Midwest Region
Conserving the Nature of America

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Ecosystem Conservation

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U.S. Fish and Wildlife Service
Division of Ecological Services
1 Federal Drive
Fort Snelling, MN 55118
Phone: (612) 713-5467
E-Mail: Tom_Magnuson@fws.gov

Imperiled Ecosystems | Invasive Species | Water-Related Issuesdesign only
Emerging Issues | Great Lakes-Big Rivers Region Priority Species

Water-Related Issues

Gulf Hypoxia

Scientific investigations in the Gulf of Mexico have documented a large area of the Louisiana continental shelf with seasonally-depleted oxygen levels (< 2mg/l). Most aquatic species cannot survive at such low oxygen levels. The oxygen depletion, referred to as hypoxia, begins in late spring, reaches a maximum in midsummer, and disappears in the fall. The hypoxic zone forms in the middle of the most important commercial and recreational fisheries in the coterminous United States and could threaten the economy of this region of the Gulf.

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Map courtesy of the U.S. Environmental Protection Agency.

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The origin of Gulf Hypoxia is through point and non-point sources of nitrates that are derived from watersheds in the Mississippi River Basin. The hypoxic zone forms during most springs when Mississippi River discharge is highest. Watersheds with excessive agricultural runoff or inadequate sewage treatment have been identified as particularly troublesome sites of nitrate pollution. Generally, excess nutrients lead to increased algal production and increased availability of organic carbon within an ecosystem, a process known as eutrophication.

There are multiple sources of excessive nutrients in watersheds, both point and non-point, and the transport and delivery of these nutrients is a complex process which is controlled by a range of factors. These include not only the chemistry, but also the ecology, hydrology, and geomorphology of the various portions of a watershed and that of the receiving system. Human activities on land can add excess nutrients to coastal areas or compromise the ability of ecosystems to remove nutrients either from the landscape or from the waterways themselves.

Pattern Tiling

Drainage of wetlands, including ephemeral basins, has negatively impacted many fish and wildlife populations. A recent agricultural trend, called pattern tiling, is to more completely drain partially drained wetlands or to add subsurface drainage to entire fields, including existing wetlands, former wetlands, and uplands. Since this often involves installing tile in a uniform grid or pattern, it is referred to as pattern tiling. Emphasis on the benefits of pattern tiling or subsurface drainage for increasing productivity on agricultural lands overshadows some of the environmental impacts of this practice.

Agricultural drainage involves the removal of water from the soil surface and/or soil profile of lands used for crop production. The main reason for agricultural drainage is to enhance crop production by providing drier field conditions for farm equipment to access farm fields and by improving the health of crops through efficient removal of water from fields and the root zone of crops after rainfall events. Research in the Midwest has shown that agricultural drainage can help reduce the year-to-year variability in crop yields, which helps reduce the risks associated with farming.

The two primary types of agricultural drainage improvement are surface and subsurface. Surface drainage improvements include land leveling and smoothing, the construction of surface water inlets to subsurface drains, and the construction of ditches and channels to drain wetlands. Land smoothing or leveling is a water management practice designed to remove soil from high spots in a field, and/or fill low spots and depressions where water may pond.

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Photo of a wetland being leveled by a bulldozer - Photo credit:  U.S. Fish and Wildlife Service
Land smoothing or leveling is a water management practice designed to remove soil from high spots in a field, and/or fill low spots and depressions where water may pond.

Ditches may be constructed to divert water to existing streams or other surface water bodies. For decades, surface drainage of lands to improve agricultural production has been practiced and has resulted in the extensive loss of wetlands in the upper Midwest. Wetland drainage is now regulated; however, some loss of wetlands continues to occur as a result of surface drainage activities.

There are currently no regulatory controls on subsurface drainage unless the practice directly drains a jurisdictional wetland. Many publicly-funded educational institutions through their agricultural extension services are offering workshops to agricultural producers on the effectiveness of subsurface drainage in increasing yield. These workshops emphasize the benefits of subsurface drainage with minimal attention paid to the environmental costs.

Fish Passage

Fish in lakes and rivers have evolved life cycle migratory patterns that require the seasonal availability of a variety of river habitats. Unfortunately, thousands of artificial barriers were constructed to impound and redirect water for irrigation, flood control, electricity, drinking water, and transportation. These barriers prevent migration of fish and other aquatic species to important habitats, and as a result many fish, crayfish, and freshwater mussels in the U.S. are either rare or threatened with extinction.

The goal of fish passage programs is to restore native fish and other aquatic species to self-sustaining levels by reconnecting habitats that have been fragmented by artificial barriers, where such reconnection results in a positive ecological effect.

The U.S. Fish and Wildlife Service's Fish Passage Program provides technical assistance and Federal funds to: remove, replace, or retrofit artificial barriers; design and construct fishways; support biological surveys of important watersheds; and monitor the effectiveness of these activities.

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Photo of a fish passage structure in Grand Portage, Minnesota - Photo credit:  U.S. Fish and Wildlife Service
A fish passage structure in Grand Portage Creek, Minnesota.

To download more information in an Adobe pdf file, please click this link: This link opens in a new windowNational Fish Passage Program – The Great Lakes, Big Rivers Region (227 KB).



Last updated: September 24, 2012