Research

Our understanding of tropical aquatic ecology and the key mechanisms behind regime shifts (such as eutrophication) lags behind that of temperate systems and often hinges on assumptions formed from limited observations (Fadum and Hall 2023). My research works to correct this imbalance while advancing our broader understanding of aquatic ecosystem biogeochemistry. One unique feature of many tropical lakes is the high temperatures (> 20 °C) of the anoxic water column in lakes which maintain stable seasonal stratification. These warm and anoxic conditions support anaerobic metabolisms that are otherwise thermally constrained at higher latitudes. I am particularly interested in how this unique thermophysical structure dictates the fate of anthropogenically sourced nutrients.

In addition to my work in Honduras, I recently began a project aimed at understanding corespiration patheways and facultative metabolic potential within the microbiome of Palau’s Marine Lakes. 

Organic matter (OM) loading is a ubiquitous effect of finfish aquaculture. One important ecological implication of OM loading (whether from aquaculture or terrestrial sources) is that it alters the biogeochemical transformations that dictate the degree to which bioavailable N is retained in an ecosystem as inorganic N, or else converted to N2O (a potent greenhouse gas) or N2. The biogeochemical impacts of aquaculture (beyond bulk nutrient additions) are poorly understood and even more poorly reflected in current sustainability standards. This has led to negative environmental consequences and ecosystem degradation, even from sustainably accredited operations (Fadum et al. 2025a).

My previous research has centered on the ecosystem ecology and environmental impacts of industrial Tilapia aquaculture in Lake Yojoa, Honduras (Fadum and Hall 2022, Fadum et al. 2023, Fadum et al. 2024a). Currently, I am working on a collaborative monitoring project with a Steelhead Trout farm in Whycocomagh Bay, Nova Scotia operated by We'koqma'q First Nation. In addition to developing more refined indices of ecological impact for the farm, I am working with colleagues at Dalhousie University to use the perturbation created by the aquaculture farm to ask foundational biogeochemical questions related to N cycling (Fadum et al. 2024b). 

Eutrophication, the deleterious growth of algae fueled by excessive nutrient additions, is one of the most pervasive anthropogenically driven changes in both inland and coastal ecosystems. My research advances our understanding of the drivers of eutrophication (as well as its impact on the aquatic microbiome) by moving beyond nutrient flux quantification and developing a robust understanding of the microbially mediated biogeochemical pathways which underpin these ecosystem-scale changes. In addition to empirical observations, I use and develop numerical models to better understand the mechanisms driving trophic state change in aquatic ecosystems.

Using first principles of chemistry and our most fundamental understandings of microbial physiology, my modeling work uses the underlying half reactions of microbial metabolisms to assess N cycling dynamics under varying environmental conditions. By using redox-constrained parameters (which may be more broadly applicable than species or location-specific parameters), my model improves our understanding of N cycling, and thus eutrophication, in environments where microbial community dynamics are largely unknown (Fadum et al. 2025). Furthermore, the model provides testable hypotheses that could generate new insights from the amassed wealth of sequencing data and associated metadata from diverse aquatic environments. The model mechanistically links microbial ecology to biogeochemical fluxes by relating the relative concentrations of functional type biomasses to nutrient transformation rates and thus moves the field one step closer to being able to estimate rates from sequencing data.