BAEN 673 / April 14, 2016
 Today’s topics
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Inputting point source data into SWAT
Nutrient transport in SWAT
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Main channel
Reservoirs
 Class on Tue (4/19) in 214 Scoates computer
lab  work on end-of-year-projects
 Report presentations (8 minutes each)
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April 28 (during class)  9 students
May 5 (during exam time)  15 students
SWAT Input: Measured Data
 SWAT documentation manual – Chapter 31
 Point source loads  water and pollutants from
sources not associated with landscape
Sewage treatment plants / groundwater recharge / etc.
Input into a stream reach in any subbasin
May be summarized as:
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Hourly / daily / monthly / yearly / average annual basis
 Use the watershed configuration file (.fig) to
setup the input of measured data  Chapter 2
An example of a Daily Point Source File:
DATE,"Floday","Sedday","Orgnday","Orgpday","No3day","Nh3day","N
o2day","Minpday","Cbodday","Disoxday","Chladay","Solpstday","Srbp
stday","Bactpday","Bactlpday","Cmtl1day","Cmtl2day","Cmtl3day“
1/2/1990,10.00,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000
1/3/1990,7.800,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000
1/4/1990,6.200,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000,0.000
- Comma delimited
- Quotation marks placed as above
Note: Use 0.000 for any missing data
For more information see the SWAT input documentation
- Recday.dat file in Chapter 31  SWAT Input Data: Measured
- Recday Command (10) - Chapter 2  SWAT Input Data: Watershed Configuration
Point Source File Definitions
Floday:
Sedday:
Orgnday:
Orgpday:
No3day:
Nh3day:
No2day:
Minpday:
Cbodday:
Contribution to streamflow for the day (m³)
Sediment loading to reach for the day (metric tons)
Organic N loading to reach for the day (kg N)
Organic P loading to reach for the day (kg P)
NO₃ loading to reach for the day (kg N)
NH₃ loading to reach for the day (kg N)
NO₂ loading to reach for the day (kg N)
Mineral P loading to reach for the day (kg P)
CBOD loading to reach for the day (kg CBOD)
Point Source File Definitions
Disoxday:
Chladay:
Solpstday:
Srbpstday:
Bactpday:
Bactlpday:
Cmtl1day:
Cmtl2day:
Cmtl3day:
Dissolved oxygen loading to reach for the day (kg O₂)
Chlorophyll loading to reach for the day (kg chla)
Soluble pesticide loading for the day (mg ai)
Sorbed pesticide loading for the day (mg ai)
Persistent bacteria loading for the day (cfu/100ml)
Less persistent bacteria loading for the day (cfu/100ml)
Conservative metal #1 loading for the day (kg)
Conservative metal #2 loading for the day (kg)
Conservative metal #3 loading for the day (kg)
Nutrient Transport in SWAT
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SWAT tracks nitrogen (N) and phosphorus (P)
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Movement
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Transformations
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N and P change forms
Transformations in soil  simulated in each HRU
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Transport with water and/or sediment
Plant use of N and P based on crop growth stage
Nitrogen cycle
Phosphorus cycle
Reference: SWAT theoretical documentation
Nutrient Transport to the
Main Channel
 Surface Runoff
 Subsurface flow in shallow groundwater
 Inorganic mass transported as follows:
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(vol. of H2O) x (avg. concentration)
 Organic mass transported
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With the sediment
Nitrogen Cycle
Mineral Form of N
SWAT Nitrogen Cycle
Manure
Nitrogen in Soils  3 Forms
Organic / Mineral Solid / Mineral in Solution
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The surface layer of most cultivated soils contains
between 0.06% and 0.3% N
 Peat soils have high N contents up to 3.5%
 Form #1: Organic Nitrogen
 Organic def: Derived from living organisms (plants or
animals)
 Organic N in soil is found in the  Humus
 Humus def: A brown or black complex variable
material resulting from partial decomposition of
plant or animal matter and forming the organic
portion of soil
Organic N (continued)
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Manure / Municipal Biosolids
 Applied to the land for agricultural production
Organic N converted to mineral forms (inorganic)
 The decay of plant and animal residues by
microorganisms results in:
 Formation of mineral forms of N (NH4+ and
NO3)
 Becomes plant available
 Assimilation of part of the organic N into
microbial tissue where it becomes immobilized
Decomposition and Mineralization
Organic N in SWAT
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Only in the first soil layer
Controlled by a decay rate constant
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updated daily
a function of the C:N and C:P ratios of the residue
a function of temperature
a function of soil water content
Nitrogen in Soils  3 Forms
Organic / Mineral Solid / Mineral in Solution
 Form #2: Mineral forms in the soil
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Mineral def: Something neither animal nor vegetable,
A solid homogeneous crystalline chemical element or
compound
Most plants can only take up nitrogen in two solid
forms:
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Nitrate ion (NO3-)
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Most plants obtain the nitrogen they need as inorganic nitrate from
the soil solution
Ammonium ion (NH4+)
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Ammonium is used less by plants for uptake because in large
concentrations it is extremely toxic.
Nitrogen in Soils  3 Forms
Organic / Mineral Solid / Mineral in Solution
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Form #3: Mineral forms go into solution very easily
 Transported by:
 Surface runoff
 Infiltration
 Nitrogen added to soil by:
 Fertilizer (inorganic)
 Manure (organic)
 Residue (organic)
Nitrogen in Soils  3 Forms
Organic / Mineral Solid / Mineral in Solution
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Fixation by bacteria (inorganic)
 Nitrogen fixation def: The metabolic assimilation
of atmospheric nitrogen into ammonia (NH4+) by:
 Rhizobia (tiny root hairs) of legumes
 Legume def: A plant whose roots form an
association with soil-borne bacteria that can
capture atmospheric nitrogen. A good example
of this are soybeans.
 Most important fixation methods
 Microorganisms
 Atmosphere is 79% N2
Rain (inorganic)
Nitrogen Removal from Soil
 Nitrogen removed from soil by:
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Plant uptake
Leaching
Volatilization
Denitrification
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Denitrification def: Chemical reduction of nitrates or nitrites
commonly by bacteria (as in soil) that usually results in the
escape of nitrogen into the air as a gas
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NO3-  N2 or N2O under anaerobic conditions
Erosion
Denitrification in SWAT
 A function of water content and temperature
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when water content > 60%  denitrification will occur
in soil
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Requires a carbon source and nitrates to be present
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when water ponded as in rice production
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large fraction of fertilizer lost by denitrification
 up to 50% losses of N
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for regular cropping systems
 10 – 20% lost to dinitrification
Nitrogen  A Reactive
Element
 Can exist in a number of valance states:
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+5  NO-3 (nitrate)
+3  NO-2 (nitrite)
-3  NH4+ (ammonium)
 The ability of N to vary valence states makes it a
highly mobile element
 SWAT monitors 5 pools of nitrogen
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NH4+ , NO-3 and 3 organic N pools associated with
crop residue / microbial biomass / soil humus
Nitrate-Nitrogen (NO3-N)
 Maximum Contaminate Limit (MCL) = 10 ppm
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Immediate reaction in some at-risk populations
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Very young / old / sick
Very difficult to filter out of water
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Reverse osmosis is one way  expensive
SWAT: Nitrogen Transport
 SWAT calculates N transport for each runoff event
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Inorganic N and Organic N
Estimates daily inorganic N and organic N in runoff
based on:
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Concentration of inorganic N and organic N in the top soil
layer
Sediment yield
Enrichment ratio
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Concentration of inorganic N and organic N in sediment is a function
of the concentrations in the soil
Phosphorus Cycle
Labile definition: Readily or continually undergoing
chemical, physical, or biological change or breakdown
Phosphorus (P)
 P is not very soluble
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Partitioned into:
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Solution phase
Sediment phase
 P combines with other ions to form insoluble
compounds that precipitate out of solution
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Leads to build-up of P near the soil surface
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Therefore available for transport by surface runoff
Phosphorus (P)
 P in runoff calculated by:
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Labile P concentration in the top 10 mm of soil
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Labile (lay-bile): continually undergoing chemical,
physical or biological change or breakdown; unstable
Runoff volume
A partitioning factor
 Sediment transport
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Same loading function as for organic N transport
Routing of Water and
Chemical in Streams
 Mass balance maintained in the main channels for:
 Water
 Sediment
 Nutrients
 Organic chemicals
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Pesticides and herbicides
 In-stream processes include:
 Transformations
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In suspension in the stream
Chemicals that have settled to the streambed
Routing of Water and
Chemical in Streams
 In-stream processes include (cont.):
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Biodegradation
Sorption to sediments
Diffusion
Deposition
Re-suspension
Volatilization
 Can also handle point discharges
Water Routing
 Processes simulated
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Evaporation
Transmission losses through the channel bed
Withdrawals
Point source discharges
Rainfall directly into the channel
Sediment Routing
 Deposition
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Particle fall velocity using Stokes Law
 Degradation
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Based on stream power
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Stream power = water density x flow rate
Re-entrains deposited material
Degrades stream bed
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Function of:
 Bed erodibility
 Cover
Nutrient Routing
 Nutrient transformations and routing
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Adapted from the QUAL2E model
Tracks nutrients
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Dissolved N in the stream
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Transported with the water
Adsorbed to the sediment
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Can be deposited with the sediment in the bed
Organic Chemical Routing
 Only one organic chemical may be transported at
one time
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Tracks organic chemicals
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Same as nutrients
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Dissolved in the stream
 Transported with the water
Adsorbed to the sediment
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Can be deposited with the sediment in the bed
Reservoir Routing
 Maintains a mass balance for:
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Inflows
Outflows
Rainfall on the surface
Evaporation
Seepage through the bottom
Withdrawals
Discharges into reservoirs
Reservoir Outflow
 User can provide measured outflow values
 For small, uncontrolled reservoirs
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User can specify a release rate (spillway flow rate)
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Flow only when water exceeds the principal storage
level
Volume exceeding the emergency spillway level
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Released in one day
 For large, managed reservoirs
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User specified monthly target release volumes
Reservoir Sediment Routing
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Sediment inflow sources
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Reservoir sediment concentration is a function of:
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In-stream sediment
Surface runoff with suspended sediment
Amount of sediment in the inflow (vol x conc)
The outflow
Storage in the reservoir
Settling is governed by Stokes Law
 Sediment in the outflow = outflow vol x suspended
sediment concentration
Reservoir Nutrient Routing
 Uses a simple phosphorus model
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Ignores lake stratification
Reservoir Pesticide Routing
 Assumes organic chemical is well mixed in:
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The surface water layer
The sediment layer
Class Wrap-up
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Next class in 214 Scoates
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Get started on your projects
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Presentation order  luck of the draw!