A
a
1
B
b
2
B b
2
B b 3
-2 0 2 4 6 8
Biomass increase (g)
A
B
-2 0 2 4 6 8
Biomass increase (g)
Koninklijke Nederlandse Akademie van de Wetenschappen
Netherlands Institute of Ecology (NIOO-KNAW), Department of Aquatic Ecology Droevendaalsesteeg 10, P.O. box 50, 6700 AB WAGENINGEN, The Netherlands E-mail: a.immers@nioo.knaw.nl - URL: http://www.nioo.knaw.nl
Anne Immers, Jessica van der Wal, Martijn Dorenbosch & Liesbeth Bakker
Department of Aquatic Ecology, Netherlands Institute of Ecology , The Netherlands
Effects of iron addition and invasive crayfish on macrophyte growth
Chara virgata Elodea nuttallii Myriophyllum spicatum P < 0.001
• High nutrient loading and a subsequent increase in water turbidity due to phytoplankton surface blooms have led to a decrease in macrophyte abundance
• Water managers have tried to resolve this problem by adding iron (Fe), in the form of iron(III)chloride, to the lake as a natural P binding agent
• After application of iron, return of macrophytes was not apparent, even though recent lab studies (BOX 1) have shown that iron addition would not inhibit macrophyte establishment1
BACKGROUND
CONCLUSIONS
• Biomass of all macrophyte species increased during lab experiments, even with high iron concentrations of 40 g Fe m
-2(BOX 1, Figure 1-2)
• Iron addition does not reduce macrophyte growth in experimental ponds (Figure 3). Chara virgata and Elodea nuttallii growth was not affected by different iron concentrations in experimental ponds and Myriophyllum spicatum biomass was significantly higher in the high iron pond compared to the low iron pond
• The invasive crayfish Procambarus clarkii negatively affects macrophyte establishment in the experimental ponds (Figure 4)
High iron
Low iron Herbivore exclosure cages (1 x 1 x 1 m) were placed in two closed off
experimental ponds in Lake Terra Nova, Loenderveen High iron pond: 1.6 mg Fe L-1 (treated with iron(III)chloride) Low iron pond: 0.2 mg Fe-1 (not treated with iron(III)chloride)
Introduction of three different macrophyte species per enclosure (Figure 3)
Besides herbivore exclosures in the experimental ponds, we placed:
crayfish enclosures, partial herbivore exclosures and open controls
METHODS
A
B C
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Chara virgata Chara globularis
Biomass increase (g)
Methods
Slow addition of 0, 20 and 40 g Fe m-2 over a time period of 5 – 12 weeks Results
0 20 40
g Fe m-2
Effects of iron addition on macrophyte growth
A A,B
B
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Elodea nuttallii
Potamogeton pectinatus
Biomass increase (g)
NS
P < 0.05
Potamogeton pectinatus
Chara globularis
BOX 1
Figure 1
Figure 21
P < 0.001
NS
RESEARCH QUESTIONS
Does iron addition hamper in situ macrophyte establishment?
Are invasive crayfish (Procambarus clarkii) responsible for macrophyte absence in the experimental ponds?
RESULTS
P < 0.005
High iron Low iron Pond NS
NS
Chara virgata Elodea nuttallii Myriophyllum spicatum
Crayfish enclosure Herbivore exclosure Treatment
Partial exclosure Open control
Figure 4 Figure 3
Herbivore exclosure
Effects of iron addition on macrophyte establishment Effects of crayfish presence on macrophyte establishment
1 Immers et al., Hydrobiologia, 2012, DOI 10.1007/s10750-011-0995-7
