Smithsonian staff worked with classes to pick sampling sites in streams close to their schools. In the spring, students and teachers collect macroinvertebrate samples as part of the Maryland Department of Natural Resources Maryland Biological Stream Survey Stream Waders program and describe their stream habitat. Data loggers were placed in and around streams to constantly collect information about air temperature, water temperature, and conductivity. Here is a map that shows where we placed our loggers!
Macroinvertebrates are collected using the Stream Waders protocols. After donning rubber boots, students use D-nets to collect invertebrates from the stream bed and carefully pick through leaf litter in search of macroinvertebrates. We transfer what we find to a sample container and preserve them in ethanol to later analyze them in the laboratory. The Stream Waders samples are returned to the Maryland Department of Natural Resources, where they will be analyzed by professional taxonomists. Students may also collect classroom samples that they can analyze themselves.
While we are in the field, we record any observations about fallen trees, high water flow, or difficult access to the stream. We also record the specific location where we took the sample.
There are many different ways to think about water quality. We are starting with putting out loggers—this is basic and cost effective, but we are hoping to add more!
Our data loggers track water temperature and salinity in the streams year round. These loggers will collect information about conductivity and temperature, which can point to changes in water quality.
Conductivity is a measure of how easily an electric charge, heat, or sound can pass through a material. In our study, we are measuring electric charge through water. Electrical current is transported by the ions in a solution. A salty solution is full of charged particles that will conduct electricity more easily than pure water. So, conductivity is really a measure of salinity: as conductivity increases, the concentration of ions (a.k.a salt) increases.
Conductivity and temperature can point to the health of an ecosystem. High conductivity can alert researchers to a higher concentration of ions, indicating more salt in the water. In the Anacostia Watershed, and other urban waterways, this is especially problematic because of road salt. In the winter, to prevent roads from freezing over, salt and sand are used on the highways to bring down the freezing temperature of ice and to add traction to icy areas. While this makes roads safer, much of that salt ends up in groundwater and in streams. Plants and animals that live in streams are freshwater organisms, and generally cannot tolerate high salinities or rapid salinity changes. If the water becomes too salty, mobile organisms, like fish or crawfish, may be able to move to less salty areas, but organisms that can’t move or that move slowly will not be able to survive.
Temperature is also an important aspect of water quality, and in urban streams high water temperature can be a problem. Water that comes off of manmade surfaces (concrete, asphalt, buildings, etc.) is hotter than water that comes off of fields or plains, so in urban areas, much of the water that enters streams, especially during storms, can be much warmer than the natural temperature range for that stream. Some stream organisms can only survive within a certain temperature range and warmer water can be stressful for some organisms, so knowing how the temperature of the stream changes through the year can tell us a lot about overall stream health.
Measuring temperature and salinity over time can help us monitor the health of these streams, and make judgements about how various environmental stressors affect different waterways.
Remember, conductivity is the measure of how easily an electric charge can pass through water, which is based on the amount of ions. So, the more ionic, or salty, the more conductivity a solution has. What does electrical conductivity have to do with TDS?
TDS stands for Total Dissolved Solids. This is a measure of the total ions in a solution. Conductivity is how easily electrical charge can pass through water, and that is determined by TDS.
We are using the conversion 1000 (μS/cm)=640 PPM
So what is a micro-Siemen?
A micro-Siemen (μS/cm) is a measure of conductivity. For example, 350.69 μS/cm is a sample measure of tap water.
Parts per million? Parts per thousand? What is this all about?
This is unit to report conductivity. For example, 50 PPM in water means there are 50 milligrams of solids per liter. Conductivity is most commonly reported in literature, press releases, and other public communication in terms of parts per thousand (PPT), so we will be using those units for this experiment. Just so we are all on the same page: 1000 PPM= 1 PPT
So, to review:
1000 (μS/cm)=640 PPM
1000 PPM= 1 PPT