U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet FS 2004-3036

August 2003

Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin

Pathways of Biological Production in Large Rivers

Large Rivers are among the Most 

Productive and Diverse Aquatic 

Ecosystems

Large rivers are among the most 

biologically productive and diverse of 

aquatic ecosystems and also provide 

important economic, recreational, and 

aesthetic values. Biological production 

is the amount of plants and animals 

produced, and diversity is the number of 

species present. Biological production 

and diversity provide value to society 

through fishing, bird-watching, and 

waterfowl hunting. Aquatic plants take 

up excess nutrients–such as nitrate and 

phosphorus–from agricultural and urban 

runoff, and some of those plants are the 

food base for waterfowl and fish. The 

walleye caught by an angler or the duck 

bagged by a hunter is the end result of a 

complex series of processes that provide 

the energy needed for these animals to 

grow and survive. To conserve these 

valued resources, it is important to 

Large rivers support production of valuable fishes, including the lake 

sturgeon, above. We are presently studying what habitats support fishes 

in the deep channels of large rivers and factors that may be affecting their 

abundance. 

The floodplains of large rivers provide a complex mix of aquatic and terrestrial habitats that 

support high biological diversity and production of plants, fish, birds, and mammals. We are 

presently studying factors that affect fish production in both the deep channels and in backwaters, 

or off-channel, areas.

understand the energy sources and pathways, or food webs, that 

result in high biological production and diversity in large rivers.

Many Theories but too Little Knowledge

Scientists don’t know the specific factors that support the high 

biological production and diversity of large rivers. We do know, 

however, that carbon and nutrients are the basic building blocks 

of biological production. Competing theories suggest that the 

main sources of carbon and nutrients constituting the fish in 

large rivers originate in the floodplains, or perhaps the upstream 

tributaries, or even the plants that grow within the river itself. 

Other theories suggest that floodplain complexity—the many 

physical processes such as changing flows and the mosaic of 

water and land habitats—is key to biological productivity. 

Many human activities on large rivers also affect biological 

production. For example, many large rivers support commercial 

navigation. Navigation traffic may directly affect plants and 
animals that live in or near the navigation 

channels. The structures that support 

navigation, such as dams and wing dikes, 

may indirectly affect plants and animals by 

changing water levels and flow patterns. In 

addition, production and biological diversity 

are affected by commercial and recreational 

harvest as well as predation and competition 

among species. Non-native species that 

have been introduced into American rivers 

can also affect production and diversity. 

A combination of these factors is likely 

at work in large rivers, but few of these 

theories or concepts have been critically 

evaluated. Thus, we are unable to predict 

how the plants and animals of large rivers 

will respond to future conditions or to 

management alternatives.

Painting the Big Picture

Scientists at the Upper Midwest 

Environmental Sciences Center seek to 

discover the major productivity pathways—

the mechanisms that support biological 

production—of the large river ecosystems of the United States. With this 

knowledge, we may develop innovative and efficient ways to conserve those 

ecosystems while continuing to provide important economic benefits. To 

accomplish this task, we are using existing data and field studies to identify 

critical productivity pathways, starting with the Upper Mississippi River 

system. Despite information from previous studies, significant gaps exists 

in our data: identification of the major energy pathways and food webs and 

the roles of river management, water-level fluctuations, habitat connections, 

nutrient processing, and floodplain complexity in the production of fishes 

and other aquatic life. This additional knowledge will provide the basis for 

predictive models of biological production in large rivers. These models will 

be useful for developing and testing innovative strategies to better manage 

large rivers.

Current and Future Studies

We are presently studying how midsummer water-level drawdowns on 

the Upper Mississippi River affect the production of aquatic plants. In a 

drawdown, managers use the river’s locks and dams to manipulate water 

levels to partly mimic the natural fluctuations that prevailed before the 

locks and dams were constructed. We are also studying the importance of 

off-channel areas and deep channels to fish production and the effects of 

dams and navigation traffic on the movements, mortality, and distribution 

of fishes. Each of these studies addresses either direct or indirect effects of 

river management on important aspects of biological production. Our current 

studies are not the end of the story. Future work will focus on the roles of 

carbon and nutrient processing and how that processing is affected by river 

management alternatives.

We are studying the effects of experimental midsummer 

water-level drawdowns on floodplain vegetation on 

the Mississippi River near Onalaska, Wisconsin. When 

river water is lowered and mudflats are exposed, plants 

valuable to wildlife are able to germinate. The upper 

photograph shows a study site soon after drawdown, and 

the lower photo shows vegetation production 22 days later.

Large rivers provide important shipping channels, but we know little about the effects of 

commercial shipping on the production of river fishes. We developed the first method for 

estimation of mortality of adult fish caused by commercial shipping. Our ongoing research seeks 

to understand whether this mortality and disturbances caused by shipping are significant to the 

production of river fishes.

For more information, contact 

Steve Gutreuter

USGS Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road

La Crosse, WI 54603

Phone: 608.783.6222

Email: sgutreuter@usgs.gov

http://www.umesc.usgs.gov/