Mahir Tajwar

Ph.D. Candidate, Earth & Environmental Sciences
Vanderbilt University

Environmental geochemistry & aquatic biogeochemistry

I am a Ph.D. candidate in Earth & Environmental Sciences at Vanderbilt University (Ayers Geochemistry Lab). I study how carbon and nutrients cycle through freshwater systems, and what those cycles reveal about the biological and geochemical processes driving them. My work pairs intensive field observation with stable isotope geochemistry and quantitative modeling, across two Middle Tennessee systems that sit at opposite ends of the trophic spectrum. My dissertation examines diel and seasonal carbon dynamics in an oligotrophic headwater lake, the effects of artificial light at night on aquatic metabolism, and phosphorus cycling in a eutrophic pond.

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Research

Carbon cycling & stable isotopes

Tracing diel and seasonal carbon dynamics and their links to freshwater ecosystem metabolism. Repeated 48-hour campaigns across four seasons at Stephens Lake resolve the daily rhythms that infrequent sampling averages away, using carbon isotopes to separate biological activity from carbonate chemistry.

Artificial light at night

Examining how altered light regimes influence dissolved oxygen and aquatic metabolism. Floating experimental stations compare red light, blue light, and unlit controls at several intensities, testing whether nighttime illumination measurably shifts oxygen production and consumption in a shallow pond.

Nutrients & phosphorus

Investigating nutrient availability and geochemical exchange between water and sediment. Direct porewater sampling at the sediment interface captures the reducing conditions that release phosphorus back into the water column, sustaining algal growth long after external inputs are controlled.

Recent publications

Recent Highlights

Mahir Tajwar receiving first place in the doctoral poster competition at TWRS 2026.

TWRS 2026 · First Place

April 16, 2026
Doctoral Student Poster Competition

Coupled Carbonate Equilibrium and Metabolic Controls on δ¹³C-DIC Variability in Freshwater Ecosystems

Tennessee Water Resources Symposium

Freshwater carbon preprint

With John C. Ayers · 2026

Coupled carbonate equilibrium and metabolic fractionation drive δ¹³C-DIC variability in freshwater ecosystems.

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AGU 2025

Presenting freshwater carbon research and discussing biogeochemical processes with the geoscience community.

PNAS Nexus article: Mitigating artificial light at night, effectiveness of policies and implications for plant phenology, 2026.

PNAS Nexus · 2026

Mitigating artificial light at night: policy effectiveness and implications for plant phenology. Geist et al., including Tajwar.

GSA Gould Research Grant

2024 · Research support for my doctoral work in freshwater biogeochemistry.

TWRS 2025 · People’s Choice

Graduate Student Poster Presentation, Tennessee Water Resources Association. Research on diel biogeochemical dynamics in an oligotrophic lake.

Google Scholar · ORCID · LinkedIn · ResearchGate