The physical characteristics and chemistry of lake waters of the Arctic LTER were sampled at various locations either weekly, monthly or once per field season depending on the site and the year.

Until 1992 (inclusive) Dissolved O2 and temperature were measured using a YSI 57 Oxygen Meter, water calibrated. Temperature and conductivity were ready by a YSI model 33 conductivity meter. Carbonate alkalinity was titrated against pH depending on expected alkalinity (Wetzel and Likens, 1979). pH was measured electrometrically with a corning portable expanded standard pH buffer and corrected for the temperature of the sample.

Secchi disk depth was measured using a 22 cm Secchi disk, a black and white disk, that is lowered by hand into the water to the depth at which it vanishes from sight. This distance was then recorded. As there is only one depth for each site, the same Secchi depth is indicated for all depths measured at a particular site on a particular day. This measurement is generally made on the shady side of the boat and measured to the nearest 0.1 meters.

For measurements with notes indicating "Kipphut data":
Dissolved oxygen was measured by Winkler titration and samples were collected with a pump or Van Dorn bottle.
The Winkler Method is described as follows: The sample is treated with manganous sulfate, potassium hydroxide, and potassium iodide (the latter two reagents combined in one solution) and finally sulfuric acid. The initial precipitate of manganous hydroxide, Mn(OH)2 combines with the dissolved oxygen (DO) in the sample to form a brown precipitate, manganese(II) hydroxide, MnO(OH)2. Upon acidification, the manganese(II) hydroxide forms manganic sulfate which acts as an oxidizing agent to release free iodine from the potassium iodide. The iodine, which is stoichiometrically equivalent to the dissolved oxygen in the sample is then titrated with sodium thiosulfate. (“Methods for Chemical Analysis of Water and Wastes,” USEPA Publication #600/4-79-020, March, 1979. )
Kipphut data temperature measurements made with a mercury thermometer

Site specific information:

The following lakes have been used as experimental from 1983-1989:
Nutrient enrichment: N2, Toolik Limno Corral
Food web manipulations: Toolik Limno Corral
Reference lakes (no manipulations): Toolik, N2 Ref, N1**

In 1985 Lake N2 was separated into two parts with a dividing curtain, with half being fertilized at a rate calculated to be approximately 5 times the normal loading of nitrogen and phosphorous. The fertilizers used were ammonium nitrate and phosphoric acid. Site names "N2 Fert" indicates measurements from the fertilized side of the curtain (Measurements beginning July 5, 1985) and "N2 Ref" indicates the control (or reference) portion of the lake which was not fertilized. The curtain was removed in 2011. Prior to 1985 and after 2011 data from this lake was simply called Lake N2.

Site N3 data was obtained for consideration of fertilizing the lake (measured only once in May, 1985)

**Lake N1 data (from 1989) contained in this file is baseline data for lake N1 in which a fertilization experiment began in 1990.

Toolik Limno Bay was the site of an experiment testing the impact of human exploitation on arctic lakes. Corrals were 5 m in diameter and 5-6 m depth open to the sediment. Four limocorrals were deployed in 1983. These were treated with nutrient additions and fish addition (arctic grayling). Methods and experimental results and discussion are found in: O'Brien, W.J., A.E. Hershey, J.E. Hobbie, M.A. Hullar, G.W. Kipphut, M.C. Miller, B. Moller & J.R. Vestal. 1992. Control mechanisms of arctic lake ecosystems: a limn corral experiment. Hydrobiologia, 240: 143-188. In Book: Toolik Lake - Ecology of an Aquatic Ecosystem in Arctic Alaska. W.J. O'Brien (ed.), Kluwer Academic Publishers, Belgium.

Reference Citations: Wetzel, R.G., G.E. Likens. 1979. Limnological Methods. Saunders. Philadelphia.