A frequently asked question on cruises is "what is the water quality?" Many of the procedures performed on the vessel help to answer that question. Water quality is defined in terms of physical, chemical, and biological parameters with respect to a certain use ( Figure 5 - Water Quality Parameters). For instance, acceptable water quality for warm water fishes would not be optimal for coldwater fishes, and standards for drinking water differ from those for boating and recreation. No single factor alone indicates good water quality, and the quality varies with factors such as season and location. Long-term water quality measurements from well-defined locations are needed to tell if conditions are changing or remaining the same.
Biological Properties of Water
Like other ecosystems, lakes and rivers host a complex combination of plants (producers), animals (consumers), and decomposers, which are interrelated through food chains and food webs. Introduction of exotic or nonindigenous species can upset the balance of existing food chains. The productivity of a body of water is dependent upon variables such as the available nutrients, light, and temperature.
Aquatic organisms are generally divided into five groups:
These organisms have a spatial distribution that is defined by regions adjacent to the shore (littoral), open waters (limnetic or pelagic), and the bottom (benthos). Plankton nets are used to sample for plankton and a PONAR grab sampler is used to collect benthic organisms.
Physical Properties of Water
Water is a unique chemical compound that exists naturally on earth in the gaseous (water vapor), liquid, and solid (ice) states. It has a maximum density at 4 C, and water boils at 100 C and freezes at 0 C. A relatively large amount of heat is needed to raise water temperature. Physical properties of water that are measured on the vessels include water transparency or clarity, color, turbidity, and temperature. Suspended particles in water influence water color and clarity. Particles can settle to the bottom and contribute to a build up of sediment. Instruments and equipment used to quantify these properties include the Secchi disk, Forel-Ule Color scale, turbidity meters, turbidity tubes, and thermometers.
Chemical Properties of Water
Water chemistry is influenced by many factors such as the geology of a region, photosynthesis and respiration, pollutant load, pressure, temperature, and time of day. Water behaves as a solvent in which a substance (solute) dissolves. The resulting solution may contain individual ions (particles with charges) or molecules. Gases, solids, and other liquids are capable of dissolving in water but some of these substances do not dissolve, e.g., they are insoluble. The solubility of a solid in water generally increases with temperature while the solubility of a gas decreases with temperature. Concentrations of a chemical in water are generally expressed in terms of milligrams per liter (mg/L), parts per million (ppm), and percent saturation for gases. Chemical properties of water explored on the basic cruise include pH, dissolved oxygen, and conductivity. Alkalinity and nutrients (phosphorus and nitrogen) may be measured on advanced trips. Heavy metals and organic compounds require specialized laboratory equipment for their measurement and are not sampled for on a standard cruise.
Evaluation of Water Quality
One of the best ways to understand water quality is to compare two areas that differ in their water quality. An underlying theme of the cruises aboard the vessels is to compare and contrast Lake Michigan with another water body. Lake Michigan has a surface area of about 22,300 square miles making it the third largest Great Lake. The flushing time of the Lake is 62 years. The average depth of Lake Michigan is 279 feet with a maximum depth of 923 feet making it the second deepest Great Lake. In contrast, Spring Lake's surface area is about 1,300 acres with inputs of water mainly through springs, streams, and precipitation. Spring Lake is connected to the Grand River. Muskegon Lake is 4,149 acres in size and it receives flow from the Muskegon River as well as tributaries such as Ryerson and Ruddiman Creeks.
Overall water quality can be evaluated by considering the trophic status or biological productivity. Eutrophication, or aging of lakes, progresses through various trophic states (oligotrophic --> mesotrophic --> eutrophic). Nutrient levels, organic matter content, dissolved oxygen levels, and water transparency indicate the trophic state or biological productivity of a water body.
The open waters of Lake Michigan are oligotrophic and some nearshore areas are mesotrophic. Oligotrophic lakes are characterized by low nutrient levels, low biomass, high oxygen concentrations, and high transparency. These lakes are usually deep. Eutrophic lakes such as Spring Lake are highly productive with high nutrient levels, high biomass, low oxygen concentration in the bottom waters, and low transparency. The large volume of organic matter accumulated in bottom sediments depletes oxygen as it decomposes. Mesotrophic lakes are between the other two trophic states in their characteristics. Of the 730 inland lakes that the Michigan Department of Environmental Quality has assessed, 27% of Michigan lakes were eutrophic, 53% were mesotrophic, and 16% were oligotrophic (MDEQ, 2004).
Lake Michigan Food Web
The general flow of biomass in Lake Michigan is through trophic levels that include the producers: phytoplankton (algae) and aquatic plants (macrophytes), and consumers: zooplankton, forage fishes, predator fishes, and fish-eating humans and other animals. The Lake Michigan food web is composed of two distinct but overlapping parts: the pelagic food web associated with offshore open water (pelagic) and the bottom (benthic) food web. Both webs are dependent upon the phytoplankton in the surface waters.
Members of the pelagic food web include small invertebrates such as cladocerans and copepods. The benthic food web is fueled by the algae, fish, and detritus (dead and decomposing organic matter) that fall from the upper part of the water column (photic zone). Two large macrobenthic animals, the opossum shrimp ( Mysis relicta) and an amphipod or "sideswimmer" ( Diporeia sp.) are important species for the food web, but their numbers have declined.
The biological integrity of the fish community that is dependent on pelagic and benthic species is no longer present. Increasing levels of fishing pressure and human-induced environmental degradation have greatly altered the composition of fish species. Additional stresses of the sea lamprey and alewife contributed to a less complex, less stable food web. Control of the sea lamprey with a 90% reduction from historic highs and introduction of salmon and trout helped to increase stability. The balance has shifted from dominance of a single fish species to a diversity of about 78 fish species in Lake Michigan and 130 in the tributaries to the lake. Alewife, rainbow smelt, and bloater represent prey species for the salmon in offshore regions. The inshore fish community includes yellow perch, walleye, smallmouth bass, pike, catfish, and panfish. Benthic food web fish include lake whitefish, round whitefish, sturgeon, suckers, and burbot.
Besides man, consumers of Great Lakes fish include birds such as herons, osprey, bald eagles, loons, cormorants, and mergansers. Minks and river otters also consume fish. The web comes full circle with the detritus and decomposers completing the cycle ( Figure 6).
Exotic or Nonindigenous Species
Exotic or nonindigenous species are plants and animals that are found beyond their original range. They may be beneficial to an ecosystem, but they can also disrupt the ecological balance of an area. Harmful aquatic nuisance species (ANS) include the zebra mussel, quagga mussel, ruffe, round goby, spiny water flea, sea lamprey, Eurasian watermilfoil, and purple loosestrife. When released into habitats where there are no natural controls such as pathogens, parasites, and predators, these species can grow at an exponential rate quickly establishing them.
Over one third of the 183 or so known aquatic nuisance species in the basin have been introduced since the opening of the St. Lawrence Seaway for shipping. Ballast water from ships is an important transporter of these species. The National Invasive Species Act of 1996 reauthorized a mandatory Great Lakes ballast program. Other means of transport for exotic species are the water used for the bait industry, food processing, exotic pet trade, and the aquarium trade. Boat transfers from one body of water to another and landscape practices are other ways of transporting aquatic nuisance species. Inland lakes as well as the Great Lakes have seen invasions of exotic species.
Data collected by citizens on exotic species can contribute to the research base for early detection of the spread of aquatic nuisance species (ANS). Participants in the cruises on the D.J. Angus and the W.G. Jackson have an opportunity to contribute to monitoring of aquatic nuisance species. Specifically, zebra mussels, quagga mussels, spiny water fleas, Eurasian watermilfoil, and purple loosestrife are species likely to be observed on cruises.
Zebra mussels ( Dreissena polymorpha) were first discovered in the Great Lakes basin in Lake Saint Clair in 1988 and Lake Michigan in 1989. They have now spread to all five Great Lakes and many inland lakes. A relative of the zebra mussel, the quagga mussel ( Dreissena bugensis) has also been discovered in the Great Lakes. They invaded in 1990. Quagga mussels have nearly replaced zebra mussels in Lake Michigan. Mussels attach to intake pipes, rocks, buoys, docks, piers, and many other submerged substrates including native clams. The dreissenid mussels are filter feeders that cause a decline in phytoplankton that would otherwise feed planktivorous fish. Colonies of zebra mussels clog water intakes and use rocky substrate that is important to fish spawning. There have been reports of mussel feeding activity increasing water clarity and leading to the growth of plants attached to lake bottoms as more sunlight penetrates deeper. Dreissenid mussels have altered microbially-mediated nutrient cycling, the nearshore phosphorus cycle, patterns of contaminated sediment burial, and bioaccumulation of contaminants. Look for zebra and quagga mussels attached to plants and in bottom samples. The free-floating larval forms of mussels, called veligers, may be found in plankton samples.
Another aquatic nuisance species found in plankton samples is the spiny water flea ( Bythotrephes cederstroemi) or B.C. Bythotrephes is a predatory, shrimp-like zooplankter that grows to about 1 cm (0.4 inch) in length. It feeds on small aquatic animals that would otherwise be food for fish. It reproduces rapidly and can monopolize the food supply. The spiny water flea is protected from fish predators by its unusually long tail spine with protruding barbs. Many fish such as young alewives, lake trout, and perch can easily capture Bythotrephes but they have a hard time swallowing it. The spiny water flea is native to Europe and China and is thought to have been transported in ballast water to the Great Lakes in the 1980s with the first appearance in Lake Michigan in 1986.
Eurasian watermilfoil ( Myriophyllum spicatum) was accidentally introduced to North America from Europe and reached the midwestern states between 1950 and 1980. Watermilfoil can form vast mats of vegetation at the waters surface, which crowds out native plants and interferes with recreation. The plant reproduces quickly through fragmentation and runners. Plant fragments cling to boats and are carried from lake to lake.
Although quite attractive, purple loosestrife ( Lythrum salicaria) is changing the character of Michigan wetlands. A native of Europe and Asia, the plant was introduced to North America in the 1800s. The main difficulty with purple loosestrife is that it thrives and reproduces in wetlands forming dense, impenetrable stands unsuitable for wildlife food, cover, or nesting sites. Native vegetation is displaced and there is a loss of species diversity as well as food sources for wildlife in wetlands. Look for purple loosestrife along the edges of rivers and inland lakes.
The round goby ( Neogobius melanostomus), a common species often caught by fisherman along piers and docks in the Great Lakes, was introduced from the Black and Caspian Seas. The relatively small-sized goby has become quite abundant in recent years feeding on bivalves, amphipod crustaceans, small fish, and fish eggs. Goby are believed to have entered the Great Lakes from discharged ballast waters where they were found in the St. Clair River in 1990. Although the full impact of this species is not yet known, gobies continue to affect other species through food competition and the predation on eggs and young fish.
Another well known exotic species to residents along the shorelines of the Great Lakes is the alewife ( Alosa psuedoharengus), which often wash ashore in great numbers during the spring. Although native to the Atlantic coast, alewife have invaded the Great Lakes competing with native fish like the lake herring, whitefish, chubs, and perch for small organisms and plankton.
Although not in Lake Michigan, there is concern about Asian Carp that have worked their way up the Mississippi River. Electrical barriers in rivers are a line of defense against carp invasion of Lake Michigan. There are several types of Asian Carp and some species jump into boats.
The latest invasive species of concern is the bloody-red shrimp Hemimysis anomala. It was first reported by NOAA from samples collected in Muskegon, Michigan in November of 2006 in waters connected to Lake Michigan. An effort is underway to document sightings of these shrimp.
A website for exotic species is found at http://www.miseagrant.umich.edu/explore/native-and-invasive-species/. For more information about Lake Michigan, see the U.S. Environmental Protection Agency Lakewide Management Plan at http://www.epa.gov/glnpo/.