LOCATION DESCRIPTION
Mirror Lake is 15 ha in area, and an oligotrophic (low productivity),
clearwater (Secchi transparency 6 to 7 m), natural water body adjacent
to HBEF. The lake normally mixes in spring and fall, and is ice-covered
from about 1 December to about 15 April each year. 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
Water samples are collected in a boat from an anchored buoy station, or
from the ice surface located at the deepest part (11 m at full pool) of
Mirror Lake. Samples for ion analysis are collected in acid-washed,
deionized water-rinsed, polyethylene bottles, using a manual closure,
plastic VanDorn collector bottle (before 1990), triggered at discrete
depths, or lifted to the surface through weighted vinyl tubing by
peristaltic pump (since 1990). DO and DIC samples are collected in
standard glass BOD bottles. Typically, water samples are taken from the
surface (<0.5m), and at depths of 2, 4, 6, 8, and 10 meters. The usual
sampling interval is 4 to 6 times each year, especially at times of
maximum and minimum thermal stratfication. Temperatures are determined
by thermistor probe (Whitney, YSI, or Digisense Models).
DATA DESCRIPTION
Concentrations (mg/L) in lake water samples from discrete depths. Base
cation, pH, and dissolved oxygen data
are available since 1967. Ammonium, anions, phosphate, and dissolved
silica have been measured routinely since 1970, although some data are
available prior to these dates for each solute. Other standard data
include temperature and specific conductance at each depth. Prior to
1990, not all records have complete solute arrays. since 1990, dissolved
in-organic carbon (DIC) and acid neutralizing capacity (ANC; alkalinity)
have also been measured on a routine basis, although prior data do
exist.
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.
