Oneida Lake: ever-changing ecosystem

Managing water resources in Oneida Lake, WM Kappel

Oneida Lake watershed: A valuable diverse ecosystem, SM Harrington

Water level management, HM Goebel

Oneida Lake: undergoing ecological change, EL Mills, KT Holeck

Evolution of the Oneida Lake fishery, T VanDeValk, L Rudstam

Regional partnerships for Oneida Lake watershed, AB Saltman

Helping to protect Oneida Lake, J Henke

Trends: technology and management of municipal wastewater, D Interdonato, E McCarthy

Outstanding young researchers

President's message, D. Ellis

Executive director's message, P Cerro-Reehil

People and places

Joint CSO/SSO meeting

Correction

Winter 2001 — Vol. 31, No. 4

by Edward L. Mills and Kristen T. Holeck

Oneida Lake and its limnology

Oneida Lake is the largest water body wholly within New York State. It is located 11 mi northeast of Syracuse. The lake's long axis is oriented west-northwest to east-southeast and is fully exposed to the prevailing winds. See Table for statistics.
 

Figure 1a. Depth of Oneida Lake (Map by Jeremy Coleman)

The lake is a shallow spoon-shaped depression that deepens toward the eastern end (Figure 1). The lake has many shoal areas, and about 26% of the lake bottom is shallower than 14 ft. Normal elevation above sea level is 364 ft during the winter and 367 ft during the summer. Water from five counties flows into Oneida Lake.

Figure 1b. Depth of Oneida Lake. (Chart by Jeremy Coleman)

The lake freezes over completely in winter with ice thickness reaching as much as 30 inches in the mid to late 1970s. Ice forms anytime from early-mid December to mid-late January. Ice-out records have been kept at the Oneida Fish Culture Station located in Constantia, NY since 1845. The earliest the ice broke up in Oneida Lake was March 2, 1903 and the latest date was April 25, 1881 and 1891.
 
Oneida Lake's physical characteristics.

Latitude	43°12.5´N
Longitude	75°55´W
Elevation	112 m	367 ft
Drainage area	3579 km²	1382 mi²
Surface area	206.7 km²	79.8 mi²
Shoal area	53.1 km²	20.5 mi²
Length	33.6 km	21 mi
Max width	8.8 km	5.5 mi
Mean width	6.1 km	3.8 mi
Max depth	16.8 m	55.1 ft
Mean depth	6.8 m	22.3 ft
Shoal	4.3 m	14.1 ft
Volume (elev 367´)	140 x 107 m³	370 billion gal
Hydraulic retention time	235 days

Unlike most north-temperate lakes, Oneida's water-column temperature is usually the same from top to bottom; the only exception occurs during prolonged calm periods when surface waters become warmer than bottom waters (“thermal stratification”). Wind-generated wave action is the principal mechanism that prevents permanent thermal stratification during the summer. Water temperatures typically increases rapidly during May and June reaching a maximum of 77°F or more in mid-summer. As air temperature declines in the fall, water temperature rapidly declines during September and October.

Biological properties

Figure 2. Oneida Lake blue-green algae bloom.

While early studies of algae blooms in Oneida Lake were largely cursory and generally descriptive, they established that the lake was naturally rich and productive (Mills et al. 1978). Consequently, nuisance blooms (Figure 2) of cyanobacteria (blue-green algae) have been recorded in Oneida Lake since the early part of the 20th century. In fact, throughout its history, Oneida Lake has exhibited summer algae blooms that were characteristic of enriched water productivity. French voyagers called Oneida Lake le lac vert, commonly referred to as “the green lake.” Seasonally, centric diatom blooms (Cyclotella sp.) typically have dominated early spring phytoplankton communities followed by a clear-water phase consisting of ultra- and nanno-plankton species like Cryptomonas sp. The algal community typically shifts to blooms of cyanobacteria which persist 1 to 3 months in late summer and early fall.

Figure 3. Daphnia galeata and Daphnia pulicaria, two common Oneida Lake zooplankton.

Zooplankton (Figure 3) play a pivotal role, serving as food for small fish and as consumers of algae. Nineteen zooplankton species have been identified in Oneida Lake, and their abundance varies both seasonally and annually (Mills, Forney, and Wagner 1987). Large-bodied Daphnia pulicaria typically dominate in the spring, grazing on algae leading to very clear water. If predation by plankton-eating fish is high, large-bodied Daphnia markedly decline and the composition shifts to smaller-bodied Daphnia galeata and D. retrocurva, and other small sized zooplankton like Chydorus, Bosmina, Diaphanosoma, and Ceriodaphnia. Studies have shown that when the biomass of young yellow perch reaches a threshold of 18 to 36 lb/acre, predation by these fish depresses stocks of Daphnia pulicaria and smaller herbivorous zooplankton appear.

Ecological changes

Phosphorus

Nuisance blooms of algae, particularly common between 1940-1960, prompted scientists to focus on phosphorus as a nutrient controlling algal abundance. Early efforts to reduce phosphorus loading to Oneida Lake began in the early 1970s and were linked to a water quality agreement between the United States and Canada that set target levels for phosphorus in offshore waters of each of the Great Lakes. Since Oneida Lake's watershed was part of the Great Lakes basin, government funding to upgrade existing sewage treatment plants and to construct new ones became available. Consequently, millions of dollars were spent to reduce phosphorus concentrations in Oneida Lake and the Great Lakes.

Figure 4. Total phosphorus (TP) and nitrate levels in Oneida Lake 1975-2000.. Click for larger image in new window.

In addition, proper management practices to reduce phosphorus losses were encouraged in the watershed. In 1973, New York State banned the use of phosphorus in household detergents, further reducing phosphorus contributions to the lake. By the mid- to late-1980s, total phosphorus concentrations were reduced to nearly one-half of what they had been in the late-1970s. Total phosphorus concentrations averaged 40 to 60 µg/L in the 1970s and early 1980s and were reduced to 20 to 30 µg/L in the 1990s (Figure 4A).

Nitrate and nitrogen

In contrast, nitrate-nitrogen concentrations in Oneida Lake have not exhibited a similar decline; mean May-October concentrations generally range between 100 and 300 µg/L (Figure 4B). Associated with the shift to lower phosphorus levels in the mid-1980s was a decline in primary production and a reduction in the number of low dissolved oxygen events in the bottom waters of Oneida Lake. In sum, efforts to reduce phosphorus loading to Oneida Lake were successful and have led to improved water quality conditions—a goal set by the Great Lakes Water Quality Agreement.

Figure 5. Hexagenia limbata, commonly know as eel fly or mayfly.

Water quality and indicator organisms

A dramatic biological event occurred in the 1960s in the benthic (bottom-dwelling) invertebrate community that reflected degraded water quality conditions. Before then, the mayfly Hexagenia limbata (commonly referred to as eel fly) was the dominant benthic organism (Figure 5), emerging from Oneida Lake in vast numbers. Densities of Hexagenia began to decline in 1959 (Jacobsen 1966) and the last mayfly was observed in the lake in 1968 (Clady and Hutchinson 1976).

Coincident with and maybe contributing to the mayfly's decline were widespread oxygen shortages. Low oxygen conditions may have been only one of several factors, however, that led to its demise including disease and chemicals, later banned, such as DDT and Dieldrin.

Chironomids, organisms more tolerant of low oxygen conditions, increased during the mayfly decline and became the dominant benthic organism. A few large mayflies have been observed in Oneida Lake in recent years. They provide further evidence of improving water quality conditions (reduced lake fertility) in Oneida Lake.

Non-native species

Biological pollution continues to be a problem in Oneida Lake. Most significant among recent biological pollutants has been the zebra mussel (Dreissena polymorpha). This animal is a small bivalve mollusk native to the Black, Caspian, and Aral seas and has a life span of 2-3 years; most adults reach shell lengths of 25 to 35 mm.

Figure 6. Zebra mussel dry biomass in Oneida Lake, 1992-2000.

Oneida Lake's well-mixed waters, warm summer temperatures, and high concentrations of calcium present an ideal environment for zebra mussels. The mussels were first sighted in Oneida Lake in 1991; dry weight biomass has ranged from 10 to 30 g/m² between 1992 and 1996; in 1997, mussel biomass reached nearly 50 g/m², and it stabilized through the year 2000 (Figure 6).

Zebra mussels are efficient filter feeders whose gills can remove microscopic particles from the water column (up to 1 qt/day). They are responsible for dramatic increases in water clarity in Oneida Lake. Soon after zebra mussels became established, secchi disc transparency increased as algal abundance declined (Figure 7). Peaks in water clarity occurred in 1994, 1995, and 1997. Signs since 1997, however, show decreasing water clarity and increasing chlorophyll concentrations, suggesting that the water clarity effects of zebra mussels have attenuated in recent years.

Figure 4. Secchi depth and chlorophyll a levels, 1975-2000.. Click for larger image in new window.

Despite increased water clarity, primary production has not declined (Idrisi et al. 2001). Increased water clarity allows more sunlight to penetrate lake water, and this change has compensated for factors that otherwise would cause a decline in primary production. The following observations evidence no decline in primary production:

• No observed decline in the biomass and
production of Daphnia sp.
• No evidence of a negative effect on the growth,
biomass, or production of plankton-eating young yellow perch (Perca flavescens).

Animals

“Turning the lights on” in a once-turbid and verdent Oneida Lake has triggered many ecological changes. With greater zebra mussel-induced light penetration, submersed aquatic plants have flourished. Before, algal blooms limited light penetration to less than 1 m during much of the submersed plant-growing season. Now, only 35 to 40% of the plant biomass is in the lake's shallows; the remainder is found at depths of 11 to 15 ft. In the late 1970s, 85 to 90% of the submersed plant biomass was found in depths of less than 6 ft.

Expansion of the weed beds to greater depths provides escape and cover for small fish and macroinvertebrates; these plant beds are the preferred habitat for smallmouth bass and sunfish. Greater light penetration has also resulted in bottom-dwelling algae mats which provide both a home and a food resource for bottom-feeding invertebrates. Clear-water conditions have allowed predators easier access to prey.

For example, fish eating birds such as double-crested cormorants undoubtedly have more success feeding on fish like walleye and yellow perch today than they would have had when the lake was green. Increased mortality of walleye and yellow perch as larvae may well be linked to increased water clarity since these fish no longer have the refuge of green water to protect them from other predators such as buckeye minnows, white perch, and adult walleye.

Zebra mussels have directly caused native bivalve clam populations to decline. Harman (2000) reports that six species of bivalves have gone extinct from direct competition from zebra mussels. The recent extinction of unionid clams contributes to a remarkable loss of molluscan fauna during the last century; species richness of Oneida Lake's molluscan fauna has declined by 42% since 1917.

Plants

Oneida Lake supports three invasive plants: Eurasian milfoil, Myriophyllum spicatum, is a submersed plant that has been documented in Oneida Lake since the 1970s. Over the last 30 years, this plant has not reached nuisance levels because, in part, of the non-native aquatic insect moth Acentria that feeds on it.

Figure 8. Water chestnut (Trapa natans) Photo by Peter Liszek

The water chestnut, Trapa natans, was first sighted in western Oneida Lake in 1999 and is currently abundant in the Seneca and Oswego Rivers (Figure 8). Water chestnut plants grow up to 16 ft. They prefer shallow mud bottom habitats in still or slowly moving water. These plants have floating leaves and spined nutlets. They can seriously affect shallow water habitats in Oneida Lake.

The third invasive plant is purple loosestrife, Lythrum salicaria. Because predators are few and because of its high reproductive capability, this plant has out-competed native cattails and generally dominates wetlands and marsh habitats around Oneida Lake.

Oneida Lake and its future

Oneida Lake is one of the finest aquatic resources on the New York landscape. Water quality conditions have greatly improved since the 1970s, and watershed additions of phosphorus are nearly half what they were two decades ago. Proactive efforts to reduce soil loss from the watershed, to minimize contributions to the lake of herbicides and pesticides, to prevent disease pathogens from entering streams, and to protect the water resources in general are essential for Oneida Lake and its future.

Biological pollution and invasive species will continue to affect Oneida Lake's waters. Prolific zebra mussel populations will undoubtedly facilitate invasions of other. A fish called the round goby, for example, may soon flourish and affect the Oneida Lake food web. Round gobies were transported to North America in the ballast water tanks of ocean-going freighters from the Black and Caspian Seas and are currently established in near-by Lake Ontario. Small gobies seek cover in aquatic plant weed beds, and adults feed on zebra mussels.

At the root of this biological pollution is the transport and release by large ships of organisms from around the globe. Until we solve this environmental problem, Oneida Lake and nearby waters will continue to be vulnerable to infestations by unwanted invaders.
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Edward L. Mills and Kristen T. Holeck are with the Department of Natural Resources and are active at the Cornell Biological Field Station on Shackelton Point in Bridgeport, NY.
 
References