Pollution of Lakes and Rivers

Chapter 3:Sediments: an ecosystem’s memory

Copyright © 2008 by DBS

Contents

• Sediments and environmental change• Sediment records from reservoirs, rivers, and others• The paleolimnological approach• Recent advances

SedimentsSediments and Environmental Change

• Lakes and their sediments collect regional and local environmental signals – sentinel ecosystems

(Carpenter and Cottingham, 1997)

• Sediment distribution depends on:– Flow rates– Topography– Climate

• Subdivides basins into 3:– erosion zone– transportation zone– accumulation zone Of most use to paleolimnologists

May be disturbed! …by what?

SedimentsSediments and Environmental Change

Physical mixing + Bioturbation

SedimentsSediments and Environmental Change

• Law of superposition – for any undisturbed sedimentary sequence, the deepest deposits are the oldest

SedimentsSediments and Environmental Change

Types of sediment material:

Allochthonous – ‘formed elsewhere’ - material from outside the lake

Autochthonous – material from inside (algal material, animals + plants)

SedimentsSediments and Environmental Change

SedimentsSediment Records from Reservoirs, Rivers, and Others

• Interpretation is more challenging– High-energy systems– High sediment loads– Changing water quality due to low residence times

Where in this river system may sediments be accumulating?

SedimentsSediment Records from Reservoirs, Rivers, and Others

• Reservoirs – man-made lakes• 2 conditions for use - continuous sedimentation, little diagenesis• Consists of 3 zones:

Callender and Van Metre, 1997

SedimentsSediment Records from Reservoirs, Rivers, and Others

Diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition

In sediments diagenesis refers to both physcial changes in the mud and the mobility of chemical species

May be less diagenesis in reservoirs due to faster accumulation rates

SedimentsThe Paleolimnological Approach

Step 1: Choice of study site– Specific local problem– Specific regional problem

Step 2: Selection of coring site(s)– Analyses are time consuming– Often based on very few or single cores– Location is based on finding an area that integrates the most representative sample– Variability studies show high reproducibility (Charles et al, 1991)

Step 3: Collection of sediment core(s)– Corer selection is based on site accessibility, climate, length and temporal resolution required

Step 4: Sectioning the sediment core(s)– Temporal resolution controls thickness– Amount of material required (analysis techniques are destructive)

Step 5: Dating– 210Pb, 137Cs, and 14C radiometric techniques

Step 6: Gathering proxy data– Physical, chemical and biological

Step 7: Interpreting proxy data for environmental assessments– Looking for trends

Step 8: Presentation of data

SedimentsThe Paleolimnological Approach

SedimentsRecent Advances

• Technological– Collection and sectioning– Resolution of timescales– Geochronology (dating)

• Amount and quality of information– Number of morphological and biochemical markers has grown– Libraries of cores and data

• Application of new procedures to interpret information– Computational methods

– Advances in statistical and data-handling techniques

SedimentsSummary

• Lakes are only temporary landscape features on the geological timescale

• Sedimenting materials:– Autochthonous – material produced in the lake– Allochthonous – originate outside the water body (e.g. eroded soils and plants)

• Provided accumulation is undisturbed information can be recovered

References

• Callender, E. and Van Metre, P.C. (1997) Reservoir sediment cores show U.S. lead declines. Environmental Science & Technology, Vol. 31, pp. 424A-428A.

• Carpenter, S.R. and Cottingham, K.L. (1997) Resilience and restoration of lakes. Conservation Ecology B(1), 2. (electronic only)

• Charles, D.F., Bonford, M.W., Fry, B.D., Furlong, E., Hites, R.A., Mitchell, M., Norton, S.A., Patterson, M.J., Smol, J.P., Uutala, A.J., White, J.R., Whitehead, D.R. and Wise, R.J. (1990) Paleoecological investigation of recent lake acidification in the Adriondack Mountains, N.Y. Journal of Paleolimnology, Vol. 3, pp. 195-241.

• Deevey, E.S., Jr. (1969) Coaxing history to conduct experiments. BioScience, Vol. 19, No. 1, pp. 40-43.

• Håkanson, L. and Jansson, M. (1983) Principles of Lake Sedimentology. Springer-Verlag, Berlin.

• Reid, M.A. and Ogden, R.W. (2006) Trend, variability or extreme event? The importance of long-term perspectives in river ecology. River Research and Applications, Vol. 22, pp. 167-177.

References

• Smol, J.P. (1990b) Paleolimnology – Recent advances and future challenges. Memoire dell’Istituto Italiano di Idrobiologia, Vol. 47, pp. 253-276.

• Smol, J.P., Birks, H.J.B. and Last, W.M. (eds.) (2001a) Tracking Environmental Change Using lake Sediments. Volume 3: Terrestrial, Algal, and Silaceous Indicators. Dordrecht: Kluwer.

• Thornton, K.W. (1990) Perspectives on reservoir limnology. In Thornton, K.W., Kimmel, B.L. and Payne, F.E. (eds.), Reservoir Limnology: Ecological Perspectives. John Wiley & Sons, New York.