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Stream Ecology (NR 280) Topic 6 – Primary Production What is production? Who contributes to primary production? Pros and cons of being an autotroph Taxonomy.

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Presentation on theme: "Stream Ecology (NR 280) Topic 6 – Primary Production What is production? Who contributes to primary production? Pros and cons of being an autotroph Taxonomy."— Presentation transcript:

1 Stream Ecology (NR 280) Topic 6 – Primary Production What is production? Who contributes to primary production? Pros and cons of being an autotroph Taxonomy of autotrophs Regulation of primary production Fate of primary production

2 Production The creation of new, living biomass from other sources of carbon and nutrients Primary production: creation of biomass from inorganic carbon (CO 2 ) and some energy source. Secondary production: creation of biomass from organic sources of carbon (e.g., heterotrophy, herbivory, predation) northlandjournal.com

3 Photosynthesis is the most common form of primary production Photosynthesis Energy Respiration Note that photosynthesis creates new biomass. Respiration utilizes biomass as a resource for activity, growth, and reproduction.

4 Primary production is accomplished by autotrophs Energy source defines classes of autotrophs – Photosynthesis (photoautotrophs): light – Chemosynthesis (chemoautotrophs): chemicals Consider – Does primary production in aquatic ecosystems differ from primary production in terrestrial systems? – Do autotrophs in aquatic systems differ from autotrophs in terrestrial systems?

5 Types of autotrophs in streams Phytoplankton (aka Potamoplankton) – Mostly microscopic algae growing suspended in streams Periphyton (benthic algae) – Microscope to macroscopic algae growing on the stream bottom, attached to various substrate – Most abundant and diverse autotrophic group in streams Macrophytes – Macroscopic, mostly vascular plants in flowing waters – Includes mosses and liverworts (called bryophytes)

6 Phytoplankton Floating, unattached algae Can be important in streams with long water residence times due to: – Large volume – Slow flow Important in large rivers – Mississippi and Nile Algal growth must exceed downstream transport

7 Phylogeny & adaptations Species are adapted to staying in suspension Adaptations include: – Small sizes – Increased surface area and unique shapes – Flagella, to move – Vacuoles for flotation and storage starcentral.mbl.edu microscopy-uk.org.uk

8 Periphyton often reside within a surface biofilm (aufwuchs) Complex community of bacteria, protozoa, small invertebrates (meiobenthos), algae, fungi – Structural protection – Enzymatic activity – Nutrient acquisition & storage Polysaccharide (Slimy!) matrix of organisms

9 Advantages of the periphytic life Consider two points of view in a field of flow – Eularian: viewer is fixed, flow moves past viewer – Lagrangian: viewer floats and moves with the flow Imagine yourself to be an aquatic autotroph – Periphyton live in a Eularian world – Phytoplankton live in a Lagrangian world Why is this important? – Both groups can be equally productive – Resources in the periphytic environment are continuously replenished – Resources in the planktonic environment can be easily depleted

10 Some challenges for the periphytic life It’s necessary to expend resources to produce some way to remain attached to the substrate (glues, basal strands) that penetrate cracks to anchor Remaining close to the stream bottom places you in the boundary layer where resource renewal can be slower. There is competition for resources (e.g., nutrients, space) similar to terrestrial systems. You can’t escape difficult conditions (e.g., high light, high temperature, low water Nevertheless, benthic autotrophs typically contribute the greatest amount of primary production on an areal basis.

11 Periphyton by substrate habitat Epilithon/epilithic Epiphyton/epiphytic Epipelon/epipelic Epipsammon/epipsammic Epidendron/epidendric Epizoon/epizooic On rocks On sediment On sand On wood On animals On plants

12 Examples Epiphytic Chamaesiphon spp. algae on Hygrohypnum moss. (Stream Bryophyte Group 1999) Epilithic green algae on a cobble. (M. Flinn photo) Epipsammon and epipelon on a mudflat. (biomareweb.org)

13 Classification of Aquatic Primary Producers 2 of 3 Kingdoms, 2 of 5 Domains Divisions Cyanobacteria Next Lecture Evolution

14 Habitat (latitude, temperature, pH, conductivity) External structures (flagella, sheathes) Internal organization (nucleus, cytoplasmic structures) Color/pigments – Chlorophylls a,b,c – Carotenoids – Phycobilins Growth form (solitary, colonial) Reproduction Cell wall chemistry Nutrition DNA and genetics Algae are a diverse group Classification and identification are specialist disciplines

15 5 most common divisions (of 10) Division Abundance Bacillariophyta (diatoms) dominant Chlorophyta (green algae) *intermediate Cyanobacteria (blue-green algae) *intermediate Chrysophyta (yellow-brown algae) low Rhodophyta (red algae) low *May dominate in eutrophic streams Different algal groups can be indicators of trophic status Good web resource: common freshwater algae

16 Bacillariophyta (Diatoms) Unicellular Cell wall: silica Construction: – 2 half valves (frustule) – A pair of slits in the valve (raphe) Most diverse and common in pristine systems

17 Chlorophyta (green algae) Form fuzzy mats that are bright appear to be green Mostly filamentous Dominate eutrophic systems

18 Cyanobacteria (blue-green algae) Absence of chloroplasts – Pigments are distributed through cell protoplasm – Wide range of pigments produce a range of colors Mostly filamentous, often have gelatinous sheathes Produce a musty smell Form mats of blue green, olive or brown color

19 Mostly motile cells with flagella Includes some filamentous and sheet-like forms More commonly found in lakes than streams Contains the pigment fucoxanthin Derived from a non-photosynthesizing ancestor Chrysophyta (yellow-brown algae) Hyalobryon

20 Rhodophyta (red algae) Multicelllular “Red” comes from phycoerythrin pigment Most are marine species Indicators of clean systems in freshwater Lemanea

21 Macrophytes – mostly vascular plants Emergent – Stand out of water – Water Willow; Pickerelweed (Pontedaria) Floating-leaved – Leaves float – e.g. Lilly pads Floating plants – Whole plant floats – Duckweeds Submerged – Underwater except for flowers – Pondweeds (Potamogeton)

22 Macrophytes include Bryophytes Non-vascular Reproduce via spores Mosses, liverworts, hornworts Adapted to high flow environments Attached to rocks Found in cool, headwater reaches M. Kendrick L. Koenig

23 Methods – Phytoplankton & Periphyton Water column – Pass defined volume through a filter – Extract CHLa in defined volume (EtOH, acetone) – Read on spectrophotometer or fluorometer Whole-rock scrubs – Scrub a defined area of rock and remove material – Filter scrubate – Process as for phytoplankton

24 Processing steps Algae suspended in waterAlgae attached to a substrate Filter to separate algae (and other particles) from water Extract CHL abc from algae (EtOH or Acetone) Analyze for CHL abc V SA V EXT M CHL /V EXT Scrub algae from a known area into a known volume of clean water V SA (V SA = f * V SRB ) V EXT M CHL /V EXT V SRB /A SRB

25 Analytical tools Beer’s Law of absorption Auto- fluoresence of substances SpectrophotometerFluorometer

26 Methods - Macrophytes Point or Clipped Quadrats

27 Stream Ecology (NR 280) Topic 6 – Primary Production What is production? Who contributes to primary production? Pros and cons of being an autotroph Taxonomy of autotrophs Regulation of primary production Fate of primary production

28 Regulation of Primary Producers Environmental factors – Light – Temperature – Substrate – Current/ Storm events Chemical Factors – Nutrients – Pollutants Biological factors – Herbivory

29 Biophysical Relationships Algal Growth Nutrients Algal Growth Light Algal Growth Temperature Jassby-Platt Photosynthesis/ Irradiance Curves α P max (I) (P I ) (T o C) Q 10 (R T ) T1T1 T2T2 R2R2 R1R1 (V S ) Michaelis-Menten kinetics ([S]) V max kmkm ½ V max

30 Regulation: Algae & light 1 Allen (1994) Shaded-adapted community Light-adapted community

31 Algae & Light 2 Benthic algae has greater photosynthetic potential than seston algae (phytoplankton) Open-canopy systems exhibit greater algal biomass Munn et al (2010) Coarse-grained Fine-grained Water column (seston) Benthic

32 Algae & Temperature Growth rate generally increases with temperature Q 10 = ~ 2 (Falkowski & Raven 2007) Photosynthesis (and growth) are sensitive to high temperatures Temperature Growth/Photosynthesis Optimal T°C = 20°C for photosynthesis (Konokpa & Brock 1978)

33 Assessing nutrient limitation Liebig’s Law of the Minimum – Growth is controlled by the scarcest resource – the “limiting nutrient” – that which limits growth Macro-nutrients are required in large amounts – C, H, N, O, P, N, Si Micro-nutrients required in lesser amounts – S, Cl, K, Na, Ca, Mg, Fe, Mn, Zn, Cu, Mo, B, Se, Co Enrich a whole-system or create a microcosm in the lab with a potential limiting nutrient – If biomass increases; the added nutrient is limiting – If no response, something else is limiting

34 Periphyton & nutrients N or P availability can rival light as the limiting factor (Allan 2007) No shade 50% shade 90% shade

35 Interaction of light and nutrients (nutrient diffusing substrate) In this case, the effect of lack of light overwhelmed the effect of added nutrients.

36 Other factors affecting primary production

37 Algae & current “Subsidy-stress” response Flow renews nutrients and gasses to algae But also exerts a shear stress causing cell sloughing and death (Allen 1994)

38 Algae & substrate Bedload movement – Rolling rocks removes algae – Sand scours – Re-deposited sediment may bury periphyton Sediment size as stability – Smaller particles are more likely to move – Boulders are most stable followed by cobble & gravel (Allan 2007)

39 Algae & grazers Losses to grazers are substantial when snails are present When snails were excluded, – AFDM, biomass and productivity increased Rosemond (1993)

40 Algae & grazers (& nutrients) Both grazers & nutrients influence algal growth  Trade-off between resistance to herbivory and competitive ability ◦ Study showed that algal species most reduced by grazing were those that increased most to nutrients

41 Fate of primary productivity? Phytoplankton – Minor: Grazing by zooplankton – Major: Export downstream Periphyton – Major: Consumed by herbivores Usually high quality food Trophic efficiency is usually low (~10%) – Major: Enters pool of particulate detritus Locally or after downstream transport Macrophytes – Consumed by herbivores – Creates considerable detritus – Secretion of DOC and DON

42 Summary of Key Points Autotrophs are fundamental to the food chains of all ecosystems – 3 generic types of autotrophs – Periphyton dominate streams Periphyton and biofilms contribute to the rich diversity of streams Biophysical and physical factors regulate autotrophic productivity Heterotrophs depend on autotrophs for their energy and raw materials


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