Total Suspended Solids
Introduction
Particulate matter in aquatic ecosystems can include a variety of materials, including phytoplankton, bacteria, protozoans, other living things, detrital organic material, and various kinds of inorganic solids, especially suspended soil particles. We have recognized for some time that excessive quantities of suspended solids can signal runoff of eroded soils and the contaminants that might be carried along. High levels of suspended solids can clog the gills of aquatic animals and cover the natural bottom with silt. The organic loadings from excessive sediment inputs can also drive oxygen consumption. Finally, phosphate is often adsorbed to sediment particles, so loading of solids will contribute to phosphate loading and eutrophication.
Methods
Most assays for suspended solids are very simple gravimetric techniques in which a raw water sample is filtered through a pre-weighed filter. After drying the filter is then weighed again; the difference (weight change in mg) is divided by the volume of water filtered to yield an estimate of total suspended solids in mg/l.
There are also techniques that use optical backscatter or some such measure of light attenuation or scattering to estimate suspended solids, but these require much more expensive instrumentation. Their advantage is that you get real time data and can do time series measurements easily.
There are also related measures of turbidity; later we will use a multi-parameter water quality monitor that includes a turbidity meter.
Assignment
You will work in groups to go out to two stormwater ponds of your choice. Collect water samples from the pond outlet, the pond itself, and at least one of the pond drains. Try to sample in an old pond and a new one. Bring your raw water samples back, filter them through preweighed glass fiber filters, and dry them until next week. Be sure to label your weighing boats and record your initial weights. After weighing the dried samples, calculate total suspended solids as above.
North Carolina has a guideline for total suspended solids of 30 mg/l. Do any of your samples show a violation? Do stormwater ponds lower suspended solids levels effectively?