Energy Pathways in Streams Secondary consumers

carnivory

Primary consumers

Dissolved organic matter

Groundwater exudates

exudates

coagulation and precipitation

Photosynthesis

Autochthonous primary production

Allochthonous primary production

herbivory detritivory

senescence

Stream Autotrophs •  Benthic algae

-  Single independent cells, often colonial (e.g., filamentous algae)

-  Each cell has nucleus, chloroplast, reproduction by cell division

-  Some cells specialized, but no tissues, vascular system, etc.

•  Macrophytes •  - multi-celled, tissues (e.g.,

reproductive, vascular)

Benthic Algae •  1) Diatoms (Bacillariophyta)

-  small, silicon frustules -  Many growth forms

-  Unicellular or colonial -  Mucilage

-  Allows adherence in fast flows

-  low C/N ratio -  Significance?

Didymosphenia geminata (aka Didymo) A stalked diatom

aka “rock snot”

Distribution in North America (2008) Didymo is spreading from historical northern, low nutrient waters to lower latitudes with more nutrient-rich waters

A threat in New Zealand

Poudre River

2) Green Algae (Chlorophyta) – different growth forms

• mostly filamentous in streams -  distinct chloroplasts -  high C/N ratio

- Significance?

Holdfasts for some marine algae

Oedogonium holdfast

How do these filaments resist erosion in fast-flowing water?

- Holdfast (specialized cell)

Blue green Algae (Cyanophyta) -  Mostly filamentous in streams -  no chloroplasts! (chlorophyll is

distributed throughout cell) -  Convert N2 gas to NO3

- (nitrate)

in anoxic heterocysts (gives advantage over green algae in N-poor water)

-  ______ C/N ratio

A commensalism between blue green alga and chironomid

Nostoc alga

Cricotopus midge

Commensalistic relationship?

•  Algal Mats and confusing terminology –  Periphyton: (“around the plant”)

•  Includes algae, microbial biofilm and detritus •  Most commonly used in context of algal biomass (“periphytic biomass”) •  Algal component alone is assessed either by examining under microscope,

or by assaying for chlorophyll-a (measure of living biomass) –  Biofilm: organic microlayer on substrates [Fig. 5.5]

•  includes bacteria and fungi (heterotrophs); may include some algae –  Aufwuchs: everything: periphyton + biofilm + micro-metazoans

•  (rather antiquated term now) BIOFILM Autotrophic inputs:

• algae Heterotrophic inputs:

• DOM-COM-POM • bacteria, fungi

Matrix: • Polysaccharide fibrils produced by bacteria and fungi • Extacellular release and cell death release enzymes and other molecular products

The “architecture” of Periphyton mats 1) Idealized Periphyton Mat: much like a forest, with “overstory”

and “understory” species [Fig. 3, Steinman]

–  Vertical placement of algal cells/species depends on growth forms

•  prostrate (adnate), stalked, filamentous, filamentous w/epiphytes

2) “Real” Periphyton Mat: addition of detritus to mat disrupts “ideal” architecture

Conceptual Model What factors regulate accrual vs. loss of algal biomass (Biggs, Fig. 6.2)

Factors that control algal growth and biomass (1) Light

–  growth response [Fig. 4.3] •  Shape of response (note saturation) •  Growth history (note light-adapted vs.

shade-adapted algal growth rates) •  Difference among species (BG’s do well at

high light intensity)

–  What factors control light in a stream? •  insolation, depth, turbidity

–  Attenuation of light in mat [draw]

shade

light

Distance from surface of mat 0 max

% of ambient light

100

min

How well would cells grow at bottom of mat?

What happens when these cells die?

(2) Nutrients … what are some? Phosphorous as PO4

-3 [phosphate] Nitrogen, mostly as NO3

- [nitrate] Carbon, mostly as HCO3

- [bicarbonate], some CO2 Silicon, as H4SiO4

[orthosilicic acid] excess PO4

-3

-  Phosphorous - most often limiting in freshwater (ratio N:P is > 16:1)

-  Nitrogen - bluegreen algae can “fix” atmospheric N2 gas to NO3

-. -  Advantage when N:P ratio < 16:1

-  Carbon - can be limiting in “soft” water (low HCO3

- availability) [Fig. 4.11] -  Silicon - rarely limiting for diatoms

-  (Redfield Ratio - C:Si:N:P = 106:15:16:1)

REDFIELD RATIO - molecular ratio of organic compounds in algae when nutrients are not limiting: C:N:P ratio generally around 106:16:1

•  (3) Current – Enhances diffusion rates (physiological enrichment)

•  Delivery of nutrients •  Disposal of wastes

Algae grown in streamside troughs for 30 days on tiles at 3 velocities

Short filaments

and diatoms

Green, BG filaments

–  Increases shear stress •  Different growth forms

favored – Diatoms (small) in faster

velocity, short filamentous –  Filamentous G, BG (large

filaments) in slower

•  Often inverse relation of algal biomass with current)

Why is chl-a the Y-axis?

•  (4) substrate – Texture and Size

•  Epi- lithic (on stone) •  pelic (on mud) •  psammic (on sand) •  phytic (on plant)

•  (5) Temperature -  greens and bluegreens do better at higher

temperatures and higher light intensities -  diatoms year-round -  seasonal shifts not as pronounced as in lakes

•  (6) Grazers (herbivory) – Mouthpart morphology determines “depth” of foraging in peiphytic mats

Snail radula rasping & scraping (some caddisflies)

Baetis mayfly gathering & biting

Heptagenia mayfly scraping & gathering

Diatoms

Green, BG filaments

What might this pattern look like if you grazing insects and snails are present in the stream??

•  (7) sloughing – autogenic process: does not require

current. Why?? [Fig. 5, Tuchman]

Colonization and cell growth

Increasing cell density

Shading and death of anchor cells Sloughing

** What other process can cause bare substratum? **

•  (8) disturbance -  substrate instability, scouring [Fig. 1, Peterson] -  response depends on

-  age of mat (timing) [Fig. 6, Peterson] -  Which “successional age” most resistant (i.e., doesn’t change

in response to scour)? -  (succession = change in species composition and biomass

over time)

•  Macrophytes –  Bryophytes (mosses) –  Angiosperms (flowering plants)

-  Characteristics of BRYOPHYTES -  attached -  Require free CO2 (can’t use HCO3) for

photosynthesis -  Common in turbulent streams with low pH …

why?? -  High CO2 from mixing with air -  Reduced boundary layers -  angiosperms absent

-  sensitive to disturbance [Fig. 4.10]

•  Characteristics of ANGIOSPERMS -  rooted (Temperate streams) -  none restricted solely to lotic -  most common in low energy habitats (silt,

low gradient) -  phenotypic variation for lotic survival …

-  smaller leaves -  shorter internodes -  vegetative reproduction

•  Phytoplankton Are there true lotic plankton?