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.

盐生产和使用的增加正在改变地球系统中盐离子的自然平衡，在整个生物物理系统中造成相互关联的影响，统称为淡水盐化综合症。在这篇综述中，我们概念化了自然盐循环，并综合了全球盐生产和河流盐浓度和通量不断增长的趋势。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带到地球表面。人类活动加速了盐通量的过程、时间尺度和幅度，并改变了其方向性，形成了人为盐循环。过去一个世纪，全球各种盐的产量迅速增加，每年生产约 300 公吨氯化钠。美国的盐预算表明，河流中的盐通量可能与人为盐通量处于相似的数量级内，并且流域中可能会出现大量的盐积累。过量的盐沿着人为盐循环传播，导致淡水盐化综合症超出淡水供应范围，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，并在超过行星边界之前减少盐化，从而对整个地球系统造成严重或不可逆转的损害。