DSD-INT 2014: 3 November 2014

Optimisation of the

nutrient reduction strategy

for the North Sea

IenM/RWS WVL : Ronald van Dokkum

Deltares: Tineke Troost , Hans Los, Jan v. Beek, Christophe

Thiange, Marc Weeber, Joost v.d Roovaart, Sibren Loos

Contents

1. Introduction

2. Approach

3. Results

4. Conclusions

2

3

Eutrophication in the North Sea

Nuisance blooms

• scum layers, bad odour, foam on beaches

Oxygen depletion

• mortality of benthic fauna

Phaeocystis

4

Assessment of ecological status

4

2008

Nitrogen targets (winterconc DIN mg/l)

In case of overlapping targets the most strict of the two is considered

5

Offshore targets (OSPAR) Coastal targets (WFD)

6 6

Project objective

• Starting point: Several areas with present nutrient concentrations

• Desired end point: target nutrient concentrations

• Potential Measures: River load reductions

Objective: To find the optimal set of river load reductions to meet all targets

Contents

1. Introduction

2. Approach

3. Results

4. Conclusions

7

8

Modeling approach

due to:

- Transboundary transport of

nutrients

- Biogeochemical processes

- Limiting factors may vary

(e.g. nitrate, phosphate, light)

Relative reduction (%) in chlorophyll concentration

following 50% river loads reduction

Non-linear response of the

ecosystem to reduced river loads

Integrated catchment and coastal model

9

Hydrology:

SOBEK-RR

Hydrodynamics:

Delft3D-FLOW

10

biogeochemical processes: Delft3D-WAQ

• N, P, Si, plankton, detritus , O2

• 4 functional groups: diatoms,

flagellates, dinoflagelates,

Phaeocystis

• 3 phenotypes adapted to

environmental conditions (light, N,

P limitation)

• Nutrient uptake, respiration,

mortality + ‘grazing’

• Decay in water & sediments,

nitrification, denitrification:

parameterised

• O2 production, consumption,

reareation

• Light extinction (CDOM, SPM,

algae, detritus)

(see e.g. Los & Wijsman, JMS, 2007)

Algae

P

N

C

N

NH4-N

NO3-N

P

PO4-P

Detritus

PNC

settlingsettling

respiration

photosynthesis

Nutrient

mineralisation

mineralisation

metabolism

mortality

DO

production

consumption

reaeration

Detritus in SedimentC N P Si

Si

Si

N2 denitrification

mineralisation & nitrification

autolysis

Si

consumption

nitrification

Grazers

grazing

grazing

oxygen

consumption

biodeposition

AIP adsorption

MicrophytobenthosC N P Si

AIP in

sediment

settling

mortality

photosynthesis

How to determine required nutrient reductions

Traditional approach (source oriented)

•Change some forcings (river loads)

•Rerun several times (scenarios)

•Look at difference between scenarios and base case

11

?

Current situation Desired end point

How to determine required nutrient reductions

12

Alternative approach (target oriented)

1. Labelling: follow fate and transport of all nutrients

2. Set up composition matrix

3. Apply optimization technique

Current situation Desired end point

Step 1. Labelling nutrients

13

• Labeling the nutrients when they enter the system and following

them throughout time and space

FR

BE

NL2

NL1

GM

UK1

UK2

Atlantic

Channel

Atm

Dep

NH4

NH4r

flux

shadow flux

NH4r / NH4 x flux

14

Step 2: From labelling to Composition Matrix

Labelling Technique

14

Area/River BE FR GM NL1 NL2 UK1 UK2 CH NA ATM PO4

UKC6 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000288 0.000012 0.022190 0.000000 0.02249

UKO5 0.000000 0.000002 0.000004 0.000002 0.000000 0.000003 0.000025 0.000244 0.022566 0.000000 0.022846

NO2 0.000003 0.000017 0.000025 0.000024 0.000001 0.000030 0.000236 0.002374 0.020817 0.000000 0.023527

DO1 0.000085 0.000215 0.000263 0.000612 0.000043 0.000435 0.001901 0.017441 0.014486 0.000000 0.035481

DC1 0.000252 0.000558 0.001977 0.002379 0.000222 0.000635 0.001018 0.030624 0.008692 0.000000 0.046357

UKC5 0.000000 0.000001 0.000001 0.000001 0.000000 0.000001 0.000657 0.000046 0.023142 0.000000 0.023849

UKC4 0.000000 0.000002 0.000001 0.000001 0.000000 0.000002 0.000378 0.000060 0.022880 0.000000 0.023324

DO2 0.000002 0.000016 0.000014 0.000016 0.000001 0.000027 0.000242 0.002743 0.020642 0.000000 0.023703

UKC3 0.000000 0.000001 0.000001 0.000001 0.000000 0.000002 0.003233 0.000048 0.022592 0.000000 0.025878

UKO4 0.000001 0.000004 0.000001 0.000003 0.000000 0.000005 0.000084 0.000107 0.021042 0.000000 0.021247

NLO3 0.000001 0.000012 0.000001 0.000008 0.000001 0.000022 0.000416 0.000890 0.020350 0.000000 0.021701

GO3 0.000002 0.000013 0.000002 0.000010 0.000001 0.000023 0.000372 0.001708 0.020178 0.000000 0.022309

DWD1 0.000237 0.000467 0.001962 0.002312 0.000248 0.000378 0.000117 0.008755 0.000984 0.000000 0.01546

UKO3 0.000001 0.000005 0.000001 0.000003 0.000000 0.000006 0.000197 0.000127 0.021148 0.000000 0.021488

GO2 0.000059 0.000172 0.000008 0.000253 0.000013 0.000524 0.002121 0.013181 0.014801 0.000000 0.031132

NLO2 0.000020 0.000084 0.000000 0.000065 0.000002 0.000198 0.001332 0.003989 0.018964 0.000000 0.024654

DWD2 0.000334 0.000651 0.003289 0.003239 0.000345 0.000558 0.000216 0.013368 0.001074 0.000000 0.023074

UKC2 0.000011 0.000090 0.000000 0.000019 0.000000 0.000206 0.003137 0.007305 0.015703 0.000000 0.026471

UKO2 0.000038 0.000271 0.000000 0.000060 0.000000 0.000436 0.001268 0.010237 0.012667 0.000000 0.024977

GO1 0.000458 0.000858 0.000415 0.002850 0.000232 0.001867 0.001296 0.044914 0.002917 0.000000 0.055807

GC1 0.000571 0.001017 0.003236 0.005270 0.000587 0.001169 0.000514 0.039424 0.001860 0.000000 0.053648

UKC1 0.000089 0.000793 0.000000 0.000132 0.000000 0.007237 0.000615 0.019530 0.001030 0.000000 0.029426

GWD1 0.000413 0.000764 0.020616 0.004109 0.000474 0.000637 0.000188 0.013233 0.000616 0.000000 0.04105

UKO1 0.000126 0.001022 0.000000 0.000201 0.000000 0.001455 0.000088 0.024638 0.000210 0.000000 0.02774

NLO1a 0.000432 0.001254 0.000000 0.000852 0.000000 0.001217 0.000008 0.024627 0.000013 0.000000 0.028403

NLO1b 0.000168 0.000701 0.000000 0.000481 0.000010 0.001295 0.001498 0.019549 0.004623 0.000000 0.028325

UKC7 0.000002 0.000455 0.000000 0.000003 0.000000 0.000248 0.000001 0.027388 0.000001 0.000000 0.028098

BO1 0.000184 0.001055 0.000000 0.000360 0.000000 0.000990 0.000007 0.025638 0.000002 0.000000 0.028236

FO1 0.000006 0.001187 0.000000 0.000010 0.000000 0.000152 0.000001 0.026008 0.000001 0.000000 0.027365

UKC8 0.000000 0.000219 0.000000 0.000000 0.000000 0.000422 0.000000 0.022732 0.000000 0.000000 0.023373

BC1 0.001958 0.001340 0.000000 0.004015 0.000000 0.000665 0.000003 0.019743 0.000005 0.000000 0.027729

NLC1 0.006215 0.001217 0.000000 0.008665 0.000000 0.000982 0.000004 0.019279 0.000023 0.000000 0.036385

NLC2a 0.001144 0.001249 0.000000 0.011720 0.000000 0.001231 0.000005 0.023109 0.000027 0.000000 0.038485

NLC2b 0.000858 0.001238 0.000000 0.009147 0.000039 0.001896 0.000071 0.028759 0.000070 0.000000 0.042078

NLC3 0.000683 0.001126 0.000003 0.004097 0.000238 0.002140 0.000445 0.030589 0.000534 0.000000 0.039855

UKC9 0.000000 0.000054 0.000000 0.000000 0.000000 0.000071 0.000000 0.022430 0.000000 0.000000 0.022555

FC2 0.000004 0.003012 0.000000 0.000008 0.000000 0.000030 0.000000 0.023247 0.000000 0.000000 0.026301

FC1 0.000000 0.000105 0.000000 0.000000 0.000000 0.000000 0.000000 0.022364 0.000000 0.000000 0.022469

GWD2 0.000416 0.000762 0.002443 0.004235 0.000541 0.000744 0.000288 0.030153 0.001288 0.000000 0.04087

NLWD 0.000522 0.000667 0.000408 0.004005 0.005824 0.001097 0.000170 0.021453 0.000289 0.000000 0.034435

…leads to…

Composition Matrix

Step 3: Optimisation

15 15

1. We replace present concentrations by desired reductions

2. Apply an optimisation technique (e.g. Linear Programming)

Area/River BE FR GM NL1 NL2 UK1 UK2 CH NA ATM PO4 PO4Reduction

UKC6 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000288 0.000012 0.022190 0.000000 0.02249 0

UKO5 0.000000 0.000002 0.000004 0.000002 0.000000 0.000003 0.000025 0.000244 0.022566 0.000000 0.022846 0

NO2 0.000003 0.000017 0.000025 0.000024 0.000001 0.000030 0.000236 0.002374 0.020817 0.000000 0.023527 0

DO1 0.000085 0.000215 0.000263 0.000612 0.000043 0.000435 0.001901 0.017441 0.014486 0.000000 0.035481 0

DC1 0.000252 0.000558 0.001977 0.002379 0.000222 0.000635 0.001018 0.030624 0.008692 0.000000 0.046357 0

UKC5 0.000000 0.000001 0.000001 0.000001 0.000000 0.000001 0.000657 0.000046 0.023142 0.000000 0.023849 0

UKC4 0.000000 0.000002 0.000001 0.000001 0.000000 0.000002 0.000378 0.000060 0.022880 0.000000 0.023324 0

DO2 0.000002 0.000016 0.000014 0.000016 0.000001 0.000027 0.000242 0.002743 0.020642 0.000000 0.023703 0

UKC3 0.000000 0.000001 0.000001 0.000001 0.000000 0.000002 0.003233 0.000048 0.022592 0.000000 0.025878 0

UKO4 0.000001 0.000004 0.000001 0.000003 0.000000 0.000005 0.000084 0.000107 0.021042 0.000000 0.021247 0

NLO3 0.000001 0.000012 0.000001 0.000008 0.000001 0.000022 0.000416 0.000890 0.020350 0.000000 0.021701 0

GO3 0.000002 0.000013 0.000002 0.000010 0.000001 0.000023 0.000372 0.001708 0.020178 0.000000 0.022309 0

DWD1 0.000237 0.000467 0.001962 0.002312 0.000248 0.000378 0.000117 0.008755 0.000984 0.000000 0.01546 0

UKO3 0.000001 0.000005 0.000001 0.000003 0.000000 0.000006 0.000197 0.000127 0.021148 0.000000 0.021488 0

GO2 0.000059 0.000172 0.000008 0.000253 0.000013 0.000524 0.002121 0.013181 0.014801 0.000000 0.031132 0

NLO2 0.000020 0.000084 0.000000 0.000065 0.000002 0.000198 0.001332 0.003989 0.018964 0.000000 0.024654 0

DWD2 0.000334 0.000651 0.003289 0.003239 0.000345 0.000558 0.000216 0.013368 0.001074 0.000000 0.023074 0

UKC2 0.000011 0.000090 0.000000 0.000019 0.000000 0.000206 0.003137 0.007305 0.015703 0.000000 0.026471 0

UKO2 0.000038 0.000271 0.000000 0.000060 0.000000 0.000436 0.001268 0.010237 0.012667 0.000000 0.024977 0

GO1 0.000458 0.000858 0.000415 0.002850 0.000232 0.001867 0.001296 0.044914 0.002917 0.000000 0.055807 0

GC1 0.000571 0.001017 0.003236 0.005270 0.000587 0.001169 0.000514 0.039424 0.001860 0.000000 0.053648 0.0080472

UKC1 0.000089 0.000793 0.000000 0.000132 0.000000 0.007237 0.000615 0.019530 0.001030 0.000000 0.029426 0.0058852

GWD1 0.000413 0.000764 0.020616 0.004109 0.000474 0.000637 0.000188 0.013233 0.000616 0.000000 0.04105 0

UKO1 0.000126 0.001022 0.000000 0.000201 0.000000 0.001455 0.000088 0.024638 0.000210 0.000000 0.02774 0

NLO1a 0.000432 0.001254 0.000000 0.000852 0.000000 0.001217 0.000008 0.024627 0.000013 0.000000 0.028403 0

NLO1b 0.000168 0.000701 0.000000 0.000481 0.000010 0.001295 0.001498 0.019549 0.004623 0.000000 0.028325 0

UKC7 0.000002 0.000455 0.000000 0.000003 0.000000 0.000248 0.000001 0.027388 0.000001 0.000000 0.028098 0

BO1 0.000184 0.001055 0.000000 0.000360 0.000000 0.000990 0.000007 0.025638 0.000002 0.000000 0.028236 0.0014118

FO1 0.000006 0.001187 0.000000 0.000010 0.000000 0.000152 0.000001 0.026008 0.000001 0.000000 0.027365 0

UKC8 0.000000 0.000219 0.000000 0.000000 0.000000 0.000422 0.000000 0.022732 0.000000 0.000000 0.023373 0

BC1 0.001958 0.001340 0.000000 0.004015 0.000000 0.000665 0.000003 0.019743 0.000005 0.000000 0.027729 0.0055458

NLC1 0.006215 0.001217 0.000000 0.008665 0.000000 0.000982 0.000004 0.019279 0.000023 0.000000 0.036385 0.007277

NLC2a 0.001144 0.001249 0.000000 0.011720 0.000000 0.001231 0.000005 0.023109 0.000027 0.000000 0.038485 0.01270005

NLC2b 0.000858 0.001238 0.000000 0.009147 0.000039 0.001896 0.000071 0.028759 0.000070 0.000000 0.042078 0.0105195

NLC3 0.000683 0.001126 0.000003 0.004097 0.000238 0.002140 0.000445 0.030589 0.000534 0.000000 0.039855 0.0039855

UKC9 0.000000 0.000054 0.000000 0.000000 0.000000 0.000071 0.000000 0.022430 0.000000 0.000000 0.022555 0

FC2 0.000004 0.003012 0.000000 0.000008 0.000000 0.000030 0.000000 0.023247 0.000000 0.000000 0.026301 0

FC1 0.000000 0.000105 0.000000 0.000000 0.000000 0.000000 0.000000 0.022364 0.000000 0.000000 0.022469 0

GWD2 0.000416 0.000762 0.002443 0.004235 0.000541 0.000744 0.000288 0.030153 0.001288 0.000000 0.04087 0

NLWD 0.000522 0.000667 0.000408 0.004005 0.005824 0.001097 0.000170 0.021453 0.000289 0.000000 0.034435 0

Step 3: Optimisation (2 x 2 example)

Ems Rhine

Reduction

goal

GC1 0.10 * f1

0.12 * f2

≥ 0.08

NLC2 0.00 * f1

0.33 * f2

≥ 0.13

1.00 * f1

0.00 * f2

≤ 0.85

0.00 * f1

1.00 * f2

≤ 0.85

16

Goal: Find set of reduction factors f1 and f2

which will achieve the targets

and be as cheap as possible

Cost

function

10 * f1

100 * f2

Optimal reduction f1 = 0.33, f2 = 0.4

Contents

1. Introduction

2. Approach

3. Results

4. Conclusions

17

Nitrogen targets (winterconc DIN mg/l)

In case of overlapping targets the most strict of the two is considered

18

Offshore targets (OSPAR) Coastal targets (WFD)

Target concentrations

0

0.5

1

1.5

2

2.5

3

Current

Target

Win

terc

on

centr

atio

ns o

f D

IN (

mg/l)

• only the most strict targets per area are shown;

• the WFD-target for the Ems-Dollard estuary is 1.33 mg/l

19

Composition Matrix

20

Optimal reduction strategy for uniform costs

Uniform costs (= equal reduction costs for all sectors and countries)

constant costs per water volume

21

Requir

ed r

iver

load r

eduction

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

Scheldt Ems Rhine IJssel

Minimum foreignreduction

Maximum Dutchreduction

Nutrient loads per sector and country

22

Economic costs

23

Economic costs

Reduction costs per sector and increase with reduction percentage.

Agriculture

Sewage water

treatment

23

Optimal reduction strategy

for economic costs – NL reductions only

None of the targets can be achieved!

24

Still some targets cannot be achieved!

Optimal reduction strategy

for economic costs – NL + foreign reductions

25

Replacing infeasible thresholds

by minimum attainable concentrations

26

Very

costly!

26

Replacing infeasible thresholds

by alternative concentrations

27

Reasonable targets,

and less costly!

Consequences for chlorophyll

28

Contents

1. Introduction

2. Approach

3. Results

4. Conclusions

29

Conclusions

Optimisation method is a quick and powerful tool to:

• optimise nutrient reductions

• check consistency and attainability of targets

• facilitate discussions between stakeholders

30