Strontium isotope geochemistry of groundwaters and streams affected by agriculture, Locust Grove, MD
Strontium isotope geochemistry of groundwaters and streams affected by agriculture, Locust Grove, MD
复制标题
DOI：
10.1016/s0883-2927(99)00075-x
复制
发表时间：
2000-06-01
影响因子：
3.4
通讯作者：
Horan, M
中科院分区：
文献类型：
--
作者：
Böhlke, JK;Horan, M
在马里兰州大西洋沿岸平原的两个小流域研究了农业对Sr同位素地球化学的影响。在1940年至1990年间，两个流域的分层浅层含氧地下水中含有NO3-、Cl、Mg、Ca和Sr等化学物质补给速率增加的可检索记录，这些化学物质补给速率增加与肥料使用增加有关。与近期农业补给相关的Sr组分具有相对的放射性成因（Sr-87/Sr-86 = 0.715），相对于饱和带氧化、非钙质部分的水岩相互作用自然获得的Sr， Sr组分具有压倒性优势。渗入相对未氧化的钙质海绿石沉积物深处的农业地下水在进行O-2还原和反硝化过程中，从早第三纪海洋CaCO3的溶解中获得了额外的Sr成分（Sr-87/Sr-86 = 0.708）。地下水排放中含有不同年龄和氧化还原状态的水的混合物。与没有农业的情况相比，该地区的两条河流被认为具有更高的Sr-87/Sr-86比率和NO3-浓度；然而，由于两个流域当地地下水流动系统中钙还原（反硝化）沉积物的平均深度不同，河流的Sr-87/Sr-86比值和NO3-浓度始终不同。研究结果表明，农业可以显著改变含水层和河流中锶的同位素地球化学特征，其影响可能与肥料的类型、来源和添加量、肥料使用历史和地下水停留时间有关。(C) 2000 Elsevier Science Ltd.版权所有。
The effects of agriculture on the isotope geochemistry of Sr were investigated in two small watersheds in the Atlantic coastal plain of Maryland. Stratified shallow oxic groundwaters in both watersheds contained a retrievable record of increasing recharge rates of chemicals including NO3-, Cl, Mg, Ca and Sr that were correlated with increasing fertilizer use between about 1940 and 1990. The component of Sr associated with recent agricultural recharge was relatively radiogenic (Sr-87/Sr-86 = 0.715) and it was overwhelming with respect to Sr acquired naturally by water-rock interactions in the oxidized, non-calcareous portion of the saturated zone. Agricultural groundwaters that penetrated relatively unoxidized calcareous glauconitic sediments at depth acquired an additional component of Sr from dissolution of early Tertiary marine CaCO3 (Sr-87/Sr-86 = 0.708) while undergoing O-2 reduction and denitrification. Ground-water discharge contained mixtures of waters of various ages and redox states. Two streams draining the area are considered to have higher Sr-87/Sr-86 ratios and NO3- concentrations than they would in the absence of agriculture; however, the streams have consistently different Sr-87/Sr-86 ratios and NO3- concentrations because the average depth to calcareous reducing (denitrifying) sediments in the local groundwater flow system was different in the two watersheds. The results of this study indicate that agriculture can alter significantly the isotope geochemistry of Sr in aquifers and streams and that the effects could vary depending on the types, sources and amounts of fertilizers added, the history of fertilizer use and groundwater residence times. (C) 2000 Elsevier Science Ltd. All rights reserved.