Soft water lakes with isoetids (SLI) are ecosystems prone to degradation due to the low buffer capacity of their waters. One of the main threats resulting from human impact is eutrophication due to agriculture, catchment urbanization and recreational use. In this paper, changes in the water chemistry and transformation of biocoenoses of one of the largest Polish SLI, Lake Jelen, over the past 30 years are presented. The lake is located within the borders of a city, and a significant part of its catchment is under agriculture and recreation use. The physicochemical (concentration of nutrients, organic matter, electrical conductivity, oxygen saturation and water pH) and biological parameters (macrophytes and phytoplankton) were measured in summer 1991, 2004, 2013 and 2018. Since the beginning of the 1990s, a gradual increase in the trophy of the lake has been observed as indicated by increased nutrient availability, deterioration of oxygen conditions and a decrease in water transparency. The alterations of water chemistry induce biological transformations, in particular, an increase in phytoplankton abundance (4-fold increase of biomass in epilimnion) as well as a gradual reduction in the range of the phytolittoral (from 10 to 6 m), a decrease in the frequency of isoetids, Lobelia dortmanna and Isoetes lacustris, and expansion of plant species characteristic for eutrophy.

中文翻译：

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人类影响对等水类软水湖水质和生物群落的影响：波兰西北部耶伦湖

具有isoetids (SLI) 的软水湖是由于其水域的低缓冲能力而易于退化的生态系统。人类影响造成的主要威胁之一是农业、集水区城市化和娱乐用途造成的富营养化。在本文中，介绍了过去 30 年来波兰最大的 SLI 之一耶伦湖的水化学变化和生物群落的转化。该湖位于城市边界内，其流域的很大一部分用于农业和娱乐用途。1991 年、2004 年、2013 年和 2018 年夏季测量了物理化学（营养物质浓度、有机物浓度、电导率、氧饱和度和水 pH 值）和生物参数（大型植物和浮游植物）。 自 1990 年代初，养分供应增加、氧气条件恶化和水透明度降低表明，湖的奖杯逐渐增加。水化学的改变引起生物转化，特别是浮游植物丰度的增加（浮游生物量增加了 4 倍）以及沿海植物的范围逐渐缩小​​（从 10 到 6 m）， isoetids、Lobelia dortmanna 和 Isoetes lacustris 的频率，以及富营养化特征的植物物种的扩展。