耕地质量监测中合理样本量配置及不确定性分析——以陕西省宝鸡市为例

耕地质量监测样本量的优化配置对降低成本,实现可持续土地资源监测与利用有重要指导价值。以陕西省宝鸡市为例,采用2018年耕地质量监测数据,运用传统统计学和地统计学方法,探讨耕地质量监测中土壤监测指标的合理样本量及不确定性。研究表明：样本变异性大小与样本量的关系并不是绝对的。样本代表性评价方法和地统计学方法较Cochran方法能有效降低样本的不确定性;样本代表性评价法适用性更广,但研究结果缺乏稳定性;地统计学方法的适用性存在局限性,可降低中等变异性指标的不确定性,但对低、高变异性指标适用性较低。中等变异性指标宜采用地统计学方法确定合理样本量;低、高变异性指标宜采用代表性评价方法确定合理样本量。     

Assessment of Ground Water Vulnerability and its Application to the Development of Protection Strategy for the Water Supply Aquifer in Owerri, Southeastern Nigeria

Pollution vulnerability of theOwerri regional water supply aquifer wasevaluated as a basis for developing appropriateprotection strategy for the groundwaterresource. The assessment was accomplished usingLegrand, GOD, Siga and DRASTIC models.Techniques of the models generally involvedparameters rating and point count systems, whichare based on the evaluation of various parameterin relation to their capacity for enhancing orattenuating contaminants in the groundwatersystem. Field and laboratory evaluations of theparameters indicate that the Owerri areagenerally occupies a nearly, flat topographywith a relatively high groundwater recharge. Thearea is underlain by predominantly sandyfacies in the Northern area which grades intogravelly sequences towards the southwest. TheSoutheastern area is distinguished by thickclayey facies that thin westwards towards theOwerri metropolis. Effective hydraulicconductivity (Kz) in the downward directionranges from 1.44 × 10^-3 to 5.6 × 10^-9 m s^-1; with the upper limits reflecting coarsesands and gravelly units. The amount of clay andclay-size particles in the sandy and gravellyunits is negligible, suggesting that thesorptive capacity of the units is low. Depth towater table decreases southwards while hydraulichead gradients vary between 0.09 and 0.22.Groundwater occurs in unconfined conditions inmost places except in the southeastern zonewhere it is semi-confined due to the presence ofa clayey unit. The groundwater vulnerabilitymap developed on the basis of the models andseveral other thematic maps shows that theOwerri metropolis and the southwest area ofOwerri have high vulnerability, indicatinggroundwater pollution. The existing wastedisposal sites in these sub-areas should beabandoned and rehabilitated to forstall furtherpollution of the groundwater system. Areas tothe North and Southeast of Owerri have moderateand low vulnerabilities, respectively,indicating the relatively lower sensitivity ofthe groundwater system in the sub-areas tocontamination. The lower sensitivity couldfurther be matched with properly engineeredsanitary landfills in the event of choice ofsites, as an additional protective strategy forthe groundwater system.