12 research outputs found
Iron addition as a shallow lake restoration measure: impacts on charophyte growth
Eutrophication has caused a decline of charophyte species in many shallow lakes in Europe. Even though external inputs of phosphorus are declining, internal loading of P from the sediment seems to delay the recovery of these systems. Iron is a useful chemical binding agent to combat internal phosphorus loading. However, the effects of iron addition on charophytes are not yet known. In this study we experimentally tested the potential toxicity of iron(III)chloride (FeCl3) on two different charophytes, Chara virgata Kützing and Chara globularis Thuiller added at the concentration of 20 g Fe m−2 and 40 g Fe m−2 to the surface water. C. virgata growth was not significantly affected, whereas C. globularis growth significantly decreased with increasing iron concentrations. Nonetheless, biomass of both species increased in all treatments relative to starting conditions. The decrease of C. globularis biomass with high iron additions may have been caused by a drop in pH and alkalinity in combination with iron induced light limitation. Iron addition over a longer time scale, however, will not cause this rapid drop in pH. Therefore, we conclude that adding iron(III)chloride in these amounts to the surface water of a lake can potentially be a useful restoration method.
Alternative stable states driven by density-dependent toxicity
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Combined effects of nitrogen enrichment, sulphur pollution and climate change on meadow vegetation N:P stoichiometry and biomass
Nitrogen (N) and sulphur (S) deposition, as
well as altered soil moisture dynamics due to climate
change can have large effects on fen meadow biogeochemistry
and vegetation. Their combined effects may
differ strongly from their separate effects, since each
process affects different nutrients through different
mechanisms. However, the impacts of these environmental
problems are rarely studied in combination. We
therefore investigated the separate and interactive
effects of current levels of N- and S-deposition and
changes in soil moisture dynamics on fen meadow
vegetation.We focused on vegetation biomass and N:P
stoichiometry, including access to soil P through root
surface phosphatase activity, in a 3-year factorial addition
experiment in an N-limited rich fen meadow in the
Biebrza valley in Poland. We applied 29.5 kg N ha-1
year-1 and 32.1 kg S ha-1 year-1, which correspond
to current deposition levels in Western Europe.
Changes in soil moisture dynamics due to climate
change were mimicked by amplified drying of the soil
in summer. This level of N-deposition had limited
effects on plant biomass production in this rich fen,
despite low foliar N:P ratios that suggest N limitation.
This level of S-deposition, however, resulted in
decreased vegetation P-uptake and biomass. We also
showed that increased summer drought resulted in
considerable increases in vegetation biomass.We found
no interactive effects on vegetation biomass or N:P
stoichiometry, possibly as a result of the limited main
effects of the separate processes