| Coal gangue is the solid waste produced in coal mining, washing and processing process, which currently occupies about 10% of the amount of coal production. Statistically, the percentage of coal gangue attains to 8%-20%, with the average about 12%, during the coal mining process. Guizhou poevince has rich resources in coal mine, and therefore the situation of coal gangue emission also becomes serious. Many researchers have studied the coal gangue yard of central Guizhou mountain area, but there were little study focusing on the pollution release and migration as well as the bioavailability of heavy metals, which is the scope of this thesis study.This thesis research investigates the characteristics and pollution situations of the coal gangue yard and the influences to plants and micro-organisms in the selected research duration and area of this study. Specifically, in the perspective of the pollution results and situation of coal gangue, this research studies the coal gangue yard paddy soil bioavailability of heavy metal content, with the aim to explore the characteristics of heavy metals migration and release in coal gangue yard paddy soil. In the perspective of plant ecology, this research investigates the influences of polluted paddy soil on crop seedling growth and microbial community functional exploration. Main research approaches and obtained results and findings of this thesis study include:(1) Inspection and sampling analysis of the polluted paddy soil around the abandoned coal yard in Guiyang city of Guizhou province, in order to investigate and explore the influences of heavy metals migration in coal gangue storaged and piled up process on the heavy metals content in the surrounding paddy soil. The analysis results showed that:the total content of gangue cadmium, arsenic and mercury were more than limited values of soil environmental quality standards of China, with mercury, cadmium most polluted, and followed by arsenic. The content of light polluted paddy soil cadmium, arsenic and mercury were more than the limit value of 8.83,0.28 and 6.53 times. The content of effective heavy metals in paddy soil were increased in different extents, in which the increase percentage of effective state cadmium, mercury attains to above 26%. Cadmium and mercury were the also main elements that excess the water quality standards in the overlying water of the surrounding paddy field and that increase significantly in this overlying water after the submerging of the polluted paddy soil. The results also indicated that the accumulation of heavy metals in the paddy soil in the surrounding of the coal gangue storage yard was mainly affected by the migration of such heavy metals in the coal gangue, with two main reasons:(i) direct irrigation for the surrounding paddy field by coal gangue gully water, which influences the content of heavy metals in the paddy soil and corresponding overlying water; and (ii) the release of heavy metals such as cadmium and mercury in the polluted paddy soil, which may greatly affect the quality of overlying water in the paddy field. Inspection and sampling analysis of the polluted paddy soil and overlying water in the paddy field around the coal yard in the mountain areas of central Guizhou province, with the aim to investigate and explore the content variation and releasing characteristics of the effective state heavy metals (e.g., chromium, copper, zinc, arsenic, cadmium, mercury and lead) in the polluted paddy soil. The results revealed that, with the increase of paddy soil pollution, the content of bioavailable cadmium increased obviously, and the average increase of such cadmium in the paddy soil with moderate and severe pollution situations are 1.30 and 2.60 times larger than that with lightly pollution situation respectively. During the rice growth period (i.e., June-August), the cadmium in overlying water of the polluted paddy soil exceeded the relevant water quality standards for all the studied samples, but average cadmium concentration (based on 3 samples) in the moderate and severe polluted paddy soils were 11.3% and 27.3% higher than that in slightly polluted paddy soil respectively.(2) During one to thirty days of the submerging period in the polluted paddy soil, the cadmium concentration in the overlying water was continuously increasing and after 20 days, the cadmium in the moderate and severe polluted paddy soils exceeded the standard. Moderate and severe pollution of paddy soil from the flooded 20 days later, the overlying water exceed the standard cadmium appeared. Mercury also has some samples exceed the standard phenomenon. There were no other heavy metal exceed the standard. The amount of soil heavy metal cadmium was higher, which could affect the release of it. Caused the phenomenon that after 30 days, it exceeded the standard. There was a positive correlation between the conductivity and the release time. The correlation coefficient was 0.9886** (p<0.01). It reached the maximum value at the 30 day. The reason was as time goes on, the electrolyte increased. Therefore the conductivity is increased. Therefore, comprehensive flooding test and field sampling and analysis results, the overlying water pollution of coal gangue yard surrounding paddy field was mainly cadmium and mercury pollution. Heavy metals in coal gangue leached by rainwater and eroded gully water. They were into the paddy field or in the surface water, caused the second pollution. Carrying the heavy metal accumulation in rice paddy soil, caused by heavy metal pollution, resulting in decreased rice yield and quality decreased.(3) Heavy polluted soil with rice, rape and lettuce, germination potential and germination rate was zero. Three kinds of plant seeds in the contaminated soil treatment are sprouting in tenth days. In addition to rice, rape and lettuce at the end of the period were completely moldy death. There were significant differences between light pollution soil and the control (distilled water) (P< 0.05). With the increase of the distance from the coal gangue, light pollution soil treatment three germination potential and germination rate were increased. Compared with the control, rice and rape, lettuce germination potential and germination rate decreased to 35.5% and 23.5%,35% and 15%,22.2% and 36.8%. Different treatments on rice and rape, lettuce fresh weight and dry weight effect compared with the control group were significant (P< 0.05). With the increase of distance from the gangue, two seedling fresh weight and dry weight increased. There were significant differences between light pollution soil and the control (distilled water) (P< 0.05). Two index of rice fell 72.36%,57.58%,91.6%,60.6%, at the same time, rape, lettuce fell 91.39%,77.4%. Heavy pollution in paddy soil rice and rape and the control (distilled water) there was a significant difference (P< 0.05). The decrease was 100%.Heavy pollution soil overlying water rice, rape and lettuce three germination potential and germination rate was zero. Heavy polluted soil overlying water rice, rape and lettuce germination potential and germination rate was zero. Three kinds of plant seeds in soil overlying water treatment are sprouting in third days. Three kinds of crops at the end of the period completely moldy died. There were significant differences between light pollution soil overlying water and the control (distilled water) (P< 0.05). Light pollution soil overlying water treatment plant seed germination under three in third days, in addition to rice, rape and lettuce at the end of the period were completely moldy death. Compared with the control group, the rice germination potential and germination rate decreased to 14.1% and 15%. Different treatments on rice and rape, lettuce fresh weight and dry weight effect compared with the control group were significant (P< 0.05). With the increase of distance from the gangue, two seedling fresh weight and dry weight increased. There were significant differences between light pollution soil overlying water and the control (distilled water) (P< 0.05). Two index of rice fell 62.6% and 61.1%. There was a significant difference between pollution degree in paddy soils overlying water and heavy pollution in paddy soils overlying water of three kinds of crops and the control (distilled water) (P< 0.05). The drop was 100%.Through the analysis of the AWCD results display from the culture of microorganisms, metabolic activity gradually increased. After being cultured for 72h increase rate began to increase significantly after 168h gradually tends to be steady.In the early treatment, microbial metabolic activity affected by heavy metal had no regularity. At 48h, in the polluted soil AWCD value was higher than the heavy polluted soil. The heavy metals in coal gangue yard surrounding paddy soil on microbial metabolic activity and time. Heavy metal pollution in long-term will cause the surrounding paddy soil microbial metabolic activity decreased obviously. There was a significant correlation between 48h activity and the content of heavy metals of microbial metabolism. At the same time the cultivation of microbial metabolic activity of heavy pollution soil AWCD value was significantly lower than the light polluted soil. That was negatively related to metabolic activity and microorganism heavy metal content. |
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