Bivalves can be used as environmental biomonitors by studying the growth rate and the structure of their shells, as well as by analysing elemental distribution in the shells.
Information about water chemistry, temperature and pH, about precipitation, food supply and other environmental parameters are stored in the bivalve shells. To be able to disclose the environmental archives within the bivalve shell, several methods have been developed in the last decade. In this thesis methods based on studies of shell structure and growth rate are presented, as well as methods using chemical analysis.
Two methods of chemical analysis have been successfully used to measure low concentrations of elements in bivalve shell: the Nuclear Microscope with its high spatial resolution and Neutron Activation Analysis, with its high multielemental capacity, as well as low detection limits.
Among the results presented are:
In freshwater bivalves from localities only slightly affected by human activities, a positive correlation between growth rate of the shells and summer temperatures was found.
The effect of acidification is clearly visible in reduction of the shell growth rate and in differences in shell structures, as well as in high concentration of zinc, cobalt and iron.
The effect of liming on the other hand is evidenced by abnormal, much higher, growth rate of the shells and in some cases even by a rupture along the whole shell.
Large differences in elemental concentrations between the two aragonitic layers of the Margaritifera margaritifera shell were found by Nuclear Microscope analysis.
Seasonal variation of manganese occurs in freshwater bivalve shells, which is correlated with the seasonal depletion of oxygen in the water.
Seasonal as well as ontogenetical variation of strontium was found in M. margaritifera shells.
The annual increments in M. margaritifera shells are composed of thin lamellae which indicate several periods of acceleration and retardation of the growth within one year. This microgrowth pattern is specific for each year in all individuals of the same age within a population.
The growth rate and structure of Macoma baltica shells indicate highly polluted environments along the southern shore of the Gulf of Finland.
A discussion about possible underlying causes for the elemental variations is presented, where environmental parameters such as pH and temperature are studied.
Uppsala: Acta Universitatis Upsaliensis , 1999. , 48 p.
1999-04-16, lecture theatre of the Palaeontology building, Dep. of Earth Sciences, Historical Geology and Palaentology, Uppsala University, Uppsala, 14:00