IOWA

Sources and Flux of Nitrate-Sources and Flux of Nitrate-Nitrogen in the Cedar River, Nitrogen in the Cedar River,

Iowa, Iowa, Chad FieldsChad Fields

Iowa Geological Survey - Iowa Geological Survey - IDNRIDNR

•90% of Iowa’s land is dedicated to agriculture

IOWAIOWACedar River

Upper Cedar River

Shell Rock River

West Fork Cedar

Beaver Creek

Black Hawk Creek

Wolf Creek

Middle Cedar

Nitrate Impaired Segment

Minnesota

Iowa

10 0 10 20 30 40 Kilometers

Southern Iowa Drift Plain

Iowan Surface

Paleozoic Plateau

Des Moines Lobe


City

Watershed Areas

More than agricultural More than agricultural issues:issues:

Des Moines LobeDes Moines Lobe Shallow BedrockShallow Bedrock IndustryIndustry SizeSize

Reason for studyReason for study

The Cedar River is used as a drinking The Cedar River is used as a drinking water source for the City of Cedar water source for the City of Cedar Rapids, Iowa.Rapids, Iowa.

As such, nitrate concentrations in the As such, nitrate concentrations in the Cedar River are regulated by the Cedar River are regulated by the EPA. EPA. <10 mg/L as N.<10 mg/L as N.

Must exceed certain EPA guidelines for (usually) concentration)…

In this case – nitrate-N

Nitrate-N Monitored at Cedar Rapids

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1/2/01 1/2/02 1/2/03 1/2/04 1/1/05Date

Nitr

ate-

N (p

pm)

--On 303(d) – impaired waterbody list-On 303(d) – impaired waterbody list-

TMDL - Total Maximum Daily TMDL - Total Maximum Daily LoadLoad

““Greatest amount of pollutant a Greatest amount of pollutant a waterbody can receive without waterbody can receive without exceeding the water quality standard.”exceeding the water quality standard.”

Usually based on concentration (10 mg/L).Usually based on concentration (10 mg/L). Usually a % reduction from one, or Usually a % reduction from one, or

multiple sources.multiple sources.

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0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000

Flow (cubic feet per second)

Nitr

ate

as N

(mg

/L)

USGS Monitoring 1906 - 1913 USGS Monitoring 1944 - 1951

Cedar Rapids Water Treatment Plant Monitoring 2001 - 2004 Station 10570002 Upstream of Cedar Rapids 2001 - 2004

TMDL EquationTMDL Equation

Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of SafetySafetyModeleModeledd

-DAFLOW-DAFLOW-WASP-WASP

RegulatedRegulated

Wastewater-Wastewater-NPDES NPDES

PermitsPermits

‘‘Natural’Natural’

-Septic-Septic-Wildlife-Wildlife-Wet Dep.-Wet Dep.-Dry Dep.-Dry Dep.

AgricultureAgriculture

-Row Crop-Row Crop-Fertilizer-Fertilizer-Manure-Manure-Septic-Septic

Safety bufferSafety buffer

-Concentration -Concentration decreasedecrease

ModelingModeling Two different models:Two different models:

DAFLOW for dischargeDAFLOW for discharge WASP for nitrateWASP for nitrate

4-year time span for each model4-year time span for each model

Important (fundamental) facts about models:Important (fundamental) facts about models: Only as good as what you put in them.Only as good as what you put in them. Only good for that moment in time.Only good for that moment in time.

DAFLOWDAFLOWWater Water ModelModel

Input PointModeled Point

WASP modelWASP model Calculates concentrations of nitrate in the Calculates concentrations of nitrate in the

stream/lake/pondstream/lake/pond User inputs given concentrationsUser inputs given concentrations

Ambient monitoringAmbient monitoring SnapshotsSnapshots NAQWA monitoringNAQWA monitoring Cedar Rapids monitoringCedar Rapids monitoring

Can incorporate processes such as instream Can incorporate processes such as instream algal uptake, mineralization, denitrification, algal uptake, mineralization, denitrification, etc.etc. Not used in this model (lack of data).Not used in this model (lack of data).

WASP + DAFLOWWASP + DAFLOWPredicted Vs. Observed Nitrate-N

y = 0.8127x + 1.4802

R2 = 0.7542

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0 2 4 6 8 10 12 14 16Observed at Cedar Rapids

Pre

dic

ted

at

Ce

da

r R

ap

ids

Model Results - TributariesModel Results - TributariesDischarge into the Middle Cedar

2,960,111 ac-ft/yr

Beaver3%

Black Haw k3%

Wolf3%

West Fork14%

Shell Rock 37%

Upper Cedar40%

Nitrate-N load to the Middle Cedar32,570 tons N/yr Upper

Cedar42%

Shell Rock 29%

West Fork16%

Wolf4%Black

Haw k5%

Beaver4%

Nitrate-N Contribution per unit area

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UpperCedar

ShellRock

WestFork

Beaver BlackHaw k

Wolf

Nit

rate

-N C

on

t. (

lbs/

ac./y

r)

Nitrate-N Concentration

0123456789

10

UpperCedar

ShellRock

WestFork

Beaver BlackHaw k

Wolf

Nit

rate

-N (

mg

/L)

Upper Cedar River

Shell Rock River

West Fork Cedar

Beaver Creek

Black Hawk Creek

Wolf Creek

Middle Cedar

Minnesota

Iowa

10 0 10 20 30 40 Kilometers

Watershed Areas


City

Model Results – Entire CedarModel Results – Entire Cedar

Upper Cedar River

Shell Rock River

West Fork Cedar

Beaver Creek

Black Hawk Creek

Wolf Creek

Middle Cedar

Minnesota

Iowa

10 0 10 20 30 40 Kilometers

Watershed Areas


City

•Discharge = 2,683,908 ac-ft/yrDischarge = 2,683,908 ac-ft/yr•Nitrate-N load = 28,561 tons/yrNitrate-N load = 28,561 tons/yr•Watershed contribution = 13.7 Watershed contribution = 13.7 lbs/ac/yrlbs/ac/yr•Daily mean concentration = 6.1 mg/LDaily mean concentration = 6.1 mg/L


Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of SafetySafetyModeleModele

dd


RegulatedRegulated


PermitsPermits


-Septic-Septic-Wildlife-Wildlife-Wet Dep.-Wet Dep.-Dry Dep.-Dry Dep.





MethodMethod

Total nitrogen sources (all nitrogen Total nitrogen sources (all nitrogen deposited has an equal chance of deposited has an equal chance of converting to nitrate in Cedar River).converting to nitrate in Cedar River). Most nitrogen travels downstream as Most nitrogen travels downstream as

nitratenitrate Point sources 1:1 ratio with nitrate loadPoint sources 1:1 ratio with nitrate load Nonpoint and background = load – point Nonpoint and background = load – point

sourcessources

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West Fork CedarRiver

Shell Rock River

Beaver Creek

Black HawkCreek

Wolf Creek

Upper CedarRiver

Middle Cedar River

Point Sources – NPDES PermitsPoint Sources – NPDES Permits

Monthly point sourcesMonthly point sources

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14000


Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of SafetySafety

ModeleModeledd


RegulatedRegulated


PermitsPermits


-Wildlife-Wildlife-Wet Dep.-Wet Dep.-Dry Dep.-Dry Dep.





Deposition – NADP and Deposition – NADP and CASTNETCASTNET

From the National From the National Atmospheric Atmospheric Deposition Deposition ProgramProgram

Quarterly loads (kg/ha) inorg. N1990’s - present

WildlifeWildlife

Deer population studies:Deer population studies: From Iowa DNRFrom Iowa DNR 0.05 lbs N/deer/day * 2 (for all wildlife)0.05 lbs N/deer/day * 2 (for all wildlife)

TMDL equationTMDL equation

Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of Load = ‘Point’ + ‘Background’ + ‘Nonpoint’ + Margin of SafetySafety

ModeleModeledd


RegulatedRegulated


PermitsPermits


-Wildlife-Wildlife-Wet Dep.-Wet Dep.-Dry Dep.-Dry Dep.





Septic SystemsSeptic Systems Septic loads = rural population * Septic loads = rural population *

average nitrate load/personaverage nitrate load/person Rural population from 2000 censusRural population from 2000 census Average nitrate load/person.Average nitrate load/person.

From Nassau, 1981From Nassau, 1981 4.5 kg nitrate-N/person/year4.5 kg nitrate-N/person/year

AgriculturalAgricultural

Manure, fertilizer and legume Manure, fertilizer and legume nitrogen levels from MWPS, 2002.nitrogen levels from MWPS, 2002. Countywide dataCountywide data 2002 landuse estimates2002 landuse estimates Confined Feeding Operation (CAFO) Confined Feeding Operation (CAFO)

permitspermits

Land use in the Cedar RiverLand use in the Cedar River

Sub-basin Area (mi2) Rowcrop Forest Grassland Developed Water OtherUpper Cedar* 1,441 72.6 4.5 18.0 3.5 0.8 0.5Shell Rock* 1,756 72.8 2.9 18.7 3.1 2.2 0.3West Fork 858 77.1 2.9 16.9 2.4 0.6 0.1Beaver Creek 399 79.8 2.3 15.0 2.5 0.4 0.0Black Hawk 339 81.2 1.7 12.6 4.2 0.3 0.1Wolf Creek 333 80.9 2.4 14.3 2.1 0.3 0.0Middle Cedar 1,223 62.8 7.4 20.9 7.0 1.7 0.2Total 6,349 72.7 4.0 17.9 3.8 1.2 0.3

Source contributions of Source contributions of nitrogennitrogen

Sub-basin Point (tonsN/yr)

Wildlife (tonsN/yr)

Septic (tonsN/yr)

Atm. Dep. (tonsN/yr)

Manure (tonsN/yr)

Legume (tonsN/yr)

Fertilizer (tonsN/yr)

Upper Cedar River 783 84 114 4,117 13,070 22,201 33,061Shell Rock River 457 51 90 4,312 9,629 23,183 38,822West Fork Cedar 44 25 36 2,097 9,298 11,364 18,702Beaver Creek 28 9 22 976 4,169 5,567 8,684Black Hawk Creek 27 7 15 828 2,264 4,835 8,574Wolf Creek 30 10 15 814 1,260 4,692 7,694Middle Cedar 1117 119 131 2,989 5,957 15,034 27,136Total 2487 306 424 16,132 45,648 86,875 142,672

Total Nitrogen Septic0.2%

Point9%

Wildlife0.1%

Legume27%

Manure14%

Atm. Dep.5%

Fertilizer45%

TMDL Load CalculationTMDL Load Calculation

June 13, 2003 modeled flow and June 13, 2003 modeled flow and measured nitrate concentrationmeasured nitrate concentration 14.66 ppm NO314.66 ppm NO3 TMDL Concentration (w/ 5% MOS) = 9.5 TMDL Concentration (w/ 5% MOS) = 9.5

ppm NO3ppm NO3

35% reduction35% reduction

Reduction ScenarioReduction Scenario

Sub-basin Point (TonsN/yr)

Wildlife (TonsN/yr)

Atm. Dep. (TonsN/yr)

Septic (TonsN/yr)

Manure (TonsN/yr)

Legume (TonsN/yr)

Fertilizer (TonsN/yr)

Upper Cedar River 794 84 4,117 114 13,070 22,201 33,061Upper Cedar TMDL NA NA NA 71 8,162 13,864 20,645Shell Rock River 464 51 4,312 90 9,629 23,183 38,822Shell Rock TMDL NA NA NA 56 6,032 14,523 24,320West Fork Cedar 45 25 2,097 36 9,298 11,364 18,702West Fork TMDL NA NA NA 23 5,865 7,168 11,796Beaver Creek 29 9 976 22 4,169 5,567 8,684Beaver Creek TMDL NA NA NA 14 2,630 3,512 5,478Black Hawk Creek 28 7 828 15 2,264 4,835 8,574Black Hawk Creek TMDL NA NA NA 10 1,428 3,050 5,408Wolf Creek 30 10 814 15 1,260 4,692 7,694Wolf Creek TMDL NA NA NA 9 792 2,947 4,833Middle Cedar 1,132 119 2,989 131 5,957 15,034 27,136Middle Cedar TMDL NA NA NA 81 3,689 9,310 16,804Total 2,521 306 16,132 608 45,648 86,875 142,672Total Cedar TMDL 2,521 306 16,132 380 28,573 54,379 89,304

*NA = not applicable (no reduction)

Other possibilitiesOther possibilities-processes-processes

Best management Best management practices to practices to change the form change the form of nitrogen.of nitrogen. Organic NOrganic N

Percent of Total Nitrogen

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

UpperCedar

ShellRock

WestFork

Beaver BlackHawk

Wolf TotalCedar

Total Kjeldahl N

Nitrate-N

Nitrate-N vs. % Rowcrop

Nitrate-N = 0.3258 * % Row crop - 18.183R2 = 0.80p = 0.017

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% Rowcrop

Nit

rate

-N (

mg

/L)

Tributary landuse and Tributary landuse and concentrationsconcentrations

Nitrate-N Vs. % Tiled

y = -0.1482x + 14.836

R2 = 0.3766

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% Tiled

Nit

rate

-N

Nitrate-N Concentration vs. % CRP

Nitrate-N = -2.512 * % CRP + 10.419R2 = 0.98p <0.001

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Nitr

ate-

N (m

g/L)

Nitrate-N Concentration vs. % Wetland

Nitrate-N = -7.4172 * % Wetland + 9.1609R2 = 0.87p = 0.007

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g/L)

ConclusionsConclusions Rowcrop agriculture is the primary Rowcrop agriculture is the primary

source of nitrate in the Cedar River.source of nitrate in the Cedar River. Reduction of fertilizer, manure inputs Reduction of fertilizer, manure inputs

could decrease nitrate levels.could decrease nitrate levels. Changing land use will also have a Changing land use will also have a

significant impact. significant impact. Conversion of nitrate to organic N Conversion of nitrate to organic N

would help decrease nitrate-N would help decrease nitrate-N concentrations.concentrations.

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