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Flashcards in Runoff and Eutrophication Deck (10)
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What are the different zones in a polluted river?

-Clean zone
-Decomposition zone
-Septic Zone
-Recovery zone
-(returns to Clean zone)


Clean zone

-Zone of river with no pollution
-Normal diversity/abundance of organisms: trout, perch, bass, mayfly, stonefly
-DO at 8ppm


Decomposition zone

-Zone of river where pollution enters the stream
-Populated by "trash fish": gars, leaches
-BOD spikes due to increased organic matter that requires oxygen for decomposition
-DO drops due to oxygen demand by bacteria


Septic zone

-Anaerobic zone
-Fish absent; fungi, sludge worms, bacteria present
-Very low DO due to bacterial decomposition
-BOD decreases as anaerobic activity increases


Recovery zone

-Less contamination present than in decomposition and septic zones
-trash fish present
-BOD declines b/c most organic material has settled as sludge
-DO increases


Urban runoff

-major pollution source with lots of BOD, suspended solids, nutrients, and microorganisms
-important in cities because urban runoff increases with hard top surfaces, no percolation into soil
-rates of runoff depend on rainfall


Remediation strategies for urban runoff

-Settling basins
-Recharge basins
-Interception of runoff


Settling basins

-Can be used to remediate urban runoff
-Removes SS and BOD, some nutrients/toxins are absorbed
-System may be overwhelmed by storms, requires long residence time and slow flow


Recharge basins

-Allows percolation of water into the ground
-Soil acts as filter to remove SS
-Dissolved contaminants will percolate into groundwater



-enrichment of an ecosystem w/ chemical nutrients, typically N or P, resulting in a depletion of dissolved oxygen
-Can occur due to natural N/P cycling
-Occurs more quickly due to wastewater discharge, urban runoff, etc.