Aquatic Ecosystems

Organic Inputs! Allochthonous organic matter

! Organic matter that is derived from outside the system (in lakes, this is usually leaves, needles, wood, and twigs from terrestrial vegetation)

! Autochthonous organic matter! Organic matter derived within the system (in lakes,

this is usually algae, mosses, and aquatic vascular macrophytes)

Trophic Properties! Autotrophic - production within the system

exceeds respiration! This is often expressed as the ratio of production to

respiration (P/R)! In autotrophic systems, P/R > 1

! Heterotrophic - respiration within the system exceeds production! In heterotrophic systems, P/R < 1

Major Habitats of Lentic Ecosystems

! Planktonic - free-floating! Phytoplankton - free-floating algae! Zooplankton - free-floating animals with limited

powers of locomotion! Tychoplankton - Suspended benthic organisms

(not true plankton)! Metaphyton - Phytoplankton existing within the

macrophyte communities of littoral zones

Nekton

! Nekton - free-swimming! Some organisms (such as larvae of fish) can

shift between planktonic to nektonic existence within their life cycle

Pleuston! Pleuston - organisms adapted to the habitat of

the air-water interface! Neuston - the microscopic component of the

pleuston! Epineuston or epipleuston are those forms that exist

on top of the water's surface! Hyponeuston or hypopleuston are those forms that

exist under the water's surface but still are associated with the air-water interface

Benthos

! Benthos - organisms that live on the bottom of a lake, stream, or river

! Benthic is the adjective that is used to describe organisms that live on the bottom

Benthos! The film of algae, bacteria, fungi, and

microscopic invertebrates that exist on substrates is known as periphyton! Periphyton literally refers to organisms living "on

plants" but is most often used in the more general sense

! The term Aufwuchs is sometimes used synonymously with periphyton

! Aufwuchs is a term derived from the German for "growth upon”

! Biofilm is most common recent term

Benthic Communities

! Epilithic - living on rock substrates! Epipelic - living on fine organic sediments

("mud")! Epiphytic - living on plants! Epizooic - living on animals! Epipsammic - living on sand grains

Littoral Zone

! Epilittoral - above the high water level and uninfluenced by spray

! Supralittoral - above the high water level and subject to spray

! Eulittoral - the shoreline region between the highest and lowest seasonal water levels

! Eulittoral plus infralittoral = littoral zone

Littoral Zone! Infralittoral

! Upper infralittoral - zone where emergent rooted macrophytes exist

! Middle infralittoral - zone where floating-leaved macrophytes exist

! Lower infralittoral - zone where rooted or adnatemacrophytes exist

! Littoriprofundal - zone where only photosynthetic algae and bacteria exist (often associated with the metalimnion)

! Profundal - zone where sediments are free of vegetation

Measure of Productionand Abundance

! Production - weight of new organic matter formed over a period of time plus any loss due to respiration, excretion, secretion, injury, death, and grazing

!

! Productivity - the rate of production

Quantity! Standing crop - weight of organic matter that

can be sampled or harvested at one time from a given area (not necessarily the whole plant)

! Biomass - the weight of all living matter in a unit area at a given time (must include the whole plant)

!

! Yield - Standing crop expressed as a rate!

Abundance! Estimation of abundance of organisms

! Enumeration! Volume! Weight

• Dry weight - dried in oven at 55ºC for at least 24 hours• Ash-free dry weight - weight of ash (determined by weighing

the residue after burning sample in furnace at 550ºC for at least 4 hours) is subtracted from the dry weight to determine ash-free dry weight

! Cellular constituents - carbon (40-60% for most plants), nitrogen, phosphorus

! Productivity

P/B Ratios

! Production to biomass ratio (P/B)! High P/B ratio for smaller organisms! P/B generally decreases with increasing size! P/B decreases with increasing trophic level