2000−2020年藏北高寒草地水源涵养功能变化及影响因素分析

Variation of Water Conservation Function and Its Influencing Factors of Alpine Grasslands in Northern Tibet from 2000 to 2020

藏北地区平均海拔4500 m以上,被称为“世界屋脊上的屋脊”,同时也是青藏高原生态安全屏障的主体,但在全球气候变化和人类活动的双重影响下,藏北高寒草地生态系统变化明显,部分区域出现退化趋势。2009年我国开始实施了《西藏生态安全屏障保护与建设工程》(以下简称工程),旨在恢复和保育高原的生态系统及其服务功能。而水源涵养是藏北高寒草地生态系统最为重要的服务功能之一,工程实施以来,藏北草地的水源涵养功能如何变化、生态工程的效益如何?本文基于InVEST模型评估了2000–2020年生态工程前后藏北草地水源涵养功能的变化,量化了气候变化和人类活动在其中的贡献率。结果表明:(1)藏北各类型草地的水源涵养能力虽然差异较大,但工程实施后水源涵养的功能均出现了明显的变化,产水量比工程实施前增加10.07%,水源涵养服务上升8.86%。其中高寒草甸区的水源涵养变化速率增长最大,由工程前的–1.84 mm yr^(–1)转变为工程后的2.24 mm yr^(–1);其次是高寒荒漠草原和高寒草原,在工程的影响下水源涵养功能下降的速率明显减缓。(2)气候变化仍是藏北草地水源涵养功能的主要影响因素,但生态工程对藏北各类高寒草地水源涵养功能变化的作用明显,在高寒草甸、高寒草原、高寒荒漠草原区分别达到了13.99%、8.75%、3.71%,有效地促进了藏北草地的水源涵养功能的改善。

With an average elevation of more than 4500 m,northern Tibet,known as the“roof of the world roof”,serves as the main body of the Qinghai-Tibetan Plateau’s ecological security barrier.However,the alpine grassland ecosystem in northern Tibet has suffered considerable alterations as a result of both climate change and overgrazing,and there is a degradation trend in some regions.In 2009,one ecological engineering,the Protection and Construction Project of Ecological Security Barrier in Tibet(hereafter referred to as the“Project”)was implemented to preserve the alpine ecosystem and restore service functions in the plateau.Water conservation is one of the most important service functions in alpine grassland ecosystem in northern Tibet,where is one part of the Asian Water Tower.To clarify the specific ecological benefits of the Project,this paper utilized the InVEST model to evaluate the variation trend of the water conservation function of alpine grasslands in northern Tibet before and after the implementation of the Project from 2000 to 2020,and contribution rate of climate change and the Project was also quantified.Results showed that:(1)Although the water conservation capacity of different grassland types in northern Tibet were varied,their water conservation function all altered dramatically after implementation of the Project.Specifically,the water yield has increased by 10.07%,and the water source supply service has increased by 8.86%.Among these grasslands,the alpine meadow had the highest increasing rate,water conservation capacity increased from–1.84 mm yr^(–1)to 2.24 mm yr^(–1)Followed by the alpine desert steppe and the alpine steppe,the rate of water conservation function were decreased significantly due to the Project.(2)Although climate is still the primary factor affecting the water conservation function of alpine grasslands in northern Tibet,the Project has effectively promoted the local water conservation function,with contribution rates of 13.99%,8.75%,and 3.71%in the alpine meadow,alpine steppe and alpine desert steppe regions respectively.