A review of the ecological impacts of water pollution on lakes: From diatom assemblages to migratory bird population declines

J. Biodiv. & Environ. Sci. Murugesan et al. REVIEW PAPER OPEN ACCESS A review of the ecological impacts of water pollution on lakes: From diatom assemblages to migratory bird population declines Arunpandiyan Murugesan1, Roshy Ann Mathews1, S. Rajakumar2, Prashanthi Devi Marimuthu*1 1Department of Environmental Science and Management, Bharathidasan University, Tiruchirappalli, Tamil Nadu, India 2Department of Marine biotechnology, Bharathidasan University, Tiruchirappalli, Tamil Nadu, India Key words: Water quality, Diatoms, Migratory birds, Eutrophication, Wetland conservation DOI: https://dx.doi.org/10.12692/jbes/27.3.23-38 [ Published: September 05, 2025 ] ABSTRACT Lakes are key freshwater ecosystems that maintain the biodiversity, regulate nutrient cycles, and provide habitat for migratory birds. Their ecological well-being is greatly impacted by water quality, which affects the composition and productivity of primary producers such as diatoms. Diatoms are sensitive bioindicators that respond spontaneously to the changing physical, chemical, and biological parameters. The dynamics of their communities extend through food webs, affecting fish, zooplankton, and, eventually, migratory bird populations. This review outlines the current scientific understanding regarding the relationships between bird communities, diatom ecology, and lake water quality, with a focus on case studies from Tamil Nadu and India. It has been demonstrated that major water quality stressors such as pollution, eutrophication, salinisation, and hydrological changes, disturb diatom assemblages, decrease the availability of prey, and deteriorate vital migratory bird stopover and breeding habitats. *Corresponding Author: Prashanthi Devi Marimuthu  [email protected] * https://orcid.org/0000-0002-5500-6085 First author: Arunpandiyan Murugesan: https://orcid.org/0000-0002-4281-725X Co-authors: Roshy Ann Mathews: https://orcid.org/0000-0003-4718-4014 S. Rajakumar: https://orcid.org/0000-0001-5122-4491 Journal of Biodiversity and Environmental Sciences | JBES ISSN: 2220-6663 (Print); 2222-3045 (Online) Website: https://www.innspub.net E-mail contact: [email protected] Vol. 27, Issue: 3, p. 23-38, 2025 J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 24 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net INTRODUCTION Lakes are critical components of the global freshwater system, supporting a wide range of biodiversity and providing essential ecosystem services. They serve as reservoirs of drinking water, irrigation sources for agriculture, habitats for aquatic organisms, and key sites for nutrient cycling (Kalff, 2002; Moss, 2010). Lakes also act as sinks for atmospheric carbon and play a significant role in local climate regulation (Tranvik et al., 2009). Their ecological functions extend to supporting socio-economic activities such as fisheries, tourism, and cultural practices (MEA, 2005; Carpenter et al., 2011). The ecological health of a lake is largely determined by its water quality, which reflects the physical, chemical, and biological characteristics of the aquatic environment. Water quality is influenced by both natural processes (e.g., seasonal turnover, precipitation) and anthropogenic pressures (e.g., agricultural runoff, industrial discharge, urban waste) (Wetzel, 2001; Smith and Schindler, 2009). Degradation of water quality can lead to eutrophication, algal blooms, hypoxia, and the collapse of aquatic food webs (Carpenter et al., 1998; Dodds et al., 2009). Assessing water quality is, therefore, essential for understanding ecosystem integrity and for guiding conservation and management actions (UNEP, 2016; Kumar et al., 2020). Role of diatoms as bioindicators Diatoms are microscopic, photosynthetic algae found in nearly all aquatic habitats. Their silicabased cell walls (frustules) preserve well in sediments, making them valuable indicators of both present and past environmental conditions (Smoland Stoermer, 2010). Due to their rapid response to changes in water chemistry— particularly nutrients, pH, and conductivity— diatoms are widely used as bioindicators in water quality assessment (Stoermer and Smol, 1999; Battarbee et al., 2001). Variations in diatom assemblages can reflect subtle ecological shifts that might not be detected through conventional chemical testing (Kelly et al., 1998). Hence, they offer a powerful tool for long-term monitoring and ecological diagnosis of freshwater systems (Round et al., 1990; Bennion et al., 2014). Migratory birds and their dependence on aquatic food webs Migratory birds, especially waterfowl and waders, rely heavily on healthy wetland and lake ecosystems during breeding, stopover, and wintering phases of their life cycle (Kear, 2005; Newton, 2008). These birds feed on a range of aquatic organisms such as insects, mollusks, crustaceans, and fish—many of which are part of food webs driven by primary productivity from organisms like diatoms (Green and Elmberg, 2014; Baldassarre, 2014). Disruption in these food webs, due to declining water quality or habitat degradation, can result in altered migration patterns, reduced survival rates, and overall population decline (Davidson, 2014; Finlayson et al., 2017). Thus, lake ecosystems form a vital ecological linkage between aquatic primary producers and higher trophic levels including birds (Weller, 1999; Wetlands International, 2021).This review aims to synthesize the current understanding of how lake water quality affects diatom communities and how these changes cascade through the food web to influence migratory bird populations. The review is structured into sections that progressively build on the interactions between water quality, diatoms, and migratory birds, followed by an analysis of conservation implications and future research directions. Lake water quality parameters Understanding lake water quality is fundamental to assessing ecosystem health and biodiversity dynamics. Various physical, chemical, and biological parameters influence the productivity, nutrient cycling, species composition, and overall ecological balance of freshwater systems (Wetzel, 2001; APHA, 2017). These parameters not only affect primary producers like diatoms but also shape the availability of food and habitat for higher trophic levels, including migratory birds (Karthick et al., 2013; Saravanan et al., 2022). In India, several studies have highlighted how water quality deterioration—driven by nutrient enrichment, J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 25 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net industrial pollution, and urban waste—has altered ecological functions of lakes and wetlands (Ramakrishnan et al., 2006; Gupta and Bhatt, 2014). Specifically in Tamil Nadu, investigations of Pallikaranai Marsh, Pulicat Lake, and Vedanthangal Bird Sanctuary have revealed how changes in pH, dissolved oxygen, and nutrient levels affect plankton communities, fish populations, and ultimately waterbird abundance (Nagarajan and Thiyagesan, 1996; Saravanan et al., 2022; Ramachandran et al., 2020). These studies underscore the interconnectedness of water quality parameters with ecological health and conservation outcomes. Influence of physical, chemical and biological parameters on plankton community Temperature Temperature plays a central role in regulating lake stratification, dissolved oxygen solubility, and biological metabolism. It influences the growth and reproduction of diatoms, with certain species preferring colder or warmer conditions (Reynolds, 2006; Wetzel, 2001). Seasonal changes in temperature can lead to thermal stratification, affecting vertical mixing of nutrients and oxygen distribution, which in turn impacts aquatic life (Kalff, 2002). Studies from Indian lakes, such as Loktak and Vembanad, demonstrate that seasonal temperature shifts significantly alter phytoplankton and zooplankton dynamics (Ramakrishnan et al., 2006; Jyothibabu et al., 2010). In Tamil Nadu, seasonal fluctuations in water temperature at Pulicat Lake have been shown to influence fish populations and waterbird abundance (Ramachandran et al., 2020). Turbidity Turbidity refers to the cloudiness of water caused by suspended solids like silt, organic matter, and plankton. High turbidity can reduce light penetration, limiting photosynthesis by diatoms and other autotrophs (Kirk, 2011). It may also clog fish gills and affect visual predators like birds that rely on clear waters to forage (Davies-Colley and Smith, 2001). In Indian wetlands, agricultural runoff and urban effluents are major contributors to turbidity (Khan and Ansari, 2005). Research on Pallikaranai Marsh, Tamil Nadu, has reported that high turbidity levels degrade aquatic productivity and reduce foraging efficiency for wading birds (Saravanan et al., 2022). Transparency Measured using a Secchi disk, transparency indicates the depth to which light can penetrate water. It is a direct measure of the water’s optical clarity. High transparency favors the growth of benthic and pelagic diatoms by enabling better light availability, while reduced transparency often signals eutrophication or pollution (Carlson, 1977; Moss, 2010). In India, transparency has been a reliable indicator for trophic status in urban lakes such as Hussain Sagar (Kumar et al., 2010). In Tamil Nadu, reduced transparency in Vedanthangal and Pulicat lakes has been linked to nutrient enrichment and algal blooms, affecting the carrying capacity for migratory birds (Nagarajan and Thiyagesan, 1996; Ramachandran et al., 2020). pH The pH of lake water affects nutrient availability, metal solubility, and the survival of aquatic organisms (Wetzel, 2001; Kalff, 2002). Diatoms are particularly sensitive to pH fluctuations; different taxa thrive under acidic, neutral, or alkaline conditions (Battarbee et al., 2010). Extreme pH values can disrupt cellular processes and lead to shifts in community composition. Indian studies, such as those from Loktak Lake and Dal Lake, demonstrate that pH fluctuations significantly influence phytoplankton diversity (Ramakrishnan et al., 2006; Rather and Khan, 2013). In Tamil Nadu, variations in pH in Pulicat Lake have been linked to changes in fish populations and waterbird foraging efficiency (Ramachandran et al., 2020). Dissolved oxygen (DO) Dissolved oxygen is vital for aerobic aquatic life. It is replenished through diffusion from the atmosphere and photosynthesis by algae, including diatoms (Wetzel, 2001). Low DO levels (hypoxia) often result from organic pollution and eutrophication, causing fish kills and the collapse of aerobic microbial activity (Dodds et al., 2009). This has cascading effects on bird food sources such as fish and invertebrates J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 26 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net (Davidson, 2014). In Indian lakes, hypoxic conditions have been reported in Hussain Sagar and Vembanad, leading to biodiversity decline (Kumar et al., 2010; Jyothibabu et al., 2010). In Tamil Nadu, DO fluctuations in Pallikaranai Marsh and Vedanthangal Bird Sanctuary have been linked to seasonal bird abundance (Saravanan et al., 2022; Nagarajan and Thiyagesan, 1996). Nutrients (Nitrogen and Phosphorus) Nitrogen (N) and phosphorus (P) are essential for primary productivity but also drive eutrophication when present in excess (Smith and Schindler, 2009). Nutrient enrichment often leads to shifts in algal communities—replacing beneficial diatoms with nuisance or toxic cyanobacteria (Carpenter et al., 1998). This alters the food base for invertebrates and fish, ultimately affecting migratory birds (Green and Elmberg, 2014). In India, high nutrient loading has been recorded in lakes like Loktak, Chilika, and Hussain Sagar (Ramakrishnan et al., 2006; Pattnaik et al., 2007). In Tamil Nadu, Pulicat Lake and Pallikaranai Marsh face nutrient-driven eutrophication from agriculture and sewage, threatening biodiversity (Ramachandran et al., 2020; Saravanan et al., 2022). Salinity Salinity influences osmoregulation in aquatic organisms and shapes species composition in freshwater lakes (Hammer, 1986). Diatoms exhibit varying tolerance to salinity; some are restricted to freshwater, while others thrive in brackish environments (Smoland Stoermer, 2010). Increased salinization due to climate change, seawater intrusion, or human activities can stress freshwater taxa and modify trophic interactions (Williams, 2001). In Indian wetlands like Sambhar Lake and Pulicat Lake, rising salinity has been shown to reduce freshwater biodiversity and affect migratory bird populations (Nagarajan andThiyagesan, 1996; Ramachandran et al., 2020). Conductivity Conductivity measures the water’s ability to conduct electricity, which correlates with ion concentration (e.g., Na⁺, Cl⁻, SO₄²⁻). It provides a general indicator of water mineralization and anthropogenic inputs (APHA, 2017). Elevated conductivity often reflects pollution or land-use change and influences diatom assemblages and habitat quality (Karthick et al., 2013). Studies from Indian wetlands, including Chilika and Pallikaranai, reveal that conductivity is strongly linked to urban effluents and agricultural runoff (Pattnaik et al., 2007; Saravanan et al., 2022). In Tamil Nadu, seasonal variations in conductivity at Vedanthangal and Pulicat lakes have been reported due to impact plankton communities and waterbird foraging grounds (Nagarajan and Thiyagesan, 1996; Ramachandran et al., 2020). Presence of algae Algae, including diatoms, form the base of the aquatic food web and are widely recognized as reliable indicators of water quality and trophic status (Reynolds, 2006; Smoland Stoermer, 2010). Their abundance, species diversity, and community composition reflect nutrient levels and ecological balance in aquatic systems. A balanced algal population supports healthy food chains, while excessive growth, particularly cyanobacterial blooms, indicates nutrient enrichment and can produce toxins harmful to aquatic fauna and humans (Paerland Otten, 2013; Saha and Paul, 2020). In Indian freshwater ecosystems, phytoplankton composition has been directly linked to eutrophication and seasonal changes (Kaushik and Saksena, 1995; Singh and Singh, 2006). Studies from Tamil Nadu lakes have reported seasonal variation in phytoplankton, especially diatoms and cyanobacteria, as effective bioindicators of water quality (Arivoli and Mohanraj, 2013; Murugan and Santhanam, 2011). Microbial activity Microbial communities play a central role in decomposition of organic matter, nutrient cycling, and sustaining energy flow in aquatic systems (Wetzel, 2001). Shifts in microbial abundance and diversity provide early warnings of deteriorating water quality. Elevated organic loads often enhance microbial respiration, leading to depletion of dissolved oxygen and creating stress for fish and invertebrates (Jindal and Sharma, 2011). In India, J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 27 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net microbial activity has been shown to increase significantly in sewage-fed and polluted water bodies, accelerating oxygen depletion (Reddy and Rao, 1986). In Tamil Nadu lakes, microbial communities such as heterotrophic bacteria have been found to correlate strongly with nutrient enrichment and organic pollution (Senthilkumar and Sivakumar, 2018). Such microbial responses highlight their significance as bioindicators of anthropogenic stress in freshwater ecosystems. Eutrophication and its effects Eutrophication is the process of nutrient enrichment, primarily with nitrogen and phosphorus, leading to excessive algal growth and loss of ecological balance in aquatic ecosystems (Wetzel, 2001; Smith et al., 1999). While it may initially enhance primary productivity, chronic eutrophication disrupts lake ecology in multiple ways. One of the most prominent impacts is the decline in diatom diversity, as fast-growing green algae and cyanobacteria dominate under high nutrient conditions (Reynolds, 2006; Saha and Paul, 2020). This dominance of cyanobacteria and green algae, which are less palatable or even toxic to grazerseventually allow diatoms to lose their dominance. This shift can lower the efficiency of energy transfer to zooplankton and invertebrates. This further reduces the nutritional quality of prey available to birds (Paerland Otten, 2013; Jeppesen et al., 2020). The excessive organic matter produced leads to oxygen depletion, particularly in bottom waters, due to microbial decomposition of algal biomass (Carpenter et al., 1998; Jindal and Sharma, 2011) as a result of microbial respiration which consumes large amounts of dissolved oxygen, leading to hypoxic or anoxic conditions. This process often triggers fish kills or increased mortality rates, reducing prey availability for piscivorous birdsand insectivorous birds (Schindler, 2001; Kaushik and Saksena, 1995). Bird species such as terns, gulls, and grebes may abandon degraded sites or suffer reproductive failure (Diaz and Rosenberg, 2008; Rabalais et al., 2014). Eutrophication also causes habitat degradation, making lakes unsuitable for foraging and nesting of migratory waterbirds (Arivoli and Mohanraj, 2013). The emergence of harmful algal blooms (HABs), dominated by toxin-producing cyanobacteria, poses direct health threats to fish, birds, and even humans (Paerland Otten, 2013). Long-term eutrophication alters species composition and food web dynamics, undermining the ability of lakes to sustain biodiversity, with severe consequences for sensitive groups such as migratory waterbirds that depend on stable, nutrientbalanced ecosystems (Murugan and Santhanam, 2011; Senthilkumar and Sivakumar, 2018). Diatoms as ecological indicators Biology and ecology of diatoms Diatoms are unicellular, photosynthetic algae belonging to the class Bacillariophyceae. They are characterized by intricately patterned, silica-based cell walls called frustules, which make them both ecologically significant and taxonomically identifiable under a microscope (Round et al., 1990; Smoland Stoermer, 2010). Diatoms occur in a wide range of aquatic habitats—from pristine mountain streams to nutrient-rich lakes—and can be found in planktonic (free-floating) and benthic (attached to surfaces) forms (Wetzel, 2001; Saha and Paul, 2020). Ecologically, diatoms are primary producers, forming the foundation of aquatic food webs. They exhibit rapid reproduction under favorable conditions, allowing them to respond quickly to environmental changes (Stoermer andSmol, 1999; Reynolds, 2006). Their sensitivity to specific environmental parameters such as nutrient levels, salinity, temperature, and pH makes them reliable indicators of ecological shifts (Ramakrishnan and Kumar, 2018; Arivoli and Mohanraj, 2013; Murugan and Santhanam, 2011). Sensitivity to water quality changes Diatoms are widely recognized as one of the most responsive groups of microorganisms to changes in water quality (Smoland Stoermer, 2010; Wetzel, 2001). Different species have distinct ecological tolerances and optima, which allow for fine-scale detection of alterations in environmental J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 28 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net conditions (Stoermer and Smol, 1999; Ramakrishnan and Kumar, 2018). For example, Eutrophic conditions known as high nutrient levels favor species like Cyclotella meneghiniana and Nitzschia palea (Reynolds, 2006; Saha and Paul, 2020). However, oligotrophic environments which are low nutrient conditionssupport species such as Fragilaria crotonensis or Achnanthes spp. (Round et al., 1990; Singh and Singh, 2006) and acidic waters promote acid-tolerant diatoms like Tabellariafenestrata, while alkaline waters favor Navicula and Gomphonema species (Battarbee et al., 2010; Arivoli and Mohanraj, 2013). Since diatoms have short generation times, they can rapidly colonize new habitats or shift in composition in response to stressors, offering a real-time assessment of lake health (Murugan and Santhanam, 2011; Senthilkumar and Sivakumar, 2018). Diatom indices and bioassessment Diatoms are extensively used in bioassessment protocols due to their sensitivity, diversity, and persistence in the sediments (Smoland Stoermer, 2010; Wetzel, 2001). Quantitative diatom indices have been developed to assess the trophic status, organic pollution, and acidification of freshwater systems (Stoermer andSmol, 1999; Ramakrishnan and Kumar, 2018). Some of the widely used indices include: 1. Trophic Diatom Index (TDI): Assesses nutrient enrichment in rivers and lakes (Kelly and Whitton, 1995; Saha and Paul, 2020). 2. Paleoecological Diatom Index: Reconstructs historical water quality using fossil diatoms from sediment cores (Battarbee et al., 2010; Singh and Singh, 2006). 3. Specific Pollution Sensitivity Index (IPS): Scores diatoms based on their tolerance to organic pollution (Coste, 1982; Arivoli and Mohanraj, 2013). These indices are instrumental in regulatory monitoring frameworks such as the European Union Water Framework Directive (WFD) and can inform conservation and management actions (Kelly et al., 1998; Murugan and Santhanam, 2011). Diatoms as a link between water quality and bird ecology Diatoms form the base of many freshwater food webs where their health directly influences the availability of resources for invertebrates and fish—critical prey for migratory birds. A decline in diatom diversity or productivity can disrupt trophic pathways, reducing biomass at higher levels (Stoermer andSmol, 1999; Battarbee et al., 2010). This can also affect the timing and quality of food during bird migration periods (Jeppesen et al., 2011; Kumar et al., 2019), lead to habitat unsuitability, causing changes in bird distribution or decline in populations (Mukherjee and Borad, 2001; Arivoli and Mohanraj, 2013).Thus, monitoring diatom communities provides not only a measure of water quality but also an indirect indicator of bird habitat quality and sustainability (Soininen, 2007; Murugan and Santhanam, 2011). Lakes and wetlands serve as complex ecological networks where energy and nutrients are transferred across multiple trophic levels formingtrophic linkages between diatoms and migratorybirds. Diatoms, as primary producers, form the base of this aquatic food web. Though birds do not directly consume diatoms, the trophic influence of diatoms cascades through invertebrates and fish to shape food availability and habitat conditions for migratory bird species (Reynolds, 2006; Jeppesen et al., 2010). Understanding these linkages is critical for assessing how changes in lake water quality can impact bird populations (Mukherjee and Borad, 2001; Arivoli and Mohanraj, 2013). Diatoms as primary producersplay an important role in food web dynamics, where theycontribute significantly to primary productivity in lakes. Through photosynthesis, they convert sunlight into biomass and oxygen, forming a major part of the phytoplankton and periphyton community. Their production supports the diet ofZooplankton like copepods and rotifers, Macroinvertebrates for e.g., insect larvae, mollusks and amphipods and also for small fish and fish larvae that graze on invertebrates or plankton. These lower trophic organisms are essential food resources for migratory waterbirds, such as ducks, shorebirds, and herons (Reynolds, 2006; Jeppesen et al., 2010; Arivoli and Mohanraj, 2013). J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 29 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net Energy transfer to birds is witnessed especially in migratory bird populations. Based on their feeding preferences migratory birds are categorized as Planktivores,such as some ducks, that consume zooplankton supported by diatom blooms; Invertivores that feed on invertebrates that rely on benthic diatoms(e.g., sandpipers, storks) and piscivores that depend on fish that are indirectly sustained by diatombased primary production(e.g., pelicans, cormorants). Disruptions at the diatom level, due to pollution, eutrophication, or salinity changes, can therefore reduce prey abundance and quality, diminishing bird foraging success (Mukherjee and Borad, 2001; Ramachandran and Rajkumar, 2018). Diatoms not only support food webs but also contribute to habitat structuring where benthic diatoms form biofilms on submerged surfaces, supporting invertebrate communities in mudflats and shallow water zones—critical feeding areas for wading birds.This critically determines the foraging behavior and habitat suitability of migratory birds as they select feeding and stopover sites based on prey availability, which is a function of underlying productivity and water quality.The periphytic diatoms influence macrophyte growth, which provides shelter and breeding grounds for aquatic organisms and nesting areas for birds.When diatom-based productivity is high and stable, these sites support higher bird abundance, diversity, and reproductive success (Waiser and Robarts, 2004; Kumar et al., 2019; Murugan and Santhanam, 2011). Above all theseasonal dynamics and migration timing play a significant role as the seasonal variation in diatom productivity also influences the timing of bird arrival and departure at wetlands, their body condition and fat reserves needed for long-distance flight and the reproductive readiness in species that nest near lakes. For instance, pre-migratory staging birds rely on nutrient-rich foraging grounds to accumulate energy. A collapse in diatom populations during critical migratory windows which can happen due to thermal stress or nutrient imbalance often delaying migration or reducing survival rates (Smoland Stoermer, 2010; Balachandran, 2006; Samikannu et al., 2020). Feedback loops between birds and lake ecosystems Migratory birds also contribute to nutrient cycling in lakes through excretion of guano, enriching shallow zones with nitrogen and phosphorus, Bioturbation from foraging, influencing sediment mixing and diatom resuspension and Seed dispersal and habitat engineering, which affects aquatic plant–diatom interactions. This creates feedback loops, where bird activity can influence the composition and productivity of diatoms, and vice versa, making the relationship between diatoms and birds mutually interdependent and dynamic (Post et al., 1998; Hahn et al., 2007; Ramachandran et al., 2017). Influence of lake degradation on migratory bird populations, conservation implications and management strategies Lakes and associated wetlands are crucial stopover, wintering, and breeding sites for millions of migratory birds worldwide. However, degradation of these habitats, especially due to declining water quality, poses serious threats to bird populations. As diatoms play a major role in sustaining lake habitats for migratory birds, any negative impact will lead to trophic disruption (Finlayson et al., 2018; Ramsar Convention Secretariat, 2021). When diatom communities are degraded, the zooplankton and macroinvertebrate populations decline and survival of fish larvae drops due to food shortage. Birds exhibit changes in feeding patterns, site fidelity, or migrate longer distances to find suitable habitats where some species may suffer population declines or altered migratory pathways. This trophic disruption can be especially harmful in regions where lakes serve as critical migratory flyways or breeding grounds, such as Ramsar wetlands or transcontinental bird routes (e.g., Central Asian Flyway, East Asia–Australasia Flyway) (Davidson, 2014; Balachandran, 2006; Samikannu et al., 2020). Therefore, changes in trophic dynamics, habitat structure, and food web stability resulting from pollution, eutrophication, or salinization can significantly alter bird behavior, foraging success, and survival as shown in Table 1. J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 30 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net Table 1. Evidence from case studies linking diatoms and migratory birds Region Key stressors Ecological Impact on diatoms / Food web Consequences for migratory birds References Chilika Lake, Odisha, India Sedimentation, eutrophication Algal blooms; reduced fish population Decline in piscivorous birds (pelicans and cormorants) Balachandra et al., 2020; Sundar and Subramanya, 2010. Keoladeo National park, Bharathpur, India Water diversion, pollution, wetland drying Habitat loss; reduced prey availability Decline in migratory waterfowl; Siberian crane (Grus leucogeranus) Vijayan, 1991; BirdLife International, 2020 Danube delta and Lake, Europe Eutrophication, industrial discharges Shift from diatoms to Cyanobacteria dominance Reduced food resource for benthic-feeding birds (snipes and sandpipers) Ibelings, 2016; Donohue et al., 2019 Great Lakes region, North America Nutrient imbalance, habitat alteration Loss of diatombased productivity; decline in invertebrates Migratory ducks and shorebirds impacted during spring/fall migrations Smith et al., 2015; Schindler, 2019 Other impacts Some cyanobacteria produce neurotoxins or hepatotoxins that can accumulate in aquatic organisms and pose direct toxic effects orhealth risks to birds. Documented bird die-offs due to cyanotoxins have occurred in several wetlands globally (Metcalf et al., 2012; Burford et al., 2020). Sub-lethal effects include impaired navigation, reproduction, or immunity (Carmichael, 2001; Miller et al., 2010). Degraded water quality often coincides with increased sedimentation and vegetation overgrowth. Loss of mudflats and shallow feeding areas are critical for waders (Ma et al., 2010; Sundar and Subramanya, 2010) and encroachment of invasive species lead to altering nesting habitats (Sharma et al., 2016). Pollution and water abstraction alter hydrological regimes, affecting the availability and timing of suitable foraging habitats. Early drying of wetlands limits resource availability during migration windows (Vijayan, 1991; Pattnaik et al., 2021). Increased salinity excludes freshwater species, reducing prey diversity (Zhang et al., 2019). Climate-induced changes—such as increased temperatures, altered precipitation patterns, and salinization—affect both diatom communities and migratory bird behavior (IPCC, 2022; Smoland Douglas, 2007). However, climate-mediated interactions across trophic levels are poorly understood (Adrian et al., 2009; Hassan et al., 2021 – Indian wetlands; Both et al., 2009; Pearce-Higgins and Green, 2014; Thackeray et al., 2016). Conservation concerns Degraded lake systems not only threaten individual species but also disrupt entire migratory flyways. Lakes serve as stepping stones across continents for millions of birds. The degradation of one or more of these critical sites can have cascading consequences across the entire migration network, especially for species already facing climate and land-use pressures (BirdLife International, 2020; Harris et al., 2019). Given the critical role of lake ecosystems in supporting biodiversity—particularly primary producers like diatoms and migratory birds at higher trophic levels—it is imperative to adopt integrated conservation and management approaches. The degradation of water quality and its cascading ecological impacts necessitate multi-pronged strategies combining restoration, monitoring, policy, and community participation (Jeppesen et al., 2020; Kumar et al., 2022; Ramsar Convention Secretariat, 2021). Consequences in behavioral and demographical changes must be addressed. Birds experiencing habitat degradation may extend migratory routes in search of suitable alternatives (Newton, 2008). They delay migration or show poor body condition due to reduced food (Davidson and Stroud, 2016). Population rates suffer due to declines in breeding success as a result of inadequate nourishment (Finlayson et al., 2018).Cumulatively, these stressors can lead to population declines, loss of J. Biodiv. & Environ. Sci. Vol. 27, Issue: 3, p. 23-38, 2025 31 Murugesan et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net genetic diversity, and changes in migration corridors, threatening the long-term viability of migratory species (Kirby et al., 2008; Ramsar Convention Secretariat, 2021). Establishing bird sanctuaries and no-disturbance zones during peak migration and nesting periods. Habitat enhancement projects such as the creation of mudflats, shallow pools, and nesting islands can improve foraging and breeding opportunities (Ma et al., 2010; Rahmani, 2012 – India). Restoring water quality is most required to reduce nutrient load. One of the most effective measures to restore water quality is limiting nutrient inputs, particularly nitrogen and phosphorus, from agricultural runoff, sewage, and industrial waste. Reducing nutrient loads helps in restoring diatom diversity and minimizing the dominance of harmful algae (Jeppesen et al., 2005; Paerland Otten, 2013). Buffer zones and vegetative filters around lakes to trap sediments and nutrients can be planned (Carpenter et al., 1998; Withers and Jarvie, 2008) along with constructed wetlands for tertiary wastewater treatment (Vymazal, 2011; Mitsch and Gosselink, 2015). Regulations on fertilizer use, especially near ecologically sensitive zones can be mandated (Smith and Schindler, 2009). Maintaining natural hydrological regimes through environmental flow releases and water level control ensures habitat availability during critical migratory periods. Periodic flushing of lakes can also help remove excess nutrients and prevent stagnation (Poff et al., 1997; Bunn and Arthington, 2002). Excessive sedimentation degrades benthic habitats crucial for periphytic diatoms and invertebrates. Desiltation efforts, when well-managed and ecologically informed, can help restore both the feeding grounds for benthic-feeding birds (Finlayson et al., 2018) as well as improve light penetration for diatom photosynthesis (Likens, 2010; Wetzel, 2001). Conservation planning should integrate Long-Term Diatom Monitoring Programs and Sediment Core Analysis. This can be successful by establishing diatom sampling stations at strategic locations in lake systems (Kelly et al., 1998; Dixit et al., 1999), creating reference libraries of diatom assemblages from pristine and degraded lakes (Soininen, 2007; Stevenson et al., 2010), including diatom indices (e.g., TDI, IPS) in national water quality monitoring protocols (Kelly and Whitton, 1995; Pandey et al., 2014 – India), studying fossil diatoms in sediment cores offers insights into historical ecological conditions, helping track changes due to land use, pollution, or climate over decades or centuries (Battarbee et al., 2001; Smoland Stoermer, 2010). This supports adaptive lake management based on long-term ecological trends (Agnihotri and Mishra, 2021 – India). Technological gaps in diatom monitoring Traditional diatom identification is labor-intensive and requires taxonomic expertise. This limits widespread adoption in routine monitoring programs (Round et al., 1990). Protecting migratory bird habitats requires conserving wetland–lake complexes, regulating tourism and development near sensitive zones, establishing sanctuaries with no-disturbance periods, and undertaking habitat enhancement through mudflats, shallow pools, and nesting islands. A systems-based, integrated approach linking water quality monitoring, diatom studies, and avian surveys under ecosystem-based management enhances resilience and early detection of degradation. Community participation through capacity-building, citizen science, sustainable farming, and ecotourism strengthens conservation outcomes while supplementing formal datasets. At the policy level, enforcing wetland laws, expanding Ramsar site management, and engaging in international agreements like the CMS and Central Asian Flyway, alongside regional collaboration on diatom monitoring, are essential. 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