Nutrient addition incubation experiments using sediments from supraglacial streams in Taylor Valley, Antarctica, December 2017


We used sediment incubations to quantify and compare nutrient uptake rates from biota living in sediment across glaciers in Taylor Valley, Antarctica. Hughes Glacier is located towards the polar plateau on the western edge of the valley and flows from the southern Kukri Hills north into the valley. Canada and Commonwealth glaciers flow south into the valley from the Asgard range. Commonwealth glacier is located closest to the ocean on the east end of the valley. Canada glacier is located mid-valley, between Hughes and Commonwealth glaciers. Sediment was brought to the lab and incubated with added nutrient solutions. Solutions were then analyzed to determine change in nutrient concentration. 

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We collected up to 10 kg of sediment from the main supraglacial stream networks of Commonwealth, Hughes, and Canada Glaciers. Specifically, sediment was collected from one location on the drainage network of three glaciers in Taylor Valley, Antarctica: Hughes Glacier (-77.73054167, 162.4337083), Canada Glacier (-77.62767, 162.96059), and Commonwealth Glacier (-77.58606667, 163.2535667). Sediment was collected using sterilized scoops, placed in Whirl-Paks and frozen for transport back to McMurdo Station. In the lab, we thawed and homogenized sediment. For each glacier, we autoclaved half the sediment at 120 C for 35 minutes. Sediment moisture content remained consistent before and after autoclaving. We then divided live and autoclaved sediments into 50 g (+/- 0.5 g) subsets and placed into a sterile 250 ml cell culture flask. We stored all flasks at -20 C until they were ready to be treated with 125 ml of a nutrient solution and placed directly into a cold water bath. Solutions were NH4Cl, NaNO3-, KH2PO43-, NaNO3- + KH2PO43-, and a deionized water control. Initial concentrations of NH4+ NO3- and PO43– were 10, 10, and 4 uM, respectively. All flasks were incubated in a large open saltwater tank (to avoid freeze over and maintain thermal stability) outside at ambient air temperature (~0 C) and under ambient light conditions (300-700 W m-2). Due to the high number of replicates, we grouped incubations by glacier and the experiment was run over the course of three days.Two flasks, one containing live and the other autoclaved sediment of each treatment (8 flasks total) were removed from the cold-water bath each hour after the start of the incubation. 110 ml of water was removed and filtered (using GF/F filters) from each flask into a clean 125 ml polyethylene bottle. The filtrate was frozen at -20 C and shipped back to the University of Colorado-Boulder for analysis. We scooped a 25 g subsample of sediment from the incubation flask into a weigh boat, weighed, and dried overnight at 55 C. Sediment was then reweighed and burned at 450 C for 4 hours, and weighed a final time to calculate percent loss on ignition (LOI). The filters were also dried, burned, and weighed to calculate loss on ignition for suspended matter.In addition to the long-duration incubation experiments, we performed a ~5-minute incubation on live and autoclaved sediments for each treatment and each glacier in triplicate. Finally, we performed KCl extracts on five replicates of 10 g of live and autoclaved sediments for each glacier using 40 ml of 2M KCl solution and extracting on a shaker table for 1 hour. The extract solution was filtered and frozen at -20 C for later analysis. We performed analysis of all filtrate from treatments and KCl extracts for N as NO3¬, and P as PO43- by Lachat (Hach instruments). All samples analyzed for ammonium used a salicylate colorimetric method and microplate reader (BioTek Instruments, inc.)


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