments were not significantly different by day 3, indicating that biological N removal was not significantly inhibited, even with high concentrations of tannic acid. Keywords: Chemical oxygen demand, Oak, Tannin, Water quality, Wood leachate.
HighlightsDenitrifying bioreactor and nutrient management effectively reduced nitrate-N loads from subsurface drainage.Constructed wetland was effective in removing total N, nitrate-N, and total P from wetland influent water.Filter strip was the most effective practice in reducing sediment, total N, and total P loads from surface runoff.Cover crop was effective in reducing sediment and total P loads from surface runoff.More research is needed on conservation practice effectiveness in reducing dissolved P loss from agricultural fields.Abstract. This article introduces a Special Collection of literature reviews documenting the performance and cost-effectiveness of six agricultural conservation practices (ACPs): conservation crop rotation, cover crop, filter strip, nutrient management, denitrifying bioreactor, and constructed wetland. The overall objectives of the Special Collection are to: (1) review published studies on ACP effectiveness in reducing nutrient and sediment losses from agricultural fields; (2) compare, integrate, and synthesize the results from those studies to obtain a systematic understanding of the mitigation efficacy of each ACP in a consistent format across the selected ACPs; and (3) assemble cost analyses and obtain general insights on performance-based costs of the ACPs. The specific objectives of this introductory article are to summarize key information from each of the six review articles and develop a comparative understanding of the performance and cost-effectiveness of the six ACPs. Among the selected ACPs, denitrifying bioreactor, constructed wetland, cover crop, crop rotation, and nutrient management were all effective in reducing nitrate-N loads in subsurface drainage, with performance effectiveness in load reduction ranging from 23% to 40%. A corn-soybean rotation (relative to continuous corn) was the most cost-effective among the selected ACPs and can reduce nitrate-N load at a net benefit of about USD $5 per kg nitrate-N compared to continuous corn. Filter strip was most effective in reducing sediment, total nitrogen (N), and total phosphorus (P) loads from surface runoff and can be effective in reducing nitrate-N and dissolved P. Cover crop was also effective in reducing sediment and total P loads. Studies of the selected ACPs for their performance effectiveness for dissolved P are limited, and results varied among the ACPs included; thus, more research is needed relative to ACP effectiveness in reducing dissolved P loss, particularly in subsurface flow. Finally, although each review article included cost-analysis information, more data and analyses are needed to better understand the cost-effectiveness of ACPs and their ecological benefits. Keywords: Constructed wetland, Cost-effectiveness, Cover crop, Crop rotation, Filter strip, Nutrient management, Denitrifying bioreactor, Reduction effectiveness.
Abstract.This article presents the development of a drainage-climate interface that incorporates climatological data, crop drainage requirements, and drainage theory into a procedure for characterizing drainage system response under different climate scenarios. The drainage-climate interface is suitable for assessing potential county-level impacts of climate change on crop production, soil hydrology and subsequently on subsurface drainage design. Climate model projections from two general circulation models (GCMs), namely CCSM4 (Community Climate System Model) and MIROC5 (Model for Interdisciplinary Research on Climate), were used to create the climatological database for the drainage-climate interface. DRAINMOD was integrated into the Visual Basic for Applications (VBA) portion of the interface to simulate the performance of subsurface drainage systems in Illinois for the near future (2040 to 2069) and the far future (2070 to 2099) periods. Case studies were developed with the interface for Adams and Champaign Counties in Illinois for their predominant soil types. Hydrologic simulations from the interface were used to determine the optimal depth and spacing of tile drains that maximize crop yield for corn and soybean during the mid and late 21st century. Drainage water management (DWM) was incorporated into the drainage-climate interface to investigate the potential of DWM in the future climate scenarios to maintain water quality, reduce nutrient losses and minimize pollutant loading from drained fields by controlling the timing and amount of water discharged from agricultural drainage systems. Results from DRAINMOD simulations with MIROC5 show a significant decline in crop yield due to extreme heat stress. Corn yield in the future showed a severe reduction while the yield for soybean demonstrated a gradual decline over the years. DWM had only a minimal effect on future crop yield trends. The drainage-climate interface simulated subsurface drainage conditions and made evident the consequences of environmental conditions on crop physiological processes under scenarios of climate change predicted by MIROC5. Keywords: Agricultural system models, Climate change impacts, Drainage-climate interface, Drainage water management, Subsurface drainage, Tile drain depth, Tile drain spacing.
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