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Volume 32 No. 1 Winter 2007
Paleolimnology: History in the Mucking
Lake folks often get into lively discussions over what the lake used to be like...more plants, fewer plants, clear water, murky water... Is there any way to really know for sure? Well, the answer is yes! In fact we can have a good idea of what lakes used to be like hundreds of years ago with a science called Paleolimnology.
Paleolimnology, sometimes referred to as "History in the Mucking," is the interpretation of past conditions and processes in lake basins. Each year since their formation, a steady rain of sediments, plant pieces, creature parts and other materials settle to the bottom of our lakes leaving a record of past conditions. Over the eons this fascinating record has remained safe and sound in the sediments waiting for someone who could unlock its secrets. In addition to providing background information on a lake, the sediments hold a record of natural and human disturbances that have occurred in the lake. The response of the lake to these disturbances provides insight into how the lake functions, and provides a better understanding of the significance of trends observed with modern monitoring programs.
Obtaining a Sediment Core
To extract the lake’s past history a sediment core is usually collected using some type of a hollow tube. The tube is pushed into the lake bottom and a cap is remotely placed on top of the tube to hold the sediment in place until it can be returned to the surface. Once collected, the core is sectioned into intervals usually of 1-2 cm. Each of these sections represent sequential chapters in time, with the top of the core being today and the bottom of the core indicating some time in the past. The time frame of interest in paleolimnological studies often is the last 200 years, which typically covers the impacts of European settlement.
Questions Answered with Paleolimnology
The science of paleolimnology can reveal many secrets from a lake’s past life. Most natural and human disturbances affecting lakes can be evaluated using paleolimnological approaches. Nutrient increases and acid rain are issues that have been extensively documented and studied with paleolimnology. Paleolimnology can give us details on the severity of human impacts and tell us within a few decades of when the impacts began. The genesis of events such as erosion, organic pollution from sewage treatment plants and animal feed lots can all be documented. Paleolimnologists can tease many messages from the sediments, such as how many and what types of aquatic plants grew in the lake, changes in species composition, past fish populations, or the frequency of algal blooms. Most recently, trends in climate change are being studied with paleolimnological techniques.
Dating Sediment Cores
An accurate sediment chronology is an essential part of a paleolimnological study. Cores are usually dated to establish the timing of past environmental changes and to determine the rate of input of materials into a lake. Paleolimnologists can accurately date sediment layers because they can be cross-checked against known historical events.
Cores are typically dated by analyzing a series of samples from the surface to a core depth that corresponds with 200 years ago. The most common dating technique for sediments deposited within the last 200 years is the lead-210 technique. Lead-210 is a naturally occuring atom that exhibits radioactivity. It enters lakes primarily through precipitation and dry deposition (i.e. dust), following the decay of an atmospheric gas called radon-222 (radon gas).
Several methods can be used to corroborate the lead-210 dating technique. Testing of atomic weapons has left stratigraphic markers (layers) in the sediments of all lakes around the world. These markers include cesium-137 (a byproduct of atmospheric nuclear testing). Atmospheric testing by the U.S.S.R. peaked in 1963. It then dramatically declined after the implementation of the Nuclear Test Ban Treaty that same year.
In southern Wisconsin another marker that is often used to confirm sediment dates is arsenic (yes, arsenic). Sodium arsenite was used during the 1950s-60s in a number of Wisconsin lakes to control aquatic plants. Records are available that document how much was applied (Lake Tides Vol. 31, No. 2, 2006). The peak in arsenic concentration in the core corresponds with the time of maximum application.
Another dating marker that can be traced in lake sediments is stable lead. It was used in leaded gasoline until its removal in the mid-1970s and provides another time marker to check on the lead-210 dating technique.
A Record in Glass
Fossils are one of the guides to the past life of a lake. The fossils used most are diatoms. These are a special type of algae that possess cell walls made of silica. Silica is the same as glass so diatoms can be preserved for thousands of years in the sediments. Diatoms are particularly useful because most of them live under well-known environmental conditions. This makes them ideal to characterize what past environmental conditions were like when they were living, such as phosphorus concentrations. Diatoms have been used to estimate trends in phosphorus, acidification, color, salinity and plant communities. Studies have allowed us to determine that some lakes are naturally acidic while others have become acidic as a result of human activities. Other algal groups such as certain blue-green and green algae are also preserved in the sediments.
Other fossils that are deposited and are useful for re-creating past environments are aquatic insect larvae and zooplankton. Insect larvae can be used to track changes in a lake’s oxygen content over time. Zooplankton are often eaten by fish and invertebrates, so changes in their numbers allow us to infer past fish populations. For example, a decline in large zooplankton is an indication of an increase in plankton-eating fish such as perch or bluegills.
Paleolimnology is a powerful tool to discover where a lake has been and maybe predict where it is going. This buried treasure of information is stored in lake sediments and we can read the sedimentary records like the pages of an ancient book. Look for more information on paleolimnology in future Lake Tides.
by Paul Garrison, Wisconsin Department of Natural Resources
Lake District Q&A
We often get phone calls and emails from Lake Tides readers with a variety of questions about lake districts. Do you have a question about lake districts that you would like to see answered in Lake Tides? Send it to email@example.com so we can include it in a future issue.
Q: What are the requirements for annual meeting notices?
A: The written notice for an annual meeting must be mailed out at least 14 days in advance to all lake district property owners whose names are listed in the tax roll. Written notice must also be mailed out to all electors (resident voters) whose addresses are known (or can be reasonably determined) or the lake district may publish notice of the meeting in two successive issues of the local newspaper.* The lake district is also required to mail notice of the annual meeting to the Wisconsin Department of Natural Resources (Lakes Management Section, 101 S. Webster Street, PO Box 7921, Madison, WI 53707-7921). Wis. Stat. §§ 33.30(2)(a)
To comply with Wisconsin’s open meetings law requirements, a lake district should also:
- post the meeting notice at least 24 hours in advance in three locations likely to be seen by the general public. As an alternative, a lake district may give notice by paid publication in the local newspaper (this covers #2).
- provide the local newspaper with a meeting notice.
- give a meeting notice to any additional media source that has requested to be notified.
For more information on Wisconsin open meetings law requirements, see the Attorney General’s Open Meetings Law Compliance Guide found at www.doj.state.wi.us
*Tax rolls are available to help lake districts generate accurate mailing lists for property owners. Mailing lists for electors (resident voters) are not always readily available, therefore, lake districts have the option of publishing the notice to get the word out to electors.
EPA Launches National Lake Survey
Our nation’s lakes will be undergoing a check-up in 2007 as the Environmental Protection Agency (EPA) initiates a statistical survey. The goal of the survey is to discover what percentages of the nation’s lakes are in good, fair or poor condition. A "stress test" will also be performed to examine the relative importance of nutrients, non-native species, lakeshore development, pathogens and other stressors on lake conditions.
The EPA’s approach is multi-faceted, and designed to strengthen state, tribal and interstate monitoring programs. This will encourage more efficient use of resources, expanded accessibility and better use of data, and partnerships among agencies and others. The survey should also set a sound baseline of data by providing documented information on the extent of water quality problems and key stressors on our nation’s lakes.
A total of 909 lakes, representing five size classes and distributed relatively evenly across the lower 48 states, are included in the survey. The lakes were selected randomly (excluding the Great Lakes) from a sample that includes freshwater lakes (natural and man-made) and ponds and reservoirs that are at least one meter deep (3.28 feet) and over 10 acres (4 hectares). A second set of samples will be conducted from 91 of the lakes. These lakes are a subset of lakes from the EPA’s National Eutrophication Survey (NES) that was conducted in 1972. Surveying these 91 lakes will allow other potential trends in water quality to be examined.
Wisconsin has 29 lakes included in the survey, ranging in size from 11-acre (4.6 hectares) Buckskin Lake in Florence County to 133,404-acre (53,989 hectares) Lake Winnebago. Two of the lakes, Blueberry Lake in Sawyer County and Haskell Lake in Vilas County, are located within tribal jurisdictions. Several of the lakes already have ongoing monitoring through citizen monitoring or other efforts, and that information will be used to supplement the national lakes survey data and provide background data for interpretation.
The EPA is providing funding and in-kind services to support the field and laboratory work needed to complete the survey. A team of Wisconsin Department of Natural Resources (WDNR) and U.S. Geological Survey staff will be sampling the selected lakes during a mid-summer sampling window. Samples to be collected include standard water quality constituents (nutrients, pH, color, chlorophyll a, etc.), water clarity, physical profiles, phytoplankton and zooplankton, a sediment core, algal toxins, pathogens, and benthos (lake-bottom organisms). In addition, a comprehensive shoreline assessment will be performed at 10 sites around each lake. These core indicators will be examined to diagnose the lake’s water quality, ecological integrity, and recreational value.
The WDNR staff has been actively involved in refining the sampling design, selecting metrics, reviewing field and laboratory protocols, conducting site reconnaissance, and communicating with other states on plans for the survey. The WDNR is planning to use the national lake survey effort to complement and enhance its own lake monitoring and assessment efforts in Wisconsin. For example, WDNR may add more lakes to better report on lake conditions representative of the full range of Wisconsin lake types. The WDNR may also collect additional data, such as detailed aquatic plant information or enhanced littoral and shoreland habitat parameters.
Results of the national survey of lakes will be analyzed and compiled during 2008, with a final report issued in 2009. For more information on the survey of the nation’s lakes, visit www.epa.gov/owow/lakes/lakessurvey
by Tim Asplund and Marilyn Larsen, Wisconsin Department of Natural Resources
February 21, 2007 – Conservation Lobby Day.
Talk with your state Assembly Representative and your state Senator about why lake stewardship is important to you. For more information: www.conservationvoters.org/Public/index.php
Mar 1-2, 2007 – American Water Resources Association (AWRA) 2007 Meeting, Wisconsin Dells.
"The Future of Wisconsin’s Water Resources: Science and Policy."
For more information: www.awra.org/state/wisconsin
March 3-5, 2007 – Midwest Aquatic Plant Management Society Annual Conference.
Wyndham Hotel in Downtown Milwaukee.
For more information: www.mapms.org/MAPMSConf2007.html
May 1, 2007 – Grants Deadlines.
Lake Protection and Lake Classification Grants
River Protection Planning Grants
River Protection Management Grants
If we had no winter, the spring
would not be so pleasant; if
we did not sometimes taste of
adversity, prosperity would not
be so welcome.
- Anne Bradstreet,
Meditations Divine and Moral, 1655,
American poet (1612 - 1672)
Lake Tides -- 905032
College of Natural Resources
University of Wisconsin
800 Reserve Street
Stevens Point, WI 54481
Volume 32 No. 1
Wisconsin Lakes Partnership
Editor: Mary Pardee
Design Editor: Amy Kowalski
Contributing Editors: Robert Korth and Tiffany Lyden, UWEX; Carroll Schaal, DNR
Photos by: Robert Korth (unless otherwise noted)
The contents of Lake Tides do not necessarily reflect the views and policies of UW-Extension, UWSP-CNR, the Wisconsin DNR or the Wisconsin Association of Lakes. Mention of trade names, commercial products, private businesses or publicly financed programs does not constitute endorsement. Lake Tides welcomes articles, letters or other news items for publication. Articles in Lake Tides may be reprinted or reproduced for further distribution with acknowledgment to the Wisconsin Lakes Partnership. If you need this material in an alternative format, please contact our office. No state tax revenue supported the printing of this document.