Spatial heterogeneity of lake eutrophication caused by physiogeographic conditions：An analysis of 143 lakes in China

In order to identify the effect of geographic characteristics on the variations of nutrient concentrations and the utilization efficiency of nutrients by phytoplankton, data from 143 lakes, from 2008 to 2010, including three very different types of topography, i.e., the first topography ladder（FTL）, second topography ladder（STL）, and third topography ladder（TTL）, were statistically analyzed. Lakes in the FTL and STL, located at high elevation（above1000 m） and low longitudes（lower than 105° E）, were sporadically oligotrophic, whereas lakes in the TTL were almost all mesotrophic and eutrophic. The trophic level index（TLI）became higher with the rise of longitude. Two turning points（5 and 15°C） on the curve of TLI as function of the average annual temperature（AAT） corresponded with the AAT in different lake regions in the STL and TTL. Because the responses of TLI to AAT differ significantly, there were variations of nutrient and algal biomass concentrations in different lake regions in the same type of topography ladder. According to the differences in utilization efficiency of total nitrogen or total phosphorus by phytoplankton, China could be partitioned into six lake regions. Scientific nutrient criteria for each lake region shall be established considering these differences in China.