Human activities, including disturbances in landscapes, impact the quality of lakes and wetlands in many ways. Eutrophication is the most pervasive problem affecting lakes; the primary cause is excessive nutrient export in runoff from urban and agricultural landscapes. Click on the images below to enlarge the pictures of a hypereutrophic and oligotrophic lake. Click your browsers back button to return to this page.
|
 |
The Upper Great Lake States of Minnesota, Wisconsin and Michigan are fortunate to have a large number of lakes (over 30,000 lakes >10 acres). These lakes are important recreational and aesthetic resources that add to the economic stability and quality of life. Protecting and monitoring lake water quality is a major concern for many local and state agencies. These organizations in Minnesota, Wisconsin, and Michigan have monitoring programs that measure physical, chemical and biological properties of the region's water resources. However, because of expense and time requirements for ground-based monitoring, it is impractical to monitor more than a small fraction of this large resource by conventional field methods. The use of remote, satellite-based sensing is a potentially cost-effective way to gather the information needed for regional water quality assessments in lake-rich areas. For more information on measurements of lake water quality, see the Minnesota Pollution Control Agencies Lake Water Quality Assessment Summary.
For effective environmental planning and management, it is vital to have long-term water quality information on a broad regional scale. Although it is not possible to go back in time and collect additional water quality information using conventional field methods, Landsat data have been collected regularly since the early 1970s, allowing the possibility of extracting historical water quality information from Landsat images. The extraction of historic and current water quality data from satellite images, coupled with existing data collection efforts may facilitate the development of comprehensive regional databases that can be used to evaluate regional differences and water quality trends over time. If used along with land-use data, this information can help determine the impacts different land-use practices have on lake conditions. Results of such analyses will likely aid local and state agencies to make informed decisions about development policy and improve the management of lake resources.
|
| Earlier research in Minnesota showed the potential of Landsat MSS imagery to assess trophic conditions (transparency and chlorophyll levels). In our initial work we successfully extended the approach to Landsat TM data. We have found strong correlations between measures of water clarity (Secchi disk transparency (SDT)) and Landsat TM spectral-radiometric responses. To expand the use of Landsat data for water quality assessments we have developed a Lake Water Quality Image Processing Protocol and have applied these techniques to create a water clarity database with over 500 lakes from the seven-county Twin Cities - |
 |
|
| Metropolitan Area (TCMA) using ten Landsat Thematic Mapper (TM) images and four Multi-Spectral Scanner (MSS) images, spanning the period 1973-1998. Click on the thumbnail to the right to view an example Water Clarity Map for the TCMA or review the ten dates of data that are on display in our LakeBrowser application. Click on this link to view a Slide Show summary of our research. |
| Recently we have applied these procedures to Landsat images and assessed the water clarity of all lakes 20 acres or larger for the entire state of Minnesota. Click on the thumbnail to the right to view the Early 1990's Water Clarity Map of Minnesota lakes. The results show excellent potential for using Landsat data to monitor lake water quality at scales that are not feasible by conventional measurement methods. This work has been expanded to the States of Wisconsin and Michigan as part of the Upper Midwest Regional Earth Sciences Application Center (RESAC) project. |
Click here for TSI Legend |
|
| More recent lake water clarity or trophic state maps of lakes 20 acres and larger have been produced from Landsat-7 EMT+ data. The ~2000 water clarity data are available in our LakeBrowser application. We are also exploring the opportunities for more frequent (intra-seasonal) lake monitoring of larger lakes and the Great Lakes using the 250, 500 and 1000 meter bands of MODIS data. And for smaller lakes we have been encouraged by preliminary results using the new IKONOS high resolution imagery for city scale water clarity assessments. In Wisconsin the ability to coordinate water quality monitoring efforts with Landsat satellite overpass dates is being examined through the RESAC Satellite Lakes Observatory Initiative (SLOI). We hope to extend this coordination effort to Minnesota and Michigan. |
)
)
)
)
){kind=link}