Remediation of freshwater Irish shallow lakes using phosphorus fixing chemicals

Abstract

Phosphorus fixing chemicals have been applied to numerous shallow lakes around the world to counteract phosphorus internal loading, as it represents a rapid and simple remediation alternative. In this project, an aluminium sulphate (alum) treatment has been implemented in three shallow Irish eutrophic lakes during 2021-2022. The lakes showed a decrease in chlorophyll a after alum dosing. The chlorophyll a peaks present in summer 2021 (up to 380 μg/l) did not appear in summer 2022, with concentrations not exceeding 100 μg/l. Likewise, total phosphorus peaks experienced in summer 2021(up to 283 μg/l) did not occur one year later, suggesting a positive effect of the restoration in controlling P internal loading. Alum did not cause drops in alkalinity or pH and the increases in aluminium were only temporary. Zooplankton abundances and biomasses were not different between the predosing and the postdosing periods in any lake, suggesting a lack of toxicity of the treatment on these organisms. Fish species specimens were captured from two of the studied lakes to conduct an acid digestion of their liver, gills and muscle to determine aluminium accumulation. The three tissue types did not experience increased Al concentration after alum dosing; with liver, gills and muscle samples averaging 54, 42 and 0 (non-detectable) ug Al/g dry tissue, respectively. Al concentrations reported infish tissue were also considerably lower than the thresholds suggested by international health organizations, meaning that the fish tested still represents a safe food source. Water physicochemical variables from the lakes were also measured using drone technology in addition to the boat methodology. Both methodologies returned identical results for nine out of ten of the variables measured. The drone-assisted water sampling was 63% faster than boat methodology, safer, less manpowered and can be used in inaccessible environments, making this technology a valuable alternative for monitoring of lakes.

Thesis is embargoed until 31st August 2027

Date of Award	Aug 2025
Original language	English
Supervisor	Joerg Arnscheidt (Supervisor) & Richard Douglas (Supervisor)