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Exam Return

84%. 78%. Exam Return. 88%. 68%. 66%. Wednesday: Schindler et al. paper. Lec 6: Primary Producers and Production. I. What & Who II. Factors Affecting Growth IV. Seasonal Succession V. Influence of Nutrients on Phytoplankton Assemblages

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Exam Return

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  1. 84% 78% • Exam Return 88% 68% 66% • Wednesday: Schindler et al. paper

  2. Lec 6: Primary Producers and Production I. What & Who II. Factors Affecting Growth IV. Seasonal Succession V. Influence of Nutrients on Phytoplankton Assemblages VI. Role of Benthic Algae on Whole-System PP VII. Primary Production VIII. Measurement of Primary Production 1

  3. 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 secondary production in aquatic habitats (generally far out weigh and out-produce more conspicuous aquatic inhabitants such as insects and fish) 2

  4. Netplankton: >70m 3

  5. 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 Ankistrodesmus Oscillatoria Anabaena 4

  6. Dinoflagellates (Pyrrhophyta) • Mobility via 1-3 flagella (max. speed ca. 1/3 mm/sec), unicellular • Photosynthetic, Parasitic & Predatory life modes; generally autotrophic, 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 5

  7. Green Algae (Chlorophyta) • 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 Pediastrum Spirogyra Cladophora Staurastrum Cosmarium (Desmids) 6

  8. 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 7 Dynobryon

  9. Chrysophyta: Diatoms • Have a cell wall called a frustule consisting 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 Synedra sp. girdle view valve view Meridion sp. partial colony (girdle view) Asterionella colony (girdle view) 8

  10. 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 algae 9

  11. =[S] [ S ] = V V max + K [ S ] s [ S ] m = m max + K [ S ] s Q m = m - ( 0 ) 1 max Q II. Factors affecting Growth: A. Use of Nutrients Rate of Growth or Nutrient uptake • Uptake into cell, Michaelis-Menten V = uptake, [S] = substrate conc. Ks = half saturation constant • Monod equation, growth µ is growth rate • Droop equation links concentration in cell (Q) and minimum conc in cell for growth (Q0) to growth 10

  12.     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            (4r2 = area of a sphere; 4/3  r3 = volume; so A / V = 3/r) C. Nutritional state of cell            a. Luxury uptake – cells take up more than they need b. Inhibition by internal stores 11

  13. 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 12

  14. III. Trophic Status A. Trophic Classification Systems for Lakes 13

  15. 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 14

  16. III. C. Why Does Nutrient Pollution Resulting in Algal Blooms Matter in Lakes? 1. Taste and odor problems 2. Blooms of toxic algae 3. Aesthetics (people less willing to pay to live near, or recreate on, eutrophic lakes) 4. Fish kills 15

  17. IV. General seasonal succession -Patterns of succession due to changing environment? SPRING               SUMMER                                         LATE SUMMER DiatomsGreensBlue-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

  18. V. Influence of Nutrient Levels on Primary Producer Community Size and Taxonomic Composition 17

  19. VI. Role of Benthic (attached) Primary Producers to Whole-Lake PP Influence of Lake Morphology 18

  20. VI. Role of Benthic (attached) Primary Producers to Whole-Lake PP General influence of lake morphology on distribution of primary production? 19

  21. VII. Primary Production A. Fate of Energy:         NPP = GPP – R         The whole process is 0.03-2% energy efficient 20

  22. B. Influence of Standing Stock or Biomass on Production -Higher nutrients > Higher biomass > Larger species & higher density > Less light penetration per unit area 21

  23. C. Measurement of Primary Production     1. 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 22

  24.     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 23

  25. c. 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 d. 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 masses 24

  26. Schindler et al. 1997 Science Influence of food web structure on carbon exchange between lakes and the atmosphere • What does the title suggest? • Premises? • Approach / Methods?

  27. Conceptual Diagram of Trophic Cascade 14

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