100 years of vegetation decline and recovery in Lake Fure, Denmark

Abstract

Summary 1.We analysed the development of submerged macrophytes in Lake Fure, Denmark, experiencing a 30-fold increase of phosphorus input from year 1900 to 1970 and a subsequent decline to twice the 1900 level in 2005. Nutrient enrichment stimulated phytoplankton growth and restricted macrophyte distribution by reducing water transparency from a summer mean of 5-6 m in the early 1900s to a minimum of 1.6 m at the peak of eutrophication, followed by recovery to a recent maximum of 4.1 m. 2. Macrophyte occurrence and abundance changed in accordance with altered environmental conditions and species' life-history traits. Small angiosperms, mosses and characeans disappeared in the 1970s to 1980s, along with all vegetation in deeper waters (5 -8 m), and have only partly recovered recently. Tall angiosperms became dominant while small species vanished. All 10 characeans originally present disappeared at the peak of eutrophication, but four reappeared. Mesotrophic macroalgae were replaced by hypertrophic species whose dominance has persisted. 3. Species richness decreased from 37 to 13 species at the peak of eutrophication, before returning to 25 species during the recent recovery. Species richness increased with transparency because deeper growth generates more niches. 4. Reduction of species distribution and richness has been reversible following nutrient reduction of the long eutrophied lake, whereas species composition and abundance have not. The historical legacy of community composition is strong, as reflected by closer correlations to time than to measures of nitrogen and phosphorus availability and water transparency. 5. Synthesis . Although phosphorus input may decline further, reassembly of the original macrophyte community will face difficulties. Oligotrophic freshwater species have become rare throughout Denmark, reducing the probability of recolonization. Species reaching Lake Fure may fail to establish because sediments have become richer in nutrients and organic matter and less consolidated, while shading and competition have increased from emergent reeds, tall submerged angiosperms and fast-growing macroalgae.

Restoring macrophyte diversity in shallow temperate lakes: biotic versus abiotic constraints

“…Furthermore, whereas macrophytes returned and species richness improved after reduction of nutrient loading, a longer term comparison shows that the species richness and macrophyte community is different from the records about a century ago, from the early 1900s, which was the start of human-induced large-scale eutrophication (Table 1). The authors suggest that this may be due to an impoverished regional species pool, where species are nowadays rare, altered sediment characteristics and competition from tall growing eutrophic species, which inhibits the return of smaller, rare, oligotrophic species (Sand-Jensen et al, 2008;Hilt et al, 2010;Dudley et al, 2012). This observation raises the question whether the changes to the aquatic habitat, particularly the sediment, and plant communities induced by eutrophication are reversible.…”

“…Possibly, the species temporarily can tolerate the less favourable conditions (Blindow, 1992a;Van den Berg et al, 1999). Based on their long-term dataset (100 years), Sand-Jensen et al (2008) elegantly show that the return of macrophytes after improved abiotic conditions in Lake Fure in Denmark, was strongly determined by the presence of clones of several species that had originated from the time before eutrophication. The historical presence of clones of species in the lake was a much more powerful predictor of vegetation composition after restoration than the altered nutrient conditions.…”

“…However, whereas biomanipulation can initially result in a strong expansion of macrophyte vegetation, which can be species rich, the community often rapidly changes and becomes dominated by eutrophic species. On one hand the abundance of eutrophic species may enhance water transparency, but on the other hand the species that dominate and grow to the water surface will limit light deeper in the water column, which will reduce the number of species that can grow under these conditions (Sand-Jensen et al, 2008). Additionally, dominance by eutrophic species does often not result in a stable vegetation and a relapse to the turbid state can occur within 10 years (Sondergaard et al, 2008).…”

Towards a more precisely defined macrophyte-dominated regime: the recent history of a shallow lake in Eastern Poland

“…However, it becomes a challenge when attempting to determine the lake regime in the distant past. Monitoring data from such periods are usually scarce or non-existent, with some exceptions (Egertson et al, 2004;Hargeby et al, 2007;Sand-Jensen et al, 2008;Hilt et al, 2013;Hobbs et al, 2014). In situation without reliable long-term monitoring data, studies into historical ecosystem state can be supported by paleolimnological analyses (Battarbee et al, 2005;Sayer et al, 2010a;Madgwick et al, 2011;Kowalewski et al, 2013Kowalewski et al, , 2015.…”

What's better, Ceratophyllum demersum L. or Myriophyllum verticillatum L., individual or combined?

“…As a result, water quality is impaired, water availability reduced, and aquatic macrophytes degraded even disappeared (Sand-Jensen et al, 2008), while the latter, in turn, aggravates the eutrophication process. In recent years, substantial efforts have been made to reestablish macrophytes in shallow lakes to improve water quality and restore ecosystem.…”