comparing agricultural and urban nutrient loads to coastal ... · nunes and ferreira: agricultural...

Comparing Agricultural and Urban Nutrient Loads to Coastal Systems

João Pedro NUNES, João Gomes FERREIRAUniversity of Aveiro, Portugal

NOVA University of Lisbon, PortugalLongline Environment, UK

Nunes and Ferreira: Agricultural and Urban Nutrient Loads to Coastal Systems

Nutrient loads and aquaculture• Aquaculture and nutrients: an ambivalent relation

− Nutrients support primary production and food, but…− Excessive loads can cause eutrophication

• Nutrient management has focused on wastewater− Point sources: easy to locate, measure and control

• Agricultural sources are more difficult to manage− Variable in space, depend on weather− Difficult to measure and to identify sources− Difficult to design control measures


Objectives of this work• Compare nutrient loads to coastal systems from wastewater and agriculture…− Recent evolution− Spatio‐temporal patterns− Sources and potential impacts

• … for two coastal systems with important aquaculture sites− Lough Foyle, UK− Ria Formosa, Portugal

Lough Foyle

Ria Formosa

Lough Foyle

Ria Formosa


Study systemsLough Foyle• Oceanic climate• Aquaculture: mussels and native oysters (bottom culture)

• Trophic status:− High nutrient loads, mostly N− Few eutrophication symptoms: shellfish filtration (?) and P limitation (?)

Ria Formosa• Mediterranean climate• Aquaculture: clams (traditional) and mussels (offshore, developing)

• Trophic status:− High nutrient loads− Few eutrophication symptoms due to strong water exchange…

− … but occasional water quality issues and macroalgae blooms

Lough Foyle

Ria Formosa

051015202530

0

50

100

150

1 2 3 4 5 6 7 8 9 101112

Tempe

rature (ºC)

Rainfall (m

m)

Month

Ria Formosa (Faro)

051015202530

0

50

100

150

1 2 3 4 5 6 7 8 9 101112

Tempe

rature (ºC)

Rainfall (m

m)

Month

Lough Foyle (Malin Head)

Lough Foyle: Loughs Agency 2012: Lough Foyle Status ReportRia Formosa: Ferreira et al. 2013: FORWARD project report

Rainfall

Temperature


Lough Foyle watershed• Area: 3709 Km2

• Wastewater discharge: 210,000 inhabitants

• Landuse:− Pasture: 54%− Rangelands: 43%− Croplands, urban: 3%

Lough Foyle


Ria Formosa Watershed• Area: 745 Km2

• Wastewater discharge: 300,000 inhabitants

• Landuse:− Croplands – intensive orchards: 18%− Croplands – rainfed orchards: 29%− Rangelands: 48%− Other crops, urban, pasture: 5%

• Contaminated coastal aquifer

Ria Formosa

Faro

Tavira

Olhão

Ria Formosa


Research framework• Large‐scale aquaculture assessment projects in both systems− Linking catchments to coasts− Linking management agencies and research institutes

− Tool: complex modelling framework

Wastewater, agriculture and stream network

Coastal ecosystems and aquaculture

Coastal water circulation

Water

Nutrients

EASE: Enhanced SMILE for Lough Foyle

Lough Foyle Ria Formosa

Framework for Ria Formosa water quality, aquaculture & resource development


Wastewater nutrient loads• Point‐sources:

− Measured, easy to quantify− Relatively constant along the year

• Recent trends:− Improved wastewater treatment by adding nutrient removal

− Ria Formosa: increase in population served by treatment plants

• Wastewater treatment close to maximum

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000


Popu

latio

n served

Before 2000 After 2010

02468

101214

Untreated

Before 200

0

After 2

010

Before 200

0

After 2

010


N lo

ads (g/pe

rson

.dy)

0

100

200

300

400

500

600

700


Nitrog

en (ton

/yr)


0

20

40

60

80

100

120

140


Phosph

orus (ton

/yr)


Nitrogen load (per inhabitant)

Population served

Total N loads Total P loads


y = ‐3E‐05x + 2.28R² = 0.0154

0

0.5

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/201

4

Nitrates (m

g N/L)

Stream

flow (m

3 /s)

Streamflow Nitrate concentration Linear (Nitrate concentration)y = ‐8E‐06x + 0.4324

R² = 0.0038

00.20.40.60.811.21.41.61.8

020406080

100120140160

01/199

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8

Nitrates (m

g N/L)

Stream

flow (m

3 /s)

Streamflow Nitrate concentration Linear (Nitrate concentration)

Agriculture nutrient loads• Diffuse sources:

− Difficult to measure, quantify and assign to sources

• Trends difficult to assess:− Monthly measurements do not capture peak flows

− High temporal variability

• What was the impact of fertilizer control measures?

Lough Foyle (Mourne)

Ria Formosa (Alportel)

Nitrate Action Plan

1994 2014

1990 2008

No streamflow data


y = ‐3E‐05x + 2.28R² = 0.0154

0

0.5

1

1.5

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/201

001

/201

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/201

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/201

301

/201

4

Nitrates (m

g N/L)

Stream

flow (m

3 /s)

Streamflow Nitrate concentration Linear (Nitrate concentration)y = ‐8E‐06x + 0.4324

R² = 0.0038

00.20.40.60.811.21.41.61.8

020406080

100120140160

01/199

0

01/199

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8

Nitrates (m

g N/L)

Stream

flow (m

3 /s)

Streamflow Nitrate concentration Linear (Nitrate concentration)

0

0.5

1

1.5

2

2.5

3

3.5

050

100150200250300350400

01/201

302

/201

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/201

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/201

3

Nitrates (m

g N/L)

Stream

flow (m

3 /s)

Streamflow Nitrate concentration

0

1

2

3

4

5

6

01020304050607080

10/200

511

/200

512

/200

501

/200

602

/200

603

/200

604

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605

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606

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607

/200

608

/200

609

/200

6

Nitrates (m

g N/L)

Stream

flow (m

3 /s)

Streamflow Nitrate ‐ official Nitrate ‐ storm

Agriculture nutrient loads• Diffuse sources:

− Difficult to measure, quantify and assign to sources

• Trends difficult to assess:− Monthly measurements do not capture peak flows

− High temporal variability

• What was the impact of fertilizer control measures?



Storm measurements : Stigter et al., 2006

2013

2005/06

Nitrate Action Plan

1994 2014

1990 2008

No streamflow data


Nutrients and aquifers• Lough Foyle: impermeable geology− Delays part of nutrient loads: spread during several months

• Ria Formosa: coastal aquifer− Permeable and already contaminated

− Flows under the coastal system: only part resurfaces

− Delays part of nutrient loads: spread during years/decades

COASTAL SYSTEM

LANDSCAPE

AQUIFER

Fertilization

WWtW WWtW

Stream network

PercolationEspecially N

WWtW: WasteWatertreatment Works


COASTAL SYSTEM

LANDSCAPE

AQUIFER

Fertilization

WWtW WWtW

Stream network

?Sediments

OCEAN

PercolationEspecially N

Nutrients and aquifers• Lough Foyle: impermeable geology− Delays part of nutrient loads: spread during several months

• Ria Formosa: coastal aquifer− Permeable and already contaminated

− Flows under the coastal system: only part resurfaces

− Delays part of nutrient loads: spread during years/decades



Nutrient load assessment strategy• Calculate daily loads and assess sources:

− Wastewater: direct measurements− Agricultural loads: hydrological model SWAT− Aquifer loads (Ria Formosa): measurements on the Ria Formosa sediment bed

Lough Foyle→ 11 WWtW→ SWAT: 330 landscape units in 29 streams→ Representative year: 2014

Ria Formosa→ 7 WWtW→ SWAT: 331 landscape units

in 50 streams→ Representative year:

10.2007 to 09.2008


Sediment measurements:

Leote et al., 2008


SWAT: Soil and Water Assessment Tool

Stream

CLIMATEHUMAN

MANAGEMENT

Plantgrowth

Hydrology

Nutrientcycling

Water and nutrientexport

LAND PHASE(for each landscape unit)

ROUTING PHASE

Water and nutrient in‐stream processes

Lake andreservoirprocesses

WATERSHED OUTPUT

Wastewater discharges

daily Δt

Landscape unit: unique combination of stream location, land cover, soil type and slope


Calibration & validation• Measurements do not capture the major peaks, especially in Ria Formosa

− Streamflow: good model performance− Nutrients: model not easy to evaluate; best available estimate

0

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/201

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/201

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/201

4

Stream

flow (m

3 /s)

Measured Simulated

0

10

20

30

40

50

60

01/200

404

/200

407

/200

410

/200

401

/200

504

/200

507

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510

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501

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604

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607

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610

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601

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704

/200

707

/200

710

/200

701

/200

804

/200

807

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810

/200

801

/200

904

/200

907

/200

910

/200

901

/201

004

/201

007

/201

010

/201

001

/201

104

/201

107

/201

110

/201

101

/201

204

/201

207

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210

/201

201

/201

304

/201

307

/201

310

/201

301

/201

404

/201

407

/201

410

/201

4

Nitrate (ton

N)

Measured Simulated

00.51

1.52

2.53

3.54

4.55

01/200

404

/200

407

/200

410

/200

401

/200

504

/200

507

/200

510

/200

501

/200

604

/200

607

/200

610

/200

601

/200

704

/200

707

/200

710

/200

701

/200

804

/200

807

/200

810

/200

801

/200

904

/200

907

/200

910

/200

901

/201

004

/201

007

/201

010

/201

001

/201

104

/201

107

/201

110

/201

101

/201

204

/201

207

/201

210

/201

201

/201

304

/201

307

/201

310

/201

301

/201

404

/201

407

/201

410

/201

4

Phosph

ate (ton

P)

Measured Simulated

020406080

100120140160

10/200

1

12/200

1

04/200

2

07/200

2

10/200

2

01/200

3

04/200

3

07/200

3

10/200

3

01/200

4

04/200

4

07/200

4

10/200

4

01/200

5

04/200

5

07/200

5

10/200

5

01/200

6

04/200

6

07/200

6

10/200

6

01/200

7

04/200

7

07/200

7

10/200

7

01/200

8

04/200

8

07/200

8

Stream

flow (m

3 /s)

Measured Simulated

00.51

1.52

2.53

3.54

4.55

10/200

1

12/200

1

04/200

2

07/200

2

10/200

2

01/200

3

04/200

3

07/200

3

10/200

3

01/200

4

04/200

4

07/200

4

10/200

4

01/200

5

04/200

5

07/200

5

10/200

5

01/200

6

04/200

6

07/200

6

10/200

6

01/200

7

04/200

7

07/200

7

10/200

7

01/200

8

04/200

8

07/200

8

Nitrate (ton

N)

Measured Simulated

00.20.40.60.81

1.21.41.61.82

10/200

1

12/200

1

04/200

2

07/200

2

10/200

2

01/200

3

04/200

3

07/200

3

10/200

3

01/200

4

04/200

4

07/200

4

10/200

4

01/200

5

04/200

5

07/200

5

10/200

5

01/200

6

04/200

6

07/200

6

10/200

6

01/200

7

04/200

7

07/200

7

10/200

7

01/200

8

04/200

8

07/200

8

Phosph

ate (ton

P)

Measured Simulated

Lough Foyle (Mourne) Ria Formosa (Alportel)

Stream

flow

Nitrate

Phosph

ate

Stream

flow

Nitrate

Phosph

ate

2004 2014 2001 2008


0

100

200

300

400

500

600

01/200

404

/200

407

/200

410

/200

401

/200

504

/200

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510

/200

501

/200

604

/200

607

/200

610

/200

601

/200

704

/200

707

/200

710

/200

701

/200

804

/200

807

/200

810

/200

801

/200

904

/200

907

/200

910

/200

901

/201

004

/201

007

/201

010

/201

001

/201

104

/201

107

/201

110

/201

101

/201

204

/201

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/201

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/201

307

/201

310

/201

301

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404

/201

407

/201

410

/201

4

Stream

flow (m

3 /s)

Measured Simulated

020406080

100120140160

10/200

1

12/200

1

04/200

2

07/200

2

10/200

2

01/200

3

04/200

3

07/200

3

10/200

3

01/200

4

04/200

4

07/200

4

10/200

4

01/200

5

04/200

5

07/200

5

10/200

5

01/200

6

04/200

6

07/200

6

10/200

6

01/200

7

04/200

7

07/200

7

10/200

7

01/200

8

04/200

8

07/200

8

Stream

flow (m

3 /s)

Measured Simulated

00.51

1.52

2.53

3.54

4.55

10/200

511

/200

512

/200

501

/200

602

/200

603

/200

604

/200

605

/200

606

/200

607

/200

608

/200

609

/200

6

Nitrate (ton

N)

Measured Simulated

Calibration & validation• Measurements do not capture the major peaks, especially in Ria Formosa

− Streamflow: good model performance− Nutrients: model not easy to evaluate; best available estimate


Stream

flow

Stream

flow

0

0.1

0.2

0.3

0.4

0.5

0.6

10/200

511

/200

512

/200

501

/200

602

/200

603

/200

604

/200

605

/200

606

/200

607

/200

608

/200

609

/200

6

Phosph

ate (ton

P)

Measured Simulated

Nitrate Phosphate


00.20.40.60.81

1.21.41.61.82

01/201

302

/201

303

/201

304

/201

305

/201

306

/201

307

/201

308

/201

309

/201

310

/201

311

/201

312

/201

3

Phosph

ate (ton

P)

Measured Simulated

0

10

20

30

40

50

60

01/201

302

/201

303

/201

304

/201

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/201

3

Nitrate (ton

N)

Measured Simulated

Nitrate Phosphate


51%48%

1%Area

72%

25%

3% 0%

Total Nitrogen

WWtW

Cropland

Rangeland

Pasture61%

33%

6%

0%

Total Phosphorus

WWtW

Cropland

Rangeland

Pasture

Nutrient budgets & sources• Agriculture loads dominate in Lough Foyle:− large watershed, no aquifer losses− high N mobilization

• N/P ratio:− Redfield Ratio (mass): N/P = 7.2− Lough Foyle: N/P = 19.8− Ria Formosa: N/P = 5.6

3%

43%54%

Area2%

7%

20%

71%

Total Nitrogen

WWtW

Cropland

Rangeland

Pasture

17%

7%

39%

37%

Total Phosphorus

WWtW

Cropland

Rangeland

Pasture

Lough Foyle

Ria Formosa

System Nitrogen PhosphorusAgriculture per area (kg/ha.yr)

Lough Foyle 21.9 0.9

Ria Formosa 2.8 0.7

Aquifer: 7%Stream: 21% Aquifer: 3%

Stream: 36%

N = 8 332 ton/yr P = 421 ton/yr

N = 642 ton/yr P = 115 ton/yr

3709 Km2

745 Km2


• Loads concentrated in Autumn and Winter:− N: regular baseflow(groundwater) + stormflow peaks

− P: stormflow peaks

• Seasonality:− Autumn/Winter:dominated by watershed and N

− Summer: dominated by wastewater, N&P equilibrium

Lough Foyle: time patterns

0

20

40

60

80

1000

50

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200

01/201

4

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04/201

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05/201

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06/201

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07/201

4

08/201

4

09/201

4

10/201

4

11/201

4

12/201

4

Rainfall (m

m)

Total N

(ton

N/d

y)

WWtW Watershed Rainfall

0

20

40

60

80

1000

5

10

15

20

01/201

4

02/201

4

03/201

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04/201

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05/201

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06/201

4

07/201

4

08/201

4

09/201

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10/201

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11/201

4

12/201

4

Rainfall (m

m)

Total P

(ton

P/d

y)

WWtW Watershed Rainfall

0

20

40

60

80

1000%

20%

40%

60%

80%

100%

01/201

4

02/201

4

03/201

4

04/201

4

05/201

4

06/201

4

07/201

4

08/201

4

09/201

4

10/201

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11/201

4

12/201

4

Rainfall (m

m)

WWtW

fractio

n

Rainfall Total N Total P

0

20

40

60

80

100020406080

100120140160180

01/201

4

02/201

4

03/201

4

04/201

4

05/201

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06/201

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07/201

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08/201

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09/201

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10/201

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11/201

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12/201

4

Rainfall (m

m)

N/P

ratio

Rainfall N/P Foyle Redfield ratio


Lough Foyle

• Agricultural loads cause:seasonality, irregularity and N dominance


0

50

100

150

2000

10

20

30

40

50

10/200

7

11/200

7

12/200

7

01/200

8

02/200

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03/200

8

04/200

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05/200

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06/200

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07/200

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08/200

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Rainfall (m

m)

Total N

(ton

N/d

y)WWtW Aquifer Watershed Rainfall

0

50

100

150

2000

5

10

15

20

10/200

7

11/200

7

12/200

7

01/200

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02/200

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05/200

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Rainfall (m

m)

Total P

(ton

P/d

y)

WWtW Aquifer Watershed Rainfall

0

50

100

150

2000%

20%

40%

60%

80%

100%

10/200

7

11/200

7

12/200

7

01/200

8

02/200

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03/200

8

04/200

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05/200

8

06/200

8

07/200

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08/200

8

09/200

8

Rainfall (m

m)

WWtW

fractio

n


0

50

100

150

20005

10152025303540

10/200

7

11/200

7

12/200

7

01/200

8

02/200

8

03/200

8

04/200

8

05/200

8

06/200

8

07/200

8

08/200

8

09/200

8

Rainfall (m

m)

N/P

ratio

Rainfall N/P R Formosa Redfield ratio

• Relatively regular loads, with irregular stormflow peaks

• Small seasonality:− Autumn to Spring:dominated by wastewater

− … except for a few days dominated by watershed stormflow

− Summer: dominated by wastewater

Ria Formosa: time patterns

• Agricultural loads cause:high irregularity (with small seasonality)

Ria Formosa

2007 2008 2007 2008Rainfall Total N Total P


Streams (ton N)WWtW (ton N)

0

50

100

150

2000

10

20

30

40

50

10/200

7

11/200

7

12/200

7

01/200

8

02/200

8

03/200

8

04/200

8

05/200

8

06/200

8

07/200

8

08/200

8

09/200

8

Rainfall (m

m)

Total N

(ton

N/d

y)

WWtW Aquifer Watershed Rainfall

Ria Formosa: spatial patterns• Contrast between annual and stormflow loads− annual: mostly western RF – WWtW− stormflow: mostly eastern RF – rivers− more sensitive coastal area due to restricted ocean exchange

• Agricultural loads may cause localized, short‐term problems

Ria Formosa

N: 72%P: 65%

N: 5%P: 9%

N: 23%P: 26%

N: 22%P: 20%

N: 22%P: 30%

N: 56%P: 50%

Annual loads

8 to 12‐Apr‐2008

Nutrient WWtW Watershed Total

Nitrogen 1.6% 30% 8%

Phosphorus 1.6% 44% 19%

Fraction of annual load in 8 to 12‐Apr‐2008

WWtW (ton N) Streams (ton N)


Agricultural impactsLough Foyle nutrient loads• Wet climate: strong seasonality + peaks after rainfall

• Wet climate + Pasture:− Abundant water mobilizes N− Vegetation cover: low P exports

• Simple geography: most loads from the estuary of River Foyle

• Simple geology: strong N load seasonality via baseflow

Ria Formosa nutrient loads• Dry climate: loads concentrated in peaks after rainfall

• Dry climate + Orchards:− Less water available to mobilize N− Lower vegetation cover: P exports

• Complex geography: load locations vary with weather

• Complex geology: not all N loads reach the coastal system

Lough Foyle

Ria Formosa


Nutrient loads and aquaculture• Aquaculture and nutrients: an ambivalent relation

− Nutrients support primary production and hence food, but…− Excessive loads can limit aquaculture through eutrophication

• Lough Foyle: low impacts despite high N loads; P limitation?

• Ria Formosa: occasional impacts due to agriculture− High loads counteracted by strong exchange with ocean…− … but occasional acute water quality issues: stormflow loads?

• Wastewater control should be supplemented with agricultural nutrient management


Agricultural nutrient management• Water Framework Directive quality goals might require load reduction to streams and coastal systems

• Challenges for agricultural nutrient management:− Monitoring: often too infrequent to understand issues− Fertilization control: limited by plant requirements− Agricultural abandonment: negative economic impacts− Long‐term contamination: nutrient stocks remain in soils and groundwater decades after fertilization control

• Innovative solutions: limiting the connectivity between fields and streams through landscape management

http://connecteur.info/


Conclusions• Agricultural nutrient loads can impact coastal systems

• With wastewater treatment widespread, nutrient management should focus on agriculture− Often as important as wastewater loads− Irregular loads, complex impacts− More challenging to monitor and control

• If farmers (land and sea) understand their watersheds, they can participate on nutrient management decisions

comparing agricultural and urban nutrient loads to coastal ... · nunes and ferreira: agricultural...

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