Freshwater Aquatic Ecosystems

What do we mean by freshwater?

Low salt concentration

Types of freshwater ecosystems

Lentic (lacustrine) - still water

Lotic (riverine) - flowing water

Lakes

Lentic

Slowly flowing or non flowing open body of water

In a depression, not in contact with ocean

There are more

small lakes then large lakes (majority in northern hemisphere)

Many Processes form

lakes

Tectonic

formed by movement of the earths crust

Kettle (pothole)

glacial ice is buried in till as the glacier retreats

Moraine

Glacial activity forms dams of debris

Earthside

earth dams a river or stream

Caldera

volcanic activity forms a hole that fills with water

Dissolution

Limestone dissolves and forms a lake

Oxbow

River changes course, “pinching off” a bend

Lakes made my organisms

beavers, bison, alligators, HUMANS

Lake habitats - distance from shore

Litoral zone, Limnetic zone, Photic zone, Aphotic zone

Litoral zone

Shallow near shore, Light penetrates all the way to the bottom, Aquatic plants, young fish

Limnetic zone

Deep water, organized by light and temperature

Photic zone

Depths that light can penetrate

Aphotic zone

water too deep for light to penetrate

Lake habitats - organized by temperature

Epilimnion, thermocline (metalimnion), hypolimnion

Epilimnion

warm water, same temperature through the layer (well mixed)

Thermocline (metalimnion)

Temperature cools rapidly with depth

Hypolimnion

Cold water, same temperature through the layer

Epilimnion and hypolimnion

don’t mix well because in summer cold water more dense than warm water, but can mix in the fall

Streams

flowing water, arranged in networks, measure in terms of flow and discharge

Velocity

how fast the water is flowing

Discharge

the volume of water passing through a channel per unit time

Watershed

The land that is drained by a defined section of the stream network (also called a catchment)

Stream order

smallest = 1

1 makes 2

2 makes 3

Generally there are more

low order streams

stream flow is maintained by

groundwater, fed by precipitation

thalweg

region of the cross section of stream where the velocity is fastest

Riffle

fast, shallow flow over boulders and cobbles which break the water surface

Pool

areas of slow flowing, deep water, often on the outside of bends

Run

smooth, unbroken flow, connecting riffles and pools

Riparian zone

area immediately adjacent to the stream

Floodplain

area from the stream back to base of the enclosing valley that floods during periods of high flow

What do streams transport?

dissolved materials, particulate materials

dissolved materials

cant be filtered out, typically evenly distributed, natural compounds, pollutants

pollutants

metals, nutrients, pharmaceuticals, acidic compounds, road salt

Total dissolved solids

total amount of dissolved materials in the water

particulate materials

larger particles, may be visible, can settle out

Water erosion

When water flow removes dissolved or solid material and transports it to and deposits it somewhere else

Deposition

sediments, soil, rocks, are added to a landmass

total suspended solids

total amount of particulate materials in the water

Why are sediments important?

Transport nutrients downstream, provide substrate for aquatic organisms in depositional areas, form deltas

River delta

triangularly-shaped landform at the mouth of rivers created by deposition of sediments

Wetlands

diverse ecosystems with unique vegetation, water-loving plants, and soil influenced by a high water table.

Hydrophytes

water loving plants

Hydric soils

frequently inundated and anaerobic

Marsh

dominated by water-tolerant herbaceous plants (not woody plants)

Swamp

dominated by water-tolerant woody plants

Bog

accumulates peat (decaying peats), acid, low nutrients, often has lots of moss

Fen

Accumulates peat, fed by groundwater, more basic than bogs, often has lots of moss

Wetlands often fluctuate

in depth