Data set creator(s): Diane McKnight
For data content questions, contact Niwot LTER data manager
For methodology questions, contact Diane McKnight
INSTAAR, University of Colorado
1560 30th St., UCB 450
Boulder, CO 80309-0450
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This dataset contains water quality measurements made on Green Lakes 1, 4, 5, and Lake Albion starting in 2000 (for Green Lake 4) and ongoing. Water samples were collected for analysis of chlorophyll a, pH, temperature, specific conductivity, dissolved oxygen (dO), % saturation, secchi depth, light attenuation, and % of surface. Most samples were collected between 0900 and 1100 MST. The first sampling date each summer occurred shortly after the ice had melted. An inflatable raft was used to reach the middle of the lake. The majority of the measurements were taken at the surface, three meters, and nine meters from the raft. However, additional measurements were taken for side projects of the long-term dataset during several of the years and are included in this dataset. Water samples were collected using a Van Dorne sampler. Field measurements were conducted using a YSI dissolved oxygen meter and a Li-Cor datalogger. Chlorophyll was extracted from filtered samples and absorbance was measured before and after acidification to quantify chlorophyll a concentration.
Green Lake 1, Green Lake 4, Green Lake 5, and Lake Albion
2000/7/6 - ongoing
during summer season
chlorophyll a, pH, temperature, conductivity, dissolved oxygen, oxygen saturation, secchi depth, light attenuation, surface light intensity, dissolved organic carbon
Elevation: 3415 m
Green Lake 4
Elevation: 3550 m
Green Lake 5, photo credit: JG Smith
Elevation: 3620 m
Elevation: 3250 m
Green Lakes Valley (City of Boulder Watershed)
Located in: City of Boulder Watershed
(Click to learn more about these locations)
More data from: Green Lake 1, Green Lake 4, Green Lake 5, Albion
Core Data Set: yes Core Area: Inorganic nutrients, Organic matter dynamics, Primary productivity
Discipline: Limnology, Biogeochemistry
Award Or Grant: DEB1027341, DEB1637686
Water samples are collected every year for chemical analysis and algal biomass beginning in the summer of 2000. The first sampling date each summer occurs shortly after Green Lake 4 is completely free of ice. Sampling takes place for 6 weeks after ice-out. An inflatable raft is used to reach the deepest portion of the lake. Samples for nutrient analysis, Chl-a, algal biomass, and phytoplankton community composition as well as dissolved organic carbon are collected at the surface and at depths of three and nine meters with a Van Dorn sampler. Water samples are also collected at the Green Lake 4 inlet and outlet.
No chlorophyll measurements were made in 2003 and 2012.
Chlorophyll a samples were filtered within 12 hours through Whatman glass fiber filters (pore size 1.2 µm) with a hand-pump filtration system, and filters were frozen in aluminum foil until they were processed. Chlorophyll was removed from the filters with hot ethanol extraction and quantified by the spectrophotometric method of Marker et al. (1980), and included a phaeopigment correction. Absorbance measurements were taken before and after acidification with hydrochloric acid at 665 and 750 nm. The following equation was used to quantify chlorophyll a concentration:
chlorophyll a (µg/L) = 29.6((665b-750b)-(665a-750a))*(v/Vz)
where 665b and 750b are the absorbances of the sample at 665 and 750 nm before acidification, 665a and 750a are the absorbances after acidification, v is the volume of ethanol solvent in mL, V is the volume of sample originally filtered in L, and z is the cuvette length in cm.
The depth of 1% irradiance was calculated for each date from light measurements taken in the field. The primary purpose of measuring light attenuation in this study was to estimate the depth at which insufficient light is available to support positive net photosynthesis.
Dissolved oxygen sampling was conducted using a YSI dissolved oxygen meter and a Li-Cor datalogger.
Percent saturation of oxygen was calculated based on dissolved oxygen concentrations.
Water is also filtered through combusted Whatman GF/F filters into combusted glass amber bottles to determine dissolved organic carbon concentration and origin (microbial or plants) of dissolved organic material (DOM).
Additionally, water from Inlet, Outlet, 0m, 3m and 9m is filtered through Millipore GF/F filters to analyze for chemical composition (nutrients) of the lake water.
Samples are processed (filtered and preserved in Lugol's solution in case of phytoplankton) immediately after sample collection.
Green Lake 5 was sampled in 2005 for the same parameters as Green Lake 4.
In 2014 an annual sampling effort for Green Lake 1 was started for the same parameters outlined above for GL4. Lake Albion was added as a sampling site in 2016.
Site codes: GL1 = Green Lake 1, GL4 = Green Lake 4, GL5 = Green Lake 5, ALB = Lake Albion.
Light attenuation values for 2008 to 2014 were set to missing pending a determination of the correct values and units.
chlorophyll a, pH, temperature, conductivity, dissolved oxygen, oxygen saturation, secchi depth, light attenuation, dissolved organic carbon, Green Lake 4, Green Lake 5, Green Lakes, Lake Albion, water samples, water quality, NWT, Niwot Ridge LTER, inorganic_nutrients, organic_matter_dynamics, limnology, aquatic, long term
COL1. label=site, type=string, units=none, missing value indicator=NaN, minimum=ALB, maximum=GL5, precision=, definition=site
COL2. label=depth/loc, type=string, units=none, missing value indicator=NaN, minimum=, maximum=, precision=, definition=depth (meters) or location
COL3. label=date, type=string, units=none, missing value indicator=NaN, minimum=2000-07-06, maximum=, precision=, definition=date (yyyy-mm-dd)
COL4. label=time, type=string, units=none, missing value indicator=NaN, minimum=00:00, maximum=24:00, precision=, definition=time (hh:mm)
COL5. label=chl_a, type=real, units=microgramPerLiter, missing value indicator=NaN, minimum=, maximum=, precision=2, definition=chlorophyll a
COL6. label=pH, type=real, units=none, missing value indicator=NaN, minimum=0, maximum=14, precision=2, definition=pH
COL7. label=temp, type=real, units=celsius, missing value indicator=NaN, minimum=, maximum=, precision=1, definition=temperature
COL8. label=std_conduct, type=real, units=microsiemen, missing value indicator=NaN, minimum=, maximum=, precision=2, definition=standardized conductivity (temp. corrected)
COL9. label=conduct, type=real, units=microsiemen, missing value indicator=NaN, minimum=, maximum=, precision=2, definition=conductivity
COL10. label=DO, type=real, units=milligramPerLiter, missing value indicator= NaN, minimum=, maximum=, precision=2, definition=dissolved oxygen
COL11. label=sat, type=real, units=none, missing value indicator=NaN, minimum=0, maximum=100, precision=1, definition=percent oxygen saturation
COL12. label=secchi, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=2, definition=secchi depth
COL13. label=light_att, type=real, units=micrometer, missing value indicator=NaN, minimum=, maximum=, precision=2, definition=light attenuation
COL14. label=surf_light, type=real, units=none, missing value indicator=NaN, minimum=0, maximum=100, precision=2,
definition=percent of surface light intensity
COL15. label=depth_light, type=real, units=meter, missing value indicator=NaN, minimum=, maximum=, precision=2,
definition=depth of 1% light attenuation
COL16. label=DOC, type=real, units=milligramPerLiter, missing value indicator=NaN, minimum=, maximum=, precision=2, definition=dissolved organic carbon
COL17. label=comments, type=string, units=none, missing value indicator=NaN, minimum=, maximum=, precision=, definition=comments
*Note: To ask a question about data content, please contact the data manager HERE
To ask a question about methodology, please contact Diane McKnight,
 Marker, A.F.H., C.A. Crowther, R.J.M. Gunn. 1980. Methanol and acetone as solvents for estimating chlorophyll a and phaeopigments by spectrophotometry. Advances in Limnology, 14 (Meas. Photosynth. Pigm. Freshwaters Stand. Methods):52-69.
 Flanagan, C.M.; McKnight, D.M.; Liptzin, D.; Williams, M.W.; Miller, M.P. 2009. Response of the phytoplankton community in an alpine lake to drought conditions: Colorado Rocky Mountain Front Range, U.S.A. Arctic, Antarctic, and Alpine Research 41(2):191-203.
The documentation, header, and data sections of this file were developed from an Excel spreadsheet provided by Diane McKnight and Alia Khan.[HCH 23 January 2013] Comments section in metadata edited, keywords added, column descriptions revised, empty data rows removed, comments column added to data, header row added,data added for 2012 and 2013.[HCH 30 October 2014] Order of variables changed for agreement with water chemistry data.[HCH 12 November 2014] Data were appended for 2014 and meta data updated to reflect addition of sampling in Green Lake 1.[HCH 15 May 2015] Units were edited.[HCH 28 April 2016] Data were appended for 2015 and 2016. Light attenuation values for 2008-2014 were set to missing due to possible value/unit problems. Metadata were updated to reflect addition of sampling in Lake Albion.[HCH 20 October 2016] Temperature units changed to celsius.[HCH 27 April 2017]
McKnight, Diane. 2017. Water quality data for Green Lake 1 Green Lake 4 Green Lake 5 Lake Albion from 2000/7/6 - ongoing, during summer season. http://niwot.colorado.edu
This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-1637686. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necesarily reflect the views of the National Science Foundation.
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