State of the Minnesota River 2002 Surface Water Quality Monitoring

STATE OF THE MINNESOTA RIVER

Basin Overview
Monitoring
Methods
Precipitation & Runoff
TSS
Phosphorus
Orthophosphorus
Nitrate-Nitrogen
Pesticides
Minor Tributaries
What We Have Learned
Further Research
For More Information

The Minnesota River has been cited as one of the most polluted rivers in the state and nation. In response to these pronouncements, considerable attention and support have been given to clean up efforts. In recent years, there have been significant improvements in point source pollution control as well as continued adoption of conservation and best management practices within the Minnesota River Basin. With these changes has come an increasing expectation that the monitoring data being collected will or can be used not only to identify potential problem areas but also to quantify the impact of these changes on water quality. This collaborative effort will serve as a foundation for gauging progress toward a cleaner Minnesota River.

The Minnesota River originates at the Minnesota-South Dakota border, flows for 335 miles through some of the richest agricultural land in Minnesota and joins the Mississippi River at Minneapolis/St. Paul. The river drains a basin of 16,770 square miles: 14,840 square miles in Minnesota, including all or parts of 37 counties; 1,610 square miles in South Dakota; and 320 square miles in North Dakota and Iowa. Minnesota’s portion of the basin is primarily used for agriculture and represents 18.5% of the state’s land mass and 29% of its cultivated land. As the state’s largest tributary of the Mississippi River, the Minnesota River’s volume increases the Mississippi’s flow by 57% and adds disproportionately to its pollutant load. Many water quality challenges relate to land uses including agricultural runoff and urban point-source discharges. While promising strides have been made to reduce point-source pollutants (like industrial and wastewater treatment plants), managing the array of nonpoint-source inputs marks the challenge ahead.

Monitoring History
State and federal agencies have collected water quality data at various locations and at various times throughout the Minnesota River Basin over the past thirty years. The most comprehensive study of water quality in the Minnesota River Basin, the 1994 Minnesota River Assessment Project (MRAP), concluded that the Minnesota River is impaired by excessive levels of nutrients and sediment. Since the MRAP report, several organizations throughout the Basin have taken responsibility for collecting additional data to better define tributary characteristics and learn more about how these tributaries affect the condition of the Minnesota River.

In many parts of the Basin, this information is used to target implementation practices that reduce nonpoint source pollution, thereby improving the overall health of the Minnesota River. Local watershed projects are supported by Clean Water Partnership grants administered by Minnesota Pollution Control Agency (MPCA). Much of the remaining data presented in this summary report is provided through monitoring programs of the Minnesota Department of Agriculture (MDA) and Metropolitan Council Environmental Services (MCES), with contributions from the United States Geological Survey (USGS), Minnesota Department of Natural Resources (MDNR) and the Minnesota State Climatology Office. See list of contributors on the back page.

MonitoringLocations
Monitoring site locations for 2002 are illustrated on the map on pages 1-2. The 2002 report includes 28 monitoring sites, a notable increase from the 10 sites included in the 2000 report. These sites are organized and reported according to mainstem, major tributaries and minor tributaries. Four sites are located on the Minnesota River mainstem, thirteen are located near the mouths of major tributaries, and eleven are located on minor tributaries. Organizing the sites in this manner allows comparisons of the data between streams and rivers of similar size.

Monitoring Season
Monitoring season is based on the portion of the year when the majority of river flow occurs. For 2002, monitoring season length was April 1–September 30. While October flows can be substantial during some years, the April 1st (or ice out) through September 30th period typically captures the months when nutrient and sediment loads are expected to be the highest.

Monitoring Focus
This monitoring summary focuses on the primary nonpoint pollutants of concern in the Basin—excessive sediment, phosphorus, orthophosphorus, nitrate-nitrogen, and pesticide concentrations. Previous studies found that the Minnesota River violated standards for bacteria, dissolved oxygen, and ammonia. In accordance with the Clean Water Act, the Minnesota Pollution Control Agency (MPCA) lists rivers and creeks within the Basin that have been designated as “impaired waters” due to pollution problems such as low dissolved oxygen, mercury, PCBs, fecal coliform, turbidity, and excess ammonia (http://www.pca.state.mn.us/water/tmdl.html). The Department of Health tracks PCB and mercury levels in fish and issues site specific fish consumption advisories (http://www.health.state.mn.us/divs/eh/fish/index.html).

Methods
Two primary methods of storm event sampling are used by projects in the Basin. Grab sampling is the collection of a discrete individual sample, either by manual means or with an autosampler. Flow-based composite sampling is the collection of a composite samples over all or part of a storm event, using an autosampler. The full report details the type of sampling methods at each site. Because this report is a joint venture of many agencies and organizations, water quality data collection efforts and data processing methodologies vary somewhat. Organizations involved in the preparation of this report are moving toward a standard set of methods, a step that will further improve the accuracy of water quality comparisons across the Basin. In the process of developing this report, specific monitoring criteria were developed that will guide monitoring organizations towards common methodologies (see full report).

Concentrations & Loads
The full report employs and explains many calculations used to describe water quality such as load, yield, and concentration. This executive summary focuses on two of these calculations—flow-weighted mean concentration (FWMC) and load. FWMC is calculated by dividing the total load (mass) for the given time period by the total flow or volume. It refers to the concentration (mg/L) of a particular pollutant taking into account the volume of water passing a sampling station over the entire sampling season. Conceptually, a FWMC would be the same as routing all the flow that passed a monitoring site during a specific timeframe into a big, well-mixed pool, and collecting and analyzing one sample from the pool to give the average concentration. A load is the estimate of pollutant total amount (mass), passing a specific location on a river during a specified interval of time.

The 2002 total precipitation map (at right) illustrates that overall totals increase as one moves eastward through the Basin. Total precipitation amounts ranged from 20 inches in the western part of the Basin to over 40 inches in portions of the eastern. The general pattern is consistent with long-term rainfall distribution in the Minnesota River Basin.

Runoff
Typically, the more precipitation that occurs in a watershed, the more runoff there will be (see runoff definition below). However, timing and intensity of precipitation, antecedent soil moisture conditions, soil types, land slope, land use, as well as other factors, can dramatically influence the seasonal or annual final runoff number. Due to geographical differences in precipitation, runoff tends to increase as one moves eastward across the Basin.

Runoff during the 2002 monitoring season varied from approximately 1 inch to greater then 11 inches. Watersheds in the western portion of the Basin exhibited lower runoff and those in the eastern portion of the Basin exhibited higher runoff.

Evaluating runoff allows for a relative comparison of the amount of water coming out of different individual watersheds or portions of the basin. Higher runoff generally results in higher pollutant loads for most nonpoint source pollutants.

The annual runoff graph (lower right) illustrates the trend of increasing runoff volume over the past several decades. Highly variable runoff from one monitoring season to another highlights the need for an on-going program that collects, analyzes, and reports on surface water quality monitoring data.

Total Suspended solids (TSS)
Total suspended solids are a major water quality concern in the Minnesota River (see box below). Soils in the Basin
have a high silt and clay content. Eighty-six percent of the suspended sediment in the Basin is characterized by fine particles of silt and clay that are easily transported in water. The Minnesota River carries more suspended sediment than most of the State’s rivers. Excess sediment degrades the river system by filling reservoirs, destroying aquatic habitats, altering biotic communities, increasing water treatment costs, and reducing the river’s aesthetic qualities.

Criteria/Standard
Minnesota does not currently have a water quality standard for total suspended solids (TSS) but does have a turbidity standard of 25 nephelometric turbidity units (NTUs). MPCA studies have shown a strong relationship between TSS and turbidty and can use TSS for a surrogate to assess water quality conditions required by the Clean Water Act. In the Western Corn Belt Plains and Northern Glaciated Plains ecoregions, which encompass the majority of the Basin, surrogate TSS thresholds of 58 and 66 mg/L, respectively, can now be used for listing impaired waters when sufficient turbidity data are lacking.

2002 Findings
For the major tributaries, substantial differences in TSS flow-weighted mean concentrations are apparent across the Minnesota River Basin with concentrations seldom exceeding 100 mg/L in major tributaries in the upper part of the Basin. In contrast, concentrations in major tributaries in the lower part of the Basin frequently are much greater than 100 mg/L.

Mainstem flow-weighted mean concentration values during 2002 ranged from 172 mg/L at Ft. Snelling to 226 mg/L at the Jordan site. These values are substantially greater than the turbidity-based thresholds of 58-66 mg/L.

Mainstem TSS loads in 2002 were substantially reduced from loads measured during 2001, reflecting less runoff during 2002 compared to the flood flows of 2001

Phosphorus
Phosphorus originates from many sources in the Minnesota River Basin and is the primary cause of algal growth, a
leading contributor to low dissolved oxygen concentrations in the lower twenty-two mile reach of the Minnesota River during low flow conditions (see box below). Elevated phosphorus concentrations during low flow often indicate point sources, whereas elevated concentrations that occur mainly during higher flow periods can indicate nonpoint sources. The average condition of the Minnesota River mainstem appears to be a FWMC of approximately 0.35 mg/L. This elevated phosphorus level is one of the main reasons the Minnesota River is considered one of the most polluted rivers in the state. Controlling phosphorus is an important part of protecting the river.

Criteria/Standard
Currently, there are no statewide standards for total
phosphorus (TP) in rivers or streams. The US Environmental Protection Agency (USEPA) states a desired goal of 0.10 mg/L for prevention of nuisance plant growth in streams. An analysis of algal productivity and TP concentration data for the Minnesota River has shown that algal productivity will not start to diminish until TP concentrations fall below approximately 0.26 mg/L. Based on this information, the Minnesota River mainstem will continue to experience undesirable levels of algal growth until TP concentrations are reduced to below this level.

2002 Findings
Total phosphorus FWMC values in the Minnesota River mainstem, six major tributaries, and five minor tributaries were greater than 0.3 mg/L during 2002. These TP concentrations are well above the USEPA desired goal of 0.1 mg/L for preventing nuisance plant growth in streams.

Total phosphorus is an issue in all major tributaries. During 2002, the bulk of total phosphorus loading from tributaries occurred in the watersheds located in the middle and lower Minnesota River Basin (i.e. downstream of Morton).

Because total phosphorus loading is strongly correlated with stream flow, year-to-year variability in runoff quantities explains much of the variability in TP loading.

Orthophosphorus FWMC values during 2002 are mostly uniform at mainstem sites and fit into a relatively narrow range of approximately 0.09 - 0.10 mg/L. The relatively large increase in OP load at the Minnesota River at Judson site reflects increased loads in four major tributaries during 2002: Chippewa River, Hawk Creek, Redwood River, and Cottonwood River.

Orthophosphorus FWMC values for Hawk Creek and the Redwood River are particularly elevated. In these watersheds, more than one half of the phosphorus load was in the OP form, which can be readily used by algae. Point sources may have influenced the concentrations as these watersheds each receive wastewater effluent from medium-sized municipalities.

Among major tributaries in the Lower Minnesota River Watershed, OP yields were greatest from the High Island Creek and Sand Creek Watersheds. Focused attention and evaluation of the major-tributary watersheds may be warranted to determine why some yield more OP than others.

Nitrate-Nitrogen (Nitrate-N)
Nitrate-nitrogen loading from the Minnesota River Basin has local and national implications. Nitrate-N is important
because it is biologically available to aquatic plants and is a major contributor to the nutrient enrichment of surface waters. Elevated nitrate concentrations in the river systems also have the potential to impact drinking water supplies (see box). Downstream, nitrate-N is the primary chemical contributing to the expanding area of low dissolved oxygen, or hypoxia zone, at the mouth of the Mississippi River in the Gulf of Mexico. Elevated nitrate-N FWMC at Fort Snelling indicates substantial nitrate enrichment that contributes to the hypoxia zone.

Criteria/Standard
Nitrate-N concentrations in drinking water supplies are a public health issue. The standard for drinking water is 10 mg/L. Average ecoregion values for minimally impacted rivers in the Minnesota River Basin can be applied for nitrate-N concentrations. Ecoregions are areas with similar physical landscape characteristics. The ecoregion target includes nitrate-N concentrations in the 0.9 - 6.5 mg/L range.

2002 Findings
The effect of drier conditions during 2002 is seen at all mainstem sites, especially in the Greater Blue Earth River where nitrate-N load declined to its lowest level since monitoring began in 2000.

The Greater Blue Earth (GBE) River stands out with the greatest FWMC values for nitrate-N. These values have been nearly constant during the three year period (9.78-9.95) despite substantial year-to-year differences in precipitation and runoff. The nitrate-N laden water of the GBE River joins the Minnesota River at its confluence at Mankato, increasing the nitrate-N FWMC of the Minnesota River.

Flow-weighted mean concentrations of nitrate-N are greater than, or very near, the 10 mg/L drinking water standard in several major tributaries starting at the Redwood River and continuing downstream. Concentrations in these tributaries stand in sharp contrast to tributaries in the upper part of the Basin where concentrations are much lower and they underscore the need for effective BMPs that can reduce nitrate-N in streams.

The MDA Monitoring and Assessment Unit collected pesticide samples from the Le Sueur River at Highway 66, the Blue Earth River below the Rapidan Dam, and the Minnesota River at Judson. Samples have been collected during 2000, 2001, and 2002. Over the three-year period, the herbicides metolachlor, atrazine and acetochlor were the most frequently detected compounds in these rivers. These herbicides are typically applied to corn and soybean fields for general weed control.

Runoff-adjusted yields indicate that the Le Sueur River and the Minnesota River at Judson delivered approximately the same pesticide yield per inch of runoff (0.28 lbs). Both the Le Sueur and the Blue Earth Rivers yielded much less total pesticide per inch of runoff in 2002 than in the previous two years.

As in the previous two years, the Le Sueur River Watershed displayed the highest cumulative pesticide yield at over 1.5 pounds per square mile. The percent land use in agricultural row crop for the Judson, Le Sueur and Blue Earth Watersheds were estimated at 60, 82 and 85 percent respectively.

In 2002, concentrations for most compounds peaked during late May and early to mid June storm events. Metolachlor concentrations typically peak earlier in the year (March or April) because the product is commonly applied in the fall. Peak concentration periods for most compounds generally occur with the first significant post-application runoff events.

Total Phosphorus (TP) - Together, Bevens and Carver creeks, two minor tributaries located in the Lower Minnesota River Watershed, contributed nearly 9 percent of the TP load at the mouth of the Minnesota River (Fort Snelling) during 2002. Total phosphorus flow-weighted mean concentrations in these streams were greater than 0.7 mg/L, the highest measured in Minnesota River tributaries in 2002 (see map).

Orthophosphorus (OP) - Elevated OP levels in minor tributaries of the lower Minnesota River Basin raise concern because those streams place readily-available phosphorus into the lower mainstem reach. Among the minor tributaries, the OP load in Bevens Creek was greater than the load in 9 of the 13 major tributaries, and its orthophosphorus flow-weighted mean concentrations (0.40-.45 mg/L) are greater than values measured in other tributaries during the 2000-2002 monitoring period. Orthophosphorus FWMC values in the other minor tributaries ranged from low (< 0.05 mg/L) to moderately high (0.15-.25 mg/L). Owing to their larger watersheds and greater OP loads, Bevens and Carver Creeks have the potential to elevate OP concentrations in the Lower Minnesota River mainstem.

Nitrate-N - Flow-weighted mean concentrations in minor tributaries that drain agricultural watersheds were substantially greater than nitrate-N concentrations measured in minor tributaries that drain mixed land use watersheds (see map).

Importance of Runoff
There was a remarkable difference between the three years with respect to runoff in the Basin. While 2000 was relatively dry in most of the Basin, 2001, a flood year, showed runoff values two to ten times greater than 2000. In 2002, runoff amounts were less than 2001 but greater than 2000. The results obtained during the past three years of monitoring continue to illustrate the strong influence that runoff exerts on the amount of sediment delivered to the Minnesota River. For example, sediment yield in the Greater Blue Earth River ranged from 126 lbs/acre during 2002 to 718 lbs/acre during 2001.

Magnitude and timing of individual runoff events also greatly affect the amount of sediment delivered. Whereas precipitation amounts and timing cannot be controlled, management alternatives that maximize water infiltration and retention and minimize soil erosion and surface runoff can be controlled and need to be aggressively promoted for reducing sediment delivery. This is especially true in the spring before crops are established.

Pollutants Increase in West-to-East Pattern
Data in this report show that watershed yields of key water-quality constituents (TSS, TP, OP, and Nitrate-N) follow a general pattern of increasing yield, often accompanied by increasing FWMC values, from west-to-east across the Minnesota River Basin. A corresponding west-to-east precipitation and runoff gradient has long been recognized and documented. The magnitude of the constituent yield response, however, appears to be greater than what would be expected from the differences in annual runoff alone.

Year to Year Fluctuations
Data in this report illustrate widely varying water quality conditions in most streams during a relatively short three-year monitoring period. These year-to-year fluctuations underscore the value of long-term data gathering using consistent and technically sound methodology at all sites across the Minnesota River Basin. Such data, collected longer term, will form a solid body of evidence that more accurately portrays stream water quality. These data will enhance the impaired waters process by providing an improved perspective of stream water quality during normal, above normal, and below normal runoff periods.

Rain Event Timing and Seasonality
The frequency, intensity, duration, and seasonal timing of precipitation events can greatly affect constituent yield, but other factors also may shape the observed responses. These factors may include differences in watershed geomorphology, vegetative cover, and alluvial progression and adjustment to climate and land-use variables. In addition, direct human influences such as cropping, urbanization, extent and coverage of conservation practices, fertilizer usage (amount and timing), and point-source inputs are all factors of constituent yield. The relative importance of these and other factors needs to be better understood as we chart a course of action to reduce pollutant levels in streams, large and small, across the Minnesota River Basin.

Elevated Phosphorus
Total phosphorus flow-weighted mean concentrations in the Minnesota River mainstem, six major tributaries, and five minor tributaries were greater than 0.30 mg/L during 2002. These TP concentrations are well above the USEPA desired goal of 0.10 mg/L for preventing nuisance plant growth in streams. An analysis of algal productivity and TP concentration data for the Minnesota River has shown that algal productivity will not start to diminish until TP concentrations fall below approximately 0.26 mg/L. Based on this information, the Minnesota River mainstem will continue to experience undesirable levels of algal growth until TP concentrations are reduced to below this level.

Information Gaps
The data do not make clear the source mobilization and transport mechanisms that deliver pollutants to streams. However, several of the organizations that contributed data for this report are collecting additional data from smaller watersheds and using that information to identify and target specific sources and areas within their respective watersheds. Detailed analysis and inclusion of data from some of these smaller watersheds in future State of the Minnesota River Reports will provide a more comprehensive assessment and may improve our understanding of pollutant source and transport mechanisms. Better communication between researchers and continued coordination of monitoring efforts will improve our understanding of the processes and enhance our ability to reduce pollutant loading. Another challenge ahead is securing funds for long term monitoring. The current monitoring network is not supported by stable funding so future assessments may be compromised by lack of data.

Most people want to know if water quality in the Minnesota River Basin is improving. Unfortunately, this seemingly simple question is difficult to answer. As we have seen, seasonal and annual fluctuations and geographic differences make this a complex question. Long term and specially focused studies are key to understanding the health of the rivers in the Minnesota River Basin. The following observations suggest directions for future studies and on-going water quality research. For specific guidance on objectives and strategies to restore the Minnesota River Basin, refer to the Minnesota River Basin Plan published on the MPCA website (http://www.pca.state.mn.us).

* More research is needed on potential water quality and aquatic-ecosystem improvements in streams located in watersheds that have extensive participation in CREP and other BMP programs. Furthermore, there needs to be continued research that will lead to new innovations for managing surface and subsurface runoff and erosion, particularly methods that can be effective during the critical May-July period.

* Monitoring data indicate regional differences in the magnitude of constituent load response to water runoff. Differences may be related to watershed soils, geology, and stream morphology, but land use, cropping practices, and conservation practices also may be affecting load response. A better understanding of these processes could help allocate BMP resources more effectively.

* Assessments are needed in major tributaries to determine the nature of the phosphorus sources and the location of source areas. Particular attention should be placed on identifying 1) highly-erodible land that is not presently treated with conservation practices, 2) land adjacent to streams and ditches, 3) actively eroding streambanks, ravines and gullies, 4) municipal and industrial point sources, 5) non-compliant animal-waste systems, and 6) other potential sources.

* More evaluation of the monitoring data and special studies are needed to learn why some of the major tributaries have greater OP/TP ratios and greater OP concentrations compared to others. Investigation of phosphorus sources and transport mechanisms may reveal new information about these processes that could lead to new approaches for reducing phosphorus loading to streams. Research projects directed at non-point source processes at both field and small-watershed scale may be needed to determine how and why the major tributaries differ in these important aspects of phosphorus dynamics.

* Elevated nitrate-N loads, yields, and FWMC values are present in most of the major tributaries starting with the Redwood River and continuing downstream. The numbers underscore the need for BMPs that reduce nitrate in streams. Source reduction, through effective nutrient management, is an important first step. More research is needed at the minor watershed scale to evaluate why agricultural watersheds deliver more nitrate-N and how those amounts can be reduced.

Contributors
Barr Engineering
Brown-Nicollet-Cottonwood Clean Water Project
Chippewa River Watershed Project
Hawk Creek Watershed Project
High Island Creek Watershed Assessment Project
Lac qui Parle-Yellow Bank Clean Water Partnership
Martin County Environmental Services
Metropolitan Council Environmental Services Program
Minnesota Department of Agriculture Monitoring and Assessment Program
Minnesota Pollution Control Agency
Redwood-Cottonwood Rivers Control Area
Watonwan River Clean Water Partnership
Water Resources Center: Minnesota State University, Mankato
Yellow Medicine River Watershed District

Contact Information
Minnesota River Basin Data Center:
Water Resources Center,
Minnesota State University, Mankato
Website: mrbdc.mnsu.edu
Phone: 507-389-5492

Minnesota Pollution Control Agency
Website: www.pca.state.mn.us

Metropolitan Council Environmental Services
Website: www.metrocouncil.org/environment/RiversLakes/

Minnesota Department of Agriculture
Website: www.mda.state.mn.us

University of Minnesota:
Department of Soil, Water, and Climate
Website: www.soils.agri.umn.edu/research/mn-river/