The US Geological Survey (USGS), Dane County, and the Madison Metropolitan Sewerage District (MMSD) fund baseflow monitoring throughout the county as part of the cooperative water resources monitoring program. Monitoring cycles through 21 sites, with about seven sites active each year. Various water quality parameters are measured to assess stream conditions during baseflow.

Photo By: Sarah Fuller

What is Baseflow Monitoring?

Stream baseflow consists primarily of groundwater discharge to streams. In some areas, groundwater may be supplemented by continuous point source discharges from wastewater treatment plants or industries. Baseflow water quality is less variable than runoff from storm events, so less frequent monitoring is necessary. This monitoring program samples streams about three times per growing season (April - October) during baseflow conditions.  At least seven sites are sampled each year on a rotating basis. Monitored chemical parameters include nitrogen, phosphorus, and chloride. Data shown here date back approximately ten years. This effort provides basic information needed for management decisions and assessing long-term trends in water quality.

What is Measured?

These parameters are used to document baseflow growing conditions.

Parameter Explanation
(cubic feet per second)
Baseflow monitoring targets conditions with stable, normal flow (discharge) unimpacted by stormwater runoff. The amount of water flowing in a stream increases after storm events, especially in watersheds with paved and impervious surfaces. Stormwater runoff can carry watershed pollutants from urban and agricultural areas into surface waters. When discharge is lower and unaffected by storm runoff, water quality reflects baseflow conditions. Baseflow is dominated by groundwater and pollutants observed under baseflow conditions can stem from shallow groundwater.
Dissolved oxygen
Dissolved oxygen (DO) is essential for aquatic organisms. Cold water holds more DO than warmer waters, so rising temperatures decrease oxygen concentrations putting cold-water adapted organisms at risk. Across Wisconsin, streams should have at least 5 mg/L DO. Trout streams should have 6 mg/L.
(standard units)
Aquatic communities are sensitive to pH conditions that are too acidic (low pH) or too basic (high pH). In natural waters, pH generally ranges from 6.5 to 8.5. Wisconsin's pH criteria specify that surface waters should have pH between 6.0 and 9.0.
Specific conductance
(microsiemens per centimeter)
Specific conductivity measures how electric current conducts through water. Increased dissolved solids generally increase water conductivity and can indicate pollution. Ions, such as chloride, increase specific conductance.
Temperature Water temperatures fluctuate with season and stream size. Different biological communities are adapted to specific temperature ranges. Fluctuations outside of this range can create inhospitable living conditions, degrading the biological community. Other water quality measures, such as DO, are dependent on temperature.
Winter de-icing and domestic water softening add chloride (Cl; a component of salt) to surface waters. Runoff carrying salt can recharge groundwater, increasing chloride concentrations.  As that groundwater contributes baseflow to surface waters in other seasons, chloride concentrations have increased over time. Chloride, an ion, increases water specific conductivity. High concentrations of chloride are toxic to aquatic life. The Wisconsin standard for chronic toxicity is 395 mg/L.
Ammonia (NH3) is associated with biological excretion, decomposition, agricultural (e.g. fertilizer and livestock waste) runoff and wastewater effluent. High concentrations of ammonia are toxic to aquatic life. EPA recommends that at pH 7 and 68 °F, ammonia should not exceed 1.9 mg/L, on average. As ammonia concentration, pH, and temperature increase, so does ammonia's aquatic toxicity.
Nitrate plus nitrite
Nitrate (NO3-) and Nitrite (NO2) are associated with decomposition, agricultural runoff, and wastewater. Nitrate can leach into groundwater and drinking water wells. Nitrate and nitrite concentrations in drinking water above 10 mg/L are harmful for infants and pregnant women. High nitrate concentrations in surface waters lead to eutrophication (increased nutrients and productivity). Algae and plants consume nitrate, and when these organisms die off, large decomposition events decrease DO and negatively impact aquatic organisms.
Nitrite (N02) is associated with agricultural runoff and wastewater. Concentrations above 1 mg/L in drinking water can be harmful for infants and pregnant women. Nitrite is mostly converted to nitrate in natural waters.
Orthophosphate (the amount of P in phosphate; P043-) is associated with wastewater, decay, erosion, stormwater runoff, and agricultural runoff. It is bioavailable and can spur primary productivity, such as algal and plant growth. Orthophosphate contributes to eutrophication (excess nutrients and growth).
Total phosphorus (TP) is associated with wastewater, decay, erosion, stormwater runoff, and agricultural runoff. It includes all forms of phosphorus, particulate and dissolved. Particulate P can be in material such as organic matter or sediment. Orthophosphates are the subset of P held as phosphate. TP contributes to eutrophication, and since it can be a limiting nutrient, increased concentrations can spur growth.
Total nitrogen
Total nitrogen (TN) is associated with wastewater, decay, and agricultural runoff. It includes all forms of nitrogen. N contributes to eutrophication, and since it can be a limiting nutrient, increased concentrations can spur growth.
Escherichia coli
(#/ 100 ml)
E. coli is measured as an indicator for presence of fecal coliform. Although E. coli may not result in illness to humans, its presence suggests that there may also be other harmful bacteria, viruses, or protozoans present that may elevate risk of water borne illnesses. E. coli can come from pet and other animal wastes. According to EPA, average conditions should not exceed 126 #/100 ml and individual samples should not exceed 235 #/100 ml.
Suspended sediment
Suspended sediment (SS) measures the material suspended (e.g. clay, sand) in the water column at the time of sampling. As flows increase, more material is moved, increasing SS concentrations. Storm flows increase erosion and carry large quantities of sediment.

Measuring various parameters shows how they interrelate and vary geographically.


Learn more about water quality trends:


These maps show monitoring sites and a summary of some water quality parameters.


See how different parameters change throughout the growing season. Choose a site and parameter to see data plotted from May through October. Colors show sampling year. Median value for a sampling day is displayed if multiple samples were collected.

Full Screen

Examine relationships between parameters. Select sites and a water quality parameter for each axis. Hover over each data point to see sample collection date and result value. Median value for a sampling day is displayed if multiple samples were collected.

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