Ni Jinren

Quantifying the synergistic effect of the precipitation and land use on sandy desertification at county level: A case study in Naiman Banner, northern China

Assessing the driving forces of sandy desertification is fundamental and important for its control. It has been widely accepted that both climatic conditions and land use have great impact on sandy desertification in northern China. However, the relative role and synergistic effect of each driving force of sandy desertification are still not clear. In this paper, an indicator named as SI was defined to represent the integrated probability of sandy desertification caused by land use. A quantitative method was developed for characterizing the relative roles of annual precipitation and land use to sandy desertification in both spatial and temporal dimensions at county level. Results showed that, at county level, land use was the main cause of sandy desertification for Naiman Banner since 1987-2009. In the case of spatial dimension, the different combination of land use types decided the distribution of sandy desertification probability and finally decided the spatial pattern of bared sand land. In the case of temporal dimension, the synergistic effect of land use and precipitation highly influenced the spatial distribution of sandy desertification.

Sorption of Triton X-100 on soil organic matter fractions: Kinetics and isotherms

Kinetics and isotherms of Triton X-100 sorption on soil, base-extracted soil (BE), humic acid (HA) and humin (HM) were investigated respectively to get better understanding on characteristics of the surfactant sorption onto different soil organic matters (SOMs). It was demonstrated that the kinetics results could be satisfactorily described by the pseudo-second order model. The half of the time to reach equilibrium (t1/2) for different sorbents followed the sequence of soil > HA > BE > HM. Furthermore, the calculated equilibrium sorption capacity (C(eq)) was found in the sequence of HA > BE > HM > soil, which agreed well with the experimental results. The isotherms of Triton X-100 sorption on soil and HA could be well described by the S-type isotherm, but BE and HM by the L-type. The isotherms of all the four sorbents were found reasonably fitted to the Langmuir equation. The K(d) value, defined as the ratio of Triton X-100 in sorbent and in the equilibrium solution for given concentrations, generally followed the order of HM > HA > soil > BE. Separated HM and HA showed high affinity for Triton X-100, but the HA and HM in soil and BE were tightly bounded by the minerals. Thus, the HA on the soil surface might dominate the sorption, whereas the bounded HM would play a key role upon the surfactants being penetrated inside the soil.

Partitioning of water soluble organic carbon in three sediment size fractions： Effect of the humic substances

Water soluble organic carbon (WSOC) in sediments plays an important role in transference and transformation of aquatic pollutants. This article investigated the inherent mechanisms of how sediment grain size affect the partitioning coefficient (k) of WSOC. Influences of NaOH extracted humic substances were particularly focused on. Sediments were sampled from two cross-sections of the middle Yellow River and sieved into three size fractions (< 63 microm, 63-100 microm, and 100-300 microm). The total concentration of WSOC in sediments (C(WSOC)) and k were estimated using multiple water-sediment ratio experiments. Results showed that C(WSOC) ranged from 0.012 to 0.022 mg/g, while k ranged from 0.8 to 3.9 L/kg. Correlations between the spectrum characteristics of NaOH extracted humic substances and k were analyzed. Strong positive correlations are determined between k and the aromaticity indicators of NaOH extracted humic substances in different sediment size fractions. Comparing with finer fractions (< 63 pm), k is higher in larger size fractions (63-100 microm and 100-300 microm) related to higher aromaticity degree of NaOH extracted humic substances mostly. While negative relationship between k and the area ratio of fourier transform infrared spectroscopy (FT-IR) at 3400 and 1430 cm(-1) implied that the lowest k was related to the highest concentration of acidic humic groups in particles < 63 microm. WSOC in finer fractions (< 63 microm) is likely to enter into pore water, which may further accelerate the transportation of aquatic contaminants from sediment to water.

Water demand for ecosystem protection in rivers with hyper-concentrated sediment-laden flow

Sediment transport is one of the main concerns in a river system with hyper-concentrated flows. Therefore, the water use for sediment transport must be considered in study on the water demand for river ecosystem. The conventional methods for calculating the Minimum Water Demand for River Ecosystem (MWDRE) are not appropriate for rivers with high sediment concentration. This paper studied the MWDRE in wet season, dry season and the whole year under different water-and-sediment conditions in the Lower Yellow River, which is regarded as a typical river with sediment-laden flows. The characteristics of MWDRE in the river are analyzed. Firstly, the water demand for sediment transport (WDST) is much larger than the demands for other riverine functions, the WDST accounts for the absolute majority of the MWDRE. Secondly, in wet season when the WDST is satisfied, not only most of the annual incoming sediment can be transported downstream, but also the water demands for other river functions can be satisfied automatically, so that the MWDRE in wet season is identical to the WDST. Thirdly, in dry season, when the WDST is satisfied, the water demands for other river functions can also be satisfied, but the low sediment transport efficiency results in significant waste of water resources. According to these characteristics and aiming at decreasing sediment deposition in the riverbed and improving the utilization efficiency of water resources, hydrological engineering works can be used to regulate or control flow and sediment so that the sediment incoming in dry season can be accumulated and be transported downstream intensively and thus efficiently in wet season.

Efficiency of sediment transport by flood and its control in the Lower Yellow River

This paper presents the characteristics of sediment transport by flood in the Lower Yellow River with the reach from Huayuankou to Gaocun, which is regarded as a typical braided pattern. The Artificial Neural Network Model on Water Use for Sediment Transport (WUST) by flood was established based on the measured data from 1980 to 1998. Consequently, simulations of controlling process of sediment transport by flood were made in terms of the control theory under different scenarios. According to the situation of sediment transport by flood in the Lower Yellow River, Open-Loop control system and feedback control system were adopted in system design. In the Open-Loop control system, numerical simulations were made to reveal the relationship between average discharge of flood and the WUST with varying sediment concentrations. The results demonstrate that sediment concentration has significant influence on the controlling process of flood flow to WUST. It is practical and efficient to control WUST if sediment concentration is less than 20 kg/m3. In the feedback control system, controlling processes of sediment concentration and flood discharge for sediment transport were simulated respectively under given conditions, and it was found that sediment transport process could be controlled completely by sediment concentration and discharge at the inlet of the reach from Huayuankou to Gaocun. Using the same method, controlling processes of sediment transport by flood in other reaches in the Lower Yellow River were also simulated. For the case of sediment concentration being 20 kg/m3, the optimized controlling discharge ranges from 2390 to 2900 m3/s in the lower reach of Huayuankou. This study is also of significance to flood control and flushing sediment in the Lower Yellow River with proper operation modes of Xiaolangdi Reservoir.

Chemical equilibrium modeling of copper precipitation in a hyper-concentrated solid-liquid system

Rapid progress has been made recently in the understanding of heavy metal sorption and speciation on sediment and soils. One aspect that was overlooked in the previous studies was the process of pollutant transformation and transportation in hyper-concentrated solid-liquid systems. In this paper, batch experiments on copper sorption in association with loess at high sediment concentrations were conducted. However, some reaction mechanisms were difficult to determine experimentally due to the limitations of speciation extraction methods. In an additional study, the MINTEQA2 chemical equilibrium model was used to calculate the speciation and precipitation of copper sorption by loess to give quantitative predictions and detailed information about the reaction process. The experiments and the modeling simulation were made under the same sorption conditions, with sediment concentrations ranging from 50 to 200 kg/m3 and adsorbates of CuSO4 and Cu(NO3)2, in order to compare their results. The modeling results clearly supported the experimental results, fully explained the mechanisms of the effects of chemical form and sediment concentration on the copper sorption, and strengthened the dominant role of carbonates among the main components of loess in the process of copper sorption.

Straight river: its formation and speciality

Straight river is generally regarded as one of the typical river patterns in conventional classifications in terms of their channel plain landforms. However, very few straight patterns were found to be distributed in wider spatial and temporal spans in the self-adjusted fluvial rivers. Thus, the questions occur such as that is it possible for a channel takes on a stable straight pattern? What are the main factors controlling the processes of the river pattern formation and transformation from a straight to other patterns? Various theories and hypotheses including geomorphic threshold hypothesis, the extreme hypothesis on energy dissipation rate, the stability theory, etc. have been developed to explain the aforementioned questions, but none of them is sound for the explanation to the straight-river formation. From the modern fluvial plain patterns, the straight patterns are not as stable as other typical patterns which occurred in nature; from the historic records of the river sedimentation, no apparent evidence was found to support the stable straight river evolution. Based on the analysis of existing theories, observations, evolvement processes of the channel patterns in the experimental results, this paper concluded that the straight pattern should not be included as one of the typical patterns that are self-formed and developed. This study is of importance to understanding of the river pattern formation and transformation.