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Li N.,ETH Zurich | Li N.,China Institute of Geo Environmental Monitoring | Kinzelbach W.,ETH Zurich | Li W.,Institute of Hydrogeology and Engineering Geology Techniques
Journal of Hydrology

Bosten Lake in the southeast of Yanqi Catchment, China, supports the downstream agricultural and natural environments. Over the last few decades the intensive agricultural activities in Yanqi Catchment resulted in decreased lake levels and deteriorated lake water quality. A two-box model is constructed to understand the evolution of lake level and salinity between 1958 and 2008. The two-box model of the lake indicates that the evaporation does have the same trend as the observed lake area and the annual average evaporation agrees with the value obtained from the Penman-Monteith approach. To achieve a correct salt balance, the ratio of outflow concentration and average lake concentration has to be around 0.7. This is due to the incomplete mixing of the lake caused by short-circuiting between tributary inflow and the main outflow via the pump stations abstracting water from the lake. This short-circuiting is investigated in more detail by a 1D numerical flow and transport model of the lake calibrated with observations of lake level and lake concentrations. The distributed model reproduces the correct time-varying outflow concentration. It is used for the assessment of two basic management options: increasing river discharge (by water saving irrigation, reduction of phreatic evaporation or reduction of agricultural area) and diverting saline drainage water to the desert.Increasing river discharge to the lake by 20% reduces the east basin salt concentration by 0.55kg/m3, while capturing all the drainage water and discharging it to depressions instead of the lake reduces the east basin salt concentration by 0.63kg/m3. A combination of increasing river inflow and decreasing drainage salt flux is sufficient to bring future lake TDS below the required 1kg/m3, to keep a lake level that sustains the lake ecosystem, and to supply more water for downstream development and ecosystem rehabilitation. © 2015 The Authors. Source

Li N.,ETH Zurich | Li N.,China Institute of Geo Environmental Monitoring | McLaughlin D.,Massachusetts Institute of Technology | Kinzelbach W.,ETH Zurich | Li W.,Institute of Hydrogeology and Engineering Geology Techniques
Journal of Hydrology

Model uncertainty needs to be quantified to provide objective assessments of the reliability of model predictions and of the risk associated with management decisions that rely on these predictions. This is particularly true in water resource studies that depend on model-based assessments of alternative management strategies. In recent decades, Bayesian data assimilation methods have been widely used in hydrology to assess uncertain model parameters and predictions. In this case study, a particular data assimilation algorithm, the Ensemble Smoother with Multiple Data Assimilation (ESMDA) (Emerick and Reynolds, 2012), is used to derive posterior samples of uncertain model parameters and forecasts for a distributed hydrological model of Yanqi basin, China. This model is constructed using MIKESHE/MIKE11software, which provides for coupling between surface and subsurface processes (DHI, 2011a-d). The random samples in the posterior parameter ensemble are obtained by using measurements to update 50 prior parameter samples generated with a Latin Hypercube Sampling (LHS) procedure. The posterior forecast samples are obtained from model runs that use the corresponding posterior parameter samples. Two iterative sample update methods are considered: one based on an a perturbed observation Kalman filter update and one based on a square root Kalman filter update. These alternatives give nearly the same results and converge in only two iterations. The uncertain parameters considered include hydraulic conductivities, drainage and river leakage factors, van Genuchten soil property parameters, and dispersion coefficients. The results show that the uncertainty in many of the parameters is reduced during the smoother updating process, reflecting information obtained from the observations. Some of the parameters are insensitive and do not benefit from measurement information. The correlation coefficients among certain parameters increase in each iteration, although they generally stay below 0.50. © 2015 Elsevier B.V. Source

Fang Y.,Nanjing University | Ma C.,Nanjing University | Ma C.,Jiangsu Collaborative Innovation Center for Climate Change | Mao L.,CAS Nanjing Institute of Geology and Palaeontology | And 2 more authors.
Review of Palaeobotany and Palynology

As an initial step to aid Quaternary pollen interpretation, we investigated modern pollen deposits from both moss polsters within the forests and surface sediments from an open swamp (Dajiuhu swamp) in the Shennongjia Mountains, central China. Pollen spectra from the moss polsters show similar patterns to local vegetation zones following an elevation gradient. Such pollen spectra reflect more local vegetation landscape than regional one. However, the pollen spectra from the Dajiuhu swamp (especially in the center area) reflect regional vegetation with more deciduous than evergreen broadleaf trees. The pollen ratio of D/E (deciduous/evergreen tree pollen) is developed and its variations in different forest zones show a rising trend with increasing elevation, which gives an alternative to interpret palaeoelevation and/or temperature changes based on Quaternary pollen in monsoon climate controlled areas. The quantitative distribution of key pollen taxa and their source areas are also discussed in this paper. Our study contributes robust bases for palaeoecological interpretation in reconstructing past vegetation and climate changes using Quaternary pollen data in Shennongjia Mountains, central China. © 2014 Elsevier B.V. Source

Zhu C.,Nanjing University | Ma C.,Nanjing University | Yu S.-Y.,CAS Institute of Earth Environment | Tang L.,CAS Nanjing Institute of Geology and Palaeontology | And 2 more authors.

Detailed pollen analyses, along with magnetic and loss-on-ignition (LOI) measurements, were conducted on a 3 m long peat sequence recovered from the Dajiuhu Basin, the Shennongjia Mountains in Central China. Ten AMS 14C dates provide a firm age control on this pollen record in terms of vegetation changes governed essentially by the rise and fall of the Asian summer monsoon during the past 16 000 years. Between 16 000 and 12 700 cal. yr BP, pollen assemblages were dominated by coniferous and broad-leaved trees, indicating a mixed forest landscape corresponding to the initial establishment of the monsoonal climate after the Last Glaciation. The progressive increases in percentages of evergreen tree pollen after 12 700 cal. yr BP point to a steady enhancement of the summer monsoon, which was episodically weakened during the Younger Dryas stadial. From 11 000 to 6000 cal. yr BP, values of coniferous and deciduous tree pollen decreased, while evergreen broad-leaved tree pollen increased substantially, implying a stronger than normal monsoonal climate condition corresponding to the Holocene Hypsithermal Interval. A great reduction in the values of evergreen tree pollen at about 4000 cal. yr BP indicates a sudden retreat of the summer monsoon from this area. © 2009 The Authors, Journal compilation © 2009 The Boreas Collegium. Source

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