Epsilon Archive for Student Projects

Abstract

Freezing is considered an effective preservation method for long time storage of water
samples, but it may however affect the chemical composition of the sample. The aim with
this study is to evaluate the effects of freezing on a restricted number of chemical variables,
which are used for both research purposes as well as environmental monitoring of
water quality. The catchment Gusseltjärn, located in central Sweden, had water samples
freeze stored for approximately 20 years before analysis. As no non-frozen samples were
analysed at time of collection this study utilised the catchments Lill Fämtan and Risfallet,
as references. In order to evaluate the effects of freezing a regression model was created
for each individual chemical variable of interest, using data from the reference catchments.
The model was then used to calculate expected concentration of what the variables should
have been without freezing and storage. A t-test was utilised to evaluate whether the differences
were of statistical significance or not. The models indicate that the concentration
for sulphur should have been 0,30 mg/l lower and that pH should have been 0,21 units
higher if the samples would not have been frozen. As Gusseltjärns water samples were
analysed by different laboratories over time, with changes of laboratory procedures as
well, this study could not distinguish whether the differences shown from the models was
caused due to long time frozen storage or change of laboratory and laboratory procedures.