In the last decades, phosphorus (P) fixing chemicals have been applied in shallow lakes to counteract eutrophication. The retention of P in the sediments and the cessation of the internal loading process are key to this technique’s success. The longevity of treatments has been varied and reasons for failures have been usually linked to inadequate control of external sources of nutrients or incorrect calculation of chemical remediation doses, among others. In this study, an aluminium sulphate (alum) restoration has been implemented in the 2021-2022 winter, in three shallow eutrophic lakes located in Ireland. The dosing of the lake’s surface was evenly performed by means of a boat that was equipped with a container which stored the alum and a chemical pump. Water quality measurements were regularly performed with a water sampler and a multiparameter sonde. The three lakes showed an immediate decrease in the chlorophyll a concentration after the alum dosing. Moreover, the summer chl a peaks, that were present in 2021 (up to 190 μg/l), didn’t appear in summer 2022, with concentrations not exceeding 30 μg/l for any of the lakes. In the same way, total phosphorus peaks experienced in summer 2021 (up to 283 μg/l) didn’t occur one year later. The alum did not trigger major alkalinity drops or pH modifications in the water column of these ecosystems. Next steps will consist of further water parameter monitoring and analysing aluminium concentrations of gills, muscle and liver in fish captured before and after the dosing to assess the potential biological impact of the restoration.

Primary Presenter: Juan Bennett, Ulster University (bennett-j7@ulster.ac.uk)

Authors:

Juan Bennett, Ulster University  (bennett-j7@ulster.ac.uk)

Richard Douglas, Ulster University  (rw.douglas@ulster.ac.uk)

Julie Campbell, Ulster University  (jm.campbell@ulster.ac.uk)

Brian Rippey, Ulster University  (bhrt.rippey@ulster.ac.uk)