Hudak Paul F
Department of Geography and the Environment, University of North Texas, 1155 Union Circle #305279, Denton, TX, 76203-5017, USA.
Bull Environ Contam Toxicol. 2018 Mar;100(3):416-420. doi: 10.1007/s00128-017-2243-y. Epub 2017 Dec 13.
Nitrate concentrations in a regionally sloping sedimentary aquifer were compiled every 4 years from 1999 to 2015. Sampled wells ranged from 14.6 m deep in the outcrop zone to 1031.4 m deep in the confined zone, with a median depth of 192.1 m. Approximately 3.6% of 138 samples collected in 2015 exceeded the drinking water standard of 44.3 mg/L; while low, this percentage was highest among five sampling years. All observed exceedances were in relatively shallow wells in the outcrop zone. Generally, the spatial pattern of nitrate occurrence persisted through time. Shallow wells tended to have higher nitrate concentrations, in addition to larger increases or decreases in concentration over time. Maximum concentrations ranged from 30.5 mg/L in 1999 to 100.5 mg/L in 2015. Over any 4-year period, the maximum concentration increase was 42.1 mg/L, and the maximum decrease was 41.0 mg/L, both occurring in wells in the outcrop zone. This study has land management implications for sloping sedimentary aquifers. Practices that alter nitrogen inputs and dilution processes in unconfined zones may produce large fluctuations in nitrate concentration over short time periods.
1999年至2015年期间，每4年对一个区域倾斜沉积含水层中的硝酸盐浓度进行一次汇总。采样井的深度从露头区的14.6米到承压区的1031.4米不等，中位数深度为192.1米。2015年采集的138个样本中，约3.6%超过了44.3毫克/升的饮用水标准；虽然这一比例较低，但在五个采样年份中是最高的。所有观测到的超标情况都出现在露头区相对较浅的井中。一般来说，硝酸盐出现的空间格局随时间持续存在。除了随着时间浓度有较大的增加或减少外，浅井的硝酸盐浓度往往更高。最大浓度范围从1999年的30.5毫克/升到2015年的100.5毫克/升。在任何4年期间，最大浓度增加为42.1毫克/升，最大浓度减少为41.0毫克/升，两者都出现在露头区的井中。本研究对倾斜沉积含水层的土地管理具有启示意义。改变非承压区氮输入和稀释过程的做法可能会在短时间内导致硝酸盐浓度出现大幅波动。
