Lec 6: Primary Producers and Production

I. What & WhoII. Factors Affecting GrowthIV. Seasonal SuccessionV. Influence of Nutrients on

Phytoplankton AssemblagesVI. Role of Benthic Algae on Whole-System PPVII. Primary ProductionVIII. Measurement of Primary Production

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I. Plankton in General• Plankton – Definition: Organisms whose

distributions are determined primarily by currents. However, many planktonic organisms have mechanisms for locomotion or can adjust their specific gravity to control depth in the water column.

• Importance:Constitute the bulk of primary and secondaryproduction in aquatic habitats (generally far outweigh and out-produce more conspicuous aquatic inhabitants such as insects and fish)

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Netplankton: >70µm

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Blue-green Algae (Cyanophyceae)• Primitive (bacteria-like): lack defined

nucleus, plastids, etc.• Asexual reproduction• Often produce and jelly-like sheath that

covers cells (difficult to consume)• Unicellular, colonial and filamentous

forms• Include N-fixing forms (often with

heterocysts)• May dominate in polluted waters• Associated with foul smells, toxic

decomposition products; give color to red sea

Microcystis

Oscillatoria

Anabaena

Ankistrodesmus

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Dinoflagellates (Pyrrhophyta)• Mobility via 1-3 flagella (max.

speed ca. 1/3 mm/sec), unicellular

• Photosynthetic, Parasitic & Predatory life modes; generallyautotrophic, but can use DOC

• Cause red-tides in Gulf of Mexico, fishy odors, luminescence, Pfisteria

• Common where NH4 and DOC are high (e.g., farm ponds, sewage oxidation ponds, etc.)

Peridinium and Ceratium

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Green Algae (Chlorophyta)

Pediastrum

Cladophora

Spirogyra

CosmariumStaurastrum(Desmids) 6

• Well developed chloroplasts, sometimes of distinctive shapes

• Large and diverse group, generally restricted to freshwater habitats

• Both sexual and asexual reproduction

• Unicellular, colonial, filamentous (some colonial and filamentous forms macroscopic)

• Dominate in lakes & bogs with low alkalinity

• Few nuisance species

Chrysophyta• Includes diatoms, yellow-green,

and golden-brown algae• Chlorophyll often masked by

other pigments• Efficient oxygen producers• Unicellular and colonial forms• Many attached species• Common in most freshwater

habitats (lakes and streams)• Asterionella sp. (associated with

eutrophic conditions) has been studied extensively

Fragellaria

7Dynobryon

• Have a cell wall called a frustuleconsisting of two parts that fit together like a petri dish

• The frustule has a high silica content and may appear ornamented

• Depending on the orientation relative to the observer, diatoms may have two shapes

• High Si content, influenced byand affect [Si]

• Diatoms often are dominant in periphyton and streams

Chrysophyta:Diatoms

Synedra sp.

valve viewgirdle view

Meridion sp.partial colony(girdle view)Asterionella

colony(girdle view)

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Algae & Water Quality

• Algae species typically are associated with specific water conditions and often have world-wide distributions. Thus, their presence in a habitat tends to be due to environmental compatibility. This is the basis for the use of these organisms as indicators of water quality.

Clean water algae9

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A. Use of Nutrients

• Uptake into cell, Michaelis-

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• Monod equation, growth µ is growth rate

• Droop equation links concentration in cell (Q) and minimum conc in cell for growth (Q0) to growth

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II. Factors affecting growth B. Cell size – amount of surface area relative to volume;

surface area/volume gets lower as cell gets bigger in Vol(4πr2 = area of a sphere; 4/3 π r3 = volume; so A / V = 3/r)

C. Nutritional state of cella. Luxury uptake – cells take up more than they need b. Inhibition by internal stores 11

D. Determining the limiting nutrient:How do we determine the limiting nutrient?

1. Liebig’s law of the minimum – only 1 thing limits growth at any one time (something else may be close)nutrient in shortest supply relative to needs

2. Bioassay techniques – add different nutrients in a factorial design and see which species respond – N, P, N+P

3. Stoichiometry: deviations from the expected Redfield ratio(Redfield Ratio: 106C:16N:1P)

4. APA: Alkaline Phosphatase Activity-Enzyme activity (excretion) is high when PO4 is low

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1 10 100Chl (µg L-1)

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N:P < 1010< N:P < 25N:P > 25

III. Trophic Status

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III. B. Why Eutrophication should be controlled before the Hypolimnion goes Anoxic

1. FePO4 dissociates in anoxic conditions

2. If hypolimnion goes anoxic then PO43-

continuously is recycled from sediments into the water column, and mixed into the epilimnion

3. Can take many years to recover from eutrophication even if point sources and non-point sources are controlled

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III. C. Why Does Nutrient Pollution Resulting in Algal Blooms Matter in Lakes?

1. Taste and odor problems2. Blooms of toxic algae3. Aesthetics (people less willing to pay to live

near, or recreate on, eutrophic lakes)4. Fish kills

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IV. General seasonal succession -Patterns of succession due to changing environment?

SPRING SUMMER LATE SUMMER Diatoms Greens Blue-greensHigh nutrients Good competitors at low nutrients Lowest nutrients (N fix.) High grazing Moderate grazing Low grazing(unpalatable) Low sinking High sinking rates Moderate sinking

WINTER – small phytoflagellates; sometimes motile dinoflagellates

-Each major group’s abundance curve is made up of individual species curves -Hundreds of species of algae live in any one lake over the course of a year -To predict each you need to know nutrient requirements,

responses to temperature, light, grazing, sinking rates 16

V. Influence of Nutrient Levels on Primary Producer Community Size and Taxonomic Composition

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VI. Role of Benthic (attached) Primary Producers to Whole-Lake PP

Influence of Lake Morphology

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VI. Role of Benthic (attached) Primary Producers to Whole-Lake PPGeneral influence of lake morphology on

distribution of primary production?

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VII. Primary Production A. Fate of Energy: NPP = GPP – R

The whole process is 0.03-2% energy efficient

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B. Influence of Standing Stock or Biomass on Production

-Higher nutrients > Higher biomass > Larger species & higher density

> Less light penetrationper unit area

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C. Measurement of Primary Production1. General equation and units

a. units of carbon produced or oxygen emitted (sometimes calories; 1 mg C~10 cal energy, depending on storage material – fat, starch…)

b. per volume or surface area of lake c. per time

2. Types of primary producers-Macrophytes, Periphyton, Phytoplankton

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3. Oxygen change methoda. Light-dark bottles

Measure initial and incubate the others for a period of time R=Initial - Dark final NPP=Light final-Initial (assumes the same respiration in the L & D) GPP=Light final -Dark final

Problems with this method: (1) Enclosure/bottle effects (2) Sensitivity(3) Is respiration light-independent?

b. Whole environment -measure oxygen change in a lake or stream over a day -avoid enclosure effects -must compensate for invasion and evasion of oxygen to the lake

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4. Carbon change -- 14C method -Add radioisotope of carbon (14C) as bicarbonate, H14CO3

-, and it is converted to labeled carbon by the algae

-Incubate in light and dark bottles -Measure of roughly NPP (how much 14C is incorporated into the

algae) -Is more sensitive than oxygen method

-Problems with this method (1) 14C and 12C don’t have the same reactivity (2) Doesn’t measure 14C that entered the cell and then left by

excretion or respiration before the end of the experiment

5. Yield method -Look at the change in algal biomass over time -No bottle effects -Only used with lots of growth so that there is no sensitivity problem -What is the problem with this measure? Doesn't account for

attrition – gives an underestimate of production -Also a problem with moving water masses – spatial heterogeneity –

may be sampling different water masses24

Schindler et al. 1997 Science

Influence of food web structure on carbonexchange between lakes and the atmosphere

• What does the title suggest?

• Premises?

• Approach / Methods?

Conceptual Diagram of Trophic Cascade

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