南京玄武湖菹草石芽空间变异及其原因探讨

SPATIAL VARIATION OF POTAMOGETON CRISPUS TURION AND ITS CAUSES OF FORMATION IN XUANWU LAKE OF NANJING

  • 摘要: 为了解玄武湖菹草石芽的空间分布状况,用网格法布设52个石芽采样点,采样点以GPS定位,在每个点采集表层底泥15cm深度以上石芽,每个点采集4个样,然后求和代表该点石芽密度。运用ArcGIS的geostatistics组件分析了玄武湖菹草石芽数量的空间变异特征及其形成原因。结果表明:①石芽数量的半方差函数可拟合为球状模型,石芽在空间呈聚集分布;②石芽在各湖中具有非常明显的空间异质性,东北湖石芽密度最大(均值30.5颗/m2),西南湖密度最小(均值10颗/m2);从石芽密度的分维数来看石芽密度的空间异质性,全方向<椭圆半长轴方向<椭圆半短轴方向上;③割草干扰、种群数量、水深、水流、立地条件的空间异质性造成石芽密度的空间异质性;④石芽数量的空间自相关尺度,远远大于菹草石芽能够自行散落的距离,说明流水的带动起了很重要的扩散作用。

     

    Abstract: In order to investigate the spatial distribution of the Potamogeton crispus turion in Xuanwu Lake, a total of 52 samples were collected by the grid method. In each sampling site positioned by GPS, four samples of P. crispus turion from 15cm depth under surface sediment were collected, summing the data to represent turion density of the site. MSpatial variation of P. crispus turion density in the Lake was studied by using the geostatistical component of ArcGIS. Compared with traditional statistical methods, the geostatistic method took directivity, distance and location of sampling points into account. Semivariogram is the specific theory of the method, it can be used to research the spatial correlation and the spatial pattern by determining differences of regional variable among equidistant sampling sites. The survey data converted by Log function were close to nomal distribution and could be discussed by semivariogram. Theortical model and curve graph of regional variable were derived respectively after calculating semivariogram of all possible distance interval, and spatial variation patten about regional variable could be analyzed quantitatively by model parameters such as nugget, sill, range, fractal dimension etc.. Furthmore, the spatial variation map of P. crispus turion was drawn by the method of Kriging interpolation. The results showed: ① The semivariogram of P. crispus turion density fitted spherical model and exhibited an intense special aggregation. ② Spatial heterogeneity of Potamogeton crispus turion density existed obviously, that is, an average density of P. crispus turion in the North-east Lake and the North-west was 30.5 and 10 ind./m2 respectively; Omnidirectional, elliptic semi-major axis and elliptic semi-minor axis fractal dimension decreased; ③ Mowing and differences of population size, water depth, substrate leaded to spatial variability of the density; ④ The scale size of spatial auto correlation of the density was bigger than distance of the tuition fallout itself, which showed flowing water played an important role in the turion diffusion.

     

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