The samples are surface water, filtered in the field through 0.45u polycarbonate filters into 125ml poly bottles. The minimum amount needed is about 60ml; if filtering is easy, fill the bottles to allow for the possibility of running duplicate scans. Color samples are collected four times per year, during the quarterly chemistry sampling weeks. Quarterly sample dates include February under ice, spring mixis, August stratification, and fall mixis. Store samples cold and dark, then allow them to warm to room temperature just before running the scans.
Instrument: Beckman Coulter DU800 spectrophotometer
Log in to the Trout Lake network via the spec computer as 'lterbc'. Turn the spec on and the room light off.
Start the DU software and wait for the initialization process to complete; this takes a few minutes.
Turn both the UV and Visible lamps on.
Select "wavelength scan" from the pull down menu. The default parameters are what we use, but check that they are set as: scan from 200-800nm, 1200nm/min, 1nm interval.
Adjust the cell holder to fit the 5cm rectangular cell.
Fill the 5cm cell with DI water, select BLANK.
When the blank is finished, leave the DI water in the spec and run it as the first sample.
For each lake sample, rinse the cell two times with sample, drain well, fill with fresh sample, polish the windows with lens paper, run the scan. Note that the cells we use have quartz windows. They are expensive and extremely easy to scratch, which renders them useless. Do not use anything other than lens paper to wipe the windows of the spec cells.
Between scans, select 'Auto Scale Y Axis' from the AXIS menu at the top of the plot.
We run the samples in order from clear to stained lakes to reduce the chance of contamination from one sample to the next. The order is: DI water, CR, SP, BM, TR, AL, CB, TB.
Save the file to the spec computer and to Groups\lter\data\color as YYMMM. Check the Color directory to make sure it did save there.
Any lakes that had absorbance values greater than 2AU are run again in a 1cm cell.
Clear the file on the DU using the CLEAR button at the top.
Edit the wavelength scan method to run from 200-400nm using the EDIT METHOD button at top. Adjust the cell holder to fit the 1cm cell.
Run a DI water blank in the 1cm cell. Run it again as your first scanned sample.
For each lake sample, rinse the cell two times with sample, drain and refill with fresh sample, polish cell windows, and run the scan.
Record the order of samples run on the data sheet.
Save the file to the spec computer and to Groups\lter\data\color as YYMMMb.
Turn off spec lamps, close DU software, turn off spec, log off computer.
Rinse the spec cells 3x with DI water, shake out excess, polish windows, set out to dry.
Rinse the sample bottles 3x with DI water, set out to dry.
Send the color data files to Aaron Stephenson via email.