Study On Lake Eutrophication As Well As The Criteria And Control Standard For Phosphorus In China

Lake eutrophication, as could be reversed by the establishment of nutrient criteria and control standards, is of great concern to the Chinese government and limnologists. By choosing28lakes located in Xinjiang Punicipality, Inner Mongolia Punicipality, Heilongjiang Province, Jilin Province, Liaoning Province, Jiangsu Province and Yunnan Province, China, the present study examined the historical changes in nutrient levels, the dominant primary producers (e.g., cyanobacteria or macrophytes), the cause of eutrophication, the correlation between the total phosphorus (TP) and Chlorophyll-a (Chl-a), and structural equation model for TP and Chl-a in these lakes. How these lakes are classified were further investigated through both field and laboratory experiments. In the meantime, a serious of mathematical methods, such as probability statistics, variance analysis, the correlated analysis, linear regression, inductive reasoning and the construction of mathematical models were applied. The criteria and control standards for TP in different lakes were further discussed. The main results were as follows:1. The historical and present levels of nutrients in the28lakes of China suggested that the nutrient concentrations in the lakes of Xinjiang and Jiangsu (e.g., macrophyte-dominated Lake Gucheng and Lake Shijiu) and the deep lakes in Yunnan Province (Lake Fuxian and Lake Lugu) were relative low while the other lakes were eutrophicated. Furthermore, the different nutrient concentrations are still increasing in most of the lakes except Lake Taihu and Lake Xuanwu, which have been well-regulated.2. A comparison between the cyanobacteria and macrophyte dominated eutrophication indicated that,①The TP concentrations were always at eutrophic or hypereutrophic levels throughout the year in cyanobacteria dominated lakes (regions). Based on the kinetics results of cyanobacterial decomposition and phosphorus release, the phosphorus flow rates in the ecosystems were found to be relatively fast, which resulted in the high dissolved phosphorus concentration, i.e., the ratios of TDP/TP were all above30%in different cyanobacteria dominated lakes (regions);②The TP concentrations in the macrophyte dominated lakes (regions) were also at eutrophic levels. However, there were relatively low phosphorus concentrations during the growth of macrophyte with extremely high TP levels when they were decomposed. For instance, the mean TP concentrations in Xukou Bay were0.353mg-L-1in December,2009, which were even higher than that in Meiliang Bay at the same period;③This study proposed the quantitative relationship between the biomass of macrophytes and the equal Chl-a values:K1=1000*(CHLequal-Chl-a)*H/Biomass (K1and H represent the transfer coefficiency for changing Biomass into CHLequal and water depth, respectively);④The aquatic parameters, including turbidities (Turbi), salinity (Sal), Secchi Disk Transparency (SD), electrical conductivity (EC) and Chl-a were major contributors to the outbreak of cyanobacterial bloom in cyanobacteria dominated lakes while SD, Tem, Turbi, dissolved oxygen (DO) and pH changed most during the growth of macrophytes in macrophyte dominated lakes (regions).3. The criteria to differentiate whether an eutrophication is caused by natural processes or as a result of the anthropogenic activities are as follows:natural dominated eutrophication occurred when the ratios of N/R>1, while anthropogenic dominated eutrophication happened as the ratios of N/R<1. Lake Hulun is naturally eutrophicated. The warm and dry climate, the ice-covered lake surface in winter and the transitory cyanobacteria bloom in summer are the main reasons for the increase of nutrients annually. Such eutrophication processes are accelerated by the enhancement of nutrients levels in the inflows, outflow alteration into inflows, the sediments’ low nutrient accumulation capacity and the decrease of aquatic products. In contrast, eutrophication due to the anthropogenic activities took place in Lake Taihu and Lake Dianchi. The inflows to these lakes are the most important source of nitrogen and phosphorus. The high population density, rapid development of industry, agriculture, and urbanization also input a substantial amount of phosphorus to these two lakes.4. The relationship between TP and the primary productivities in the lake ecosystems can be simulated using the equation Rmax=ko/(1-η)(Rmax represents the capacity of changing TP into the actual primary productivity (Chl-a), k0is the slope of linear regression between TP and Chl-a for the standing crop of the28lakes examined, and η means the phosphorus transfer efficiency in the lake ecosystem) with some fundamental assumptions and mathematical derivation. Then the equation Rmax=0.001024*e0.001024*Tem was used to describe the relationship between Rmax and the accumulated temperature (Tem) with a threshold for Tern between3400℃·d and4730℃·d. The phosphorus flows slowly as Temp is lower than3400℃·d, and flows fast when Tern is above4730℃·d.5. The28lakes in China could be categorized, as fast, intermediate and low speed ecosystems based on their P flow rate, as cyanobacteria-and macrophyte-dominated lakes based on their primary producer composition, as naturally happening and anthropogenically caused eutrophicated lakes based on the extent of anthropogenic interference, as shallow and deep lakes according to the water depth.6. Base on the categorization of the28lakes, the TP criteria and the corresponding control standards were formulated with the combination of probability statistics and Carlson models. Accordingly, the reference values for TP criterion and control standard were0.08and0.20mg-L-1for Lake Hulun,0.03and0.06mg-L-1for Lake Taihu,0.08and0.15mg-L-1for Lake Dianchi, respectively.The conclusions of this study thus provide important theoretical foundations for the establishment of the different lake ecoregions as well as the formulation of nutrients criteria and standards by the central and local governments.