Transcript Aquatic Ecosystem Overview:

Aquatic Ecosystem Overview:
• We need to understand the physical (e.g. hydrodynamics) and
chemical environment that ultimately control the productivity,
interactions, and evolution of life in aquatic ecosystems.
• Organisms reside in habitats characterized by their physicochemical
setting, perform a particular niche or function, and represent a
particular trophic level.
• Individual organisms are members of a population, which interacts
with other populations within a community.
• Ecosystems may possess multiple community types based on
groupings of common habitat and/or niche characteristics.
– Littoral (fringe with light)
– Plankton (drifting)
– Detritus (dead organics)
- Benthic (bottom)
- Nekton (swimming)
- Groundwater (subsurface; hyporheic)
The Lake
Example:
Know your lake regions
for benthic and open
water habitats.
(Cole, 1994; Fig 2.1)
Temperate lake formed by
geological faulting, depicted
during the summer season.
Density differences due to
temperature result in stable
layers, or strata. This process
is called stratification.
Why the difference in
O2 and CO2?
Biological Productivity (Trophic Status)
Volumetric units: mg C/m3/d
(Rawson Diagram):
Areal units: mg C/m2/d
(Cole, 1994; Fig 1.1)
Productivity and Trophic Status
• Ecosystem productivity is generally classified according to trophic
states for convenience (see Dodds pp 337-341):
– Oligotrophic (low)
– Mesotrophic (medium)
– Eutrophic (high)
• These states represent ranges within a continuum of potential
productivity within a system.
• The impetus for identifying trophic state came from observations that
certain biota (from algal to fish species) were often associated with
specific nutrient levels.
• Being able to classify systems is convenient for comparison of
different areas as well as for defining management goals and
reference points.
• Trophic state is generally defined as a function of phytoplankton
biomass / chlorophyll concentrations, nutrient concentrations, and/or
water clarity.
Probability Distribution
(Dodds, 2002; Fig. 17.2)
Fixed Boundary Classifications
OECD = Organization for Economic Cooperation and Development
Total P = phosphorous in dissolved and solid forms; inorganic and organic.
Mean Chl = annual average of chlorophyll a.
Mean Secchi = average depth to which a black and white disc can no longer be seen.
(Dodds, 2002)
Continuous Value Scale
(Carlson, 1977)
(Dodds, 2002; Fig. 17.2)
Stream Ecosystems
• Unless flow is slow enough, stream systems
usually do not have a truly planktonic biomass of
primary producers. Trophic state is measured by:
– Attached benthic algae (periphyton) biomass
– Nutrient (N & P) concentrations
• Due to dependence of streams on terrestrial
(allocthonous) organic matter, primary producers
are not always a good indicator of system
productivity.