van der Schans Martin L, Harter Thomas, Leijnse Anton, Mathews Marsha C, Meyer Roland D
Grontmij, Houten, The Netherlands.
J Contam Hydrol. 2009 Nov 3;110(1-2):9-21. doi: 10.1016/j.jconhyd.2009.06.002. Epub 2009 Jun 30.
Dairy farms comprise a complex landscape of groundwater pollution sources. The objective of our work is to develop a method to quantify nitrate leaching to shallow groundwater from different management units at dairy farms. Total nitrate loads are determined by the sequential calibration of a sub-regional scale and a farm-scale three-dimensional groundwater flow and transport model using observations at different spatial scales. These observations include local measurements of groundwater heads and nitrate concentrations in an extensive monitoring well network, providing data at a scale of a few meters and measurements of discharge rates and nitrate concentrations in a tile-drain network, providing data integrated across multiple farms. The various measurement scales are different from the spatial scales of the calibration parameters, which are the recharge and nitrogen leaching rates from individual management units. The calibration procedure offers a conceptual framework for using field measurements at different spatial scales to estimate recharge N concentrations at the management unit scale. It provides a map of spatially varying dairy farming impact on groundwater nitrogen. The method is applied to a dairy farm located in a relatively vulnerable hydrogeologic region in California. Potential sources within the dairy farm are divided into three categories, representing different manure management units: animal exercise yards and feeding areas (corrals), liquid manure holding ponds, and manure irrigated forage fields. Estimated average nitrogen leaching is 872 kg/ha/year, 807 kg/ha/year and 486 kg/ha/year for corrals, ponds and fields respectively. Results are applied to evaluate the accuracy of nitrogen mass balances often used by regulatory agencies to assess groundwater impacts. Calibrated leaching rates compare favorably to field and farm scale nitrogen mass balances. These data and interpretations provide a basis for developing improved management strategies.
奶牛场构成了一个复杂的地下水污染源景观。我们工作的目标是开发一种方法，用于量化奶牛场不同管理单元向浅层地下水的硝酸盐淋失量。通过使用不同空间尺度的观测数据，对区域尺度和农场尺度的三维地下水流与运移模型进行序贯校准，来确定总硝酸盐负荷。这些观测包括在广泛的监测井网络中对地下水位和硝酸盐浓度的局部测量，提供了几米尺度的数据，以及在排水管网中对排放速率和硝酸盐浓度的测量，提供了跨多个农场整合的数据。各种测量尺度与校准参数的空间尺度不同，校准参数是各个管理单元的补给率和氮淋失率。校准程序提供了一个概念框架，用于利用不同空间尺度的现场测量来估计管理单元尺度上的补给氮浓度。它提供了一幅奶牛养殖对地下水氮的空间变化影响图。该方法应用于加利福尼亚州一个相对脆弱的水文地质区域的奶牛场。奶牛场内的潜在污染源分为三类，代表不同粪便管理单元：动物运动场和饲养区（畜栏）、液体粪便储存池以及粪便灌溉的饲料地。畜栏、池塘和田地的估计平均氮淋失量分别为872千克/公顷/年、807千克/公顷/年和486千克/公顷/年。结果用于评估监管机构通常用来评估地下水影响的氮质量平衡的准确性。校准后的淋失率与现场和农场尺度的氮质量平衡相比具有优势。这些数据和解释为制定改进的管理策略提供了基础。
