PLEASANT LAKE
Pennellville, New York

A Preliminary Limnological Investigation

Prepared by

Bruce Gilman, Professor Natural Resources Conservation

Community College of the Finger Lakes

Canandaigua, New York 14424

Collection of field data was achieved by my fall semester Limnology class. I am particularly grateful for their assistance. I also thank my colleague, Dr. Frank Smith, for his comments while I was preparing this report. Lastly, none of this would have been possible without my first being introduced to Pleasant Lake by shoreline resident (and brother-in-law) Paul Thomas.

INTRODUCTION

Limnology is the study of inland waters. It would include field investigations of ponds, streams and lakes for their physical, chemical and biological characteristics. Many of these characteristics change seasonally while others remain virtually constant. This report summarizes preliminary Limnological data collected after one-day being spent at Pleasant Lake. As a result this is a brief glimpse, a beginning look at water quality and related issues on the lake. Future field study would enhance our understanding of the Pleasant Lake aquatic system.

The landscape running across southern Oswego county is dominated by disintegration features formed at the end of the Wisconsin stage of the Pleistocene Ice Age. These features include coarse melt out, till, kames, kettles and kettle hole lakes. Pleasant Lake (Figure 1) is one of the larger kettle hole lakes formed when a block of glacial ice broke free of the ice margin and was subsequently surrounded and buried by coarse till. It has a rather small watershed, land surrounding it that drains to the lake through intermittently flowing streams (Figure 2). Therefore, water level in the lake is probably maintained by a groundwater aquifer rather than by surface runoff.

MATERIALS AND METHODS

The college class visited Pleasant Lake on October 14, 1990 as part of a course activity. Students worked in small teams on a variety of exercises. One team used a staff gauge to record water depth at 28 widely scattered locations. Isobaths, underwater contour lines, were hand drawn on a map then lake volume was calculated with the microcomputer program,LIKVOL.

Another team sampled surface water at 3 locations near the western end of the lake. They measured dissolved oxygen, alkalinity 4nd,water pH. Dissolved oxygen is needed for the respiration of all aerobic organisms that inhabit the lake, including fish, insects and mollusks. A minimal level of 6 mg/l should be present year-round to support a warm water fishery. As oxygen gas is less. soluble in warmer water, summer monitoring of dissolved oxygen at all lake depths is recommended. Alkalinity measurements indicate the abundance of bicarbonate ions dissolved in the water.

These bicarbonate ions act as important buffering compounds, negating the effect of any acidic precipitation or runoff that the lake might receive. An alkalinity level of at least 75 mg/l is desirable. Water pH measures the concentration of acidity. To protect aquatic organisms, pH near the neutral point (7.0) is preferred. A third team of students used a seine net along the northwestern shoreline to assess the fish populations living there. The bottom substrate was partly decomposed peat. This type of fieldwork should be repeated on other substrates within the lake to obtain more comprehensive information on fish populations.

There are several additional water quality tests that the Pleasant Lake Association may wish to consider for the future. Water clarity can be easily measured with a Secchi disk. it is carefully lowered over the shady side of a boat near midday. When it disappears from view, the length of rope in the water is recorded. This information establishes how deep sunlight will penetrate into the water column. Sunlight, of course, is needed to support the growth of suspended plants (phytoplankton, algae) and rooted plants (macrophytes, weeds). Most other lake organisms rely on plant growth for their own sustenance. Low secchi disk readings, less than 3 feet, usually indicate that the disk is blocked from view by suspended organisms (phytoplankton and the zooplankton that graze on them) or by suspended sediment that may be originating from Waterershed erosion.Nutrient levels ultimately control the growth of all lake organisms. Dissolved concentrations of ammonia, nitrate, orthophosphate and total phosphorus are periodically monitored in many lakes. Acceptable levels vary with each nutrient and for each lake situation. Generally lower levels are preferred, with higher levels suggesting management problems like fertilizer runoff or surface outbreaks from septic systems.

Bacteriological contamination can be routinely checked at an inexpensive cost through hospital, county health departments and consultant laboratories. New York State certifies some, but not all, of these laboratories. If coliform bacteria, common intestinal microbes, are found in the lake water then a recent episode of fecal contamination is indicated. Faulty septic systems, barnyard runoff or large numbers of migratory waterfowl are usually suspect.

Results and Discussions

A bathymetric map, showing underwater contour lines, is presented in Figure 3.

Pleasant Lake is a shallow kettle hole lake that reaches warm summer water temperatures. Thermal stratification in the zone of maximum water depth is probably absent, or at best fragile and easily disrupted by winds across the surface. The lake would be classified as a cold, monomictic lake meaning that the lake has complete ice cover during the winter season and that it mixes (turns over) during the spring season.

Water chemical conditions, also presented in Table 1, suggest a "healthy" lake environment. Dissolved oxygen is near saturation for that time of the year, a very good condition f or aerobic aquatic organisms. Alkalinity levels indicate a large quantity of buffering compounds dissolved in the water. As a result, water pH is near the neutral point on the pH scale. A cautionary comment is needed here, however. There are many other water conditions that should be chemically measured before the overall lake condition can be described as "healthy".

In conclusion, these Limnological characteristics of Pleasant Lake begin to tell the story of its formation, quality and value to man.

Detailed physical properties of the lake and watershed are provided in Table 1.

Table 1 Characteristics of Pleasant Lake

Physical Properties

Maximum Length (L) 2737.5 ft

Maximum Width (b) 958.1 ft

Average Width (B) 664.3 ft

Maximum Depth (z,,,) 11.5 ft

Average Depth (2) 5.0 ft

Volume (V), 8,555,090.0 cubic ft

64,010,429.0 gallons

Surface elevation 403.0 ft

Lake Surface Area (A0) 38.9 acres

Watershed Surface Area 99.1 acres

Watershed :Lake Ratio 2.5 to 1.0

Length of Shoreline (SL) 7345.6 ft

Insulosity (area of islands) 0.1 acres

Shoreline Development Index 1.6

(closeness of lake shape to a circle).

Estimated percent of lake bottom at various depths

0 - 5 feet 45.4 %

6 -10 feet 50.5%

over 10 feet 4.1 %

Chemical Conditions

(.data collected on October 14, 1990 at, surface)

Dissolved Oxygen 9.2 mg/l

Alkalinity 330.0 mg/l

Water pH 6.9

Biological Activities

Table 2 lists some of the additional organisms observed that fall day. Year round residents of the lake could add much needed detail to these preliminary lists.

Table 2 Organisms observed at Pleasant Lake on October 14, 1990

Birds: great blue heron

green backed heron

Canada goose mallard

Fish: bluegill sunfish

largemouth bass

pumpkinseed sunfish

yellow perch

Reptiles: painted turtle

Insects: dragonfly

predaceous water bug

Mollusks: snail

Plants: coon tail

rose-colored water lily

cattail

water willow

button bush

winterberry

tupelo

Pleasant Lake By-Laws

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