Nutrient Export Coefficient Modeling in Mediterranean Coastal Streams

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Nutrient Export Coefficient Modeling in
Mediterranean Coastal Streams
Timothy H. Robinson, Al Leydecker, Arturo A.
Keller and John M. Melack Bren School of
Environmental Science Management University of
California, Santa Barbara, USA
UC Marine Council
Santa Barbara Coastal LTER - NSF
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Watershed Characteristics
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Specifics
Analyzing for Ammonium (NH4), Nitrate
(NO3-), Total Dissolve Nitrogen (TDN), Phosphate
(PO43-), Total Particulate Carbon (TPC), Total
Particulate Nitrogen (TPN), Total Particulate
Phosphate (TPP), Total Suspended Sediments (TSS)
and major ions at selected locations

• Frequency
• Regular sampling
• Once every 2 weeks during the dry season
• Once a week during the wet season
• Storm sampling
• Every hour on the rising limb of the hydrograph
• Every 2-4 hours on the falling limb of the
  hydrograph

Project duration WY2001, WY2002 and WY2003
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Annual Basin Nutrient ExportWater Year 2001 and
2002
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Nutrient Export Coefficient Model (NEC-M)

• Abbreviation key
• L Nutrient Export (loss) (mass area-1 time-1)
• E Export Coefficient Function
• b Watershed Response Variable
• LU Land use
• S Soils

• P Precipitation
• A Land Use Area
• I Nutrient input rate
• K Down Stream Distance-Decay Function
• k and a Coefficients

• t Time
• d Distance Traveled Downstream
• v Average Velocity Traveled
• Downstream
• Datm Atmospheric deposition

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Spatial Extent of Land Use Class (A)
WY2001 WY2002 WY2003

• Land Use
• Chaparral/Forest
• Avocado
• Greenhouse
• Nursery
• Residential
• Commercial

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Nutrient Export WY2002

• Hourly time-step
• Hydrology
• Pressure Transducer
• Observed stage
• HEC-RAS
• Stream Chemistry
• Modeling

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Nutrient Export Coefficient (E)
Franklin Creek
E Export Coefficient Function b Watershed
Response Variable S Soils P Precipitation
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Scaling the Export Coefficient (b)

• Storm to Storm relationships.
• Volume Weighted Mean Concentrations vs.
  Cumulative Rainfall.
• Volume Weighted Mean Concentrations vs.
  Rainfall/Runoff Ratio.
• Topographic Index (TI) variable source area.
• Antecedent Soil Moisture Content SSURGO soils
  data, texture-gtporosity, infiltration rates,
  evapotranspiration rates, depth to impervious
  layer, etc.

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Nutrient Flux (normalized by runoff)
WY2002
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VWM vs. Runoff/Rainfall
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Conclusions

• High frequency storm sampling is critical.
• Nutrient Export Coefficients in Mediterranean
  climates must be a function that is related to
  the watershed runoff response and not a single
  annual term.
• Analysis of the final year of data will solidify
  scaling techniques in NEC-M.
• Future work implement the model in the study
  watersheds and test its portability in a
  catchment outside of the area (e.g. Spain).

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Questions
Thank you !
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Nutrient Watershed Flux
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Climatic Regime
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Sampling Site Locations
WY2001 WY2002 WY2003

• Land Use
• Chaparral/Forest
• Avocado
• Greenhouse
• Nursery
• Residential
• Commercial

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Linkage Stream Network Chemistry

• Arc Hydro Geodatabase geometric network
  representation of the connectivity of surface
  water
• HydroNetwork
• HydroEdge
• HydroJunctions
• SchematicLinksNodes
• HydroPointEvent
• HydroLineEvent

Drainage Network Sampling Points
DEM analysis
Visual Basic for Application
MS Excel/Access
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Measuring Stream Flow
Staff Gauges and Pressure Transducers Surveying
the Cross-Sections Developing Rating Curves
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Nutrient Loading Development of a Nutrient Flux
Model
Stream Chemistry
Observed Stage
PT Stage (5-min)
Stage-Discharge Relationship (HEC-RAS)
Observed Flow
PT Flow (5-min)
Stream Chemistry
Flow (hourly)
Flow (hourly)
Stream Chemistry (hourly)
Observed Flow (hourly)
Identify Baseflow, Peakflow.. Nut. Conc.
Flow (hourly)
Stream Chemistry (model/obs)
Linear extrapolation
Annual Nutrient Loading
Nut. Flux (conc/flow)
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Precipitation WY2002
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Nutrient Flux (normalized by runoff)
WY2002
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Attenuation (K)

• Distance from stream
• Distance from basin outlet
• Type of riparian corridor
• Dispersal Area and Trapping Likelihood (BI
  Index)

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VWM vs. Cumulative Rainfall
VWM - Volume Weighted Mean
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VWM vs. Cumulative Rainfall
VWM - Volume Weighted Mean
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VWM vs. Runoff/Rainfall