Responses Of Typical River Water Quality To Urbanization And Key Hydrological Factors

Environmental pollution,especially water pollution has become a more and more serious problems during the process of rapid urbanization in china.Water pollution is extremely complex under the interference of human activities,and may combined point source pollution with nonpoint source pollution.Water environment are often influenced by the Space-time configuration of the level of urbanization indicators on different scales,as well as flow and source/sink landscapes characteristic.Thus,it's helpful to understand the water quality mechanism associated with the level of urbanization indicators,flow and source/sink landscapes-ponds.However,previous studies mainly focused on a single spatial or temporal scale,and there is still many river water quality problems left for research and discussion from the angle of flow and ponds.Therefore,On the basis of the research on water quality and its temporal and spatial distribution features,Analysis the influence of urbanization level on water quality at multi-spatial scales,and explore the influence mechanism between flow or small water body-ponds and water quality.This study has important theoretical and practical significanc.In this paper,three typical rivers in the center of Guangzhou city were chosen as the research object.Based on the water quality and hydrological measured data at the same time in 54 monitoring sections of three rivers and 7 ponds along the sensitive rivers for a hydrological year,assessing the overall pollution and temporal and spatial variation characteristics of the river water quality,then explore.The Responses of typical river water quality to urbanization at multi-spatial scales and key hydrological factors using the principles of hydrology,landscape ecology,environmental ecology and the technology of RS and GIS.The main results were as follows:?1?Most of the 54 monitoring sections in the three typical river were in serious pollution levels,especially TN and NH₃-N concentrations were seriously overweight.TP concentrations exceeded the rate of 50%in Shahe river and Chebei river,but TP and CODcr concentrations were still in limit levels in Wu river.The three typical rivers water quality showed significant spatial variability:Pollution levels in the order Chebei river>Shahe river>Wu river,downstream>midstream>upstream.Four water quality indicators in three typical rivers was not greatly different between dry season and rainy season except TP pollution in Wu river.Overall temporal variability was not obvious.?2?The quantitative analysis rusults of representative urbanization indicators in multi-scales shows that,Chebei river on the whole is located in rapid urbanization areas,while most of Wu river is located in the edge of urbanizationand Shahe river in the completely urbanization area.Three rivers upstream is lower in urbanization rate Compared to the middle and lower reaches.Spearman correlation analysis showed that:because of water quality indicators,spatial scale,seasonal variation and regional differences lead to the different relationship between TN,NH₃-N,TP,CODcr and the representative urbanization indicators,The best analysis scale for Chebei river water quality indicators?except CODcr?is in100m riparian buffer zone,while Shahe river?except CODcr?in administrative streetand Wu river in 200m riparian buffer zone.Stepwise regression analysis showed that the major impact factors on three rivers water pollution in dry or rainy seasons are more complex,but in rainy season is relatively simple.Chebei river water quality mainly affected by the forest and garden landscape pattern index in dry and rain season.And also affected by grassland area ratio?PLAND5?in dry season.Shahe river water quality mainly affected by grassland landscape shape index?LSI5?during the rainy season.when mainly affected by the distance to commercial centers?Dis_CBD?and the impervious surface coverage during dry season;the main impact factors of Wu river water quality were randomness,but the distance to the commercial center was the main contribution factor for TN concentration whether it is in the rainy season or in the dry season.?3?TN concentration in three monitoring sections,TP concentration in upstream and midstream monitoring sections and NH3-N concentration in midstream and downstream in Chebei river had significant negative correlation on the flow?Sig<0.05?,but the correlation between flow and CODcr concentration is not obvious.It's indicates that water pollution concentration levels decreased gradually as the flow increased.But the relationship between water quality indicators concentration and flow is non-linear.That is to say there is an extreme value in flow and the change of water concentration:Within the scope of extreme value,flow play a dilution effect and self-purification capacity for water quality,Otherwise the rivers will lose self-control capacity beyond the extreme value range.In other words water quality will deteriorate due to the increase of flow.Besides,the relationship between upstream or downstream water quality and flow was also differences.The ponds has an obvious effect on nitrogen and phosphorus nonpoint source pollution caused by rainfall runoff by its interception and retention capacity as a key source of nonpoint source pollution or sink landscape.This suggests that we can make use of the widespread pond systems to intercept and store point source pollution caused by rainfall runoff in order to achieve the objective of reducing non-point source pollution load into the river.The exceedances of four water quality indicators in seven ponds were:TN?86%?>CODcr?71%?>NH3-N?43%?>TP?29%?,It illustrated that ponds water quality was mainly polluted by TN.water quality in ponds overall was better than their upstream and downstream.Combined with student's t-test on the water quality indicators in the downstream sampling,we can infer that the influence of No.1 pond?General pond?up the left tributary on Chebei river water quality is not significant,No.2 pond?professional fishpond?up the left tributary acted a"source"effect on Chebei river water quality,No.5 pond?landscape pond?in the middle left tributary,No.6 pond?experimental aquaculture pond?up the right tributary and No.7 pond?fishing pond?downstream acted as"sink"effect,but it needs to be multiple monitoring and further explored 3 pond?landscape pond?and No.4 pond?fishing pond?in the middle left tributary act as"source"or"sink"effect.?4?Combination of the above conclusion,field research and summarizing the course of river management in Guangzhou,found that the main cause of pollution in the three typical rivers were follow:Interception-pollutant was not complete,rain and polluted water were not separate apart,many industrial enterprises and farmers poured untreated wastewater without due approval,non-point source caused by rainfall runoff,river volume relatively less during dry season which was easy to cause riverbed silting,embankment made of reinforced concrete has lost ecological functions and the intermittent"campaign-style"governance mode.According to the above results puts forward Seven target-oriented proposals and countermeasures on water pollution comprehensive treatment:a.Interception-pollutant beffore treat pollution,reduce pollution emissions from the source;b.dredging;c.Joint operation of water quantity and quality;d.Ecological restoration;e.Builting and maintain sink landscapes;f.Comprehensive management from the optimum scale;g.Establishing the"normalization"governance model.