On October 20, Paige, Isabella, Ashley, Amber and Cross performed chemistries on the Horseshoe Crab tank. We found that both Ammonia and Nitrite levels were too high!
We looked at the nitrogen cycle chart.
We had two hypotheses:
- we were feeding the crabs too much and the food was rotting before it could be eaten.
- There was not enough good bacteria.
The team decided that we should not feed the crabs unless all the food was gone. We will ask the librarians to keep an eye on the amount of food in the tank.
Paige suggested that we look under a microscope to see if there were enough bacteria. We talked about the problem of telling the difference between good and bad bacteria. (Miss Linda has been thinking about this. We will bring a microscope to the next meeting to see if we can tell the difference.) Miss Linda said that we have some good bacteria that we can add to the tank.
We also changed some of the water in the tank to reduce the ammonia levels.
Salinity
The Club then analyzed the salinitiy (saltiness) of the tank. We then compared it with the salt level of tap water and the salt level of water from the Lighthouse beach in Havre de Grace (Lat 39 degrees 32.389 minutes N Long 76 degrees 5.087 minutes W)
Here are our results
- Tank water 22 ppt
- Tap water 3 ppt
- Bay water 6 ppt
Since we know that horseshoe crabs do best in water with salinity between 20-30 ppt, Havre de Grace would probably not be a good place to release them. The Club hypothesizes that the water from the Susquehanna river makes the water less salty up near Havre de Grace.
The Club then went to the Eyes on the Bay website.
http://mddnr.chesapeakebay.net/eyesonthebay/index.cfm
We looked at the buoys that were monitoring salinity and used a conversion chart to change salinity using PSU (practical salinity units) to ppt. We discovered that as we moved down the bay, salinity increased. The buoy at Annapolis registered 7.31 PSUs which converts to about 9.35 ppt. Miss Linda was surprised that this was so low. When she looked at this buoy some time ago, it was registering about 22 ppt. We will need to check this again as the seasons change.
The next Let's Do Science Club meeting will be Nov 17 at 2 pm. We will be checking the ammonia levels in the tank to see if we have corrected the problem and we will be looking a little more at salinity.
