Energy Pathways in Streams

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Randell Cross
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1 Energy Pathways in Streams Secondary consumers carnivory Primary consumers herbivory detritivory coagulation and precipitation senescence Autochthonous primary production Photosynthesis Allochthonous primary production exudates Dissolved organic matter exudates Groundwater

reproduction by cell division - Some cells specialized, but no tissues,

2 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)

3 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?

4 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 nutrientrich waters Poudre River A threat in New Zealand

5 2) Green Algae (Chlorophyta) different growth forms mostly filamentous in streams - distinct chloroplasts - high C/N ratio - Significance?

6 How do these filaments resist erosion in fast-flowing water? - Holdfast (specialized cell) Holdfasts for some marine algae Oedogonium holdfast

7 Blue green Algae (Cyanophyta) - Mostly filamentous in streams - no chloroplasts! (chlorophyll is distributed throughout cell) - Convert N 2 gas to NO 3 - (nitrate) in anoxic heterocysts (gives advantage over green algae in N- poor water) - C/N ratio

8 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 )

5] includes bacteria and fungi (heterotrophs); may include some algae Aufwuchs: everything: periphyton + biofilm + micro-metazoans (rather antiquated term now) BIOFILM Autotrophic inputs:

9 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

10 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

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

shade-adapted algal growth rates) Difference among species (BG s do well at high light intensity) What factors control light in

12 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] 100 shade light % of ambient light How well would cells grow at bottom of mat? min What happens when these cells die? 0 max Distance from surface of mat

13 (2) Nutrients what are some? Phosphorous as PO 4-3 [phosphate] Nitrogen, mostly as NO 3 - [nitrate] Carbon, mostly as HCO 3 - [bicarbonate], some CO 2 Silicon, as H 4 SiO 4 [orthosilicic acid] excess PO 4-3 REDFIELD RATIO - molecular ratio of organic compounds in algae when nutrients are not limiting: C:N:P ratio generally around 106:16:1 - Phosphorous - most often limiting in freshwater (ratio N:P is > 16:1) - Nitrogen - bluegreen algae can fix atmospheric N 2 gas to NO Advantage when N:P ratio < 16:1 - Carbon - can be limiting in soft water (low HCO 3 - availability) [Fig. 4.11] - Silicon - rarely limiting for diatoms - (Redfield Ratio - C:Si:N:P = 106:15:16:1)

(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 Increases shear stress

14 (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 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) Green, BG filaments Short filaments and diatoms Why is chl-a the Y-axis?

15 (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

16 (6) Grazers (herbivory) Mouthpart morphology determines depth of foraging in peiphytic mats Baetis mayfly gathering & biting Heptagenia mayfly scraping & gathering Snail radula rasping & scraping (some caddisflies)

17 What might this pattern look like if you grazing insects and snails are present in the stream?? Green, BG filaments Diatoms

18 (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? **

19 (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)

21 Macrophytes Bryophytes (mosses) Angiosperms (flowering plants) - Characteristics of BRYOPHYTES - attached - Require free CO 2 (can t use HCO 3 ) for photosynthesis - Common in turbulent streams with low ph why?? - High CO 2 from mixing with air - Reduced boundary layers - angiosperms absent - sensitive to disturbance [Fig. 4.10]

22 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?

Stream Autotrophs. Benthic 10/3/13

Stream Autotrophs. Benthic 10/3/13 Stream Autotrophs Benthic -, often colonial (e.g., filamentous algae) - Each cell has nucleus, chloroplast, reproduction by cell division - Some cells specialized, but no tissues, vascular system, etc.