Aquatic Ecosystems
Chapter 24
Classification of systems

Aquatic systems classified by physical environment
–
Salinity most important
–
Marine divided broadly into coastal and open water
–
Freshwater divided into lotic (flowing water ) and lentic (non-flowing water)

All aquatic ecosystems are linked hydrologically
Lakes

Inland depressions containing standing water
– Ponds are shallow enough to have rooted vegetation in the center

Can be formed by many processes, physical and biological
– Glacial activity
– Geologic movement
– River flow
– Beaver dams
Lake habitats

Light important in lake ecosystems

Temperatures vary
–
Seasonally
–
With depth

Oxygen levels vary
–
Seasonally
–
With depth
Lake zonation

Lakes are divided into vertical and horizontal zones
–
Vertical zones determined by light
 Compensation point important
Compensation depth
Life in lakes

Most life in littoral zone

Inputs organic matter into the system

Fish are flattened to navigate vegetation
Periphyton

Benthic algal growth is abundance in littoral zone

Also called aufwuchs

Limnetic zone

Dominated by zooplankton and phytoplankton

Spring bloom after turnover
Nekton

Fish move to preferred habitat
–
Bass in surface waters (warm water species)
–
Lake trout in deep waters (cold water species)
Profundal zone

Dependent on rain of organic material for energy

Oxygen is limiting

Benthic area is anaerobic
Eutrophication

Process of adding nutrients to an ecosystem

Natural waters vary in their level of eutrophication from oligotrophic to eutrophic
–
Depends on character of local ecosystems, geology, etc.
Eutrophic lakes

Have a high surface to volume ratio

N & P stimulate algal growth

Low oxygen in bottom sediments and deeper lake
Oligotrophic lakes
 Have low surface to water volume ratio
 Clear and blue
 Phosphorus is limiting
 Oxygen remains high in hypolimnion
 Bottom sediments are inorganic primarily

Species diversity is high
Measuring light penetration
 Carlson’s Trophic State Index (TSI)
Dystrophic lake

Receive humic materials from surrounding landscape
Rivers are dynamic

Fast flowing and steep in some areas

Slow flowing and flat in others


Fast streams are 50 cm/s
– Small particles washed away
Slower waters drop sediment
Streams are classified into orders

Single streams are first order

When they join, it becomes second order

Increases in order when a stream of the same order joins it
On a smaller scale…

Pools
– Decomposition

Riffles
– Production
Life in moving habitats

Adaptations for life in currents

Streamlined

Adhesive ability
Fast water species
Slow water species
Invertebrate feeding guilds

Shredders
–
Break down coarse particulate organic matter (CPOM)
Invertebrate feeding guilds

Filtering collectors or gathering collectors
–
Eat fine particulate organic matter (FPOM) and associated bacteria
Invertebrate feeding guilds

Grazers
Invertebrate feeding guilds

Gougers
Invertebrate feeding guilds

Predators
Continuum of environments
Measuring stream flow