Abstract
There is currently a lack of evidence surrounding changes in the health
of riparian zones under different land-use patterns within
mega-reservoirs and around dams. Scientific evidence for the
quantitative effects of stress indicators is vague and varies
significantly among reservoirs and dams worldwide. In this study, we
used a field-based approach to evaluate riparian health
changes—influenced by pressure indicators—across 274 transects from
three land-use areas (rural, rural–urban transitional, and urban) in
the Three Gorges Dam Reservoir (TGDR) in China during 2019. Multivariate
statistical techniques were applied to test for riparian zone changes
under these variant land-use patterns. Our results showed that 13
pressure indicators significantly influenced 27 health indicators
(including parameters for habitat, plant cover, regeneration, erosion,
and exotics) of the riparian zones from the three land-use areas
differently. Our results also showed that parameters for plant cover,
erosion, and exotics were major contributors within the selected
riparian health indicators, whereas land-use designs, farming systems,
and pollutant activity variables were the pressure indicators with the
strongest impact. Pearson correlation (with r ranging from -0.731
to 0.989) showed that urban transects exhibited the strongest
comparative interaction, whereas rural–urban transitional transects
formed the weakest association. Furthermore, the agglomerative
hierarchical cluster analysis revealed similarities between rural and
rural–urban transitional sites while confirming substantial
dissimilarity in urban locations. These comprehensive and relevant
results provide essential information for reservoir administrators to
implement functional changes suited to TGDR land-use scenarios.
Keywords: land-use patterns, rapid appraisal, stress
indicators, quantitative assessment, riparian health condition, Three
Gorges Dam Reservoir
1. Introduction
Human activities have caused substantial disorder in reservoir riparian
zones across several countries (Arif et al., 2021; He et al., 2020),
such as deterioration caused by urbanization and other industrial
development (Belete et al., 2020; Bombino et al., 2019). Riparian zones
ensure preliminary reservoir safety and, ultimately, naturally improve
water quality on a large scale (Mello et al., 2018; Shahariar et al.
2021). Reservoirs and lakes are essential water sources that promote
human welfare, production, and life-cycle conservation, and they provide
90% of the biosphere’s freshwater (Dai et al., 2017). Reservoir
riparian zones are biodiversity hotspots that form some of the world’s
most important natural ecological landscapes (Tape et al., 2016; Yu et
al., 2016). However, these buffer zones are also among the most
sensitive and non-recoverable natural ecosystems. Despite the increasing
positive global effect of reservoirs, their riparian zones are changing
and deteriorating owing to variations in land-use patterns (Dempsey et
al., 2017; Weldegebriel et al. 2021). The impacts of land-use patterns
on riparian health are complex (Castillo et al., 2012), and there is an
urgent need to understand the relationship between land-use variation
and the condition of riparian zones in reservoirs (Mello et al., 2018;
Yu et al., 2016). Research on this topic is a prerequisite for managing
large dams; it would produce vital information to help determine the
potential impacts of land-use changes on the riparian zones of large
reservoirs such as the Three Gorges Dam Reservoir (TGDR).
Due to the demand for urban and industrial land use, natural land
surfaces are repeatedly converted to artificial land surfaces,
consequently weakening marginal areas and causing increased heavy-metal
loads and low water quality (Woźniak et al., 2022; Yu et al., 2016).
These changes directly modify the land’s physical features and alter
riparian ecosystems along with their associated biodiversity, instream
habitats, and water characteristics (Bombino et al., 2019;
Puntenney-Desmond et al., 2020; Tape et al., 2016). Land use with a
higher level of human activity, including industrial, commercial,
residential, and transport activities, tends to permanently impact the
riparian zone (Bombino et al., 2008; Catford et al., 2013; Galia et al.,
2016). In earlier quantitative studies, negative correlations were found
between artificial land use and riparian ecosystems (Rivaes et al.,
2015; Shieh et al., 2007). However, the relationships between riparian
health conditions and pressure activities, such as agricultural cropping
and the implementation of farming systems, are more complicated.
Previous studies have indicated that land-use changes and extensive
environmentally unfriendly events might influence the vegetation in
buffer zones, thereby significantly affecting riparian health and
rapidly altering the area’s physical features (Castillo et al., 2012;
Sowińska-Świerkosz et al., 2014; Tao et al., 2020). Multipurpose studies
have been conducted on riparian zones in various parts of China, as well
as worldwide, and their impacts were assessed under different land-use
scenarios (Yu et al., 2016; Zheng et al., 2021a). However, the
literature is limited in terms of studies investigating the riparian
zone response against pressure indicators from variant land-use patterns
in extra-large reservoirs and around mega-dams such as the TGDR.
Therefore, there is an urgent need to examine how riparian zones react
under different land uses to ensure the conservation and sustainable
management of these ecological landscapes.
However, land-use effects may vary in buffer zones depending on their
particular use (Ferreira et al., 2005). Agricultural activities
significantly affect rural sections, while concrete structures impact
urban areas (Zheng et al., 2021b; Petts & Gurnell, 2005). Results from
quantitative studies that compared correlations between near- and
far-field developments showed a higher correlation in the near-field
events, confirming that pressure impact was progressive within these
regions, owing to their limited width (Johansen et al., 2007).
Therefore, there is a need to understand the relationship between land
use and riparian health variables on different scales. Such an
understanding would be critical to the logical establishment of the
whole riparian catchment zone and support the monitoring process.
Similarly, watershed protection strategies are mainly subject to the
land-use patterns and management practices of individual regions
(Nilsson & Svedmark, 2002). The demand for effective policies in China
is at present higher than in the 1950s. The increasing population
incentivizes planners to introduce substantial developments in the
agricultural sector to meet the public’s needs, which is the principal
factor that resulted in the status change of water bodies. The area
reduction ratio is particularly high for these water bodies, increasing
from 135 to 8,700 km2 from the 1970s to 2016 (Dai et
al., 2017). The Chinese government is continuously implementing
strategies to conserve water resources at the national level and is
building new dams to ensure the optimal use of water sources. Due to the
long history of human settlement in the area, the rivers in southwest
China are among the most threatened ecosystems (Yuan et al., 2021), and
their riparian zones are susceptible to prolonged submergence (Sarneel
et al., 2019). Since big reservoirs can hold water for an extended
period, riparian ecosystems and biodiversity can quickly deteriorate in
reservoir regions (Zheng et al., 2021a; Wang et al., 2016; Yang et al.,
2014). Compared with other rivers, the Yangtze River—the primary
source of the TGDR—is extremely fragile. A previous report highlighted
major pressures the river faced and described it as the world’s most
polluted waterway (Arif et al., 2021). These environmental and physical
variations are the consequences of human disturbance that have altered
the Yangtze River’s land-use pattern.
This study focuses on various water sources flowing into the TGDR, the
largest deep-water reservoir in China and the primary freshwater source
of southwest China (Chen et al., 2021; He et al., 2021). The riparian
zones of the TGDR are very vulnerable owing to their geomorphology and
specific geographic locations, which are particularly important with
regards to their ecological and environmental role (Sang et al., 2019).
Once the river ecosystem is damaged, it is challenging to restore it to
its original condition (Ding et al., 2021). Riparian health conditions
in the TGDR are declining, and the problem has intensified because of
recent land-use variations. However, the pressure effects cannot be
fundamentally determined in the reservoir basin merely via the point
source (Dempsey et al., 2017). Statistical models and theoretical
studies are needed, as these generate technical information to combat
the pressure effects of different land uses in various riparian zones of
mega-dams. This study’s primary objective was to investigate changes
within the riparian zones of reservoirs and dams under the influence of
stress indicators from different land uses (i.e., rural, rural–urban
transitional, and urban). More precisely, we examined the variation
between riparian health and pressure situations observed in rural,
rural–urban transitional, and urban areas and identified the key
indicators responsible for the total variation in these three regions’
riparian zones. Furthermore, we explored the correlations between sets
of pressure indicators and riparian health indicators (RHIs) and
measured the ability of variables to interact with one another. Finally,
we classified the statistical similarities between land-use sites along
the TGDR. This research will help establish strategies to manage
riparian zones under variant land uses on a large scale.