Analysis of Spatial–Temporal Variations and Driving Factors of Typical Tail-Reach Wetlands in the Ili-Balkhash Basin, Central Asia

Abstract

The Ili River Delta (IRD) is the largest delta in the arid zone of Central Asia. Since the 1970s, the entire delta system has undergone a series of changes due to climate change and the impoundment of the Kapchagay Reservoir upstream of the delta, triggering an ecological crisis. Wetlands play a crucial ecological role in biodiversity conservation. Most studies have mainly focused on the response of vegetation and soil microbial to ecological changes in the delta, ignoring the dynamic processes of wetlands changes. Hence, such changes in the IRD and the underlying mechanisms need to be investigated in depth. In this study, wetlands in the IRD from 1975 to 2020 were extracted based on Landsat images using the object-oriented method; changes in the wetland area, wetland landscape pattern, NDVI, and NPP were analyzed; and the contributions of natural and human factors to wetland evolution were quantified. The results indicated the following: (1) From 1975 to 2020, the wetland area of the IRD showed an increasing trend, and changes in the wetland area were mainly found in the middle part of the delta near the Saryesik Peninsula. (2) The wetland landscape pattern in the IRD changed markedly from 1975 to 2020. The dominant patches of the wetland in the middle of the delta continued to expand; the patch aggregation index (AI) increased, and the landscape fragmentation index (LFI) decreased. (3) From 2000 to 2020, the average annual normalized difference vegetation index (NDVI) and net primary productivity (NPP) in the IRD increased, which is consistent with the change in wetland expansion. (4) Inflow to the delta from the Ili River and the water level of Balkhash Lake are significantly correlated with the wetland area, which are the dominant factors driving wetland evolution; and water evaporation from the Kapchagay Reservoir and irrigation water diversion on the left bank of the reservoir obviously intensified the process of lake water level decline and wetland degradation during 1970 to 1985. These results can provide scientific background for making informed ecological protection decisions in the IRD under the impacts of climate change and human activities.

Predicting and evaluating seasonal water turbidity in Lake Balkhash, Kazakhstan, using remote sensing and GIS

“…In the subsequent years, the lake WL experienced two decreases and rises, with low stands in 2009 (342.41 m asl) and 2015 (342.51 m asl). The most recent lake level rise occurred over 2017-2018, with the highest WL for the observation period reached in 2018 with 343.03 m asl (Cao et al, 2022). Lake levels have been falling ever since at a rate of 21 cm/yr and reached a level equivalent to that of 2002 in our final observation year 2022.…”

“…Several studies have documented increasing temperatures in this region (Propastin, 2012;Qi et al, 2020), resulting in high evaporation rates (Abdrahimov et al, 2020) and exacerbating discharge patterns through an increase in water level (Qi et al, 2020;Moldakhanova et al, 2023). It is important to note that the major contributing rivers -Ile, Karatal, Lepsy and Aksu -are fed by glaciers and snowmelt, and are consequently highly sensitive to temperature-driven impacts (Kaldybayev et al, 2016;Sala et al, 2016;Mischke, 2020;Cao et al, 2022) on runoff and the seasonal distribution of water. During winter, the lake is mostly frozen; the lake surface starts melting in the early March, with the onset of spring (Petr, 1992).…”

“…The Ile-Balkhash catchment experiences a continental climate and diverse geomorphology, spanning highest glaciated mountains of Khan Tengri peak rising to 6995 m asl, and terminating in the desert at 340 m asl with lowest point in the Lake Balkhash (Cao et al, 2022). The extreme climate supports desert and steppe vegetation near the lake, with deciduous trees and coniferous forests, alpine meadows and tundra vegetation with increasing altitude (Mischke et al, 2020).…”

“…In our study, we observed an increase in shrubland areas (Figure 7B) within the basin, which has likely contributed to soil erosion control and, consequently, might have helped in reducing the lake water turbidity. The Ile-Balkhash basin has also been marked by an expansion of wetland areas, mostly associated with the southeastern part of the lake (Cao et al, 2022). These wetlands serve as natural filters, trapping sediment carried by runoff before it reaches the lake (Johnston, 1991;Mereta et al, 2020), thereby decreasing turbidity levels.…”

“…These wetlands serve as natural filters, trapping sediment carried by runoff before it reaches the lake (Johnston, 1991;Mereta et al, 2020), thereby decreasing turbidity levels. In summary, the increase in wetland areas around Lake Balkhash can act as a vital mechanism for mitigating turbidity and promoting the overall health and ecological balance of inland lakes (Cao et al, 2022). Conversely, barren landscapes are prone to erosion, leading to sediment runoff and positively contribute to water turbidity.…”