Insight into factors controlling formation rates of pedogenic carbonates: A combined geochemical and isotopic approach in dryland soils of the US Southwest
Insight into factors controlling formation rates of pedogenic carbonates: A combined geochemical and isotopic approach in dryland soils of the US Southwest
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深入了解成土碳酸盐形成速率的控制因素：美国西南部旱地土壤的地球化学和同位素联合方法
DOI：
10.1016/j.chemgeo.2017.10.014
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发表时间：
2019
期刊：
影响因子：
3.9
通讯作者：
Ma, Lin
中科院分区：
文献类型：
--
作者：
Nyachoti, Syprose;Jin, Lixin;Tweedie, Craig E.;Ma, Lin
成土碳酸盐的自然积累已得到充分记录，但很少有研究关注农业旱地碳酸盐的形成。本研究旨在确定集约灌溉土壤中成土碳酸盐的积累率，并确定美国西南部耕地旱地漫灌、盐负荷和土壤-大气二氧化碳交换之间的关键联系。我们结合元素化学（CaO、土壤有机碳和无机碳含量）、矿物学和 U 系列（238U-234U-230Th）不平衡测年技术来研究成土碳酸盐的钙源、年龄和形成速率。研究地点包括德克萨斯州西部埃尔帕索附近的一个灌溉苜蓿田和新墨西哥州南部美国农业部乔纳达实验范围内的一个非灌溉天然旱地。我们的结果表明，大量溶解的钙和无机碳以及其他可溶性元素通过德克萨斯州埃尔帕索的灌溉水进入农田，而灰尘和降雨对于乔纳达自然土壤中的盐负荷很重要。散装土壤中的 U 系列活度比 (234U/238U) 和 (230Th/238U) 表明风成沉积物在灌溉和自然地点的浅层土壤中添加了 U 和修饰的 U 同位素。土壤剖面内 234U 的迁移率与 U 的淋滤（并推断其他可溶性离子）和碳酸盐在深度的积累有关。成土碳酸盐的 U 系列测年技术揭示了与自然地点相比，灌溉地点存在更年轻的碳酸盐。灌溉土壤中的成土碳酸盐形成率也远高于非灌溉土壤，这可能是灌溉水中溶解的钙和无机碳流入的结果。这项研究证明了旱地农业扩张和土地利用变化有可能增加成土碳酸盐积累率。这些变化可能对全球碳循环产生重要影响，因为预计到本世纪中叶，旱地将成为最广阔的陆地生物群落，而旱地农业正在迅速扩张。
Natural accumulation of pedogenic carbonates has been well documented but few studies have focused on carbonate formation in agricultural drylands. This study aims to determine accumulation rates of pedogenic carbonates in intensively irrigated soils, and to define key linkages between flood irrigation, salt loading and soil-atmosphere CO2exchange in cultivated drylands of the southwestern United States. We used a combination of elemental chemistry (CaO, soil organic and inorganic carbon contents), mineralogy, and U-series (238U-234U-230Th) disequilibrium dating technique to investigate calcium sources, ages and formation rates of pedogenic carbonates. Study sites include an irrigated alfalfa field near El Paso in western Texas and a non-irrigated natural dryland site on the USDA Jornada Experimental Range of southern New Mexico. Our results showed that large amounts of dissolved calcium and inorganic carbon along with other soluble elements were loaded onto agricultural fields through irrigation waters in El Paso, TX while dust and rainfall were important for salt loading in natural soils of the Jornada. U-series activity ratios, (234U/238U) and (230Th/238U), in bulk soils suggested eolian deposits added U and modified U isotopes in shallow soils at both the irrigated and natural sites. Mobility of234U within the soil profile is related to leaching of U (and by inference other soluble ions) and carbonate accumulation at depth. The U-series dating technique in pedogenic carbonates revealed the presence of much younger carbonates at the irrigated site compared to the natural site. Pedogenic carbonate formation rates in the irrigated soils were also much higher than those in the non-irrigated soils, likely a result of influxes from dissolved Ca and inorganic carbon in water used for irrigation. This study demonstrates the potential for agricultural expansion and land use change in drylands to increase rate of pedogenic carbonate accumulation. Such changes may have important implications to global carbon cycling since drylands are forecast to become the most expansive terrestrial biome by mid-century and dryland agriculture is expanding quickly.
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影响因子：
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