Dynamical Evolution On Sustainability Of The Liangzhou District Agro-ecosystem

Quantitative evaluation is a key field of the sustainable development and a judgment whether man's activity has been in its ecological carrying capacity. Making a thorough study to find out development strategy of the Liangzhou district has an important scientific and practical significance. Based on many statistical and finding data, a systematic research has focused on the energy flow and its transformation, ecological footprint and environment asset and liability through applying such research modes and analyzing methods like energy analysis, ecological footprint and environment asset and liability etc. Based on the research, the conclusions drawn are as follows:1.Conclusions drawn on the basis of the study on energy characteristic and developing law of Liangzhou district agro-ecosystem have shown that the agricultural production in this area has the character with inorganic energy input. The energy input level has been gradually increasing annually and reached 112.85X1010 J/hm2.a in 2000, but it was just still within an appropriate range, only reached the maximum energy input value of 57.6%. This means, there are still spaces for energy input in this area. Meanwhile, the inorganic energy input was increased by 50.85 times compared with -that in 1955, while the organic energy input at the same period was increased by 80.54%. The structures of energy input also changed radically, from an organic energy input dependant pattern to an inorganic energy input dependant one. The period of transformation had come being in 1970.The ratio between the total amounts of energy input between inorganic and organic in 1949 was 1:12.94, and was 2.29:1 in 2000. The energy output capacity in 2000 wasincreased by 3.26 times compared with that in 1955.But the proportion between output and input at the same period decreased from 2.394 to 1.205.2. Research on the ecological footprint in Liangzhou district has shown that the ecological footprint and ecological carrying capacity had a trend of periodic increment. The ecological carrying capacity was on the remainder stage from 1949 to 1980, both the ecological carrying capacity and footprint were on a low growth stage at the same period. From 1980 to 1985, they both were on a rapid growth stage, which showed a relative balance for a short period. From 1985 to 2000, the ecological carrying capacity was on deficit stage, both the ecological carrying capacity and footprint assumed a decline tendency. The transformation period between ecological remainder and deficit was in 1975, and the deficits had negative increment with acceleration in recent years. These deficits have shown that the agricultural development in Liangzhou district has deviated far away from a sustainable one. Viewed the sustainable conception, agricultural development in Liangzhou district can be sustainable from 1949 to 1970 and can't be sustainable since 1970.3.Study on environmental asset and liability in Liangzhou district has shown that the environmental assets have been reducing continually. Changed by stages into assumed a decreasing tendency during 1949 to 1975. Then it somewhat rose since 1975. The environmental liabilities also have been decreasing, and it was increased by -69.75 times in 2000 compared with that in 1949. The environmental net assets assumed a decline tendency from 1949 to 2000 and it was increased by -3.77 times in 2000 compared with that in 1949. The transformation period between the environmental assets and liabilities was 1975. These negative net assets have shownthat the agricultural development in this area has deviated far away from a sustainable one.The agricultural development in Liangzhou district can be in the first ecological level from 1949 to 1970 and be in the second ecological level since 1970.4. A general train of thought for the sustainable development of the Liangzhou district agro-ecosystem has been put forward: some ecological engineering should be implemented, ecological environment should be improved, agricultural and industrial structure s...