Lec 6: Primary Producers and Production

Transcription

1 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

2 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

3 Netplankton: >70µm 3

4 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 Ankistrodesmus Microcystis Oscillatoria Anabaena 4

5 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 NH 4 and DOC are high (e.g., farm ponds, sewage oxidation ponds, etc.) Peridinium and Ceratium 5

6 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 Cladophora Spirogyra Staurastrum (Desmids) Cosmarium 6

7 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 Dynobryon 7

8 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 by and affect [Si] Diatoms often are dominant in periphyton and streams girdle view Asterionella colony (girdle view) Synedra sp. valve view Meridion sp. partial colony (girdle view) 8

9 Algae & Water Quality Algae species typically are associated with specific water conditions and often have worldwide 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

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

11 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 (4πr 2 = area of a sphere; 4/3 π r 3 = 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

12 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 PO 4 is low 12

13 100 III. Trophic Status Chl a (µg L -1 ) N:P < 10 10< N:P < 25 N:P > 25 A. Trophic Classification Systems for Lakes Proportion Ultra-oligotrophic TP (µg L -1 ) Oligotrophic Mesotrophic Eutrophic Hypertrophic A Trophic state Secchi depth (m) Phosphorus (µg L -1 ) Chlorophyll (µg L -1 ) B Chl (µg L -1 )

14 III. B. Why Eutrophication should be controlled before the Hypolimnion goes Anoxic 1. FePO 4 dissociates in anoxic conditions 2. If hypolimnion goes anoxic then PO 4 3- 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 nonpoint sources are controlled 14

15 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

16 IV. General seasonal succession -Patterns of succession due to changing environment? SPRING SUMMER LATE SUMMER Diatoms Greens Blue-greens High 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

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

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

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

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

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

22 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

23 3. Oxygen change method a. 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

24 4. Carbon change C method -Add radioisotope of carbon ( 14 C) as bicarbonate, H 14 CO 3-, and it is converted to labeled carbon by the algae -Incubate in light and dark bottles -Measure of roughly NPP (how much 14 C is incorporated into the algae) -Is more sensitive than oxygen method -Problems with this method (1) 14 C and 12 C don t have the same reactivity (2) Doesn t measure 14 C 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 masses 24

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

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27 Conceptual Diagram of Trophic Cascade 14

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