Biology is the study of life. The biological systems of a watershed encompass the plant and animal species that are present in the stream, the riparian lands, and the contributing watershed.
These living organisms interact to create a flow of materials and energy essential for healthy natural communities to thrive. These biotic interactions also create ecosystem services that are important to our human communities. These include:
- recycling carbon, nitrogen, and phosphorus to the air, water, and soil
- regulating greenhouse gases
- providing water treatment
- controlling erosion
- enhancing soil quality
- stimulating plant growth
Healthy ecosystems also provide cultural benefits, such as religious, aesthetic, or recreational opportunities that humans value.
The diversity of Minnesota's biological systems is enhanced by its location near the geographic center of the continent where three major biomes meet, the prairie, boreal forest and eastern deciduous forest. As an example of this diversity, over 2,000 known native wildlife species exist in Minnesota.
However, approximately sixteen percent (346) of these wildlife species have been identified as "species in greatest conservation need" (SGCN) because they are rare, declining or vulnerable (Minnesota DNR, Wildlife Action Plan 2015-2025, pg 19). The loss, degradation and fragmentation of habitats are important drivers of SGCN population declines. These habitat stressors will be excerbated by a changing climate (WAP, pg 28).
Some examples of threats to biological health include:
- conversion of land to managed production systems
- alteration of hydrologic cycles
- fragmentation of habitat
- introduction of non-native (invasive) species
- chemical disruption of life cycles from contaminants
- rapid climate change
- expansion of infrastructure
Explore the Biology Health Scores to see a series of index values that show health trends for biological systems in Minnesota.
Healthy watersheds sustain dynamic, resilient ecosystems teeming with aquatic and terrestrial life. Ecosystems in a watershed, whether aquatic, riparian, or terrestrial, are strengthened by habitat and biological diversity. More diverse ecosystems have been found to be more resilient to disturbance (e.g. flood, fire, drought, outbreaks, overgrazing) and are more productive.
Ecosystem biodiversity is crucial to human welfare because ecosystems bestow:
- Marketable values: derived goods and products essential to life, including food, medicine, and industrial products, genetic resources for crop breeding, and natural pest control services from ecosystems.
- Ecosystem services: flows of energy (photosynthetic & chemical) and materials (nutrients, water) between the biotic community and the water, air, and soil that provide greenhouse gas regulation, water treatment, erosion control, soil quality control, and plant growth. Ecosystem services can also include cultural benefits, such as religious, aesthetic, recreational, or inspirational values that humans derive from ecosystems(Naeem, 2).
Threats to Biodiversity
Biodiversity is threatened by human activities that alter and/or simplify the landscape, such as agricultural practices, urbanization, and channelization.
There are many examples of disturbances such as:
- Streams with dams that block migration and completely alter natural flow regimes; excessive sedimentation that degrades habitat quality; and straightened or channelized streams that simplify essential habitat diversity.
- Lakes with nutrient loading that leads to extreme algal growth, excessive sedimentation that degrades habitat quality, and shoreline development that removes or degrades crucial habitat.
In response to these disturbances, plant and animal diversity declines because of habitat loss or degradation.
When a stream is straightened, the riparian habitats and in-stream biological communities become simplified. The loss of meanders changes relationships between all the components of watershed health.
Measurements of biodiversity often concentrate on the diversity of species. Diversity can be measured by the total number of species (species richness) and the evenness of abundances of those species (species evenness).
In addition to measuring species, biodiversity measurements consider the diversity of ecosystem types (e.g. grasslands, wetlands, rivers, lakes, forests, agricultural). Diversity increases as the number of species, species evenness, or the types of ecosystems increases.
For more detail about the diversity of changing stream habitats and the River Continuum Concept, read RCC.
Several life forms spend most, if not all, of their lives in aquatic ecosystems. These aquatic organisms include types of bacteria, algae, plants, zooplankton, crayfish, insects, mussels, fish, amphibians, reptiles, and mammals. The diversity of aquatic organisms depends on the variety of aquatic habitats.
- A sinuous stream provides more habitats than a straight channel.
- A streambed composed of rocks and sediment of many sizes provides a greater assortment of habitats than a streambed of uniform sediment.
- Lakes with natural shorelines and clear water provide more habitats than highly altered, turbid lakes.
Streams include an added degree of habitat and biological diversity along a longitudinal gradient, from the headwaters to the lower reaches. The River Continuum Concept describes how the structure of the stream and its biological communities evolve along the length of the river. In general, as the size of the stream grows, so does the diversity of habitat, invertebrates, and fish.
Shallow lakes are another example of a productive system with a continuum of habitat types. High nutrient content (phosphorus, nitrogen, and minerals) together with the sunlight available through shallow water, leads to abundant aquatic plant life. Stands of emergent and floating-leaved plants such as cattails, bulrush, and water lily, as well as submerged plants such as coontail, create an extensive littoral zone. These plants provide excellent food and habitat for a variety of animal life, and also anchor sediments, maintaining water clarity (Conroy 2005). Shallow lakes are well recognized as important as breeding areas for waterfowl species, such as the lesser scaup, northern pintail, and common moorhen.
Terrestrial, Riparian Habitats
Terrestrial plants around a lake, along the stream, in the floodplain, and in the valley are vital to the character of these aquatic habitats. The pattern of vegetation along a stream corridor or around a lake will depend on climate; disturbance such as flood, erosion, and fire; formation of floodplains; soil type; and soil moisture.
Plant communities form a mosaic, depending on conditions along the stream and in the floodplain. The disturbance of periodic floods provides an opportunity for new plant growth. For example, plains cottonwood, black willow, and silver maple are adapted to taking root in recently deposited sediments. Because these species are able to withstand deposition of sediment and scouring that exposes their root systems, they can outcompete other tree species in a floodplain environment.
Clearing stream or lakeside riparian vegetation for lawns has a detrimental effect on the biotic systems.
Shoreline plants are important sources of shade and energy. Throughout a stream’s length and around a lake, the vegetation along the riparian corridor intercepts flows of incoming runoff, nutrients and contaminants. Plants are critical components of nitrogen, carbon, and oxygen cycles—serving as production sites and conversion centers for life-sustaining elements. A biologically diverse plant community is more resilient to disturbances and disease than simplified communities or monocultures (Tilman et al., 1996); (Tilman et al., 1997). Deep-rooted native plants anchor soil in place and stabilize streambanks. Plants at the water’s edge also serve as buffers from bank erosion, absorbing the energy of lapping waves and swift currents. The proportion of vegetation to paved surfaces throughout a watershed is an important factor in the water quality of that watershed.
A mosaic of terrestrial plant communities provides more diverse habitats that support more diverse animal communities than homogeneous plant communities, such as cornfields. Fens, marshes, floodplain forests, outwash plains, oxbow lakes, side channels, mudflats, shrub swamps, sand prairies and wet meadows are examples of habitats that support a rich diversity of life. The physical structure of the habitat in large part determines habitat quality.
Because many animals require both upland and aquatic habitats for their life cycles, it is essential to keep these physical habitats connected. It is important to also protect habitats along lateral and longitudinal gradients to allow movement of migrating and traveling wildlife. Long wooded stream courses provide many species, especially mammals, important avenues of movement to other habitats. Larger river corridors are major continental flyways for migrating birds.
The existence of streams, lakes, and wetlands becomes especially important in altered and developed landscapes. In urban and agricultural areas, the floodplain of a river is sometimes the only stretch of remaining native habitat for birds, mammals, amphibians, reptiles and invertebrates. Under such circumstances, the wooded streamside may have the best or only available cover for large mammals, such as fox, raccoon, and deer. More about the importance of landscape connectivity and corridors can be found in Connectivity Concepts.
The Minnesota River Valley as an example of an important corridor of native plant communities that lies within an mainly agricultural or urban part of Minnesota. This corridor supports some of the state’s rarest plant species and noteworthy concentrations of animals. The natural corridors created by the steep topography of southeastern Minnesota are home to some of the state’s rarest reptiles and amphibians. The Timber rattlesnake and the five-lined skink are examples of remnant populations dependent on unique habitats associated with these steep bluffs and wooded valleys.
Endangered, Threatened, and Species of Special Concern
A species is considered endangered if the species is threatened with extinction throughout all or a significant portion of its range within Minnesota.
A species is considered threatened if the species is likely to become endangered within the foreseeable future throughout all or a significant portion of its range within Minnesota.
A species is considered a species of special concern if, although the species is not endangered or threatened, it is extremely uncommon in Minnesota, or has unique or highly specific habitat requirements and deserves careful monitoring of its status. Species on the periphery of their range that are not listed as threatened may be included in this category along with those species that were once threatened or endangered but now have increasing or protected, stable populations. For more information see endangered, threatened, and special concern species.
Species in Greatest Conservation Need (SGCN)
Species in greatest conservation need (SGCN) are defined as native animals whose populations are rare, declining, or vulnerable to decline and are below levels desirable to ensure their long-term health and stability. The Minnesota Wildlife Action Plan 2015-2025 is a strategic plan the addresses the primary causes of species population declines: habitat loss, degradation and fragmentation, non-habitat issues (low reproduction, poor dispersal ability, disease) and climate change impacts. In Minnesota 346 species meet the definition of species in greatest conservation need. These species includes mammals, birds, reptiles, amphibians, fishes, insects, and mollusks, and represent about sixteen percent of the greater than 2100 known native animals in Minnesota.
For example, within the vertebrate groups, one-quarter to over half of the total number of species are species in greatest conservation need. More information and complete species lists are available here.
Total # of Species
% of SGCN