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Virginia Coastal Reserve History
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The Virginia Coast Reserves on the Eastern Shore of virginia is home to several organisms, marshes, and barrier islands. Seagrass meadows within this ecosystem provide habitat, food, carbon sequestration, and shoreline protection. The seagrass meadows on the Virginia Coast reserve are crucial for a shallow marine environment. In the 1930’s the seagrass population were wiped out, and remained locally extinct for 70 years. In 2005 the Nature Conservancy successfully restored the seagrass population. Unfortunately in 2015, ecological drawbacks such as increasing frequency of marine heat waves due to climate change set the recovery of seagrass back.
Benthic microalgae are an important part of marine ecosystems. Benthic microalgae takes up carbon during photosynthesis, and releases the carbon as a extracellular polysaccharide. The polysaccharide that is released into the sediment to aid in sediment stabilization, and carbon sequestration. Benthic microalgae are affected by increased temperature. If benthic microalgae continue to produce polysaccharides during underwater heat waves it may make it easier for seagrass to recover.
Problem Statement
Benthic microalgae live in a dynamic habitat with moving water, varying temperature, and light levels. To adequately study them in the lab, we need to mimic all of these conditions.
Market Research
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The picture (left) is the most common approach to studying coastal underwater environments, however, it lacks a tidal range which immensely effects the amount of sunlight organisms receive throughout the day.
The machine (right) can accurately simulate underwater coastal environments at a cost of $16,000. Nonetheless, it is too expensive for small liberal arts colleges to operate.
Design Criteria
Heat stressed benthic microalgae must be 5°C > 23.0°C-25.0°C (average temperature)
Tidal range cycle ≥ 1 meter in 6.5 hours
Light Intensity 0-2000 lm/ft² at sea floor
-Water must circulate the nutrients in the system making the dissolved oxygen content >4 mg/L to prevent asphyxiation
Design Constraints
Utilize two potentially working environmental chambers
Limited chamber space: 0.71x1.32x1.47 meters
Electrical limitations inside chamber 15A/125V
$1250 budget
Brainstorming Sketches
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We brainstormed ideas and favored a solution like the tank with magnetic spin bars in sediment cores (middle)
After viewing more complex systems we decided to include a tidal range by pumping water from a reservoir to a tank with sediment cores (left and right)
Final Solution
After finding out we only had one growth chamber operational, we became even more limited in space
We decided to combine the water supply the tanks use and have one tank at high tide drain into the other at low tide
One tank in each pair of tanks would have an aquarium heater (not drawn) to heat stress the water in that tank
Water Pump System
I successfully created an electronic circuit that accurately controls the tidal range by programming an Arduino Uno connected to two water pumps. Eventually I switched to using aquarium auto dosing pumps and fountain pumps after battling powering issues inside the chamber while crunched by time. These new pumps were later tested and proved successful without drawing too much power.
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Water Column Tank
Initially, I tried using various sheet plastics (acrylic, polyethylene, polypropylene etc.) and custom tank molds to build 6 tanks that were 12x12x49Â inches tall. However, the amount of plastic was too expensive to order. So I cut sections 12"x24' of SDR 35 pipe and secured the bottom with end caps and flex tape to build 6 tanks.
Water Temperature
To make sure the heat stressed water doesn't change the temperature of the normal water when transferred through the pumps over the tidal cycle, we designed this experiment. According to our results we did not give the heat stressed tank enough time to get between 28-30 degrees , which explains the large increase in the graph during high tide. After the tanks switch from low to high tide the aquarium heaters were able to hold the temperature at the parameters we set. Overall the test was a success and we were able to prove the concept works.
Depth and Water Movement
After having trouble controlling the fountain pumps, we chose to use the aquarium auto dosing pump to produce the tidal cycle. In this experiment we tested the tidal range and accuracy of water pumps. We found they could successfully be powered and control the depth accurately. However, according to our data they could only produce a tidal range of roughly 0.72 meters. The water depth in tank one strays off from the rest of the tanks towards the end of the cycle due to a calibration error we detected.
Light Intensity
To supply enough light intensity to the microalgae, we had to upgrade our lighting system. The lights built into the chamber all alone were not nearly enough. Eventually we decided to remove the chamber lights due to their power consumption with little output. We used aquarium lights which could produce 10 times the amount of lumens per square foot. To amplify the light intensity, we spray painted the inside of the tanks white.
Future Itertions
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We want to increase the amount of light intensity inside the tanks with more or higher intensity lights. We would also like to increase the amount of tidal movement by decreasing the volume of the tanks or using more pumps. Overall this research project was successful, my team was able to prove the design concept worked but needs more refinement to achieve the rest of the design criteria before use in labs for research.
Thank you
Dr. Sarah Sojka
Randolph College Summer Research program
Anheuser-Busch Coastal Research Center (ABCRC) of the University of Virginia
Randolph College Department of Theater
Dr. Peter Sheldon
Leif Kvarnes
Zacariah Payne
Brad Zylstra