By: Sarah H Burnet
Sunset visit to Nuolja with Lapporten in background
It’s been two weeks after leaving Abisko, Sweden and after witnessing three season changes (Spring-Summer-Fall) and I take my leave before winter takes hold. If you followed along with my Instagram take-over for ASLO, you know that I don’t mind spending time in colder conditions (even in a walk-in refrigerator for sample collection), especially when sediment cores are involved. But I’ll admit I do not mind being back in shorts and sandal weather after returning to Idaho.
Photo of Lake Torneträsk
Prior to my sitting in a refrigerator, I collected triplicate sediment cores from seven lakes around Abisko, Sweden while collaborating with Dr. Jan Karlsson. Those cores were transported to the Climate Impacts Research Centre (CIRC) in Abisko and placed in the fridge to start incubations with oxygen present in the water (oxic conditions). I also attempted to mimic low-oxygen (anoxic) lake conditions by adding anoxic water into the cores. This changes the sediment to a reduced state and allows P to solubilize and enter the water column in what is termed ‘internal loading’. The goal of my LOREX work was to test the hypothesis that the exchange of nutrients between sediment and water at these seven lakes will vary with altitude and varying headwater characteristics. Understanding this fraction is crucial to place whole-lake P-budgets in context for i) remediation programs and ii) to predict future changes such as those related to climatic warming. Also, many thanks to the CIRC interns Julia and Nick for helping during the core collections!
Sediment core collections completed at lake BD03 with CIRC interns Julia and Nick (photo by Joëlle Winnmöller)
Water samples were collected from the cores for the analysis of total (TP) and dissolved phosphorus (DP) at predetermined intervals throughout the oxic and anoxic incubations. Temperature, dissolved oxygen (DO), and pH in each core were also measured on each sampling occasion. Sampling of all 21 cores took about 2-3 hours in the 10°C fridge so I was well bundled up. But with some good music or podcasts sampling went by quickly! Once samples are analyzed (to be completed at Umeå this fall), I will calculate the release of TP and DP over the incubation period. While lakes in the arctic generally have low productivity and are nutrient poor, the use of these sediment incubations to measure the potential for nutrient release is critical to understanding the contribution of sediment to the nutrient budget.
Incubation set-up for sediment cores in walk-in fridge for data and nutrients collection
Toward the end of my time in Abisko, I sectioned each sediment core for measurements of water content and organic matter. The organic matter values can provide an idea if the lakes differ in how much material is present to decay, possibly causing anoxic conditions. It is also beneficial to section since you can see how the porosity and particle size can change from lake to lake, and even sediment texture.
Sediment core sectioning
Ashed sections of sediment cores for organic matter calculations
One aspect that has drawn me to studying lake and reservoir sediments is discovering the amount of lake history and past conditions of the lake you are studying. Whether that be the zooplankton, nutrients, particle size, phytoplankton, pollen, contaminants, lake health, etc. All just waiting patiently to be examined. Maybe even by me.