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Aquatic Ecology Freshwater - Part 4

Aquatic Ecology Freshwater - Part 4. Prof. Dr. N. De Pauw. AECO. Laboratory of Environmental Toxicology and Aquatic Ecology. Aquatic Ecology. Course Contents. Place of limnology in natural sciences Historical development of limnology

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Aquatic Ecology Freshwater - Part 4

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  1. Aquatic Ecology Freshwater - Part 4 Prof. Dr. N. De Pauw AECO Laboratory of Environmental Toxicology and Aquatic Ecology Aquatic Ecology

  2. Course Contents • Place of limnology in natural sciences • Historical development of limnology • The water cycle, distribution, age and genesis of inland waters • Structure and physical properties of water • Physical relationships in natural water bodies • Communities of living organisms in natural waters • Materials budget in natural waters I • (= gases, solid and dissolved substances, importance of sediments) • 8. Materials budget in natural waters II • (= production, consumption, decomposition)

  3. 7. Materials budget of natural waters I Contents (1) 7.1. Introduction 7.2. Dissolved gases and dissolved solids 7.3. Gases dissolved in water 7.3.1. Solubility of gases in water 7.3.2. Oxygen content and oxygen budget 7.3.3. Carbon dioxide, carbonic acid and carbonates 7.3.4. Methane and hydrogen sulphide 7.3.5. Nitrogen

  4. 7. Materials budget of natural waters I Contents (2) 7.4 Solids dissolved in water 7.4.1. Solubility of solids in water 7.4.2. Nitrogen compounds 7.4.3. Phosphorous compounds 7.4.4. Sulphur compounds 7.4.5. Iron and manganese 7.4.6. Silica 7.5. Dissolved organic matter in natural waters 7.6. Sediment and the materials budget 7.7. Materials budget of flowing waters

  5. 7. Materials budget of natural waters I 7.1. Introduction = Sum of materials and energy turnover in an ecosystem FOUNDATIONS • Water as a solvent • Dissolved and particulate materials • 3.Organisms in water

  6. 7. Materials budget of natural waters I 7.1. Introduction Characterized by the following processes • 1. Bio-activity of organisms • Production • Consumption • Organisms in water • 2. Chemical and biological transport of material + energy • Into the sediment • Release from the sediment • 3. Transport of material + energy • In lakes : seasonal rhythm • In rivers : unidirectional transport • 4. Exchange • With atmosphere (precipitation) • In and outflow • Absorption and desorption (suspended particles)

  7. 7. Materials budget of natural waters I Contents (1) 7.1. Introduction 7.2. Dissolved gases and dissolved solids 7.3. Gases dissolved in water 7.3.1. Solubility of gases in water 7.3.2. Oxygen content and oxygen budget 7.3.3. Carbon dioxide, carbonic acid and carbonates 7.3.4. Methane and hydrogen sulphide 7.3.5. Nitrogen

  8. 7.2. Dissolved gases and dissolved solids Spatial and temporal distribution dependent on : • Hydrological factors • Precipitation • Inflow and outflow • Chemical factors • Solution processes • Complex formation • Physical factors • Temperature • Optical properties • Movement of water • Biological factors • Photosynthesis • Respiration • Mineralisation

  9. 7.2. Dissolved gases and solids • Physico-chemical processes • Dissolution and precipitation of solids • Absorption and desorption of gases • Ion exchange at solid surfaces • Chemical processes • Redox processes • Soluble complex formation • Hydrolytic cleavage • Biochemical processes • Mineralisation of organic matter • Photosynthesis • Respiration

  10. Dissolved substances in fresh and seawater • In freshwater :calcium carbonate + silicates + nitrates • In seawater : sodium chloride • Besides inorganic materials indefinite number of organic compounds • LAW OF THE MINIMUM (Liebig): • Yield dependent on whatever growth factor is at a minimum in proportion to all similar factors (e.g. phosphorous vs nitrogen)

  11. 7. Materials budget of natural waters I Contents (1) 7.1. Introduction 7.2. Dissolved gases and dissolved solids 7.3. Gases dissolved in water 7.3.1. Solubility of gasses in water 7.3.2. Oxygen content and oxygen budget 7.3.3. Carbon dioxide, carbonic acid and carbonates 7.3.4. Methane and hydrogen sulphide 7.3.5. Nitrogen

  12. 7.3. Dissolved gases in water O2 and CO2Direct indicators of biological activity N2 Metabolic cycle of specific micro-organisms H2S and CH4 Present in localised amounts due to baterial activity

  13. 7.3.1. Solubility of gases in water • Henry’s law: • Solubility of a gas decreases with : • Increasing temperature • Decreasing pressure • Quantity of dissolved gas : • Cs = Saturation concentration of the gas • Ks = Temperature dependent solubility • Pt = Partial pressure of the gas • CO2 has highest solubility • CO2 + H2O  H2CO3 / CaCO3 Cs = Ks * Pt

  14. 7.3.1. Solubility of gases in water • Important : • Saturation of the gas : oversaturation – undersaturation • O2 and CO2 : produced or consumed by living organisms • Increasing temperature decrease of oxygen concentration •  increase in oxygen demand organisms • Compensation in warmer water : • Water movement in flowing water • Water movement by animals themselves

  15. 7.3.2. Oxygen content and oxygen budget of surface waters Factors affecting the oxygen balance • Oxygen balance less positive if : • Input decreases • Losses increase • Deductions : • Flowing waters with rapid movements and shallower depth have a more favourable oxygen balance than still waters • Input of organic matter into water body has an adverse effect on its oxygen balance (greater effect in still than in flowing water)

  16. Dissolved oxygen in lakes • O2 from atmosphere  water  greater depths by water movements: • During seasonal turnover : O2 rich water  bottom • During summer stagnation phase : • Inepilimnion: • O2 from atmosphere + photosynthesis • O2 oversaturation during the day + O2 deficit during the night • Diurnal fluctuations of pH and CO2 • In hypolimnion: • Exclusively oxygen depletion processes : • Heaviest oxygen demand imposed by microbial mineralisation of plant and animal residues deposited in profundal zone • Quantity of organic matter dependent on : • Production in epilimnion • Sinking and degradation rate of dead organisms • Depth of the water

  17. Classification of lakes in temperate zones On basis of volume ratio Epilimnion / Hypolimnion(E / H) Oligotrophic : ratio  1  Eutrophic : ratio > 1

  18. Relationship between production, depth and trophic status • HOLOMICTIC LAKE • Oligotrophic lake: Orthograde O2 profile • Hypolimnic oxygen uptake low during stagnation period • Eutrophic lake : Clinograde O2 profile • Hypolimnic oxygen maybe completely exhausted • Heterograde O2 profile consequence of: • Metalimnic photosynthesis maximum • or • Intensive decomposition in thermocline • MEROMICTIC LAKE • Monimolimnion : permanently free of oxygen • In tropical lakes :hypolimnion (> 20 °C) = O2 totally depleted

  19. Oxygen budget of flowing waters • Oxygen budget affected by : • Degradable organic matter carried along • Organic effluents • Clues provided to oxygen budget : • In lakes:Vertical differences in O2 concentration • In rivers:Diurnal O2 saturation profile

  20. Dissolved oxygen in flowing waters • Different types of waters according to diurnal oxygen profiles : • Type 1 : Abiotic flowing waters • O2 level temperature dependent • Type 2 : Unpolluted flowing waters • Oversaturation during day, deficit during night • Type 3 : Slightly polluted flowing waters • No oversaturation during day, deficit during night, • Type 4 : Strongly polluted flowing waters • Continuous oxygen deficit • As a result of self-purification capacity of flowing waters  • succesion of types 4-3-2 along the river course

  21. 7.3.3. Carbon dioxide, Carbonic acid, Carbonate • Sources: • Atmosphere • Precipitation • Infiltration through soil (groundwater) • Metabolic activity of the organisms • Aerobic decomposition : C  CO2 • Anaerobic decomposition : CO2 + CH4 • CO2 + H2O  H2CO3  H + HCO3-  H + CO3-- • Proportions of CO2, HCO3- and CO3-- : pH dependent

  22. When adding CO2 • CaCO3 + CO2 + H2O  Ca(HCO3)2 • Insoluble Soluble form • form = C reserve for photosynthesis • Excessive CO2 may dissolve chalk • When removing CO2 • Ca(HCO3)2 CO2 + CaCO3 + H2O • Chemical decarbonation • Crust of CaCO3 on stones, mosses, leaves (travertine) • Biogenic decarbonation • Crust of CaCO3 on leaves of submerged plants • Fine cristals of chalk formed by phytoplankton: Calcium-apatite

  23. By the presence of calcium carbonate in its blue-green water, the Havasu creek in the Grand Canyon National park, slowly deposits stone called travertine.

  24. Tuff formations at Mono Lake (California). They were formed by the interaction of calcareous groundwater with the CaCO3 and other minerals in the lake.

  25. Hardness • Chalk content expressed as temporary hardness • on a scale of German degrees of hardness • 1 dH° = 10 mg/L CaO or 18 mg/L CaCO3 • 1 dH° = 7.1 mg/L MgO or 15 mg/L CO3 < 10 dH° = soft water 20 dH° = hard water > 30 dH° = not usable anymore as drinking water

  26. Buffering action • Great biological importance attached to pronounced • buffering action of CO2-calciumbicarbonate mixtures  • Acidic waters with low chalk content: weakly buffered •  may undergo high pH rise > 9 • Calcarous waters : strongly buffered •  normal pH range 7 – 8 • CO2 consumption compensated by decomposition of Ca(HCO3)2 •  pH increase remains small • Finally CaCO3 + H2O  Ca(OH)2 + CO2 •  pH increases up to 11 (CO2 only present as CO3 ions)

  27. Abatement of acidification by means of addition of chalk

  28. Vertical distribution of CO2 • In lakes:vertical distribution of CO2 arises from activity of • Autotrophs :Epilimnion  uitputting van CO2 (planten) • Heterotrophs :Hypolimnion  CO2 generated, • recombines with precipitated CaCO3 • in epilimnion • In flowing waters:relationship much simpler :see figure

  29. 7.3.4. Methane and hydrogen sulphide Result of anaerobic decomposition of organic matter CH4Released to atmosphere Oxidized to formaldehyde H2S Dissolves readily in water N2 Certain bacteria (cyanobacteria) can fix N N2 + 12 ATP + 6 H  2 NH3 + 12 ADP + 12 P N-fixation at sediment-water interface

  30. 7. Materials budget of natural waters I Contents (2) 7.4 Solids dissolved in water 7.4.1. Solubility of solids in water 7.4.2. Nitrogen compounds 7.4.3. Phosphorous compounds 7.4.4. Sulphur compounds 7.4.5. Iron and manganese 7.4.6. Silica 7.5. Dissolved organic matter in natural waters 7.6. Sediment and the materials budget 7.7. Materials budget of flowing waters

  31. 7.4.1. Solubility of solids in water • Water is a particularly suitable solvent for electrolytes: • High dielectric constant • Ability to form hydrates • Solubility of solid substances dependent on: • - pH • - Eh • Most substances dissolve either: • In molecular form • As ion • In colloidal form

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