A 25-year retrospective analysis of factors influencing success of aluminum treatment for lake restoration

O Agstam-Norlin,E.E Lannergård,E Rydin,M.N Futter,B.J Huser

doi:10.1016/j.watres.2021.117267

O Agstam-Norlin, E.E Lannergård + Show 3 more

Open Access

https://doi.org/10.1016/j.watres.2021.117267

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Abstract

For more than 50 years, aluminum (Al)-salts have been used with varying degrees of success to inactivate excess mobile phosphorus (P) in lake sediments and restore lake water quality. Here, we analyzed the factors influencing effectiveness and longevity of Al-treatments performed in six Swedish lakes over the past 25 years. Trends in post-treatment measurements of total phosphorus (TP), Chlorophyll a (Chl_a), Secchi disk depth (SD) and internal P loading rates (Li) were analyzed and compared to pre-treatment conditions. All measured water quality parameters improved significantly during at least the first 4 years post-treatment and determination of direct effects of Al-treatment on sediment P release (Li) was possible for three lakes. Improvements in TP (-29 to -80%), Chl_a (-50 to -78%), SD (7 to 121%) and Li (-68 to -94%) were observed. Treatment longevity, determined via decreases in surface water TP after treatment, varied from 7 to >47 years. Lake type, Al dose, and relative watershed area were related to longevity. In addition, greater binding efficiency between Al and P was positively related to treatment longevity, which has not previously been shown. Our findings also demonstrate that adequate, long-term monitoring programs, including proper determination of external loads, are crucial to document the effect of Al-treatment on sediment P release and lake water quality.

Highlights

Excess internal loading of phosphorus (P) in lakes, a result of historical sediment P accumulation from external sources, is often the most important driver of in-lake P cycling and eutrophication (e.g. Pilgrim et al, 2007, Sondergaard et al, 2003)
Nutrient-related water quality variables improved after Altreatment in all lakes (Table 2)
Al dose needs to be large enough to inactivate the entire pool of excess mobile P in the lake sediment, which drives the long term potential for internal loading

Summary

Introduction

Excess internal loading of phosphorus (P) in lakes, a result of historical sediment P accumulation from external sources, is often the most important driver of in-lake P cycling and eutrophication (e.g. Pilgrim et al, 2007, Sondergaard et al, 2003). Excess internal loading of phosphorus (P) in lakes, a result of historical sediment P accumulation from external sources, is often the most important driver of in-lake P cycling and eutrophication External P sources, e.g., leaching from agricultural soils and municipal/industrial wastewater are the primary source of excess nutrients in lakes (Conley et al, 2009). Even when external nutrient sources are controlled, recovery can be delayed by decades or longer due to the release of legacy (or mobile) P from lake sediments (Sas 1990). For more than 50 years, aluminum (Al)salts have been used to permanently inactivate excess mobile P in lake sediments and restore lake water quality (Huser et al, 2016b; Welch and Cooke 1999).

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