The (ARCSSTK) did extensive research during 2009-2011 field seasons in Arctic Alaska. Specifically, the ARCSSTK goal Streams goal was to quantify the relative influences of thermokarst inputs on the biogeochemical structure and function of receiving streams. Throughout the project, samples were collected from Benthic Rock Scrubs and measured for cholorophyll-a and particulate carbon (C), nitrogen (N) and phosphorus (P).
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The entire surface of rocks fitting into an area of 703cm^2 (this was the area of the bin ARCSSTK used, not the 546cm2 used in the past) were scrubbed with a brass brush.
The slurry was brought to a volume of 1 L.The samples were returned to the lab
where they were filtered through a GF/C or GF/F glass fiber filter.
For Chl a:
The filters were then placed in 10 ml of 90% buffered acetone and extracted in the dark for 24 hours. The samples
were then read on a Turner 111 (1990-1991) and Turner 450 (1992-1997), TurnerDesigns 10AU (1998-2010) Fluorometers.
Beginning in 2004, samples were analyzed for for chlorophyll a. After taking an initial fluorescence reading the sample was acidified with 100uL of 0.3N HCl and the sample was read again after waiting approximately 90 seconds. To calculate chlorophyll a concentration the second value is subtracted from the first value. The two different values represent total chlorophyll concentration and phaeophytin pigment concentration, by subtracting the phaeophytin from total chlorophyll, chlorophyll a is determined.
Reference Citations: R.G. Wetzel and G.E. Likens. 1979. Limnological Methods. Saunders. Philadelphia.
Notes: In 2004 several adjustments were made to the protocol from 2003. Extraction took place at approximately 4C using chilled acetone. A multipoint curve was analyzed using a chl a stock std. A Turner Designs solid standard could then be utilized as a check. GF/F 25mm filters were used. Additionally, chl a was corrected for pheophytin following EPA 445 and data is reported in corrected chl a. For more information please reference the chlorophyll protocol available on the Arctic LTER website.
Particulate Carbon and Nitrogen (PC or PN):
The PE2400 CHN uses a combustion method to convert the sample elements to the simple gases (CO2, H2O, and N2). The sample is first oxidized in a pure oxygen environment; the resulting gases are then controlled to exact conditions of pressure, temperature, and volume. Finally, the product gases are separated. Then, under steady-state conditions, the gases are measured as a function of thermal conductivity. A known standard is first analyzed to calibrate the analyzer in micrograms. The calibration factor is then used to determine unknowns. All quantitation is performed on a weight percent basis, using a gravimetric technique. The systems uses a steady state, wavefront chromatographic approach to searate the measured gases. This approach involves separating a continuous homogenized mixture of gases through a chromatographic column. As the gases elute, each gas
separates as a steady state step, with each subsequent gas added to the previous one. Consequently, each step becomes the reference for the subsequent signal.
Particulate Phosphorus (PP):
Particulate matter collected on a glass fiber filter is ignited at low temperature to destroy organic matter. The ignited filter is heated with dilute HCl, which extracts the phosphorus and converts it to ortho-phosphate. The phosphorus is then analyzed by a version of the reactive phosphorus method.
Arctic LTER Streams Protocol
annual data is updated into new file
v1. October 2014: metadata added, file contains all benthic data, except for some missing Chla data from 2011, will update - JL