State of the Lake Report Portage Lake 2013
Submitted by Herb Lenon, PhD Fisheries Biologist,
(Portage Lake Watershed Forever Invasive Species Committee Member)
During the early months of 2013, Herb Lenon reviewed 39 years of historical water quality data that was available for Portage Lake. Herb is a key member of the Portage Lake Watershed Forever and Onekama Township Invasive Species Committee. Since 2008, he has worked with the committee to provide expanded over-site and definition of the water quality indicators needed to closely monitor Portage lake. . The committee also hired a lake manager to assist in collecting sufficient water quality data to assure that our treatment of the invasive species in and around our lake was not having a negative impact on the lake
The data that was used in this report was obtained from Michigan Department of Natural Resource lake studies in 1974, 1976, 1985, 1999 and 2009. Other data came from the NW Planning and Development Commission Cladophora Algae Shoreline Survey in 1983, repeated by watershed volunteers in 2008, a thorough 12 month study of the lake and tributaries done by the EPA/Snell Environmental Group, Inc. in 1991 a 3 month limnological study done by Great Lakes Water Quality in 2006 and a 6 month limnolgical study was done by the USGS in 2009. Continuing Studies of 4 parameters, spring and fall have been done by the Onekama School students since 1993, and these also have been included in the report.
Yearly extensive studies of invasive species and water quality began in the Fall of 2008 with a plant survey by Professional Lake Management.. The results of this study prompted the Invasive Species Committee of the Watershed to work with Onekama Township to pass a 5 year SAD for the treatment of invasive species in and around Portage Lake. The water quality monitoring was an important part of this program. From 2009 to 2012 the manager from Lakeshore Environmental and the invasive species committee have overseen the treatment and monitoring of the lake. In 2013 Professional Lake Management was contracted to be the lake manager.
Currently 11 water chemistry parameters are monitored twice/year. Phytoplankton and e-coli bacteria are also evaluated. 8 tributary streams and creeks are evaluated with 9 parameters twice/year and 5-7 storm drains are evaluated with 9-11 parameter once/year. Eurasian water milfoil and phragmites have been treated each year since 2009. The phragmites is under control and the eurasian water milfoil remains below the amount that was first treated.
The classification of the productivity of freshwater lakes was developed in Germany in the 1920’s. Productivity is defined as the rate at which energy is stored by photosynthesis in rooted plants, algae and diatoms to form organic substances. More simply, excessive nutrients provide food for plants to grow more. Less is good.
There are three trophic levels.
Oligotrophic – BEST – These are lakes that are deep and have low productivity. Oligotrophic lakes generally have high levels of dissolved oxygen even at significant depths that allow for survival of species such as trout and whitefish even during the warmest periods of the year.
Mesotrophic – GOOD – These lakes fall in the middle of the spectrum between oligotrophic and eutrophic. Bear Lake and most lakes in Michigan are in this category.
Eutrophic – BAD – These lakes have very high levels of productivity. They are generally shallower, and in terms of ecological succession are considered geologically old. The key to increased productivity of eutrophic lakes, in addition to its shallower depth, is often the availability of nutrients, particularly phosphorus and nitrogen that support plant growth. Lakes that are in an extreme eutrophic state have large areas of rooted aquatic plant growth, occasional significant algal blooms and some depletion of oxygen.