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algal blooms and deadzones.docx

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Life Sciences
Luc Bernier

March 21 , 2013 Life Sci 2H03: Environmental Life Sciences Algal Blooms and Dead Zones Algal Blooms and Dead Zones Oligotrophic Environments - low nutrient levels - good light penetration - low algal growth - high dissolved O 2 - great abundance of fish species requiring high O 2 - prestine waters - most natural lakes or bodies of water tend to be oligotrophic, low supply of nutrients which keeps in check the growth of algae Eutrophic Environments - high nutrient levels - poor light penetration - high algal growth - low dissolved O 2 - fish species tolerant of low O 2 - lower biodiversity - dense carpets of floating algae - fungi and microboes actively use the oxygen to breakdown - triggered by abundance of nutrients in the water column Eutrophication Process - frequency has increased in the past 50 years - source of increase in the amount of nutrients is coming from the Mississippi river (nitrogen or phosphorous) - dying and settling at the bottom of the water column becoming a source of energy for decomposers - consume all of the oxygen at the expense of other organisms - in most coastal waters, the temperature of the water varies so the surface is warm and fairly light floating on top of deeper water, water does not mix - diffusion of oxygen from the surface to the bottom - we end up with two strata of water that are completely different Hypoxia - waters with a dissolved oxygen (DO) concentration less than 2mg/L are defined as: hypoxic - DO = 0mg/L: anoxia - In most species of fish once we reach the 1-2 threshold most will be dying or dead - Higher values when most aquatic organisms are able to thrive - As a result of intense consumption of oxygen waters become hypoxic or anoxic Interaction of Eutrophication/Hypoxia and Energy Flow in Ecosystems - normoxia: much less organic material to decompose in relation to oxygen - degraded by mobile predators - as there a transition to hypoxic, the mobile predators are expelled - most of the flow of energy is derived from microbes in anoxia and hypoxia - persistency of these conditions - anoxia: H 2 which is toxic, so only microbes can survive under these conditions Sources of Nutrient Loads - natural or Human sources - after a flood when a lot of soil is eroded can cause algal blooms due to increase in released nutrients - human activity leads to vast quantity of nutrients from sewage or intensive agriculture (live stock, waste) - point source: specific source (from sewage treatment plant that does not control or from different agricultural activities) - sewage is less of a problem as government has increased guidelines in terms of nutrient release - emerging economies still have these guidelines, not necessarily the same standards - once you control the source it’s easy to turn off the supply Non-Point Sources of Nutrients - diffuse source - increasing input of nutrients to coastal areas - from large urban centers which have multiple points of discharge - cropland where fertilizers are spread over a large area - difficult to control as there is a large mass of nutrients coming from different sources - phosphorous is typically the problem Strong Correlation with Population Growth - problem increasing since the 18 century due to population growth and the activities associated with population growth - projections - if nothing changes we can expect the formation of dead zones will be increasing Eutrophication/Hypoxia: A Global Problem - virtually very little zone of hypoxic waters prior to WWII - explosion of hypoxic waters happens after WWII - mimics the growth of population and the demand of resources, as well as the
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