基于VMOD模型的若尔盖泥炭沼泽地下水数值模拟
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摘要
若尔盖泥炭沼泽自20世纪50年代以来发生显著的面积萎缩,导致其失水的重要机制之一是自然沟道的溯源下切与横向侵蚀,进而疏干沟道两侧沼泽的地表水和泥炭层的地下水,加速泥炭沼泽地的萎缩。基于2016—2017年夏季野外观测与Visual MODFLOW地下水模型,分别研究局部2种典型泥炭地的地下水运动和沟道对泥炭地地下水的横向水力梯度的影响。结果表明:地下水流运动偏向于沟道方向,且当沟道切穿泥炭层后此趋势更加显著,垂直沟道方向水力梯度约增大79%。证实自然沟道不仅在降雨期对地表水具有排水作用,其溯源下切直至切穿泥炭层的过程促进沟道两侧地下水在非降雨期不断流失,并在河道两侧形成泥炭沼泽的疏干带。该研究对若尔盖湿地修复与保护中沟道切穿泥炭层区域提出了相应的建议措施。
Peatland swamp in the Zoige Plateau has been shrinking rapidly since 1950 s,where one of the important mechanisms causing water loss in peatland is headward and lateral erosion of natural gullies. Natural gullies drain partially surface water in rainfall season and groundwater in non-rainfall season,both of which accelerate the shrinkage of the swamp. Field observations were conducted in the Zoige Peatland in summer of 2016-2017 and Visual MODFLOW groundwater model was used to study groundwater movement in local peatland and the influence of natural gullies on hydraulic gradient in peat layer near the gully. Results indicate that the movement direction of groundwater is more inclined to the gully greater than that along the terrain slope. Moreover,this trend is more pronounced after the gullies cut through the peat layer,i. e.,the hydraulic gradient in the direction perpendicular to the gully increased by about 79%. It definitely shows that the natural gullies could not only drain off surface water in rainfall season,but also facilitate the loss of groundwater on peatland on both sides of gullies during non-rainfall season. This drainage process leads to the formation of dewatering belt on both sides of gullies. This study is of great importance to the adoption of the targeted measures to protect the peatland in Zoige Plateau from cutting through by the gullies.
Peatland swamp in the Zoige Plateau has been shrinking rapidly since 1950 s,where one of the important mechanisms causing water loss in peatland is headward and lateral erosion of natural gullies. Natural gullies drain partially surface water in rainfall season and groundwater in non-rainfall season,both of which accelerate the shrinkage of the swamp. Field observations were conducted in the Zoige Peatland in summer of 2016-2017 and Visual MODFLOW groundwater model was used to study groundwater movement in local peatland and the influence of natural gullies on hydraulic gradient in peat layer near the gully. Results indicate that the movement direction of groundwater is more inclined to the gully greater than that along the terrain slope. Moreover,this trend is more pronounced after the gullies cut through the peat layer,i. e.,the hydraulic gradient in the direction perpendicular to the gully increased by about 79%. It definitely shows that the natural gullies could not only drain off surface water in rainfall season,but also facilitate the loss of groundwater on peatland on both sides of gullies during non-rainfall season. This drainage process leads to the formation of dewatering belt on both sides of gullies. This study is of great importance to the adoption of the targeted measures to protect the peatland in Zoige Plateau from cutting through by the gullies.
引文
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[2]黄咸雨,张志麒,王红梅,等.神农架大九湖泥炭湿地关键带监测进展[J].地球科学:中国地质大学学报,2017,42(6):1026-1038.[HUANGXian-yu,ZHANGZhi-qi,WANGHong-mei,et al. Overview on Critical Zone Observatory at Dajiuhu Peatland,Shennongjia[J]. Earth Science:Journal of China University of Geosciences,2017,42(6):1026-1038.]
[3]孙广友.论若尔盖高原泥炭赋存规律成矿类型及资源储量[J].自然资源学报,1992,7(4):334-346.[SUN Guang-you. A Study on the Mineral Formation Law,Classification and Reserves of the Peat in the Ruoergai Plateau[J]. Journal of Natural Resources,1992,7(4):334-346.]
[4] ZHANG Y,WANG G X,WANG Y B. Changes in Alpine Wetland Ecosystems of the Qinghai-Tibetan Plateau From 1967 to 2004[J]. Environmental Monitoring and Assessment,2011,180(1/2/3/4):189-199.
[5]王焱,刘国东,蹇依,等.郎川公路附近湿地地下水文数值模拟[J].人民长江,2008,39(2):17-19.
[6]李丽,高俊琴,雷光春,等.若尔盖不同地下水位泥炭湿地土壤有机碳和全氮分布规律[J].生态学杂志,2011,30(11):2449-2455.[LI Li,GAO Jun-qin,LEI Guang-chun,et al. Distribution Patterns of Soil Organic Carbon and Total Nirogen in Zoige Peat Land With Different Ground Water Table[J]. Chinese Journal of Ecology,2011,30(11):2449-2455.]
[7] LI M,LI L X,LIAO H S,et al. The Influence of Drainage on Wetland Degradation in Zoige Plateau[J]. Disaster Advances,2012,5(4):659-666.
[8]李志威,王兆印,张晨笛,等.若尔盖沼泽湿地的萎缩机制[J].水科学进展,2014,25(2):172-180.[LI Zhi-wei,WANG Zhao-yin,ZHANG Cheng-di,et al. A Study on the Mechanism of Wetland Degradation in Ruoergai Swamp[J]. Advances in Water Science,2014,25(2):172-180.]
[9]朱海丽,李志威,胡夏嵩,等.黄河源草甸型弯曲河流的悬臂式崩岸机制[J].水利学报,2015,46(7):836-843.[ZHU Hai-li,LI Zhi-wei,HU Xia-song,et al. Cantilever Bank Failure Mechanism of Meadow Meandering River in the Yellow River Source Region[J]. Journal of Hydraulic Engineering,2015,46(7):836-843.]
[10] KIRUBAKARAN M,JOHNNY J C,SAMSON S. MODFLO W.Based Groundwater Budgeting Using GIS:A Case Study From Tirunelveli Taluk,Tirunelveli District,Tamil Nadu,India[J].Journal of the Indian Society of Remote Sensing,2018(11):1-10.
[11] LI X,HE X,YANG G,et al. Study on Groundwater Using Visual MODFLOW in the Manas River Basin,China[J]. Water Policy,2016,18(5):1139-1154.
[12] MELIKADZE G,ZHUKOVA N,TODADZE M,et al. Numerical Modelling of Groundwater System in the East Georgia′s Lowland[J]. Journal of the Georgian Geophysical Society,2016,18:59-66.
[13] CHETHAN NL,PATIL N S. Modeling of Groundwater Heads for the Climate Change Scenarios[J]. International Research Journal of Engineering and Technology,2016,3(7):260-263.
[14]刁维杰,冯忠伦,刘希琛,等.基于Visual MODFLOW的潍坊市北部地区水资源优化配置[J].水电能源科学,2017,35(4):25-28.[DIAO Wei-jie,FENG Zhong-lun,LIU Xi-sheng,et al.Optimal Allocation of Water Resource in North of Weifang Based on Visual MODFLOW[J]. Water Resources and Power,2017,35(4):25-28.]
[15] BUJAKOWSKI F,FALKOWSKI T,WIERZBICKI G,et al. Using Hydrodynamic Modelling to Assess the Impact of the Development on Hydrogeological Conditions in a Polygenic River Valley Marginal Zone[J]. Annals of Warsaw University of Life Sciences,Land Reclamation,2014,46(1):43-55.
[16] CRUZ-FUENTES T,MAR′IA DEL C C,JAVIER H,et al. Groundwater Salinity and Hydrochemical Processes in the Volcano-Sedimentary Aquifer of La Aldea,Gran Canaria,Canary Islands,Spain[J]. Science of the Total Environment,2014,484:154-166.
[17] HARKINS N,KIRBY E,HEIMSATH A,et al. Transient Fluvial Incision in the Headwaters of the Yellow River,Northeastern Tibet,China[J]. Journal of Geophysical Research Atmospheres,2007,112(F3):3-4.
[18] CRADDOCK W H,KIRBY E,HARKINS N W,et al. Rapid Fluvial Incision Along the Yellow River During Headward Basin Integration[J]. Nature Geoscience,2010,3(3):209-213.
[19] FISHER A S,PODNIESINSKI G S,LEOPOLD D J. Effects of Drainage Ditches on Vegetation Patterns in Abandoned Agricultural Peatlands in Central New York[J]. Wetlands,1996,16(4):397-409.
[20] CHASON D B,SIEGEL D I. Hydraulic Conductivity and Related Physical Properties of Peat,Lost River Peatland,Northern Minnesota[J]. Soil Science,1986,142(2):91-99.
[21] FRASER C J D,ROULET N T,LAFLEUR M. Groundwater Flow Patterns in a Large Peatland[J]. Journal of Hydrology,2001,246(1/2/3/4):142-154.
[22] ZHENG C M,BENNETT G D. Applied Contaminant Transport Modeling[M]. 2nd ed. Hoboken,USA:John Wiley&Sons,2002:191-193.
[23] NEUZIL C E. Groundwater Flow in Low Permeability Environment[J]. Water Resources Research,1986,22(8):1163-1195.
[24] HART D J,BRADBURY K R,FEINSTEIN D. The Vertical Hydraulic Conductivity of an Aquitard at Two Spatial Scales[J].Ground Water,2006,44(2):201-211.
[25] RONKANEN AK,KLOVE B. Hydraulics and Flow Modelling of Water Treatment Wetlands Constructed on Peatlands in Northern Finland[J]. Water Research,2008,42(14):3826-3836.
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