Kaushal Sujay S, Likens Gene E, Mayer Paul M, Shatkay Ruth R, Shelton Sydney A, Grant Stanley B, Utz Ryan M, Yaculak Alexis M, Maas Carly M, Reimer Jenna E, Bhide Shantanu V, Malin Joseph T, Rippy Megan A
Department of Geology & Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA.
Cary Institute of Ecosystem Studies, Millbrook, NY, USA.
Nat Rev Earth Environ. 2023 Oct 31;4:770-784. doi: 10.1038/s43017-023-00485-y.
Increasing salt production and use is shifting the natural balances of salt ions across Earth systems, causing interrelated effects across biophysical systems collectively known as freshwater salinization syndrome. In this Review, we conceptualize the natural salt cycle and synthesize increasing global trends of salt production and riverine salt concentrations and fluxes. The natural salt cycle is primarily driven by relatively slow geologic and hydrologic processes that bring different salts to the surface of the Earth. Anthropogenic activities have accelerated the processes, timescales and magnitudes of salt fluxes and altered their directionality, creating an anthropogenic salt cycle. Global salt production has increased rapidly over the past century for different salts, with approximately 300 Mt of NaCl produced per year. A salt budget for the USA suggests that salt fluxes in rivers can be within similar orders of magnitude as anthropogenic salt fluxes, and there can be substantial accumulation of salt in watersheds. Excess salt propagates along the anthropogenic salt cycle, causing freshwater salinization syndrome to extend beyond freshwater supplies and affect food and energy production, air quality, human health and infrastructure. There is a need to identify environmental limits and thresholds for salt ions and reduce salinization before planetary boundaries are exceeded, causing serious or irreversible damage across Earth systems.
盐产量和使用量的增加正在改变地球系统中盐离子的自然平衡，在生物物理系统中引发一系列相互关联的效应，统称为淡水盐渍化综合征。在本综述中，我们对自然盐循环进行了概念化，并综合了全球盐产量以及河流盐浓度和通量不断增加的趋势。自然盐循环主要由相对缓慢的地质和水文过程驱动，这些过程将不同的盐分带到地球表面。人为活动加速了盐通量的过程、时间尺度和规模，并改变了它们的方向性，从而形成了人为盐循环。在过去的一个世纪里，不同盐分的全球盐产量迅速增加，每年生产约3亿吨氯化钠。美国的盐收支表明，河流中的盐通量可能与人为盐通量处于相似的数量级，并且流域内可能会有大量的盐分积累。过量的盐分沿着人为盐循环传播，导致淡水盐渍化综合征超出淡水供应范围，影响粮食和能源生产、空气质量、人类健康和基础设施。有必要确定盐离子的环境限制和阈值，并在超过地球边界之前减少盐渍化，以免对地球系统造成严重或不可逆转的损害。
