Transformation and Simplification of Aquatic Vegetation Structure and Reoligotrophication of a Lake During the Last 40 Years

Abstract

The recovery or reconstruction of aquatic vegetation has recently been reported as a result of water quality improvement after anthropogenic eutrophication. The objectives of this study were: to investigate long-term trends in aquatic vegetation abundance in relation to decreasing water fertility and to present new directions in changes of the submerged aquatic vegetation structure, species richness, and biodiversity in Lake Kuźnickie (western Poland) with the perspective of the last 40 years (1978–2018). Lake Kuźnickie is an example of water quality improvement taking place without any additional reclamation measures, except a reduction in nutrient discharge into the lake from its direct catchment. Currently, the study lake represents a mesotrophic status. The Trophy State Index evidenced a decrease in the lake’s fertility compared to previous decades. The water quality improvement manifests in a significant reduction in the total phosphorus concentration. An analysis of the spatial changes in the phytolittoral evidenced a decrease in rush vegetation between 1978 and 2018 by over 2 ha. In the period 1978–2018, the aquatic vegetation structure in Lake Kuźnickie underwent significant reconstruction. Currently, charophytes play a much greater role in the lake compared to the last 40 years, contributing to the maintenance of the lake’s high water quality. Moreover, the endangered charophyte Lychnothamnus barbatus has recovered. Concurrently, however, the biodiversity and species richness of the submerged vegetation has decreased. At present, only four species dominate in the lake, including two charophytes L. barbatus , Nitellopsis obtusa , and two vascular plants Ceratophyllum demersum and Myriophyllum spicatum . Over 40 years, Lake Kuźnickie has changed from a eutrophic lake dominated by vascular plants to a mesotrophic lake with a codominant contribution by charophytes. The lake is characterized by good water quality, optimal for the development of aquatic vegetation, especially charophytes.

Impact of Nitellopsis obtusa (Desv.) J. Groves, a regionally alien and invasive charophyte, on macrophyte diversity in the species native range

“…On the contrary, as shown in the study in Lake Constance, abundant recovery of N. obtusa was observed along with re-oligotrophication of water (Murphy et al, 2018). Our research in Lake Kuźnickie (W Poland), in which N. obtusa is one of co-dominants of the lake submerged vegetation (Brzozowski et al, 2018), also revealed that the increasing share of N. obtusa in submerged vegetation and the spread of this macroalga in the form of monospecific beds coincided with a decrease in total phosphorus concentration and water quality improvement (Brzozowski et al, 2021). Co-occurrence of N. obtusa with aquatic macrophytes across environmental conditions and the native and invaded geographical range Taking into account the predictability and unpredictability of threats to local biodiversity resulting from the expansion of N. obtusa in the area where it is an invasive alien species, and changes in its distribution within the native range (Alix et al, 2017;Karol & Sleith, 2017;Larkin et al, 2018), it seems important to recognize which species may and most often coexist with the charophyte studied under certain environmental conditions.…”

Preliminary evidence of an endangered species benefiting from moderate climate warming: A palaeolimnological study of the charophyte Lychnothamnus barbatus

“…Desvaux) J. Groves. The lake water quality has improved in recent years, with the lake now classified as mesotrophic (Brzozowski & Pełechaty, 2020; Brzozowski et al, 2021).…”

“…Based on the literature (Raabe et al, 2012; Sinkevičienė & Urbaitė‐Maževič, 2012; Karol et al, 2017) and our observations (Pełechaty, Brzozowski & Pietruczuk, 2017), a research hypothesis was formulated: that environmental changes related to global warming provide a competitive advantage to the endangered and indicatory L. barbatus , favouring its spread and expansion in the littoral regions of lakes in temperate climatic zones. The present study was conducted in Lake Kuźnickie that currently hosts one of the most abundant and well‐developed populations of L. barbatus (Brzozowski et al, 2019; Brzozowski et al, 2021). The hypothesis was verified by reconstructing the history of L. barbatus in this model lake by applying an analysis of macroremains in the dated lake sediment cores in the context of climate and lake catchment changes.…”

Aegagropila linnaei Kütz. (Chlorophyta), Paludicola keratophyta (Bory) M.L.Vis et Necchi (Rhodophyta) та Lychnothamnus barbatus (Meyen) Leonhardi (Charophyta) – candidates for inclusion in the Red Data Book of Ukraine

“…Проте відзначався різними дослідниками як в оліготрофних, так і у високоевтрофних водоймах. Популяції нечисленні (Brzozowski et al, 2021).…”