The efficacy of water resource management and protection hinges on a profound understanding of the controlling factors and regulatory mechanisms that shape groundwater chemistry within aquifers. Despite this, our comprehension of how groundwater chemistry and ion sources vary across diverse aquifer types remained limited. To bridge this gap, our study conducted a detailed hydrochemical and statistical investigation of porous, fissured, and karst aquifers. By applying multivariate statistical techniques, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), the hydrochemical characteristics and main ion sources of each aquifer type, as well as distinct controlling factors and regulation patterns, were determined. Notably, evaporation predominantly affected the hydrochemistry of porous aquifers, whereas mineral dissolution and rock weathering processes played a pivotal role in shaping the groundwater evolution of fissured and karst aquifers. HCO₃⁻ and SO₄²⁻ are the most common anions of all types, while Na⁺ is dominant in porous and fissured aquifers and Ca²⁺ is dominant in karst aquifers. The most common hydrochemical types identified were HCO₃-Ca·Mg (accounting for approximately 56.84%) and SO₄·Cl-Na (constituting approximately 21.75%). PCA results revealed that lateral recharge from fissured aquifers in hilly regions into the groundwater of porous aquifer, and wastewater discharge and agricultural fertilizer application, significantly impact the groundwater chemistry across all three aquifer types. It is worth noting that the dissolution of carbonate minerals, often influenced by human activities, had a profound effect on the hydrochemistry of each aquifer. Conversely, the dissolution of evaporitic minerals affected groundwater chemistry primarily through cation exchange processes. In summary, the hydrochemical characteristics of these aquifer types were predominantly shaped by a complex interplay of mineral dissolution, cation exchange, evaporation, and anthropogenic activities, with notable contributions from fissured aquifer recharge and pollution. These insights were critical for informing national-level strategies for groundwater resource protection and management.

Hulun Buir Grassland is a world-famous natural pasture. The Chenbalhu Banner coalfield, the hinterland of the grassland, is located on the west slope of the Great Khingan Mountains and on the north bank of the Hailar River in China. The proven geological reserves of coal are 17 billion tons. Hulun Buir Grassland plays a role in the ecological barrier, regional coal industry, power transmission from west to east and power transmission from north to south. The proportion of local groundwater in irrigation, domestic and industrial production water sources is about 86%. The large-scale exploitation of coal resources and the continuous emergence of large unit and coal-fired power plants have consumed a large amount of local water resources, resulting in the decrease of the local groundwater level and changing the natural flow field of groundwater. This paper studies the background hydrochemical values and evaluates the irrigatibility of the whole Chenbaerhu Banner coalfield, and studies the impact of coal industry chains such as mining areas and coal chemical plants on the hydrochemistry characteristics of groundwater. The above two studies provide important guiding values for guiding local economic structure planning, groundwater resources exploitation and ecological governance. The study found that Na⁺ and HCO₃⁻ in the groundwater in the study area occupy a dominant position. Referring to the comparison of the lowest values of three types of water standards in the Quality Standards for Groundwater (GB/T14848-2017), the amount of NH₄⁺, Na⁺ and NO₂⁻ exceeding the standard is close to more than 30%. The main chemical types of river water in the study area are HCO₃⁻ Na and HCO₃⁻ Ca·Na, the main chemical types of surface water are HCO₃⁻ Na and HCO₃⁻ Na·Ca, and the main chemical type of confined water is HCO₃⁻Na. The formation of hydrochemical types is mainly affected by the dissolution, filtration and evaporation of rocks, specifically the dissolution and filtration of sodium and calcium salts. The chemical correlation analysis of groundwater shows that there are abnormal values at many points in the study area. Further combining with the horizontal comparison of surface human activities in the study area, it shows that the influence scope of coal mine production and coal chemical plants on groundwater is extremely limited. The local groundwater is mainly polluted by a large quantity of local cattle and sheep manure, industrial and domestic sewage pollution and farmland fertilizer.