Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Seasonal stable isotope composition of bivalve growth

increments and ambient water in the rivers Rhine and Meuse

Emma VersteeghHubert Vonhof, Simon Troelstra, Dick Kroon

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Freshwater mussels

Species: Unio pictorum & U. tumidus

Aragonite shells

Seasonal growth increments

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Oxygen isotopes

Meuse

Low δ18O in winter due to depleted precipitation

High δ18O in summer due to increased evaporation and enriched summer precipitation

Rhine

Additional factor: Alpine snow melt in summer → negative excursions in summer

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

δ18O rivers

Snow melt

High discharge

Flood

Dry summer

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Research questions

• Can shell incremental stable isotope chemistry be used as a proxy of past seasonal changes in river water composition?– Are δ18Oar values in shells in equilibrium with δ18Ow values of

ambient water?– Are seasonal δ13CHCO3- patterns within river water recorded in the

range of δ13C values within shell aragonite?

• Can we calculate intra-seasonal growth rates by matching relationships between stable oxygen and carbon isotope chemistry of river water and shell records?

• What are the environmental factors driving seasonal growth rate changes?

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Monitoring experiment: collecting and tagging Unionids

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Monitoring experiment: cages in fish ladders

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Monitoring locations

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Methods

• Water sampling

• Microsampling– Merchantek Micromill

• Stable isotopes– Finnigan Delta+ with

Gasbench II

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Predicted shell δ18O

Water δ18O & T → shell δ18O

1000 ln α = 2.559 (106 T-2) + 0.175

Grossman & Ku (1986); Dettman et al. (1999)

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Predicted shell δ18OMeuse Lek (Rhine distributary)

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

δ13C of HCO3-

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Shell δ18O records

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Shell δ13C records

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Matching shell and water records

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Matching shell and water records

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Intra-seasonal growth

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Conclusions• Unio pictorum and U. tumidus precipitate their

shell in oxygen isotopic equilibrium with ambient water

• Seasonal variation in δ13C values of dissolved inorganic carbon are recorded in shell aragonite

• Growth onset and cessation are induced by water temperature

• Growth rate is mainly influenced by food availability (primary productivity)

• Unionid stable isotope chemistry can serve as a proxy for past water composition (and related floods, droughts, primary productivity)

Bivalve Workshop, Vrije Universiteit Brussels, 4-5 May 2009

Thank you!