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University of Minnesota
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Methods for Experiment 280 -

Water Sampling

Every two weeks, beginning in late May and ending in late August, a team of 2-4 students (graduate and undergraduate), faculty or staff will visit Cedar Creek and sample from the road or from canoe the following locations:

1. Cedar Creek Upper (Xylite St. NE overpass at N end of property)
2. Cedar Creek Lower (Fawn Lake Dr. NE overpass near E end of property)
3. Fish Lake
4. Beckman Lake Bog
5. Cedar Bog Lake
6. Ice Lake

Physical data (temperature, light) and chemical data/samples (DO, various forms of carbon, nitrogen and phosphorus) will be take at each location. Approximately 20 L of water will be removed and transported back to St. Paul for the purpose of conducting short-term nutrient limitation bioassay studies. Water samples are held in coolers and transported to St. Paul lab where they are held in refrigerated rooms. They are subsampled and filtered for various analyses within 24 hours, usually the same day.

adge280 - Surface water chemistry

Lab Protocol References for acke280-surface water chemistry

Holmes et al. 1999. A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Can. J. Fish. Aquat. Sci. 56: 1801-1808.

Taylor et al. 2007. Improving the fluorometric ammonium method: matrix effects, background fluorescence, and standard additions. J. N. Am. Benthol. Soc. 26(2): 167-177.

Lachat Instruments Data Pack Ulta Low Flow Methods September 2009

J. D. H. Strickland and T. R. Parsons: A Practical Handbook of Seawater Analysis. Ottawa: Fisheries Research Board of Canada, Bulletin 167, 1968.

Sampling and lab analyses methods

Beginning on July 8, 2013, an 80 um pre-filtration was performed for all whole water, 0.7 fraction water, and particulate samples. Before this date, little material > 80um was observed. Detection limits determined by 2.57*sd where sd is the standard deviation of concentrations inferred for a set of blanks measured over multiple runs. Empty cells in the dataset data reflect values below the detection limit.

ParameterDefinitionMethodsNotesData AnalysisDetection limit
POC (ug/L)Particulate Organic CarbonSample collected on ashed GF/F filter. Frozen, dried at 60C. Run on Perkin Elmer 2400 CHN analyzer. Values reported usually are means of two filtered samples.
DIC (mg/L)Dissolved inorganic carbon.`Contains carbonates and CO2. Single sample, machine takes four readings, best three are averaged.
DOC (mg/L)Dissolved Organic CarbonGF/F filtrate. Reported as NPOC using Shimadzu TOC/VCSH or TOC/L. Post acification to pH of 2 and sparging with purified air. Organic carbon present in a sample in a nonvolatile form.Single sample, machine takes four readings, best three are averaged.
PON (ug/L)Particulate Organic NitrogenSample collected on ashed GF/F filter. Frozen, dried at 60C. Run on Perkin Elmer 2400 CHN analyzer. Values reported usually are means of two filtered samples.
TN (mg/L)Total NitrogenWhole or 80um filtered water (depending on week) run through TOC/L.Single sample, machine takes four readings, best three are averaged. 0.2
TDN (mg/L)Total Dissolved Nitrogen.GF/F filtrate. Using Shimadzu TOC/VCSH or TOC/L with TNM-1 attachment. High detection for nitrates, nitrites and ammonia and the majority of other organic N compounds. Low detection for hydrazines, pyrazolones and azide.Single sample, machine takes four readings, best three are averaged. 0.2
NO3 (umol/L)NitrateGF/F filtrate sample is frozen. Thawed sample is run using Cd-reduction protocol on a Lachat flow injection analyzer.Single sample, two to five pulls on Lachat are averaged.2.31
NH4 (umol/L)AmmoniuumGF/F filtered sample is frozen. Low value (<1 uM) samples, Taylor: Thawed samples are added to an OPA working reagent per Taylor 2007, using a combination of Holmes 1999 Methods A and B. Standard addition series done on all samples. Background fluorescence measured after adding working reagent and reading immediately. High value (> 1 uM) samples, Lachat: QickChem Method 10-107-06-1-J Ammonia Phenolate. Single sample, two to five pulls on Lachat are averaged, one standard addition series performed for Taylor.
TP (umol/L)Total PhosphorusWhole or 80 um filtered water depending on week. Perfulfate digestion; molybdate ascorbic acid reagent, run on benchtop using UV/VIS spectrophotometer with 10 cm path lengthSingle sample, single spec value with approximately 10% replicated to assess lab variation. 0.164
PP (umol/L)Particulate phosphorusSample filtered onto 25 mm acid-rinsed (approximately 10mL 1% HCl, followed by 50 mL nanopure, rinsed on filter tower) precombusted GF/F filter. Frozen. Dried at 60 C. Analyzed using persulfate then ammonium molybdate reaction.Values reported usually are means of two filtered samples.
TDP (umol/L)Total Dissolved PhosphorusAcid- rinsed-GF/F filtered water. Persulfate digestion; molybdate ascorbic acid reagent, run on benchtop using UV/VIS spectrophotometer with 10 cm path lengthSingle sample, single spec value with approximately 10% replicated to assess lab variation. 0.164
SRP (umol/L)Soluble Reactive PhosphorusAcid- rinsed-GF/F filtered water. Molybdate ascorbic acid reagent, run on benchtop using UV/VIS spectrophotometer with 10 cm path length.Single sample, single spec value with approximately 10% replicated to assess lab variation. 0.236
Chl-a (ug/L)Chlorophyll aSample filtered onto 25 mm 0.2 um cellulose nitrate filter and frozen. Extracted with 90% Acetone in the refridgerator for 20-24 h (no grinding of filer). Then measured on a Turner 10-AU using narrow band width filters per Welschmeyer 1994 or on Turner TD-700. Once every 4 y, Turner Design liquid standard is used for recalibration. Solid standard used in between. Single sample, single spec value with approximately 10% replicated to assess lab variation.
Si (umol/L)Dissolved Reactive SilicaGF/F filtered. Ammonium molybdate method from A Practical Handbook of Seawater Analysis. Single sample, single spec value with approximately 10% replicated to assess lab variation. 2.729