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Understanding the Basics of Limnology
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Outline • Watershed Processes • Lake Formation • Physical Features of Lakes • Lake Processes • Lake Chemistry • Lake Biology • Lake Management
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WATERSHED PROCESSES
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A Lake is a Reflection of its Watershed:
• Rainfall collects within the lake basin
• Water runs down hill • Runoff carries nutrients,
soil and pollutants with it • Watershed slope,
geology and soils affect runoff
• Human land uses influence the amount and quality of runoff water.
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Watershed Features Affect the Amount of Runoff
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Nonpoint Source Suspended Solids Loss From Various Land Uses
0
5000
10000
15000
20000
25000
30000
Kg/h
a yr
Pasture Forest Residential Cropland DevelopingUrban
lowhigh
Source: Sonzogni et al. (1980)
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Nonpoint Total Phosphorus Loss from Various Land Uses
0
5
10
15
20
25
kg/h
a yr
Pasture Woodland Residential Cropland DevelopingUrban
LowHigh
Source: Sonzogni et al. (1980)
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Watershed size and its effect on lakes
Lake Surface Area = 100 acres Lake Surface Area = 100 acres>runoff>sediment and nutrient loading<hydraulic residence time
Small Watershed
Large Watershed
<runoff<sediment and nutrient loading>hydraulic residence time
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LAKE FORMATION
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LAKE FORMATION
• G.E. Hutchinson identified 76 ways lakes may form
• Include: earthquakes, volcanoes, oxbows, faults in the Earth’s crust and glaciers
• Lake formation affects lake size, shape and depth and watershed characteristics
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Lake Formation
• Most natural Midwestern lakes were formed by glaciers >10,000 yrs ago
• Glaciers scoured out lake basins
• Ice blocks formed depressions that filled and became lakes (kettle or ice block lakes)
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Coverage of last glacial episode ~ 10,000 years before present
Natural lakes
Impoundments
Coal Mine lakes
Lake Distribution
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PHYSICAL FEATURES
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Bathymetric maps are a great source of lake morphometry information!
• Lake area (Ao) • Maximum depth (Zmax) • Mean depth (Z) • Shoreline Length (L) • Deep holes • Shallow areas • Volume (V) can be
calculated from this map. (V = Ao* Z)
Shallowslope
Steepslope
38 ft.
Clear Lake153 acresMax.Depth = 38'Surveyed: 6/8/83
N
zzz
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Lake Shape and Shoreline Length
Area = 100 acres Area = 100 acres Shoreline = 7,400 feet Shoreline = 12,000
feet
Round Lake Crooked Lake
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Lake Shape & Orientation and Wind Fetch
Wind Direction Wind Direction •long fetch = more internal mixing •short fetch = less
internal mixing
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LAKE PROCESSES
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Solar Energy – the engine that powers lake ecosystems!
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Light Attenuation SUNLIGHT
Reflected
Scattered
Absorbed - water - dissolved color - particles
-particles
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Lake Depth and Productivity
Sufficient light for algae to grow
Sufficient light for algae to grow
Limit of light penetration
Deep Lake Shallow Lake
•Most of lake volume can support algae.
•Small % of lake volume can support algae.
- 1% light level - defines euphotic zone
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thermocline
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Thermal Stratification ice
0 10 20 30 °C 0 10 20 30 °C
0 10 20 30 °C 0 10 20 30 °C
Winter Spring
Summer Fall
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Physical Features Summary
• Lake Shape (morphometry) - wind fetch - shoreline length • Lake Volume - productivity • Lake Depth -stratification
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Photosynthesis
carbon dioxide + water + nutrients + light glucose + oxygen
Respiration
glucose + oxygen carbon dioxide + water + ENERGY
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Dallas Lake – Temp. & D.O.
-35
-30
-25
-20
-15
-10
-5
0
0 5 10 15 20 25 30Value
Dept
h (m
)
Temp ( C)D.O. (ppm)
Anoxic
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Oxygen is Often Low in the Hypolimnion
Decomposers consume O2
Isolated from atmosphere
Too dark for photosynthesis
Mixing Zone Dead plants
epilimnion
metalimnion
hypolimnion
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Not all deep lakes are anoxic Lake James, Indiana
-30
-25
-20
-15
-10
-5
0
0 5 10 15 20 25
Value
Dep
th (m
)
Temp ( C)D.O. (ppm)
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LAKE CHEMISTRY
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Water Chemistry
• Nutrients – Nitrogen – Phosphorus – Carbon
• Suspended sediments
• Trace metals – Mercury
• Organic contaminants
– Pesticides – Algal toxins
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Phosphorus Release from Sediments (Internal Loading)
FePO 4
PO PO PO 4 4 4
FePO
4
No Dissolved Oxygen in Hypolimnion
Sediments
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Internal Phosphorus Cycling
Dead plants settle down to the sediments
Bacteria decompose the plant materials
Oxygen is consumed by the bacteria during decomposition
Phosphorus is released from the sediments back into the water where it encourages the growth of more plants
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Sediment P Release – Dallas Lake
-35
-30
-25
-20
-15
-10
-5
0
0 5 10 15 20 25 30Value
Dept
h (m
)
Temp ( C)D.O. (ppm)
[TP] = 55 µg/L
[TP] = 259 µg/L
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Redox Changes in Lake Shakamak NO3
- NH4+ SRP
0.823 0.067 0.016 mg/L
0.382 4.581 0.286
0
1
2
3
4
5
6
70 5 10 15 20 25 30
Value
Dep
th (m
)
TemperatureD.O.
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LAKE BIOLOGY
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Lake Communities
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Aquatic plants are primary producers
Open Submergent Floating Emergent Wet Meadow Terrestrial Water aquatics Aquatics
e.g. algae watermilfoil pond lily arrowhead sedges shrubs pondweeds spatterdock cattail trees
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Aquatic macrophytes have many positive attributes
• Help protect shorelines from erosive waves
• Stabilize littoral sediments • Help block out lake sounds • Provide visual screen for privacy • Are important habitat for fish and
other aquatic life • Many are aesthetically pleasing
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The Aquatic Food Web bass, pike, walleye minnows, YOY sunfish aquatic equivalent to cows primary producers also
include macrophytes stir up sediments and
nutrients from bottom sediments
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Phytoplankton (aka: Algae)
• Microscopic plants • Are primary producers • Produce oxygen during photosynthesis • Are important at the base of the food chain • Chlorophyll pigment gives green color • Groups are often differentiated by color • Too many may cause problems
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Types of Algae Diatoms • Have hard shells made from
silica • Shells remain in sediments
1,000s of years • Often abundant in spring
Green Algae • Bright green chlorophyll • Are generally considered
“good” algae • Important food for zooplankton • Often abundant in early summer
Asterionella Dinobryon (a yellow-brown alga)
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The Amazing Blue-Greens • Often become a nuisance
when excess phosphorus is available
• Dominate during the warm summer months
• Can out-compete other “desirable” algae
Competitive Advantages • Buoyancy regulation • Nitrogen fixation • Gelatinous sheath • Large size • Some produce toxins • Unpalatable
Anabaena
Coelosphaerium
Heterocyst
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Zooplankton Daphnia ~ 2.5mm Bosmina ~ 0.5 mm
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The Aquatic Food Web bass, pike, walleye minnows, YOY sunfish aquatic equivalent to cows primary producers also
include macrophytes stir up sediments and
nutrients from bottom sediments
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Planktivores
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LAKE MANAGEMENT
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Eutrophication
Process of excessive addition of: 1. Inorganic nutrients 2. Organic matter, and 3. Silt to lakes leading to increased biological production and a decrease in lake
volume.
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Nitrogen • Atmospheric nitrogen (N2) isn’t usable by plants • Most blue-green algae can “fix” atmospheric nitrogen • Ammonia (NH4) is formed as a product of decomposition • NH4 and NO3 are both used by algae • Sources include: fertilizer, sewage waste, animal waste,
atmosphere
Phosphorus • No atmospheric gaseous phase • Sources: fertilizer, animal and human wastes,
detergents, natural rocks • Found in runoff and precipitation • Is the primary plant nutrient of algae
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Lawn Fertilizer • 29-3-4 on label means • 29 parts N : 3 parts P : 4 parts K
Most lawns have plenty of available phosphorus!
Phosphorus-free lawn fertilizers are becoming widely available.
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Limiting Nutrient Concept
• Definition: that essential material that is in least supply and limits the growth of the plant.
• Phosphorus is often the limiting nutrient to algae.
• Other limiting factors = temperature, light.
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Trophic Classification Classification Transparency Nutrients Algae D.O. Fish Oligotrophic clear Low
TP < 6 µg/L few algae Hypo has D.O. can support
salmonids (trout and salmon)
Mesotrophic Less clear Moderate TP 10-30 µg/L
healthy populations of algae
Less D.O. in hypo
lack of salmonids
Eutrophic transparency <2 meters
High TP > 35 µg/L
abundant algae and weeds
No D.O. in the hypo during the summer
Hypereutrophic transparency <1 meter
extremely high TP > 80 µg/L
thick algal scum Dense weeds
No D.O. in the hypo during the summer
EUTR
OPH
ICAT
ION
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Carlson’s Trophic State Index (TSI)
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Cultural Eutrophication • May take only
decades • Rapid decline
caused by human activities
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Plant-dominated lake
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Algae-dominated lake
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Why does the ‘plant phase’ persist? • Tall or emergent plants reach
for the light • Some plants secrete algae
inhibitors • Zooplankton grazers of algae
find refuge within the rooted plants
• Rooted plants stabilize the sediments – preventing sediment-disturbing waves
• Few boats operate within the rooted plants
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Why does the algae stage persist?
• Algae shade out rooted plants • Begin growth earlier in the
spring • Uptake CO2 more efficiently • Without plants, algal grazers
are eaten by fish • Rough fish such as carp keep
water turbid and nutrient-rich
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Lake Management Goal • Maintaining a healthy
ecological balance in our lakes
Depends on: • physical, • chemical, and • biological factors
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Major Demands (Stressors) on Indiana Lakes
• Eutrophication • Shoreline Development (and Re-development) • Over Use • Exotic Species
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Indiana Clean Lakes Program
• Sponsored by Indiana Department of Environmental Management (IDEM)
• Administered by I.U. School of Public and Environmental Affairs (SPEA)
• Created in 1989