As valued and well used as Prior Lake and Spring Lake are, there is still much mystery below the surface. Where are certain plant species growing, and why there? Have invasive species treatments been effective? How does plant growth affect lake clarity? To address these questions, the Prior Lake-Spring Lake Watershed District (PLSLWD) is taking action.
In 2013, the PLSLWD started using a program called BioBase, an Automated Vegetation Mapping program, to determine how lake vegetation is changing over time. BioBase uses sonar to detect a lake’s depth, bottom hardness, and vegetation density. With this information, the PLSLWD can make many comparisons which will help influence management decisions within the district.
To begin with, baseline conditions must be documented. Data is collected for the BioBase program by staff and volunteers who take readings with the sonar equipment. This raw sonar data is then processed and maps are created to illustrate conditions. Once the baseline maps have been established, information can be compared across one season or many years. With enough data, the District can determine if there has been a significant permanent change in vegetation, or if a seasonal fluke in the weather is altering water quality. Nature does not follow strict lines, but it does have patterns we can track. Because the District can detect these patterns with the BioBase program, it can identify trouble spots caused by invasive forces or human interference.
One way the District is using BioBase data is to track the location of the invasive curly-leaf pondweed. By comparing plant location from surveys and recording the density data before-and-after treatment, PLSLWD staff can determine how effective the treatments are. For example, treatments in Crystal Bay in 2015 proved to be very effective in reducing curly-leaf pondweed, while treatments in the south central and southwest part of Upper Prior Lake appear to have been ineffective as the invasive species flourished. Based off of the evidence created by the BioBase maps, the PLSLWD was able to receive a credit from the contractor for curly-leaf pondweed treatment in 2015, which was used to target these identified areas in 2016.
Water clarity is another area being looked into on the lakes. A study in 1992 has shown that 40% of plant area cover that promotes optimal water clarity (Canfield and Hoyer). PAC is simply the overall surface area of lake bottom that has vegetation growth. The PLSLWD has calculated PAC of some of the lakes from the data collected with BioBase and found that Lower Prior has achieved the optimal PAC (43.2%) but that Spring Lake (12.0%) and Upper Prior (7.9%) do not have enough vegetation meet optimal plant area cover. This tells PLSLWD staff that water clarity issues on Upper Prior Lake and Spring Lake could be related to a lack of healthy plant cover and provides the District with a starting point for solving water clarity issues on these and other monitored lakes.
Besides treating invasive species and improving water clarity, there are many other uses for the BioBase data. For example; PLSLWD staff can use bottom hardness data to evaluate reasons why native plants may or may not be growing in lakes, use lake depth data to help predict any obstacles when seining carp, and continue taking action on water quality issues.
However, none of this would be possible without our generous sponsors and volunteers who donate their time and watercrafts to the Watershed District BioBase program. The PLSLWD wants to thank: Your Boat Club, for providing boats for staff to map on Upper and Lower Prior Lakes; the City of Prior Lake, for lending their boat for staff to use on Spring Lake; the Shakopee Mdewakanton Sioux Community, for providing a boat and staff to monitor Arctic Lake; the Prior Lake Association, for donating funds to the program; and our many volunteers; Mike Spanier, John Sporney, Jeff Will, Ken and Marcia Rodning and many others who have shown enough care and concern to take it upon themselves to donate both their time and boats for mapping.
This project cannot be sustained by the PLSLWD staff alone and counts on the local community to continue taking an active interest in figuring out how to keep our lakes healthy. The PLSLWD is looking for more volunteers for the 2016 season, especially on lakes that have not been mapped yet. If you are interested in helping us solve the mysteries within our lakes, please contact Sarah Mielke at PLSLWD; 612-361-3295 or firstname.lastname@example.org. Also, please keep a look out on our website for the full BioBase report coming out mid-June.
Canfield DE Jr, Hoyer MV. 1992. Aquatic macrophytes and their relation to the limnology of Florida lakes. Bureau of Aquatic Plant Management, Florida Department of Natural Resources, Tallahassee, Florida, 32303.