Lecture 6: Surface Water Quality modeling Flashcards
what is DO? properties? what is the MI DO standard? DOD?
dissolved oxygen, organisms in water need oxygen to survive. DOsat is saturation level given temperature (decreases with temp). DO is replenished by re-aeration (dependent on surface area) and photosynthesis
Michigan DO standard is 7 mg/L
Dissolved oxygen Deficit = DOsat - DO
what is BOD? types?
aerobic respiration by microorganisms as they consume waste in the water. the primary sink for DO, can be broken into CBOD and NBOD, ultimate BOD, or BOD5 is amt of oxygen consumed over 5 days in a sealed container
Describe the equation for re-aeration rate
gradient driven first order : dDO/dt = k (DOsat - DO)
Describe the oxygen sag curve, and the physical representation
clean zone, decomposition zone, septic zone, recovery zone, clean zone
describe what the curves for DO and BOD look like as you move forward in distance/time
what is the streeter-phelps model?
steady state modeling of DO, using rearation and first order BOD decay
define fickian diffusion. when is it most important?
movement of molecules due to thermal motion (brownian diffusion). NO BULK FLOW. depends on temperature, size and viscosity,
Flux = - D dC/dx
where D is the diffusion coefficient, and its constant
this is Not eddy diffusion (orders of magnitude higher)
most important at small scales: intracellular interfaces, boundary layer interfaces
How do you combine fickian diffusion with bulk flow and reaction to see how the concentration of a pollutant is changing in time?
The advection diffusion equation:
advection is bulk motion (U dC/dx), diffusion is spreading (ficks second law, D d2C/dx2) , time-varying is emission rate and distribution change in time
dC/dt = D d2C/dx2 - U dC/dx - kc
this is also called the continuity equation, conservation of mass,
Is fickian diffusion appropriate for the simple sediment-water model we discussed in class? how could we change the model to make it more appropriate? bu whats wrong with this one too?
assumptions: no advection in sediment, no reaction, source is unlimited, constant diffusion coeff, no loss to atm, no turbulence
so this isn’t appropriate because the assumption of no turbulence in the water column is invalid
if you change to microscale sediment model, then no turbulence is ok, and you have losses to water column now, but D is likely not constant through sediment that varies in how tightly its packed
types of turbulence / dispersive flow and compare with diffusive mixing
laminar - smooth unidirectional flows
transitional
turbulent - U is irregular and varies in space and time
shear induces mixing
E, Dispersion coefficient is very similar to diffusive coefficient except it refers to turbulence in the transport media. amount of dispersion (i.e., eddy diffusion) in horizontal is usually much greater than in vertical
in open water systems E»_space; D
when in the model you do E* = E + D
What 15 consitutents can QUAL2E model? what type of streams can you use QUAL2E on (what is the underlying assumption)?
DO, BOD, Temp, Algae as chorophyll a, Organic Nitrogen, Ammonia, Nitrate, Nitrite, Organic Phosphorus, Dissolved Phosphorus, Coliforms, Arbitrary non-conservative pollutant, 3 conservative pollutants
applicable to dendritic streams that are well mixed, assumption is that major transport mechanisms (advection and dispersion) are only significant along axis flow
What is the definite of a bioaccumulative chemical of concern (4)?
chemical which accumulates, half life > 8 weeks in all media, human health BAF > 1000 after considering internal degradation or activation , BAF based on measurements or methodology
What are the 3 types of biological accumulation and factors?
Bioaccumulation - net accumulation of substance as a result of all env factors (i.e., total uptake)
Bioaccumulation factor - ratio of a substance’s concentration in tissue to its concentration in water
Bioconcentration - non-dietary uptake of a chemical (e.g., through gills)
Bioconcentration factor - ratio of substance’s concentration in tissue to conc in water where non-dietary is only pathway
biota-sediemtn accumulation factor - ratio of lipid normalized conc in water to carbon-normalized conc in surface sediment
What factors determine BCF?
lipid content, distribution, biotransformations, inter-intra species variation, environmental conditions, dissolved fraction vs particulate fraction (aka bioavailability)
