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Food Sources in lotic systems Flashcards

1
Q

How are lotic systems sustained?

A

Autotrophs (primary producers)

Surrounding terrestrial ecosystems (organic matter) that are in the catchment

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2
Q

What does organic matter provide for a lotic system?

A

Important energy input in the food web

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3
Q

What are food webs called when they are dominated by Organic matter (OM)?

A

Detrital or detritus based

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4
Q

What are the two dominant sources of food in lotic systems?

A
  • Allochthonous

- Autochthonous

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5
Q

Describe Allochthonous food sources

A
  • Organic matter (OM) or detritus
  • All forms of non-living (OM)
  • Can exceed energy fixed by photosynthesis
  • Headwater streams & lowland rivers
  • Particulate & dissolved forms
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6
Q

Describe Autochthonous food sources

A
  • Primary production - plants and algae
  • Energy is passed onto primary consumers directly via grazing
  • Indirectly by death of plants/ loss of plant parts
  • Middle order stream
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7
Q

What does CPOM stand for?

A

Coarse Particulate Organic Matter

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8
Q

What affects the quantity of CPOM?

A

Depend on inputs, retentivity of the stream bed and presence of decomposer community

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9
Q

What size is CPOM?

A

Greater than 1 mm in size

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10
Q

What affects the leaf litter input into a lotic system

A

Nature of the riparian vegetation

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11
Q

What can be observed in relation to CPOM and increasing stream order?

A

There is a clear decrease in CPOM with increasing stream order

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12
Q

Where is Coarse Particulate Organic matter mainly found?

A

Present in headwater streams and lowland flood plains

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13
Q

What is CPOM dominated by?

A

Macroinvertebrates shredders and collectors

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14
Q

What does FPOM stand for?

A

Fine particulate Organic matter

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15
Q

What size is Fine particulate Organic matter?

A

Particles between 0.5 um and 1 mm

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16
Q

What factors play a role in FPOM availability and transport?

A
  • Flow regime
  • Disturbances
  • Presence of debris dams
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17
Q

Where does FPOM occur on/ associated with

A

The substrate in suspension (movement of gravel, sand, slit)

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18
Q

What are the three major sources of FPOM?

A
  • Breakdown of larger CPOM Via shredders, microbial processes and physical abrasion
  • Faeces and associated microflora
  • Adjacent terrestrial areas via wind and surface runoff
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19
Q

Where is fine particle organic matter present in a river

A

Present in middle order streams

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20
Q

What dominates the microbial community in FPOM?

21
Q

What else dominates FPOM?

A

Macroinvertebrate collectors and shredders

22
Q

What does DOM stand for?

A

Dissolved Organic Matter

23
Q

What size is Dissolved Organic matter?

A

Particles < 0.45 um

24
Q

What percentage of Organic matter does dissolved organic matter contribute?

A

45-50% of Organic Matter in running waters

25
What is dissolved organic matter a major source of for heterotrophic microorganisms?
Major C source
26
What are two important fractions of DOM?
Organic N and P
27
Where does 30% of Dissolved Organic Matter come from?
Terrestrial ecosystems
28
What are three instream sources of DOM?
- Leaching of CPOM and FPOM (30% = terrestrial) - Exudates (fluid) from algae, higher plants, heterotrophs and animal excretions - Soil and groundwater
29
Where is DOM mainly present in rivers?
Lowland rivers
30
What is DOM dominated by?
Macroinvertebrate collectors
31
What removes DOM from lotic water?
Abiotic and biotic processes
32
Describe how abiotic processes remove DOM from the water
- Absorption onto clays and chemical complexing with oxides of AI and FE - Accounts for 1/3 of initial removal of DOM from water - Locked away due to microbial uptake
33
Describe how biotic processes remove DOM from the water
- Uptake by microorganisms & assimilation of the Organic C into microbial biomass - Consumption of this heterotrophic production - Mineralization to CO2 by community respiration
34
What is autumn shed leaves?
Major organic matter input for small temperate (broadleaved) forested streams
35
What are the key processes for when leaves enter the stream?
1. Leaves become wetted 2. Followed by a period of microbial colonization & growth which causes numerous changes in leaf condition 3. Fragmentation by mechanical means 4. Macroinvertebrate activity enhances fragmentation and mineralization
36
Describe stage 1. Leaves Become wetted in detail
- Leach solute organic and inorganic (N,P) constituents | - Leaching of 25% initial dry weight occurs over the first 24hrs
37
Describe stage 2. Microbial colonization
- This growth causes the condition of the leaves to change - Primarily done by aquatic fungi (hyphomycetes) and bacteria - Fungi degrade polysaccharides in cell walls and hyphae penetrate leaf tissue making leaves soft - Alters palpability of leaves for detritivores - Fragments leave material - Converts 75% of leaf mass to FPOM over 6 weeks
38
Describe stage 3. Fragmentation
The leaves are broken up the river flow
39
Describe stage 4. Macroinvertebrate activity
- Shredders bite out the softer parts between the leaf veins leaving a vascular skeleton which is consumed - Feeding activity speeds up breakdown of CPOM to FPOM via creation of smaller particles through fragmentation or in the production of faeces
40
Where does the energy requirements for shredders come from?
From the detritus | -A poor food source- so shredders must consume large quantities
41
What factors affect the rate of breakdown of Autumn shed leaves?
1. Variation in timing of leaf fall 2. Chemical and structural differences of leaves 3. Feeding activities of detritivores 4. Environmental variables
42
Describe 1. Variation in timing of leaf fall
Things are changing/ climate
43
Describe 2. Chemical and structural differences among leaves
- Non woody plant leaves decompose much more quickly than leaves of woody plants (65 days vs. 100-150 days) - Leaves with a high initial nutrient conc. (N&P) decompose rapidly - Leaves with a high lignin content have a very slow breakdown process eg. beech leaves
44
What are the fastest type of leaves to decay?
-Submerged and floating macrophytes are among the fastest to decay (<30 days) - contain least amount of support material (cellulose)
45
What can inhibit leaf decay?
-Chemical inhibitors also impede leaf decay eg. tannins through outer coatings on the cuticle of conifer needles slow fungal invasion
46
Describe 3. Feeding activity of detritivores
- Species-specific rates of leaf conditioning by aquatic fungi - Diversity of aquatic fungi present - Presence of microbial populations
47
Describe 4. Environmental variables
-Breakdown rates are faster at warmer temperatures in nutrient rich systems
48
What are three other factors that Affect the Process of Autumn shed leaves?
- Low pH retards decomposition by inhibiting the activity of microorganisms and invertebrates - Hydrologic fluctuations (flow) can cause abrasion and fragmentation - Metal pollution can decrease decomposition rates by negatively affecting shredders and microorganisms

Limnology (2 decks)

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