Physical, chemical, hydrologic, and biologic factors affecting nitrate (NO3-) removal were evaluated in three agricultural streams draining orchard/dairy and row crop settings. Using 3-d “snapshots” during biotically active periods, we estimated reachlevel NO3- sources, NO3- mass balance, in-stream processing (nitrification, denitrification, and NO3- uptake), and NO3- retention potential associated with surface water transport and ground water discharge. Ground water contributed 5 to 11% to stream discharge along the study reaches and 8 to 42% of gross NO3- input. Streambed processes potentially reduced 45 to 75% of ground water NO3- before discharge to surface water. In all streams, transient storage was of little importance for surface water NO3- retention. Estimated nitrification (1.6–4.4 mg N m−2 h−1) and unamended denitrification rates (2.0–16.3 mg N m−2 h−1) in sediment slurries were high relative to pristine streams. Denitrification of NO3- was largely independent of nitrification because both stream and ground water were sources of NO3-. Unamended denitrification rates extrapolated to the reach-scale accounted for \u3c5% of NO3- exported from the reaches minimally reducing downstream loads. Nitrate retention as a percentage of gross NO3- inputs was \u3e30% in an organic-poor, autotrophic stream with the lowest denitrification potentials and highest benthic chlorophyll a, photosynthesis/respiration ratio, pH, dissolved oxygen, and diurnal NO3- variation. Biotic processing potentially removed 75% of ground water NO3- at this site, suggesting an important role for photosynthetic assimilation of ground water NO3- relative to subsurface denitrification as water passed directly through benthic diatom beds.
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机译:在排水果园/奶牛场和大田作物的三种农业流中,评估了影响硝酸盐(NO3-)去除的物理,化学,水文和生物因素。在生物活跃时期使用3-d“快照”,我们估算了NO3的排放量,NO3的质量平衡,流中处理(硝化,反硝化和NO3的吸收)以及与地表水运输和运输相关的NO3保留潜力。地下水排放。在研究期间,地下水贡献了5至11%的水流,占总NO3输入量的8至42%。在排放到地表水中之前,流化床工艺可能会减少45%至75%的地下水NO3-。在所有溪流中,瞬时存储对于地表水NO3-的保留意义不大。相对于原始流,泥浆中的估计硝化(1.6–4.4 mg N m-2 h-1)和未修正的反硝化速率(2.0–16.3 mg N m-2 h-1)高。 NO3-的反硝化在很大程度上与硝化无关,因为溪流和地下水都是NO3-的来源。外推到覆盖范围的未修改反硝化率占从覆盖范围输出的NO3的5%,从而最小程度地减少了下游负荷。在具有低反硝化潜力和最高底栖叶绿素a,光合作用/呼吸比,pH,溶解氧和NO3-日变化的有机贫瘠,自养流中,硝酸盐截留量占NO3-输入总量的百分比为\ u3e30%。生物处理可能会在该位置去除75%的地下水NO3-,这表明相对于地下反硝化,由于水直接通过底栖硅藻床,因此对NO3-的光合作用具有重要作用。
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