Valida ion o a Lag angian model o la ge-scale mac oplas ic ace
anspo using mussel-peg in NW Spain (Ría de A ousa)
Sa a Cloux
a,
⁎,Sil ia Allen-Pe kins
b
,Hilda de Pablo
c
,Daniel Ga aboa-Paz
a
,
Ped o Mon e o
b
,Vicen e Pé ez Muñuzu i
a
a
CRETUS, Nonlinea Physics G oup, Facul y o Physics, Uni e si y o San iago de Compos ela, Spain
b
INTECMAR, Ins . Tecnolóxico pa a o Con ol do Medio Ma iño de Galicia, Vilaga cía de A ousa, Spain
c
MARETEC, Ins i u o Supe io Técnico, Uni e sidade de Lisboa, Po ugal
HIGHLIGHTS
•The s udy a ea o ien a ion wi h espec o
he in e idal mo emen plays a majo
ole.
•Wind e ec has a g ea influence on he
dis ibu ion o ma ine deb is accumula-
ion on he Ria de A ousa.
•The beaching pa ame iza ion can ep e-
sen di e en e en ion scena ios.
GRAPHICAL ABSTRACT
ABSTRACTARTICLE INFO
A icle his o y:
Recei ed 16 No embe 2021
Recei ed in e ised o m 18 Janua y 2022
Accep ed 18 Janua y 2022
A ailable online 29 Janua y 2022
Edi o : Ke in V. Thomas
Ma ine deb is is a g owing p oblem in ecen yea s due o popula ion g ow h a ound he wo ld. The inco ec manage-
men o plas ic was e causes hese bodies each he seas and oceans, becoming a wo ldwide p oblem. Once hey each
he seas and oceans, hey begin a long pe iod o deg ada ion, mo ing om a mac o s a e (plas ics whose diame e is
g ea e han 0.5 cm) o a mic o s a e (diame e less han 0.5 cm). The mic oplas ics sp ead h oughou he oceans, en-
e ing he ood chain o ma ine species and, subsequen ly, o humans. The e o e, i is impo an o s op he p oblem
while i emains a he mac oscale. In his wo k, a alida ion o a ecen ly de eloped Lag angian compu a ional
model o ack he mo emen o mac o plas ics in seas and oceans is p esen ed. This alida ion is pe o med on a e-
gional scale, in he Ría de A ousa, one o he mos impo an es ua ies o mussel cul i a ion in no hwes e n Spain.
Du ing mussel cul i a ion in a s, a ype o floa ing plas ic s ick a e eleased, he mussel-pegs. The po en ial o his
s udy is ha we can compa e he accumula ion esul s o he model wi h he accumula ion da a collec ed on he Ga-
lician beaches. In a gene al amewo k, he influence o wind on he spa ial dis ibu ion o he accumula ions gi en
by he model was obse ed. Fo he moni o ing da a, simila esul s we e ound o he accumula ion ends o e
he en i e o al pe iod. Fo he mon hly ep esen a ion, some disc epancies we e obse ed. These di e ences can be
a ibu ed o pa icula synop ic si ua ions, poo ep oduc ion o he coas line o o he e y o ien a ion o he s udy
a ea wi h espec o he in e idal dynamics.
Keywo ds:
Mac oplas ics
Mussel-pegs
NW Spain
Lag angian- acking
Moni o ing
Ría de A ousa
Science o he To al En i onmen 822 (2022) 153338
⁎Co esponding au ho .
E-mail add esses: [email protected] (S. Cloux), scace es@in ecma .gal (S. Allen-Pe kins), hildadepablo@ ecnico.ulisboa.p (H. de Pablo), angeldaniel.ga aboa@ou look.es (D. Ga aboa-Paz),
pmon e o@in ecma .gal (P. Mon e o), pe [email protected] (V. Pé ez Muñuzu i).
h p://dx.doi.o g/10.1016/j.sci o en .2022.153338
0048-9697/© 2022 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/).
Con en s lis s a ailable a ScienceDi ec
Science o he To al En i onmen
jou nal homepage: www.else ie .com/loca e/sci o en
1. In oduc ion
Conce n abou ma ine li e has inc eased in ecen decades (Rangel-
Bui ago e al., 2020). This is pa icula ly ue o plas ics (also e e ed o
as plas ic bodies o plas ic deb is), which a e he majo i y o li e consis ing
o objec s ha ha e been manu ac u ed o used by people be o e being
dumped in i e s, seas and beaches (Williams and Rangel-Bui ago,
2019). These plas ic bodies ep esen a huge p oblem o ou oceans and
coas s (Amelia e al., 2021;K ause e al., 2020), ha ing a g ea impac
no only on he en i onmen , bu also on he human and ma ine wildli e
heal h (Ka balaei e al., 2018). As hey can emain floa ing in he ocean
o yea s, hese plas ics a e b oken down in o small agmen s by a ious
agen s (wind, salini y, sola adia ion, empe a u e and mechanical s ess
due o cu en s and wa es mo ion) as epo ed Min e al. (2020) and
Wayman and Niemann (2021). I is possible o di e en ia e be ween
mac oplas ics (whose diame e is g ea e han 0.5 cm) and mic oplas ics
(whose diame e is less han 0.5 cm). These small bodies en e he ophic
chain o ma ine animals and hen, humans. The e ec s o e animal and
human heal h a e i ual unknown (Akdogan and Gu en, 2019;Hwang
e al., 2020). In addi ion, he e a e huge economic losses o ma ine-
ela ed sec o s (Abalansa e al., 2020). The spa io- empo al moni o ing o
mic oplas ics is di ficul (Li e al., 2020;Ca e e o e al., 2022). The e o e,
p e en ion is he fi s ac ion equi ed, ocusing on he s udy o
mac oplas ics in i e s and coas s in hei ini ial s a e (Rangel-Bui ago
e al., 2020).
Despi e being one o he main pollu an s in he ocean, he anspo o
ma ine plas ics h ough ocean ci cula ion emains poo ly unde s ood
(Chassigne e al., 2021). Se e al ac o s can influence he unde s anding
and desc ip ion o he mo emen o his ma ine li e , as epo ed Van
Sebille e al., 2020. No only in e ms o ocean p ope ies such as empe a-
u e, salini y, o biodeg ada ion (Coope and Co co an, 2012;U banek
e al., 2018); bu also depending on he cha ac e is ics o he plas ic body
(such as i s weigh , densi y and deg ada ion). S udies ha e beendone ode-
ec mic oplas ic acumula ions by using sa elli e images. Da aasu en e al.
(2018) uses SAR sa eli e in o ma ion o de ec hese plas ic pa ches o e
he oceans. Goddijn-Mu phy and Williamson (2019) uses he mal in a ed
(TIR) sensing o y o con ol wa e pollu ion by plas ics. They applied a-
dia i e ans e heo y o es ima e he su ace ac ion o wa e co e ed by
plas ic li e . D i e s acking can also be use ul o de ec con e gence
zones depending on he oceanic dynamic (Maximenko e al., 2012). An-
o he way o s udy he e olu ion o plas ics is he de ec ion on beaches.
This ype o s udy equi es ained pe sonnel as well as he de e mina ion
o he ype o plas ic body o be s udied. Howe e , many inconsis encies
can a ise in his ype o s udy, as he de ec ion o plas ic pa icles in sand
may depend on mul iple ac o s such as pe sonal expe ience o isibili y
(La e s e al., 2016). Mo eo e , in his kind o s udy he o igin o he plas-
ics collec ed on he beach is unknown. I is he e o e c i ical o ocus on he
anspo o mac oplas ics ha mo e on he su ace, be o e deg ading and
sinking. Ac ually, he mos app op ia e way o s udy he influence o plas-
ics is he use o Lag angian anspo ools. Lag angian me hodologies
a e widely used in ma ine li e anspo s udies (Ca lson e al., 2017).
The e a e many s udies using Lag angian models in di e en pa s o he
wo ld o ack he mo emen o plas ic in he ocean and sea (Chassigne
e al., 2021;Poli ikos e al., 2020;Tu ell, 2020;Khoi unnisa e al., 2020;
Zambianchi e al., 2017;Sousa e al., 2021). These models a e based on su -
ace cu en models o define he mo emen o plas ics, s udy hei o igin
and hei a e, since hey can p o ide he posi ion (x,y,z) a each ime
s ep. In his s udy, a Lag angian model was conside ed o simula e he
anspo o he mussel-pegs along one o he mos impo an es ua ies o
he Galician coas o he mussel a ming indus y.
Galicia has a coas line o 1195 km (as epo ed he Ins i u o Nacional de
Es adis ia, INE). Geog aphically, he Rías a e one o he peculia i ies o Ga-
lician coas (see Fig. 1). They a e inden a ions in he coas whe e he sea
flooded i e alleys by lowe ing he land le el ( ela i e ise in sea le el).
These kind o es ua ies a e impo an o fishing, con ibu ing o he ac
ha he Galician coas is one o he mos impo an fishing and sea ood
a eas in he wo ld (Laba a e al., 2004). The es ua ies a e adi ionally di-
ided in o Rías Al as and Rías Baixas, acco ding o hei posi ion wi h e-
spec o Finis e e as he mos wes e n cape o Galicia. In Galicia, he
eno mous impo ance o mollusc aquacul u e, mainly mussels, makes i
he mos impo an economic ac i i y in he communi y (Laba a e al.,
2004;Laba a and Fe nández-Rei iz, 2019). Mussels a e cul i a ed in a s
(Fig. 2). These a e floa ing nu se ies consis ing o a ec angula wooden
s uc u e o which he mussel opes a e a ached. The wooden s uc u es
a e a ached o floa ing bodies ha hold hem on he su ace o he sea,
and also fixed o he seafloo by a chain (see Fig. 2). They a e hus
suspended cul u es g owing in he wa e column. The mussel spawn is
w apped a ound he ope wi h he help o a fine biodeg adable ayon ne ,
gi ing he mussel enough ime o a ach i sel o he ope. A e a ew
mon hs, due o he conside able inc ease in weigh o he mussels, i be-
comes necessa y o di ide he opes, i.e. o make new opes o lowe mussel
densi y. Then, e e y 30–40 cm o ope, wooden (in he pas ) o plas ic
(mo e common nowadays) s icks a e placed be ween he s ands o ope
o p e en clus e s o mussels om becoming de ached as shown in Fig. 2
b. These mussel-pegs p o ide a be e g ip on he ope, p e en de achmen
and make i easie o fix he mussels. They a e plas ic pieces 225 mm long
by 30 mm wide (see Fig. 2c). The wo k o s inging, un olding and
ex ac ing he mussels means ha he mussel-pegs, ei he whole o b oken,
a e eleased and acciden ally all in o he sea, becoming one o he mos
common ypes o ma ine li e in he Galician coas . Because he la ge ex-
ension o he c op, as well as he ele an quan i y o hese plas ics icks e-
leased in o he wa e and hei cha ac e is ics ( hey ha e a known o igin,
a e easy o cha ac e ize and o coun ), hey can be used as indica o s o ma-
ine li e a eas o accumula ion. The s udy he e p esen ed is loca ed in he
Ría de A ousa as pa o he Rías Baixas. This pa icula es ua y is he mos
ac i e inden a ion o he mussel p oduc ion (Comeau e al., 2018).
Since he e is no deg ada ion o he mussel-peg om he ime i is e-
leased un il i eaches he coas , i can be conside ed as a mac oplas ic
body. In addi ion, due o he collec ions o mussel peg on beaches, i is pos-
sible o know how his ype o plas ic accumula es along he coas line o he
A ousa es ua y. The e o e, he main objec i e o his s udy is o know
whe he a Lag angian model can p o ide a good es ima ion on he accumu-
la ion o ma ine li e along he coas line in a small egion wi h he dynam-
ics o he Ría de A ousa. A simila s udy was ca ied by Decle ck e al.
(2019) and Ca lson e al. (2017) by using d i e ajec o ies and floa ing
mac o deb is espec i ely. In he p esen wo k, a new ool ecen ly
de eloped by he Ins i u o Supe io Técnico de Lisboa and he Uni e si y
o San iago de Compos ela, he MOHID-Wa e Lag angian model was
used. The me hodology o which is desc ibed in he Me hods sec ion.
Al hough he Illa de A ousa is pa o he Ría de A ousa, om he e on we
will e e o he Ría de A ousa as he inland coas al egion, excluding he
Illa de A ousa.
The objec i e o his s udy is o de e mine whe he he mussel-peg is a
good Lag angian indica o . Then, could he me hodology he e be used o
alida e he ecen ly de eloped MOHID-Lag angian ool and o de e mine
acc e ion zones? This s udy p o ides new insigh o Lag angian s udy in
high esolu ion a eas whe e he o ien a ion and cha ac e iza ion o he
s udy a ea plays an majo ole.
2. Me hods
2.1. S udy a ea
The Ría de A ousa (Fig. 1b) is loca ed a he no hwes coas o he Ibe-
ian Peninsula (Fig. 1a), being pa o he Rías Baixas o he Galician coas .
I is he la ges es ua y on he sou h Galician coas , wi h a su ace a ea o
230 km
2
app oxima ely. I can be subdi ided in o wo zones: he inne
zone (98 km
2
), mo e exposed o flu ial p ocesses, shallowe and mo e iso-
la ed habi a s, and he ou e zone (132 km
2
), wi h g ea e in e ac ion wi h
oceanic p ocesses (O o, 1975;Rosón e al., 1995;Ál a ez-Salgado e al.,
1996), deepe and mo e exposed habi a s (Ou ei o e al., 2018). The a e -
age sea le el oscilla ion is a ound 2.5 m, making i a meso- idal es ua y
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
2
(be ween 2 and 4 m idal ange). The a e age wa e heigh anges be ween
1 and 2.5 m o he sp ing and summe seasons, while o he au umn and
win e mon hs, his alue oscilla es be ween 3 and 5 m (Conselle ia de
Medio Ambien e, 2010). These a ia ions in sea le el heigh gi e ise o cy-
clical mo emen s o incoming and ou going wa e , called idal cu en s,
which can be o g ea in ensi y.
The Ría de A ousa as a pa ially mixed es ua y (Rosón e al., 1995;
Dye , 1973) and a e age he cu en s o e se e al idal cycles because
he esidual ci cula ion ob ained is posi i e in wo laye s: an inflow cu -
en o sal wa e h ough he bo om om he ocean and an ou flow cu -
en o b ackish wa e h ough he su ace. In he Ría de A ousa he e
a e also se e al sou ces o s a ifica ion: eshwa e inpu s, hea flow
h ough he a mosphe e- ia in e ace and wa e exchanges be ween
he shel and he es ua y. All o hese gi e ise o longi udinal densi y
g adien s, which ac as d i e s o he posi i e ci cula ion desc ibed
abo e. Winds also ha e a g ea influence on he a iabili y o he esid-
ual ci cula ion bo h on he shel and in he es ua y, which can lead o
h ee di e en scena ios: (i) ein o ced posi i e ci cula ion when
winds om he no h domina e, (ii) a si ua ion o elaxa ion in ansi-
ion pe iods wi h a e y slow posi i e ci cula ion main ained o days,
and (iii) an in e se o nega i e ci cula ion a o ed by winds om he
sou h. In addi ion, depending on i s ba hyme y, he Galician coas
can be cha ac e ized in di e en ways. Al hough i is possible o dis in-
guish be ween 11 ypes o pu e ypologies, he eno mous a ie y on he
Galician coas and he changing hyd odynamic condi ions gi e ise o
he appea ance o an ex ensi e se ies o in e media e ypologies. In pa -
icula , he beaches o he Ría de A ousa a e small, o g ea ypological
a ie y, and nume ous due o he in ense ac u ing o he e ain
(Conselle ia de Medio Ambien e, 2010). In pa icula , his es ua y is
domina ed by shel beaches, which means ha he e a e ocky in e idal
zones ha influence he dynamics. Compu a ionally, depending on he
g id mesh, ocky a eas may no be ep esen ed so Lag angian pa icles
mo e eely wi hou beaching, o a leas be delayed by he p esence
o obs acles. Fig. 3 shows he na iga ion cha s o he s udy a eas. As
i can be seen, mos o hem ha e ocky in e idal zones jus in on o
hecollec iona ea,bu o Ba añaandAduana egions.Fo hecase
o Po co beach (Fig. 3 e. i) he collec ion a ea is loca ed on he le
side o he bu e , in on o he Pun al de las Sinas. Compu a ionally,
his e ec can only be pa ame e ized in he MOHID-Lag angian by he
beaching ac o and he beaching le el.
Fig. 1. Maps showing he Galician coas (solid black line on he le map) and he Ría de A ousa (blue squa e on he le map); and he spa ial dis ibu ion o he mussel a s
(blue do s on he igh map).
Fig. 2. Schema ic o a mussel cul i a ion a . (a) Shows he main componen s o he pan: (i) wooden s uc u e, (ii) floa s, (iii) cul i a ion opes and(i ) ancho ing.(b) Shows
he a angemen o he mussel-peg on he ope and (c) he dimensions o he mussel-peg.
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
3
Fig. 3. Na iga ion cha s o he Ría de A ousa (a). Going om sou h o no h and om wes o eas in each image, he shaded a eas co espond o: (b.i) Mosquei os, (b.ii) Fon án, (c.iii) Illa, (c.i ) Ninei iños, (d. ) Ba aña, (e. i) Po co,
(e. ii) Aduana, ( . iii) S1,( .ix) S2, ( .x) S3, ( .xi) S4, ( .xii) S5, ( .xiii) S6, ( .xi ) S7, ( .x ) S8, ( .x i) S9, (g.x ii) Cas iñei as and (g.x iii) Ca ei o.
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
4
2.2. Inpu da a. Hyd odynamic model
The MOHID-Lag angian model (www.mohid.com) was employed, a e-
cen Lag angian ool de eloped o he dynamic s udy o ma ine anspo .
In pa icula , i was used i o ack o wa d in ime he anspo o ma ine
deb is in he oceans and o es ima e i s accumula ion along he coas . I is a
comple e high- esolu ion Lag angian acking model ha can unc ion as a
lib a y o he MOHID Wa e modelling sys emo asa s and-alone p og am.
Wo king independen ly, ou Lag angian model will be o ced wi h he cu -
en alues ob ained using he MOHID-Wa e 3D hyd odynamic model
(Ma ins e al., 2001) o ep oduce he cu en , salini y and empe a u e
in he RV. This ope a ional sys em is daily execu ed by Me eoGalicia
(www.me eogalicia.gal) o ob ain he ad ec i e con ibu ion. The ou pu
esul s has a 300 m o ho izon al esolu ion and he e ical disc e iza ion
consis s by wo domains wi h an in e ace a 8.68 m. While he uppe
domain is composed by 11 sigma laye s, ha ing a high esolu ion in he
op laye accoun ing o he wind influence, he bo om domain has 16 z-
le el laye s. The WRF model (Wea he Resea ch and Fo ecas ing Model)
p o ides he su ace bounda y condi ion, applied o he Rías Baixas a ea
wi h 1.3 km ho izon al esolu ion. A de ailed examina ion o his modelop-
e a ed by Me eoGalicia can be ound in Huhn e al. (2012) and Venâncio
e al. (2019). Fu he mo e, he model also con ains he Ve dugo-Oi abén
i e s discha ges h ough he SWAT model. Besides, ROMS coas al model
is also used as bounda y condi ions.
2.3. Lag angian model
To ack pa icles, MOHID-Lag angian module uses he concep o
ace , whose posi ion (x,y,z) is well-known a each ime s ep. The mo e-
men o he ace s depends on he eloci y om he hyd odynamic mod-
ule, he wind om he su ace module and he andom eloci y om he
wa es ac ion. The eloci y field is in e pola ed om he hyd odynamic
eule ian eloci y field o ob ain a new g id wi h a esolu ion se by he
use . To calcula e he posi ion o he pa icle, his eloci y field and a di u-
si e e m a e in eg a ed as:
dxi
d ¼ ixi ðÞ, ðÞþDi(1)
whe e
i
is he eloci y field a a ins an and x
i
posi ion, and D
i
is he di u-
sion eloci y, calcula ed as de Pablo e al. (n.d.) desc ibed. The s eng h o
his module lies in he pa ame e iza ion o beaching. I is possible o gi e a
h eshold dep h alue abo e which he pa icle is s anded in he sand, as
well as a p obabili y ha he pa icles will be s anded. These wo a gu-
men s can accoun o di e en scena ios in which accumula ion can
occu . Ano he obus ness o his model is ha i can be sepa a ed he accu-
mula ions on he coas acco ding o he emission sou ces. This means ha
he influence o each emission sou ce can be sepa a ely e alua ed.
In his s udy, h ee di e en scena ios we e conside ed (see Table 1 in
he Supplemen a y ma e ial).Fi s , he e ec o accumula ion along he en-
i e coas is calcula ed o a ime pe iod o 1.5 yea s ( om Oc obe 1, 2018
o Ap il 1, 2020). Wi hin his pe iod, h ee di e en wind o ien a ion si u-
a ions we e selec ed. Fo each, pe cen iles P25, P50, P75 and P95 we e cal-
cula ed wi h espec o he maximum accumula ion o all segmen s. This
makes i possible o dis inguish be ween high and low accumula ion
zones and o show he spa ial dis ibu ion o ma ine li e wi hin he Ría
de A ousa. The second scena io akes place in he Illa de A ousa om Oc o-
be 1, 2018 o June 1, 2019; and he hi d scena io, om Oc obe 1, 2020 o
Ap il 1, 2021, akes place along he no h o he Ría de A ousa sho e. These
wo las ime pe iods ha e been chosen acco ding o he wo beach moni-
o ing da a he e p esen ed. To es ima e he accumula ion a ios along he
coas al line, he sho e o he Ría de A ousa is di ided in o 427 segmen s
(see Fig. 4). These segmen s (also called bu e s) ha e 1000 m leng h by
100 m o wid h each. These dimensions has been se o ensu e he bes e-
p oduc ion o he coas line, since a lowe esolu ion canno ensu e he co -
ec defini ion along he coas . Because somes udy egions a e composed o
di e en beaches wi hin one single sho e segmen , especially in he second
case, he s udy egions we e joined by segmen s, he e e e enced as S1, S2,
S3, S5, S6, S7, S8 and S9 (see Fig. 3 ). In he hi d scena io, nine beaches
we e selec ed. A o al o 18 s udy a eas a e a ailable o compa ison o sim-
ula ed and expe imen ally collec ed da a. Since he ex en o he bu e may
be la ge han he ex en o he sho e whe e collec ions ake place, he es i-
ma ed accumula ion will be g ea e han he ac ual accumula ion. The e-
o e, he esul s ob ained om he simula ion a e co ec ed using an a ea
ac o . This ac o is calcula ed as he a io o he moni o ed beach a ea o
he compu a ional bu e a ea.
The simula ion domain co e om 9.15°W o 8.15°W and om 42.2°N
o 42.6°N wi h a 200 m spa ial esolu ion and 3 h empo al esolu ion. Ac-
co ding o he mussel a dis ibu ion, he emission poin s we e es ablished
a he same loca ion (see Fig. 1c). Fo he en i e simula ion pe iod, Lag ang-
ian pa icles a e eleased om all emission poin s e e y hou . Mussel-pegs
collec ed on he sampling beaches can come om o he es ua ies wi h shell-
fish ac i i y. To conside his e ec , wo emission poin s we e also consid-
e ed a he no he n and sou he n edges o he simula ion domain. Fo
each polygon, emission poin s a e assumed e e y 140 m along he polygon
geome y. In he case o ex e nal sou ces, we define a egula emission wi h
an a ea o 9 km
2
. Because he di e si y o beaches in he Ría de A ousa, sim-
ula ions ha e been ca ied ou a ying he p obabili y o s anding. This is
in ended o simula e h ee possible e en ion scena ios. The 80% beaching
ac o eflec s a eas o high e en ion, 50% beaching ac o eflec s medium
e en ion and 20% beaching ac o eflec s a eas o low e en ion, mainly
ocky ones. Then, ends we e calcula ed using ela i e accumula ion (%
RA) o each beach. Fo each s udy a ea, he mean accumula ion e e y
4 h is ob ained. This is in ended o smoo h possible a ypical e ec s due o
pa icula synop ic wea he condi ions. Fo each ime pe iod conside ed,
he o al accumula ion (A
TOT
) and he maximum accumula ion be ween
he whole conside ed s udy a eas (A
MAX
) a e ob ained. The ela i e pe cen -
age o each egion is ob ained by di iding he accumula ion o ha a ea by
he maximum accumula ion as,
%RA ¼ATOT
AMAX
(2)
2.4. Obse a ional da a. Beaches collec ion
The moni o ing da a p esen ed he e is pa o one o he s a egies o he
CleanA lan ic p ojec . This p ojec aims o p o ec biodi e si y and ecosys-
em se ices in he A lan ic A ea by imp o ing capaci ies o moni o ing,
p e en ion and emo al o mac o ma ine li e . Thep ojec alsocon ibu es
o aising awa eness and imp o ing ma ine li e managemen sys ems. As
pa o his p ojec , a s udy has been conduc ed o analyze di e en s a e-
gies o iden i ying ma ine deb is accumula ion a eas ha can be inco po-
a ed in o moni o ing, cleanup and collec ion p o ocols. One o he
s a egies es ed was he use o mussel a s as an indica o o plas ic deb is
accumula ion. These indica o s, along wi h o he measu es and p oxies,
(i.e., oceanog aphic cu en s, socioeconomic da a), can be used o de ec
he p esenceo ma ineli e in each habi a andspa ial and empo al ends
in accumula ion (GESAMP).
The e o e, he sampling plan was designed wi h he in en ion o de e -
mine he main egions o li e accumula ion along he island's coas line
and whe he he e a e any specific loca ions ha s and ou om he es .
The chosen beaches me he ollowing equi emen s (1) o be o med by
sand o g a el and exposed o he open sea, (2) o be accessible o he sam-
ple s h oughou he yea , as well as o acili a e he emo al o ma ine li -
e , and (3) no o be subjec o o he li e emo al ac i i ies. A weekly
equency was es ablished, and da a collec ion was always conduc ed one
hou a e high ide o a oid sampling being a ec ed by he ising ide. A
each collec ion, he numbe o mussel-pegs ound, bo h whole and b oken,
was coun ed and emo ed om he beaches. The sampling o all selec ed
beaches was ca ied ou in wo campaigns: A) Illa de A ousa: ca ied ou be-
ween Oc obe 2018 and Ap il 2019. The poin s loca ed in A Illa de A ousa
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
5

we e sampled as pa o a ci izen science p ojec . B) Ría de A ousa: ca ied
ou be ween Oc obe 2020 and Ma s 2021. The poin s loca ed on he coas
o his es ua y we e sampled by expe echnicians in coas al sampling who
usually ca y ou bo h sampling wo k on he selec ed beaches and ad ice o
he shellfish sec o as pa o hei daily du ies.
3. Resul s and discussion
Fig. 4a shows he spa ial dis ibu ion o accumula ions o an emission
pe iod o one yea and a hal ob ained om he compu a ional model.
Knowing he empo al dis ibu ion o accumula ions o each coas al seg-
men , he o al accumula ion was calcula ed. The P25, P50, P75 and P95
(25 h, 50 h, 75 h, 95 h pe cen iles) we e used o es ablish he h esholds
o e y low, low, medium, high and e y high accumula ions. The a eas
wi h he lowes deb is accumula ion a e a e he ou e mos , i.e., hose
mos exposed o oceanic ac ion. On he o he hand, g ea e accumula ions
appea owa ds he inne pa o he es ua y. Gi en ha he cu en s
en e om he sou h, in a no heas e ly di ec ion, and d ain owa ds he
no h in a no hwes e ly di ec ion, he main accumula ions appea in he
coas al segmen s o ien ed owa ds he sou h and sou heas , coinciding
wi h his mo emen . This map (Fig. 4) shows wo clea ly defined accumu-
la ion zones. One in he no heas o he es ua y and he o he in he no h-
wes o he cen al island (A Illa). Likewise, he en i e in e media e inne
egion shows high accumula ion alues abo e P50. Tu ning now o he
s udy o wind ac ion, Fig. 4b co esponds o an eas e ly wind, Fig. 4c con-
side s a sou heas e ly wind ac ion and Fig. 4d conside s a no hwes e ly
wind ac ion. These h ee si ua ions demons a e he significan influence
o his agen . Thus, an eas e ly wind si ua ion will cause a g ea e accumu-
la ion on he coas line wi h he same o ien a ion. In he case o a p edomi-
nan ly no heas e ly wind, he d ainage o he es ua yis a o ed. The e o e,
he inne mos zone egis e s a lowe accumula ion, while he ou e mos e-
gions wi h he same o ien a ion egis e highe accumula ion alues. Fo
he las si ua ion, a p edominan ly sou hwes e ly wind a o s he high ac-
cumula ions on beaches wi h he same o ien a ion and loca ed in he in e-
io egion.
This e ec is smoo hed in he simula ion esul s, since he a e age accu-
mula ion e e y 4 h has been calcula ed o he se o bu e s; and hen he
empo al accumula ion pe bu e has been es ima ed. The esul s a e p e-
sen ed in wo pe spec i es: (1) o he whole simula ion pe iod and (2) sep-
a a ed by mon hs.
3.1. Illa de A ousa
Compa ing now he moni o ing da awi h he simula ed da a, he esul s
can be sepa a ed by segmen s. Fo he fi s ime pe iod ( om he 2018 Oc-
obe 1 o 2019 May 1), Fig. 5 shows he esul s o nine di e en coas al
line segmen s. I is impo an o no e ha he compa ison e e s o ends,
no o ne da a, i.e. bo h da a se ies (simula ed and obse a ional) ha e
Fig. 4. Accumula ion a ios in he Ría de A ousa along he 427 segmen s o a pe iod o one and a hal yea s ( om 2018 Oc obe 1 o 2020 Ap il 1) ob ained om he
compu a ional model. The classifica ion ‘ e y low’co esponds o accumula ion alues below P25; ‘low’, be ween P25 and P50; ‘medium’, be ween P50 and P75; ‘high’,
be ween P75 and P95; and ‘ e y high’, abo e P95. The black a ow shows he wind di ec ion. a) Conside s he whole ime pe iod, b) co esponds o an eas e ly wind on
he 30 h Janua y 2019, c) co esponds o a sou heas e ly wind ac ion on he 7 h May 2019 and d) co esponds o a no hwes e ly wind ac ion on he 10 h Janua y 2019.
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
6
been no malized acco ding o he maximum ound in each s udy egion. In
all o hem he s anding ac o has been a ied o see which one es ima ed
a be e accumula ion. As can be seen, in he cases whe e i di e s, he 20%
s anding ac o fi s be e . Since he Illa de A ousa a ea is a mos ly ocky
a ea (see Fig. 3 ) i is highly unlikely ha mussel-pegs each sand a eas.
Howe e , i can be s a ed ha he compu a ional modelis able o ep oduce
he gene al end o accumula ion in he s udied a eas, wi h he excep ion
o S4. In his case, he bu e used o he accumula ion coun does no eli-
ably ep oduce he sho eline. Because he spa ial esolu ion o he bu e s
along he coas al line, he e a e cases whe e he sho e p ofile is no well
enough eplica ed. In he case o S4, he bu e o ien a ion is sligh ly di e -
en om he ac ual o ien a ion o he moni o ed beach. This o ien a ion
causes he simula ed ci cula ion o ba ely each his egion, so ha a
smalle numbe o pa icles a e always ound. Finally, i was calcula ed
he ela i e con ibu ion o he wo ex e nal emission sou ces. In his
case, only 3% o he pa icles ha ha e eached he coas come om ex e -
nal sou ces. This makes sense, since hese sou ces will a ec he ou e mos
egions, which a e he mos influenced by oceanic ac ion. So i makes sense
ha only a small ac ion o he pa icles emi ed by hese sou ces will be
s anded on he coas .
Fig. 6 shows he mon hly compa ison be ween simula ed and mon-
i o ing da a. This highe empo al esolu ion shows mo e disc epancies
han in he p e ious ep esen a ion. He e i is impo an o iden i y he
causes ha can p oduce dispa i y be ween simula ed and moni o ing
esul s. The fi s and mos impo an is he ela ionship be ween he
s udy a ea o ien a ion and he in e idal mo ion. The mo e he beach
is o ien ed owa ds he idal mo emen , he la ge he numbe o com-
pu a ionally accumula ed pa icles is. Howe e , he ba hyme y o he
egion can lead o accumula ion alues below he compu a ional es i-
ma ion. Since he ocky egions nea he coas may ac as low e en ion
ac o s, he moni o ing da a on he beach may be lowe han expec ed.
In he case o he Illa, his is wha happens in S2, S3, S5, S6. All hese
egions a e hea ily a ec ed by in e idal mo ion. This means ha he
g ea e he numbe o pa icles passing h ough an in e media e
zone, he g ea e he accumula ion eco ded in ha zone, since 80%
o hepa iclesp esen a es andedon hesand(in hecaseo se ing
he s anding a 80%). This ac is clea ly mo e accen ua ed in S7 and
S9 due o he ac ha hei sou he n o ien a ion esul s in a highe
numbe o pa icles being ecei ed in bo h egions du ing ising
ides. Fig. 3 shows ha all a eas o he island ha e ocky in e idal
zones ha will ha e an e ec on he moni o ing da a a he beaches,
as his alue is usually lowe han ha es ima ed by he model. In
cases whe e he collec ion alue is highe , i may be due o a pa icula
synop ic si ua ion on he pa icula collec ion day. Being he wes e n-
mos a ea o he Ibe ian Peninsula, Galicia, and in pa icula he wes
coas , o en su e s om a ious a mosphe ic phenomena coming
om he No h A lan ic. Specifically, in he mon h o Oc obe 2018,
wo hu icane e en s eached he coas o Galicia, leading o an anom-
alous synop ic si ua ion. The mon h o No embe 2018 was cha ac e -
ized by he appea ance o a g ea s o m, causing a ypical wind
si ua ions. Finally, he mon h o Decembe 2018 was cha ac e ized
by high al i ude squalls du ing he fi s 20 days o he mon h. All
hese synop ic si ua ion can a ec he moni o ing da a. The case o
S4, as men ioned abo e, p esen s a ep esen a ion p oblem, since he
o ien a ion o he bu e ep esen a ion means ha ha dly any pa icles
each his a ea. Finally, S1 and S8 a e he bes es ima ed egions du ing
he whole pe iod. Respec ing o he beaching pa ame e iza ion, in his
pa icula s udy, no di e ences we e obse ed.
3.2. Ría de A ousa
Fo heRíadeA ousa, hesame endsasin hep e ioussubsec ion
we ecalcula ed.Fo heaccumula iono e heen i esimula ionpe-
iod,simila esul sa e oundin he endo hesimula edda awi h
e e ence o he sampled da a (see Fig. 7). Ba aña beach eaches he
maximum accumula ion alue bo h in he simula ion and in he
beach collec ions, while he minimum alue is es ima ed o Ninei iños
by using bo h me hodologies. Fo his beach, he moni o ed da a show
a concen a ion o 0.31% wi h espec o he o al li e collec ed on all
beaches sampled. I is possible o find a clea dispa i y be ween simula-
ion and obse a ion o Ca ei o beach. In pa icula , his beach is lo-
ca edinahighlyexposeda eao hees ua y ooceanicac ion.In
addi ion, i s posi ion makes i possible ha he accumula ions ob-
se ed on he beach come om poin s ou side he es ua y, pa icula ly
om he mussel cul i a ion a eas o Ría de Pon e ed a. Al hough his
ac has been ied o o e come his ac wi h wo ex e nal emission
sou ces, he pe cen age o pa icles eaching he coas om ex e nal
sou cesisonly3%.He e, hebeha io o beaching o he las s udy e-
gions is simila o he p e ious case. The highes alues o ela i e ac-
cumula ion occu o a beaching alue o 80% while he lowes
alues a e eco ded o a beaching o 20%.
The impo ance o beach o ien a ion in ela ion wi h he in e idal
mo ion is obse ed in Fig. 8 o he mon hly accumula ion. This is he
case o he Illa and Fon án beaches. The alues es ima ed by he
model a e highe han hose collec ed on beaches because he in e idal
mo emen makes i di ficul o mussel-pegs o accumula e on hese
beaches. Oceanic influence mus also be aken in o accoun . As in he
p e ious case, in he egions mo e exposed o oceanic ci cula ion he
model will p esen a lowe accumula ion alue. Compu a ionally, o
he Ca ei o and Cas iñei as egions his beha io is ound. Howe e ,
in he case o Ca ei o, high accumula ion alues a e eco ded in he
beach collec ions. This is due o he ac ha , despi e being in one o
he ou e mos a eas o he Ría, i s o ien a ion does no a o he es ua y
dynamics o clean his a ea. Mo eo e , being a ocky a ea, he dynamics
in his egion will be slowe in eali y. This is no he case o he model.
In he case o Cas iñei as, i s o ien a ion makes he oceanic ac ion ha e a
g ea e e ec , so he accumula ion alues a e low in bo h me hods.
Mo eo e , i may happen, as in he case o Aduana, ha an h opogenic
cons uc ions such as a dyke a e no included in he coas al managemen
plans, so hey a e also no aken in o accoun in simula ions o his ype.
Howe e , in eali y, hese ypes o cons uc ions ha e an e ec ha is
eflec ed in he moni o ing da a. The e o e, he Lag angian model on
his beach always epo s la ge alues han hose ac ually ound in he
collec ed ones. Finally, o iden a ions ha do no p esen any o hese
ac o s, as i is he case o Ba aña and Po co, he moni o ing da a on
he beach can be well ep oduced compu a ionally. Du ing his s udy pe-
iod, he mon hs o Janua y and Feb ua y we e cha ac e ized by he oc-
cu ence o s o ms ha a ec ed he egion. In hese wo mon hs, Galicia
su e ed om ou di e en s ong squalls. In ou compa ison, bo h
mon hs s and ou o ha ing dispa i ies be ween simula ed da a and
moni o ing da a. Wi h espec o beaching, i can be concluded ha no
significan di e ences can be seen in mos cases. Howe e , in hose
cases in which he ci cula ion a o s he appea ance o a g ea e numbe
Fig. 5. Compa ison o ends in he accumula ion o mussel-pegs o di e en sho e
segmen s in he Illa de A ousa om Oc obe 2018 o Ap il 2019. Simula ions ha e
been pe o med o di e en beaching alues: 20% (ligh o ange), 50% (medium
o ange) and 80% (da k o ange). The moni o ing da a a e shown in b own.
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
7
o pa icles o e a gi en s udy egion, he pe cen age es ablished mus be
aken in o accoun , since he highe he pe cen age, he g ea e he dis-
pa i y be ween esul s wi h di e en beaching may appea , as in he
case o Po co beach in he mon hs o Oc obe and Ma ch.
These esul s indica e he MOHID-Lag angian model is able o es ima e
easonably well he accumula ion o s icks bo h on he Illa de A ousa and on
he Ría de A ousa. The e a e pa icula cases, such as some synop ic si ua-
ions, which cause dispa i ies be ween he model esul s and he
Fig. 6. Compa ison o ends in he accumula ion o mussel-pegs o di e en sho e segmen s in he Illa de A ousa o a mon hly ep esen a ion om Oc obe 2018 o Ap il
2019. a) Oc obe 2018, b) No embe 2018, c) Decembe 2018, d) Janua y 2019, e) Feb ua y 2019, ) Ma s 2019, g) Ap il 2019. Simula ions ha e been pe o med o
di e en beaching alues: 20% (ligh o ange), 50% (medium o ange) and 80% (da k o ange). The moni o ing da a a e shown in b own.
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
8
moni o ing da a collec ed on he beach. Ano he sou ce o dispa i y is he
ba hyme y o he accumula ion zones, whe e a high esolu ion model
should be implemen ed.
4. Conclusions
The g ow h o plas ic inpu s in o he seas and open ocean is a majo
p oblem. Howe e , floa ing plas ic deb is can be used as an ideal ace
o de e mine a eas o accumula ion as well as hei poin s o o igin.
This ype o s udy is possible h ough he use o Lag angian me hods.
This pape p esen s a ecen ly de eloped Lag angian ool ha has
been alida ed using a floa ing plas ic; mussel-pegs. No e ha , al-
hough heda a alida iono hesemodelshas obedoneona egional
scale, hey can be implemen ed on an in e na ional scheme. Fu he -
mo e, he obus ness o his s udy lies in he ac ha he emi ing
sou ces a e well known. Fo his eason, i is easible o use such mon-
i o ing da a o alida e he MOHID-Lag angian model. Howe e , he
p ecise compu a ional ep oduc ion o his si ua ion is complex, since
he ac ual emission om he a s is unknown, as mussel s icks a e
no emi ed a each mussel collec ion and he mussel collec ion is no
pe o med pe iodically. In addi ion, he esidence ime o he mussel
s icks is no de e mined and i is no possible o di e en ia e whe he
he o igin o a pa icula plas ic s ick comes om he a o his es ua y
o om ano he . Fu he mo e, he whole ecep o poin s a e equally
p obable o ecei e ma ine li e accumula ion, i.e. all sho eline seg-
men s can eco d accumula ion wi h he same p obabili y. Thus, he
model igno es ocky egions. The e o e, i is possible o find acc e ion
zones in ocky egions whe e no eal acc e ion occu s. In addi ion, du -
ing sampling, he sa e y o he sample s was always he op p io i y.
Thus, sampling was always conduc ed du ing dayligh hou s and was
suspended in cases whe e sa e y could be comp omised (ad e se
wea he condi ionsandCOVIDp o ocols)Howe e ,asi isbasedon
he oppo uni y gi en by ci izen science and he sampling wo k o he
p o essionals, he eco ds we e made weekly on di e en days o he
week. This means ha , in his case, i will be mo e di ficul o cha ac-
e ize he possible wea he si ua ions ep esen ed by he expe imen al
da a. Fo each o he beaches sampled, a specific o mwasde eloped o
eco d in o ma ion on mussel-pegs accumula ion a eas. In addi ion,
he samplings we e comple ed wi h pho og aphs o e i y he eliabil-
i y o he da a. All hese ac o s can ha e an impac on he compa ison
esul s.
In his s udy i has been used a egional Lag angian model o s udy he
accumula ion o ma ine li e in he Ría deA ousa. Th ee di e en ime sce-
na ios ha e been simula ed: (1) one and a hal yea s o see he global end;
(2) se en mon hs o compa e wi h he moni o ing da a in he Illa de A ousa
and (3) six mon hs o compa e wi h he moni o ing da a in he Ría de
A ousa.
This kind o s udies a e highly ele an o es whe he compu a-
ional models, in his case he MOHID-Lag angian, a e capable o e-
p oducing he obse a ional esul s. The fi s esul s show he spa ial
dis ibu ion o ma ine li e in he Ría de A ousa. Using he P25, P50,
P75 and P95, he accumula ion zones along he coas line can be quali-
a i ely di e en ia ed. The a eas mos exposed o oceanic ac ion a e
hose wi h he lowes accumula ion a ios. Due o he ci cula ion o
cu en s, he la ges accumula ions occu a he ou e mos o he cu -
en sin hees ua y.I wasalso ound ha windhasag ea influence
on he modelling. The acc e ion zones a y depending on he wind di-
ec ion. As o he compa ison be ween he model and he moni o ing
da a collec ed on he coas s, highly a o able esul s ha e been ound
o bo h s udy pe iods. In bo h scena ios i was possible o ep oduce
hegene al endo eacha ea o heen i e imepe iodwi h heexcep-
iono wo egionsin hecaseo heIlla,andonein hecaseo heRía.
In he case o he Illa, hese wo dispa i ies a e di ec ly ela ed o he o i-
en a ion o he bu e wi h espec o he dynamics o he es ua y. In one
case, he compu a ional exposu e o he dynamics o his egion does no
co espond o he eal one, a o ing he a i al o ewe pa icles in his
s udy a ea. In he o he case, he o ien a ion o he bu e is o ally a o able
o he oceanic ci cula ion, which causes a high numbe o pa icles o be
s anded in his a ea. A simila mon hly beha io is ound o all he
s udy zones, excep o he mon hs o No embe and Decembe . In hese
cases, he influence o No h A lan ic hu icanes could be he cause o
hese anomalous beha io s.
Fo he Ría, he o e all end is well ep oduced by he Lag angian
model, wi h he excep ion o Ca ei o beach. The la ge a iabili y o
his egion makes i , in a compu a ional sense, one o he cleanes
a eas in his s udy. Howe e , i s pa icula o ien a ion makes he accu-
mula ions moni o ed in his beach highe han expec ed. On a mon hly
basis, he impo ance o he o ien a ion o he beach wi h espec o he
in e idal dynamics is also obse ed. Thus, he impo ance o aking
in o accoun a co ec ep oduc ion o he coas al p ofile is also
highligh ed.
Al hough he esul s ob ained in his s udy ha e been sa is ac o y,
we would like o conclude his a icle wi h a se ies o ecommenda ions
o he design o u u e s udies, as well as o moni o ing da a. The
knowledge o he s udy a ea is impo an o e alua e whe he i can be
ep esen ed ai h ully in a compu a ional way. Spa ial esolu ion
p oblems can lead o unexpec ed and e oneous esul s, as i was ou
case wi h he S4 segmen . The compu a ional o ien a ion o he co e-
sponding bu e caused ha only ew pa icles eached his egion,
while a mo e a o able o ien a ion and close o he eal one, he accu-
mula ion in his a ea could ha e been be e es ima ed. As has been
shown, ba hyme y plays a majo ole and i mus be conside ed o
he co ec in e p e a ion o he egion dynamics.
In addi ion, i is impo an o ake his ype o compa ison wi h cau-
ion, gi en ha compu a ionally we ob ain a con inuous ime se ies o
ma ine deb is accumula ion a he sho eline. Howe e , he esul s ob-
ained in he collec ion co espond o ce ain si ua ions ha depend
on mul iple ac o s and ha may no be ep esen a i e o he empo al
end o accumula ion in a pa icula egion. These ac o s can be clas-
sified as en i onmen al and human a iables and bo h can ha e a de -
imen al e ec on he ob ained esul s. En i onmen al ac o s a e
impossible o con ol, bu i is impo an o keep hem in mind when
analyzing he esul s. As we ha e seen, synop ic si ua ions a e key o lo-
ca e po en ial ma ine li e accumula ion a eas so he es ablishmen o
consolida ed campaigns ha conside hese condi ions o define he
moni o ing pe iods is highly ecommended. Human in e e ence is eas-
ily con ollable. We would like o highligh some indica ions o be
aken in o accoun in u u e s udies. Mus be ensu ed ha he o al o
he planned samples a e ca ied ou a he scheduled da e and ime.
All sampling mus be gone on he same day and a e he peak o high
ide, p e e ably wo hou s la e . This ensu es ha all floa ing pa icles
Fig. 7. Six mon h compa ison o ends in he accumula ion o mussel-pegs o
di e en sho e segmen s in he Ría de A ousa, om Oc obe 2020 o Ma ch 2021.
Simula ions ha e been pe o med o di e en beaching alues: 20% (ligh
g een), 50% (medium g een) and 80% (da k g een). The moni o ing da a a e
p esen ed in da kes g een.
S. Cloux e al. Science o he To al En i onmen 822 (2022) 153338
9