1980-2005年三江源区水源涵养生态系统服务功能评估分析

随着科学技术的持续发展和世界经济的快速增长，人类对自然的干预越来越严重，对周围的生态环境造成了巨大的影响，生态经济学应运而生不断发展，生态系统服务功能能够反映生态系统和自然资本的价值，为国家、地区的决策者提供一个背景值，同时对建设项目的环境影响评价提供理论依据.基于GIS的生态系统服务功能价值评估与权衡模型(InVEST)可用于定量评估生态系统服务功能及价值，在国外已经有较好的应用成果.水源涵养是生态系统的重要服务功能之一，也是生态系统服务功能间接使用价值的重要组成部分.本文以青海省三江源区为研究区域，首先对InVEST模型中的水源涵养模块及其参数、指标等进行了一系列修改和校验，在此基础上对三江源区的水源涵养生态系统服务功能进行了评估，对1980-2005年期间的水源涵养量变化做了分析，并提出建立生态补偿机制的相关建议，主要结论如下:(1)三江源区平均水源涵养量的变化从1980年代的222.6mm下降到95年的174.7mm，到2000年增加到194.3mm，2000年至2005年时间段内，三江源区平均水源涵养量持续增加，达到203.0mm.(2)近30年三江源区水源涵养量整体呈下降趋势，1980-1995年期间，治多县中部、曲麻莱县北部的水源涵养量呈增加趋势，而曲麻莱县东部和南部、称多县西南部呈减少趋势，长江流域水源涵养量下降趋势较明显;1995至2000年间，曲麻莱县、称多县、囊谦县水源涵养量增加，其中曲麻莱县增加较明显，其他地区的水源涵养量均有不同程度的减少，黄河流域水源涵养量下降明显;2000年之后，三江源东部地区(称多县以东)水源涵养量有不同程度的增加，其中，泽库县、河南蒙古族自治县、久治县、班玛县增加最明显，而长江流域和澜沧江流域水源涵养量出现下降趋势.(3)气候变化与人类活动可能是导致三江源区生态系统水源涵养功能时空变化的主要原因.近50年来(1961年以来)三江源地区地表气温明显上升.黄河源区增暖幅度明显高于长江源区和澜沧江源区;三江源地区年降水量呈减少趋势，冰川萎缩、冻土消融是全球气候变暖在这一特定区域响应的具体体现，1999年代全球和三江源地区气候变暖的强度增大，大风日数增多、地表蒸发加大、干旱指数上升、地表水分损失加剧，冰川退缩和冻土消融的速度也相应加快.夏季温度升高、降水减少的暖干化趋势，90年代以来不但没有减弱，反而有所加剧，并逐步扩展到春、秋季节，这种多数季节气候暖干化的响应背景是该地区周边冰川退缩、冻土退化、湖泊萎缩、草场退化、土地荒漠化、水土流失、生物多样性遭受破坏的最直接原因之一，人类活动则可直接导致地表植被的变化进而影响下垫面状况.(4)生态补偿机制对于生态保护及人与自然的和谐具有重要意义，是一种以生态保护成本及服务价值为依据，通过市场或行政手段调整各方利益的环境经济政策.三江源区作为我国重要的生态功能区，孕育和滋养了中华民族千万年的大江大河，年均产水量611亿m3，是全国海拔最高、类型较齐全、影响范围最广的水源涵养生态功能区，维系着中国乃至全球的生态系统安全，因此，保护三江源区生态环境，建立区域生态补偿机制对于保护中华民族可持续发展十分重要.本文将介绍生态补偿机制的理论基础和实践依据，并对建立三江源区水源涵养生态补偿机制的实践进行探索.

Against the backdrop of continuous advancements in science and technology and rapid global economic growth, human intervention in nature has intensified, exerting profound impacts on the surrounding ecological environment. As a result, ecological economics emerged and has been continuously developing. Ecosystem service functions can reflect the value of ecosystems and natural capital, providing baseline data for policymakers at national and regional levels, while also offering theoretical support for environmental impact assessments of construction projects. The InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model based on Geographic Information System (GIS) can be used to quantitatively evaluate ecosystem service functions and their values, and has achieved favorable application outcomes overseas. Water conservation is one of the core ecosystem service functions, and also a key component of the indirect use value of ecosystem services. Taking the Three-River Source Region in Qinghai Province as the study area, this paper first conducted a series of modifications and calibrations to the water conservation module, its parameters and indicators within the InVEST model. Based on this, it evaluated the water conservation ecosystem service functions of the Three-River Source Region, analyzed the changes in water conservation volume during the period 1980–2005, and put forward relevant recommendations for establishing an ecological compensation mechanism. The main conclusions are as follows:
(1) The average water conservation volume in the Three-River Source Region decreased from 222.6 mm in the 1980s to 174.7 mm in 1995, then rose to 194.3 mm in 2000. During the period from 2000 to 2005, the average water conservation volume continued to increase, reaching 203.0 mm.
(2) Over the past 30 years, the overall water conservation volume in the Three-River Source Region has shown a downward trend. During 1980–1995, water conservation volumes increased in central Zhiduo County and northern Qumalai County, but decreased in eastern and southern Qumalai County and southwestern Chengduo County; the water conservation volume in the Yangtze River Basin exhibited a notable downward trend. From 1995 to 2000, water conservation volumes increased in Qumalai County, Chengduo County and Nangqên County, with a particularly significant increase in Qumalai County, while other regions saw varying degrees of reduction, and the water conservation volume in the Yellow River Basin decreased significantly. After 2000, water conservation volumes in the eastern part of the Three-River Source Region (east of Chengduo County) increased to varying degrees, with the most prominent increases in Zêkog County, Henan Mongolian Autonomous County, Jiuzhi County and Baima County, while the water conservation volumes in the Yangtze River Basin and Lancang River Basin showed downward trends.
(3) Climate change and human activities are likely the main drivers of the spatiotemporal variations in the water conservation function of the ecosystem in the Three-River Source Region. Over the past 50 years (since 1961), the surface air temperature in the Three-River Source Region has risen significantly. The warming magnitude in the Yellow River Source Region is noticeably higher than that in the Yangtze River and Lancang River Source Regions. The annual precipitation in the Three-River Source Region shows a decreasing trend. Glacier retreat and permafrost thaw are specific manifestations of the regional response to global warming. In the 1990s, the intensity of global warming and warming in the Three-River Source Region increased, with more gale days, enhanced surface evaporation, rising drought indices, aggravated surface water loss, and accelerated glacier retreat and permafrost thaw. The warm-drying trend characterized by rising summer temperatures and decreasing precipitation has not weakened but intensified since the 1990s, and has gradually spread to spring and autumn. This background of warm-drying climate responses in most seasons is one of the most direct causes of glacier retreat, permafrost degradation, lake shrinkage, grassland degradation, land desertification, soil erosion and biodiversity loss in and around the region. Human activities can directly alter surface vegetation, thereby affecting the underlying surface conditions.
(4) The ecological compensation mechanism, an environmental and economic policy that adjusts the interests of all parties through market or administrative means based on ecological protection costs and service values, is of great significance for ecological conservation and the harmony between humans and nature. As an important ecological function zone in China, the Three-River Source Region has nurtured the great rivers that have sustained the Chinese nation for thousands of years, with an annual water yield of 61.1 billion m³. It is the water conservation ecological function zone with the highest elevation, most complete types and the widest impact scope in China, and maintains ecological security in China and even the world. Therefore, protecting the ecological environment of the Three-River Source Region and establishing a regional ecological compensation mechanism are critical for the sustainable development of the Chinese nation. This paper will introduce the theoretical basis and practical foundation of the ecological compensation mechanism, and explore the practice of establishing an ecological compensation mechanism for water conservation in the Three-River Source Region.