Date of Award
5-2024
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
Huan Feng
Committee Member
Yang Deng
Committee Member
Duke Ophori
Committee Member
Qingzhi Zhu
Abstract
Toxic metal pollution is a leading environmental concern for aquatic systems globally and remedial dredging has been widely employed to mitigate its harmful impacts. In terms of the short-term impacts of remedial dredging, mixed results are reported in several studies. Despite its immediate negative impacts including saturation of water with toxic metals, increased turbidity, and sediment resuspension, positive impacts can be recorded over a stabilization period of 6 – 24 months after dredging. Nevertheless, the sustainability of these recorded positive effects cannot be ascertained as some studies have reported long-term regression in remediated sites’ conditions. Evaluation of success determinants, site-measure compatibility, and determination of supplementary measures are key to achieving and sustaining the projected benefits of remedial dredging and justifying its overall cost. This multi-component study reviewed published literatures that documented the outcomes of short- and long-term dredging projects in toxic metal-polluted systems globally with a broad goal of examining how sediment removal impacts toxic metal dynamics in the aquatic system and understanding why the sustenance of positive impacts is controversial. In the meantime, this study also explored the preventative and remedial management strategies for attaining and sustaining positive dredging outcomes. The purpose of this study is to provide key recommendations for decision-making and policy development in aquatic toxic metal remediation.
Surface sediments form an integral component of freshwater ecosystems and they are a major sink-and-source for toxic pollutants, providing a reliable indication of a water body’s integrity. Distinct freshwater sediment investigations have informed the conclusions made about the ecological and pollution status of aquatic systems worldwide, but a widespread evaluation of the global status of freshwater sediments is lacking. From our perspective, an extensive environmental analysis of the available published data can address this need and improve our wholesome understanding of toxic metal impacts on global freshwater systems. Thus, surface sediment metal data collected from 149 freshwater sites in 32 countries were systematically analyzed using standard environmental indices (e.g. geoaccumulation index, modified hazard quotient, enrichment factor, etc.) and multivariate statistical methods (MSA). Average concentrations of all the metals except cobalt and zinc exceeded the recommended limits. Arsenic, cadmium, and mercury registered the highest frequency of severe pollution impacts on 29 – 69% of the sites. 4 to 31% of the studied sites recorded considerable to severe aquatic biota risk majorly from arsenic, cadmium, chromium, and nickel while 65% of the sites recorded severe ecological risk (CSI > 5, RI ~ 600). A high linear correlation with low ordination stress (R2 = 0.93, Stress = 0.023) from non-metric multidimensional scaling agreed with the Pearson correlation analysis results, while principal component analysis revealed four major components that explained 89% of the data variance. Source enrichment investigation indicates that pollution is a result of geogenic and anthropogenic contributions. The common anthropogenic sources among study sites include industrial and municipal wastewater and sewage, agriculture, surface runoff, fossil fuel emissions, and mining activities. The study can serve as a reference for future pollution studies, create extensive awareness of the dire ecological status of freshwater systems, and ultimately elicit site-specific remediation and mitigation action plans from policymakers.
While several studies have reported success with remedial sediment dredging, the sustainability of these impacts remains unclear. This preliminary study aimed to investigate the short- and long-term effects of remedial dredging on metal contamination, dredging efficacy and ecological status of the Lower Passaic River. To accomplish this, pre- and post-dredging data were statistically analyzed and evaluated using geochemical indices. Short-term results show effective heavy metal reduction although their concentrations became elevated in the water column, increasing bioaccumulation risk in aquatic biota. In the long term, metal concentrations increased in surface sediments. Ecological assessment revealed that Cu, Hg, and Pb pose greater risks while Ag remained abundant despite dredging. Further investigation suggests that post-dredging residuals, surface runoff, and sewage pollution may contribute significantly to recontamination and continued pollution. Depletion in long-term dredging efficacy from spring to summer suggests that season-influenced changes in temperature, algae growth, and stormwater discharge may have played a role.
File Format
Recommended Citation
Soetan, Oluwafemi, "Evaluation of Heavy Metal Pollution, Water Quality, and the Effectiveness of Remedial Sediment Dredging in the Lower Passaic River, New Jersey" (2024). Theses, Dissertations and Culminating Projects. 1483.
https://digitalcommons.montclair.edu/etd/1483
