The Role of Riparian Buffers in Agricultural and Urban
Settings in Minnesota
Erica DeJong, Louis Hendrix, Eliza Leahy and Adrienne McDonnell
Macalester College – St. Paul, MN
Buffers in an Agricultural
Setting
Wetlands: Riparian wetlands hold water for a longer period of time and are located
in isolated depressions adjacent to streams and rivers. It is easier to restore
wetlands than to create new ones. This is mainly because the site has functioned in
that location before, and the former hydrology and soil can be restored relatively
easily. Restoring these wetlands would mean to discontinue growing crops, and
Agricultural runoff: Agricultural pollution can be divided into four groups: removing drainage systems and flood control structures.
sediment, nutrients, chemicals, and metals. Pollution can either be point
Wetlands work in the same way as forest buffers. The organisms present can take
or nonpoint source pollution of which agriculture mostly deals with the last. nutrients up; pollution is slowed down while it is stored in the soil; and nitrogen is
Pollution from manure or attached to sediment effect water transparency
denitrificated.
and quality adversely. Species will grow differently when overexposed to
Grasslands: The main purpose of grasslands is to protect river water quality. They
certain nutrients and chemicals. With new input of limiting resources shifts can slow the runoff from fields, trap and filter sediment, nutrients and pesticides
might occur in dominating species.
before entering the stream or river. Grass filter strips are often placed between
When infiltrating the groundwater chemicals and other pollution also
agricultural fields or in combination with forest and wetland buffers as supplements.
influence the drinking water of humans. Long-term low-level exposures to
these pollutants are a great concern for human health.
Inputs of heavy metals in an agricultural area are significantly less
dangerous than in urban areas or areas of mining, but they can still be
harmful.
Monitoring runoff: A new strategy, developed by Mr. Friend and Ms.
Yuan, monitors river water quality by using a hyperspectral camera that
can record many layers at the same time. These fly-over recordings, in
combination with water samples from the river, can map the sources of
sediment and pollution. This information can be used for policy and
planning.
Buffers: Buffers can prevent erosion and slow down the inputs to the
river. Mainly, there are three different buffer types: forests, wetlands, and
grasslands.
Forests: The United States Department of Agriculture defines a forested
buffer as “an area of trees and shrubs located adjacent to streams, lakes,
ponds, and wetlands.”
Forest buffers ideally consist of several zones: zone 1 is not harvested
and only has native species; zone 2 is a managed forest; (optional) zone
3 is a grass strip.
Forest buffers can use the nutrients, slow them down by storing them, or
nitrogen can be turned into a nitrate gas by anaerobic microorganisms in
the buffer. This process is called denitrification.
Buffers in an Urban Setting
Introduction: Urbanization, and specifically the expanses of impervious surfaces
that accompany it, alters the water quality, flow and flood regime, and channel
morphology of nearby rivers and streams. Compared to natural vegetative cover,
impervious surfaces increase the volume of runoff and decrease infiltration ad
groundwater recharge: in natural landscapes, roughly 50% of storm water
recharges the groundwater, while only 10% becomes runoff; in large urban areas
(75-100% impervious surface cover), only 15% of storm water becomes
groundwater while 55% becomes runoff (“Hard Surfaces” 2007). This causes
flashier hydrographs in nearby streams, as well as the transportation of urban
pollutants, such as sediment, nutrients, chemicals, and heavy metals.
Pollutants: Sedimentation in urban streams can be caused by exposed
construction sites, in which the sediment is already loosened, or from bank erosion,
due to a lack of vegetative roots to keep the soil in place. Once sediment enters the
stream, it can accumulate along the benthic layer, changing channel morphology,
decreasing storage capacity, and altering the habitat for benthic invertebrates. It
can also become suspended within the water channel, increasing turbidity and
diminishing the photic zone (Wegner, 1999).
Nutrients, such as phosphorous and nitrogen from lawn fertilizers, industrial waste,
sewage treatment plants, pet waste, or poorly built and overflowing sewer systems
can serve as fertilizers within aquatic ecosystems, causing eutrophication and large
algal blooms (“The Effects of Urbanization of water Quality” 2009). When these
algal blooms die, they create hypoxic conditions within the ecosystem, often
causing large fish kills.
Urban runoff also delivers waterborne pathogens, heavy metals, pesticides, and
herbicides to aquatic ecosystems, all of which can be toxic to aquatic organisms and
humans. Additionally, urban runoff tends to be warmer in temperature, due to industrial
inputs and storage in shallow stormwater basins. These warmer temperatures can
threaten coldwater species and are exacerbated by logging near the ecosystems edge.
http://www.wviz.org/water/picUrbanTemp.jpg
Buffers Within an Urban Context: While unregulated urban development has the
potential to severely degrade aquatic ecosystems, the establishment of native, riparian
buffer zones can mitigate its impacts as well as restore urban streams to a more natural
equilibrium. Within an urban context, buffers can be integrated into the city in a variety of
unique forms– namely greenways and parks. These options are attractive for city
planning because they offer services to humans, as well as protect nearby aquatic
ecosystems (Lindsey, 2003).
Natural vegetation and riparian buffers slow the flow of runoff, allowing sediment to settle
out of the water and back into the soil. Additionally, as runoff slows, flood events will
become less flashy, and the presence of vegetation will prevent riverbank erosion.
Riparian buffers reduce phosphorous inputs as the vegetation within the buffer can use
phosphorous for its own growth or store it within the soil (Wegner, 1999). They also
reduce nitrogen loading in two ways: the vegetation within the zone can use the to
fertilize its own growth, and microbial organisms can perform denitrification, transforming
nitrogen into nitrogen gas and allowing it to be released into the atmosphere (Mayer,
Paul M. et. al., 2005). Simultaneously to trapping sediment, phosphorous, and nitrogen,
riparian buffers can trap herbicides, pesticides, waterborne pathogens, and heavy metals
and store them in the soil.
http://www.mda.state.mn.us/protecting/conservation/practices/buffergrass.aspx
http://pond.dnr.cornell.edu/Pond/fishmanagement.htm
The Minnesota River Basin
Wetland Buffers: There has already been a significant amount of wetland
restoration in the state of Minnesota (Minnesota Dept. of Agriculture & Minnesota's
Farm Bureau Federation, 2007). However, there are parts of the Minnesota River
Basin that likely have the potential for much more wetland restoration to take place.
The Minnesota River Basin currently suffers from significant agricultural
As an addendum to the Wetlands Conservation Plan of 1991, a Restoration Strategy
pollution. A promising solution, however, is the use of riparian buffers to
was compiled in January 2009 (Minnesota Board of Water and Soil Resources,
act as filters for excess nutrients and sediment that enter the basin
through agricultural runoff. Types of agricultural pollution in the Minnesota 2009). The strategy most specifically outlined in this document was the
River include elevated levels of fecal coliform, a surplus of nutrients such “prioritization” of wetlands statewide. In order to accomplish the goal of the plan, the
project coordinated a “Restorable Wetlands Inventory (RWI)” for the state of
as phosphorous and nitrates, and excessive sedimentation (Minnesota
Minnesota in order to identify all the wetlands that are capable of being restored.
River Basin Data Center, 2005).
This map indicates a vast potential for wetland restoration in the Minnesota River
Conservation Reserve Program (CRP/CREP): The state of Minnesota is Basin.
known to be one of the nation’s CRP leaders in the area of sustainable
agricultural management techniques, notably that of riparian buffers. As of
July 2007, Minnesota held the third most participation in the amount of its
farms participating in CRP in the United States (Minnesota Dept. of
Agriculture & Minnesota's Farm Bureau Federation, 2007). Among this
land, 60% of it is designated as being devoted to ecosystem conservation
– including wetland restoration and water quality management.
http://www.mnsoybean.org/documents/agscontribution_wetlands.pdf
http://www.mnsoybean.org/documents/agscontribution-habitat.pdf
Grass Filter Strip Buffers: Minnesota regulates sustainable agricultural practices
Forested Buffers: One major agency focused on the use of agroforestry
by having certain riparian buffer requirements on land adjacent to public waterways
in Minnesota is the Minnesota Agroforestry Cooperative (MAC). According (Minnesota Dept. of Agriculture, 2009). Many farmers put grass filter strip buffers to
to the initiative’s website, the benefit of growing trees for profit includes
use in order to meet these regulations. Most significant in their impact on freshwater
more than just monetary gains. Tree farming has the ability to “enhance
systems is the grass filter strips’ ability to prevent erosion of soil, and therefore,
water quality,” “reduce sediment,” “control erosion,” “reduce floods,” and
increased freshwater sedimentation.
“filtrate pollution” (Renewing the Countryside, 2005-2008).
The Mississippi River Corridor
http://files.dnr.state.mn.us/waters/watermgmt_section/critical_area/mississippi_river_corridor_critical_area_report.pdf
Buffers in a City Environment: The application of buffers in a city setting
is more complicated than that in an agricultural setting because urban
riverfront property is used for urban development, residential development,
commercial river traffic, and recreation. In addition, while farmland can be
returned to natural vegetation at a relatively quick pace, cities have
systematically built over the natural landscape, making the downtown area
a “concrete island” (Saint Paul on the MS Development Framework). In the
end, a city must approach buffers as part of a larger development strategy,
while independent groups may take more of a strictly environmental
approach, which involves many involved parties.
State Critical Area Plan – In 1976 the Twin Cities river corridor was designated
as a State Critical Area, which mandated that the river must be protected and
preserved. After the 2001 adoption of the Corridor Plan, a task force was
created to update the City’s Critical Area zoning regulations so that they are
consistent with the recommendations from the Corridor Plan; these regulations
bring the ideas into concrete law (MS River Corridor Critical Area, 2008). The
zoning amendment propositions, which would create stricter regulations for the
river’s shorelands (including the use of buffers), are currently under review by
the City Council (Simison, 2008).
National Great River Park - The other major plan in the works, entitled The
National Great River Park Master Plan, once again comes from the design team
at the Riverfront Corporation. This plan will be incorporated into St. Paul’s
Comprehensive Plan as a new chapter, hopefully within the next year (Minutes,
2009). The National Great River Park’s (NGRP) motto is “More nature, more
urban, more connected” (The Saint Paul Comprehensive Plan, 2008). The Park
is envisioned as a linked system of all of the natural areas and parks along the
26 miles of the St. Paul Mississippi waterfront (of which there are 3,500 acres of
parks, public space, natural areas and wetlands).
The St. Paul Example: The St. Paul Riverfront Corporation – The
Riverfront Corporation is a private nonprofit in a formal partnership with St.
Paul. This group took on the challenge of approaching St. Paul as a living
ecosystem in the 1990’s. The result was the St. Paul on the Mississippi
Development Framework, which the Riverfront Corporation continues to
promote through its multi-disciplinary design team at the Saint Paul on the
Mississippi Design Center. While not an official governmental plan, the
Framework, which was completed in 1997, serves as a foundation for more
concrete policy. It provides the City of St. Paul with specific principles with
which to move forward with (re)development.
St. Paul’s Comprehensive Plan and the Mississippi River Corridor Plan while the Framework has elegant recommendations, as a whole it was not
adopted as part of St. Paul’s Comprehensive Plan, the city’s guiding
program with which state statute requires the city’s ordinances, programs,
and fiscal tools to be consistent (p. 3 implementation pdf). However, the
City adopted an updated version of the Mississippi River Corridor Plan in
2001, which is currently the guiding policy on the river and was influenced
by and is consistent with the Framework.
http://www.rwmwd.org/vertical/Sites/{AB493DE7-F6CB-4A58-AFE056D80D38CD24}/uploads/{541E4CF 6-A9ED-4F1D-BCED7E6695C37470}.PDF