Date of Award
5-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
College/School
College of Science and Mathematics
Department/Program
Earth and Environmental Studies
Thesis Sponsor/Dissertation Chair/Project Chair
Nina Goodey
Committee Member
Yang Deng
Committee Member
Jessica Hua
Abstract
Freshwater ecosystems are increasingly exposed to co-occurring anthropogenic stressors, especially pesticides and road de-icing salts. However, their individual and combined effects on water quality, nutrient cycling, and primary producers are not well synthesized. This dissertation combines two critical reviews with meta-analysis and factorial microcosm experiments to assess how chemical contaminants and salinization alter freshwater ecosystem structure and function. The first review compiles evidence that road salts (NaCl, CaCl2, MgCl2) disrupt thermal stratification, decrease benthic respiration, alter dissolved oxygen levels, increase turbidity, and change pH. These physicochemical changes affect pesticide persistence, degradation, sorption behavior, and bioavailability, thus influencing toxicity pathways and nutrient processing. The second review focuses specifically on phytoplankton, showing that pesticides interfere with photosystem II, inhibit carbon fixation, and reduce growth, while salinity causes osmotic stress, ionic imbalances, and oxidative damage. Combined exposures modify membrane permeability and pesticide solubility, often resulting in non-additive effects and shifts in community composition toward salt- or contaminant-tolerant species, with implications for primary production and trophic transfer. A meta-analysis was conducted to assess variability in algal sensitivity to pesticide groups. Standardized 96-h inhibition data for Selenastrum capricornutum indicated strong chemical class-dependent effects, with the highest inhibition observed for inorganic compounds (g = −3.52) and natural-product-derived compounds (g = −3.13), compared to weaker effects for nitrogen-rich heterocycles (g = 0.23), organophosphates (g = 0.09), and synthetic auxins (g = 0.15). The overall pooled effect was not statistically significant, indicating high heterogeneity across chemical classes. A series of multi-stressor microcosm experiments examined the individual and interactive effects of pesticides and road salt on freshwater primary producers and water quality. In atrazine (1–5 μg L⁻¹) with NaCl (120–230 mg L⁻¹), chlorophyll synergistically increased across combined treatments without changes in cell abundance, indicating physiological decoupling. In atrazine (50–100 μg L⁻¹), cypermethrin (50 μg L⁻¹), and NaCl (860 mg L⁻¹) exposures, significant interaction effects were observed for chlorophyll, including Atrazine × Cypermethrin (p < 0.001) and Atrazine × NaCl (p < 0.001), with a strong increase under the tertiary mixture (p < 0.001). Additionally, significant reductions in total nitrogen and CDOM were observed under the three-way mixture (p < 0.001). In ProcellaCOR (10–50 μg L⁻¹) and NaCl (860 mg L⁻¹) systems, salinity significantly reduced chlorophyll, lipids, biomass, and cell abundance in Scenedesmus obliquus (p < 0.001), while in Synechococcus elongatus, chlorophyll exhibited a significant interaction effect between florpyrauxifen-benzyl and salinity (p = 0.004), with declines occurring only under the high-concentration mixture. Cyanobacteria exhibited greater tolerance to salinity than green algae, particularly in maintaining cell abundance. Overall, this dissertation shows that salinization often acts as a primary ecological filter, while pesticide effects are chemical-specific and strongly context-dependent. Algal and cyanobacterial responses to chemical mixtures depend on thresholds, are species-specific, and are mechanistically linked to both physiological stress and nutrient dynamics. These findings highlight the importance of integrated multi-stressor approaches for predicting freshwater ecosystem responses to rising chemical and osmotic pressures.
File Format
Recommended Citation
Ahmed, Arif, "Effects of Independent and Combined Anthropogenic Stressors on Freshwater Ecosystems" (2026). Theses, Dissertations and Culminating Projects. 1721.
https://digitalcommons.montclair.edu/etd/1721