Groundwater Replenishment Doesn't Guarantee a Carbon Sink in Lower Tarim River, China

A recent study published in the Journal of Hydrology reveals a surprising outcome in one of the world's driest regions: despite improvements in vegetation productivity driven by groundwater replenishment, the ecosystem remains a net carbon source. This challenges the common assumption that increased plant growth in arid areas naturally enhances carbon sequestration.

Led by Prof. HAO Xingming from the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences, the researchers focused on the lower reaches of the Tarim River in northwest China—a hyper-arid environment heavily dependent on groundwater. The team examined the effects of two decades of ecological water transfers, designed to restore degraded riparian zones, on regional carbon dynamics.

Using an advanced version of the Carnegie–Ames–Stanford Approach model, the researchers found that although net primary productivity (NPP) and net ecosystem productivity (NEP) increased alongside rising groundwater levels (GWL), over two-thirds of the area continued to emit more carbon than it absorbed. By 2020, only 30.8% of the region had become a carbon sink.

“Our findings demonstrate that higher vegetation productivity does not automatically translate into net carbon gains,” said CI Mengtao, the study’s first author. “Even after sustained ecological water transfer efforts, most of the riparian corridor remains a carbon source.”

In addition, the team employed remote sensing data, machine learning algorithms—including deep forests and random forests—and a convergent cross mapping (CCM) approach to analyze the causality between fluctuations in groundwater levels and carbon fluxes. They identified critical groundwater thresholds: when GWL dropped below –4.84 meters, both NPP and NEP were significantly inhibited. Notably, the causal relationship between GWL and productivity was spatially heterogeneous—areas closer to the river exhibited stronger responses to GWL variations, while regions farther away showed limited gains, mainly due to reduced water availability and soil salinization.

The study underscores the nuanced interplay between water availability and ecosystem function in arid regions and carries important implications for environmental management.

Read the full article: https://doi.org/10.1016/j.jhydrol.2025.133663

Contact

LONG Huaping

Xinjiang Institute of Ecology and Geography

E-mail: longhp@ms.xjb.ac.cn

Web: http://english.egi.cas.cn