Spatial-temporal Distribution Of Suspended Sediment And Its Hydrodynamic Response In Poyang Lake Based On Remote Sensing And Numerical Simulation

Due to the influence of natural factors and human disturbance,lake issues such as area shrinking,water-quality deteriorating,serious ecological environment deterioration,and decline in function and benefit have emerged.The study on the temporal and spatial distribution characteristics and influence mechanism of suspended solids on lake water are of great significance to maintain the sustainable development of lake ecosystem.The Poyang Lake,a highly dynamic lake,was taken as the research object in this paper,and the remote sensing monitoring mechanism,temporal and spatial distribution pattern and hydrodynamic response of suspended solids in the Poyang Lake were studiedvia on-site monitoring,numerical simulation,remote sensing technology,and so on.The principal conclusions are the following:（1）The optical data set of vertical water body in the Poyang Lake was established to reveal the spatial variation characteristics of intrinsic optical parameters（IOP）of the water body of Poyang Lake in different periods.The vertical measurement method for the inherent optical parameters（IOP）of shallow lake water body was proposed.The backscattering probability of Poyang Lake water body wascalculated for the first time,and the optical data set of vertical water body in the Poyang Lake was established for the construction of the water-body IOP parametric model.The backscattering coefficient of Poyang Lake in the vertical direction in different periods increased with increase of water depth,and the spatial difference was significant.（2）The influence mechanism of vertical distribution of suspended solids in Poyang Lake on remote sensing reflectance(R_rs)was revealed.According to the radiation transfer theory,an optical vertical model applicable to non-uniform water body of lake was constructed,and the spectral reflectance values above the water surfaces with different types of suspended matters in the lake were acquired.Inorganic suspended matter was the dominant factor affecting R_rsabove the water surface of Poyang Lake;The concentration of inorganic suspended matters in vertically uniform water body directly affected the shape and value of remote sensing reflectance curve.The R_rs value increased with the increase of the concentration.In contrast,chlorophyll-a（Chl-a）had a minor impact on R_rs,and its concentration had a negative correlation with remote sensing reflectance;The types with concentration of inorganic suspended matters（ρ（ISM））linearly distributed and concentration of chlorophyll-a(ρ（Chl-a）exponentially distributed in the vertical direction accounted for a large proportion;If the surface concentration ofρ（ISM）was low,the change in slope had a great impact on R_rs,especially at 590?700 nm,and the maximum relative change rate 32.65%was observed at 590 nm;The vertical distribution ofρ（Chl-a）had a relatively significant impact on the R_rs in the range of400?600 nm.R_rs decreased with the increase of the curvature ofρ（Chl-a）-vertical-distribution exponential function.The higher the surface concentration ofρ（Chl-a）was,the more significant the impact of the curvature on R_rswas,and the relative change rate at 585nm reached 43.74%.（3）A remote sensing inversion method of suspended-matter concentration in the surface water of Poyang Lake was established on the basis of vertical characteristics.The suspended-matter concentration in low-suspended-matter-concentration water body was correlated with the difference between red and near-red bands,showing an exponential-function relationship;The suspended-matter concentration inhigh-suspended-matter-concentration water body was correlated with the ratio between green andred bands,showing aquadratic-function relationship.The relative errors of suspended-matter concentration values calculated by classification and inversion smaller than 30%accounted for 87.5%,while those of the others accounted for62.5%.Therefore,the inversion accuracy can be improved by this method.Additionally,the error caused by the heterogeneity of vertical distribution can be effectively reduced.（4）The planar distribution law and hydrodynamic response of suspended-matter concentration in the water body of Poyang Lake were revealed.A water-body suspended-matter model combing the estuaries of“Five rivers”and lake regions was established by remote sensing inversion coupled with numerical simulations.The multi-index calibration and verification method was innovatively adopted.The simulation results were consistent with the real values,and the accuracy was significantly improved.From the years of 2008 to 2013,the suspended-matter concentrations in different regions of the Poyang Lake were significantly different from the spatial point of view.The concentration in the northern region was significantly higher than that of the southern region,and that in the main region was the minimum;The concentration in the main region exhibited obvious seasonal difference:The water-body suspended-matter concentration was low in the rainy season,and the suspended-matter concentrations in the water bodies of rivers flowing into lake in the dry season were higher than those in the rainy season.The flow velocity in the Poyang Lake reached a minimum in the rainy season and maximumin the dry season.The suspended-matter concentrations in the outlet section of the lake were principally affected by the sediment entrained by rivers and lake bed scouring;The flow velocity in the inlet section reached a maximum in the normal season and minimum in the rainy season.The suspended-matter concentration in the high-flow-velocity area increased with the increase of flow velocity.The suspended-matter concentration in this area was greatly affected by the sediment entrained by rivers;In the regions with inconsistent flow directions,the suspended-matter concentration in the high-flow-velocity area increased with the increase of flow velocity.The suspended solids principally originated from lake bed scouring,and were affected by sand mining and other artificial factors.（5）The vertical distribution law and hydrodynamic response of suspended-matter concentration in the water body of Poyang Lake were revealed.An IOP-based inversion model of optically active substances in the Poyang Lake was constructed.The simulation results were in good agreement with the measured data,and the continuous information of suspended-matterand Chl-a concentrations in the vertical direction was obtained.The results showed that the majority of water body of Poyang Lake was heterogeneous in the vertical direction:The suspended-matter concentrations in 65.7%of the monitoring stations were vertically heterogeneous,and principally exhibited linear-function distributions;The concentrations of Chl-a in 85.1%of stations were also vertically heterogeneous with exponential-function distributions under most circumstances.The 50%particle-size cumulative distribution(D₅₀)of the Poyang Lake increased in the vertically downward direction.The vertical variation of water body D₅₀ was significantly influenced by the flow velocity.