What is a smart wetland?

A Smart Wetland is a small constructed wetland specifically designed to use naturally occurring processes to remove excess nutrients from agricultural tile drainage before it leaves the cropland.

The constructed wetland is "SMART" because it is

Image provided by NRCS.

  • specifically sited and designed to reduce nutrient loss via tile drainage

  • a measurable practice in terms of directly monitoring nutrient removal, because its nutrient removal effectiveness can be directly monitored.

  • in alignment with Illinois' systems approach to nutrient loss reduction

  • a resilient and relevant practice for a sustainable and productive farming operation, that keeps working even as weather patterns change

  • a time-saving practice that can remove nutrients for 30+ years with very little maintenance

This practice reduces the number of crop nutrients flowing into Illinois waterways, then into the Mississippi River, and ultimately into the Gulf of Mexico, where they create the annual "dead zone".

The position, size, and depth are the key components of a Smart Wetland.

The best position for a Smart Wetland is within a waterway or adjacent to an existing ditch or stream to intercept and capture drain tile outflow. Ideally, these locations are those small pieces of hard-to-farm or negative-revenue lands often found on a farm. The wetland can easily be designed to treat 30 to 200 acres of drained cropland.

The constructed wetland size is determined based on a ratio. The wetland treatment area should be .5-5% of the tile drainage area being captured. This ensures that the wetland's capacity is large enough to remove nutrients effectively.

The ideal depth of water for a Smart Wetland is 12-18 inches. This shallow marsh ecosystem with emergent vegetation has the conditions needed to remove nitrates via a process called denitrification. While this depth is good for removing nutrients, it is not deep enough for fish.

This Smart Wetland in Bureau County is next to a waterway.

This Smart Wetland is sized proportionately to the fields it treats.

This Smart Wetland has shallow water. Photo by Mahsa Izadmehr.

 

How is a smart wetland different from a restored wetland?

The Wetlands Initiative's Dixon Waterfowl Refuge is a restored wetland near Hennepin, IL.

Wetlands are the parts of our landscape that are defined by the presence of water, hydrophytic (water-loving) plants, and hydric soils. Wetland ecosystems provide many direct and indirect benefits, such as wildlife habitat, biodiversity, flood storage, groundwater recharge, and water quality improvement. All wetlands - whether natural, restored, or constructed - can naturally improve water quality.

What are the differences between restored, created, and constructed wetlands?

Restored wetlands are areas that were originally wetland, but the hydrology, vegetation, or soils were altered or degraded by human activities. Wetland restoration establishes conditions and functions similar to the original wetland prior to disturbance. Wetland restoration typically focuses on wildlife habitat and biodiversity.

A Smart Wetland in Bureau County, Illinois, showing a variety of vegetation. Photo by Mahsa Izadmehr.

Wetland creation establishes a wetland in an area where a wetland never previously existed.

According to the Illinois Natural Resources Conservation Service practice standard, a constructed wetland is "an artificial ecosystem with hydrophytic (water-loving) vegetation for water treatment."

Smart Wetlands are constructed wetlands, as Smart Wetlands are designed and sited specifically to capture and treat cropland tile drainage runoff. Smart Wetlands can be built in areas that were either never wetland or former wetlands that are now farmed. However, Smart Wetlands or constructed wetlands cannot be located on land identified as a wetland under Farm Bill conservation compliance provisions or under the jurisdiction of the Clean Water Act.

 

How do wetlands remove nutrients?

Image provided by USGS.

Nitrogen and phosphorus are essential for all living things, but when too much of these nutrients enter aquatic environments, it can have a negative impact. Nutrient pollution has impacted many Illinois streams, rivers, and lakes resulting in serious environmental and human health issues. To help protect local water bodies and the Gulf of Mexico, Illinois and 11 other states in the Mississippi River Basin have developed strategies to reduce their nutrient loads as part of a national plan to reduce the size of the Gulf of Mexico “dead zone”.

Wetlands remove nitrogen, phosphorus, and other pollutants through a combination of physical, chemical, and biological processes. As water slowly flows through a shallow wetland full of vegetation, these naturally occurring processes adsorb/absorb, transform, sequester, and remove the nutrients and other chemicals. All of these processes occur throughout the different wetland compartments, which include water, biota (plants, algae, and bacteria), dead plant matter, and soil.

While the dominant removal processes for nitrogen and phosphorus are different, both nutrients are utilized by wetland biota. Wetland plants uptake inorganic nitrogen and phosphorus forms through their roots and/or foliage during the spring and summer and convert them into organic compounds for growth. However, this only provides temporary storage of the nutrients. The majority of these assimilated nutrients are released back into the water and soils when plants grow old and decompose during the fall and winter.

 

NITROGEN

Symbols courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science.

Nitrogen removal involves bacteria (or microbes) that conduct numerous chemical reactions. These microbes are found on the solid surfaces within the wetland, such as soil, litter, and submerged plant stems and leaves. The main transformation processes are ammonification (organic nitrogen converted to ammonia), nitrification (ammonia converted to nitrate or nitrite), and denitrification, where nitrate (NO3) is converted into nitrogen gas (N2) which composes 85% of our atmosphere.

Denitrification is the dominant, sustainable removal process in wetlands that receive high nitrate loadings from agricultural tile drainage runoff. Denitrification is mainly performed by bacteria that are heterotrophic, meaning they require a carbon source for growth and energy. Wetland plants are a vital source of this carbon. Since denitrification is performed by microbes, the process is temperature-dependent. Higher rates of denitrification occur during the hotter summer months when the bacteria are more active.

Symbols courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science.

phosphorus

Unlike nitrogen, phosphorus is removed primarily through physical and chemical processes. Phosphorus typically enters wetlands attached to small soil particles (particulate form) in dissolved PO4 ions. Particulate phosphorus is deposited in wetlands in the form of sediment. The leaves and stems of wetland plants slow the water and allow particulate to fall. The dissolved form of phosphorus (phosphate) accumulates quickly in sediments through sorption and precipitation processes.

However, wetland soils have a limited amount of phosphorus they can hold. In order to continuously remove phosphorus, new soils need to be "built" within the wetland from remnant plant stems, leaves, root debris, and undecomposable parts of dead algae, bacteria, fungi, and invertebrates. The growth, or accretion, of new material in the wetland is the only sustainable removal and storage process for phosphorus.

 
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Could a Smart Wetland be right for your farm? Request a consultation.