Nutrient Concentrations in Coastal Streams, Variation with Land Use in the

Carpinteria Valley (Santa Barbara Coastal LTER)

Timothy H. RobinsonJohn M. MelackArturo A. Keller

Bren School of Environmental Science and ManagementUniversity of California Santa Barbara

Outline of the talk

Project overview

Sampling strategy and location

Measuring stream nutrient concentrations and flow

Nutrient loading and the development of a flux model

Basin outlet mass flux

Comparison of nutrient loading by land use type

Nutrient export coefficient modeling

Integration with an urban growth model

Project Overview

Watersheds Drainage Area Max-Elevation Ave-Slope Urban Agriculture Chaparral/Forest(km2) (m) (ft) (%) (%) (%) (%)

Carpinteria 39.2 1424 4672 38 2 11 85Franklin 11.6 533 1749 20 29 30 40

Santa Monica 9.8 1192 3911 45 3 3 93

Methodology

Identify land use classes and sampling site locations: Chaparral/Forest, Avocado, Greenhouse, Open-Field Nursery, Residential and Commercial

Sampling strategies: Subcatchment, point discharge and above-below

Sampling methods: Manual sample or ISCO auto-sampler

GIS database development

Data analysis

Nutrient flux calculation (hydrology and stream chemistry)

Nutrient export coefficient model development

Integration with an urban growth model

Sampling Site Locations

Measuring Nutrient Concentrations

Grab samples and ISCO auto- samplers

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 a week during the wet seasonOnce every 2 weeks during the dry season

• Storm sampling:Every hour on the rising limb of the hydrographEvery 2-4 hours on the falling limb of the hydrograph

Specifics:

Measuring Stream Flow

Staff Gauges and Pressure TransducersSurveying the Cross-Sections

Developing Rating Curves

Stream Chemistry and Hydrology

0

300

600

900

1200

10/30 10/31 11/1

Nitr

ate

(µM

)

0.6

0.8

1.0

1.2

1.4

Stag

e at

out

let (

ft)

outlet

commercial

residential

chaparral/forest

stage-recorded

Carpinteria Creek (WY-2002)

General Trends in Nutrient Concentrationsby Watershed

1

10

100

1000

10000

Franklin Carpinteria Santa Monica

nitr

ate

(µM

)

baseflow

stormflow

1

10

100

Franklin Carpinteria Santa Monica

phos

phat

e (µ

M)

baseflowstormflow

Nutrient LoadingDevelopment of a Nutrient Flux Model

StreamChemistry

ObservedStage

PTStage

(5-min)

ObservedFlow

PTFlow

(5-min)Stream

Chemistry

Stage-Discharge Relationship(HEC-RAS)

Flow(hourly)Flow

(hourly)

StreamChemistry(hourly)

Identify: Baseflow, Peakflow..

Nut. Conc.Flow

(hourly)

StreamChemistry

(model/obs)

Nut. Flux(conc/flow)

AnnualAnnualNutrient LoadingNutrient Loading

ObservedFlow

(hourly)

Linear extrapolation

0

20

40

60

80

100

120

140

160

10/28 11/7 11/17 11/27 12/7 12/17

Conc

entr

atio

ns (u

M)

0

0.5

1

1.5

2

2.5

3

3.5

4

Flow

(cfs

)

Model-NO3Series2FlowNO3 observedNO3 modeled

Modeled vs. Observed

Residential - CP30

Cumulative Nitrate ExportNursery Site

0

20

40

60

80

100

120

140

160

180

10/26 11/5 11/15 11/25 12/5 12/15 12/25

Cum

ulat

ive

Expo

rt (K

mol

)

0

20

40

60

80

100

120

Flow

(cfs

)

NO3-FK07NO3-FK06Flow-FK07Flow-FK06

1

10

100

1000

10000

5-Jan 15-Jan 25-Jan 4-Feb 14-Feb 24-Feb 6-Mar

cum

ulat

ive

expo

rt(K

mol

)

0

50

100

150

200

250

flow

(cfs

)

NH4 NO3 PO4

TDN flow

WY 2001

Basin Nutrient Export Franklin Creek Watershed

0

2,000

4,000

6,000

8,000

10,000

12,000

Santa Monica Franklin Carpinteria

Nutri

ent L

oadi

ng (k

g/yr

)

NH4-N

NO3-N

DON-N

PO4-P

WY2001 Basin Outlet Mass Flux

WY 2001

Comparison of Flux afterNormalizing with Runoff

1

10

100

Oct. 30 Nov. 29 Dec. 20Date of Storms

Expo

rt (g

/ha-

mm

)

NO3-residentialNO3-commercialNO3-greenhouse

0

1

10

100

1000

Oct. 30 Nov. 29 Dec. 20Date of Storms

Expo

rt (g

/ha-

mm

)

PO4-residentialPO4-commercialPO4-greenhouse

AAGISGISEE

IIInterviewInterview

IILiteratureLiterature

KKLiteratureLiterature

LUE tkeK

kk ttD/VD/V

LULUGISGIS

Abbreviation key:• E – Export Coefficient Function• B – Watershed Response Variable• S – Soils• P - Precipitation

Nutrient Export Coefficient Model

DKIAEL atmiiii

DDatmatmLTERLTER

DDatmatmLiteratureLiterature

S+P +ASMCS+P +ASMC

• ASMC – Antecedent Soil Moisture Content• K – Down Stream Distance-Decay Function• k + – Coefficients• t – Time

• D – Distance Traveled Downstream• V – Average Velocity Traveled Downstream

L

Integration with an Urban Growth Model (SLEUTH)

• SLEUTH : an urban growth model implemented for the Santa Barbara area that predicts future land use, example 2050

• Enables comparison of future loadings to standards being set for stream water quality regulations (TMDLs)

• Evaluation of proposed BMP mitigations

Conclusions• Stream nutrient concentrations only partially tell the story

• Hydrology is the critical element of any flux calculation, which is necessary to characterize nutrient loading

• The finer the sampling strategy the better the results, particularly with urban/agriculturally dominated sites

• Creating a dedicated and enthusiastic group of stream samplers is a crucial component of any project of this nature

• Nutrient export coefficients for a Mediterranean climate need to accommodate the high inter/intra-year storm variability

• A minimum of two years of data are needed to statistically validate model results

• Hope for rain!!

Questions

Thank you