PhD Research (Project 3- Ongoing):  Nutrient and Cyanotoxin Dynamics in a Eutrophic Pond: Linking Phosphorus Cycling, Internal Loading, and Microcystin Partitioning

This chapter investigates how nitrogen and phosphorus cycle through TSU Farm Pond, a shallow eutrophic pond in Middle Tennessee, and how those nutrient dynamics relate to cyanobacterial activity and cyanotoxin occurrence. The study examines spatial gradients along the pond's inlet-wetland-outlet flow path and seasonal shifts across all four seasons, integrating water-column chemistry, sediment porewater, and sediment analysis to build a mechanistic picture of nutrient retention, transformation, and release.

The work is organized around four connected questions: how nitrogen-to-phosphorus stoichiometry relates to phytoplankton and cyanobacterial response; how phosphorus speciation is controlled by biological versus chemical conditions; whether iron-mediated redox processes at the sediment-water interface drive internal phosphorus loading; and how the cyanotoxin microcystin partitions between dissolved, cell-associated, porewater, and sediment-bound pools. A central innovation is the direct measurement of porewater chemistry, using an MHE PushPoint sampler with a flow cell coupled to a multiparameter sonde, to capture the reducing conditions and dissolved iron, phosphate, and toxin gradients that conventional water-column sampling misses.

Analytical methods span ion chromatography, ICP-OES and ICP-MS, colorimetric nutrient analysis, sediment and aqueous organic carbon quantification, and ELISA-based microcystin measurement in collaboration with an external cyanotoxin laboratory. Rather than relying on equilibrium geochemical modeling alone, the study prioritizes direct field measurement of kinetically controlled processes, pairing porewater geochemistry with toxin partitioning to test whether the same organic-rich, reducing sediments that recycle phosphorus also act as an internal reservoir and source of cyanotoxin.

By connecting nutrient stoichiometry, redox-driven internal loading, and cyanotoxin dynamics within a single freshwater system, this work contributes a mechanistically integrated understanding of eutrophication in small shallow ponds, systems that are widespread across agricultural and peri-urban landscapes yet underrepresented in biogeochemical research, with direct relevance to managing nutrient pollution and cyanotoxin risk.

PhD Research (Project 2 - Ongoing):  Artificial Light at Night (ALAN) and Pond Metabolism: A Wavelength-Specific Floating Station Experiment

This chapter examines how artificial light at night (ALAN) affects dissolved oxygen dynamics, light attenuation, and ecosystem metabolism in TSU Farm Pond, a shallow eutrophic pond in Nashville, Tennessee. Light pollution is a growing but underexplored ecological stressor in freshwater systems, particularly with respect to primary productivity and diel oxygen dynamics. Because the pond is eutrophic and experiences large diel oxygen swings with periods of hypoxia, it offers a sensitive setting for detecting metabolic responses to nighttime light.

Custom floating experimental stations are being deployed to compare monochromatic red light, monochromatic blue light, and a no-light control. Each station isolates a defined water volume and suspends sensors at a fixed depth. Dissolved oxygen and water temperature are measured using MiniDOT loggers, underwater photosynthetically active radiation (PAR) using a LI-COR LI-192 quantum sensor, and light exposure using HOBO loggers. A shore-based station built around a Campbell Scientific CR1000X datalogger records wind speed, air temperature, barometric pressure, and relative humidity to support gas exchange modeling, and is powered by a solar charging system with an AGM battery bank. Light treatments are applied across multiple intensity levels to help identify the lower intensity threshold at which nighttime photosynthesis becomes detectable.

Gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) will be estimated from diel dissolved oxygen time series. Because artificial light modifies the assumption of darkness that underlies standard nighttime metabolism estimates, treatment effects are expected to require careful interpretation rather than direct application of conventional diel models. Wavelength-specific attenuation is also being characterized, since blue and red light are expected to differ in penetration depth and scattering behavior in turbid, chlorophyll-rich water.

This work is designed to test whether nighttime artificial light measurably alters oxygen production and consumption in a eutrophic pond, and whether the response depends on wavelength and intensity. Beyond the metabolic measurements, the project involves developing field infrastructure for controlled nighttime light manipulation in shallow freshwater systems, including floating station design, treatment isolation, sensor integration, and autonomous power and logging. Results may inform nighttime lighting guidance near urban freshwater bodies.

PhD Research (Project 1 - Completed):  Temporal Patterns of Biogeochemical Processes and Stable Isotope Dynamics in an Oligotrophic Headwater Lake

Lakes function as dynamic biogeochemical systems, yet diel and seasonal couplings between metabolic processes and geochemical signals remain poorly constrained in oligotrophic, minimally impacted environments. This study investigates the temporal patterns of ecosystem metabolism and carbon isotopes in a shallow, headwater lake in Middle Tennessee. Intensive 48-hour sampling campaigns were conducted in each of the four seasons to capture diel fluctuations in temperature, dissolved oxygen, pH, redox-sensitive metals (Fe, Mn, Al, Cu), and major ions (Ca, Mg, and HCO₃⁻). Stable isotopes (δ¹³C-DIC, δ¹⁸O-H₂O, and δ²H-H₂O) were measured to trace metabolic processes, carbon cycling, and hydrologic influences. Results reveal clear diel cycles in oxygen, pH, and δ¹³C-DIC across all seasons, with daytime photosynthetic uptake of lighter carbon isotopes and nocturnal enrichment driven by respiration. Isotopic enrichment in δ¹⁸O and δ²H during summer further suggests intensified evaporation under warmer conditions. Lake metabolism modeling shows marked seasonal contrasts, with gross primary production (GPP) and net ecosystem productivity (NEP) peaking in summer, coinciding with elevated temperatures and higher light availability. Average NEP across the four seasons is positive, indicating that the lake generally functions as a carbon sink. The amplitude of daily δ¹³C-DIC shifts is highest in spring and summer, aligning with higher autotrophic productivity. These patterns suggest a tight coupling between biological metabolism and carbon isotope fractionation in this unpolluted lake system. This study highlights the importance of integrating stable isotopes with ecosystem metabolism modeling to detect seasonal shifts in carbon cycling. It establishes a high-resolution baseline of carbon dynamics in oligotrophic freshwater systems and provides a framework for evaluating future biogeochemical responses to environmental change.

BDWD Project: Groundwater Contamination and Health Risk Assessment in Northern and Southwestern Bangladesh: Multi-Seasonal and Probabilistic Insights into Potentially Toxic Elements 

This research portfolio presents a comprehensive evaluation of groundwater contamination and associated human health risks across three hydrogeologically distinct regions of Bangladesh: the Tista Floodplain (Rangpur), the Barind Tract (Rajshahi), and the southwestern districts. The studies collectively analyzed over 425 groundwater samples across both wet and dry seasons to examine the concentration patterns of key potentially toxic elements (PTEs)—namely arsenic (As), aluminum (Al), copper (Cu), manganese (Mn), chromium (Cr), and boron (B)—using atomic absorption spectrophotometry and UV–VIS spectrophotometry.

Contamination was quantified using multiple pollution indices, including the Metal Evaluation Index (MEI), Nemerow Pollution Index (NPI), Degree of Contamination (Cd), and the Poseidon Index (PoS). The results consistently identified Mn and As as major contaminants exceeding WHO standards in most locations, particularly during the dry season. Spatial and seasonal variability was evident, with the Nilphamari and Rajshahi regions showing moderate to severe contamination levels.

Health risks were assessed using USEPA-based methodologies such as Chronic Daily Intake (CDI), Hazard Quotient (HQ), and Hazard Index (HI), with probabilistic risk modeling performed via Monte Carlo simulations (10,000 iterations, 95% CI). Results indicated that children are at greater non-carcinogenic risk than adults, with cumulative PTE exposure posing a potential health threat even when individual elements appeared within safe limits.

Advanced statistical tools including ANOVA, effect size analysis, Principal Component Analysis (PCA), and Hierarchical Cluster Analysis (HCA), were employed to identify spatial clusters and contaminant correlations. These studies underscore the urgent need for region-specific groundwater monitoring, safe tubewell zoning, and public awareness campaigns on the health implications of long-term exposure to contaminated groundwater.

Collectively, this body of work contributes to a growing body of environmental health literature and offers a scalable, data-driven framework for assessing groundwater safety in other vulnerable regions.

Master's Research: Urban and Coastal Groundwater Geochemistry in Bangladesh: Integrating Hydrochemical Characterization, Contamination Risk, and Water Quality Assessment Using Advanced Multivariate Approaches 

This portfolio presents an integrated investigation into the hydrogeochemical dynamics, contamination profiles, and water quality status of groundwater across three diverse regions of Bangladesh: urban Dhaka, coastal Hatiya Island, and surrounding peri-urban zones. Groundwater in these regions plays a vital role in sustaining drinking and irrigation demands, yet remains vulnerable to natural geogenic processes and anthropogenic pressures. Utilizing a multidisciplinary framework—combining geochemical analyses, multivariate statistics, pollution indices, and geospatial mapping—this body of work offers novel insights into groundwater quality and potential public health risks.

In Dhaka, a megacity undergoing rapid urbanization, groundwater samples revealed a dominance of calcium-bicarbonate facies, with significant contributions from cation exchange and silicate weathering. PCA and hierarchical cluster analyses attributed the variance to both natural mineral dissolution and anthropogenic sources. While Water Quality Index (WQI) values showed most samples to be suitable for irrigation, some were unsuitable for drinking.

A complementary study on potential toxic elements (PTEs) in Dhaka revealed elevated manganese (Mn) levels in over two-thirds of the samples, with hazard index (HI) values indicating higher health risks for children. Pollution indices like MEI, NPI, and Cd confirmed significant contamination despite low arsenic or chromium presence.

In Hatiya Island, groundwater was strongly influenced by saltwater intrusion and geogenic processes. Major ions and trace metals (Fe, I, Br, Mn, As) were mapped and analyzed, showing that only 40% of samples were safe for drinking, and 46% were unsuitable for irrigation. PCA and correlation analyses confirmed salinization and metal leaching as key influencing factors.

Altogether, this research underscores the urgent need for sustainable groundwater governance in both urban and coastal Bangladesh. The methodologies and findings provide a robust baseline for future monitoring, resource management, and public health interventions in hydrogeochemically sensitive zones. 

Collaborative Project: Microplastic Contamination in Industrial Soils of Bangladesh: First Assessments from Coal Mining and Manufacturing Regions 

This research portfolio highlights two of the first comprehensive investigations of microplastic (MP) contamination in industrial terrestrial environments of Bangladesh, focusing on the Barapukuria coal mining zone and the Narayanganj industrial belt. These studies fill a critical data gap in the assessment of microplastic pollution in soil systems, particularly in areas with heavy industrialization and land-use pressures.

In the Barapukuria coal mining region, twelve soil samples were collected across diverse land uses—rural, urban, suburban, and industrial. MPs were extracted using standardized density separation and sieving techniques, and identified under a stereomicroscope. Concentrations ranged from 1 to 15 items/100 g (mean: 6.75 ± 5.3), with fibers being the most dominant shape, followed by fragments and films. Land-use analysis revealed significantly higher MP abundance in industrial and coal-mining zones, compared to rural and suburban areas.

In Narayanganj, a parallel study examined 12 soil samples from urban farmlands, peri-urban areas, and industrial sites. The study recorded a total of 151 MPs (mean: 12.6 ± 7.9 particles/kg), again dominated by fibers (60.3%) with notable presence of fragments, films, and foam. Polymer identification via micro-FTIR spectroscopy revealed the prevalence of polyamide and polypropylene. Risk assessment indices placed the region within hazard categories II and III, indicating moderate to high ecological risk levels.

Together, these studies establish critical baseline data on terrestrial MP pollution in industrial Bangladesh. The integration of field-based soil sampling, microscopy, polymer identification, land-use overlays, and hazard categorization provides a scalable framework for environmental risk monitoring. The findings call for urgent policy attention and mitigation strategies to control microplastic inputs from industrial waste streams, particularly in regions where soil contamination can translate into food chain exposure and public health risks. These works serve as pioneering efforts in addressing terrestrial plastic pollution in South Asia's emerging industrial landscapes. 

Collaborative Project: Trace Element Contamination in Mining-Affected Soils: A Case Study from the Barapukuria Coal Mine Region, Bangladesh 

This study presents a focused assessment of trace element contamination in surface soils surrounding the Barapukuria coal mine, the only active underground coal mine in Bangladesh. Coal mining and associated industrial activities have raised concerns about the mobilization of potentially toxic elements (PTEs) into surrounding terrestrial ecosystems. To evaluate the severity and distribution of contamination, representative soil samples were collected from areas adjacent to the mining operations and analyzed for a range of heavy metals and radionuclides.

Pollution levels were quantified using established indices, including the Heavy Metal Pollution Index (HPI), Contamination Factor (CF), and Degree of Contamination (Cd), providing a multifaceted view of environmental risk. Elevated concentrations of sulfur (S), arsenic (As), barium (Ba), and fluoride (F) were detected, frequently exceeding maximum permissible limits. According to the HPI, over 71% of the samples fell within the "high contamination" category, aligning closely with the results obtained from Cd and CF indices. The CF provided more granularity, particularly highlighting localized hotspots of elemental accumulation.

In addition to trace metal assessments, a subset of samples was screened for radioactive elements, revealing medium-level contamination in approximately 14% of cases. Notably, 14.28% of the soil samples were highly contaminated by a combination of S, Cl, and F, suggesting both geogenic enrichment and anthropogenic influence from coal mining residues and waste disposal.

This study contributes essential baseline data for long-term monitoring and risk mitigation strategies in the Barapukuria mining region. It underscores the necessity for stricter environmental safeguards, proper waste management protocols, and soil remediation initiatives. The findings also emphasize the need for continued ecological and public health surveillance in mining-affected landscapes where the accumulation of trace elements may lead to chronic environmental degradation and exposure risks for surrounding communities.

Master's Research: Microplastic Pollution in Coastal Sediments of Bangladesh: Characterization, Polymer Profiling, and Spatial Distribution from Cox’s Bazar to St. Martin’s Island 

This portfolio presents a dual-site assessment of microplastic (MP) contamination in the coastal sediments of two ecologically and economically critical regions in southeastern Bangladesh: Cox’s Bazar and St. Martin’s Island. As coastal tourism, urbanization, and industrial activities expand, these studies provide the first spatially explicit and polymer-specific evaluations of microplastic pollution along the nation's shoreline, offering baseline data crucial for future coastal management strategies.

At Cox’s Bazar, sediment samples collected from multiple locations revealed widespread MP presence, with fiber-type microplastics (<1 mm) comprising over 70% of all particles. Visual analysis and scanning electron microscopy (SEM) were employed for morphological characterization, while attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) identified diverse polymers such as rayon, nylon, polyethylene (PE), polystyrene (PS), polypropylene (PP), and epoxy. Quantitative analysis showed the highest MP abundance at Laboni Point (111 items/100 g) and Kolatoli (97 items/100 g), indicating strong anthropogenic influence from tourism-heavy zones.

On St. Martin’s Island, 12 intertidal sediment samples showed MP concentrations averaging 20.8 items/100 g. Fiber was again the dominant type, followed by film, fragment, and foam. Polymer identification confirmed rayon, nylon, and PE as the most common constituents. Spatial differences revealed higher contamination at Uttar Para compared to Dakhin Para, reflecting growing pressures from unplanned development and tourism.

These complementary studies emphasize the ubiquity and variation of microplastic contamination in Bangladesh’s coastal ecosystems. The integration of field sampling, stereomicroscopy, FTIR-based polymer identification, and GIS-based spatial mapping allowed for comprehensive documentation of MP distribution and sources. Collectively, the findings underscore an urgent need for region-specific mitigation strategies, public education on plastic waste, and regulatory policies to manage and reduce the ecological risks posed by microplastics in Bangladesh’s fragile coastal zones.