Environment
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A Flow-through Exposure System for Evaluating Suspended Sediments Effects on Aquatic Life
Chapters
Summary January 9th, 2017
A robust and flexible flow-through exposure system designed to maintain sediment in suspension is presented. The system is used to investigate the effects of suspended sediment on various aquatic species and life stages in the laboratory.
Transcript
The overall goal of this experimental technology is delivering a robust and flexible flow-through exposure system for maintaining sediment and suspension, to investigate the effects of suspended sediment on various aquatic species and life stages in the laboratory. This technology can help us answer key questions in the field of environmental toxicology to improve our understanding about the effects of physical stressors such as suspended sediments in aquatic environments. The main advantage of this technology is the ability to simulate sediment suspension for incoming management practices to reduce the interactions between aquatic organisms and suspended sediments.
Though this method can provide insight into the effects of dredging, it can also be used to evaluate the effects of suspended sediments resulting from vessel traffic, freshets, and storms. Visual demonstration of this technology is critical, as steps in its construction combined with its calibration are critical to successful application. Begin building and assembly of the module and water bath as described in the text protocol.
To construct an overflow drain, use a hole saw to cut a 2.54 centimeter diameter hole five centimeters from the top of a 19 liter domed bottom polyethylene tank. Install a bulkhead fitting and an insert on the exterior of the bulkhead to serve as the overflow drain. To construct the slurry water inlet, use a hole saw to cut another 2.54 centimeter diameter hole five centimeters from the top of the aquarium.
Install another bulkhead fitting and a threaded elbow hose barb. For constructing the pump outlet, cut the same type of hole through the middle of the tank bottom and install a bulkhead fitting. Thread the exterior side of the bulkhead with an elbow hose fitting.
To construct the pump inlet, cut another hole located off-center of the tank bottom and install a bulkhead fitting. Thread the exterior side of the bulkhead with an elbow hose fitting. On the exterior side of the water bath tank, measure nine centimeters from the bottom and draw a line along the length of the tank.
Following the line, cut a pair of 2.54 centimeter diameter holes along the length of the water bath for each aquarium and install bulkhead fittings. Mount magnetic drive pumps to a stand that will fit under the water bath along the side containing the holes and bulkhead fittings for connecting to the aquaria. Install an inline cord switch for each pump, or wire the pumps to a switch box for power.
Thread the exterior side of the water bath tank bulkheads with hose barbs. Attach vinyl tubing to the pump inlet and outlet before connection it to the bulkheads going to the appropriate aquarium. Inside the water bath, install a quick disconnect insert into the bulkhead.
After connecting each aquarium to a pump, attach vinyl tubing to the hose barbs installed on the bottom of the aquaria and attach the tubing to the quick disconnect valve hose barb. Next, connect the quick disconnects between the pump and the aquarium. Install a ball valve in this connection to isolate the pump for maintenance purposes.
Next, connect each aquarium's overflow drain to common drain via vinyl tubing. Then connect the common drain to the water bath drain. Connect each aquarium slurry water inlet to the slurry and water system installed on top of the module.
Connect the slurry tank drain to the inlet of an air-operated double-diaphragm pump that has been mounted onto a stand next to a slurry tank. Incorporate a PVCT to direct the slurry to the pump or to the laboratory drain. Also incorporate valves connecting the tank and the pump to isolate them for maintenance.
To power the pump, connect it to the laboratory building's air compressor. Mount a PVC pipe on top of the modules and create a recirculation line to provide the slurry to each aquarium upon demand. At the point of use located farthest from the slurry reservoir, install a return line to transport the unused slurry back to the reservoir.
Use flexible PVC and union fittings to connect between the modules. Connect the slurry solenoid valves to the recirculating slurry pipe using tees, ball valves, and union fittings, to isolate solenoids from the main PVC pipe for maintenance. Insuring that each solenoid valve is located above the aquarium that it supplies, connect the solenoid valves to the corresponding aquaria as described in the text protocol.
Install an optical backscatter sensor or OBS in each aquarium next to the slurry water inlet to measure turbidity. Position the sensor so that it is submerged about five centimeters below the water surface with the sensor facing towards the middle of the tank. Use a clamp or other device to mount the sensor.
Install an OBS in the slurry reservoir and position the sensor so that it is completely submerged about 20 centimeters below the water surface. Next, wire the water and slurry solenoid valves. The OBS is located in each aquarium and slurry tank and a thermal couple located at each water bath, into electrical junction boxes mounted on top of the module into a data acquisition device.
Install quick disconnects at the terminal ends of all wiring wherever possible. Proceed to design a computer application for data acquisition, instrument control, and automation as described in the text protocol. To prepare for the experiment start the pump to recirculate carbon filtered tap water that has been used to fill the slurry tank.
In a separate container, use a mechanical mixer to homogenize the test sediment. After the sediment is homogenized, remove a small portion and introduce it into the slurry tank using a graduated polypropylene beaker. Continue to introduce sediment until 1000 NTU is achieved.
In the program, navigate to the water bath tab and start all aquarium profiles. After operating the FLEES for at least one hour so NTUs can stabilize in each aquarium, turn the data logging on to record NTU readings by each aquarium OBS. For TSS measurement, collect three 100 milliliter water samples from each aquarium assigned a TSS treatment of less than 500 milligrams per liter.
Separately collect three 50 milliliter water samples from each aquarium assigned a TSS treatment of greater than or equal to 500 milligrams per liter. Measure the TSS by vacuum filtering the samples through pre-weighed 0.45 micron filter paper. Immediately post-filtering, dry the filter and contents at 105 degrees Celsius for a minimum of four hours.
And then reweigh to the nearest 0.1 milligram. Use the average of the three samples as a measure of TSS in each aquarium. To perform the experiment, first turn on all FLEES hardware used for data acquisition, instrument control, and automation.
After filling the aquaria, water baths, and water reservoir with the desired test water, start all water chiller heat exchangers. Also, confirm and adjust the light cycle. Start the pump to recirculate carbon filtered tap water that has been used to fill the slurry tank.
Then, remove a small portion of homogenize sediment and introduce it into the slurry tank. Continue to introduce sediment until 1000 NTU is reached. Then create a profile for each aquarium as described in the text protocol.
After animals are stocked into the aquaria as described in the text protocol access the GUI and navigate to the water bath tab to start all aquarium profiles. Following operation of the FLEES for at least one hour, turn the data logging on to record NTU readings by each aquarium OBS. NTU and corresponding TSS concentrations are maintained in experimental aquaria to achieve target-suspended sediment concentrations.
In this example, the FLEES evaluated whether the suspended sediment could be maintained over a three day period. Similarly, NTU and corresponding TSS concentrations can be maintained at considerably lower concentrations representing ambient conditions. The FLEES is calibrated using test sediment to quantify the relationship between TSS and turbidity to ensure target TSS concentrations are achieved.
The relationship between NTU and TSS is displayed for an example test sediment evaluated in the FLEES. Once FLEES is constructed and operating properly, it is flexible enough to evaluate the effects of suspended sediments to multiple aquatic species in life stages of varying sizes, from eggs to adults, depending upon the species. It is important to remember that the most critical step in the methodology is to calibrate the FLEES with every test sediment.
So the relationship between total suspended solids and turbidity can be quantified, thereby enabling the matching of target TSS concentrations. After its development, the FLEES technology paved the way for researchers in the field of environmental toxicology to investigate the effects of suspended sediments on a wide variety of aquatic organisms. After watching this video, you should have a good understanding of how to construct and utilize the technology in your own laboratory.
As the automation and programming features enable total suspended solids concentrations to be easily adjusted to meet experimental needs.
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