Daphnia Bioassay for Salt Toxicity

As students at Edgewood College we have been involved in an extensive project working with the Lake Wingra watershed. Our part in the project was to determine what effects salt has on living organisms in the watershed. We used daphnia as an bioassay for this experiment. We found that the salt levels in lake wingra are potentially harmful to the organisms living in the watershed.

Project completed by Jamie Melchert and Kari Saunders, students in Jim Lorman's (e-mail -  lorman@edgewood.edu) Natural Science class.

About Daphnia
Why Use Daphnia? Daphnia are excellent to use in bioassays because they are very sensitive to any changes in water chemistry. Daphnia are easy to raise in an aquarium. Daphnia are transparent so it is very easy to determine if they are eating and reproducing.

Culturing Daphnia
Pictures of Daphnia

Bioassays: What are they?
What is a Bioassay Test? A Bioassay test involves exposing organisms to various levels of a chemical to determine its toxicity. A specific response or endpoint is selected for measurement. Endpoints for Daphnia include: death, increased heart rate, or decreased appetite. By doing a bioassay test we can determine the LD50.

Our Bioassay Test
In our test we used daphnia for our organisms. In this test we wanted to determine what increased levels of salt in the watershed will do to these organisms.

Why is the LD50 important?
The LD50 shows us what level of sodium chloride (or any chemical or toxin) kills 50% of an organism in a 48 hour period of time. This level is important because it shows us what the lethal amount of chloride in Lake Wingra could be.

Procedures

Starting Our Experiment/Results of our Experiment
Our highest concentration of sodium chloride was 10g/L because we know that daphnia will not survive in these conditions.

Our lowest concentration of sodium chloride was 0.63g/L because this is a level at which we would not expect many deaths.

The levels in between the high and low levels will determine what salt levels are potentially dangerous for organisms living in the watershed.

Our goal in this experiment was to determine the acute toxicity of salt on Daphnia.

This is important since this will indicate at what salt concentration we need to start worrying about the safety of our watershed.