Relationship Between Soil and Water Conservation Practices and Soil Conditions in Low Mountain and Hilly Region of Northeast China

The soil and water conservation practices of ecological restoration(ER),fish scale pit(FP),furrow and ridge tillage across the slope(FR),shrub strips(SS),and vegetation-covered ridge(VR)are characteristic of the Jixing small watershed of the low mountain and hilly region of Jilin Province,Northeast China.This study aims to elucidate the effects of soil and water conservation practices on soil conditions after the short-term implementation of practices.Soil samples were collected from five soil and water conservation sites(ER,FP,FR,SS,and VR)and two controls(BL and CT)to investigate their properties.To evaluate the influence of soil and water conservation practices on soil quality,an integrated quantitative index,soil quality index(QI),was developed to compare the soil quality under the different soil and water conservation practices.The results show that not all soil and water conservation practices can improve the soil conditions and not all soil properties,especially soil organic carbon(SOC),can be recovered under soil and water conservation practice in short-term.Moreover,the QI in the five soil and water conservation practices and two controls was in the following order:ER>VR>BL>FR>CT>SS>FP.ER exhibited a higher soil quality value on a slope scale.In the low mountain and hilly region of Northeast China,ER is a better choice than the conversion of farmlands to planted grasslands and woodlands early in the soil and water conservation program.

Measurement errors on sediment concentration from traditional runoff collection tanks and its correction possibility

Runoff plots are widely used worldwide to monitor water and soil losses.Sediment concentration in runoff collection tank is measured by stirring-sampling procedure,but this method may produce high measurement error due to the uneven mixing of collected sediments with water and soil particle deposition.This study aimed to identify the relationship between actual and measured sediment concentrations,so as to estimate the systematic error of sediment concentration measurement from runoff collection tank by traditional stirring-sampling procedure and the possibility to eliminate it.Four major soils including black soil,silt loess,clay loess,and purple soil in China were used to determine the correlation between the measured and designed sediment concentrations in laboratory.Tested sediment concentration was 1,2,5,8,10,20,50,80,100,200,500,800,and 1000 kg/m^(3),and total sediment-laden water volume was 50 L and 100 L.Five samples were collected successively from collection tank for each treatment and their sediment concentrations were measured by conventional oven-drying method.The results showed that all the measured sediment concentration values were smaller than the designed ones,but both the measured and designed values were linearly correlated significantly with determination coefficients greater than 0.8,generally.In the whole tested concentration range,the systematical error was-0.19 to-319.95 kg/m^(3) and relative error was 0.30%-84.5% for the 4 tested soils and 2 total sediment-laden water volumes.These results indicated a necessity and possibility to correct conventional sediment concentration measurement value.The result is usable to assess and correct the measurement error of sediment concentrations from traditional runoff plot.

Correction of measurement errors on sediment concentration sampled by stirring-sampling method from traditional runoff collection tanks

Stirring-sampling method is a widely adopted method to measure sediment concentrations in collection tanks of runoff plots,but with high systematic measurement errors.This research aimed to advance an approach for building correction equations to remove measurement errors in designed sediment concentration range.Experimental data of sediment measurement from the stirring-sampling method,with four representative soils,under the designed sediment concentrations(1,2,5,8,10,20,50,80,100,200,500,800,and 1000 kg/m^(3))were used to demonstrate the correction methodological process.Two correction methods(step-wise correction and universal correction)were suggested for the trial in this study based on the distribution of measurement errors.In the step-wise correction,the correction equations were made with a series of linear functions without intercept for the low concentration group(0-20 kg/m^(3)),a series of linear functions with intercept for the high(20-200 kg/m^(3))and extremely high(200-1000 kg/m^(3))concentration groups,consecutively.The correction equations were a series of power functions in the universal correction.For the step-wise correction,most of the relative errors of correction sediment concentrations were smaller than 15%and 10%under high and extremely high concentration groups,but the corrected accuracy was not good in the sediment concentration of 1,2,5 kg/m^(3)with the corrected relative errors of 0.20%-206.07%.For the universal correction,the corrected relative errors(0.19%-31.81%)of the four soils were low under the condition of extremely high sediment concentrations,but other corrected accuracies weren’t good with the corrected relative errors of 0.68%-1154.71%.The corrected accuracy of step-wise correction is higher than that of the universal correction,but the universal correction is more convenient.These results indicated that the correction equations could efficiently revise the measurement errors of the tested soils and that this method can be generalized to other soil types and was meaningful in monitoring soil erosion.