Total particulate material (TPM) is an estimate of the mass of particles in the water column. In this method particles are defined as material not passing through a polycarbonate track-etched (PCTE) filter having a 0.4mm pore size.
- PCTE filters with pore size of 0.4 µm (Fisher Catalog No. 09-732-37)
- petri dishes for filter storage (Fisher Catalog No. 08-757-19)
- microbalance with calibration weights
- two flat-tip forceps
- freezer storage space
- oven capable of 40 - 60°C
- in-line filter holders for TPM collection
- Milty Pro Zerostat 3 pistol
1. In the winter or early spring, weigh 100 filters for use in the summer. This should be sufficient for all the TPM and sediment trap needs for the ice-free season. Handle the filters by the edges with a flat tipped forceps, placing each into a numbered petri dish. Label the dishes consecutively from YY-01 to YY-100, so that each filter-dish combination has a unique identification number. Since the filters themselves cannot be labeled, the filters must remain in the labeled petri dish except when in use.
1. Before going into the field, load preweighed filters into numbered inline filter holders, recording filter number and filter holder on the datasheet. Collect TPM samples at the same depths as the other LTER chemistry samples using an inline filtration setup.
2. Filter directly into a graduated cylinder, pumping until the flow is reduced to a drip. Record the volume filtered on the field data sheet. Remove and reattach the filter holder backwards on the line, then reverse the peristaltic pump in order to suck the excess water through the filter.
3. Store the used filter holders in a cold cooler. At the lab, remove the filters from the filter holders folding them in half with the sediment side in, and return them to the numbered dishes. Store them in the freezer until they can be dried.
PROCESSING SAMPLE FILTERS
1. Dry the filters in a 40-60°C oven, in the petri dishes with the covers slightly open, for 48 hours. After drying, close the dishes and store the filters at room temperature until they can be weighed. Follow the same weighing procedure that is used for weighing filters before use.
1. The day that filters are to be weighed, set the sample filters and five control filters out on the counter by the balance, with the petri dish lids partially open. Allow the filters to equilibrate with the atmospheric humidity near the microbalance for several hours before weighing. Cover the filters with a clean plastic bag to prevent dust from settling onto them.
2. Calibrate the microbalance before each use using a 20mg weight. After every five filters weighed, check the tare by recording the weight of a 10 mg weight to determine if the microbalance is consistent. Recalibrate the balance after 50 TPMs are weighed or when starting another day’s work.
3. Before placing filter on pan, zap it with the Milty Pro Zerostat 3 pistol to ensure the filter is free of static cling. Follow instructions on pistol box. After placing each filter on the balance pan, wait for the balance to give a constant weight. This waiting period should be standardized. We wait 45 seconds, then for the reading to be stable for 10 seconds before taking a number. Weigh filters to the nearest microgram (e.g. 15.126 mg). Always engage the pan brake when loading or unloading the balance. The stirrups that the pans are suspended from are extremely fragile, and the balance is unusable if they are broken off.
4. Differences in humidity between weighing dates can greatly affect TPM values. The five control filters are used to correct for humidity effects. These filters are weighed every time TPM filters are weighed. The average difference between the ‘before’ and ‘after’ weights of the five control filters is used to correct sample filter weights for humidity.
To determine the mass of particles in the water column sample:
mass on filter (mg) / volume filtered (L) = TPM (mg/L)
TPM data are then entered into the web based data form for inclusion in the LTER database.