Plankton and Chemical–Physical Development in Six Swedish West Coast Lakes under Acidic and Limed Conditions

Abstract

Increases in pH from 4.5–5.3 to 7–7.6 after liming (1978–85) in six acidified lakes in the west coast area of Sweden caused increased concentration of humic compounds and decreased transparency compared with levels before liming. Concentrations of total P increased markedly whereas those of NO3-N decreased. The phytoplankton composition changed completely in all lakes shortly after liming, but a species richness similar to that in unacidified lakes was not reached until after 2–5 yr, and in the previously most acidified lakes, several species remained absent. The composition of the phytoplankton indicated increased primary production. The volumetric dominance within the zooplankton shifted generally from Eudiaptomus–Holopedium to Cyclops–Daphnia. The occurrence of Rotatoria and Cladocera species increased and the composition became similar to that in unacidified lakes 2–5 yr after liming. The biotic development is largely explained by chemical–physical changes such as increased pH, reduced Al concentration, increased P concentration, and increased organic content, particularly humus.

Development of subfossil Daphnia and Chaoborus assemblages in relation to progressive acidification and fish community alterations in SW Sweden

“…The genus Daphnia is an important biological indicator in this respect since their ephippia are easily detected during analysis of sediment samples and since most species are considered acid-sensitive (Brett, 1989). There may be differences between Daphnia species in sensitivity to acidification but in SW Sweden all Daphnia are usually lost in clear-water lakes with pH below 5.3-5.7 (Hörnström et al, 1984(Hörnström et al, , 1993.…”

Zooplankton response to long-term liming: Comparison of 15 limed and 15 reference lakes in Sweden

“…Mean zooplankton biovolume in the lakes included in the study ranked limed4neutral4 acid but was not significantly different between lake groups. It is important to note that this is a result for a period far away from initial liming (418 years), which may contradict earlier results gained within few years after initial liming which often showed significantly higher biomasses (Brett, 1989;Ho¨rnstro¨m et al, 1993;Nyberg, 1998;Stenson & Svensson, 1995) but also lower biomasses (Brett, 1989;Dillon, Yan, Scheider, & Conroy, 1979;Schaffner, 1989). However, despite of lacking differences in total biomass, there were structural differences between the communities of acid and neutral lakes indicated by different shares of the major taxonomic groups (Rotatoria, Cladocera and Copepoda) so that acid lakes hosted more abundant rotifer communities relative to both cladocerans and copepods.…”

“…2). Although knowledge of expected communities of nonacid Swedish lakes is still incomplete, different regional studies (Ho¨rnstro¨m, Ekstro¨m, Fro¨berg, & Ek, 1993;Pejler, 1965) indicate that the achieved communities in limed lakes are the expected ones, given their position in an altitudinal and latitudinal gradient. These gradients also affect the total species number in the neutral and ISELAW lakes so that the expected number of taxa typically spanned 15-20 in northern Sweden and 20-25 in southern Sweden (Persson & Ekstro¨m, 2001).…”

Discostella tatrica sp. nov. (Bacillariophyceae) - a small centric diatom from the Tatra Mountain lakes (Slovakia/Poland).

“…One explanation for the Discostella distribution in the Tatras is probably its requirement for neutral pH (higher levels of ANC). Indeed, several previous studies have demonstrated the absence of centric diatoms in acid lakes and subsequent re-colonization after lake water pH increases (hörNström et al 1993;hörNström 1999). Therefore, centric diatoms could indicate the recovery of lakes from acidification.…”