Walker Branch Watershed Stream Chemistry

The long-term Walker Branch stream chemistry monitoring is intended to provide data on watershed output of chemicals via streamflow and long-term changes in stream chemical composition.

This data set contains a single spreadsheet with the results of physical and chemical stream measurements for the period 1989 through 2011.

Walker Branch Watershed is drained by two first-order streams, West and East Forks. Weirs (120 degree V-notch) are located near the confluence of the West and East Forks and water level is recorded at 15-minute intervals for the calculation of discharge.

Spatial Extent:
West Fork subcatchment = 38.4 ha
East Fork subcatchment = 59.1 ha

GIS data set information
See Walker Branch Watershed Project website:
http://walkerbranch.ornl.gov

The Walker Branch Watershed data provided on this site are freely available and were furnished by ORNL scientists who encourage their use. Please kindly inform the Data Center Contact of any publication plans. Please acknowledge the data source as a citation or in the acknowledgments as given in the Data Set Citation.

Sampling:
Weekly sampling of stream water was begun in the West Fork in 1989 and in the East Fork in 1995. Grab samples are collected between the hours of 0900 and 1200 on Tuesdays. In some years, grab samples were collected on 1-3 additional dates of high discharge. Samples are collected at a site approximately 60 m upstream from the weir in the West Fork and approximately 20 m downstream from the weir in the East Fork (weirs are approximately 30 m upstream of the confluence of the West and East Forks). Weir stage is recorded at the time of sampling each stream to calculate stream discharge. Water temperature and specific conductance are measured in the field using an ORION Model 122 meter. Water samples are collected and returned to the laboratory within 1 hour for processing and analysis.

Laboratory processing and analysis:
In the laboratory, unfiltered samples are analyzed for pH and alkalinity. pH is determined within 1 hour (sample not equilibrated with the atmosphere). Samples for alkalinity are refrigerated until analysis (within 3 months). Alkalinity is measured by titration with 0.01 N HCl to a pH of 4.5. Approximately 250 mL of stream water is filtered (0.4 um pore size Nuclepore polycarbonate filters) within 1 hour of return from the field for analysis of solutes. Separate filtered samples are stored for the following analyses: (1) soluble N and P concentrations (frozen), (2) dissolved organic carbon (DOC) concentrations (acidified to a pH < 3 and refrigerated), (3) Cl and SO4 concentrations (refrigerated), and (4) major cations, metals, and Si (acidified to 0.2% HNO3 and stored at room temperature). Analytical methods are described below. An additional unfiltered sample is frozen for later analysis of total phosphorus using the same method as described below for total soluble phosphorus.

Analytical methods:

NH4 - Automated phenate colorimetry (American Public Health Association, APHA 1995) using Bran Luebbe TRAACS autoanalyzer prior to July 1999 and Bran Luebbe AAIII autoanalyzer after July 1999.

NO2 + NO3
Automated Cu-Cd reduction followed by azo dye colorimetry (APHA 1995)
using Bran Luebbe TRAACS autoanalyzer prior to July 1999 and Bran Luebbe AAIII autoanalyzer after July 1999.

Total soluble N
Alkaline persulfate digestion followed by NO3 analysis prior to May 1996 (APHA 1995); UV oxidation followed by NO3 analysis between May 1996 and April 2000; High temperature combustion (Shimadzu TNM-1) after April 2000.

Soluble reactive P
Ascorbic acid method (APHA 1995) using 10 cm pathlength spectrophotometric cell.

Total soluble P
Persulfate oxidation followed by ascorbic acid method (APHA 1995)

Dissolved organic carbon
OI model 700 TC analyzer prior to March 1992; High temperature combustion using Shimadzu Model 5000 TOC analyzer after March 1992.

Cl and SO4
Ion chromatography (APHA 1995)

Ca, Mg, Na, Fe, Mn, Si, Al, trace metals
Inductively coupled plasma emission spectroscopy (APHA 1995)

Reference:
American Public Health Association (APHA). 1995. Standard Methods for the Examination of Water and Waste Water. 19th edition, American Public Health Association, Washington, DC.

Publications:

Mulholland, P. J. 1992. Regulation of nutrient concentrations in a temperate forest stream: roles of upland, riparian, and instream processes. Limnology and Oceanography 37:1512-1526.

Mulholland, P. J. 1993. Hydrometric and stream chemistry evidence of three storm flowpaths in Walker Branch Watershed. J. of Hydrology 151:291-316.

Mulholland, P. J., and W. R. Hill. 1997. Seasonal patterns in streamwater nutrient and dissolved organic carbon concentrations: Separating catchment flow path and in-stream effects. Water Resources Research 33:1297-1306.

Mulholland, P. J. 2004. The importance of in-stream uptake for regulating stream concentrations and outputs of N and P from a forested watershed: evidence from long-term chemistry records for Walker Branch Watershed. Biogeochemistry 70:403-426.