Impact of Environmental Factors on Aquatic Ecosystem

1. Introduction

Aquatic ecosystems are facing unprecedented challenges due to anthropogenic activities and climate change [1]. Environmental factors such as hydrological alterations, pollution, eutrophication, and habitat degradation significantly affect biodiversity, water quality, and ecosystem services [2]. Understanding these impacts is critical for developing effective conservation and management strategies [3]. This Special Issue explores the multifaceted effects of environmental stressors on aquatic ecosystems through innovative methodologies, case studies, and interdisciplinary approaches. Its contributions highlight advancements in monitoring, modeling, and remediation techniques, offering insights into the resilience and vulnerability of aquatic environments.

This Special Issue of Water addresses these challenges by synthesizing cutting-edge research on the multifaceted impacts of environmental stressors across rivers, lakes, wetlands, and reservoirs. Its contributions highlight innovative methodologies—from advanced biomonitoring techniques to hybrid remediation strategies—that bridge gaps between theoretical understanding and practical conservation. By integrating interdisciplinary approaches (e.g., hydrology, ecotoxicology, remote sensing, and microbial ecology), this collection not only diagnoses ecosystem degradation, but also proposes scalable solutions tailored to diverse geographical and socioecological contexts.

Aquatic ecosystems face tipping points, where cumulative stressors may trigger irreversible shifts in function [4]. For instance, eutrophication-driven algal blooms, heavy metal bioaccumulation, and habitat fragmentation increasingly compromise water security and human health [5]. This issue underscores the need for science-based policy interventions, emphasizing resilience-building through adaptive management, community engagement, and technological innovation.

2. An Overview of the Contributions to This Special Issue

The 13 articles in this Special Issue address diverse aspects of aquatic ecosystem dynamics, and can be grouped into the following five thematic categories.

2.1. Hydrological and Morphological Influences on Aquatic Ecosystems

Hydrological and geomorphological changes profoundly affect riverine and lacustrine ecosystems. Yu et al. (Contribution 1) investigated how river sinuosity impacts the hydrodynamic conditions and ecological flow requirements in the Nansha River, China. Using the River2D model, they demonstrated that moderate sinuosity enhanced depth and velocity diversity, optimizing habitats for target species like Cyprinus carpio. Li et al. (Contribution 2) examined the morphological traits of Cynodon dactylon in the Three Gorges Reservoir’s riparian zone, linking plant adaptations to fluctuating water levels and sediment properties. Their findings revealed that soil moisture and nutrient gradients drive root and stem plasticity, enabling survival under prolonged submersion. Hong et al. (Contribution 3) combined LSTM and InVEST models to assess hydrological evolution and habitat quality in the Xiangjiang River Basin, identifying climate change and human activities as primary drivers of habitat fragmentation. Lastly, Firsova et al. (Contribution 4) explored how Lake Baikal’s cold waters influence phytoplankton dynamics in the Irkutsk Reservoir, showing seasonal shifts in community structure driven by temperature and nutrient inputs.

2.2. Pollution Sources, Impacts, and Remediation Strategies

Pollution mitigation and remediation are central to restoring aquatic health. Sun et al. (Contribution 5) developed biochar/clay composite particles immobilized with Flavobacterium and Aquamicrobium species, achieving >80% removal of ammonia and petroleum hydrocarbons in contaminated wetlands. Sobiecka et al. (Contribution 6) demonstrated the efficacy of macrophytes (e.g., Elodea canadensis) in removing chlorpyrifos, with enzymatic responses (e.g., glutathione-S-transferase) indicating adaptive oxidative stress mechanisms. Papakonstantinou et al. (Contribution 7) assessed heavy metal contamination in Greece’s Gialova Lagoon, identifying localized hotspots for Mo and Pb and emphasizing the role of sediment geochemistry in pollutant retention. Vallese et al. (Contribution 8) employed electrochemical detection to quantify Cd and Pb bioaccumulation in Cyprinus carpio, revealing tissue-specific metal accumulation patterns in the Colorado River. Vivien and Ferrari (Contribution 9) used oligochaete communities to evaluate wastewater treatment plant effluents, showing improved post-upgrade stream health through reduced pollutant loads.

2.3. Biomonitoring and Ecological Health Assessment

Biomonitoring tools provide critical insights into ecosystem stress. Kim et al. (Contribution 10) analyzed ferritin gene expression in Litopenaeus vannamei postlarvae, linking thermal and salinity stress to oxidative responses. Melkonyan et al. (Contribution 11) integrated acetylcholinesterase activity and oxidative stress biomarkers to assess whitefish health in Lake Sevan, Armenia, identifying eutrophication and hypoxia as key stressors.

2.4. Eutrophication and Algal Community Dynamics

Eutrophication drives shifts in primary producer communities. Ban et al. (Contribution 12) utilized satellite-derived ocean color data to estimate phytoplankton productivity in Qinghai Lake, revealing oligotrophic conditions with seasonal peaks in chlorophyll-a. Yang et al. (Contribution 13) studied filamentous algae (Cladophora, Spirogyra) in the Taihang catchment, showing nutrient-dependent succession and interactions with macrobenthos that influence habitat heterogeneity.

2.5. Advanced Technologies and Modeling Applications

Innovative technologies enhance monitoring and predictive capabilities. Hong et al. (Contribution 3) and Ban et al. (Contribution 12) exemplified the integration of hydrological (LSTM) and ecological (InVEST) models with remote sensing to track habitat and productivity changes. Vallese et al. (Contribution 8) advanced automated electrochemical detection for real-time heavy metal monitoring, validated against ICP-AES.

3. Conclusions

The studies in this Special Issue underscore the complexity of environmental impacts on aquatic ecosystems and the need for multidisciplinary solutions. The key findings include the following:

• Hydrological and morphological alterations require balanced management to sustain biodiversity and ecological flows;
• Pollution remediation benefits from hybrid approaches (e.g., biochar–microbe composites, phytoremediation) tailored to local conditions;
• Biomonitoring tools (e.g., enzymatic biomarkers, oligochaete indices) are vital for early stress detection and policy formulation;
• Remote sensing and modeling bridge spatial–temporal gaps in ecosystem assessment.

Future research should prioritize long-term monitoring, community engagement, and adaptive management to address emerging challenges like climate change and microplastic pollution. This collection advances our understanding of aquatic ecosystem resilience, providing a foundation for sustainable water resource management.