state of the lake 2011
Lake Keeper Report
Final Report For 2011
by Don Mayland
- Introduction Section 1
- Water Quality Data Section 2
- Mussel, Snail, Weed and Bird Inventories Section 3
Since the mid 1970s many studies of the water quality in Lake Wononscopomuc have been conducted. Throughout the late 1970s until the early 1990s Ted Davis, a Limnologist on the faculty of the Hotchkiss School, was the primary source of data about the lake. In addition, Richard Miller of Union Carbide Corp. conducted a study of water quality in 1977. Both the Davis and Miller studies were undertaken because of the visible deterioration of the water quality in the lake.
Oscillatoria Rubescens, a blue green algae, had established a large population and was causing a dramatic decline in water clarity. There were several years when the color of the water was blood red in the spring and early summer. The reddish filamentous O. Rubescens is often associated with cultural eutrophication . This was the tipping point that inspired the creation of the Lake Wononscopomuc Association and the desire to discover the sources of this cultural eutrophication…..and to do something about it. In addition, it was during this period of time that Eurasian Milfoil first appeared in the lake.
In 2003, Greg Bugbee of the Connecticut Agricultural Experiment Station did some water sampling. In 2006 Nina Caraco conducted a study of the lake and produced a paper in which she encouraged the continued monitoring of the water quality and the harvesting of the milfoil and removal of the biomass. The firm of Aquatic Control Technologies, Inc. has frequently been hired to do specific sampling and weed inventorying. All of this sampling has been conducted on a sporadic basis, however. In addition no effort was made to compile a comprehensive data base about the water quality in Lakeville Lake.
The Lake Keeper program, which was started in 2009 through the efforts of the Lake Wononscopomuc Association, has as its objective the construction of this data base. It has been a three year effort with sampling done approximately 12 to 15 times each year between April and November. Sampling began in 2009 and continued in 2010, with the last year being 2011.
The sampling program has been funded in equal parts by The Lake Wononscopomuc Association, The Town of Salisbury and The Hotchkiss School. The actual field work was performed by Marine Study Program, Inc with the principal guidance of Donald Mayland. Chris Oostenink has been a major contributor. He is a teacher in the Science Department at The Hotchkiss School and his background and education is in fresh water biology. He has been the “go to guy” when questions about the data have come up. In addition, he spent many hours in the 20’ Whaler provided by The Hotchkiss School helping with the leg work involved with the sampling.
Additional sampling help came along during the 2011 field season in the form of students from the Marvelwood School. This school has a strong program of community service. Early in 2011 several students volunteered to work with the Lake Keeper program as a fulfillment of their community service requirement. They were active in helping to gather water quality data when the weather permitted and they played a major role in compiling the data into easily read graphs and tables. A special thanks goes to these students.
We conducted water sampling at three locations. The graphs, tables and map indicate these as buoys A, B and C. These buoys were chosen for two reasons; one of practicality and the other with a more scientific basis. The fact that the buoys already existed as permanent moorings for the Hotchkiss Sailing Team’s committee boat eliminated any anchoring problems that would have clearly existed, as the depths at these buoys range from a low of 60′ at Buoy C to a high of 110′ at Buoy B. The locations of the buoys also were perfect in terms of the quality of the sampling that was done. Buoy A is in the SE corner of the Lake, near the inflow of the major feeder stream, Succor Brook. Buoy B marks the deepest spot in the lake, almost in the center and Buoy C is in the NE corner of the lake, near the outflow at the Town Grove.
On a few occasions we conducted some specific sampling in the feeder streams that enter the lake from springs and storm drainage. You will find a map under Tab 8 of this report that labels both the buoys and the streams that we sampled.
These streams are labeled numerically from S1 to S11. Only one stream has continual flow in all seasons and that is Succor Brook, labeled S1. The Stream labeled S6 has continual flow for much of the year but will go dry when rainfall is low. All of the other streams are mainly drainage from rain and snow melt runoff.
The depths at the buoys enabled us to sample near the surface, at a depth of 10′, below the summer thermocline at a depth of 30’ and a few feet from the bottom at a depth of 50′. We sampled at a fourth depth of 95′ at Buoy B in order to get readings near the bottom at that location. Every effort was made to sample at the same time of day, usually mid morning, and in the same weather conditions.
Sampling Techniques and Instruments Used
At each buoy and at each depth we sampled for the following:
- Temperature (in degrees Celsius)
- Visibility (in meters)
- Dissolved Oxygen (measured in Mg/L and % saturation)
- Total Phosphorus (Mg/L)
The following instruments were used to collect data:
- Dissolved Oxygen…Yellow Springs instruments(YSI) 550A
- Conductivity…………YSI model 30- SCT
- pH…………………………Oakton pH Testr 2
- Temperature………..both the YSI 550A and the YSI model 30- SCT
- Visibility……………….Secchi Disk
Total Phosphorus was sampled using a Van Dorn (horizontal) water sampler. These samples were taken to The Carey Institute of Ecosystems Studies in Millbrook New York where they were analyzed.
In addition to water quality data we collected, information about the zooplankton and phyto plankton populations in the lake, the bird life around the lake shore, fish populations and snail and mussel populations. This information can be found in section 3 of this report.
Water Quality Data
Dissolved Oxygen is one of the most important gases found in the water. It gets into the water column in the lake by wind mixing, plant life carrying on photosynthesis and gas contained in the groundwater and surface water entering the lake. The solubility of oxygen, as well as other gases, depends on water temperature. The colder the water the more gas it can hold.
Lakeville Lake is highly stratified from May to early November. The deep water (hypolimnium) does not get above 7.5 degrees Celsius at any time during the year. However, the data collected has clearly shown that this hypolimnium layer becomes hypoxic by July. This is the case at all three sampling sites. It is most pronounced, however, at buoy B where the deep water sampling is at a depth of 95 feet.
This hypoxic condition occurs because of the pronounced stratification mentioned above. Once the thermocline sets up there is no mixing of surface water which becomes oxygenated from stream and surface water runoff and wind mixing. In addition, plant life is very pronounced in the epilimnial layer (less than 25’ in depth) which means that photosynthesis also contributes to the dissolved oxygen content in this shallow water. None of this oxygenated water makes it through the thermocline to the deep water. In addition, oxygen that is dissolved in the water in the hypolimnium gets used up by the bacteria that work on the decaying organic material that does sink to the bottom. So, as much as the deep water is capable of holding more dissolved oxygen there simply isn’t that much of it that reaches that deep water, and what does get that deep gets used up in the decaying process.
The water quality standard for the “warm water” (epilimnial layer) in a natural lake is generally considered to be 5 Mg/L. This is the minimum amount of oxygen needed for fish, such as sunfish, bass and perch to survive and grow. The standard for trout water (the hypoliminial layer) is 7 Mg/L. In all three years that we sampled mid June was the time period when the dissolved oxygen level near the bottom at all three buoys fell below 7 Mg/L. It never fell below 7Mg/L at the 30’ or 10’ depths. At all three buoys, once the level was below 7Mg/L it stayed below that level until we ceased sampling in November.
3 year averages for dissolved oxygen Mg/L
(Dissolved Oxygen below trout standards)
(Dissolved oxygen below trout and warm water fish standards)
During the late spring, summer and early fall months Lakeville Lake is highly stratified. It is the deepest natural lake in Connecticut, reaching a maximum depth of 110’. Water temperatures near the bottom at all three buoys never got above 7.5 degrees celsius. At the bottom ,in the deepest section of the lake(buoy B), it never got above 6.5 degrees Celsius.
The thermocline typically sets up at a depth of 28’ to 30’ during the mid summer. It first sets up, in April at a depth of approximately 12’. The thermocline disappears and the fall turn over takes place, usually, in the first week of November. This means that from mid April to early November there is little or no oxygenated surface (less than 10’) water mixing with the bottom water. The graph of the temperature and dissolved oxygen profiles that we recorded indicate this. The temperature and dissolved oxygen readings stay unchanged to about 10’. Then they begin to gradually drop to a depth of 20’ (location of the thermocline). At 20’ they both take a dramatic drop and then gradually go down as the depth increases.
Thermocline @ approximately 12’
Thermocline @ approximately 20’
Thermocline @ approximately 28’
Thermocline @ approximately 28’
Thermocline @ approximately 28’
Thermocline has disappeared by the end of the month
Phosphorus is a chemical that is found in abundance in the natural environment. A certain amount of it is needed to support plant growth, both on land and in the water. However, a major problem for lakes, rivers and streams in Connecticut is the abnormal amount of phosphorus that enters them because of human activities. This abnormal influx is a major cause of algal blooms. When algae die they sink to the bottom and bacteria work on their decomposition. This contributes to the depletion of oxygen (hypoxic condition) which means that fish life, such as trout, cannot survive for long in these bottom waters.
This problem is most pronounced in deep lakes, such as Lakeville Lake, where there is little mixing of the top layer of well oxygenated waters with the deep water because of the thermocline. We sampled for phosphorus three to four times in each of the three years of the project. Sampling began in April and ended in November. The samples were analyzed at the Carey Institute of Ecosystems Studies in Millbrook, NY.
We also took stream samples on occasions when flow rates were high due to heavy rainfall. The runoff during these times from road surfaces, fertilized lawns and septic field leeching made it more likely that total phosphorus readings would be elevated. As you can see in the data, however, this was not the case. P levels stayed consistent with what we had been finding in the shallow water of the lake during the three years we sampled. The highest total phosphorus readings were near the bottom (95′) at buoy B. We sampled three times, early spring, mid summer and mid fall at all three buoys and at depths of 10′, 30′ 50′ (also 95′ at buoy B). The readings were in the .205 to .255 Mg/L range at the 95′ depth. Based on the water quality index of Lillie and Mason for Wisconsin lakes, seen below, these readings put the bottom water in Lakeville Lake in the very poor category, in fact, worse than the very poor category in this index. The water above the 30′ level(summer thermocline) at all three buoys qualified as good to very good, according to the index.
Lillie and Mason Index (see bibliography)
Total Phosphorus in (Mg/L)
.15 Very Poor
.060 Average for impoundments
.030 Average for Natural Lakes
.010 very good
Water samples to test for total phosphorus were taken three to four times per year in each of the three years of the project.
However, except for April and October, sampling was not always done during the same months. Therefore, some of the readings, labeled “3 year averages” are actually single readings, not averages.
During the sampling season of 2011 we also obtained phosphorus readings from several of the small streams in the water shed that flow into the lake. The streams that we sampled and the readings that we obtained are as follows:
pH is another important indicator of the water quality of the lake. Low pH levels, meaning the water is acidic, can mean a difficult environment in which many forms of aquatic life can survive and reproduce. Lakeville Lake lies in a geologic zone known as the marble valley, where limestone is prevalent. Therefore the lake has high pH readings and produces a great amount of Marl( a calcium carbonate precipitate). pH and Phosphorus are related in that high pH readings can cause the release of phosphorus from bottom sediments (internal loading).
The highest pH reading that we recorded was 9.3 at the surface at Buoy B in the month of May in 2011. The lowest was 7.4, at the bottom at Buoy C in August of 2010. The average pH during the three years of the project and at all depths and Buoys was 8.9.
Visibility readings are important in several ways. First, it tells how much biological activity is going on. Zooplankton and phytoplankton are important components of the food chain . Ironically, they are also inhibitors of visibility. Too much of the wrong kind plankton can be harmful, both biologically and esthetically. This is also true of algae. Low Secchi disk readings in Lakeville Lake have often been the result of algae such as Gloeotrichia and Ocillatoria Reubescens. A consistent change in water clarity can be an early indicator of a change in the chemistry and biological activity in the lake.
The visibility in the lake stayed consistent during the three years of our study. Visibility generally improved as the seasons progressed. The highest visibility reading we got was 6.5 meters. This was recorded in September, 2010.
However, Secchi disk readings do not record a visibility fact that has been occurring in the lake for many years. As divers we have witnessed a condition where the visibility is greatly reduced starting at a depth of approximately 30’ and extending down to a depth of approximately 45’. Often times the water will be quite clear below this layer of extremely poor visibility and Secchi disk readings often indicate good visibility above the layer. This could be caused by an algae that needs cold water and the sunlight it receives, although minimal, at these depths. Below 45’ there is not enough sunlight to promote algae growth. Above 30’ the water temperatures in the late spring, summer and early fall are too high for the algae. However, this is just a theory and greater research about this situation is needed.
3 Year Visibility Averages: (in Meters)
Conductivity is a measure of how easily an electric current moves through water between two electrodes. It is a good indicator of the total dissolved solids(TDS) in the lake. During the three years of our sampling the conductivity readings stayed consistent The lowest reading we received was 212.6 in 2011 at a depth of 50. There is some increase in conductivity in the deeper water of the lake, where we received a reading as high as 425.9 in 95’(bottom) at Buoy B in May , 2010.
Mussel, Snail, Weed and Bird Inventories
In 2011 we began an inventory of mussels and snails in Lakeville Lake. During all three sampling seasons we checked for the appearance of adult Zebra Mussels by inspecting rock outcroppings along the shore by the Town Grove and the Shore by the Hotchkiss Jetty. We also inspected the submerged rock walls that separate the two large basins in the lake. These inspections were done using scuba equipment and they extended down to a depth of 40 feet. In addition, the weeds brought up by the harvester were frequently checked for Zebra Mussels by David Bayersdorfer, the operator of that machine. No adult Zebra Mussels have been found during any of the inspections
We did over 20 dives in the lake during the spring summer and fall of 2011 and collected mussel shells and snail shells on each of these dives. Despite all of these samplings we identified only two types of mussels and two types of snails. The mussels were Eastern Floaters and a species of Sphaerium (fingernail clam). The snails that we identified, again only two, were Viviparus georgianus and Planorbella Campanulata.
Eurasian Milfoil continues to be the dominant aquatic weed in the lake. As an invasive it has taken hold on all bottom areas that are less than 20’ in depth. The use of chemical retardants has clearly been turned down at several meetings of the residents of the town. Therefore mechanical and biological controls remain as the only possibilities of holding this weed in check. The Town, with the support of the Lake Association and the Hotchkiss School, carries on a vigorous effort at mechanical harvesting. In addition benthic barriers(Aqua Net) are used to kill weeds in the swim areas at the Town Grove.
Our divers have long observed that Caddisfly Larvae consume a great deal of milfoil. When the population of the larvae is high they can actually destroy many of the established beds in the lake. We have also witnessed, however, that the population of Caddisfly Larvae is variable. Some years they are very apparent and other years they are difficult to find.
The “crashes” of milfoil that we have observed clearly correspond to the times when the Caddisfly population is large.
Mechanical harvesting, with all of its imperfections, is still the most viable control of the milfoil in the lake.
When milfoil is removed, either by mechanical or biological means, we have observed that Chara tends to take over the area. This is encouraging as Chara covers the bottom and offers serious completion to the milfoil.
The 2011 data contains an inventory of the bird life that we witnessed on the days that we sampled. Canada Geese, Common Merganser Ducks, Coots, Mallard Ducks and Ring Billed Gulls were the most common water birds that we observed. In the past three years a small population (less than 20) of Double Crested Cormorants has also appeared. The overall bird population has increased on the lake, especially the Coots and Merganser Ducks. This is likely due to the mild winters which has meant longer periods of open water in the winter months. During the winter of 2011-12 the ice cover lasted only 17 days.
|4/15/11||pair of loons, pair of geese on island|
|4/25/11||2 pairs of geese (forming nests), 25 cormorants, numerous tree swallows, 8 Herring Gulls|
|5/12/11||no, gulls, no cormorants, no geese|
|5/19/11||No gulls, cormorants, geese, or ducks. Pair of Loons on the lake|
|6/3/11||No gulls, cormorants, geese, ducks, or loons. One Great Blue Heron|
|6/14/11||2 herons, 1 Merganser duck, 2 Tree Swallows|
|6/28/11||Two Mergansers, 20+ Geese, Two Herons, Two Mallards|
|7/29/11||20+ Gulls (ring billed), One Bald Eagle|
|8/8/11||Ring Billed Gulls, One Cormorant|
|9/8/11||Ring Billed Gulls, Osprey|
|9/21/11||15+ Cormorants, One Bald Eagle, One Osprey, No geese, Ring Billed Gills|