Potato Lake 2010 Project Results and APM Plan Saturday May 28, 2011 Dave Blumer, Jake Macholl SEH Lake Scientists
Lake and Aquatic Plant Management Planning Goal: To maintain or improve the overall condition of Potato Lake for current and future lake users to enjoy Plant management Nutrient management Watershed management Shoreline management
Project Overview from May 2010 Phase One Lake Sampling Twice a month Three depths Multiple parameters Tributary Sampling 5 sites Outlet Monitoring Lake level Flow Volume Precipitation Monitoring Historic Paleocore Phase Two Plant Surveys Early season CLP & EWM Lake User Survey Crystal Lake/Price Pond Sampling Watershed Evaluation Education Invasive species Best Management Practices Function of the lake *Original proposal included four phases
Things to Determine Water budget Lake residence time Changes in lake level In-lake nutrient load Sources of nutrients Changes over time Plant management scenarios that maintain a balance between lake use and plant growth Nutrient management scenarios to reduce sources of phosphorous
Lake Inventory Physical Characteristics Water Quality Lake Inflow, Outflow, and Retention Time Soils Groundwater/conductivity Historic Conditions Nutrient Modeling Aquatic Plants/Invasive Species
Physical Characteristics Potato Lake 229 acres, Crystal Lake 22 acres, Price Pond 13 acres Watershed covers 3,229 acres (68% forest, 15.1% agriculture, 8.7% open water, 5.3% wetland, and 2.9% residential area) Headwaters of Potato Creek
Water Quality Water clarity Surface and bottom water chemistry Dissolved oxygen and temperature profiles Tributary sampling Outflow monitoring
General Comments No significant change in water clarity in the last 13 years 2005-2007 were the worst years according to CLMN data (drought induced?) Big shift in water clarity every year in July Chlorophyll peaks in late summer at an average concentration for northern WI lakes Total phosphorus values were average for northern WI lakes at the surface and in the middle of the water column Total phosphorus was very high in the bottom waters in July and August indicating internal release of phosphorus from the sediment The nitrogen to phosphorus ratio in 2010 indicates that phosphorus is the limiting nutrient in Potato Lake
2010 Water Clarity (46 readings) 2010 Apr May Jun Jul Aug Sep Oct 0 2 SECCHI DEPTH, IN FEET 4 6 8 10 12 14 16 18 20 Secchi Measure This decline in water clarity is seen every year since 1998
Dissolved Oxygen and Temperature Lake models and collected data suggest the lake is polymictic Potato Lake is mostly mixed with frequent short periods of stratification Stratification occurs, but may only last a few hours to a few days When stratified, dissolved oxygen concentrations are reduced or disappear completely in the bottom waters and phosphorus is released Remixing can bring that phosphorus back to the surface waters *Thus the lake acts like a phosphorus pump alternately stratifying and then mixing bringing phosphorus to the surface
Lake Inflow, Outflow, and Retention Time Ephemeral Streams The average phosphorus concentration measured in stream inputs was higher than the phosphorus being taken out of the lake by outflow Water retention time in Potato Lake is approximately 1.8 years Potato Lake is a phosphorus sink Under hi-flow conditions lake retention time may drop to 0.5 years Unknown if the excess phosphorus in the lake is removed primarily by plants, or deposited in the sediment
Concerns at the Outlet Dam Illegal cobble dams in the culvert may cause more harm than good Difficult to calculate true flow Does not raise the water level as much as one would expect Reduces rooted plant growth Inhibits fish passage May increase shoreland erosion Erodes the roadway *Erosion and reduction of rooted plants adds more unwanted nutrients to the lake to be used by algae
Soil Types in the Watershed and around the Lake Watershed soils classified as sandy loam, that is highly erodible particularly on steep slopes Allow rapid movement of water through it Good for preventing surface runoff Bad for filtering septic system loads Rapid movement of groundwater
Lake Conductivity Survey High conductivity indicates more minerals and salts in the water East shore and spring hole have the highest values Sources of minerals and salts Groundwater flow through local geology and soils Decomposing organic matter Presence of road salt or agricultural runoff Lawn fertilizers Septic system discharges We need to know more about the groundwater coming into Potato Lake
Historic Water Quality and Aquatic Plant Conditions Paleocore Results Had lots of plants Still has lots of plants, but not necessarily more plants Aquatic plant make-up has changed from smaller low growing species to larger and taller plant species More recently phosphorus levels have gone up, but significant changes in water quality haven t reflected that until the last few years Larger plants pull nutrients from the sediment Smaller plants attached to the larger plants pull nutrients directly from the water This change in plant make-up may have been able to cope with increased levels of phosphorus entering the system
How much Phosphorus is coming into the lake, and from where? Total Phosphorus Inputs to Potato Lake based on Modeling (450 lbs total phosphorus) 134 93 44 176 Crystal Lake Price Pond Septic Systems Internal Loading Unspecified 3
Aquatic Plants and Invasive Species Wild Rice Very abundant Highly prized and protected Basically untouchable A lucky to have resource Has helped to maintain water quality
Aquatic Invasive Species None were found!
Lake and Plant Facts the individual plants in Potato Lake are not unique or rare, but the overall community is 33 different species (state average is 21) FQI = 33.6 (state average is 22.2) No aquatic invasive species Abundant wild rice Lots of filamentous algae, but not where it is usually found Several species of plants that are dominant in Potato Lake, but nowhere else (flat-stem and Friess pondweed) Water with high mineral content leading to marl build-up on plants Up-welling or spring holes that are clearly visible and that impact conditions in the littoral zone
What makes Potato Lake Unique Black Globs of colonial blue-green algae (aphanocapsa) Pronghorn Clubtail (Gomphus graslinellus)
My Conclusions Potato Lake has successfully adapted to a build up of phosphorus over the course of many years The majority of water quality and excessive plant growth problems that people are concerned about are the result of the lake trying to cope with increased phosphorus inputs Potato Lake may not be able to handle these inputs further and maintain the high quality system you are used to Continual build-up of phosphorus will tip the lake over to an algae dominated rather than plant dominated system We need more information about individual sources of phosphorus, their impacts to the lake, and what we can do about them. Plant management to remove vegetation is a bad idea at the present time.
Increases in phosphorus levels only cause problems when a body of water can no longer handle those inputs