LOCATION DESCRIPTION
Collected from below the Mirror Lake dam, but above the USGS stream-gauging flume. The dam is a concrete and stone structure, with un-treated, wooden spillway boards, that remain in place year-round. Outflow from the lake over the dam varies from 1 to 1000 L/sec, depending on lake pool level and seasonal hydrology. Mirror Lake is 15 ha in size, 11 m deep, and an oligotrophic, clearwater, natural water body adjacent to HBEF. Numerous studies have been conducted on Mirror Lake since the mid-1960s, including extensive physical, chemical, biological, and paleoecological research which are described in detail in the book: An Ecosystem Approach to Aquatic Ecology (Likens, 1985).
SAMPLING DESIGN
Samples are collected in acid-washed, deionized water-rinsed, polyethylene bottles, from water flowing over the spillway boards. The normal sampling interval is weekly, with more frequent samples taken at times of increased discharge. At low lake pool levels, samples may be taken from leakage through small gaps in the boards.
DATA DESCRIPTION
Concentrations (mg/L) in weekly streamwater samples. Base cations and pH are available since 1967. Ammonium, anions, and dissolved silica have been measured since 1970, and phosphate was routinely determined first in 1972, although some data are available for each solute prior to these dates.
NOTE REGARDING NITRATE DATA: After careful and exhaustive inter- and intra-laboratory tests we determined that nitrate concentrations in stream water were no longer remaining stable after collection, as they had in the past (see Buso, Likens and Eaton 2000). It is possible that the biological community in some streams of the HBEF has changed in recent years, affecting the nitrate concentration in complicated ways. While there was no systematic bias to the data, the situation occurred primarily during summer, when nitrate concentrations and streamflows are very low. Thus, we urge some caution in using the streamwater nitrate data collected since 2006, when nitrate stability was last confirmed. In 2013, new protocols were instituted to prevent decay of nitrate concentrations after collection and the problem has been resolved. There is no evidence that nitrate concentrations in the long-term precipitation record have been affected.
Buso, Donald C.; Likens, Gene E.; Eaton, John S. 2000. Chemistry of precipitation, streamwater, and lakewater from the Hubbard Brook Ecosystem Study: a record of sampl
ing protocols and analytical procedures. Gen. Tech. Rep. NE-275. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 52
p.
Likens, G.E. (1985). An Ecosystem approach to aquatic ecology: Mirror Lake and its environment. Springer-Verlag New York, Inc.
