Regional Differences And Responses To Climate Change Of Nutrient Ecological Effects In Lakes/Reservoirs Of China

Most lakes/reservoirs in the world are facing serious threat of eutrophication by the dual influence of anthropogenic activities and climate change.Moreover,the process of lake eutrophication is accelerated by increasingly severe climate change.The approach to quantitatively evaluate the impact of climate change on nutrient ecological effects of lakes/reservoirs and to analyze the influence on nutrients criteria is an urgent problem to be solved in formulating water environment management schemes for adapting climate change.In accordance with lacking of the quantitative evaluation approach for the impact of climate change on nutrient ecological effects of lakes/reservoirs,the water quality and meteorological data of 167 lakes/reservoirs in China's mainland(excluding the Qingzang Plateau)were collected to quantitative analyze the impact of climate change on nutrient ecological effects of lakes/reservoirs in our country from different spatial-temporal angles,as well as different national-regional scales in this study.Generalized additive models were used to build the relationship of climate variables and nutrient ecological effects,which could quantity the impact of climate change on nutrient ecological effects.The approach of establishing nutrient criteria affected by climate change was formed.The national nutrient criteria and regional nutrient criteria,where was the sensitive area of climate change,were deduced,and the change of the nutrient criteria with the influence of climate change were predicted.The main findings and results were shown as follows:(1)Considering the impact of climatic and geographical conditions on nutrient ecological effect,Bayesian information criterion was used to select climate variables,which has the most significant influence on nutrient ecological effect,and air temperature was selected eventually.The relationship between air temperature,geographic location and the availability of nutrients to algae were built by generalized additive model,and the contribution of air temperature to Chl a/TN(42.46%)and Chl a/TP(37.18%),as well as the contribution of geographic location to Chl a/TN(41.98%)and Chl a/TP(51.86%)were quantified.The spatial and temporal estimates of the availability of nutrients to algae within China's mainland(excluding the Qingzang Plateau)were produced for the first time,and the spatial and temporal diversities of Chl a/TP and Chl a/TN were revealed.According to the result,high spatial variability of nutrient ecological effects driven primarily by geographic location,and high interannual variability was driven by annual average temperature.Regions with high relative interannual variability coincided with regions having high nutrient effects.(2)Based on the fact that nutrient ecological effects of lakes/reservoirs are affected by air temperature significantly,the relationship between chlorophyll a(Chl a),total nitrogen(TN)and total phosphorus(TP)were established by generalized additive model,and the contribution of TN(19.17%),TP(25.76%)and air temperature(7.36%)to the variation of Chl a were estimated.The approach of establishing nutrient criteria in response to climate change was formed by incorporating generalized additive model and stressor-response model.The nutrient criteria in China during the baseline period(1996-2005)was deduced,which were 0.88 TN mg/L and 0.021 TP mg/L,respectively.The ensemble mean values of global circulation models was calculated to predict the nutrient criteria of lakes/reservoirs in China.According to the results,the predicted future nutrient criteria in China showed downward trends for all the climate scenarios,and the most significant decreasing trend happened under RCP 8.5 scenario.By the end of this century,the nutrient criteria of TN and TP predicted by the single-nutrient models were decreased by 46.17%and 15.24%respectively,indicating that efforts to reduce TP inputs would generally be more effective than efforts to reduce TN inputs for phosphorus-limited lakes/reservoirs.The nutrient criteria predicted by double-nutrient model dropped slighter than the single-nutrient model,indicating that under a dual nutrient management strategy,each nutrient could be controlled under less-strict criteria than under single-nutrient management strategies.(3)In addition to air temperature,the changes of precipitation,wind speed,relative humidity and other climate variables could also affect nutrient ecological effect of lakes/reservoirs.The lakes/reservoirs in Heilongjiang Province,where is one of most sensitive regions to climate change in China,were selected to research.Covariance analysis was used to identify the climate variables which had significant impact on the relationship between nutrients and Chl a,and nonlinear regression model was used to predict the variation tendency of nutrient criteria under the stress of climate variables.The results showed that nutrient criteria could be decreased by the influence of relative humidity and precipitation increasing,as well as the decreasing wind speed Furthermore,generalized additive model were used to quantitatively analyze the variation of nutrient criteria under the stress of climate variables.With the influence of wind speed and relative humidity,the predicted criteria of TP after 30 years decreased by 68.1%and 23.4%,respectively,compared with the lower limit of the current criteria.With the influence of relative humidity or precipitation,the predicted criteria of TN decreased by 37.4%and 34.1%respectively after 30 years.