LOICZ biogeochemical budgets of six North African coastal lagoons: an

application in the framework of the MaghLag network

Gianmarco Giordani, Maria Snoussi and MaghLag partners

Objectives

• Applied the LOICZ biogeochemical approach to the MaghLag coastal systems:– Moulay Bouselham (Morocco, Atlantic Coast)– Nador (Morocco, Mediterranean Coast)– El Mellah (Algeria)– Bizerte (Tunisia)– El Biban (Tunisia)– Ghar el Melh (Tunisia)

• Support cooperation and networking among North African Countries

Main characteristics of LOICZ Biogeochemical model (LOICZ-BM)

• Use a general approach that can be apply to the majority of coastal systems.

• Use few data that are normally collected in the monitoring activities

• Easily applicable and with results that can be easily understood

• Robust;• Informative about processes of CNP fluxes.

Output of the LOICZ-BM

Important information on:

•Water fluxes through the system (residence time)

•Nutrient fluxes (input, output, source, sink)

•Ecosystemic functions linked to the metabolism (NEM, Nfix-denitr)

Details, tutorial and examples at the LOICZ- Biogeochemical Modelling Node web page : http://nest.su.se/mnode/

Location of the MaghLag sites

Main characteristics: Mediterranean climate with 2 main seasons (wet and dry) (except Moulay Bouselham): High freshwater inputs are observed during wet season. Dry season is characterized by strong marine intrusion due to high evaporation rates in comparison with precipitation. Most of nutrient and pollutants are delivered during wet season.Main human impacts are relative to population, agriculture and livestock, occasionally industries play some roles. Strong economic growth is expected in the near future with consequent increase of human impacts.

Algerie

Datasets

• Water fluxes, salinities and nutrient concentrations are relative to few years in the last decade.

• Most of the data are relative to published papers or specific research activities and usually are incomplete and/or have few replicates

• No data are available from routine monitoring• Big efforts from the participants to find

consistent information !!

Main problems (we’re working on them..)

• Moulay Bouselham:– NEM and (Nfix-denit) values are too high

• Nador:– Nutrients concentrations are available only for wet season;– Salinity in the system (Ssys) is too similar to salinity in the Sea (Ssea), salt

budgets would provide too rough estimates of exchange flow (Vx) between Sea and system

• Mellah:– Vx is negative in the dry season since there is marine intrusion but Ssys is lower

than Ssea (a significant freshwater input is missing?)

• Mellah, Ghar el Melh and El Biban– Nutrient inputs from the watershed are missing (a rough estimation was

conducted from the list of human activities conducted in the watershed and standard coefficients to convert them in nutrient inputs considering soil retention)

• All data need to be validated !!

Water and salt budgets

• Eight consistent water and salt budgets are obtained • All of them follow the one-box one layer model• Wet and dry seasons budgets are available for Bizerte

and Moulay Bouselham• Wet season budgets are available for Nador and El

Mellah• Annual budgets are available for El Biban and Ghar el

Melh lagoons

Area versus Water residence time

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50

100

150

200

250

300

0 50 100 150 200 250

Wat

er re

side

nce

time

(d)

Area (km2)

El Biban annual (EB-a)

Bizerte dry (B-d) and wet (B-w) season

Nador wet season (N-w)

Moulay Bouselham dry (MB-d) and wet (MB-w)

season

El Mellah wet season

(EM-w)

Ghar el Melh annual (G-a)

Sites with high water residence time are more sensitive to pollution than small sites with fast water renewal

Water Fluxes

-5000

0

5000

10000

15000

20000

25000

30000

35000

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

wat

er fl

uxes

(103

m3

d-1)

Vr Vx

High water fluxes are reported for MB (probably due to high tidal flushing) and N in wet season. Low water fuxes are reported for EM and G probably because of their sizeMarine intrusions are reported for B-d and EB-a.

Vr= residual flow(negative => water export from the lagoonpositive => marine water intrusionVx = exchange flow(always positive is the lagoon water replaced with marine water)

Nutrient fluxesIn the systems where direct estimations are not available (El Mellah,

Ghar el Melh and El Biban), nutrient loads are estimated as follwing:

Human activities conversion:STANDARD COEFFICIENT (per individual) (OECD, 2008)• Inhabitants: 22 mol P/y ; 321 mol N/y• Cattles/camels: 239 mol P/y ; 3914 mol N/y• Sheep/goats: 26 mol P/y ; 350 mol N/y• Poultry: 5 mol P/y ; 34 mol N/y

50% of the loads of humans and 95% for animals was retained in the soil before reaching the system.

Nador and El Mellah are the systems that received the highest DIP loadsDIP loads to Bizerte are minimal and limited to the wet season

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5

10

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45

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

DIP load from the watershed to lagoon unit surface (mmol m-2 y-1)

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900

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

DIN load from the watershed to lagoon unit surface (mmol m-2 y-1)

Nador and El Mellah are still the systems that received the highest DIN loadsBizerte received high DIN loads in the wet season. The loads to the other systems are lower than 50 mmol m-2 y-1

0

10

20

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MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

DIN/DIP ratio in the watershed loads

Redfield Ratio 16:1

Redfield DIN:DIP ratio in the loads are generally considered as “balanced”. Higher ratios are indicative of agriculture pollution (not point source of pollution): Bizerte?Lower ratios are indicative or urban pollution (point source pollution ): Moulay Bouselham ??El Mellah, Ghar El Melh and El Biban have ratios similar to Redfield since they are calculated

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

DDIPmmol m-2 d-1

-2

-1.5

-1

-0.5

0

0.5

1

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

DDINmmol m-2 d-1

*1 *2

*1 =18.32 mmol m-2 d-1

*2= 50.44 mmol m-2 d-1Nutrient internal transformation ( D positive => source; D negative => sink) DIP:High seasonal variation in Moulay BouselhamEl Mellah, Ghar el Melh and El Biban are DIP sinksNador is a modest source of DIP and Bizerte is well balanced

DIN: Moulay Bouselham have very high values (to be checked).Nador , El Mellah and El Biban are DIN sinkBizerte is a DIN source

-40

-30

-20

-10

0

10

20

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

NEMmmol m-2 d-1

Ecosystemic functions: Net Ecosystem metabolism (NEM) = (p-r)

NEM overlap DDIP since is based on DDIP and C:P ratio of the dominant primary producers that in all system is considered 106:1 (Redifield: phytoplancton).High seasonal variation in Moulay BouselhamIn El Mellah, Ghar el Melh and El Biban production (p) dominate over respiration (r)Nador and Bizerte are well balanced

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

MB-w MB-d N-w EM-w B-w B-d G-a Eb-a

(Nfix-denit)mmol m-2 d-1

Ecosystemic functions: N fixation – denitrification = (Nfix-denit)

* *

* Out of range

It’s always the more problematic result as it’s at the end of all calculations and all errors accumulate. Moulay Bouselham have values higher than 20 mmol m-2 d-1 (not consisent).Nador and El Mellah are net denitrifier, while in Bizerte, Ghar el Melh and El Biban , N fixation is the dominat process.

Concluding remarks

•LOICZ biogeochemical approach is a good tool to collect information and identify data gaps in coastal systems. It supports collaboration among different researchers and data owners.

•In MaghLag lagoons ,this exercise is only at the beginning but interesting indications are emerging. Anyway the results have to be considered as preliminary.

•Available datasets are not exhaustive and with low numbers of replicates. Temporal and seasonal variations are usually not considered. LOICZ approach can be a useful tool to orient future monitoring and research activities

•All data and results need to be validated. Sensitivity analyses could be useful tools to support results and identify uncertainties.

•MaghLag is a great opportunity for consolidating cooperation and networking among North-African countries which share common threats, perspectives and goals.

Thanks for your attention!!!!!

Merci pur votre attention !!!!

Merci Gianmarco!