Stanley Jim, Reading Lucy
Queensland University of Technology, 2 George St, Brisbane City, 4000, QLD, Australia.
Heliyon. 2020 Dec 3;6(12):e05507. doi: 10.1016/j.heliyon.2020.e05507. eCollection 2020 Dec.
The transport of nitrogen (N) to groundwater and surface water in the form of nitrate (NO ), as a by-product of the application of N-rich fertilisers, has been studied extensively. Yet, in the catchments adjacent to the Great Barrier Reef (GBR) in tropical north Queensland, Australia, NO transport in groundwater is not regularly monitored. An assessment of groundwater chemistry in the Liverpool Creek catchment of Queensland's wet-tropics region was conducted by regular sampling and analysis of groundwater over 12 months, through wet and dry seasons. A distinct spatial variability in groundwater chemistry was observed; groundwater aquifers with very low dissolved oxygen (DO) and NO consistently displayed relatively higher concentrations of sulphate (SO ), sulphur (S) and ferrous iron (Fe) and low concentrations of dissolved organic carbon (DOC) (<2 ppm). Combined with averaged measured redox potential (Eh) of <250 mV, this indicates certain regions of the catchment have conditions favourable for removal of NO via autotrophic denitrification (DN), while other groundwater aquifers retained NO concentrations just above the acceptable trigger limits defined in regional water quality guidelines. Observations indicate that the naturally heterogeneous structure of the coastal alluvium contributes to the distinct variability in groundwater chemistry over small distances, with NO concentrations influenced by a combination of DN, lateral shallow drainage and potential adsorption to clay surfaces within the alluvial sediments.
作为富含氮的肥料施用的副产品，氮（N）以硝酸盐（NO）的形式向地下水和地表水的迁移已得到广泛研究。然而，在澳大利亚昆士兰州北部热带地区大堡礁（GBR）附近的集水区，地下水的NO迁移并未得到定期监测。通过在12个月内（涵盖雨季和旱季）对地下水进行定期采样和分析，对昆士兰州湿热带地区利物浦溪集水区的地下水化学进行了评估。观察到地下水化学存在明显的空间变异性；溶解氧（DO）和NO含量极低的地下水含水层始终显示出相对较高的硫酸盐（SO）、硫（S）和亚铁（Fe）浓度以及较低的溶解有机碳（DOC）浓度（<2 ppm）。结合平均测量的氧化还原电位（Eh）<250 mV，这表明集水区的某些区域具有通过自养反硝化作用（DN）去除NO的有利条件，而其他地下水含水层的NO浓度仅略高于区域水质指南中定义的可接受触发限值。观察结果表明，沿海冲积层自然的非均质结构导致了小范围内地下水化学的明显变异性，NO浓度受DN、侧向浅层排水以及冲积沉积物中粘土表面潜在吸附作用的综合影响。
