Coal dust chokes plants and trees in mining areas

A recent study in Odisha, used remote sensing and on ground sampling methods to find that coal dust impacts several plant functions, including carbon uptake.
Opencast mining often leads to severe air pollution due to the extractive nature of the process.
Using freely available satellite data has the potential to upscale such research.

A new study based in Odisha sheds light on how satellite imagery can help determine the impacts of coal mining dust on vegetation and finds that dust could be impacting photosynthetic processes more than previously thought.

Researchers from the University of Southampton in the U.K. and the National Institute of Technology in Rourkela, Odisha, used remote sensing techniques to estimate foliar dust – dust that accumulates on the leaves of plants – on vegetation in Jharsuguda district, which is home to several opencast mines operated by Mahanadi Coalfields Limited. Odisha is the second largest coal mining state in India, after Jharkhand, contributing to around a quarter of India’s annual coal production.

“When we think about coal mining, we often think about direct, visible impacts on pollution and health. But the aim of this study was to look at the hidden impacts of mining dust that are less obvious but have implications for the broader environment,” Jadunandan Dash, professor of remote sensing at the University of Southampton and a co-author of the study, told Mongabay India.

Using remote sensing to detect mining dust

Opencast mining involves removing soil overburden and rocks to excavate coal deposits found beneath the surface. This extractive process can severely pollute the air around the mining and buffer zones. Understanding the impacts of coal dust on vegetation can help manage and mitigate possible ecological impacts on plant functions, the paper says.

Satellite imagery “can capture fine-scale variations, offers wide area coverage, regular monitoring, non‐invasive data collection, multi‐spectral capabilities, data integration, and global accessibility,” says the paper. The researchers also collected samples on the ground to more accurately assess foliar dust levels.

Dust accumulated on leaves. A recent study on plants near a coal mine in Odisha found that dust that accumulates on the leaves of plants could impact the photosynthesis process. Representative image by Divya Kilikar/Mongabay.

Four optical multispectral satellite data sources were used and compared with each other – Landsat-8, Landsat-9, Sentinel-2, and PlanetScope. While each satellite is attuned to capturing areas that are affected by dust, comparing the accuracy of each satellite’s image serves multiple purposes, said Dash. “We wanted to compare the data of freely available sources such as Landsat with PlanetScope, which is a commercial satellite whose data can’t be accessed freely. What we found is that there isn’t a significant difference, which means our research can be upscaled.”

A total of 300 dusty leaves were also collected from 30 locations across Jharsuguda’s coal mining regions. Each dusty leaf was weighed using a high-precision electronic weighing machine and then weighed again after being wiped clean. This was done to determine the concentration of dust in the areas sampled, the paper says.

How dust affects plant functions

The research found that higher dust accumulation resulted in decreased visible reflectance across all satellite sensors. Dust was also associated with lower levels of gross primary productivity (GPP) – the rate at which plants fix carbon dioxide during photosynthesis. On average, dust deposition caused GPP to reduce by approximately two to three grams of carbon. “These findings suggested that elevated foliar dust concentration potentially limits the vegetation’s ability to perform optimal photosynthesis, and affects the ecosystem’s overall carbon uptake,” the paper says. The two-to-three-gram reduction in GPP is a loss of about 10 to 20% of a plant’s carbon uptake potential on average, Dash explained.

Dust also caused negative relationships with plant water use efficiency and evapotranspiration, and led to higher leaf temperatures, causing thermal imbalance. Apart from affecting photosynthetic processes, foliar dust may “affect stomatal conductance, reducing water loss through transpiration,” the paper says.

Mitigating mining dust

Narayan Kayet, research scientist at the Bengaluru-based Environmental Management and Policy Research Institute, has also studied the impacts of coal mining dust on vegetation using satellite imagery. His research, based in Jharkhand’s Jharia coal field, found that the highest coal dust loads tended to be found along mining transport routes, rail lines, and dump areas, tailing ponds, backfilling, and coal stockyard sides. “The dust caused severe degradation and less canopy cover along these routes. We used hyperspectral data which is of higher resolution,” he said.

According to Kayet, research of this kind reveals gaps in policy that can be addressed by implementing measures to reduce dust collecting on plants. “Measures like anti-dust water sprays can help reduce dust,” Kayet said.

Banner image: Work in progress at a coal mine in Jharsuguda district, Odisha. Image by India Water Portal via Flickr (CC BY-NC-SA 2.0).