古尔班通古特沙漠西部地下水位和水质变化对植被的影响

通过对比分析古尔班通古特沙漠西部3a地下水位和水质的变化特点,研究了地下水位和水质变化对地表土壤理化性质、植物多样性、及建群种梭梭种群生长与更新的影响。发现地下水位和土壤理化性质空间变异较大,最浅地下水位为3.3 m,最深可达24.2 m,主要集中在6-8 m;土壤电导率、pH值、Cl^-和SO₄^2-均在表层0-40 cm含量较高,变异系数随土层深度的增加而减小。在时间上地下水位受准噶尔盆地上游农田用水的影响,水位呈季节性波动。一年中最高水位出现在4月,最低水位在7月。玛纳斯河向下游输水对提高盆地地下水位具有明显作用,地下水位平均可升高4.3 cm,地下水矿化度平均增幅1 g/L。地下水位对退化区物种多样性影响不大,但对梭梭生长产生显著影响。梭梭生长的适宜地下水位为5-8 m,且地下水矿化度小于4 g/L。地下水位大于8 m导致梭梭种群衰退,而地下水位小于4 m时,地下水矿化度影响土壤表层积盐,进而显著地降低物种多样性,阻碍梭梭幼苗更新,导致梭梭种群衰败。总结认为准噶尔盆地上游的玛纳斯河断流和农业灌溉对古尔班通古特沙漠西部平原地区的地下水位和水质产生显著影响,梭梭退化与地下水位变化显著相关,必须引起高度重视。

Variations in groundwater levels and quality and their effects on vegetation in the western Grurbantonggut Desert

Groundwater is a key component of the water cycle in arid ecosystems due to low precipitation, high surface runoff and high evaporative demand. It has a direct influence on the growth and development of natural vegetation, species diversity, and ecosystem metabolism. This study reports on the variation in groundwater levels and quality in the western region of the Grurbantonggut Desert over three consecutive years. We investigated how groundwater level and quality affect physical and chemical properties of soil, species diversity, and the growth and regeneration of Haloxylon ammodendron. We established 20 inspection wells for measuring groundwater level over a period of three consecutive years. These inspection wells were set up at intervals of 7km to 10km from west to east in longitude and north to south in latitude, which according to the situation of the degenerate and distribution of Haloxylon ammodendron population in the study area. The study area contain habitat which is plain and small and big sand-dunes. The results show that groundwater levels varies widely in this area, ranging from 3.3m to 24.2m, averaging 6m to 8m. The soil physical-chemical factors also vary greatly across this area. Soil EC, pH, Cl^- and SO₄^2- have higher values at depths of 0cm to 40cm; their coefficients of variation decrease at greater depths. The groundwater level exhibits seasonal variation, influenced by upstream irrigation. The highest and lowest groundwater levels appear in April and July, respectively. The Manas River plays an important role in recharging groundwater in the study area, which of course varies between years. Approximately 75% of the groundwater level found in the inspection wells rises in 2010 compared with last year, which rises seasonally by 4.3cm on average, while the mineralization increases to 1g/L on average. The groundwater level has a weak effect on species diversity in the degraded area, while it has a significant impact on the growth of Haloxylon ammodendron. We find that the suitable groundwater level for growing Haloxylon ammodendron is 5m to 8m and the optimal mineralization level is less than 4g/L. Haloxylon ammodendron populations decline when groundwater level is more than 8m. When the groundwater level is less than 4m, groundwater mineralization causes salt deposition on the soil surface. This reduces the level of species diversity significantly and blocks the regeneration of Haloxylon ammodendron. This in turn leads to declines in the Haloxylon ammodendron population. In summary, the depletion of the Manas River related to agricultural irrigation influences the groundwater levels and the quality of the ecosystem in the western Grurbantonggut Desert. The decline in the Haloxylon ammodendron population is significantly correlated with groundwater levels. This should be considered in future natural resource conservation planning for this area.