A Citizen's Guide to Understanding and Monitoring Lakes and Streams

Chapter 4 - From the Field to the Lab

Measuring Total Suspended Solids and Turbidity in lakes and streams

Field Sampling Considerations

There are no special field sampling concerns associated with these parameters other than those described in the section on basic sample collection techniques. It is especially important for these parameters that the sample is collected from undisturbed water. Once you step into a stream, you stir up the stream bottom – that’s why you step upstream, lean, and reach into the current for the sample. In lakes, boat propeller action also may disrupt sediments in shallow areas. Again, do not sample from disrupted water.

Measurements Methods

TSS

1. Before sampling, prepare glass fiber filters by first soaking them in distilled water, drying them at 103^o C, and weighing and recording their weights.
2. Place the dried, weighed glass fiber filter onto a filtering flask – wrinkled side up. Shake the sample bottle first, then pour in the water and turn on the pump. (The amount of water you need to filter may change according to water conditions. Start with 100 mL. Use less volume if the filter gets clogged too quickly and more if the water filters through very fast.) Record the volume of water filtered.
3. Dry the filter at 103 to 105^o C, let it cool to room temperature, and weigh it. Dry it, cool it, and weigh it again. Continue until the fiber reaches a constant weight. Record the end weight.
4. The increase in weight represents TSS. Calculate TSS by using the equation below.

TSS (mg/L) = ([A-B]*1000)/C

Where A = End weight of the filter

B = Initial weight of the filter

C = Volume of water filtered

Turbidity

Turbidity is a measurement of the optical property of water – a measure of the amount of light that is scattered and absorbed by particles in the sample. It is a simple measurement that requires the use of either a nephelometer or Jackson turbidimeter to compare a reference solution to the sample. Turbidity measurement does not require any sample preparation, other than shaking the sample bottle well before analysis. The sample is simply poured into a glass tube, placed inside the instrument with a reference solution and the result is read directly from the instrument. (The nephelometer has recently become recognized as the more accurate and recommended piece of equipment for this analysis. However, if a Jackson turbidimeter is what you have available, it will work fine.)

TSS and turbidity samples should be held in the dark on ice or at 4^o C. In this condition, TSS Samples can be held for up to 7 days and turbidity samples for up to 2 days.

QA/QC Considerations

Randomly select 5 to 10 percent of the samples and collect lab replicates for them. Lab QA/QC will involve selecting duplicate analysis, and calibration of all equipment used.

The next section discusses chlorophyll a measurement in lakes.

Measuring Temperature | Measuring Dissolved Oxygen | Measuring pH | Measuring Secchi Disk Depth | Measuring Nutrient Concentrations | Measuring TSS | Measuring Chlorophyll a | Measuring Fecal Bacteria

Return to Table of Contents