| Jilin area has delimited drinking water sources of groundwater. As important supplementary sources, the amount and quality of groundwater are closely related to people’s daily life and work. In recent years, under the influence of both natural conditions and human activities, the spatial distribution features and evolutionary process have been affected to some extent. Such problems as water-level falls, water pollution and water scarcity have arisen. In order to scientifically understand the groundwater evolutionary law of the Jilin areas, to take effective measures in water resource management and to render the use of groundwater resources sustainable, it is necessary to conduct a study of groundwater spatio-temporal evolution and control management. This article,on the basis of systematic analysis of long-time measured data of groundwater, has examined dynamic characteristics, spatial distribution and evolutionary law of groundwater in the Jilin area, discussed driving factors behind groundwater spatio-temporal evolution and the influencing extent, put forward, with early warning of groundwater safety in mind, multiple management strategies with regard to groundwater level, amount and water pollution carrying capacity, which has important theoretical and practical significance for reasonable use and comprehensive management of groundwater resources. Major achievements are as follows.(1) Study of evolutionary characteristics of groundwater level and groundwater storageBased on regional groundwater monitoring conditions and results deriving from statistical analysis of groundwater level, diagrams of water level dynamic process lines and partitioned burial depths were drawn in order to study groundwater level change process over time and spatial distribution characteristics. Results show that phreatic water level exhibits various fall patterns in different regions, mostly within a modest range of 3m. Regions with water-level fall are concentrated at the area from Huapichang Township to Gudianzi Township along the Aolong River basin, the Jinzhu Township along The Second Songhua River basin and Fate Township along the Kacha River basin; confined water level with a significantly larger range of water-level fluctuation than that of phreatic water. At Huapichang Township along the Aolong River basin and Fate Township along the Kacha River basin, there exists a groundwater drawdown funnel, with the central area of the funnel buried over 30 m deep.Results of calculation and analysis to groundwater resources in the Jilin area showed that Jilin City and Jiaohe City with a higher modulus of groundwater resources than average modulus, Shulan City and Panshi City had a lower resources modulus. And the groundwater resources quantity changed with a rising after decreased trend. In the Jilin area, human exploitation of groundwater has become the main mode of drainage. There was a balance between water exploitation and supply in Jilin City and some years of Huadian City; there is greater potential for exploitation in other regions.(2) Study of the spatio-temporal evolutionary law of groundwater qualityAccording to the results of statistical analysis of groundwater chemistry characteristics, there was a small area of brackish water in 2002 and 2014 in the study area; at other times, the water is chiefly freshwater. The distribution of total hardness is stable, but with a trend of gradual increase. HCO3- is a major anion, with a stable content in groundwater, Cl- and SO42- are the main variables for transformation of water chemistry category of anions; the average concentration of Ca2+ is generally higher than that of other cations, in most basins as the major cations. Durov figures also reveal that water chemistry types consist primarily of HCO3-Ca, HCO3·SO4-Ca, HCO3-Ca·Mg and HCO3-Ca·Na in the region. In different areas there is a varying degree of excess nitrogen, as the main pollutant in groundwater of the study area. There was an enormously excess NH4+ in 1990; but in subsequent years it showed a downward trend year by year, and at present the situation has eased. The issue of excess NO2- and NO3- has intensified over the years, with an excess NO3- concentration in 41% of the phreatic water today, but in 17% of the confined water; the ratio of excess NO2- is over 52% in both phreatic water and confined water. Areas with excess NO2- are mainly irrigation areas throughout the Aolong River basin and the Second Songhua River basin. In addition, there is an excess of total iron along the basins of the Aolong River, Huifa River and Jiaohe River. There are only few places with excess F-; there is a slight excess of oxygen consumption along the basins of the Second Songhua River and Jiaohe River.An evaluation of the groundwater quality was conducted on the basis of rough set theory and support vector machine theory. Evaluation results show that for all years there is an excess of class IV in the phreatic water along the basins of the Second Songhua River and Aolong River and confined water quality is improving considerably. Along the basin of the Xilin River phreatic water quality shows a trend of improvement, and confined water quality deteriorates from class III to class IV; phreatic water quality along the basins of Huifa River, Jiaohe River, and Yinma River shows a trend of falling. Up until 2014, in most areas along the basins the water quality was poor in class IV and groundwater quality was worsening.(3) Analysis of the influence factors behind spatio-temporal evolution of groundwaterA periodicity analysis was made of such natural factors for affecting groundwater evolutionary process as temperature, precipitation, evaporation capacity and fluvial runoff by using wavelet analysis, and gray correlation analysis was conducted to study the extent of correlation between natural and human factors and water level and quality, and to explore the external factors affecting groundwater spatio-temporal evolution. With regard to natural factors, both precipitation and evaporation capacity make a great impact on groundwater level and quality, as major factors in different basins; specifically, precipitation has a great impact on groundwater level and evaporation capacity influences the concentration of nitrogen. With reference to human factors, irrigation water seepage makes a great impact on the basin of the Second Songhua River, Aolong River and Kacha River, where there is a wide area of farming in the northwest. In this way, the water level during irrigation time is raised, and the accompanying nitrogen pollutants exert certain influence on water quality. Human exploitation has a direct influence on water level; during exploitation time, groundwater level declines significantly.(4) Study of early warning about groundwater safety and multiple managementOn the basis of groundwater observation data, combined with the findings of the above-mentioned research, a danger line was determined about water level, water quality and quantity in Jilin City. A comprehensive judgment was made about current conditions and future warning by means of water quantity balance method and linear programming, with water level and water pollution carrying capacity as constraint conditions, to discuss the amount of water use in Jilin City proper, and to advance multiple groundwater management schemes. Early warning results show that the scope for early warning in Jilin City is expanding, heavy warning area has expanded 15% after five years. The warning was serious for both current groundwater and future use, especially along the Aolong River basin. The range for warning covers more than 85% of the Aolong River basin. When water level is at a level of medium control, the area from south of Tuchengzi to Gudianzi Township, and Mangniu River are 2-degree area for water regulation; it is necessary to reduce the exploitation amount of groundwater according to the control program, and to keep the amount of exploitation within a reasonable range; due to excessive overexploitation of groundwater in the area from Huapichang to Dasuihe Township, Soudengzhan Township along the basin of the Aolong River, Jiuzhan Township, the north of Wulajie Township and Jiangbei Township along the basin of the Second Songhua River, there is a wide area for severe warning, as first-degree area for water regulation; it is imperative to formulate effective control measures to avoid further overexploitation that will result in geological problems. If a more stringent rule is imposed about water level, the east of Dasuihe Township and Jinzhu Township also belong to the 2-degree area for water regulation, and Baishan Township changed from 2-degree area to 1-degree area. |
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