The laser ablation ⁴⁰Ar/³⁹Ar method makes it possible to date quanterary volcanic rocks precisely. So far, it lacks an assessment criterion that can be used to estimate the reliability of test data and geochronological information. The mean square weighted deviation (MSWD) and the number of measurement (n value) are used to be the crucial parameter to evaluate sample properties and experimental standard. When applying laser ablation ⁴⁰Ar/³⁹Ar method to date young volcanic rocks, a best-fit ⁴⁰Ar/³⁹Ar isochron diagram requires isotopic homogeneity of the sample and permanent closure of the isotope system at the same time. While MSWD, which is related to n value, is a parameter to determine whether the data are located in the same normal distribution, or in other words, whether the sample has a unified true age, it is applicable to use MSWD and n value to estimate the level of confidence placed on the computed mean. The critical values of MSWD for the 99.7% confidence interval using differing degrees of freedom are calculated in this paper. It is important to note that MSWD is available in evaluating dating result of both apparent and isochron ages. For the samples which tend to have heterogeneous initial ⁴⁰Ar/³⁶Ar ratios or different closure times, MSWD combined with the probability density of apparent ages can be used to distinguish different groups of samples, calculate the isochron ages respectively, and interpret the result after accounting for the various parameters to evaluate the data quality.

Taking Lake Dianchi Watershed as study area, the dynamics change degree of land use types in the watershed was analyzed based on interpretation data from TM image in 1990 and 1999. The direction of land use conversion was quantitatively analyzed by land use transfer matrix based on the Markov model. Meanwhile, land use change tendency of 2008 was simulated and forecasted based on land use conversion rules using multi-criteria evaluation method from GIS and combining with CA-Markov model. Compared with the interpretation data of 2008, Kappa coefficient of the simulated results was 0.7338, indicating that the simulated results were credible. The spatial patterns of land use change in 2017 and 2026 were simulated by using CA-Markov model. The results show that land use change is also active in this watershed and ecological restoration and reconstruction is still confronted with pressure. Farmland, forest, water and unused land will reduce from 2008 to 2026, while the grassland and construction land will continue to increase. Compared with the trend of land use from 1990 to 2008, the simulated result indicate that farmland, forest and construction land from 2008 to 2026 will keep the same change trend while grassland, water and unused land show the opposite change trend. Construction land will expand on the basis of the present and the change of water is little. Although forest resources will decrease in future, it is still the main land use types in watershed. Construction land expansion significantly increases the load of non-point source pollution in Dianchi. Unreasonable land use is one of the major causes of the water quality degradation in Dianchi Lake currently, and it is going to increase the pressure on the water environment and ecology of water basin in the future. Therefore, to maintain enough arable land per capita, lower fertilization strength, improve land utilization levels, keep a sufficient amount of ecological land, use construction land frugally and intensively, are some important measures to reduce the potential of non-point source pollution in the area. The research can provide scientific support for rational planning and management of land use, the policies formulating of ecological restoration and economic development.