Limnology 101An Introduction to Lake Science

10 August 2017Prairie Lakes Conference

John C. Holz, PhDSenior Limnologist

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LIMNOLOGY DEFINED

• Limnology (from Greek limne, “lake” and logos, “knowledge”) is the study of inland waters.

• Covers geological, physical, chemical and biological attributes of land-bound freshwater and saline systems, including:

• Lakes• Ponds• Impoundments• Rivers• Streams• Wetlands

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THE WATERSHED

USGSpenntwplanco.org

HUC8 Watershed Boundaries

• Section of land where all water runoff flows to a common basin

• Runoff carries nutrients, sediment and pollutants

• Runoff affected by slope, geology, soils and land use

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THE TALE OF TWO WATERSHEDS

Lake Michell, SDWS:L = 524:1

Five Island Lake, IAWS:L = 9:1

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LAKE FORMATION & BASIN TYPES

• Hutchinson identified 76 ways lakes may form

• Including: earthquakes, volcanos, oxbows, glaciers, faults in the Earth’s crust

• Lake formation affects lake size, shape, depth and watershed characteristics

Crater Lake, OR

NASA

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GLACIAL LAKES

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GLACIAL LAKES

*D. Lusch, MSU

Most Midwestern Lakes were formed over 10,000 years ago

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OXBOW LAKES

Carter Lake, IA Lake Manawa, IA

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IMPOUNDMENTS

Lake Wanahoo, NE

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IMPOUNDMENTS VS. NATURAL LAKES

Impoundments Natural Lakes

Shoreline Astatic Stable

Water Level Large fluctuations Natural

Littoral Zone Irregular Stable

Flushing Rate High Low

Sedimentation Rate High Low

Nutrient Loading High & variable Low & stable

Turbidity High Low

Stratification Irregular Natural

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THERMAL STRATIFICATION

• Maximum density = 3.94 oC• Ice at 0 oC is 8.5% less dense that water at 0.1 oC• Water above 3.94 oC gets less dense as it warms• Surface water is warmer than deep water in the summer (thermal stratification)

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THERMAL STRATIFICATION & MIXING

quia.com

• Dimictic vs. Polymictic Lakes

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THERMAL STRATIFICATION & OXYGEN

• PhotosynthesisCO2 + H2O + nutrients + light glucose + O2

• Respirationglucose + O2 CO2 + H2O + energy

quia.com

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NUTRIENTS

• Limiting Nutrient Concept: The nutrient in short supply relative to others will be exhausted first and limit cellular growth

• Phosphorus (P) is an essential element and is the most common limiting nutrient in lakes

• Excessive concentrations of P is a key driver of a variety of lake water quality problems

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NUTRIENT SOURCES

Internal Loading

External Loading

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EXTERNAL NUTRIENT SOURCES

Septic Systems Lawn Fertilizers Agriculture

Stormwater Livestock

COW

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INTERNAL NUTRIENT SOURCES

Dissolved P Loading Sediment Coring: Five Island Lake, IA

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INTERNAL NUTRIENT SOURCES

Particulate P Loading

Jet Ski: Carter Lake, IA

Common Carp

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LAKE FOOD CHAIN

• Bass, pike, walleye

• Minnows, YOY sunfish, alewife

• Daphnia, copepods, rotifers

• Diatoms, green algae, cyanobacteria

• Phosphorus

• Common Carp, Buffalo

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PHYTOPLANKTON (ALGAE)

• Microscopic plants• Base of food chain• Produce O2

• Chlorophyll pigment gives green color• Groups often differentiated by color• Too many cause problems• Require phosphorus for production of

adenosine triphosphate (ATP)• Transports chemical energy within cells

for metabolism• Growth limited by phosphorus

Vollenweider (1968)

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PHYTOPLANKTON (ALGAE)

Green Algae Diatoms

Cyanobacteria (aka Blue-green algae)

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WATER QUALITY CHALLENGES

Algal Blooms Algal Toxins Low Clarity

Fish Kills Recreation/Property Value Declines

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ZOOPLANKTON

• Tiny, free-floating invertebrate animals• Feed on algae and bacteria• Important food source for planktivores• Most are transparent (camouflage)• Can increase population size by 30% in a day• Lifespan of up to 30 days

Daphnia

Copepod

Rotifer

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PLANKTIVOROUS FISH

• Feed on zooplankton• Different species feed on different sized zooplankton• Food source for piscivorous fish

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LAKE FOOD CHAIN

• Bass, pike, walleye

• Minnows, YOY sunfish, alewife

• Daphnia, copepods, rotifers

• Diatoms, green algae, cyanobacteria

• Phosphorus

• Common Carp, Buffalo

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TROPHIC CLASSIFICATION

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SHALLOW LAKE ECOLOGY

Plant-Dominated State Algae-Dominated State

• Shallow lake water quality controlled by both nutrients and rough fish• Alternate Stable State theory predicts two lake conditions• A management approach is to control both phosphorus and rough fish density

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QUESTIONS?

Dr. Ben Maas, BVU