•Lakes have zonation structured by physical forces such as light, wind and waves.

•different zones in the lake had different types of plants and animals

http://www.d.umn.edu/~seawww/depth/rivers/art/figure1_4.jpg

The River Continuum Concept•Zones in a river system are less distinct•But they are functionally very important

Physical forces change gradually along a river•Elevation ↓•Slope ↓•Temperature and nutrients ↑ •Drainage area and discharge ↑•Width of channel and floodplain ↑•Mean velocity ↑•Mean depth ↑•Turbidity ↑•Sediments, erosional, alluvial, to depositional

•Shading ↓•Periphyton, macrophytes ↑, then ↓ •Phytoplankton and zooplankton ↑ •Coarse detritus input highest upstream•Fine detritus accumulates downstream•Benthic invertebrate community changes

shredders, grazers, collectors•Fish community changes

•Cold water to warm water species

Allochthonous input—Detritus processing

•Dead plant biomass breaks down slowly and their nutrients can remain tied up in as organic detritus for long periods of time

•Primary production in many ecosystems depends more on its recycling rate ie mainly decomposition of plant detritus, than on loading rates

•Aquatic plants break down more rapidly than terrestrial plants, and woody plants are very slow to decompose because they contain lignin, which most bacteria and fungi can’t digest.

Leaf processing•Wetting and breadown of cuticle•Leaching of soluble components (DOM)•Colonization by bacteria and fungi•Increase in protein content•Colonization by invertebrates•Enhances microbial action•Breakdown into small fragments

Invertebrate detritiivores find leaves much more to their liking after they have been colonized by bacteria and fungi

Shredders enhance microbial action(bacteria & fungi)

•convert CPOM to FPOM

•Food for microdetritivores

Detritus processing in a stream

Processing of FPOM by microdetritivores

Shredders-macrodetritivores collectors-microdetritivoresFilter-feeders, deposit-feeders

Litter bag experiments have been used to study decomposition of detritus

Weight remaining %

0.5 mm mesh

100 %

10 20 30

2 mm meshLarger invertebrates get into the litter bags if the mesh is coarse

•Nutrient content of the detritus, especially N greatly increases decomposition rate,

•as does increased temperature

•and mesh size

days

The interplay between the autochothonous and the allochtonous food chain

Allochthonous input Autochthonous input

http://www.btwatershed.org/Newsletter/2002Newsletter/Fall2002/nabs%20river%20continuum%20concept20%25.jpg

•Mountain and prairie headwater streams are unshaded

•Therefore less detritus dominated than eastern deciduous streams which start at lower altitude

•Their seasonal range of discharges also tends to be higher than most eastern streams.

Stream Fragmentation, A wier blocking fish movement

a hanging culvert can block fish movement

http://www.nzfreshwater.org/thumbnails/culvert.jpg

http://www.cee.mtu.edu/~dwatkins/images/aqua3pics/hatchery-weir.jpg

The River Discontinuum: Dams and wiers

Dams/Reservoirs interrupt the river continuum