Lower River Study: Highlights

The Metropolitan Council led a co- and sediment. The pollutants come water quality under critical condi- operative effort to develop a water- from point (specific) sources, like tions for oxygen. Special studies quality model of the lower 40 miles industrial and wastewater pipes, were designed to answer specific of the Minnesota River, which is and nonpoint (diffuse) sources, like questions, such as whether ground- located in the southwest runoff from farms, lawns, feedlots, water inputs were significant, and area. Six federal, state, and local and parking lots. to support key model inputs, such agencies sponsored the project, as the rates of oxygen production and many groups provided technic- and respiration by algae. The study al assistance. The goal was to build attempted to measure all major a planning tool for wastewater fa- sources and sinks of oxygen and cilities and watersheds. The part- nutrients using a variety of me- ners chose a well accepted and thods from sending a scuba diver to widely applied model, CE-QUAL- the river bed to capture sediment W2, and conducted a three-year rates to floating a dome on the sur- monitoring program to support it. face to capture atmospheric rates.

The Lower Minnesota River lies at the juncture of two contrasting The model will be used to set ap- landscapes: a predominantly agri- propriate pollutant limits for dis- cultural watershed to the and charges from point sources and an expanding metropolitan area to establish goals for reducing pollu- the east. It is a valuable natural tant loads from watersheds. The resource and home to one of only Council plans to use the model for four national wildlife refuges in an wastewater facility planning for urban area. Approaching its conflu- future growth in the southwest. ence with the in The MPCA plans to use the model the heart of the Twin Cities, the to reevaluate allowable pollutant Minnesota River becomes a work- loads to the Lower Minnesota River ing river accommodating a dredged from point and nonpoint sources. navigation channel for barge traffic, two major wastewater treatment Modeling water quality Monitoring water quality facilities, an electrical power gene- rating plant, and stormwater from The CE-QUAL-W2 model is a com- For many years, the Council has municipalities and an international puter program containing a set of conducted river, stream, lake, and airport. equations that attempts to describe effluent monitoring in the metro all relevant processes impacting area, including five stations on the water quality in a river. For exam- Minnesota River near Jordan, Sha- ple, to understand how algae affect kopee, Savage, Black Dog, and Fort oxygen levels, the model must de- Snelling. The Council and local scribe the relationships of algae to groups monitor water quality in a nutrients, light, temperature, flow, number of tributaries, and the and grazers as well as the relation- Council monitors effluent quality at ships of living and dead algae to the Blue Lake and Seneca wastewa- oxygen production and demand. ter treatment facilities, which dis-

charge to the Minnesota River. A computer model cannot perfectly

mimic a river, but modelers can test The Lower Minnesota River is listed For three years, 2004-2006, the how close it comes. The Lower as impaired by low oxygen levels water-quality monitoring programs Minnesota River Model was tested and high turbidity by the Minnesota were enhanced to fulfill model data against seven years of data repre- Pollution Control Agency (MPCA). requirements. More intensive mon- senting a wide range of conditions. These problems have been linked itoring was conducted at low river Low oxygen and high algal levels to excess levels of algae, nutrients, flows during the summer to capture Metropolitan Council  390 Robert Street North  Saint Paul, Minnesota 55101-1805  (651) 602-1000  Fax 602-1550  TTY 291-0904 Metro Info Line 602-1888  [email protected]  www.metrocouncil.org are most often a problem at low complex with physical factors do- tinue to enrich the river with nu- flows in summer, while sediment minating at higher flows, and bio- trients. Discharges from the power and nutrient loads are associated logical factors (algae) playing an plant and airport may also impact with high flows. The model was increasing role at lower flows. river water quality but additional tested against the special data col- study of these sources is needed. lected during 2004-2006 plus data from 1988 (drought year), 2001 As demonstrated in test results, the (flood year), and 2002-2003 (nor- Lower Minnesota River Model is an mal years). Graphs were plotted acceptable tool for studying oxy- and statistical tests were applied to gen, nutrients, algae, and turbidity evaluate how well model results under a variety of conditions. The matched actual measurements. model will also facilitate decision making by allowing planners to test different management scenarios.

During 2004-2006, the headwaters Project sponsors upstream of Jordan contributed over 88% of the sediment and nu- Metropolitan Council, U.S. Army trient loads to the Lower Minneso- Corps of Engineers, Minnesota Pol- ta River. At lower flows, the portion lution Control Agency, U.S. Geolog- of nutrient loads contributed by the ical Survey, Lower Minnesota River Blue Lake and Seneca facilities in- Watershed District, Metropolitan creased. The lower 40 miles were a Airports Commission Select findings deposition zone (sink) for sediment and phosphorus but a source of For more information Hydrodynamics—the physics of ammonium nitrogen. water movement—play a promi- On the Council’s website, you can nent role in water quality. For a High levels of nutrients in the Min- find more information: majority of the year, river flow is nesota River support high levels of algae. Under summer low-flow the main driver of water quality. Lower Minnesota River Study conditions, algae appear to die off Greater depths and slower veloci- Project documents in the lower reaches as greater ties in the navigation channel in- Water-quality monitoring depths and slower currents move creasingly affect water quality at River, tributaries, effluent algae out of the narrow light zone lower flows in summer. Water-quality management in this turbid river. As a result, less Planning and practices oxygen is produced and algal de- Despite efforts to reduce sediment Wastewater treatment composition leads to nutrient recy- loads to the river, concentrations of Blue Lake and Seneca cling and oxygen demand. suspended solids remain high. Par- ticles suspended in the river reduce If you have comments or questions, Algal production and respiration light and water clarity, which in contact Judy Sventek at turn negatively impact algae and are strong components of oxygen [email protected], other aquatic life. dynamics in the river, especially 651-602-1156, or Hong Wong at during summer low-flow conditions [email protected], Nutrient levels are high as well. when respiration tends to outpace 651-602-1079. Nitrate is the most abundant form production. Decomposition of non- of nitrogen, and orthophosphate living organic matter (e.g., dead represents a third of the phospho- algae, leaves, grass, crop residue, rus. Both forms are dissolved and and wastewater) in the water and readily available to fuel algae. sediment bed is also a factor. Roughly one-half of the phosphorus in particles can be easily recycled to Effluent quality at the Blue Lake orthophosphate under certain con- and Seneca facilities has improved ditions, which may impact down- greatly since the 1980s. While stream sites on the Mississippi Riv- current loads have little effect on er. Phosphorus dynamics were oxygen levels in the river, they con-

Metropolitan Council  390 Robert Street North  Saint Paul, Minnesota 55101-1805  (651) 602-1000  Fax 602-1550  TTY 291-0904 Metro Info Line 602-1888  [email protected]  www.metrocouncil.org