By Stephanie Owens
It has been a whirlwind of field work and lab work over the past month, but my LOREX research project has now come to an end. I was investigating copepod growth rates (a measure of secondary productivity) in Stordalen Mire in relation to dissolved organic carbon (DOC) to better understand how climate change (which will likely increase DOC into aquatic systems) will affect aquatic food web productivity.
Copepods were collected from three different sites, size fractionated to get an artificial cohort, and allowed to incubate in situ for two days. Both size fractioning and incubating required me to get a bit crafty. I created different sized sieves with PVC and different mesh sizes (pic 1).
1. Supplies for copepod growth rate experiments
I also created a floating chamber out of plastic poles, mesh, zip ties, and floaties (pic. 2), which allowed copepods in bottles to incubate. I also took DOC and nutrient samples concurrently with growth rate experiments.
2. Floating incubation chamber
In total, I conducted 10 growth rate experiments. I am incredibly thankful to interns Mathilde and Pierre from France for helping me in the field. It was a lot faster with their help and a lot more enjoyable!
Once the field work was complete it was time to process the growth rate samples in the lab. I imaged copepods (pic 3) with a digital camera attached to a microscope and then used ImageJ software to determine average size (pic 4). I was then able to determine initial size of copepods and the final size of copepods after two days and calculate the change in mass over time, aka growth rate.
3. Imaged copepods
4. Microscope with digital camera attached
I generated a lot of data and am excited to see how individual growth rates relate to DOC measurements, which will be analyzed in mid-September. On average our preliminary data showed that growth rates increased from sites with higher DOC to sites with lower DOC (pic 5), which suggests copepod growth rates are negatively related to DOC. This means as climate change increases terrestrial runoff into aquatic systems we could see a decrease in secondary production which could ultimately affect higher trophic level species, like fish. The more we know about how climate change will affect food web dynamics the better we can prepare and create sustainable solutions.
5. Copepod growth rates in relation to site in decreasing DOC
I am thankful to the LOREX program for allowing me to come to Sweden to do this research and connect with scientists that I will continue to collaborate with when I return home.