| In recent years,with increasing of non-point source pollution,surface water quality worsen.The water quality safety of Hexi reservoir directly affects the residents health,which is the main drinking water for four hundred thousand surrounding villages and towns.First,to reveal the characteristic of nitrogen and phosphorus runoff loss in the land rain collecting area of hexi reservoir with different agricultural land use pattern under the condition of natural rainfall.In addition,to explore the influence of different fertilization management mode on nitrogen and phosphorus loss in surface runoff and screen the best fertilization management mode in catchment area of Hexi reservoir.For another,the output of the non-point source pollution directly affect the water quality of hexi reservoir.Therefore,in order to understand the water quality situation and forecasting cyanobacterial blooms of Hexi reservoir,the text selected 7 representational points and 10 water quality parameters to real-time monitoring.Then set up a nonlinear multiple regression prediction model based on the monitoring data,which has important significance to ascertain the main restrictive factors and ensure water quality safety of Hexi reservoir,in addition,timely prevention and predict the occurrence of algae bloom.Main original conclusions are shown as follows.1.Under different land uses,the concentration of annual nitrogen runoff erosion condition is cultivation land(156.92kg/(hm2·a))upland(114.24kg/(hm2·a))>nursery land(35.61kg/(hm2·a))>fallow land(3.99kg/(hm2·a))>woodland(1.59 kg/(hm2·a)).It shown that cultivation land and upland is a major source of nitrogen runoff erosion in rain collecting area,which will reduce significantly nitrogen runoff non-point source output and recede potential impact on water quality of hexi reservoir by carry on the management.In addition,particles nitrogen is the main form of runoff of nitrogen loss,next is nitrate nitrogen under different land uses.Furthermore,the different land uses upland,cultivation land,woodland,fallow land,nursery land annual runoff loss of particles nitrogen loss in proportion to the total nitrogen respectively accounted for about 61.67%,61.42%,75,56%,65.09%and 69.11%;annual loss of nitrate nitrogen loss in proportion to the total nitrogen respectively is 26.35%,28.57%,21.34%,16.27%,23.18%.Under different land uses,the concentration of annual soil loss is:upland(1067.39kg/(hm2 a))>cultivation land(859.49kg/(hm2·a))>nursery land(282.11kg/(hm2·a))>fallow land(177.47kg/(hm2·a))>fallow land(101.73 kg/(hm2·a))>woodland(24.02kg/(hm2·a)),the concentration of annual soil phosphorus runoff erosion condition is cultivation land(39.23 kg/(hm2·a))>upland(32.84 kg/(hm2·a))>nursery land(9.60kg/(hm2·a))>fallow land(1.77 kg/(hm2·a))>woodland(0.51 kg/(hm2·a)).It shown that cultivation land and upland is a major source of nitrogen runoff erosion in rain collecting area,which will reduce significantly soil phosphorus runoff non-point source output and recede potential impact on water quality of hexi reservoir by carry on the management.In addition,particles phosphorus is the main form of runoff of phosphorus loss,next is dissolved phosphorus under different land uses.Furthermore,the different land uses upland,cultivation land,wood land,fallow land,nursery land annual runoff loss of particles phosphorus loss in proportion to the total phosphorus respectively accounted for about 74.03%,79.44%,55.18%,68.16%,66.09%.and,annual loss of dissolved phosphorus loss in proportion to the total phosphorus respectively is 25.97%,20,56%,44.82%,31.84%and 33.91%.2.Under different fertilization management modes,the order of the concentration of annual nitrogen runoff erosion was:broadcast placement(contrast)>plastic mulching>band placement>hole placement>setting buffer for planting grass around nursery land>straw mulching.The mean annual runoff loads of total nitrogen from broadcast placement(contrast),plastic mulching,band placement,hole placement,setting buffer for planting grass around nursery land and straw mulching were 35.61kg/(hm2·a),18.30 kg/(hm2·a),15.86 kg/(hm2·a),12.94 kg/(hm2·a),8.18 kg/(hm2·a)and 3.44kg/(hm2·a)respectively.Which indicated that hole placement,setting buffer for planting grass and straw mulching were better fertilization management mode,and it would reduce significantly nitrogen runoff non-point source output of nursery land and recede the potential impact on water quality of hexi reservoir by optimum combination of above better fertilization management mode in Nursery Land in catchment area of Hexi reservoir in Changxing county.In addition,particles nitrogen was the main and first form of nitrogen loss in runoff,next form was nitrate nitrogen under all fertilization management modes.Furthermore,to the management mode broadcast placement(contrast),plastic mulching,straw mulching,setting buffer for planting grassaround nursery land,band placement and hole placement,annual runoff loss of particles nitrogen loss in proportion to the total nitrogen respectively accounted for about 69.11%,68.87%,68.04%,61.89%,61.17%and 65.09%;annual loss of nitrate nitrogen loss in proportion to the total nitrogen respectively accounted for about 23.18%,23.36%,20.21%,27.20%,32.02%and 28.71%.Under different fertilization management modes,the order of the concentration of annual phosphorus runoff erosion was:broadcast placement(contrast)>plastic mulching>band placement>hole placement>setting buffer for planting grass around nursery land>straw mulching.The mean annual runoff loads of total phosphorus from broadcast placement(contrast),plastic mulching,band placement,hole placement,setting buffer for planting grass around nursery land and straw mulching were 9.60kg/(hm2·a),9.14kg/(hm2·a),5.49 kg/(hm2·a),4.44kg/(hm2·a),2.48kg/(hm2·a)and 1.37 kg/(hm2·a)respectively,Which indicated that hole placement,setting buffer for planting grass and straw mulching were better fertilization management mode,and it would reduce significantly phosphorus runoff non-point source output of nursery land and recede the potential impact on water quality of Hexi reservoir by optimum combination of above better fertilization management mode in nursery land in catchment area of Hexi reservoir in changxing county.In addition,particles phosphorus was the main and first form of phosphorus loss in runoff,next form was dissolved phosphorus under all fertilization management modes.Furthermore,to the management mode broadcast placement(contrast),plastic mulching,straw mulching,setting buffer for planting grassaround nursery land,band placement and hole placement,annual runoff loss of particles phosphorus loss in proportion to the total phosphorus respectively accounted for about 66.09%,70.69%,67.97%,71.63%,68.11%and 67.87%.3.Dissolved oxygen basically come up to the national water quality I level standard,permanganate index,ammonia nitrogen,total phosphorus,basically come up to the nationalⅡlevel standard,most of total nitrogen in water quality come up to the national water qualityⅢclass standard,in part or not even reach national V class standard.water quality has deteriorating trend,which is continuously by the national water qualityⅡintoⅢclass standard.Total phosphorus(x1)and water temperature(x2),permanganate index(x3),total nitrogen(x4)and ammonia nitrogen(x5)have a good relationship with chlorophyll a(y1)and algae density(y2),all of them are restrictive factors of cyanobacterial blooms in Hexi reservoir,and the correlation coefficient(R squared)were 0.6269,0.5608,0.5296,0.6269,0.4201 and 0.4220,0.7150,0.9390,0.7370,0.4520.Then multivariate nonlinear regression prediction model is constructed by using SPSS.Results show that the predicted values of the average absolute error is-0.001 lmg/L and the average relative error is-11.76%for the chlorophyll a concentration;the predicted values of the average absolute error is 8.22 ten thousand/L,the average relative error is-1.08%for the algae density concentration.The concentration change trend of agreement between measured and predicted has the same change of the chlorophyll a and algae density,theremore,has a good correlation correlation between of them,coefficient R squared is 0.9650 and 0.9390.The results of general prediction conform to the requirement and satisfy the water quality monitoring of Hexi reservior. |
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