Aquatic Plant Mapping and Water Quality Monitoring at Congamond Lake 2009

Prepared for:

Conservation Commission Southwick, MA

Prepared by: Northeast Aquatic Research

Mansfield, CT

March 11, 2010

Table of Content List of Tables.........................................................................................2 Introduction ..........................................................................................3

Study Scope .......................................................................................4 Aquatic Plant Survey.............................................................................4

Methods .........................................................................................4 Aquatic Plant Community Structure .......................................................5 Aquatic Plant Species Results ...............................................................9

Water Quality ...................................................................................... 18 Temperature/Dissolved Oxygen/Water Clarity ............................................ 19 Nutrients......................................................................................... 25 Alkalinity/pH/Conductivity ................................................................... 29 Plankton ......................................................................................... 32

Conclusions ......................................................................................... 35 References.......................................................................................... 37

List of Tables Table 1 - Dates of visits and tasks conducted during this study .............................4 Table 2 – Aquatic plants observed in Congamond Lake during 2009 survey.............. 11 Table 3 – Percent occurrence of aquatic plants observed during this study............. 13 Table 4 – Water sampling depths used during this study.................................... 18 Table 5 – Thermocline depths (meters) for Congamond Lake during 2009............... 21 Table 6 - Secchi disk depths (meters) for Congamond Lake during 2009................. 23 Table 7 - Location (meters below the surface) of Anoxic Boundaries In Congamond Lake during 2009. ................................................................................. 24 Table 8 - Lake trophic categories and ranges of indicator parameters................... 26 Table 9 - Total phosphorus (ppb) testing results for Congamond Lake in 2009 ......... 26 Table 10 – Ammonia nitrogen (ppb) in Congamond Lake during 2009 .................... 28 Table 11 - Total nitrogen (ppb) in Congamond Lake during 2009 ......................... 29 Table 12 – Alkalinity of Congamond Lake water during 2009............................... 31 Table 13 – pH values in Congamond Lake waters during 2009 ............................. 31 Table 14 – Calcium concentrations in Congamond Lake during 2009 ..................... 31 Table 15 – Conductance (µmhos/cm) values in Congamond Lake during 2009 .......... 31 Table 16 – Total Iron (mg/L) values in Congamond Lake during 2009 .................... 32 Table 17 - Phytoplankton Counts in Cells/ml For Congamond Lake....................... 33

Introduction Congamond Lake is a 472 acre lake located on the border of Suffield, Connecticut and

Southwick, Massachusetts. The lake consists of three basins, called South, Middle, and

North Ponds. South Pond has a surface area of 147 acres and maximum depth of 26

feet. Middle Pond, the largest of the three, has a surface area of 278 acres and a

maximum depth of 37 feet. North Pond, the smallest and the deepest of the three,

has a surface area of 47 acres and maximum depth of 40 feet. Each of the three

ponds are isolated from each other by shallow water tunnels under Congamond Road

separating South and Middle Ponds, and Point Grove Road separating Middle from

North Pond

Congamond Lake – showing South Pond, foreground, Middle Pond, center, and North Pond at the top of the picture.

Study Scope Northeast Aquatic Research was contracted to conduct a survey of aquatic plants in

each of the three ponds and collect water quality information during the summer of

2009 (see Table 1 for dates of the visits). The aquatic plant survey consisted of

collecting species presence at GPS waypoints along the entire shoreline of the lake.

Two sets of water quality sampling trips were made using sites located in the deepest

water of each of the three basins. Water samples were collected form basic water

quality parameters, specifically plant nutrients phosphorus and nitrogen. A profile of

water temperature and dissolved oxygen was collected by measuring these values at

each one meter depth increment. One sample was collected for plankton enumeration

and one sample was collected for Chlorophyll-a determination. Two samples of

sediments were collected from different areas of the lake for analysis of residual

diquat.

Table 1 - Dates of visits and tasks conducted during this study

Task September 9, 2009 September 14, 2009 October 14,2009

Water Quality Sampling X X

Aquatic Plant Survey X

Sediment Samples X

Aquatic Plant Survey

Methods The aquatic plant investigation was conducted on September 14, 2009. The survey

consisted of observing the littoral zone along the entire shoreline of the lake. The

littoral zone is the shallow water area of the lake that supports rooted aquatic

vegetation. Water depths were continuously monitored using an electronic depth

sounder to identify the width of the littoral zone. The aquatic plants occurring within

the boundaries of the littoral zone were identified and growth characteristics

recorded. Formal observation points were made using GPS to be later downloaded to

Google Earth for map creation. At each formal observation point, all aquatic plant

species present at that location were identified. Species presence at each point was

determined by viewing the community from the boat until all readily identifiable

species were recorded. Samples of plants were then collected and brought into the

boat using a modified rake attached to a 16-foot extendable pole. Specimens of

species that could not be identified in the field were retained for closer examination

later.

Typically, observation points were located equidistant between the shoreline and the

outer edge of the littoral zone; however, when the littoral zone was wide additional

points were made so that the plant community between the shore and the outer edge

of the littoral zone was assessed. Characteristics of beds, such as density, growth to

the surface and percent composition were recorded at each observation point. In this

way, 234 observation waypoints were made during the survey, 48 in North Pond, 105 in

Middle Pond, and 81 in South Pond. The littoral zone between waypoints was visually

inspected to verify that species composition did not change. The locations of the

observation points are shown in Map 1.

Aquatic Plant Community Structure Aquatic plants are an important part of lake systems. They support a diverse

community of organisms, mostly invertebrates that support the food chain in lakes.

Aquatic plants also intercept runoff, store nutrients, and stabilize sediments. Aquatic

plants create habitat for fisheries, providing for spawning, nursery areas for young

fish, cover from predation, and ambush sites for predators. Aquatic plants in lakes

occur in three distinct habitat forms, emergent, floating-leaved, and submersed.

1. Emergent plants are those rooted in shallow water, between 0.5 and 4 feet of

water, but have a majority of stems and leaves out of the water. Generally, these

species grow along natural wetland shorelines where the soils are saturated. Rarely

do emergent plants grow in water past about 1 foot of depth. Species in this group

include cattails, bulrush, pickerelweed, and phragmites.

2. Floating-leaved plants are the water lilies, water shield, and a few of the

pondweeds. These plants produce primarily floating leaves with little or no

underwater leaf development. Water lilies are generally restricted to shallow waters

of less than about 6 feet. A subclass of floating-leaved plants is the tiny free-floating

plants, duckweed and watermeal. These tiny plants, less than a quarter of inch in

size, usually grow near the shore in quite waters.

Map 1 – Location of waypoints used in aquatic plant distribution survey of Congamond Lake conducted during this study

3. Submersed plants are those that grow entirely underwater growing out to deeper

waters of the lake. Submersed plants include Eurasian milfoil and tape grass. These

plants are rooted in the sediments reaching various heights into the water column.

Sometimes submersed plants can reach the water surface to form floating leaves or

short aerial flowers. When some submersed plants reach the water surface, the shoots

spread out and continue to grow forming dense “topped-out” growths. Eurasian

milfoil commonly does this. Two of the pondweeds can do this to a lesser extent,

large-leaf pondweed and floating-leaved pondweed. However, most native plants

develop shoots that remain underwater, unless they grow in shallow water.

Aquatic plants require sufficient light to grow. The area of the lake where submersed

plants can occur is called the photic zone. This part of the lake is defined as the area

where sunlight reaches the bottom. The maximum depth of the photic zone can be

estimated using the Secchi disk depth (Canfield et al., 1985). For Congamond Lake,

the average Secchi disk depth from all basins is 6.5 feet, suggesting the maximum

depth plants can grow will be about 6.5 feet. However, North Pond was clearer than

Middle and South Ponds with an average Secchi depth of 10 feet. South Pond was

more turbid than the other basins with an average Secchi depth of 4.5 feet. This

indicates that generally, plants will be found out about 10 feet in North Pond, but only

to about 5 feet in South Pond. It is important to note that these depths are based on

late summer readings. The water clarity is probably better in May and June suggesting

that the photic zone has not been accurately identified by data collected during this

study.

The chart in Figure 1 shows the number of species found at different water depths.

The highest numbers of species found at any observation point was 9. Generally, 5 to

7 species were found at observation points where the water depths were between 1

and 6 feet. No more than 3 species were found when water was between 6 and 10 feet

deep, although one observation point in North Pond had 5 species in water 9.5 feet

deep. There were only 5 observation points were a single species, either tape grass or

large-leaf pondweed, occurred in water depths of 10 to 13 feet. No plants were found

in water deeper than 13 feet.

Figure 1 – Relationship between number of species of aquatic plants and water depth

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Water depth (feet)

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Aquatic Plant Species Results The aquatic plant survey of Congamond Lake revealed 38 species of aquatic plants.

Two invasive, non-native, submersed species were observed, Eurasian milfoil and

minor naiad. Two invasive, non-native, shoreline species were observed, common

reed-phramites, and purple loosestrife. Eurasian milfoil was found at only two

locations in the lake, one plant was found in North Pond, and a few plants in a loose

cluster were found in South Pond. The minor naiad, a new invader to New England,

first records in MA and CT are 1974 (1980), and 1995, respectively (Les & Mehrhoff

1999). Minor naiad was found at only two observation points, one in South Pond and

one in Middle Pond. The locations of these sightings are shown in Map 2.

The presence of the two shoreline invasive plants, phragmites and purple loosestrife

were not specifically surveyed for in Congamond Lake. Notes were kept when their

presence was obvious not each time they occurred. Because these plants can spread

rapidly spread along shoreline edges the location of the sightings is shown on Map 1.

Phragmites has been in CT/MA for many years having replaced or in the process of

replacing cattails in many wetlands. Purple loosestrife is a more recent invader that

has very similar habitat preferences. Phragmites was found noted in place in Middle

Pond, purple loosestrife was noted in three sites in South Pond.

Map 2 – Locations of invasive aquatic plants in Congamond Lake Sept. 14, 2009

The complete list of species encountered during this survey is given in Table 2. The

table divides the species into three habitat types emergent, floating-leaved, and

submersed. There were 7 emergent species, 6 floating-leaved species, and 25

submersed species for a total of 38 species of aquatic plants.

The emergent species include Eastern Bur-reed, pickerelweed and spikerush. These

shoreline plants typically grow in shallow water of wetlands edges. Eastern bur-reed

and pickerelweed are large robust plants growing to about a 2 feet tall, pickerelweed

has large spike of conspicuous purple flowers.

The floating-leaved plants found included both white and yellow water lilies and

aquatic smartweed. Both water lilies form large floating leaves several inches across

and each has large flowers. The yellow water lily flowers early in the season

sometimes as early as May, while white water lily produces flowers later in the

summer. Aquatic smartweed forms floating shoots and leaves that spread over the

water surface. There were three species of the tiny non-rooted floating plants,

duckweed, watermeal and great duckweed. These are the tiniest of the vascular

plants, watermeal is about 1 mm in diameter, while duckweed and great duckweed

are slightly larger, up to about 5 mm. These species are generally found together in

quite water, usually sheltered coves and small windless ponds.

There was a high diversity of submersed plants in Congamond Lake. Six of the species

were found in shallow water of only a few feet deep, leafless milfoil, golden pert,

waterwort, aquatic moss, arrowhead and floating-leaf pondweed. The first four are

small inconspicuous plants that have a short stature and may only be a few inches tall.

Floating-leaf pondweed has floating leaves about 2 inches long that can form a dense

surface mat.

The remaining submersed species occurred at all depths between the shore and the

outer edge of the littoral zone. As shown in Figure 1 most species were found in

water depths between 2 and 6 feet.

Table 2 – Aquatic plants observed in Congamond Lake during 2009 survey

Common Name Species Name Habitat

Emergent Species

Eastern Bur-reed Sparganium americanium Along the shore in water up to 1 foot deep

Cattail Typha sp. Shoreline –typically above the water line

Purple Loosestrife Lythrum salicaria Shoreline - typically above the water line

Pickerelweed Pontederia cordata Along the shore in water up to 1 foot deep

Spikerush Eleocharis sp. Along the shore in water up to 1 foot deep

Common Reed Phragmites Shoreline - typically above the water line

Floating-Leaved Species

Water Willow Decodon verticillatus Shoreline - in water up to 1 foot deep

Yellow Water-lily Nuphar variegata Large floating leaves – yellow flowers

White Water-lily Nymphea odorata Large floating leaves – white flowers

Duckweed Lemna minor tiny floating leaves – not rooted

Great Duckweed Spirodela polyrhiza tiny floating leaves – not rooted

Water Meal Wolffia sp. very tiny floating leaves – not rooted

Smartweed Polygonum amphibiumFloating leaves and shoots – typically

rooted on shore and spreads over water surface

Submersed Species

Coontail Ceratophyllum demersum any depth –shallow

Muskgrass Chara any depth - to very deep

Waterwort Elatine sp. shallow water < 3 feet

Slender Waterweed Elodea nuttallii any depth (in LZ)

Aquatic Moss Fontinalis sp. shallow water < 3 feet

Golden Pert Gradiola aurea shallow water < 3 foot

Eurasian Milfoil Myriophyllum spicatum any depth (in LZ)

Leafless Milfoil Myriophyllum tenellum shallow water < 3 feet

Water Naiad Najas flexilis any depth (in LZ)

Southern Water-naiad Najas guadalupensis any depth (in LZ)

Minor Naiad Najas minor any depth (in LZ)

Large-leaf Pondweed Potamogeton amplifolius any depth (in LZ)

Thread-leaved Pondweed Potamogeton bicupulatus any depth (in LZ)

Grassy Pondweed Potamogeton gramineus any depth (in LZ)

Pondweed x cross Potamogeton hybrid any depth (in LZ)

Illinois Pondweed Potamogeton illinoensis mostly deeper water (in LZ)

Floating-leaf Pondweed Potamogeton natans shallow water < 3 feet

Clasping-leaved Pondweed Potamogeton perfoliatus any depth (in LZ)

Small Pondweed Potamogeton pusillus any depth (in LZ)

Robbins Pondweed Potamogeton robbinsii any depth (in LZ)

Sterile submersed Arrowhead Sagittaria cristata shallow water < 3 feet

Arrowhead Sagittaria gaminea any depth (in LZ)

Sago Pondweed Stuckenia pectinata any depth (in LZ)

Tape grass Vallisneria americana any depth (in LZ)

Yellow Star-grass Zosterella dubia any depth (in LZ)

Bold species are non-native and invasive

The percent occurrence of each aquatic plant species observed during this study is

given in Table 3. The table lists the frequency at which each species was found as a

percentage of the total number of observation points (234). The values indicate how

common each species was at the time of the survey. Because the entire shoreline was

surveyed, these occurrence numbers are good estimates of the relative dominance of

each species in Congamond Lake in September 2009. Only 5 species had dominance

values over 10%, 14 species had occurrences between 2 and 10%, and 20 species were

found at fewer than 2% of the points.

The most dominant aquatic plant in Congamond Lake at the time of the survey was

tape grass, appearing at half (50%) of the observation points. The second highest

occurring species was white water lily at 28% of the sites, yellow water lily, usually

associated with white water lily preferring the same habitat conditions, occurred at

12% of the sites. In almost all cases, the two species were encountered together. The

third most widespread species was Robbins pondweed at 18%. Interestingly, mats of

filamentous algae occurred at 13% of the sites. Filamentous algae was more common

than most of the aquatic plants observed in Congamond Lake. This type of algae

typically grows as dense mats that cover the bottom in shallow water where the

sediments are predominantly muck.

Table 3 – Percent occurrence of aquatic plants observed during this study

Species Name Common Name Percent Occurrence

Vallisneria americana Tape grass 50

Nymphaea odorata White Water Lily 28

Potamogeton robbinsii Robbins Pondweed 18

Filamentous algae 13

Potamogeton amplifolius Large-leaf Pondweed 12

Nuphar variegata Yellow Water Lily 12

Chara Muskgrass 7

Potamogeton bicupulatus Thread-leaved Pondweed 7

Najas flexilis Water Naiad 6

Potamogeton pusillus Small Pondweed 6

Typha sp. Cattail 6

Elodea nuttallii Slender Waterweed 5

Pontederia cordata Pickerelweed 3

Sagittaria cristata Sterile submersed arrowhead 3

Elatine sp. Waterwort 2

Myriophyllum spicatum Eurasian Milfoil 2

Potamogeton perfoliatus Clasping-leaved Pondweed 2

Eleocharis sp. Spikerush 2

Ceratophyllum demersum Coontail 2

Lythrum salicaria Purple Loosestrife 2

Najas minor Minor Naiad 1

Lemna minor Duckweed 1

Spirodela polyrhiza Great duckweed 1

Polygonum amphibium Smartweed 1

Najas guadalupensis Southern Water-naiad 1

Zosterella dubia Yellow Star-grass 1

Myriophyllum tenellum Leafless milfoil 1

Wolffia sp. Water Meal 1

Decodon verticillatus Water Willow 1

Sagittaria gaminea Arrowhead 1

Potamogeton gramineus Grassy Pondweed 1

Potamogeton hybrid Pondweed x cross 1

Gratiola aurea Golden Pert < 1

Fontinalis sp. Aquatic Moss < 1

Sparganium americanum Bur-reed -emergent < 1

Potamogeton illinoensis Illinois Pondweed < 1

Stuckenia pectinata Sago Pondweed < 1

Potamogeton natans Floating-leaf Pondweed < 1

Phragmites australis Common Reed < 1

The survey found a couple of pondweeds that could not be identified. Specimens of

these plants were submitted for review and were identified as hybrids. These plants

are marked as Pondweed x cross in Table 3.

Tape grass (Vallisneria americana) was found at half of the observation points. The

locations were tape grass was found in Congamond Lake are shown in Map 3.

Generally, areas along the littoral zone of the lake where plants were found contained

tape grass.

Map 3 - Locations of Tape grass in Congamond Lake September 14, 2009

The location of two water lilies, White Water Lily (Nymphaea odorata), and Yellow

Water Lily (Nuphar variegata) are shown in Map 4. The largest beds were in South

Pond. Some small beds were found in Middle Pond, but these beds were usually of

fewer plants. There were also small beds of water lilies along the west shore of North

Pond.

Map 4 - Locations of White and Yellow Water Lilies in Congamond Lake September 14, 2009

The two pondweeds, Robbins Pondweed (Potamogeton robbinsii) and Large-leaf

Pondweed (Potamogeton amplifolius) were found sporadically around the lake (Map5).

There were large beds of Robbins pondweed in South Pond, along sections of the west

and south shores, generally in areas were water lilies were also present. There was

also a large bed of Robbins pondweed in South Pond. Large-leaf pondweed was not

found to form large beds anywhere in the lake.

Map 5 - Locations of Large-leaf pondweed and Robbins Pondweed in Congamond Lake on September 14, 2009

Water Quality Three in-lake stations were established, one in of the three basins. Each station was

located in the area of the deepest water of the basin. Map 6 shows the water depth

contour map of Congamond Lake used as a guide in locating the deepest water of each

basin. The location of each station is also shown; North Pond had a maximum depth of

38 feet, Middle Pond had a maximum depth of 36 feet and South Pond had a maximum

depth 25 feet. The site of deepest water in North Pond was close to where the map

indicated the maximum depth would be, but in Middle and South Ponds, the location

of deepest water was found in to be different, indicating that map is inaccurate.

At each lake station, the water clarity was measured with a Secchi disk, and the water

temperature and dissolved oxygen of the water was measured at each one meter

depth increment. Water samples were collected from three depths, top, middle, and

bottom, depths given in Table 4, for analysis of total phosphorus, ammonium nitrogen,

nitrate nitrogen, total kjeldahl nitrogen, alkalinity, conductivity, pH, calcium, and

total iron. One water sample was collected from 1 meter depth during each visit from

Middle Pond for determination of Chlorophyll-a. One vertical plankton tow was made

during each visit to collect a sample of phytoplankton and zooplankton organisms in

the water column. In addition, two sediment samples were collected for analysis of

the herbicide diquat. One was collected from Middle Pond and one from South Pond.

Sediment was taken from the top 5 cm within the 2009 treatment areas.

Table 4 – Water sampling depths used during this study

South Pond Middle Pond North Pond

Top 1 meter (3 feet) 1 meter (3 feet) 1 meter (3 feet)

Middle 3 meters (10 feet) 6 meters (20 feet) 5 meters (16 feet)

Bottom 7 meters (23 feet) 10 meters (33 feet) 11 meters (36 feet)

Map 6 – Congamond Lake water depth contours in feet. Also shown are locations of water quality stations and sediment sampling sites

Temperature/Dissolved Oxygen/Water Clarity

Water Temperature

A lake can be initially characterized by the seasonal patterns of water clarity and

water temperature. These two factors interact to give the lake its thermal

configuration, that is, the layers of upper warm water and deeper cooler water. This

layering, called stratification, is the fundamental aspect of a lake that governs many

of the important processes that occur during the year. The pattern of layering is

repeated each year, usually with a high degree of regularity. Each season, lakes

progress through a series of steps beginning with ice-out in the spring, warming during

the summer, and cooling in the fall. In the spring, after ice-out, the lake has

uniformly cold water from top to bottom. As the sun increases in strength during April

and May, the water at the surface warms due to the penetration of sun’s rays into the

ater, with the depth of warming determined by water clarity.

isothermal, it continues cooling uniformly until winter when ice forms

n the surface.

e maximum value of mixing resistance demarcates the location of

e thermocline.

w

Warmed water floats over colder deep water that receives little sunlight. The warm

upper layer is mixed by wind action and generally has sufficient dissolved oxygen

because it is in equilibrium (oxygen from the air saturates the water evenly) with the

atmosphere. The warm surface water layer is called the Epilimnion. The cold dark

bottom water typically loses oxygen during the summer months. The cold-water layer

is called the Hypolimnion. During stratification, those two layers are separated by a

boundary called the Thermocline, also called the Metalimnion or middle layer. During

the late summer and early fall the water in the lake begins to cool and eventually the

whole lake becomes isothermal, or has the same temperature from top to bottom.

Once the lake is

o

The water temperature measurements collected during this study shows the lake

developed strong stratification by the time of the first measurements on September 9,

2009. Figure 2 shows the mixing resistance values for each of the three basins of

Congamond Lake on September 9, 2009. The mixing resistance is a unit-less number

that describes the difference in water density between each one-meter water depth.

Values over 30 indicate weak stratification, values over 60 indicate strong

stratification. Th

th

Figure 2 – Mixing resistance values for the three basins of Congamond Lake on September 9, 2009

0 10 20 30 40 50 60 70 80 90 100

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North Pond

Middle Pond

South Pond

The location of the thermocline in each basin during this study is given in Table 5.

Thermocline depths in Middle and North Ponds were similar in September, between

about 7.5 and 8 meters. This means that waters shallower than this depth were

epilimnetic waters of uniform water temperatures, and water below this depth were

hypolimnetic waters isolated from the atmosphere. South Pond had a thermocline

depth of 5.8 meters, shallower than the other two basins. In October, the thermocline

had migrated downward by 2.5 meters in Middle Pond, and 1 meter in North Pond,

while completely disappearing in South Pond. These values represent late summer

conditions when thermocline structure has already begun to erode downward due to

decreasing solar energy and cooler air temperatures. Mid-summer thermocline depths

are probably going to be slightly deeper than the Secchi depths, about 4 to 5 meters.

Table 5 – Thermocline depths (meters) for Congamond Lake during 2009

Date South Pond Middle Pond North Pond

9-9-09 5.8 7.6 7.9

10-14-09 none 10.0 8.9

Water Clarity –Secchi Disk

Secchi disk depth is a way of measuring water clarity. Clarity of lake water is one of

the most fundamental and important aspects of lake condition. Clarity of water is the

most valued aesthetic element of a lake; transparent water signifies health and

cleanliness.

The universal method of measuring water clarity is by the Secchi disk. Several types

of disks are used today, but each variation traces back to an all white disk used in

1865 by Father Pietro Angelo Secchi, a Jesuit astronomer and science advisor to the

Pope (Hutchinson, 1975). He is credited as the first to measure water clarity using a

lowered disk, so the disk is named for him. The disk is lowered into the water until no

longer visible, and then slowly raised until it is visible again; the average of the two

depths is recorded as the Secchi disk depth.

The depth measured by a Secchi disk is where approximately 10% of the surface light

reaches. Below the Secchi disk depth, light penetration tails off exponentially

becoming completely dark at about twice the Secchi disk depth or the depth where <

1% surface light reaches. Light transparency can be lessened by anything in the water

that increases the turbidity. Very fine silt particles can stay suspended in the water

column for many days, especially if there is continuing mixing. Commonly however,

the decrease in Secchi disk depth is attributed to increased abundance of algae in the

water. Algae growth is a result of higher levels of phosphorus in the water so Secchi

disk depth is also related to the quantity of phosphorus in the water. These three

factors: water clarity, algae abundance, and phosphorus concentration are the three

most important factors used to describe lake condition.

Water clarity readings taken in Congamond Lake during this study are given in Table 6.

During this study, South Pond had the poorest clarity readings, mean of 1.3 meters,

while North Pond had the best clarity readings, mean of 2.8 meters. The large

difference in water clarity between the different basins indicates a source of nutrients

and algae production occurs in South Pond. The poorest clarity reading in South Pond

was 1 meter in October, while on the same date the clarity in North Pond was 3

meters.

Table 6 - Secchi disk depths (meters) for Congamond Lake during 2009

Date South Pond Middle Pond North

Pond

9-9-09 1.7 1.9 2.6

10-14-09 1.0 1.8 3.0

Average 1.3 1.8 2.8

Dissolved Oxygen

Dissolved oxygen, or oxygen, is a gas that dissolves in water from diffusion out of the

atmosphere, and from photosynthesis by aquatic plants. The temperature of the

water directly affects the maximum quantity of oxygen that can be dissolved in the

water with colder water containing more than warmer water.

During the early spring, after the ice has left the lake, dissolved oxygen from the

atmosphere saturates the entire water column. Once the thermocline begins

separating the lake into upper and lower layers, the oxygen content in the deepest

waters dwindles because there is no re-supply from the now cut off atmosphere. This

process continues during summer when the thermocline is strongest. The dissolved

oxygen content in the water under the thermocline continues to decline until it

becomes depleted. One dissolved oxygen was been depleted the water is referred to

as anoxic. The process of dissolved oxygen loss starts at the sediment surface

typically in late May or early June, but quickly rises into the water column during

summer. The ascending anoxic boundary reaches a maximum depth sometime in mid

to late summer based on the equilibrium between oxygen diffusing downward from the

atmosphere and the dissolved oxygen consumption rate at the bottom. In the late

summer and early fall the upper water cools causing the thermocline to descend

bringing oxygen with it so that by mid-fall oxygen has mixed all the way to the

bottom.

The anoxic boundary was prominent in Congamond Lake during September but was

located at different depths in each of the three basins (Table 7). In North Pond, the

boundary was located at 7.8 meters, with a total depth of 11.5 meters there was 5

meters of anoxic water between 8 meters and the bottom. In Middle Pond, the anoxic

boundary was located at 5.8 meters, with a total depth of 11 meters there was 6

meters of anoxic water between 6 meters and the bottom. In South Pond, the anoxic

boundary was located at 5 meters, with a total depth of 8 meters there was 3 meters

of anoxic water between 5 meters and the bottom.

In October, the lake was becoming mixed so the anoxic boundary was located at

deeper depths in the water column. In Middle and North Ponds, the anoxic boundary

was located at about 9 meters, with 2 to 3 meters of anoxic water remaining over the

bottom on that date. In South Pond, the anoxic boundary had disappeared as oxygen

rich water had mixed to the bottom.

Table 7 - Location (meters below the surface) of Anoxic Boundaries In Congamond Lake during 2009.

Date South Pond Middle Pond North Pond 9-9-09 4.92 5.8 7.8

10-14-09 none 9.3 8.9

Typically, the anoxic water at the bottom of a lake contains high amounts of dissolved

constituents including, phosphorus, nitrogen, and iron because without oxygen these

materials can remain dissolved in the water. In the presence of oxygen iron

precipitates usually taking phosphorus with it, and nitrogen, generally as ammonia, is

oxidized to nitrate or assimilated into organic forms. Because phosphorus can

accumulate in anoxic water the juxtaposition of the anoxic boundary and the

thermocline is critical. When the anoxic boundary is close to, or above the

thermocline, phosphorus can diffuse upward into the epilimnion where it becomes

available to phytoplankton. The chart in Figure 3 shows the location of both the

thermocline and the anoxic boundary in each of the three basins on September 9,

2009. The anoxic boundary was above the thermocline in both the South and Middle

Pond on that date. This condition is a precursor for internal loading of phosphorus in

Congamond Lake.

Figure 3 – Location of Anoxic Boundary and Thermocline on September 9, 2009 in Congamond Lake

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Sept. 9, 2009

Nutrients

Phosphorus

Phosphorus is the nutrient that is in the shortest supply in fresh waters. Plants as the

foundation of the food chain require a number of essential elements for growth, but

phosphorus has the highest ratio of supply and demand. Almost three times the next

highest on the list -nitrogen. Phosphorus is the nutrient that determines the overall

health of lakes. As phosphorus increases plant growth is stimulated. Higher

abundance of algae in the water column decreases the penetration of light, linking

phosphorus to water clarity. Phosphorus originates principally from the weathering of

rocks in the drainage basin. Watershed disturbance releases phosphorus because it is

bound tightly with soils, whenever soil erosion occurs phosphorus will be transported

with the silt. All impervious surfaces will be a source of phosphorus. Most domestic

waste water systems are a source of phosphorus. Phosphorus is also part of rain and

dry fall. Waterfowl can be source of phosphorus if their numbers are high enough.

The CT DEP differentiates the trophic condition of lakes using phosphorus, nitrogen,

Secchi disk depth, and chlorophyll a, see Table 8. The nutrients phosphorus and

nitrogen are the growth factors and Secchi disk depth and chlorophyll-a are the

response indicators, in that adding the nutrients (phosphorus primarily) results in

decreases in Secchi as the chlorophyll-a increases. Phosphorus concentrations

observed in Congamond Lake during this study are given in Table 9. All values were

above 10 ppb so the lake is clearly not oligotrophic. Values in South and Middle Ponds

were always above 20 ppb with most values above 30 ppb. The bottom value at South

Pond in Sept. was 252 ppb, and from Middle Pond in Oct. was 196 ppb indicating

accumulating phosphorus on those dates. North Basin phosphorus was low at the

surface between 10 and 20 ppb, and moderate at the bottom, between 30 and 40 ppb.

Table 8 - Lake trophic categories and ranges of indicator parameters

Category T.P. (ppb)

T. Nitrogen (ppb)

Secchi Depth (m)

Chlorophyll a (ppb)

Oligotrophic 0 – 10 0 – 200 6+ 0 – 2

Oligo-mesotrophic 10 – 15 200- 300 4 – 6 2 – 5

Mesotrophic 15 – 25 300 - 500 3 – 4 5 – 10

Meso-eutrophic 25 – 30 500 - 600 2 – 3 10 – 15

Eutrophic 30 – 50 600 - 1000 1 – 2 15 – 30

Highly Eutrophic 50 + 1000 + 0 – 1 30 +

Source = CT DEP 1982 Table 9 - Total phosphorus (ppb) testing results for Congamond Lake in 2009

South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 27 43 22 25 13 15

Middle 29 52 24 21 22 12

Bottom 252 47 26 196 42 43

Average 103 47 24 81 26 23

The phosphorus concentrations in Congamond Lake shows strong evidence for internal

loading occurring in South Pond and possible evidence for internal loading in Middle

Pond. North Pond appears to have low internal loading with good phosphorus

concentrations in upper waters. South Pond may have significant enough internal

loading rates combined with the shallower depths allowing for quicker mixing and loss

of thermocline structure that phosphorus is exported to Middle Pond. This would be

the case if epilimnion waters in the South and Middle basins were more or less in

equilibrium. As phosphorus diffuses to the epilimnion in South Pond, the higher

phosphorus levels there will migrate to Middle Pond. With only late summer data from

one year this is conjecture at this point.

With only two data points (Sept. and Oct.), it is impossible to tell if the lake is

trending toward more of less phosphorus in the water. Lakes can show seemingly

large annual variation when the phosphorus concentration is this low. The relationship

between phosphorus and water clarity in Connecticut lakes is shown in Figure 4. The

Connecticut lake data from the 1970s are shown as small circles (data from Frink and

Norvell, 1984). The relationship shown in Figure 4 illustrates the non-linear

relationship between phosphorus and water clarity. As phosphorus concentration

increases water clarity decreases, first rapidly and then slower until the phosphorus

concentration reaches about 30 ppb, after which water clarity is not further decreased

with higher phosphorus concentrations. This indicates that water clarity decreases,

caused by phytoplankton in the water column, is very sensitive to changes in

phosphorus when the concentration is low. < 20 ppb, but at higher phosphorus

concentrations, > 30 ppb, the amount of algae in the water column is sufficiently great

enough to cause growth limitation due to self-shading. Once a lake reaches this

condition, phosphorus greater than 30 ppb, the production of phytoplankton and

recycling of phosphorus are resistant to change because the phosphorus is internally

held by either living or dead algae and the magnitude of dead algae sinking to the

bottom is large enough to maintain anoxic conditions there ensuring further internal

loading. This negative feedback loop perpetuates the eutrophic condition.

Figure 4 – Relationship between phosphorus and Secchi disk depth in CT Lakes, showing values for Congamond Lake basins during 2009

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North Pond

Nitrogen

Nitrogen is the nutrient in second highest supply to demand for plants after

phosphorus. There is more nitrogen available usually so it is not as needed as

phosphorus is. However, it is still a necessary ingredient for plant growth. Nitrogen

tends to be of poor supply in lake sediments because of transformation into nitrogen

gas. Because of the loss of nitrogen from the sediments through the gases phase

aquatic plants can be limited by nitrogen availability.

Nitrogen occurs in three different forms in freshwater lakes. There are two ionic

forms, nitrate, and ammonia, which will fluctuate depending on the concentration of

dissolved oxygen present. An organic form is bound to other minerals and elements in

complex compounds. These organic forms of nitrogen can be protein, amino acids, or

partially decomposed plant material. Organic nitrogen is more refractory, requiring

some decomposition that uses dissolved oxygen before being used as a plant nutrient.

The ammonia concentration was very high in bottom water of both South and Middle

Ponds in September (Table 10). In October, South Pond was mixed to the bottom

causing ammonia concentrations to increase uniformly throughout the water column.

Similar levels of ammonia were observed in Middle Pond in October but bottom levels

continued to increase because that basin had not fully oxygenated to the bottom.

North Pond showed low ammonia levels in the surface and middle depths, and

moderate levels at the bottom.

Table 10 – Ammonia nitrogen (ppb) in Congamond Lake during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 50 198 28 212 17 16

Middle 46 198 92 210 32 19

Bottom 4,160 202 1,930 2,900 600 850

The levels of total nitrogen in Congamond Lake observed during this study are given in

Table 11. Total nitrogen is the sum of organic nitrogen and nitrate/nitrite nitrogen.

The levels of total nitrogen were very high in bottom waters and became very high

throughout the water column in October because of the lake mixing.

Table 11 - Total nitrogen (ppb) in Congamond Lake during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 780 1,109 555 1,052 705 600

Middle 690 1,187 590 967 635 615

Bottom 5,500 819 2,470 5,875 1,700 2,510

Alkalinity/pH/Conductivity Alkalinity - pH

Lake water is in equilibrium with the carbon dioxide in the atmosphere. The gaseous

carbon dioxide from the atmosphere dissolves into water and forms carbonic acid

(H2CO3), which immediately dissociates (splits into component parts), into bicarbonate

and carbonate ions (HCO3 and CO3). The action of these two ions determines the

alkalinity and pH of the water. Both these ions are negatively charged, binding readily

to calcium and other positive ions in the water (others usually present at much lower

levels than calcium are potassium and sodium). With more calcium in the water, more

bicarbonate can accumulate as the compound calcium carbonate (CaCO3). Alkalinity is

the measure of how much calcium carbonate occurs in the water. Water with high

levels of CaCO3 alkalinity is considered hard water, usually over 50 mg/L CaCO3. Most

of Connecticut lakes have alkalinity values between 0 and 120 mg/L with a mean value

of 20 mg CaCO3.

The pH of the water is a measure of the hydrogen ion concentration. When the

gaseous carbon dioxide dissolves and dissociates into lake water a small amount of

ionic hydrogen is released. The ionic hydrogen is written as H+. In chemistry, the

accumulation of H+ ions constitutes an increase in acidity. The opposite of the H+ ion

is the OH-ion. The accumulation of OH- ions increases the alkaline nature of the

water. The two processes are opposed to each other, as acid and alkaline conditions

cannot co-occur. The pH of the water is a measure of the amount of H+ ions as the

reciprocal log of its concentration, hence the little ‘p’ indicating log value. As the H+

increases, the pH goes down, acid values are between 0 and 7, and as OH- increases,

the pH goes up, and alkaline values are between 7 and 14. When the two are equal,

the pH is 7, indicating neutral conditions.

One further step is needed to complete our discussion of the pH relationship in fresh

water. As already pointed out, carbon dioxide gas dissolves in water to form carbonic

acid which is weakly acidic. Rain falling on the landscape contains some carbonic acid

at a natural pH of 5.6. Rainwater that percolates through the soil dissolves calcium

from the rocks and soils. The calcium goes into solution in the ground water and

enters the lake as dissolved calcium ions with the ground water. Once in the lake,

calcium binds with bicarbonate and carbonate making alkalinity.

Air pollution, specifically nitric and sulfuric acids from coal plants and automobile

exhaust, has caused the pH of the rain to decrease by adding H+ ions to the

atmosphere. Normally rain has a pH value of 5.6, when the pH is lower than this value

the rain is referred to as acid rain. The nitric and sulfuric acids in the atmosphere

cause the pH of the rain to be as low as pH 3, with pH of low 4 common. These acids

are neutralized by the alkalinity of the water, which is defined as the quantity of

CaCO3 in the water. The increase of H+ from the acidic rain is neutralized by the

quantity of bicarbonate and carbonate ions (HCO3 and CO3) in the water. However,

bicarbonate and carbonate neutralization of acid, or buffering, is dependant on the

amount of calcium in the water, or the alkalinity. Alkalinity is low because the

watershed is composed of rock material deficient in alkaline minerals; there is little

calcium to wash into the lake. If the neutralizing capacity is low the pH of the lake

declines eventually coming into equilibrium with the rain and stream water pH.

Alkalinity and pH were measured in Congamond Lake during this study, alkalinity

ranged from 22 to 104 mg CaCO3/L, pH ranged from 6.7 to 7.6 (see Tables 12 and 13).

The CT DEP defined water bodies as acid threatened when the alkalinity is below 5 mg

CaCO3/L. Congamond Lake is not acid threatened; instead, the pH data show the lake

to be on the alkaline side of neutral. The data shows North Pond to have about half

the alkalinity as South and Middle Ponds. Bottom water alkalinity was significantly

elevated in South and Middle Ponds indicating generation of alkalinity components.

Calcium concentration ranged between a low of 11 mg/L to a high of 104 mg/L (Table

14). Interestingly calcium decreased by about half between September and October

lake wide, although alkalinity did not show a concomitant change. Because usually

calcium is the dominant component of alkalinity, a 50% decrease in calcium should

have caused a decrease in the alkalinity value. Because alkalinity did not change

other components such as chloride, sodium or potassium are needed in the water to

balance the loss of calcium.

Table 12 – Alkalinity of Congamond Lake waters during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 44 48 40 42 24 22

Middle 44 48 44 42 24 22

Bottom 104 48 60 74 32 32

Table 13 – pH values in Congamond Lake waters during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 7.3 7.6 7.4 7.5 7.2 7.4

Middle 7.3 7.6 7.2 7.5 7.2 7.5

Bottom 6.8 7.6 6.9 7.0 6.7 6.8

Table 14 – Calcium concentrations in Congamond Lake during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 44 20 40 17 24 11

Middle 44 20 44 18 24 11

Bottom 104 20 60 22 32 12

Conductivity - Conductance

The conductance of the water is its ability of conduct an electrical current. The

property of water to do so is attributable to the sum of all the ions in the water. The

units “mhos” are the reciprocal of ohms, a standard unit of electrical resistance. The

measurement of conductivity is typically dominated by calcium but the other common

ionic minerals are included; potassium, magnesium, sodium, chloride, and sulfate.

Conductivity values for Congamond Lake measured during this study varied between

115 and 266 µmhos/cm (Table 15). Conductivity was highest at the bottom where the

water was anoxic and ionic materials accumulated. Again, the North Pond had the

lowest levels, while South Pond had highest levels.

Table 15 – Conductance (µmhos/cm) values in Congamond Lake during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 171 191 172 186 115 125

Middle 171 192 177 186 118 126

Bottom 266 192 204 241 131 142

Total Iron

Iron is natural occurring element in lake water. Generally, in the presence of

dissolved oxygen iron is maintained at very low levels, < 0.1 mg/L. However, in

bottom waters when dissolved oxygen has been depleted iron can accumulate as a

dissolved ion (ferrous iron). In Congamond Lake, iron was very low in surface and

middle depth waters but was at high levels in the bottom water of South Pond in

September when the water was devoid of dissolved oxygen (Table 16). Middle Pond

also showed iron accumulation but at a lesser degree than South Pond. Again, North

Pond had lowest iron levels.

Table 16 – Total Iron (mg/L) values in Congamond Lake during 2009 South Pond Middle Pond North Pond 9-Sep 14-Oct 9-Sep 14-Oct 9-Sep 14-Oct

Surface 0.045 0.15 < 0.02 0.08 < 0.02 0.047

Middle 0.041 0.16 0.045 0.09 0.024 0.045

Bottom 5.9 0.2 1.0 1.8 0.91 0.85

Diquat in Sediment

Two samples of lake sediments were collected from areas within the 2009 herbicide

treatment areas (see Map 6 for collection locations). Each sample consisted of

surfical sediments taken from the top couple of centimeters. Samples were shipped to

SunLabs Inc. in Tampa FL for analysis. No diquat was detectable in either sample.

Plankton Phytoplankton are simple single celled plants that float in the water column. “Phyto”

means plant and plankton has its root in Greek for wandering. These microscopic

plants occur either as single cells or as colonies that can take many shapes.

Phytoplankton, or algae as they are commonly referred, are composed of organisms

from many different taxonomic groups. Typically, Diatoms, and Chrysophytes (Golden-

brown algae), occupy cleaner waters and Green algae, and Bluegreen algae more

eutrophic water. High numbers of cells in the water causes water to become green

but it can also be brown or bluegreen. Bluegreen algae generally form the worst

blooms that are responsible for reduced water clarity during summer and fall. The

loss of Secchi disk depth is usually directly attributable to an increase in the number

of bluegreen algae cells in the water.

Crustacean zooplankton are small aquatic crustaceans found in most lakes and ponds.

They are mostly free swimming ranging in size from 0.4 to 2.5 mm. There are two

groups of crustacean zooplankton, cladocerans and copepods. The most important

cladoceran is Daphnia, also known as “water fleas”. These organisms are the major

herbivores in lakes, grazing principally on phytoplankton in the open water. Large

bodied cladocerians, are those over 1 mm in size, have very efficient filtration rates.

Copepods are omnivorous feeding on a variety foods. Together, the crustacean

zooplankton are important prey for juvenile and adult fish forming the foundation of

the food chain.

Phytoplankton

The phytoplankton in the Congamond were collected from the water quality station in

Middle Pond. Blue-green algae was very numerous in September, the total bluegreen

cell count was more than 22,000 cells/mL (Table 17). The most abundant bluegreen

alga taxon Lyngbya, although Anabaena, and in October Microcystis, also present in

high numbers. Diatoms, mostly Tabellaria, were present in high numbers in

September. Greens were present in but at lower numbers.

Table 17 - Phytoplankton Counts in Cells/ml For Congamond Lake Taxon 9-Sep 14-Oct

BLUE GREENS Anabaena 2,443 5,328 Gleocapsa 59 0 Microcystis 0 2,796 Oscillatoria 206 0 Lyngbya 19,472 2,649

Total 22,181 10,785 GREENS

Chlamydomonas 368 0 Chlorella 74 883 Coelastrum 15 74 Dictyosphaerium 118 29 Gloeocystis 206 0 Mougeotia 206 0 Scenedesmus 118 235

Total 1,104 1,222 DIATOMS

Melosira 0 29 Synedra 0 486 Tabellaria 2,134 221

Total 2,134 736 DINOFLAGELLATES

Ceratium 0 15

Total Cells /mL 25,418 12,731

Zooplankton

The densities of different groups of zooplankton collected in Congamond Lake during

this study are shown in Figure 5. Cladocera zooplankton in Congamond were all small

bodied organisms of less than 0.6 mm in size, were normally these animals are

between 1 and 2 mm in size. The lack of large bodied Cladocera in the samples

indicates intense grazing by fish populations, possibly either yellow perch or

landlocked alewives. Other, mostly all small, zooplankton, organisms, were present at

moderate to low numbers including copepods and calanoids. There were some rotifers

but again these were also poorly represented.

Figure 5 – Zooplankton densities in Congamond Lake

9-Sep 14-Oct

Lg Cladocera

Sm Cladocera

Lg Copeopoda

Sm Copeopoda

Copeopod Nauplii

Rotifera

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Congamond ZOOPLANKTON DENSITY

Conclusions The aquatic plants in Congamond Lake were characterized as a tape grass/pondweed

association with areas of water lilies. The lake had a high diversity of species (38) but

only 5 occurred at more than 10% of the observation sites. Two invasive aquatic plants

were found Eurasian milfoil and Minor Naiad. Eurasian milfoil was present at only 5

points (2%), three in South Pond (each near the small bay on the east side of the lake),

and two in North Pond. The North Pond sites had only individual milfoil plants

scattered along the shoreline and mixed with other native species. The South Pond

sites, clustered together near the existing buoys marking the exclusion zone, were

more robust than the North Pond plants but still did not reach the surface. No topped

out beds of milfoil were found. Minor naiad was found at 3 points (1.3%), two points

were near the northern tunnel in Middle Pond, and one site was in South Pond near the

southern tunnel. There were stretches of shoreline in Middle Pond that had no plants,

or only very tiny bottom plants.

The water quality results show that Congamond Lake has a variable trophic condition,

with South Pond eutrophic, and North Pond mesotophic. The eutrophic terms means

that phosphorus content in South Pond exceeded 30 ppb and water clarity was less

than 2 meters and mesotrophic means that phosphorus content was between 15 and 20

ppb and water clarity was between 3 and 4 meters. North Pond did not quite fit these

categories, having slightly less phosphorus with slightly poorer clarity. South Pond

appears to generate a significant amount of phosphorus internally from sediment

release. It is possible that phosphorus released from sediments in South Pond mixes

throughout the water column by late summer because the thermocline erodes quickly

in that basin causing bottom phosphorous to diffuse into upper waters. Higher

phosphorus levels in South Pond may contribute to phosphorus values in Middle Pond.

Temperature and dissolved oxygen measurements show that Congamond Lake formed

a strong thermocline between 6 and 8 meters with complete oxygen loss below that.

Oxygen loss was more pronounced in South and Middle Ponds. In September, South

Pond had an anoxic boundary located at 4.9 meters below the surface. In Middle

Pond, the anoxic boundary was located at 5.8 meters below the surface. In

comparison, the anoxic boundary in North Pond was located 7.8 meters below the

surface. In October, dissolved oxygen was replenished a couple of meters downward

in Middle and North Ponds but not to the bottom. In South Pond in October, dissolved

oxygen levels were replenished to the bottom. The loss of dissolved oxygen was up to

or above the thermocline in each basin in September, and did not fully re-oxygen by

October in Middle and North Ponds indicating that decomposition and oxygen loss rates

are severe in the lake.

The lake has very high number of bluegreen algae in the water in September. The

bluegreens were dominated by the taxon; Lyngbya and Anabaena. Both these groups

have species that are known toxin producers (Graneli & Turner 2006). It would be

worthwhile to have the water tested for Microcystin, the only toxin that can be readily

analyzed for at this time.

References Canfield D.E., K.A. Langeland, S.R. Linda, and W.T. Haller. 1985. Relations Between Water Transparency and Maximum Depth of Macrophyte Colonization in Lakes. J. Aquat. Plant Manage. 23:25-28. Connecticut Department of Environmental Protection. 1982. The Trophic Classification of Seventy Connecticut Lakes. Water Compliance Unit. Hartford, CT. Frink C.R., and W.A. Norvell. 1984. Chemical and Physical Properties of Connecticut Lakes. The Connecticut Agricultural Experiment Station. Bulletin 817. New Haven, CT. Graneli E. and J. T. Turner. 2006. Ecology of Harmful Algae. Ecological Studies, Vol. 189. Springer-Verlag. Berlin Heidelberg. Jacobs R.P., and E.B. O’Donnell. 2002. A Fisheries Guide to Lakes and Ponds of Connecticut. Connecticut Department of Environmental Protection. Bulletin 35. Hartford, CT. Les, D. H., and L. J. Mehrhoff. 1999. Introduction Of Nonindigenous Aquatic Vascular Plants In Southern New England: A Historical Perspective. Bio. Invasions. 1: 281-300.