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Livestock grazing and vegetative filter strip buffer effects on runoff sediment, nitrate, and phosphorus losses

机译:牲畜放牧和营养滤带缓冲对径流沉积物,硝酸盐和磷损失的影响

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摘要

Livestock grazing in the Midwestern United States can result in significant levels of runoff sediment and nutrient losses to surface water resources. Some of these contaminants can increase stream eutrophication and are suspected of contributing to hypoxic conditions in the Gulf of Mexico. This research quantified effects of livestock grazing management practices and vegetative filter strip buffers on runoff depth and mass losses of total solids, nitrate-nitrogen (NO3-N), and ortho-phosphorus (PO4-P) under natural hydrologic conditions. Runoff data were collected from 12 rainfall events during 2001 to 2003 at an Iowa State University research farm in central Iowa, United States. Three vegetative buffers (paddock area:vegetative buffer area ratios of 1:0.2, 1:0.1, and 1:0 no buffer [control]) and three grazing management practices (continuous, rotational, and no grazing [control]) comprised nine treatment combinations (vegetative buffer ratio/grazing management practice) replicated in three 1.35 ha (3.34 ac) plot areas. The total 4.05 ha (10.02 ac) study area also included nine 0.4 ha (1.0 ac) paddocks and 27 vegetative buffer runoff collection units distributed in a randomized complete block design. The study site was established on uneven terrain with a maximum of 15% slopes and consisted of approximately 100% cool-season smooth bromegrass. Average paddock and vegetative buffer plant tiller densities estimated during the 2003 project season were approximately 62 million and 93 million tillers ha−1 (153 million and 230 million tillers ac−1), respectively. Runoff sample collection pipe leakage discovered and corrected during 2001 possibly reduced runoff depth and affected runoff contaminant mass losses data values. Consequently, 2001 runoff analysis results were limited to treatment comparisons within the 2001 season and were not compared with 2002 and 2003 data. Analysis results from 2001 showed no significant differences in average losses of runoff, total solids, NO3-N, and PO4-P among the nine vegetative buffer/grazing practice treatment combinations. Results from 2002 indicated significantly higher losses of runoff and total solids from 1:0 no buffer/rotational grazing and 1:0 no buffer/continuous grazing treatment combination plots, respectively, compared among other 2002 season treatment combinations. The 2003 results showed significantly higher runoff and total solids losses from 1:0 no buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and from 1:0.1 vegetative buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and with respective 2002 treatment combinations. However, the 2003 results indicated effective vegetative buffer performance with significantly lower runoff, total solids, and NO3-N losses from the larger 1:0.2 buffer area compared among the smaller 1:0.1 buffer area and 1:0 no buffer treatment combinations. The 2003 results also indicated a highly significant increase in losses of NO3-N from 1:0.1 buffer/no grazing treatment combination plots compared among other 2003 season treatment combinations and with respective 2002 treatment combinations. Overall results from this study suggest a shift from significantly higher 2002 season plot losses of continuous and rotational grazing treatment combinations to significantly higher 2003 season losses of no grazing treatment combinations. We speculate this shift to significantly higher runoff and contaminant losses from no grazing treatment combination plots during 2003 reflects the variability inherent to a complex and dynamic soil-water environment of livestock grazing areas. However, we also hypothesize the environmental conditions that largely consisted of a dense perennial cool-season grass type, high-relief landscape, and relatively high total rainfall depth may not necessarily include livestock grazing activities.
机译:在美国中西部地区放牧的牲畜会导致径流沉积物和营养物质大量流失到地表水资源中。这些污染物中的一些会增加河流富营养化,并被怀疑是造成墨西哥湾缺氧的原因。这项研究量化了牲畜放牧管理实践和营养滤带缓冲对天然水文条件下径流深度和总固体,硝酸盐氮(NO3-N)和正磷(PO4-P)的质量损失的影响。在2001年至2003年期间,从美国爱荷华州中部的爱荷华州立大学研究农场收集了12个降雨事件的径流数据。三种营养缓冲液(围场面积:营养缓冲液面积比为1:0.2、1:0.1和1:0:无缓冲液[控制])和三种放牧管理措施(连续,轮换和无放牧[控制])包括九种处理方法在三个1.35公顷(3.34 ac)的样地中重复进行的组合(营养缓冲比/放牧管理实践)。整个4.05公顷(10.02 ac)的研究区域还包括9个0.4公顷(1.0 ac)的围场和27个无性完整地块设计分布的营养缓冲径流收集单位。研究地点位于不平坦的地形上,最大坡度为15%,由大约100%的凉爽季节光滑的草皮草组成。 2003年项目季节估计的平均围场和植物性缓冲植物分till密度分别约为6200万和9300万株ha-1(1.53亿和2.3亿株ac-1)。在2001年发现并纠正了径流样品收集管泄漏的情况,可能会减小径流深度并影响径流污染物质量损失数据值。因此,2001年径流分析结果仅限于2001年季节内的处理比较,而没有与2002年和2003年的数据进行比较。 2001年的分析结果显示,在9种营养缓冲/放牧实践处理组合中,径流,总固体,NO3-N和PO4-P的平均损失没有显着差异。 2002年的结果表明,与其他2002年季节处理组合相比,分别从1:0无缓冲/旋转放牧和1:0无缓冲/连续放牧的处理组合地块,径流和总固体的损失显着增加。 2003年的结果显示,与所有2003年处理组合相比,从1:0无缓冲/无放牧处理组合地块和与所有2003年处理组合之间和与1:2003无营养缓冲/无放牧处理组合地块相比,径流量和总固体损失显着更高各自的2002年治疗组合。但是,2003年的结果表明,与较小的1:0.1缓冲区域和1:0无缓冲处理组合相比,有效的植物缓冲性能良好,径流量,总固体含量和较大的1:0.2缓冲区域中的NO3-N损失显着降低。 2003年的结果还表明,与其他2003年季节处理组合以及2002年各自的处理组合相比,从1:0.1缓冲液/不放牧处理组合地块中NO3-N的损失显着增加。这项研究的总体结果表明,连续和轮作放牧处理组合的2002年季积损失明显高于无牧草处理组合的2003年季损失。我们推测这种转变将使径流大大增加,并且在2003年没有进行放牧处理的地块上污染物的损失反映了牲畜放牧地区复杂而动态的土壤-水环境固有的可变性。但是,我们还假设环境条件主要由多年生的浓密冷季草类型,高浮雕景观和相对较高的总降雨深度组成,不一定包含放牧活动。

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