Sampling West Hill Pond
Updated: Aug 17, 2021
What could be better than sampling Connecticut's most pristine lake with long-term friends, the Snieckuses, on a glorious summer day? My high school buddies Chris and Mark Sneickus recently moved to their newly built dream house on West Hill Pond and like many lake associated residents they want to ensure its beauty, and better understanding their lake's ecology, in order to sustain the aquatic ecosystem they love. G.Eco. embarked with the Sneickus family on their noble vessel, the STS, which stands for any number of things depending on the situation. Today STS stood for Science Toward Sustainability!
Some basic lake sampling gear includes a secchi disk, depth sampler, and syringe clamp. The black and white secchi disk, far left above and held by Chris, is used for measuring water clarity, which is associated with the amount of suspended solids, like algae and bacteria, in the water. The depth sampler, center above and held by me (Dr Golden) is used for collecting and testing water samples from below the surface. The syringe clamp, far right and held by Mark, is actually a wood clamp adapted specifically to hold a 60 cc syringe in order to squeeze water through syringe filters. This Yost brand clamp has been affectionately named "Jost" (pronounced yoest).
Careful preparation for environmental DNA sampling prior to actually sampling is equally important to careful sampling. Environmental DNA refers to bits of DNA that are constantly shed by organisms into the environment. This DNA can be sampled by filtering water and collecting the material left on the filter. The DNA is then preserved and sent to a laboratory for DNA extraction and sequencing. Once sequenced, this decoded DNA can be used to determine which organisms are present in lakes, ponds, streams, etc. Today's eDNA sampling examines which fish species are present in West Hill Pond.
Mrs. Cummings, our high school Qualitative Analysis teacher, gets credit for teaching us to always triple rinse our laboratory equipment, a technique that still serves well.
The first few syringes full of water pass through the filter easily. It becomes progressively more difficult to pass water through the filter, however, as the filter begins clogging with suspended particles from the lake water.
The adapted syringe clamp allows for a greater volume of water to pass through the tiny syringe filter, which provides greater probability of capturing more DNA from the water. Capturing as much DNA as possible is particularly important for assessing presence of rare, threatened, or invasive species that might be present but in low numbers. Abundant species are more easily assessed, even with a small amount of water filtered, because their DNA is more abundant in the water compared to species in low abundance.
When forcing water through the filter becomes difficult, even for Jost, the filter is removed from the syringe, loaded with a preservative, and then shipped to the lab for sequencing.
Other suspended material, including algae, bacteria, and debris, can influence water clarity and make a lake appear green or murky. Water clarity can be monitored by slowly lowering a black and white secchi disk vertically into the water until it can no longer be seen. The greater the depth of disappearance the clearer the water and clear water is an indication of a healthy aquatic ecosystem.
Today West Hill Pond's water clarity was exceptionally good, with a secchi depth of over 5 meters. Last time I visited the Snieckuses, however, they had a suspicious looking algal bloom at the surface. I used my empty latte glass to scooped up a water sample in order to examine it under the microscope and discovered it contained some potentially harmful cyanobacteria, also called Harmful Algal Blooms, or HABs (below). Cyanobacteria are present in almost all water bodies and can lurk at depth until conditions become favorable at or near the surface. They then become buoyant in order to take advantage of good surface conditions. This can occur after a rainstorm, for example, when runoff from land provides a nutrient pulse to a lake or pond. Often these blooms are harmless and conditions return to normal quickly, but if conditions persist cyanobacteria can produce toxins that are harmful to animals, including dogs and humans.
We used multiple analytical probes to further assess water quality at the water surface and at 5 meter depth using the depth sampler (shown below).
This depth sampler is a variation on the classic Van Dorn water sampler. The clever design, using what looks like two wiffle balls, a hitch pin, and bungees, allows the open PVC tube to descend through the water column to a desired depth. Once at that depth, a good yank on the line pulls the hitch pin out, triggering the wiffle balls to seal both ends of the PVC tube, effectively trapping the subsurface water inside the tube.
We tested a water sample collected at 5m depth using a multi-probe meter, which measures temperature, pH, conductivity, and suspended solids, and an optical dissolved oxygen probe, which measures oxygen concentration in mg/L.
Water Quality Results: No sign of HABs today and all water quality measurements taken at the surface and at depth indicated a healthy aquatic ecosystem for West Hill Pond. We'll need to be patient to discover which fish species are present in our eDNA samples because sequencing DNA takes time. However, I'll provide an update as soon as the data are in!