Quantitative responses of lake phytoplankton to eutrophication in Northern Europe

Abstract

Based on the currently largest available dataset of phytoplankton in lakes in northern Europe, we quantified the responses of three major phytoplankton classes to eutrophication.Responses were quantified by modeling the proportional biovolumes of a given group along the eutrophication gradient, using generalized additive models. Chlorophyll-a was chosen as a proxy for eutrophication because all classes showed more consistent responses to Chlorophyll-a than to total phosphorus.Chrysophytes often dominate in (ultra-) oligotrophic lakes, and showed a clear decrease along the eutrophication gradient. Pennate diatoms were found to be most abundant at moderate eutrophication level (spring-samples). Cyanobacteria often dominate under eutrophic conditions, especially in clear-water lakes at chlorophyll-a levels > 10 µg L -1 (late summer samples).We compare the relationships among types of lakes, based on the lake typology of the northern geographic intercalibration group, and among countries sharing common lake types. Significant differences were found especially between humic and clear-water lakes, and between low-and moderately alkaline lakes, but we could not identify significant differences between shallow and deep lakes.Country-specific differences in response curves were especially pronounced between lakes in Norway and Finland, while Swedish lakes showed an intermediate pattern, indicating that countryspecific differences reflect large-scale geographic and climatic differences in the study area.REBECCA MS no.04

Cyanobacterial blooms: Statistical models describing risk factors for national-scale lake assessment and lake management

“…Supporting evidence of a relationship between nutrient enrichment and cyanobacterial abundance is largely derived from long-term studies of enrichment at a few selected individual sites, usually lowland, alkaline, eutrophic lakes, and often examining individual cyanobacterial species. There have been a few published studies examining the relative % abundance of cyanobacteria across eutrophication gradients in large datasets (Downing et al, 2001;Ptacnik et al, 2008), but a more comprehensive quantitative analysis of what factors affect actual cyanobacterial abundance across a wide range of lake types at a regional or national scale has not been carried out.…”

Water colour, phosphorus and alkalinity are the major determinants of the dominant phytoplankton species in European lakes

“…Common ways to cope with this complexity is to "boil it down" to major taxonomic groups (e.g. Duarte et al, 1992;Ptacnik et al, 2008), functional groups (Reynolds et al, 2002, Padisák et al, 2003 or strategist groups (Grime, 1979;Reynolds, 1988) or to calculate various indices to characterize different aspects of the community structure, such as diversity (Shannon, 1948;Simpson, 1949;Margalef, 1958) or evenness (Pielou, 1975). For many purposes even the simplest parameter, the number of species (Hill, 1973), may be the most useful measure of local or regional diversity.…”

“…Table 1. Examples of broad-scale studies on phytoplankton community composition Scope of study Selection of lakes Reference Gradients in phytoplankton community structure with increasing lake trophic status 165 lakes in Florida Duarte et al (1992) Patterns in phytoplankton taxonomic composition across lakes of differing nutrient status 91 temperate lakes Watson et al (1997) Responses of three major phytoplankton classes to eutrophication 850 lakes from Scandinavia and the United Kingdom Ptacnik et al (2008) Relationship between phytoplankton species richness and productivity including six major taxonomic groups 33 well-studied lakes on different continents Dodson et al (2000) Geographic gradients in phytoplankton biodiversity at species-level over a continental scale 540 lakes and reservoirs on the continental U.S. Stomp et al (2011) Community structure of summer phytoplankton 73 nutrient-poor Swedish lakes Willén et al (1990) Dominant species and functional assemblages in late summer phytoplankton 80 Hungarian small shallow lakes Padisák et al, 2003 Type-specific and indicator taxa of phytoplankton as a quality criterion for assessing the ecological status 55 Finnish boreal lakes Lepistö et al (2004) In Europe the implementation of the Water Framework Directive (Directive, 2000) has given a new impetus to freshwater ecological studies at species and community level and the need for comparisons over broad geographical ranges shifted to the forefront of research. Chemical and biological data from more than 5,000 lakes in 20…”

Ecological threshold responses in European lakes and their applicability for the Water Framework Directive (WFD) implementation: synthesis of lakes results from the REBECCA project

“…4 Ecological status class boundaries (high/good (H/G): vertical blue line, and good/moderate (G/M): vertical green line) for the Northern lowland lake type L-N1 (moderate alkalinity, clear-water lakes) agreed by all countries in the Northern intercalibration group (NGIG) based on response curves for major phytoplankton group indicators, expressed as proportion of total biovolume (y-axis) along the trophic gradient, expressed by chlorophyll a (Chl-a, unit lg/l, x-axis). The response curves are based on results given by Ptacnik et al 2008, this issue and the indicators are also explained in that article. Data on chrysophytes and Cyanobacteria are from late summer (July-September), whereas data on pinnate diatoms are from spring/early summer (May-July).…”