Duff John H, Tesoriero Anthony J, Richardson William B, Strauss Eric A, Munn Mark D
U.S. Geological Survey, Water Resources Div., 345 Middlefield Road, MS 439, Menlo Park, CA 94025, USA.
J Environ Qual. 2008 May 2;37(3):1133-44. doi: 10.2134/jeq2007.0187. Print 2008 May-Jun.
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 reach-level 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 <5% of NO3(-) exported from the reaches minimally reducing downstream loads. Nitrate retention as a percentage of gross NO3(-) inputs was >30% 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.
在三条流经果园/奶牛场和大田作物种植区的农业溪流中，对影响硝酸盐（NO3(-)）去除的物理、化学、水文和生物因素进行了评估。在生物活跃期使用三维“快照”，我们估算了河段尺度的NO3(-)来源、NO3(-)质量平衡、河道内处理过程（硝化作用、反硝化作用和NO3(-)吸收）以及与地表水输送和地下水排放相关的NO3(-)保留潜力。在研究河段，地下水对溪流流量的贡献率为5%至11%，对总NO3(-)输入的贡献率为8%至42%。在排放到地表水之前，河床过程可能会减少45%至75%的地下水NO3(-)。在所有溪流中，暂态存储对地表水NO3(-)保留的重要性不大。相对于原始溪流，沉积物浆液中估算的硝化作用速率（1.6 - 4.4 mg N m(-2) h(-1)）和未修正的反硝化作用速率（2.0 - 16.3 mg N m(-2) h(-1)）较高。NO3(-)的反硝化作用在很大程度上独立于硝化作用，因为溪流和地下水都是NO3(-)的来源。外推到河段尺度的未修正反硝化作用速率占河段输出的NO3(-)的比例小于5%，对减少下游负荷的作用极小。在一条反硝化潜力最低、底栖叶绿素a含量最高、光合作用/呼吸比、pH值、溶解氧和NO3(-)日变化最大的贫有机自养溪流中，NO3(-)保留占总NO3(-)输入的百分比大于30%。在该地点，生物处理过程可能去除了75%的地下水NO3(-)，这表明当水流直接通过底栖硅藻床时，相对于地下反硝化作用，地下水NO3(-)的光合同化作用具有重要作用。
