基于变异系数的植被NPP人为影响定量研究——以石羊河流域为例

人类活动是NPP变化的重要影响因子,定量计算NPP人为影响值具有较重要的意义。提出基于变异系数法的NPP人为影响模型,对其基本概念、理论基础、计算流程等进行了阐述,并以石羊河流域为研究区,分析该流域NPP人为影响分布规律。研究结果表明:(1)该模型基于一种间接计算的思想回避了人为作用的复杂过程,模型理论科学,以变异系数为参数,所需参数少,技术可行,计算结果为NPP值,易于定量评价。(2)2000—2010年期间,石羊河流域人类活动对植被NPP的影响广泛而严重,年均影响值大于40g C m~(-2)a~(-1)的面积占96.21%,影响程度严重以上占26.94%。NPP人为正负影响均较大,正影响年均为1.63×106g C m~(-2)a~(-1),负影响年均为1.21×106g C m~(-2)a~(-1),年均净增加4.20×105g C m~(-2)a~(-1);正向平均影响强度为136.84 g C m~(-2)a~(-1),负向平均影响强度为100.32 g C m~(-2)a~(-1),全流域表现为正影响。(3)凉州区是人为影响最为剧烈的地区,表现为强烈正影响;其次是天祝县,为强烈负影响;接下来是民勤县,表现为正影响;其它县区依次是永昌、古浪、肃南和金昌。(4)2000—2010期间,NPP人为影响值变化较大,人为活动减弱面积占53.90%,增加占46.10%;影响值正向减弱8.12×105g C m~(-2)a~(-1),负向减弱8.07×105g C m~(-2)a~(-1),正向增强8.02×105g C m~(-2)a~(-1),负向增强3.94×105g C m~(-2)a~(-1),人为活动影响净减少4.25×105g C m~(-2)a~(-1),人为作用总体呈减弱趋势。

The impact of human activities on net primary productivity based on the coefficient of variation: A case study of the Shiyang River Basin

Human activities can heavily influence changes in net primary productivity (NPP), and for this reason, the quantitative calculation of NPP as influenced by humans (NPP_H) has a vital significance. In this paper, a model of human impact on NPP is proposed based on the coefficient of variation. The basic concept, theoretical foundation, and calculation are discussed, and the distribution and variation of NPP_H in the Shiyang River Basin are analyzed. The following conclusions were made. (1) The model is based on the indirect method, which avoids the complexities of human activity In addition, the NPP_H model has other advantages, including its scientificity in theory, fewer input parameters as it uses only the coefficient of variation, feasibility and easy obtainability technology, and a straightforward quantitative evaluation of human activity on NPP. (2) The effect of human activity on NPP was widespread and severe in the Shiyang River Basin during 2000-2010. The area with an annual average NPP_H value greater than 40 gC m^-2a^-1 was 96.21%, and the area with a degree of human impact greater than severe was 20%. There were two main features when the spatial distribution of the influence of human activities on NPP was considered. The first was the intense positive influence of human activity on three oases (Minqin, Wuwei, and Jinchang), where there is cultivated land, and the second is the strong negative influence on the junction of Sunan, Tianzhu, Gulang, and Yongchang, where the vegetation consists mainly of grassland and the predominant human-related activity is grazing. Thus, the human impact on NPP was both positive and negative, and significant for both. The average positive annual value as affected by humans was 1.63×10⁶ gC m^-2a^-1, and the negative value was 1.21×10⁶ gC m^-2a^-1, producing a net value of 4.20×10⁵ gC m^-2a^-1. The positive effect averaged 136.84 gC m^-2a^-1, and the corresponding negative effect was 100.32 gC m^-2a^-1; therefore, overall, the Shiyang River Basin was positively influenced by humans. The degree of human impact on different areas varied from slight to general, serious, and severe, with the percentages gradually decreasing from 45.96% to 27.11%, 18.58%, and 8.38%, respectively. The areas of positive and negative influence were roughly equal in degree, but the positive influence was slightly more than negative in the severe and general degree categories, and the negative influence was slightly more than the positive in the slight and serious degree areas. (3) Ganzhou county was the area most intensely and positively influenced by human activity. In contrast, Tianzhu county showed a strong negative influence. Minqin county showed a positive influence, which positive effect of the total in second place and effect of average in three place and negative effect all in second about total and average. The other areas influenced by human activity were Yongchang, Gulang, Sunan and Jinchang. (4) The NPP_H varied greatly in this period and showed as decreasing trend. In some regions, human influence has decreased (53.9%), while in other areas human activity has enhanced (46.1%). The positive effect was weakened by 8.12×10⁵ gC m^-2a^-1, the negative effect was weakened by 8.07×10⁵gC m^-2a^-1, and the positive effect was enhanced by 8.02×10⁵gC m^-2a^-1, and the negative effect was enhanced by 3.94×10⁵gC m^-2a^-1, giving a net reduction of 4.25×10⁵gC m^-2a^-1, indicating that overall, human activity showed a decreasing trend.