2007 National Lake Survey - Wisconsin Results

Indicators of Ecological Integrity

Ecological integrity describes the 'naturalness' of a lake based on different assemblages of the aquatic community and their physical habitats. Ecosystems have integrity when the composition and abundance of native plants, animals, and their physical components and processes remain intact and undisturbed.

To understand each lake's ecological integrity, the Survey looked at the following:

• Phytoplankton
• Zooplankton
• Sediment invertebrates
• Diatoms
• Mercury
• Shoreland habitat

Phytoplankton

Phytoplankton are tiny, algal, microorganisms that float in the water and photosynthesize like land plants. They form the base of the food chain in most lakes and are usually limited to the photoic zone, or the depth to which sunlight penetrates. They are short-lived and highly responsive to changes in water clarity and nutrients. As part of this survey, phytoplankton will be categorized into groups with similar physical, chemical, and biological environmental demands, such as light, temperature, predation, and depth of mixing layer.

Major groups of phytoplankton in Wisconsin lakes include:

• Blue-green algae are photosynthesizing bacteria that are some of the most ancient life forms on earth. They are found in all waters and may cause nuisance algal blooms and water quality problems in aquatic systems that have high nutrient contents.
• Green algae can be single celled are form in long filaments. Green algae are often visible growing on rocks near shore and often look plant-like although they are not.
• Diatoms are photosynthetic single celled organisms that may grow in small colonies. Diatoms are most common in colder months where other algae are less common and can be identified by their yellow-brown color.

Zooplankton

Zooplankton are drifting or weakly-swimming animal microorganisms that live in the water column. They are commonly composed of protozoans, rotifers, larger crustaceans, such as cladocerans and copepods, as well as insect larvae and aquatic mites. Like phytoplankton, zooplankton make excellent indicators of environmental conditions in a lake because of their sensitivity to changes in water quality. Some common stresses that affect zooplankton include low dissolved oxygen, high nutrient levels, toxic contaminants, turbidity, poor food quality, and predation.

Major groups of zooplankton in Wisconsin lakes include:

• Water Fleas this crustacean is the most numerous group in zooplankton that can sometimes be observed with the naked eye growing up to 6 millimeters in length.
• Ostracods are found in all aquatic environments. They are smaller than water fleas (~1mm) but have a hard shell that fossilizes well and are an important group in dating ancient rock layers’
• Copepods are found in every aquatic environment and are among the most abundant organisms in the ocean making them among the most abundant organisms in the world as of all zooplankton they are important components of the aquatic food web.

Sediment Invertebrates

Benthic macroinvertebrates are insects and small animals without backbones that live in the lake bottom attached to rocks, woody debris, aquatic plants, and burrowed into the sediment. Some examples include snails, clams, crayfish, aquatic worms, leeches, insects and their larval and nympth stages. They are generally immobile and tend to respond to a wide array of environmental conditions. As a result, they can be used to determine the type of stress, such as pollution, affecting a particular lake.

Major groups of benthic macroinvertebrates in Wisconsin lakes include:

• Chironomids are known as the non-biting midges because as adults they resemble mosquitoes or gnats but lack biting mouthparts. As juveniles they are entirely aquatic appearing like small worms often commonly refereed to as redworms because man species have a red coloration.
• Amphipods are crustaceans found in numerous aquatic habitats throughout the world. They are often called scuds or side-swimmers because they appear sideways while the scurry around the bottom.
• Mayflies are aquatic insects that spend most of their life underwater in streams, rivers and lakes. Mayfly adults emerge, often in large groups, once or twice a year and live as winged adults for a short period (30 minutes to 2 days).

Diatoms

Diatoms are a type of algae that possess siliceous (glass) cell walls and are usually abundant and diverse in lakes. Because their glass walls make them highly resistant to degradation, they are particularly useful when studying a lake's history. For example, certain types are found in nutrient-poor (oligotrophic) lakes, while other types grow in nutrient-rich (eutrophic) environments. By determining changes in the diatom community from the bottom of the sediment core to the top of the core we can infer how water quality has changed from pre-settlement to the present day for a particular lake.

Mercury

Mercury is found naturally in the environment--but much of the mercury in the atmosphere is the result of the burning of coal for energy. Atmospheric mercury eventually settles into lakes through wet or dry deposition where it can then be transformed by bacteria into methylmercury, a highly toxic form that accumulates in the tissue of fish and shellfish.

Birds and animals that eat fish and shellfish are more exposed to mercury than other animals in water ecosystems. As a result, predators that eat fish-eating animals may be highly exposed. The effects of such expore include reduced reproduction, slower growth and development, abnormal behavior and even death. Likewise, human methylmercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages. The Survey will analyze mercury concentrations in surface sediment from the center of each lake to better predict the impacts of mercury deposition on a watershed.

Shoreland habitat

At ten plots around each lake, a physical habitat survey was conducted to assess the composition of the shoreline and littoral zone, or nearshore lake bed. The surveys collected information on the lake bed substrate, indications of fish habitat, composition and percent coverage of nearshore vegetation, and the level of human disturbance, such as houses and roads.

The data will be used to interpret the water quality results by acting as the link between large watershed-scale influences and those that directly affect aquatic organisms on a daily basis. It will also help with in the diagnosis of probable causes of ecological degradation in lakes, such as soil erosion due to agriculture or construction. Last, the surveys will be used as a benchmark against which to compare future shoreline surveys that may capture habitat changes induced by human development or climate change.