Difference between sediment samples from coal mine subsidence water and soil samples around it

Coal plays a predominant role in the energy structure of China. The North China Plain is very rich of coal resources, multiple large coalfields and hundreds of coalmines are distributed across this plain. Due to the little dip angle coal seam, thick sediment loose layer, high phreatic water level in North China Plain, the collapse land was lower than surface, the different depth and different size of subsidence lake were formed, at the same time, mining activities could significantly change the water cycle over space and time of subsidence area, especially the underground water circulation of unsaturated zone, where is closely connected with the ground water.

Huainan City is one of 13 million-ton coal bases of China, where coal production has exceeded 60 million tons per year due to the continual demands of economic growth, in light of underground water hydrology, massive underground mining has resulted in large area of land subsidence and submergence. By the end of 2014, land subsidence areas reached 235 km², of which 30%-50% were submerged.

Coal mine subsidence water is a special kind lake compared to the natural lake, since most of the sediment of it was soil from submerged farmland, which could affect the quality of overlaying water, and could be an important potential pollutant source.

Considering the sediment of subsidence water originated form submerged farmland, there are two important issues to discuss.

l What is the difference between sediment and its adjacent inundated soils in the initial-stage of coal mine subsidence waters

l Could submerged agriculture topsoil be the pollutant source to the subsidence water?

Sediments released nitrogen in form of ammonia, especially under anaerobic conditions. On the contrary, sediment enriched nitrogen from the overlying water under both anaerobic and aerobic conditions. Sediments showed phosphorus releasing potential while soils didn't.

During the initial stage (5-10 years) in the waters of subsidence processes, low water depth (2 5 m) and intensive mixing aerobic environments would promote concentration of organic matters, nitrogen, phosphorus from overlying water to sediment, resulting in less risk of nutrient internal loading.