Evaluation of aluminum treatment efficiency on water quality and internal phosphorus cycling in six Danish lakes

Abstract

If dosed sufficiently relative to the pool of excess phosphorus (P) in the lake sediment and lake water, aluminum (Al) is hypothesized to block sediment P release and thereby improve water clarity in eutrophic lakes. Aluminum has been used in [200 lakes worldwide, but in some 30% of the known cases water clarity did not improve beyond the first year, likely because of underdosing or continued high external P loading. We evaluate the viability of the aluminum dosing hypothesis for six Danish lakes that received Al in a molar ratio of \2-10 relative to the potentially mobile P pool. Lake water total P declined to values that could be predicted from the external P loading but increased again in the two lakes receiving the lowest Al doses. Lasting ([2-3 years) improvement of water clarity was only observed in two lakes. Sediment P release rates, which were measured in four lakes, declined significantly but then increased gradually again in the two lakes receiving the lowest doses. We conclude that if external P-loading is sufficiently low, lasting improvement of water quality can be obtained if Al is dosed 10:1 or higher relative to the size of the mobile P pool.

Preface: Advances in phosphorus inactivation

“…Empirically, it has been suggested that Al doses must be at least 10 times the targeted P mass (Jensen et al 2015, Huser et al 2016b. A minimum ratio of Al:P mass of 10:1 is supported by treatment results from Cape Cod, Massachusetts , whereas higher Al:P ratios may be necessary to overcome interferences and inefficiencies in some lakes (Huser 2017, James 2017.…”

“…Certainly continued inputs from watersheds are important, and gradual burial of the treated sediment will lead to renewed internal loading, but that process seems to be slow in stratified lakes and where the watershed:lake area ratio is low (Huser et al 2016b). Two internal mechanisms that control internal P loading after treatment are upward migration of P from below the inactivated zone in the sediment (Lewandowski et al 2003, James 2017) and release from organic matter through decay (Jensen et al 2015). Both can be important P sources and are likely to contribute in most lakes.…”

How to combat cyanobacterial blooms: strategy toward preventive lake restoration and reactive control measures

“…Important issues are the choice of appropriate P adsorptive, dose, and the longevity of an application (Zamparas and Zacharias 2014). Longevity might be impaired by low doses (Cooke et al 2005;Jensen et al 2015), chemical aging (Søndergaard et al 2007;de Vicente et al 2008), or physical redistribution in lake sediment. A single big dose might be less effective than smaller doses due to aging of the active compound (de Vicente et al 2008;Jensen et al 2015).…”

“…Longevity might be impaired by low doses (Cooke et al 2005;Jensen et al 2015), chemical aging (Søndergaard et al 2007;de Vicente et al 2008), or physical redistribution in lake sediment. A single big dose might be less effective than smaller doses due to aging of the active compound (de Vicente et al 2008;Jensen et al 2015). Douglas et al (2016) reviewed solid-phase phosphorus adsorbents, categorized in: naturally occurring minerals, soils, suspended particles or earth materials; natural or synthetically produced materials; modified clay mineral or soils; and mining, mineral processing, and industrial by-products.…”

Longevity and effectiveness of aluminum addition to reduce sediment phosphorus release and restore lake water quality

“…Aluminum (Al)-salts have been used to reduce P cycling in lakes around the world for nearly half a century (Landner, 1970;Kennedy et al, 1987;Cooke et al, 2005;Jensen et al, 2015). The success of past treatments has varied greatly, with studies showing longevity of water quality improvements ranging from months to 20 years (Welch and Cooke, 1999).…”