Abstract: Abstract: There exist remarkable regional differences on the lake nutrient and its eutrophication effect in China. It is the premise to explore the features of lake nutrient and its determinacy on the ecological division to carry out effective measures on the breaking-out of lake eutrophication. In the case study of Yunnan-Guizhou Plateau, the contents of Chlorophyll-a(Chl-a), total nitrogen (TN) and total phosphorus (TP) of lake water are inverted via the remote sensing inversion algorithm. An index system is also established by including the information from geophysical, geographical, ecosystem and human dimensions to evaluate the levels of land nutrients and all the information is mapped onto the small watersheds delimitated based on DEM data covering the entire study region. Meanwhile, the effect of each index on the ratio of Chl-a over P (Chl-a/P) and the ratio of chl-a over N(Chl-a/N) is quantitatively analyzed by applying mathematical statistics method on the small watershed scale so as to calculate the evaluation scores of two lake nutrient ecological zones who will then be clustered according to the small watershed scale via the dual-constraint space clustering algorithm. After a couple rounds of handlings, ecological zones reflecting the pattern of the lake nutrient concentrations are finally formed.
The paper concludes a couple of key findings. A small number of sites based monitoring data can be used to deduce the surface of lake nutrient level through the remote sensing inversion model, which makes up the deficiency that the few sites-based monitoring data are always hard to supply enough information for the lake nutrient ecological division. By exploring the relationship between each index factor and Chl-a/P and Chl-a/N on the lake water, organic combination of microscopic indexes of the lake water and macroscopic indexes of the watersheds on the lake nutrient ecological division is thus realized. By applying the dual-constraint spatial clustering algorithm to carry on the lakes nutrient ecological zoning to meet the requirements of space continuity kept while the evaluation scores are guaranteed. Corresponding to the spatial difference of geophysical and geographical conditions, land use and human intervention intensity, the Yunnan-Guizhou Plateau is divided into four ecological parts, i.e., north Yunnan Plateau lakes, the southern Yunnan valley, mountain lakes and karst lakes zones located between east Yunnan, west Guangxi and south Guizhou and northeast Guizhou plateau. The study indicates that the lake nutrient ecological division approach base one dual-constraint space clustering algorithm can be used to other places and be recommended as reference approach of the lake nutrient ecological division to multiple scales of areas.

Key words: dual-constraint spatial cluster, ecoregion, lake nutrient, remote sensing inversion, subtropical moist zone on the Yunnan-Guizhou Plateau