Texas A&M AgriLife Research, Texas A&M University System, P.O. Box 1658, Vernon, TX 76385, United States.
Texas A&M AgriLife Research, Texas A&M University System, P.O. Box 1658, Vernon, TX 76385, United States.
Sci Total Environ. 2014 Feb 15;472:370-80. doi: 10.1016/j.scitotenv.2013.10.120. Epub 2013 Dec 1.
We assessed spatial distribution of total dissolved solids (TDS) in shallow (<50 m), intermediate (50-150 m), and deep (>150 m) municipal (domestic and public supply) wells in nine major aquifers in Texas for the 1960s-1970s and 1990s-2000s periods using geochemical data obtained from the Texas Water Development Board. For both time periods, the highest median groundwater TDS concentrations in shallow wells were found in the Ogallala and Pecos Valley aquifers and that in the deep wells were found in the Trinity aquifer. In the Ogallala, Pecos Valley, Seymour and Gulf Coast aquifers, >60% of observations from shallow wells exceeded the secondary maximum contaminant level (SMCL) for TDS (500 mg L(-1)) in both time periods. In the Trinity aquifer, 72% of deep water quality observations exceeded the SMCL in the 1990s-2000s as compared to 64% observations in the 1960s-1970s. In the Ogallala, Edwards-Trinity (plateau), and Edwards (Balcones Fault Zone) aquifers, extent of salinization decreased significantly (p<0.05) with well depth, indicating surficial salinity sources. Geochemical ratios revealed strong adverse effects of chloride (Cl(-)) and sulfate (SO4(2-)) on groundwater salinization throughout the state. Persistent salinity hotspots were identified in west (southern Ogallala, north-west Edwards-Trinity (plateau) and Pecos Valley aquifers), north central (Trinity-downdip aquifer) and south (southern Gulf Coast aquifer) Texas. In west Texas, mixed cation SO4-Cl facies led to groundwater salinization, as compared to Na-Cl facies in the southern Gulf Coast, and Ca-Na-HCO3 and Na-HCO3 facies transitioning to Na-Cl facies in the Trinity-downdip regions. Groundwater mixing ensuing from cross-formational flow, seepage from saline plumes and playas, evaporative enrichment, and irrigation return flow had led to progressive groundwater salinization in west Texas, as compared to ion-exchange processes in the north-central Texas, and seawater intrusion coupled with salt dissolution and irrigation return flow in the southern Gulf Coast regions.
我们利用德克萨斯州水资源委员会获得的地球化学数据，评估了 20 世纪 60 年代至 70 年代和 90 年代至 2000 年代期间，该州 9 个主要含水层中浅层（<50 米）、中层（50-150 米）和深层（>150 米）市政（民用和公共供水）井中总溶解固体（TDS）的空间分布情况。在这两个时期，浅层井中地下水 TDS 浓度的最高中位数均出现在奥加拉拉和佩科斯河谷含水层中，而深层井中的最高中位数则出现在三一含水层中。在奥加拉拉、佩科斯河谷、西摩和墨西哥湾沿岸含水层中，两个时期浅层井中超过 60%的观测值超过 TDS 的二级最大污染物水平（SMCL）（500mg/L）。与 20 世纪 60 年代至 70 年代相比，20 世纪 90 年代至 2000 年代，三一含水层中 72%的深层水质观测值超过了 SMCL，而在 20 世纪 60 年代至 70 年代，这一比例为 64%。在奥加拉拉、爱德华兹-三一（高原）和爱德华兹（巴尔科内斯断层带）含水层中，随着井深的增加，盐化程度显著降低（p<0.05），这表明表层盐分来源。地球化学比值表明，氯化物（Cl(-)）和硫酸盐（SO4(2-))对全州地下水盐化的影响很大。在德克萨斯州西部（南部奥加拉拉、西北部爱德华兹-三一（高原）和佩科斯河谷含水层）、中北部（三一顺倾含水层）和南部（墨西哥湾沿岸南部含水层）确定了持续存在的盐分热点。在德克萨斯州西部，混合阳离子 SO4-Cl 相导致地下水盐化，而在墨西哥湾沿岸南部则为 Na-Cl 相，在三一顺倾区则为 Ca-Na-HCO3 和 Na-HCO3 相过渡到 Na-Cl 相。跨层流动、咸水羽流和潟湖的渗漏、蒸发浓缩以及灌溉回流水导致德克萨斯州西部的地下水逐渐盐化，而在中北部德克萨斯州，离子交换过程以及墨西哥湾沿岸南部地区的海水入侵、盐溶解和灌溉回流水导致地下水盐化。
