Constraints on the biological recovery of the Bohemian Forest lakes from acid stress

Abstract

Summary The response of planktonic (phytoplankton, ciliates, rotifers and crustaceans) and littoral (Ephemeroptera, Plecoptera, Trichoptera and Heteroptera: Nepomorpha) assemblages to chemical recovery was studied over a twelve‐year period (1999–2011) in eight glacial lakes in the Bohemian Forest (central Europe). The region suffered from high atmospheric pollution from the 1950s to the late 1980s, but has since been recovering from acidification due to 86% and 44% decrease in sulphur and nitrogen deposition, respectively, during the 1990s–2000s. Despite the rapid improvement in water chemistry of all the eight studied lakes, only four have partly recovered so far (low‐aluminium lakes), while the other four lakes still remain strongly acidic (high‐aluminium lakes). All present lake assemblages are dissimilar by 40–90% from those during the early phase of chemical recovery as a result of species (re)colonisation (ciliates, crustaceans and insects) in the high‐Al lakes, and considerable species replacement (zooplankton) and (re)colonisation (insects) in the low‐Al lakes. Phytoplankton remained very similar in the high‐Al lakes, but changed (loss and/or replacement of some acid‐tolerant species) in the low‐Al lakes. Aluminium (Al) concentrations were dominant in structuring the assemblages of phytoplankton, rotifers and Nepomorpha, but also affected crustaceans through the seston carbon to phosphorus (P) ratio. Both direct (toxicity) and indirect (P availability) effects of Al control biological recovery in the Bohemian Forest lakes. A concentration of 200 μg L−1 of total Al is the main barrier preventing the high‐Al lakes from recovery. In contrast, pH and total P rather than Al significantly influenced Ephemeroptera, Plecoptera and Trichoptera. Although biotic responses (especially in the low‐Al lakes) showed important signs of recovery, such as reappearance of some indigenous or acid‐sensitive species, decline in eurytopic acid‐tolerant species and colonisation by vagile species, the assemblages of all the lakes still suffer from acid stress. Our results also indicate an increasing role of biotic interactions between colonisers and residents leading to the reconstruction of aquatic food webs in the low‐Al lakes.

High turnover rates of aerobic anoxygenic phototrophs in European freshwater lakes

“…A much different situation has been found in Lake Ple sn e. This mountain lake suffered from a strong acidification due to the acid rains during the second half of the 20 th century. The drop in water pH caused the release of aluminum ions from the bedrock, resulting in the extiction of all the crustacean zooplankton species (Vrba et al, 2016). Nowadays, the lake contains high biomass of filamentous bacteria (Vrba et al, 2003) composed mostly of AAP bacteria (see Supporting Information Fig.…”

“…13°51'55” E) at an altitude of 1090 m a.s.l. The lake was heavily impacted by acid rains between the 1960's until the 1980's, which led to a strong acidification with water pH values of 4.0‐4.8 and the complete extinction of any crustacean zooplankton as well as fish (Vrba et al, ). The absence of these grazers resulted in its mesotrophic character with a relatively high standing stock of phytoplankton and unusual filamentous bacteria (Vrba et al, 2003) leading to a low water transparency (Secchi depth ∼ 1 m).…”

European aquatic ecological assessment methods: A critical review of their sensitivity to key pressures

“…Acidification is a problem most often reported from rivers and lakes in Northern Europe, especially Scandinavian countries, UK and Ireland ( Aherne and Curtis, 2003 ; Posch et al, 2019 ). However, a recent study has shown that acidified surface waters may occur particularly in the following regions ( Austnes et al, 2018 ): the Pyrenees, border regions of Belgium, Luxembourg, France and Germany, mountainous regions on the borders of the Czech Republic (see Oulehle et al, 2017 ), Germany and Austria (see Vrba et al, 2016 ), the Tatra Mountains, the Italian Alps and northern Croatia.…”

Effects of tree dieback on lake water acidity in the unmanaged catchment of Plešné Lake, Czech Republic

“…Hence, we do not expect dramatic changes in lake water acidity after the decreased leaching of NO 3 − and P during forest regeneration. In contrast, a slow increase in water pH and ANC can be expected due to continuing ecosystem recovery from acidification (Oulehle et al ), similarly to other less acidified lakes in the same region (Vrba et al ).…”

“…This situation differs from that in Rachelsee (another acidified lake in the same mountain area) where zooplankton recovery remarkably accelerated after tree dieback in its catchment (Vrba et al ). In Plešné Lake, two invertebrate predators, the introduced C. abyssorum together with original acid‐tolerant Heterocope saliens , reduced the rotifer abundance by three orders of magnitude until 2011 (Vrba et al ). More recent data, however, suggests an increase in rotifer abundance (Šorf M., pers.…”