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Limnology > Food Sources in lotic systems > Flashcards

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?

A

Bacteria

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
Q

What is dissolved organic matter a major source of for heterotrophic microorganisms?

A

Major C source

26
Q

What are two important fractions of DOM?

A

Organic N and P

27
Q

Where does 30% of Dissolved Organic Matter come from?

A

Terrestrial ecosystems

28
Q

What are three instream sources of DOM?

A
  • Leaching of CPOM and FPOM (30% = terrestrial)
  • Exudates (fluid) from algae, higher plants, heterotrophs and animal excretions
  • Soil and groundwater
29
Q

Where is DOM mainly present in rivers?

A

Lowland rivers

30
Q

What is DOM dominated by?

A

Macroinvertebrate collectors

31
Q

What removes DOM from lotic water?

A

Abiotic and biotic processes

32
Q

Describe how abiotic processes remove DOM from the water

A
  • 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
Q

Describe how biotic processes remove DOM from the water

A
  • Uptake by microorganisms & assimilation of the Organic C into microbial biomass
  • Consumption of this heterotrophic production
  • Mineralization to CO2 by community respiration
34
Q

What is autumn shed leaves?

A

Major organic matter input for small temperate (broadleaved) forested streams

35
Q

What are the key processes for when leaves enter the stream?

A
  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
Q

Describe stage 1. Leaves Become wetted in detail

A
  • Leach solute organic and inorganic (N,P) constituents

- Leaching of 25% initial dry weight occurs over the first 24hrs

37
Q

Describe stage 2. Microbial colonization

A
  • 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
Q

Describe stage 3. Fragmentation

A

The leaves are broken up the river flow

39
Q

Describe stage 4. Macroinvertebrate activity

A
  • 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
Q

Where does the energy requirements for shredders come from?

A

From the detritus

-A poor food source- so shredders must consume large quantities

41
Q

What factors affect the rate of breakdown of Autumn shed leaves?

A
  1. Variation in timing of leaf fall
  2. Chemical and structural differences of leaves
  3. Feeding activities of detritivores
  4. Environmental variables
42
Q

Describe 1. Variation in timing of leaf fall

A

Things are changing/ climate

43
Q

Describe 2. Chemical and structural differences among leaves

A
  • 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
Q

What are the fastest type of leaves to decay?

A

-Submerged and floating macrophytes are among the fastest to decay (<30 days) - contain least amount of support material (cellulose)

45
Q

What can inhibit leaf decay?

A

-Chemical inhibitors also impede leaf decay eg. tannins through outer coatings on the cuticle of conifer needles slow fungal invasion

46
Q

Describe 3. Feeding activity of detritivores

A
  • Species-specific rates of leaf conditioning by aquatic fungi
  • Diversity of aquatic fungi present
  • Presence of microbial populations
47
Q

Describe 4. Environmental variables

A

-Breakdown rates are faster at warmer temperatures in nutrient rich systems

48
Q

What are three other factors that Affect the Process of Autumn shed leaves?

A
  • 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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