Watershed Pollutant Load Monitoring Network
The Watershed Pollutant Load Monitoring Network (WPLMN) is designed to measure and compare regional differences and long-term trends in sediment and nutrients among Minnesota’s major rivers including the Red, Rainy, St. Croix, Minnesota, and Mississippi and the major tributaries (8 digit HUC scale) draining to these rivers. The network was established in 2007 following passage of Minnesota’s Clean Water Legacy Act with subsequent funding from the Clean Water Fund of the Minnesota Clean Water, Land and Legacy Amendment. Site-specific stream flow data from the United States Geological Survey (USGS) and Minnesota Department of Natural Resources (DNR) gaging stations is combined with water quality data collected by the Metropolitan Council Environmental Services (MCES), local monitoring organizations, universities, and WPLMN staff to compute pollutant loads at river monitoring sites across Minnesota.
Monitoring sites span three ranges of scale: 1) Basin (Mississippi, Minnesota, Rainy, Red, St Croix rivers); 2) Major Watershed (8 digit HUCs); and 3) Subwatershed (drainage areas of approximately 300-500 mi2 within 8 digit HUCs). Water quality and flow data are collected and loads calculated on an annual time scale for the Basin and Major Watershed sites. Subwatershed sites are only monitored during the open water season; pollutant loads for these sites are calculated seasonally. For more information see the fact sheet below:
Pollutant load monitoring sites in Minnesota
Click on the map to see details and data from the monitoring sites.
Monitoring
Program goals
The Watershed Load Monitoring Network is tied to the goals of the 1972 Clean Water Act for restoring and protecting the multiple beneficial uses and ecological integrity of America's waters.
Primary goals:
- Measure and compare regional differences in water quality.
- Determine long-term trends in water quality.
Data will also be used to assist with: impaired waters assessments; watershed and water quality studies and reports; watershed modeling efforts: and to measure the ongoing effectiveness of major watershed protection and restoration plans.
Location of monitoring sites
Establishment and sampling of the Basin and Major Watershed sites began in 2007 with all sites established by 2009.
Subwatershed site determination and establishment occurred in 2011 for the NE and NW regions of the state with sampling commencing in 2012. Subwatershed site determination for the remainder of Minnesota will occur in 2013 with sampling to begin in 2013 or 2014 dependent upon region. Due to slight programmatic changes, redetermination of NE and NW Subwatershed sites will occur in 2013. There are currently 24 and 21 Subwatershed sites in the NW and NE regions of the state respectively with 12 and 29 proposed for the SE and SW regions, respectively. The following criteria are considered in Subwatershed site selection.
- Approximate drainage area of approximately 300 to 500 mi2 (on average).
- Hydrologic breaks such as major river forks/branches.
- Major changes in land use, geography, geology, or other physiographic/anthropogenic influences may result in concentration/flow shifts in water quality.
- Approximately 2-3 subwatershed monitoring sites per major watershed, depending on the size of the Major Watershed.
Monitoring strategy and sampling procedures
Approximately 35 water quality samples are collected annually at Basin and Major Watershed sites and 25 samples collected seasonally at Subwatershed sites. Water quality measurements collected include both field and laboratory measurements. Annual water quality and daily average discharge data are coupled in Flux32 pollutant load modeling software to calculate pollutant loads. Primary output includes annual/seasonal and daily pollutant loads and flow weighted mean concentrations (pollutant load/total flow volume). Loads and flow weighted mean concentrations are calculated for total suspended solids (TSS), total phosphorus (TP), dissolved ortho phosphorus (OP), nitrate plus nitrite nitrogen (NO3+NO2 -N) and total Kjeldahl nitrogen (TKN). Field measurements include: pH, dissolved oxygen, specific conductance, temperature, and sechi tube. All labs used in the program are certified by the Minnesota Department of Health and are included in the MPCA Sampling and Analytical Services master contract.
MPCA WPLMN staff and their monitoring partners collect water quality samples at or near USGS or MDNR flow gaging stations. Water quality samples are collected from the thalweg (the line of fastest flow within a stream cross section) of the channel, slightly below the water surface using a weighted bucket or horizontal sampler. Since concentration and flow often correlate for many of the monitored analytes, sample collection frequency is greatest during periods of moderate and high flow. Low flow periods are sampled less frequently as concentrations are generally more stable when compared to periods of elevated flow. Despite discharge related differences in sample collection frequency, this staggered approach to sampling generally results in samples being well distributed over the entire range of flows.
For detailed procedural information, see the
Major Watershed Load Monitoring Standard Operating Procedures (wq-cm1-02) .

Example: Lac qui Parle River hydrograph with sample collection dates plotted
In-field measurements
|
pH |
pH is a measure of acidity and alkalinity of a solution on a scale of 0 to 14, where 7 is neutral and lower numbers represent acidity and higher numbers represent alkalinity; the optimal range for most organisms is 6.5 to 8.2. Dissolved oxygen (DO) is indirectly affected by changes in pH. The toxicity of many compounds can be altered if pH changes, because pH alters chemical and biological reactions and processes. Changes in pH are predominantly related to the health of aquatic organisms, especially fish and invertebrates. |
|---|---|
|
Temperature |
Temperature is a measure of warmth or coldness of a substance with reference to a standard value (USGS). Temperature affects many physical, biological and chemical characteristics such as dissolved oxygen, rate of photosynthesis, metabolic rates and sensitivity to toxics, parasites and disease |
|
Specific Conductance |
Specific Conductance is a measure of the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge). Conductivity is affected by temperature: the warmer the water, the higher the conductivity. For this reason, conductivity is reported as conductivity at 25 degrees Celsius (25 C). Conductivity is useful as a general measure of stream water quality. Each stream tends to have a relatively constant range of conductivity that, once established, can be used as a baseline for comparison with regular conductivity measurements. Significant changes in conductivity could then be an indicator that a discharge or some other source of pollution has entered a stream (USEPA). |
|
Dissolved oxygen |
Dissolved oxygen is a measure of the amount of gaseous oxygen (O2) dissolved in water. Oxygen gets into water by diffusion from the surrounding air, aeration (rapid movement of water), and as a waste product of photosynthesis. Adequate dissolved oxygen is necessary for good water quality and oxygen is a necessary element to all forms of life. As dissolved oxygen levels in water drop below 5.0 mg/l, aquatic life is put under stress. The lower the concentration, the greater the stress. Oxygen levels that remain below 1-2 mg/l for a few hours can result in large fish kills. |
|
Secchi tube |
Designed to function like the traditional Secchi disk used in lake monitoring, a sechi tube reading is an indirect measure of the amount of dissolved and suspended material present in the water. |
Laboratory analysis
|
Total suspended solids (TSS) |
Total Suspended Solids (TSS) are solids in water that can be trapped by a filter. TSS can include a wide variety of material, such as inorganic sediments like silt and clay and organic material like decaying plant and animal matter. High concentrations of suspended solids can cause many problems for stream health and aquatic life. The decrease in water clarity caused by TSS can affect the ability of fish to see and catch food. Suspended sediment can also clog fish gills, reduce growth rates, decrease resistance to disease, and prevent egg and larval development. When suspended solids settle to the bottom of a water body, they can smother the eggs of fish and aquatic insects, as well as suffocate newly hatched insect larvae. Settling sediments can fill in spaces between rocks reducing the amount of space where aquatic organisms can reside. |
|---|---|
|
Suspended volatile solids (SVS |
Suspended Volatile Solids is a measure of the amount of total suspended solids that are lost on ignition (heating to 550 degree C). This measure is often used to determine the proportion of TSS composed of organic matter. |
|
Turbidity |
Turbidity is the measurement of scattered light that results from the interaction between a beam of light and particulate material in a liquid sample. It is an expression of the optical properties of a sample that causes these light rays to be scattered and absorbed rather than transmitted in straight lines through the sample1. Turbidity of water is often caused by the presence of suspended and dissolved matter such as clay, silt, finely divided organic matter, plankton, other microscopic organisms, organic acids, and dyes. Turbidity has been used as a key indicator for water quality to assess the health and quality of environmental water sources. Higher turbidity values are typically associated with poorer water quality. |
|
Dissolved ortho phosphorus (OP) |
Dissolved orthophosphate is a measure of the filterable (soluble, inorganic) fraction of phosphorus, the form directly taken up by plant cells. |
|
Total phosphorus (TP) |
Phosphorus exists in water in either a particulate phase or a dissolved phase. Particulate matter includes living and dead plankton, precipitates of phosphorus, phosphorus adsorbed to particulates, and amorphous phosphorus. The dissolved phase includes inorganic phosphorus and organic phosphorus. Total phosphorus (TP) is a measure of all the forms of phosphorus, dissolved or particulate, found in a sample. Phosphorus is a nutrient required by all organisms for the basic processes of life. Phosphorus is a natural element found in rocks, soils and organic material. Phosphorus clings tightly to soil particles and is used by plants, so its concentrations in clean waters are generally very low. In freshwater lakes and rivers, phosphorus is often found to be the growth-limiting nutrient, because it occurs in the least amount relative to the needs of plants. If excessive amounts of phosphorus are added to the water, algae and aquatic plants can be produced in large quantities. When these algae die, bacteria decompose them, and use up oxygen.2 |
|
Nitrate plus nitrite nitrogen (NO3+NO2-N) |
Nitrate (NO3) is highly soluble (dissolves easily) in water and is stable over a wide range of environmental conditions. It is easily transported in streams and groundwater. Nitrates feed plankton (microscopic plants and animals that live in water), aquatic plants, and algae, which are then eaten by fish. Nitrite (NO2) is relatively short-lived in water because it is quickly converted to nitrate by bacteria. Nitrogen is required by all organisms for the basic processes of life to make proteins, to grow, and to reproduce. Nitrogen is very common and found in many forms in the environment. Inorganic forms include nitrate (NO3), nitrite (NO2), ammonia (NH3), and nitrogen gas (N2). Excessive concentrations of nitrate and/or nitrite can be harmful to humans and wildlife.2 |
|
Total Kjeldahl nitrogen (TKN) |
The measure of the sum of organic nitrogen, ammonia and ammonium: used in the calculation of total nitrogen. Ammonia, is an inorganic form of nitrogen and is the least stable form of nitrogen in water. Ammonia is easily transformed to nitrate in waters that contain oxygen and can be transformed to nitrogen gas in waters that are low in oxygen. Ammonia is found in water in two forms - the ammonium ion (NH4+), and dissolved, unionized (no electrical charge) ammonia gas (NH3). (NH3) is much more toxic to aquatic organisms than the ammonium ion (NH4+). When plants and animals die, organic nitrogen contained within is broken down by bacteria to form ammonia (NH3). |
|
Total nitrogen |
The sum of nitrate plus nitrate nitrogen and total nitrogen. Total nitrogen is the measure of all organic and inorganic forms of nitrogen contained within a water quality sample. |
References:
- S. Clesceri, L. Greenberg, A and Eater 1998. “Method 2130. Turbidity”, Standard Methods for the Examination of Water and Wastewater, 20th Ed. , American Public Health Association, Washington DC.
- Murphy, Shelia, 2007. Boulder Area Sustainability Information Network.
Analytical procedures
A pollutant load is the amount (mass) of a pollutant passing a stream location over a unit of time. The Watershed Pollutant Load Monitoring Network (WPLMN) calculates pollutant loads by coupling water quality and discharge data from United States Geological Survey and Minnesota Department of Natural Resources flow gaging stations to create mathematical relationships (using Flux32 model) to predict pollution concentrations on days when samples are not collected.
Flux32 is windows based interactive software developed by Dave Soballe, US Army Corps of Engineers, in conjunction with the Minnesota Pollution Control Agency. Flux32 is based on the original FLUX application written by William Walker, Ph. D., under sponsorship of the U.S. Army Corps of Engineers (USACE) in the 1980s as a DOS-based program for personal computers. Flux32 is user friendly and capable of sophisticated examinations and evaluations of data and flow relations and calculation of material fluxes (loads) in streams. Primary output includes annual and daily pollutant loads and concentrations. Annual pollutant loads and flow weighted mean concentrations of total suspended solids (TSS), total phosphorus (TP), dissolved orthophosphate (DOP), nitrate plus nitrite nitrogen (NO2+NO3-N) and total kjeldahl nitrogen (TKN) are calculated for all sites within the WPLMN.
How are pollutant loads calculated?
The monitoring and load calculation period for rivers within the Major WPLMN is January 1st through December 31st, and seasonally, ice out through October 31, for the Intermediate sites. Daily pollutant loads are calculated by multiplying daily average flow times the actual or estimated daily pollutant concentration. Annual or seasonal loads are the sum of daily loads across the monitoring period.

Products/Data
Products
- Long Term Average and Annual statewide water quality summaries - Flow-weighted mean concentrations calculated for total suspended solids (TSS), total phosphorus (TP), dissolved orthophosphate (DOP), total Kjeldahl (TKN), and nitrate plus nitrite nitrogen.
- Maps:
- Watershed Average (2007-2009)
- Main Stem Flow Concentrations (2007-2009)
Watershed Pollutant Load Monitoring Network
Pollutant Averages 2007-2009
Mississippi River Basin Pollutant Loads as a % of the Load Measured at Lock & Dam #3 (Ave. Monitoring Site Pollutant Load/ Ave. Pollutant Load at Lock & Dam #3)
|
Nitrate + Nitrite Nitrogen |
Total Nitrogen |
Total Phosphorus |
Total Suspended Solids |
|---|---|---|---|
|
|
|
|
|
- Data files:
-
2007-2009 Average Loads (wq-cm4-05) -
2007-2009 Annual Loads (wq-cm4-04)
-
- Watershed Monitoring and assessment reports:
- Minnesota Watersheds Monitoring and Assessment Report – click on each watershed to see the watershed report.
- Water quality trends – Several years of data are required to determine increasing and decreasing trends in water quality. Results are currently unavailable.
Databases
- DNR/MPCA Cooperative Stream Gaging Network - USGS, DNR, and MPCA – Stream discharge and links to Division of Waters Resources, climate information, river levels, water quality information, recreation, and commonly used hydrological terms.
- USGS – USGS discharge information.
- Environmental Data Access – Water quality data collected for all MPCA monitoring programs.
Contacts/Links
Contact information
Contact the monitoring staff in your region to answer your questions or for more information about the Major Watershed Load Monitoring Program.
|
Monitoring Coordinator |
Patrick Baskfield, 507-344-5240 |
|---|---|
|
Metropolitan Council |
Karen Jensen, 651-602-1000 |
|
Central Minnesota |
Jim MacArthur, 218-316-3881 |
|
East Central Minnesota |
Gerry Flom, 651-757-2363 |
|
Northwestern Minnesota |
Andy Butzer, 218-846-0485 |
|
Northeastern Minnesota |
Stacia Grayson, 218-302-6631 |
|
Southwestern Minnesota |
Kelli Nerem 507-476-4251 |
|
Southeastern Minnesota |
Mike Walerak, 507-206-2623 |
Who collects WPLMN water quality samples?
- MPCA Major Watershed Load Monitoring Staff
- Metropolitan Council Environmental Services
- Local groups:
- Chippewa River Watershed Project
- Redwood Cottonwood Rivers Control Area
- Hawk Creek Watershed Project
- Minnesota State University, Mankato - Minnesota River Basin Data Center
- International Water Institute
- Lake of the Woods Soil and Water Conservation District
- Carlton County SWCD
- University of MN - NRRI
- Koochiching County SWCD
- Itasca County SWCD
- Cannon River Watershed Partnership
- Zumbro Watershed Partnership
- Fillmore Soil and Water Conservation District
Links to related information
Flux32 software
Flux32 Software
Flux32 is windows based interactive software developed by Dave Soballe, US Army Corps of Engineers, in conjunction with the Minnesota Pollution Control Agency. Flux32 is based on the original FLUX application written by William Walker, Ph.D., under sponsorship of the U.S. Army Corps of Engineers (USACE) in the 1980s as a DOS-based program for personal computers. Flux32 is user friendly and capable of sophisticated examinations and evaluations of data and flow relations and calculation of material fluxes (loads) in streams.
Download Flux32:
- ftp://simpletools.dyndns.org/FLUX_Updates/ (User name: guest, Password: password)
- Updates and new tools are being developed for Flux32; check the link above for periodic updates.
WPLMN Grants
Information about grants opportunities is available on the Watershed Pollutant Load Monitoring Sampling Grants page.
