Impacts of Stressors on Riparian Health Indicators in the Upper and Lower Indus River Basins in Pakistan

Abstract

Riparian zones along rivers and streams provide ecosystem services that may change over time as disturbances increase and deteriorate these buffer zones globally. The effect of stressors on ecosystem services along the rivers in underdeveloped countries is unclear, which impacts the environment directly in the form of riparian health indicators (RHIs). This study fills this gap and measures the impact of stressors on RHIs (parameters of habitat, plant cover, regeneration, exotics, and erosion) in the Indus River basin (IRB) in Pakistan. Data on 11 stressors and 27 RHIs were collected using a field-based approach in 269 transects in the upper and lower Indus basins (UIB and LIB) in 2020 and analyzed using multivariate statistical methods. The Kruskal-Wallis tests (p < 0.05) indicated that RHIs varied significantly under the influence of stressors in the UIB and LIB. However, their highest mean values were found in the UIB. Principal component analysis revealed the key RHIs and stressors, which explained 62.50% and 77.10% of the variance, respectively. The Pearson correlation showed that stressors had greater impacts on RHIs in LIB (with r ranging from -0.42 to 0.56). Our results also showed that stressors affected RHI indices with r ranging from -0.39 to 0.50 (on habitat), -0.36 to 0.46 (on plant cover), -0.34 to 0.35 (on regeneration), -0.34 to 0.56 (on erosion), and -0.42 to 0.23 (on exotics). Furthermore, it was confirmed by the agglomerative hierarchical cluster that indices and sub-indices of RHIs and stressors differ across the UIB and LIB. These findings may serve as guidance for managers of large rivers and ecosystem service providers to minimize the environmental impact of stressors in terms of RHIs.

Keywords: Indus River; Terbela Dam Reservoir; ecosystem function; environmental indicators; pressure indicators; rapid appraisal; riparian health assessment.

Figure 1

Location of sample sites in the upper and lower Indus basin riparian zones of the Indus River in Pakistan.

Figure 2

List of the riparian health indicators (a) and stressors (b), along with their respective abbreviations inside the parentheses, used for the upper and lower Indus basin riparian zones of the Indus River in Pakistan.

Figure 3

Box and whisker plots for riparian health indicators (a–f) and stressors (g) measured in the upper and lower Indus basin riparian zones of the Indus River in Pakistan. The y-axis denotes the mean scores with 95% confidence interval (CI). The silver horizontal line represents the median, and the silver triangle sign symbolizes the mean. The boxes represent the 25th–75th percentiles, and the whiskers outside the boxes represent the 10th–90th percentiles. The silver curve symbolizes the shape of data distribution, whereas the orange rhombus represents data distribution. Note: significance is at p < 0.01 (**) or p < 0.05 (*) of the Kruskal–Wallis tests. Moreover, pairwise comparisons between the upper and lower Indus basins are marked with non-identical lowercase letters (a,b) using Dunn-Bonferroni post hoc tests.

Figure 4

Factor analysis (PCA) plots of riparian health indicators (a) and stressors (b) for the upper and lower Indus basin riparian zones of the Indus River in Pakistan. The PCA factor loadings of riparian health (a) and stressor (b) indicator components explain 62.5% and 77.1% of the total variation, respectively. See more details in Figure 2.

Figure 5

Heat maps of Pearson’s correlation for riparian health indicators with stressors for the upper (a) and lower (b) Indus basin riparian zones of the Indus River in Pakistan. A dark color indicates a strong relationship, whereas a light color represents a weak relationship. *** Correlation is significant at the 0.001 level (two-tailed); ** Correlation is significant at the 0.01 level (two-tailed); * Correlation is significant at the 0.05 level (two-tailed). See more details in Figure 2.

Figure 6

Dendrograms produced by agglomerative hierarchical clustering for riparian health indicators sub-indexes/index with stressors index for the upper (a) and lower (b) Indus basin riparian zones of the Indus River in Pakistan.