Thayalakumaran Thabo, Lenahan Matthew J, Bristow Keith L
Cooperative Research Centre for Irrigation Futures and CSIRO Water for a Healthy Country National Research Flagship, CSIRO Land and Water, PMB Aitkenvale, Townsville, Queensland, 4814, Australia.
Currently with Department of Environment and Primary Industries-Agriculture Research, 32 Lincoln Square Nth, Carlton, Vic, 3053, Australia.
Ground Water. 2015 Jul-Aug;53(4):525-30. doi: 10.1111/gwat.12258. Epub 2014 Sep 11.
Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarcane on the Burdekin coastal plain of tropical northeast Australia. The maximum value of 82 mg/L is to our knowledge the highest DOC reported for groundwater beneath irrigated cropping systems. More than half of the groundwater sampled in January 2004 (n = 46) exhibited DOC concentrations greater than 30 mg/L. DOC was progressively lower in October 2004 and January 2005, with a total decrease greater than 90% indicating varying load(s) to the aquifer. It was hypothesized that the elevated DOC found in this groundwater system is sourced at or near the soil surface and supplied to the aquifer via vertical recharge following above average rainfall. Possible sources of DOC include organic-rich sugar mill by-products applied as fertilizer and/or sugarcane sap released during harvest. CFC-12 vertical flow rates supported the hypothesis that elevated DOC (>40 mg/L) in the groundwater results from recharge events in which annual precipitation exceeds 1500 mm/year (average = 960 mm/year). Occurrence of elevated DOC concentrations, absence of electron acceptors (O2 and NO3 (-) ) and both Fe(2+) and Mn(2+) greater than 1 mg/L in shallow groundwater suggest that the DOC compounds are chemically labile. The consequence of high concentrations of labile DOC may be positive (e.g., denitrification) or negative (e.g., enhanced metal mobility and biofouling), and highlights the need to account for a wider range of water quality parameters when considering the impacts of land use on the ecology of receiving waters and/or suitability of groundwater for irrigated agriculture.
在澳大利亚东北部热带地区的伯德金沿海平原，灌溉甘蔗地之下的地下水中检测到溶解有机碳（DOC）含量升高。据我们所知，82毫克/升的最大值是灌溉种植系统之下地下水中报告的最高DOC值。2004年1月采集的地下水样本（n = 46）中，超过一半的样本DOC浓度大于30毫克/升。2004年10月和2005年1月，DOC含量逐渐降低，总降幅超过90%，这表明进入含水层的负荷有所变化。据推测，该地下水系统中升高的DOC源自土壤表层或其附近，并在降雨高于平均水平后通过垂直补给进入含水层。DOC的可能来源包括作为肥料施用的富含有机物的糖厂副产品和/或收获期间释放的甘蔗汁。CFC - 12垂直流速支持了这样的假设，即地下水中升高的DOC（>40毫克/升）是由年降水量超过1500毫米/年（平均 = 960毫米/年）的补给事件造成的。浅层地下水中DOC浓度升高、缺乏电子受体（O2和NO3(-)）以及Fe(2+)和Mn(2+)均大于1毫克/升，这表明DOC化合物在化学上不稳定。高浓度不稳定DOC的后果可能是积极的（例如反硝化作用）或消极的（例如增强金属迁移率和生物污染），这突出表明在考虑土地利用对受纳水体生态的影响和/或地下水对灌溉农业的适用性时，需要考虑更广泛的水质参数。
