Although the treatment of eutrophied lakes with aluminium (Al) compounds has been established for more than 40 years, publications reporting on long-term consequences for phytoplankton are rare. Here we present observations from Lake Barleber for the period 1985–2016. The lake was treated in autumn 1986 because of high phosphorus (P) concentrations and cyanobacteria blooms, which limited the lake's recreational use. Within six weeks 480 t of Al sulphate solution (37 t of Al) were applied to the lake. This was equivalent to a dose of 36 g Al³⁺ m⁻² or 5.7 mg Al³⁺ L⁻¹. Already after having applied half of the Al sulphate, the concentration of soluble reactive phosphorus (SRP) reached its analytical limit of quantification (3 μg L⁻¹). Removal rates calculated after completion of the treatment were 98% for SRP and 90% for total phosphorus (TP). In the following 13 years from 1987 to 1999, cyanobacteria were almost absent. In the years 2000 to 2003 as well as in 2005 and 2014 they appeared in low abundances. In the period 1987–2014, almost complete absence of cyanobacteria and high transparency provided good conditions for recreational use of Lake Barleber. Compared to pre-treatment conditions, phytoplankton biomass increased temporarily from 1987 to 2016. This increase in biomass did not interfere with the use for bathing and swimming, because phytoplankton community composition changed towards a dominance of chlorophytes and dinophytes. In 2016, however, P concentration and cyanobacterial biomass rose again to the level of the last pre-treatment years (TP 134 μg L⁻¹, cyanobacterial biomass 1 mg L⁻¹; averages for the period May–October). We conclude that Al treatment is effective and can last for decades. For recreational lake use, the effects of the alum treatment on phytoplankton community composition showed to be more important than its effects on total phytoplankton biomass.

尽管用铝（Al）化合物处理富营养化湖泊已有40多年的历史，但很少有报道对浮游植物造成长期影响的出版物。在这里，我们介绍了1985-2016年Barleber湖的观测资料。由于高的磷（P）浓度和蓝细菌的花开，1986年秋天对该湖进行了处理，这限制了湖的娱乐用途。在六周内，将480吨硫酸铝溶液（37吨铝）应用于湖泊。这相当于36 g Al ³⁺ m ^-2或5.7 mg Al ³⁺ L ^-1的剂量。在使用一半的硫酸铝后，可溶性反应性磷（SRP）的浓度已达到其定量分析极限（3μgL^-1）。处理完成后计算的去除率，SRP为98％，总磷（TP）为90％。在从1987年到1999年的接下来的13年中，几乎没有蓝细菌。在2000年至2003年以及2005年和2014年，它们的数量很少。在1987-2014年期间，几乎完全没有蓝细菌和高透明度，为休闲使用Barleber湖提供了良好条件。与预处理条件相比，浮游植物的生物量在1987年至2016年间暂时增加。由于浮游植物的群落组成朝着绿藻类和藻类植物的优势发展，生物量的增加并未干扰沐浴和游泳的使用。然而，在2016年，磷的浓度和蓝细菌生物量再次上升至最近的预处理年份（TP 134μgL^-1，蓝藻生物量1 mg L ^-1 ; 5月至10月的平均值）。我们得出结论，铝的治疗是有效的，可以持续数十年。对于休闲湖的利用，明矾处理对浮游植物群落组成的影响比对浮游植物总生物量的影响更为重要。