| The Jilantai Salt Lake is an important lake salt production base in China,and located at the southwest edge of Ulan Buh Desert.Sand calamity in Jilantai Salt seriously restricted the exploitation and salt quality of salt lake.It was urgent to prevent wind and fix sand and protect salt lake resources.In this thesis,we take different protective function zones of the salt lake protection system in Jilantai(fixing shifting-sand zone,fencing dune for grass recovery zone,preventing wind and stopping sand zone and salt lake protection forest zone)as research objects.Through a combination of data collection,field positioning observation and indoor experiments,we analyzed spatial distribution characteristics of grain size composition and soil nutrients in different protection function areas of the salt lake protection system,and revealed the main factors affecting soil nutrients in the salt lake protection system.The distribution and development of undergrowth herbaceous vegetation in different protection function areas were studied;Changes in wind speed,sand transport,dustfall and surface erosion of different protection function areas of the salt lake protection system were measured,and the benefits of wind-preventing and sand-resisting and sediment prevention in different protection functional areas of the salt lake protection system were revealed;Taking clipping Hedysarum scoparium as an example,this thesis revealed the effect of branch mulch on the regeneration and rejuvenation of Hedysarum scoparium.The results shows that:(1)All protection function areas of salt lake protection system have low overall soil nutrient content.Soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),available nitrogen(AN)and available phosphorus(AP)ranged from 0.58 to 1.09 g/kg,0.04 to 0.34 g/kg,0.20 to 0.25 g/kg and 4.12 to 6.71 mg/kg and 0.48 to 6.71 mg/kg,respectively.The construction of salt lake protection system has a positive effect on soil nutrients.The salt lake protection system gradually increased from outside to inside,and the soil nutrient restoration index ranged from 7.83% to 480.77%.Among them,Haloxylon ammodendron had the greatest effect on soil nutrient improvement.The soil C/N ratios,C/P ratios and N/P ratios of the salt lake protection system ranged from 3.15 to 23.24,2.84 to 4.63 and 0.20 to 1.37,respectively.The degree of deficiency of soil carbon,nitrogen and phosphorus elements in the fixing shifting-sand zone and fencing dune for grass recovery zone was: N>C>P.The deficiencies of soil carbon,nitrogen and phosphorus elements in preventing wind and stopping sand zone and salt lake protection forest zone was: C>N>P.(2)The herbaceous vegetation of the Jilantai salt lake protection system was single in number and poor in species composition with the characteristics of simple species composition and low diversity.6 species,18 genera and 18 families were found in the region,including 6 Chenopodiaceae,4 Poaceae,3 Asteraceae and 3 Leguminosae accounting for more than 88.89% of the overall plant species.The Shannon-Wiener diversity index,Pielou evenness index,Simpson dominance index and Margarlef richness index of understory herbaceous vegetation in the salt lake protection system ranged from0.79~1.77,0.90~0.96,0.53~0.80 and 0.62~1.75,respectively.The construction of salt lake protection system is not conducive to the growth of herbaceous plants.Redundancy analysis(RDA analysis)showed that soil moisture(SM)and SOC were the main factors affecting the diversity of undergrowth herbs.(3)The surface aerodynamic roughness and frictional wind speed were significantly increased in all functional areas of the salt lake protection system compared to moving dune.Among them,the aerodynamic roughness increased by 4.3,15.0,26.0 and 17.0times,and the frictional wind speed increased by 1.6,2.4,5.9 and 7.3 times in each protection function area,respectively.The existence of surface rough elements in each functional area obviously changed the distribution of near-surface airflow,reduced the wind speed in the adjoining layer,weakened the erosion capacity of airflow,and then improved the wind erosion resistance of the surface.In the horizontal and vertical directions,windbreak effect of each functional area tended to increase at different wind speeds,but the difference in the height of the surface cover led to a large difference in windbreak effect of each surface height at different wind speeds.(4)The order of sediment transport in each protective function zone was: active longitudinal dune>fixing shifting-sand zone>fencing dune for grass recovery zone>salt lake protection forest zone>preventing wind and stopping sand zone.Horizontal sediment transport rate decreased as an exponent relationship and sand blocking rate gradually increased from fixing shifting-sand zone to salt lake protection forest zone.The sand retention rate gradually increased overall with the increase of wind speed.The dust-falling of Jilantai Salt Lake protection system was mainly composed of very fine sand and fine sand.The dust-falling amount was mainly concentrated in spring and winter,accounting for 77.52%~87.04% of the annual dustfall.Average wind speed,blowing dust days,strong wind days and sandstorm days were the main meteorological factors affecting the amount of dust-falling amount.The monthly variation of surface erosion and deposition showed obvious fluctuation in different protective function zone of Jilantai salt lake protection system.Fixing shifting-sand zone and fencing dune for grass recovery zone were mainly wind erosion.However,preventing wind and stopping sand zone and salt lake protection forest zone were mainly wind deposition.The surface sedimentary materials tended to be refined from outside to inside.(5)With different optimization measures,different protection function area of salt lake protection system can effectively improve its ecological benefits.According to breakage degree of sand barriers in different slopes,mechanical sand barriers of different materials and specifications are reasonably configured in fixing shifting-sand zone,and combined with planting in the barrier grid can maintain the continuous function of sand barriers.Stubble nourishment of Nitraria tangutorum shrubs in fencing dune for grass recovery zone can effectively improve the growth,biomass accumulation and soil water content of Nitraria tangutorum nekbhas.In both preventing wind and stopping sand zone and salt lake protection forest zone,clipping Hedysarum scoparium is used as an optimization measure,which can increase vegetation coverage,vegetation density,vegetation height,above-ground biomass and vegetation diversity under Hedysarum scoparium forests,improve soil physical and chemical properties,and facilitate the self-renewal of Hedysarum scoparium forests.The capacity of wind and sand control gradually increased with the addition of clipping Hedysarum scoparium. |
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