Lentic SystemsLentic Systems

Lakes and PondsLakes and Ponds

Formation of LakesFormation of Lakes

Glacier lakesGlacier lakes Oxbow lakesOxbow lakes PlayasPlayas Man-made lakesMan-made lakes

Glacier LakesGlacier Lakes

Carved out by glaciers (glaciation), Carved out by glaciers (glaciation), which fill with waterwhich fill with water

Northern U.S. and CanadaNorthern U.S. and Canada

How Does Glaciation How Does Glaciation Work?Work?

As the glaciers move they act as scouring As the glaciers move they act as scouring pads on the ground underneath them.pads on the ground underneath them.

Near the end of the last glacial period, Near the end of the last glacial period, roughly 10,000 years ago, glaciers began roughly 10,000 years ago, glaciers began to retreat to retreat

A retreating glacier often left behind large A retreating glacier often left behind large deposits of ice in hollows between hills deposits of ice in hollows between hills which later melted to create lakes.which later melted to create lakes. Rocks are eroded and mineral deposits Rocks are eroded and mineral deposits

become sediments at the bottom of the lakebecome sediments at the bottom of the lake Some suspended minerals are used by algae Some suspended minerals are used by algae

for growth, making the water appear greenfor growth, making the water appear green

The Great The Great Lakes in Lakes in northern U.S. northern U.S. are the are the largest glacial largest glacial lakes in the lakes in the world.world.

The Seven Rila Lakes in Rila, The Seven Rila Lakes in Rila, BulgariaBulgaria

Lake Jokulsarlon, in Lake Jokulsarlon, in Iceland. Iceland.

Oxbow LakesOxbow Lakes

Formed by meandering Formed by meandering rivers rivers

Loops of river gets cut off Loops of river gets cut off Lakes are long and Lakes are long and

narrow, and usually U-narrow, and usually U-shapedshaped

Common in low valleys Common in low valleys and flat coastal areasand flat coastal areas

Oxbow LakeOxbow Lake

An oxbow in the making: meanders An oxbow in the making: meanders and sandbank deposition on the and sandbank deposition on the Nowitna River, AlaskaNowitna River, Alaska

How Does an Oxbow Lake How Does an Oxbow Lake Form?Form?

(1) On the inside of the loop, the river (1) On the inside of the loop, the river travels more slowly leading to travels more slowly leading to deposition of silt. deposition of silt.

(2) Meanwhile water on the outside edges (2) Meanwhile water on the outside edges tends to flow faster, which erodes the tends to flow faster, which erodes the banks making the meander even wider. banks making the meander even wider.

(3) Over time the loop of the meander (3) Over time the loop of the meander widens until the neck vanishes widens until the neck vanishes altogether.altogether.

(4) Then the meander is removed from (4) Then the meander is removed from the river's current and the the river's current and the horseshoe shaped oxbow lake is horseshoe shaped oxbow lake is formed. formed.

-- Without a current to move the -- Without a current to move the water along, sediment builds up water along, sediment builds up along the banks and fills in the lake. along the banks and fills in the lake.

Oxbow LakeOxbow Lake

Oxbow lake and the Chippewa River Oxbow lake and the Chippewa River in in Eau Claire, Wisconsin. Eau Claire, Wisconsin.

PlayasPlayas Formed from multiple things Formed from multiple things

that leave a depressionthat leave a depression Soil erosion, wind, animal Soil erosion, wind, animal

herdsherds

Small, shallow, and circularSmall, shallow, and circular Common in dry plains areasCommon in dry plains areas These lakes are ephemeral, These lakes are ephemeral,

and only form at certain and only form at certain times of the yeartimes of the year

Playas are important habitat for Playas are important habitat for migratory birds and waterfowl. migratory birds and waterfowl.

The Red-winged Blackbird, Blue-winged The Red-winged Blackbird, Blue-winged Teal, and the Mallard can all be found in Teal, and the Mallard can all be found in playa lakes at some time of the year. playa lakes at some time of the year. 

Sandhill cranes winter in playa lakesSandhill cranes winter in playa lakes

Playa lakes in Kansas Playa lakes in Kansas agricultural areaagricultural area

Man-Made LakesMan-Made Lakes

Lake Mead is formed as Lake Mead is formed as a result of damming the a result of damming the Colorado River by the Colorado River by the Hoover Dam in NevadaHoover Dam in Nevada

Water reservoirs formed fromWater reservoirs formed from Damming riversDamming rivers Old rock quarries or minesOld rock quarries or mines Stock ponds on farms and ranchesStock ponds on farms and ranches

Zipingpu Dam on the Min River in Zipingpu Dam on the Min River in ChinaChina

Lentic HabitatsLentic Habitats

Characterized byCharacterized by The shorelineThe shoreline The sides of the The sides of the

basinbasin The surface of The surface of

the waterthe water The bottom The bottom

sedimentssediments

Zones of Lentic HabitatsZones of Lentic Habitats

Littoral Littoral zonezone

Limnetic Limnetic zonezone

Profundal Profundal zonezone

Littoral ZoneLittoral Zone

Along shore where light can penetrate Along shore where light can penetrate to the bottomto the bottom

Rooted plants can growRooted plants can grow Shores have coarse sediments from action Shores have coarse sediments from action

of wavesof waves Sheltered areas have finer sediments (silt Sheltered areas have finer sediments (silt

and clay) – plant growth in this zoneand clay) – plant growth in this zone Animal life includesAnimal life includes

Invertebrates common to lotic habitatsInvertebrates common to lotic habitats Small fishSmall fish

Limnetic ZoneLimnetic Zone

Upper open water area of a pond Upper open water area of a pond or lakeor lake

Lack of rooted plants because light Lack of rooted plants because light can’t penetrate the bottomcan’t penetrate the bottom

Plankton and fish are commonPlankton and fish are common

Profundal ZoneProfundal Zone

Deep, bottom-water areaDeep, bottom-water area No light penetration No light penetration No photosynthetic organisms or No photosynthetic organisms or

rooted plantsrooted plants Sediments are silt and clay mixed Sediments are silt and clay mixed

with organic matter that settles to with organic matter that settles to the bottomthe bottom

Organisms living here are tolerant Organisms living here are tolerant of little or no light or oxygenof little or no light or oxygen..

Biological ProductivityBiological Productivity

The amount of plankton, algae, The amount of plankton, algae, aquatic macroinvertebrates and fish aquatic macroinvertebrates and fish that a body of water can produce that a body of water can produce and sustainand sustain

Usually limited to the depth of light Usually limited to the depth of light penetrationpenetration Light penetration is limited by color of Light penetration is limited by color of

the water and amount of suspended the water and amount of suspended solidssolids

Ponds vs. LakesPonds vs. Lakes

Pond = body of Pond = body of water where light water where light penetrates all the penetrates all the way to the bottomway to the bottom

Lake = depth of light Lake = depth of light penetration varies penetration varies from several inches from several inches to several feetto several feet

Determining the Trophic Determining the Trophic StateState

Total Plant NutrientsTotal Plant Nutrients Phosphorous and nitrogen are needed Phosphorous and nitrogen are needed

for plant growth and maintenancefor plant growth and maintenance Certain level is needed (too much or too Certain level is needed (too much or too

little is not a good thing)little is not a good thing) If nutrients are too high, algae blooms If nutrients are too high, algae blooms

occuroccur Increase the turbidity of the waterIncrease the turbidity of the water Decrease the oxygen levelsDecrease the oxygen levels

Chlorophyll AChlorophyll A Measure of the algae populationMeasure of the algae population Influenced by the amount of nutrientsInfluenced by the amount of nutrients

Water Clarity (turbidity)Water Clarity (turbidity) Water clarity determines how far light Water clarity determines how far light

can penetratecan penetrate Phytoplankton and plants need light to Phytoplankton and plants need light to

grow, so they won’t grow if light is grow, so they won’t grow if light is limitedlimited

Algae blooms cause lower water clarityAlgae blooms cause lower water clarity

Characteristics of Characteristics of Biological ProductivityBiological Productivity

4 categories of lake classification 4 categories of lake classification based on biological productivitybased on biological productivity OligotrophicOligotrophic MesotrophicMesotrophic EutrophicEutrophic hypereutrophichypereutrophic

Oligotrophic LakesOligotrophic Lakes

Nutrient level and Nutrient level and productivity is lowproductivity is low

Water is clearWater is clear Low aquatic plants Low aquatic plants

and planktonand plankton Few fishFew fish Sandy bottoms with Sandy bottoms with

little organic materiallittle organic material

Mesotrophic LakesMesotrophic Lakes

Nutrients and Nutrients and productivity is productivity is moderatemoderate

Some aquatic Some aquatic plantsplants

Water clarity is Water clarity is becoming becoming somewhat cloudysomewhat cloudy

Littoral habitat in a mesotrophic Littoral habitat in a mesotrophic lakelake

Eutrophic LakesEutrophic Lakes Nutrient level and Nutrient level and

productivity is highproductivity is high Large populations of Large populations of

algae, plankton, fish, algae, plankton, fish, plants, and plants, and macroinvertebratesmacroinvertebrates

Frequent plankton bloomsFrequent plankton blooms Sediments with high Sediments with high

organic matter organic matter Water is commonly Water is commonly

coloredcolored

HypereutrophicHypereutrophic

Nutrient levels and Nutrient levels and productivity are very productivity are very highhigh

Large populations of Large populations of aquatic plants and aquatic plants and animalsanimals

Frequent plankton Frequent plankton bloomsblooms

Sediments with most Sediments with most organic matterorganic matter

Ponds and Shallow LakesPonds and Shallow Lakes

Temperature and dissolved oxygen Temperature and dissolved oxygen remains about the same from top to remains about the same from top to bottombottom

Water is easily mixed by the windWater is easily mixed by the wind Photosynthesis and plant growth can Photosynthesis and plant growth can

occur from top to bottom (since light occur from top to bottom (since light can penetrate all the way down)can penetrate all the way down)

Deep LakesDeep Lakes

Water temperature and dissolved Water temperature and dissolved oxygen levels can remain same from oxygen levels can remain same from top to bottom layers in the wintertop to bottom layers in the winter

During warm summer months, During warm summer months, layers formlayers form The surface if warmed up by the sunThe surface if warmed up by the sun Denser, colder water remains below itDenser, colder water remains below it Doesn’t get mixed by the windDoesn’t get mixed by the wind

Fall TurnoverFall Turnover

Effects of TurnoversEffects of Turnovers

Mixing of once layered water returns Mixing of once layered water returns oxygen levels to the deep areas. oxygen levels to the deep areas.

Areas in the south have one turnover Areas in the south have one turnover per year in the fall.per year in the fall.

In the north, lakes become stratified in In the north, lakes become stratified in the summer and the winter (because the summer and the winter (because ice forms on the surface, causing ice forms on the surface, causing inverse stratification). Thus, there are inverse stratification). Thus, there are two turnovers (fall and spring).two turnovers (fall and spring).

Zones of StratificationZones of Stratification

Three distinct layers form in deep Three distinct layers form in deep lakes during the summer months:lakes during the summer months: EpilimnionEpilimnion MetalimnionMetalimnion HypolimnionHypolimnion

EpilimnionEpilimnion Warmest zone near the Warmest zone near the

surfacesurface Circulates freely with Circulates freely with

varying temperatures varying temperatures according to location on according to location on the globethe globe

Wind and currents mix Wind and currents mix surface watersurface water

Most organisms found in Most organisms found in this layerthis layer

Area of greatest Area of greatest productivityproductivity

Greatest light penetrationGreatest light penetration Greatest oxygen contentGreatest oxygen content

MetalimnionMetalimnion

Middle layerMiddle layer Steep declines in Steep declines in

temperature temperature (area of the (area of the thermocline)thermocline)

Temp. decreases Temp. decreases 11ooC per meter of C per meter of depthdepth

HypolimnionHypolimnion Third layerThird layer Deep and cold with little to no temperature changeDeep and cold with little to no temperature change Low oxygen due to few or no plantsLow oxygen due to few or no plants Little to no mixing by windLittle to no mixing by wind Bottom-dwelling organisms and bacteria feed on Bottom-dwelling organisms and bacteria feed on

organic matter and further deplete the oxygenorganic matter and further deplete the oxygen Little or no light penetrationLittle or no light penetration

Ecological SuccessionEcological Succession Lakes and ponds evolve differently then Lakes and ponds evolve differently then

flowing water ecosystems.flowing water ecosystems.

Over time, sediments become higher on Over time, sediments become higher on the floor of ponds and lakes, and build up. the floor of ponds and lakes, and build up. The shallower the lake becomes, the The shallower the lake becomes, the further light can penetrate, so more further light can penetrate, so more plants grow on the bottom.plants grow on the bottom.

Water tolerant plants and shrubs move in. Water tolerant plants and shrubs move in. Marshes, swamps, and bogs are usually Marshes, swamps, and bogs are usually

the mature stage of a lake.the mature stage of a lake.

A lake gradually A lake gradually fills with organic fills with organic and inorganic and inorganic sediments, sediments, shrinking the shrinking the area of the pondarea of the pond

A bog forms, then A bog forms, then a marshy areaa marshy area

Finally, a Finally, a meadow meadow completes the completes the succession stagessuccession stages