Lake Balaton, the largest lake in Central Europe, underwent severe eutrophication from the 1960s to the 1990s, due to phosphorus loadings from external anthropogenic sources. The subsequent and complex eutrophication control and lake restoration program resulted in a significant decrease in the external phosphorus loading to the lake. Consequently, Lake Balaton has been returning to its former meso-eutrophic character. In this paper, we explore the long-term dynamics of chlorophyll a (Chl a) concentration, a proxy for phytoplankton biomass, and zooplankton biomass in Lake Balaton during its re-oligotrophication period from 2001 to 2017, and attempt to draw some conclusions on the subsequent changes in the fish stock. We found a proportional decrease in zooplankton and phytoplankton biomasses at moderate phytoplankton levels. However, below a certain phytoplankton concentration (< 10 μg l−1 Chl a), the decrease in phytoplankton biomass was not coupled with a further decline in zooplankton biomass because the fraction of small phytoplankton, edible for zooplankton, showed a much smaller decrease in biomass compared with large non-edible phytoplankton. Thus, improvements in water quality (i.e., reduced nutrient loading), partly via concomitant changes in the phytoplankton size distribution, did not cause a large difference in the fish stock in this shallow lake.

中文翻译：

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巴拉顿湖 20 年来的贫营养化及其对浮游植物和浮游动物生物量之间关系的影响

由于外部人为来源的磷负荷，中欧最大的湖泊巴拉顿湖从 1960 年代到 1990 年代经历了严重的富营养化。随后复杂的富营养化控制和湖泊恢复计划导致湖泊外部磷负荷显着下降。因此，巴拉顿湖已经恢复到以前的中型富营养化特征。在本文中，我们探讨了 2001 年至 2017 年巴拉顿湖再贫营养化期间叶绿素 a (Chl a) 浓度（浮游植物生物量的代表）和浮游动物生物量的长期动态，并试图得出一些结论鱼类种群的后续变化。我们发现浮游动物和浮游植物生物量在中等浮游植物水平下成比例减少。然而，低于一定的浮游植物浓度（< 10 μg l−1 Chl a），浮游植物生物量的减少并不伴随浮游动物生物量的进一步下降，因为与浮游动物可食用的小型浮游植物相比，生物量的下降幅度要小得多含有大量不可食用的浮游植物。因此，部分由于浮游植物大小分布的伴随变化而导致的水质改善（即减少营养负荷）并没有导致这个浅湖中鱼类种群的巨大差异。