Lecture 4: Water Column-Primary Production PDF

Lecture 4 Water Column-Production in the Water Column 1  5. Water Column-Primary Production Primary producers=> autotrophs CO2+H2O CH2O+O2 (light, pigment) Oxygenic photosynthesis H2O as electron donor Anoxygenic photosynthesis...

Lecture 4 Water Column-Production in the Water Column 1  5. Water Column-Primary Production Primary producers=> autotrophs CO2+H2O CH2O+O2 (light, pigment) Oxygenic photosynthesis H2O as electron donor Anoxygenic photosynthesis H2S used as donor CO2+O2+H2S CH2O +4S+ 3H2O Requirements for photosynthesis – Carbon dioxide, water, Nitrate, phosphate, trace elements, light Organisms can also fix CO2 by use of chemical energy in reduced environments- chemosynthetic Primary production is the main source of energy that maintains an ecosystem 2  5. Water Column-Primary Production Two-models of production and energy flux Bottom-up control: involves factors that directly impact on Primary Production such as reduced nutrients, light, temperature Top-down: Involves factors that affect organism high up in the food chain 3  5. Water Column-Primary Production Bottom-up control mechanism of primary production – Heat Stratification => heating of surface water –thermocline – Light => level at which 1% of surface light penetrates – Nutrients Stratification => heating of surface water –Nutricline Vertical water mixing- breakdown stratification 4  5. Water Column-Primary Production Light: – Light intensity= rate at which photons strike a given surface – Light intensity varies in time and space – Euphotic zone characterized by enough light intensity – Clear oceanic /deep lake photosynthesis => 100m http://www.waterontheweb.org/under/lakeecology/04_light.html 5 5. Water Column-Primary Production 6  5. Water Column-Primary Production Nutrients: Nutrient concentration in the surface waters influences production Physical processes causing water mixing are important They provide nutrients at the photic zone and include: 1. Seasonal changes in temperature (cooling and wind action) 2. Upwelling driven by river runoff-estuaries 3. Upwelling driven by tidal waves-estuaries 4. Wind-driven vertical transport/upwelling in lakes 5. Wind-driven coastal upwelling-Oceans 6. Upwelling driven by large-scale circulation-ocean 7  5. Water Column-Primary Production – Seasonal changes in temperature (cooling and wind action) Spring phytoplankton bloom, no growth in winter Common in both temperate lakes and ocean (till 100-200m) Also local factors will influence the specific water body Meromictic lakes: lack complete mixing 8 Water mixing - Temperature and nutrient profiles 9  5. Water Column-Primary Production – Upwelling driven by river runoff-estuaries This occurs in semi-enclosed arm of the sea where the river enters the sea River water being less saline rides over ocean saline water A pycnocline is developed when the sea is relatively calm Surface winds and waves causes waves on the surface that progressively continue into the pycnocline The wave cause instability of the pycnocline Progressive mixing of fresh and salt water Freshwater carried into sea water = entrainment Salt water moves upwards to take the place of entrained water This bottom water is loaded with nutrients 10 Upwelling in estuaries 11  5. Water Column-Primary Production Upwelling driven by tidal mixing –estuaries Tides: Caused by gravitational pull of sun and moon – regular rise and fall of sea level which vary from place to place Estuaries that have high tidal range have strong currents generated that run on the rising then on the falling tide Tidal currents moving over the bottom generate turbulence in the above water If they are strong enough then stratification due to salinity difference is broken resulting in tidally mixed estuary Thus nutrient rich bottom water comes to the surface But turbidity could result in lower phytoplankton production in mixed waters compared to stratified waters 12  5. Water Column-Primary Production Wind-driven vertical transport/upwelling –lakes – Strong winds over lake surface blowing in one direction – Thermocline is depressed on one side of the lake – Corresponding rise of thermocline on the other creates instability – When winds stop unstable situation of thermocline leads to vertical water mixing 13 Wind driven upwelling -lakes 14  5. Water Column-Primary Production – Wind-driven coastal upwelling-Oceans Long shore winds that are converted to offshore winds Nutrient rich waters are brought to the surface plus optimum light and temp Primary production enhanced 15  5. Water Column-Primary Production – Upwelling driven by large-scale circulation in the ocean Equatorial upwelling Antarctic divergence 16  5. Water Column-Primary Production – Upwelling driven by large-scale circulation in the ocean Equatorial upwelling – Tropical waters are permanently stratified (lakes, oceans) – There being no seasonal cooling – Thus less productive than temperate waters – But upwelling mechanisms can lead to enhanced production – There are westwards flowing currents along the equator in Atlantic and Pacific oceans – Coriolis force then cause divergence to right in the north and to the left in the south of equator – Thus upwelling of nutrient rich waters arise along the equator and stimulate phytoplankton production. 17  5. Water Column-Primary Production – Upwelling driven by large-scale circulation in the ocean…… Antarctic divergence – Close to coast of Antarctica are currents – A westwards and eastwards flowing – Coriolis effect causes deflection to the left in the southern hemisphere – Thus deflection of the two currents in the opposite direction results in upwelling at the Antarctica coast – Hence high productivity at the Antarctica divergence 18 19  5. Water Column-Primary Production – Conclusion Lakes & oceans are seasonally or permanently stratified Supply of nutrients in surface zone or the well-lit zone also referred to as photic zone is reduced Breakdown of thermocline and vertical transport of water results in nutrients being brought to the surface By understanding these mechanism it helps one to understand the broad scale distribution of production zones in open water-both in lakes and oceans 20