Lee, Yao-Han (2023) Zostera muelleri as a bioindicator of heavy metal pollution in marine ecosystems. PhD thesis, Victoria University.

Abstract

Seagrass has been shown by previous researchers, over four decades, to be a useful bioindicator of heavy metal pollution in marine environments. Despite the large data base resulting from these studies to date there has been no method for exploiting this data in its entirety for the monitoring of sites in general and for identifying pollution events. This project has devised and tested a simple, standard method to identify heavy metal pollution in different marine environments. The assay is based on the benchmarking of any given set of analytical data for heavy metal levels in whole-plant seagrass tissue against heavy metal concentration magnitude ranges, derived from the totality of the available international data. Notably, this subsumes the broad range of geographical locations, climatic conditions, different seagrass species and the different plant organs analysed, that are inherent in the available data sets. Thus, magnitude criteria have been established for “normal” (background) versus “elevated” and “polluted” levels for the “anthropogenic” metals, As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn. Concurrently, an experimental case study was devised and carried out to implement and test the devised assay. Employing the regional seagrass species Zostera muelleri (Eelgrass), samples were collected from locations in Port Phillip Bay (PPB), Western Port (WP) and Corner Inlet (CI) over a five-year period, from 2015 to 2020, across six seasons, and were processed and analysed for their heavy metal content by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). According to the derived assay, the metal levels found in the case studies carried out for the three bays, were compared to the totality of the international database. Notably, of the six seasonal periods, Winter 2018 data (except for Cu and Mn) showed evidence of a gross heavy metal contamination event, affecting all bays. Therefore, the data for the other seasons have been compared separately from that of the “aberrant” Winter 2018 season. This study has found that for all seasons and across all bays, As was very highly elevated and Cd and Pb significantly elevated. For As and Pb, PPB and WP were comparable, with CI being less affected for both metals. For Cd, the pollution levels were comparable across all three bays. For all seasons, Co was also generally elevated across the bays, except for (all bays) Summer 2015/16 and PPB Autumn 2019, with CI being less affected overall. Generally, over all seasons and bays, Cr levels were not highly elevated. However, a slight elevation was observed for WP and CI Summer 2019/18, PPB and WP Autumn 2019 and WP Winter 2019. PPB and WP appear more affected than CI. Cu levels were within background for all seasons, except for Summer 2015/2016, where a slight elevation was observed for PPB and CI. Generally, the Cu levels for PPB > WP > CI. For all seasons, Mn levels were well within background across all the bays and tended to be lower in WP than in PPB or CI. Across all seasons, Ni levels were well within background across all the bays, with the levels for PPB and WP being comparable and the levels for CI being consistently lower. For all seasons, Zn levels across all the bays were essentially within background, with evidence of a slight elevation in PPB Summer 2015/16. There was a progressive increase in Zn levels for WP from Spring 2018 to Winter 2019, with a slight elevation being evident for the latter season.

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