Chemical parameters

Sampling of the Kuparuk River for sestonic and benthic nutrients typically occurred three times through the course of the summer, on a monthly basis. Each reach of the river was included in the monthly survey. For sestonic nutrients, samples were filtered on-site using a syringe, a 25mm filter cassette, and 25 mm GF/C filters. Typically, we filtered 500 mL of river water through each filter, after which the filter was transferred with clean forceps into a Petri dish and dried at 60^oC for 24 hours upon return to the field station. Two replicate filters were collected for analysis of particulate carbon, nitrogen and phosphorus. Filtered water samples were preserved according to their respective analysis. Ammonium, nitrate, and soluble reactive phosphorus (SRP) samples were frozen; total dissolved phosphorus (TDP), total dissolved nitrogen (TDN), dissolved organic carbon (DOC), and cation samples were acidified with hydrochloric acid and refrigerated; and alkalinity and anion samples were refrigerated. At the end of the season, all water samples and filters were returned to the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts until 2011 and thereafter to the University of Vermont (UVM) in Burlington, Vermont, for chemical analysis.

Epilithic algae were scrubbed from rock surfaces with a wire bristle brush into a known volume of water (the “scrubbate”) and aliquots were taken to determine chlorophyll and particulate nutrient concentrations. From 1983 to 2004, epilithic algae was collected using the 2 x 2 rock scrub method, while the “whole rock” method has been used from 2004 to present (Peterson et al., 1993). A known volume of scrubbate from either method was filtered in-lab onto 25 mm GF/C filters. The chlorophyll filters were then frozen from 1-7 days, then placed in 10ml of 90% buffered acetone and extracted for 24 hours. Chlorophyll samples were read on a fluorometer at the field station. The filters for particulate C, N and P and ash free dry mass were dried at 60 ^oC for 24 hours, then shipped and analyzed at MBL until 2011 and have since been analyzed at UVM.

Through the course of the UKRE several biological parameters were monitored including macroinvertebrates, Arctic Grayling, and aquatic bryophyte cover.

Macroinvertebrates were collected using Surber samplers (25 cm x 25 cm frame fitted with a 243 μm mesh net). Two replicate samples of macroinvertebrates were collected on each date at each site. Samples were preserved in 4% formaldehyde. At the end of the field season, samples were shipped to Dr. Alex Huryn who verified identifications of all major species. Macroinvertebrates were removed by hand under 15X magnification, then identified and counted. All values are the mean of the replicates and have been converted to individuals per square meter.

Arctic Grayling (Thymallus arcticus), both adults and young-of-the-year (YOY), on the Kuparuk River were captured during the field season measured, weighed, and released. At the beginning of Arctic Grayling monitoring, fish were tagged with a colored, numbered floy tag, then in 1993, researchers started PIT tagging the Grayling. These PIT tags can be read with an antenna to track the migration of the grayling throughout the Kuparuk River system. The YOY are most typically caught using aquarium dip-nets, but have occasionally been caught via electrofishing in the past. Dr. Linda Deegan has managed the collection and analysis of this data.

A point transect method was used to monitor percent cover of dominant bryophytes and other macroalgae easily identifiable by eye in the experimental reaches of the Kuparuk River beginning in 1993 and to the present. Typically, point transects were done at least twice during the field season. Percent cover was recorded in specific riffle habitats and in some (early) years in specific pool habitats. The exact locations of transects within specific riffles differed slightly from year to year, but the specific riffles that were monitored remained constant. Typically at least 50 point observations were evenly spaced at intervals of 20 to 50 cm along each transect which spanned the entire width of the river. We collected observations along five transects at each sampling station resulting in at least 250 points per station. Cover type frequency was determined from the number of times each cover type was encountered, divided by the total number of points observed along each transect. The mean and standard deviation of 5 transects were used to characterize cover at a site. Sites within reaches (rather than transects within sites) are the replicable units. Only one cover type was recorded as present at any observation point. “Bare” recordings in the field notes were assumed to consist of an epilithic biofilm of diatoms and other microalgae as reported by Miller et al. (1992) and are recorded in the database here as ”Epilithic algae”.