FRESHWATER BIOMESFreshwater biomes are usually

characterized by a salt concentration of less than 1%.

Freshwater biomes are closely linked to the soils and biotic components of the terrestrial biomes through which they pass or in which they are situated.

The particular characteristics of a freshwater biome are also influenced by the patterns and speed of water flow and the climate to which the biome is exposed.

LAKES and PONDS

Lakes and PondsLarge(Lakes) and Small(Ponds), natural bodies of standing fresh waterFormed when depressions in earth’s surface are filled with:

Precipitation Runoff Groundwater

Large lakes may have many of same characteristics as oceans

Classification Depending on the amount of organic matter

produced.

OLIGOTROPHICdeepcoldsmall surface area relative to depthnutrient-poorphytoplankton are sparse, not very

productivedon’t contain much lifewaters often very clearsediments low in decomposable organic

matter

MESOTROPHICmoderate nutrient contentmoderate amount of phytoplanktonreasonably productive

EUTROPHICshallowwarmlarge surface area relative to depthnutrient-richphytoplankton more plentiful and productivewaters often murkyhigh organic matter content in benthos

leads to high decomposition rates and potentially low oxygen

EUTROPHICATION Oligotrophic lakes may develop into eutrophic lakes over

time.

Runoff from surrounding terrestrial habitats brings in mineral nutrients and sediments.

Human activities increase the nutrient content of runoff due to lawn and agricultural fertilizers; municipal wastes dumped into lakes dramatically enriches the nitrogen and phosphorus concentrations which increases phytoplankton and plant growth.

Algal blooms and increased plant growth results in more detritus and can lead to oxygen depletion due to increased decomposition.

The lake environment is generally classified on the basis of three criteria:

1. LIGHT PENETRATION

• Photic Zone• Aphotic Zone

2. DISTANCE FROM THE SHORE AND WATER DEPTH

• Littoral Zone• Limnetic Zone

3. OPEN• Pelagic Zone

BOTTOM • Benthic Zone

ZONATION IN A LAKE

Littoral Zoneshallow, well-lit, close to shore.rooted and floating plants flourish

Limnetic Zonewell-lit, open surface water, farther from shore, extending to depth

penetrated by lightoccupied by phytoplankton, zooplankton, higher animalsproduces food and oxygen that supports most of lake’s consumers

Profundal Zoneconsists of deep, aphotic regionstoo dark for photosynthesisoxygen levels are lowinhabited by fish adapted to cool dark waters

Benthic Zonebottom of lakeinhabited by organisms that can tolerate cool temperatures and

low oxygen levels

WETLANDSareas of standing water that support aquatic plantsamong the richest biomes for its diverse communitiesmarshes, swamps, and bogs are considered wetlandscan be freshwater or saltwaterplant species adapted to the very moist and humid

conditions are called hydrophytes

RIVERS and STREAMSbodies of water that move continuously in one

direction

water changes from their point of origin (headwaters) to where they empty into a larger body of water (mouth)

In the headwaters, the water is cold and clear, carries little sediment, and has few mineral nutrients.

Near the mouth, water moves slowly and is more turbid due to sediment entering from other streams and erosion; the nutrient content is also higher.

Source Zonecontains headwaters (headwater streams)often begins as springs or snowmeltcoldclearcarries little sedimentcontains relatively few nutrientschannels usually narrowcurrent is swiftsubstrate is rocky

Transition Zonecontains wider, lower elevation streamsstreams join to form tributarieswarmerless clearcarries more sedimentcontains more nutrientschannels usually widercurrent is slowersubstrate begins to accumulate silt

Floodplain Zonetributaries join to form rivers

which empty into oceans at estuarieswarmer stillmurkycarries substantially more sedimentcontains substantially more nutrientschannels wider, wide mouthcurrent relatively slowsubstrate silty from deposition of sediment