Submerged Macrophyte Responses to Reduced Phosphorus Concentrations in Two Peri‐Urban Lakes

Abstract

Eutrophication of two urban temperate dimictic lakes in Berlin (Germany), smaller Schlachtensee (0.4 km 2 ) and larger Lake Tegel (3 km 2 ), caused total phosphorus (TP) concentrations up to 800 μg/L and a complete loss of their diverse submerged vegetation in the 1960s due to poor light conditions. Phosphorus stripping of their inflow began in the 1980s and caused a pronounced decline of their epilimnetic TP concentrations, eventually leading to reduced phytoplankton biomass and turbidity. Despite increased light availability, recovery of abundance as well as species diversity of submerged macrophytes was delayed by more than a decade, especially in the smaller lake. Slow oxidization of sapropelic sediment unsuitable for macrophyte growth, periphyton shading, herbivory, and/or lack of a viable seed bank were potential hampering factors. The present submerged vegetation, however, may already support mechanisms positively influencing water transparency such as providing habitat to enhance the ratio of piscivorous to planktivorous fish. Characeae meadows, typical for both lakes during their former mesotrophic state, so far only reoccurred in smaller Schlachtensee. Neither species composition nor abundance reversed back to the macrophyte community present in the nineteenth century. Although TP concentrations may decline further and some rare species have been detected, reassembly of this plant community will most probably not occur because many submerged macrophyte species have become rare throughout northwest Europe.

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.…”

“…However, with increasing nutrient loading, phytoplankton biomass may increase, creating water turbidity which may result in light limitation and disappearance of submerged macrophytes (Scheffer et al, 1993). However, before the water becomes turbid, there can be direct shading of macrophyte leaves by the accumulation of epiphyton or filamentous algae, which causes macrophyte decline or inhibits their return (Phillips et al, 1978;Weisner et al, 1997;Jones & Sayer, 2003;Roberts et al, 2003;Irfanullah & Moss, 2004;Hilt et al, 2010). Besides the indirect effect of nutrients on macrophyte growth (via light limitation), certain nutrients can be toxic for macrophytes, including ammonium which can be toxic at high concentrations for many macrophyte species (Smolders & Roelofs, 1996), whereas nitrate has been shown to reduce the growth of Chara species (Lambert & Davy, 2011).…”

Toward an Era of Restoration in Ecology: Successes, Failures, and Opportunities Ahead

“…Local extinctions of desirable native species accompanied by dominance of exotic species with strong impacts on ecosystem processes commonly have slowed or stopped recovery in both terrestrial and aquatic restorations (Florens et al 2010, Hilt et al 2010, Tanentzap et al 2009). For instance, a 70-year restoration of a shallow lake via reduction of nutrient loading reestablished some aspects of community structure, but owing to the regional loss of rare species, diversity remained lower than in the reference period (Louette et al 2009).…”

Clear, crashing, turbid and back – long‐term changes in macrophyte assemblages in a shallow lake

“…Therefore, the lake acted as a net P source for 6 years after the external load reduction despite a water retention time of only 0.1-0.16 years. P. pectinatus also dominated in other previously turbid, temperate European lakes after phosphorus load reduction and no other internal measures (Germany: Kabus et al, 2007;Bl€ uml et al, 2008;Hilt et al, 2010;Sweden: Blindow, 1992;Strand, 1999; The Netherlands: Scheffer, De Redelijkheid & Noppert, 1992;Van den Berg et al, 1999;Denmark: Schriver et al, 1995;U.K. Spring water clarity became higher than during the 'crashing' phase, but the lake has remained turbid during summer.…”