MARINE ECOLOGY PROGRESS SERIES
Ma Ecol P og Se
Vol. 353: 27–40, 2008
doi: 10.3354/meps07197 Published Janua y 17
INTRODUCTION
New p oduc ion (NP; see Table 1 o lis o abb e ia-
ions) is he ac ion o p ima y p oduc ion (Pg) ha is
suppo ed by alloch honous nu ien sal s (Dugdale &
Goe ing 1967) and is a key a iable o unde s anding
ma ine ecosys ems unc ioning (e.g. exploi a ion o
ma ine esou ces global clima e change). The e o e,
NP no only ep esen s he h eshold o biomass
exploi a ion (Quiñones & Pla 1991), bu also a ec s
he e iciency o he biological pump as a ap o
an h opogenic CO2(Longhu s 1991).
The mos s aigh o wa d way o es ima e NP is o
conside he nu ien balance (inpu minus ou pu ) in a
gi en ecosys em (Smi h & Hollibaugh 1993, Wollas
1993). Howe e , his concep ually simple me hod
© In e -Resea ch 2008 · www.in - es.com*Email: [email p o ec ed] o [email p o ec ed]
Physical–biological coupling in he coas al
upwelling sys em o he Ría de Vigo (NW Spain).
I: In si u app oach
S. Pied acoba1, 2,*, M. Nie o-Cid1, C. Sou o2, M. Gilco o2, 3, G. Rosón2,
X. A. Ál a ez-Salgado1, R. Va ela2, F. G. Figuei as1
1CSIC, Ins i u o de In es igacións Ma iñas, Edua do Cabello 6, 36208 Vigo, Spain
2Facul ade de Ciencias do Ma , Uni e sidade de Vigo, Ma cosende, 36200 Vigo, Spain
3School o Chemis y, Physics & Ea h Sciences, Flinde s Uni e si y, GPO Box 2100, 5001 Adelaide, Aus alia
ABSTRACT: The a e o he ino ganic and o ganic ni ogen apped in he coas al upwelling sys em
o Ría de Vigo (NW Spain) was s udied a he 2 o 4 d ime-scale du ing July and Sep embe 2002.
A ansien geochemical model was applied o he measu ed esidual cu en s and concen a ions o
ino ganic ni ogen (NT), and dissol ed (DON) and pa icula e (PON) o ganic N o ob ain (1) he ne
balance o inpu s minus ou pu s (i – o); (2) he ne accumula ion; and (3) he ne ecosys em p oduc ion
(NEP) o NT, DON and PON. P e iously unaccoun ed la e al a ia ions in esidual cu en s and
N species concen a ions in he ía we e conside ed. The ía was au o ophic du ing July (a e age
NEP, 107 mg N m–2 d–1). Abou 25% o his ma e ial was expo ed o he shel and he emaining 75%
was ans e ed o he sedimen s o p omo ed o highe ophic le els. Du ing summe upwelling
episodes, 30 o 70% o he o ganic N expo ed o he shel came om ma e ials p e iously accumu-
la ed in he ía. By con as , du ing summe elaxa ion, 60 o 70% o he accumula ed o ganic N came
om in si u con e sion o NTand he emaining 30 o 40% was alloch honous. As shown by o he
au ho s, NEP was a he low du ing in ense upwelling and inc eased o high alues du ing i s sub-
sequen elaxa ion. In Sep embe , he me abolism changed om he e o ophic o sligh ly au o ophic
(a e age NEP, 26 mg N m–2 d–1). The DON and PON impo ed om he shel du ing au umn down-
welling expe ienced a di e en a e: DON was consumed and PON accumula ed in he ía. By
con as , DON and PON we e p oduced in si u a he expense o N nu ien s p e iously accumula ed
in o he sys em du ing au umn elaxa ion. The oles o e ical con ec ion and u bulen mixing in
he e iliza ion o he pho ic laye we e also assessed. Mixing was he mos impo an e iliza ion
mechanism, ensu ing anspo o nu ien s unde upwelling and downwelling condi ions.
KEY WORDS: Ni ogen luxes · Geochemical model · Upwelling · Downwelling · Rías Baixas
(NW Spain)
Resale o epublica ion no pe mi ed wi hou w i en consen o he publishe
Ma Ecol P og Se 353: 27–40, 2008
in ol es ope a ional di icul ies: eloci y and u bulen
di usion p o iles, oge he wi h nu ien concen a-
ions, ha e o be de e mined wi h a equency highe
han he lushing ime o he s udy sys em. Fo his ea-
son, di e en indi ec me hods ha e been de eloped
o e he las ew decades o e alua e NP.
G a i a ional sinking and subsequen mine aliza ion
is he main a e o NP in as a eas o he open ocean,
whe e he ho izon al ci cula ion is qui e slow and mos
o Pg is p ocessed wi hin he mic obial loop (Legend e
& Rassoulzadegan 1995, Co ne & Biddanda 2002).
The e o e, assuming s eady-s a e condi ions, NP
should be equal o he sedimen a ion a e measu ed a
he base o he pho ic laye (Eppley & Pe e son 1979).
In i o app oaches ha e also been used o es ima e
N; hese include he 15N-labeled ni a e/ammonium+
u ea me hod (Dugdale & Goe ing 1967) o he ligh –
da k oxygen incuba ion me hod (S ickland & Pa sons
1972), in which i is assumed ha he ne communi y
p oduc ion (NCP) es ima ed in he ligh bo le is equal
o he NP (Quiñones & Pla 1991). Howe e , he appli-
ca ion o he la e me hod in sub opical gy es has led
o con o e sial esul s (au o ophic NCP > 0 o he e o-
ophic NCP < 0; Williams 1998, Se e e al. 2001, del
Gio gio & Dua e 2002). In any case, he alidi y o
shallow sedimen aps (Buessele 1991, Ducklow e al.
1995), 15N-labeled incuba ions (Legend e & Gosselin
1989, Wa a e al. 1995), and ligh –da k oxygen incu-
ba ions (Hansell e al. 2004) o es ima e NP has been
openly challenged.
The e alua ion o NP is mo e di icul in coas al sys-
ems, due o he enhanced ho izon al ad ec ion, and
he ans e ence o a signi ican ac ion o Pg o me a-
zoans (Legend e & Rassoulzadegan 1995, Co ne &
Biddanda 2002). In he pa icula case o coas al
upwelling sys ems a empe a e la i udes, he sho
lushing imes and he non-s eady-s a e condi ions
inc ease he complexi y o NP es ima ion (Ál a ez-
Salgado e al. 1996a, Smi h & Hollibaugh 1997). The
mass balance app oach using sedimen aps and/o
in i o incuba ions may no e lec an accu a e NP
es ima e o hese ecosys ems (Smi h & Hollibaugh
1997, Ál a ez-Salgado e al. 2001).
In his s udy and i s companion pape (Pied acoba e
al. 2008 his olume) we es ima e he NP in a coas al
upwelling sys em (Ría de Vigo, NW Spain) unde con-
as ing upwelling (July) and downwelling (Sep em-
be ) condi ions using mass balance, sedimen ap, and
in i o incuba ion app oaches. Pa I is ocused on he
es ima ion o he inpu s minus ou pu s balance o ni o-
gen species ( o al nu ien s, NT; dissol ed o ganic
ni ogen, DON; pa icula e o ganic ni ogen, PON) on
a sho ime-scale (<4 d) by combining dynamic and
chemical de e mina ions along a ans e se sec ion in
he cen al segmen o he Ría de Vigo. A mass balance
box model was de eloped o e alua e he ela i e
impo ance o ne accumula ion and ne ecosys em
p oduc ion (NEP = NP) as a mechanism o o ganic and
ino ganic ni ogen apping in his ecosys em. P e i-
ous geochemical balances applied in he Ría de Vigo
(Ál a ez-Salgado e al. 2000, Gilco o e al. 2001) es i-
ma ed he eloci y ield om salini y and empe a u e
dis ibu ions. In he p esen s udy, NP was es ima ed
om di ec cu en measu emen s. In addi ion, he la -
e al a iabili y o hese cu en s was conside ed o he
i s ime. In Pa II, he me abolism o he Ría de Vigo
is assessed while conside ing he oxygen p oduc ion/
28
A
F ee su ace a ea o he ía
A
S
,
A
B
Su ace and bo om a eas o he ans e se
sec ion
ADCP Acous ic Dopple cu en p o ile
chl aChlo ophyll a
C
S
,
C
B
A e age su ace and bo om concen a-
ions o C
DON Dissol ed o ganic ni ogen
DOM Dissol ed o ganic ma e
ENACW Eas e n No h A lan ic Cen al Wa e
F
x Flux o any species ca ied by a ho izon al
con ec i e low (
Q
S,
Q
B
)
F
Z
Flux o any species ca ied by e ical
con ec i e low (
Q
Z
)
KZ
Tu bulen mixing coe icien
LNM Le el o no mo emen
<N> B un -Väisälä equency
N
T
Dissol ed ino ganic ni ogen
NEP Ne ecosys em p oduc ion
NEP
T
Ne ecosys em p oduc ion o N
T
NEP
D
Ne ecosys em p oduc ion o DON
NEP
P
Ne ecosys em p oduc ion o PON
NEP
SED
Ne balance o PON sedimen a ion, PON
and esuspension and N
T
di usion om he
sedimen
M
Z
Ve ical di usi e luxes
o – i Ne budge o ou pu s minus inpu s
(o – i)
T
Ne budge o ou pu s minus inpu s o N
T
(o – i)
P
Ne budge o ou pu s minus inpu s o PON
(o – i)
D
Ne budge o ou pu s minus inpu s o DON
PON Pa icula e o ganic ni ogen
PAR Pho osyn he ic a ailable adia ion
Q
B
Bo om ho izon al low
Q
S
Su ace ho izon al low
Q
Z
Ve ical low
R
i
Richa dson numbe
ρDensi y
U
0
Tidal eloci y ampli ude
V Volume
V
X
Ho izon al con ec i e eloci y
V
Z
Ve ical con ec i e eloci y
VMADCP Vessel-moun ed acous ic Dopple cu en
p o ile
Δ(V·N
T
)兾Δ
Accumula ion o N
T
Δ(V· DON)兾Δ
Accumula ion o DON
Δ(V· PON)兾Δ
Accumula ion o PON
Table 1. Glossa y o ele an e ms
Pied acoba e al.: Physical–biological coupling in Ría de Vigo. I
espi a ion balance. Sedimen a ion and mic ozoo-
plank on g azing a es, es ima ed o he i s ime in
he Ría de Vigo, a e also conside ed. The NP es ima-
ions ob ained by he in si u (Pa I) and in i o (Pa II)
app oaches a e compa ed and he possible causes o
he obse ed disc epancies a e discussed.
MATERIALS AND METHODS
Su ey a ea. The Ría de Vigo is a la ge (2.76 km3)
V-shaped inden a ion in he wes e n coas o he Ibe -
ian Peninsula (Fig. 1). I expe iences wind-d i en
upwelling o cold, sal y and nu ien - ich Eas e n
No h A lan ic Cen al Wa e (ENACW) om Ap il-
May o Sep embe -Oc obe (Woos e e al. 1976, F aga
1981). Upwelling e en s occu wi h a 1 o 2 wk e-
quency (Blan on e al. 1987, Ál a ez-Salgado e al.
1993). Downwelling is he dominan p ocess he es o
he yea ; i is cha ac e ized by he ad ec ion o wa m
and nu ien -poo shel su ace wa e o he ía (Cas o
e al. 1997). The main ibu a y is he i e Oi abén-
Ve dugo, which d ains an a e age annual low o
15 m3s–1 (Noguei a e al. 1997) in o San Simón Bay, a
semi-enclosed basin o ~20 km2(Fig. 1).
Sampling s a egy. Fi e s a ions in he middle seg-
men o he Ría de Vigo (41 ± 2 m max. dep h) we e
sampled abou 1 h be o e sun ise on 15, 18, 22 and
26 July and 17, 19, 23 and 26 Sep embe 2002. Wa e
samples om S n 00 (Fig. 1) we e aken wi h a ose e
sample equipped wi h wel e 10 l PVC Niskin bo les
wi h s ainless-s eel in e nal sp ings, while wa e sam-
ples om S ns R01 and R03 loca ed a he no he n and
sou he n ends o he segmen , we e aken wi h 5 l PVC
Niskin bo les. A S n 00, salini y and empe a u e
we e eco ded wi h an SBE 9/11 CTD p obe a ached
o he ose e sample . Conduc i i y measu emen s
we e con e ed in o p ac ical salini y scale alues wi h
he equa ion o UNESCO (1985). Wa e samples we e
collec ed om 5 dep hs: a he su ace o a he dep h
o 50% o he pho osyn he ically a ailable adia ion
(PAR, µE m–2 s–1) pene a ion (2.5 ± 0.3 m), a 25% o
PAR pene a ion (7 ± 1 m), a 1% o PAR pene a ion
(14.2 ± 2.2 m), a 26.2 ± 1.2 m, and a he bo om.
29
Vigo
Pon e ed a
A ousa Ri e
Oi abén
Ve dugo
Sillei o
buoy
Rande
S ai
Ibe ian
Peninsula
c
2
4
5
9
1
00
a
1000 1500 2000
–40
–30
–20
–10
0
7.3-10.8
NS CS
5.9-15.2 SS
6.3-10.6
NB SB
6.2-15.3
N(R03) S(R01)
9.5-17.0
b
9.0º 8.9º 8.8º
Longi ude (Wes )
42.1º
42.2º
La i ude (No h)
Rande S ai
San Simon Bay
C. Ma
Cíes Islands
P. Bo nei a
DCM12 & CTD
CTD s a ion
Ría de Vigo
R03
R01
20 m
20 m
60 m
80 m
Fig. 1. Ría de Vigo (NW Spain). (a) The longi udinal ansec epea ed du ing he 60
isi s om 1990 o 1997. The c oss-ha ched zone is he ee su ace a ea o he olume
bounded by he s udy ans e se sec ion. (b) The 5 sec o s— 3 a he su ace (NS, CS
and SS) and 2 a he bo om (NB and SB)— de ined o s udy he la e al a iabili y o he
middle ía. (c) The Ría de Vigo in ela ion o he Rías Baixas and he loca ion o he Sea
wa ch buoy o Pue os del Es ado o Cape Sillei o
Ma Ecol P og Se 353: 27–40, 2008
A S ns R01 and R03, salini y and empe a u e we e
eco ded wi h a CTD SBE-25 and wa e samples we e
collec ed om 2 dep hs: su ace and bo om.
Wind and cu en measu emen s. Coas al wind da a
we e ob ained om he Seawa ch buoy o Cape
Sillei o (www.pue os.es; ou Fig. 1), a ep esen a i e
si e o winds blowing o he Ría de Vigo (He e a e
al. 2005). Low-pass il e ed winds a e used o de ine
he p e ailing oceanog aphic scena io in he ía du ing
each pe iod. The hea balance and eshwa e lux o
each sampling da e we e aken om Pied acoba e al.
(2005).
Cu en eloci y p o iles we e measu ed aboa d
RV ‘My ilus’ wi h an RDI essel-moun ed b oad-
band acous ic Dopple cu en p o ile (VMADCP) o
300 kHz along he ans e se sec ion joining S ns R01
and R03 on 18 and 22 July and 19 Sep embe 2002.
In addi ion, cu en p o iles we e measu ed wi h
an Aande a DCM12 acous ic Dopple cu en p o ile
(ADCP) moo ed a S n 00. The moo ing was deployed
om 10 o 29 July and om 17 o 26 Sep embe 2002.
The DCM12 lay on he seabed, eco ding, a 30 min
in e als, he cu en in eg a ed in 5 e ical cells
11 m hick. DCM12 and VMADCP da a we e o a ed
coun e clockwise 30° o p oduce a longi udinal and
a ans e sal componen ela i e o he main axis o
he ía.
A C++ e sion o he HAMSOM model (3D, z-coo di-
na e A akawa-C g id), ba oclinic, semi-implici ini e–
di e ence nume ical p edic ion model), ecen ly ali-
da ed in he ou e (Sou o e al. 2003) and inne (Diz
e al. 2004) Ría de Vigo, was used o ep oduce he
la e al a iabili y o he sub idal cu en ield on 15 and
26 July and 17, 23 and 26 Sep embe 2002. The
accu acy o he model o ep oduce he la e al cu en
ield da a has been success ully es ed by Pied acoba
e al. (unpubl.).
Ho izon al ad ec ion. Fi e sec o s— 3 a he su ace
(NS, CS and SS) and 2 a he bo om (NB and SB)—
we e de ined o accoun o he la e al a iabili y in he
middle ía (Fig. 1b). The c i e ion o di ide he su ace
and bo om sec o s was based on he le el o no ho i-
zon al mo ion, aking in o accoun he da a om he
DCM12 and he VMADCP, and he ou pu s o he
HAMSOM model. Ho izon al ad ec ion eloci ies
we e a e aged in he 5 sec o s.
Ve ical ad ec ion. The Ría de Vigo was isi ed o
he pu pose o measu ing mass balances 60 imes om
1990 o 1997. Fig. 1a shows he longi udinal ansec
epea ed du ing he 60 isi s. The good ela ionship
be ween he bo om ho izon al low (QB) and he e i-
cal low (QZ) ob ained om he mass balances (Fig. 1b)
pe mi s calcula ion o he unknown QZ(in m3s–1) om
he measu ed QB(in m3s–1) in his s udy (n a e he
pai s o consecu i e sampling):
QZ= –212(±43) + 0.73(±0.03)· QB
= +0.92, p < 0.001, n = 47 (1)
The e ical con ec i e eloci y (VZ) was calcula ed
conside ing he su ace a ea o he shaded zone in he
inse o Fig. 1a. The e ical displacemen o he le el
o no mo emen (LNM) be ween 2 consecu i e su eys
was also calcula ed.
Ve ical mixing. The u bulen mixing coe icien ,
KZ(m2d–1), was pa ame e ized acco ding o Munk &
Ande son (1948), using he ADCP and CTD da a:
KZ= K0·(1 + 10 · Ri)1
/2(2)
K0= 3 ×10–3·U0·Z(3)
(4)
whe e K0is he eddy coe icien o neu al s abili y, U0
is he ampli ude o he idal eloci y om 0 o Zm
dep h, Riis he Richa dson numbe , ρis he a e age
densi y, and gis he g a i y accele a ion. Veloci y
dimensions we e ob ained by di iding KZby Z/2, he
dis ance be ween he g a i y cen e s o he uppe and
lowe laye .
S abili y. The wa e column a e age B un -Väisälä
equency, <N> (in min–1), a S n 00 (Fig. 1) was calcu-
la ed as ollows: <N> = {4g(ρl– ρu)兾(ρl+ ρu)Z}1
/2, whe e
ρland ρu a e he a e age densi y o he uppe and
lowe laye s.
Chemical a iables. Salini y (S, accu acy ± 0.003),
N-nu ien s (NH4+, ±0.05 µM; NO2–, ±0.02 µM; and
NO3–, ±0.1 µM), DON (±0.2 µmol N l–1), suspended
PON (±0.1 µmol N l–1), and chl a(±0.05 mg m–3) we e
measu ed as desc ibed elsewhe e.
Ho izon al/ e ical luxes. A e age concen a ions
(µmol kg–1) o all species we e calcula ed om he 3
s a ions loca ed along he middle segmen o he ía by
means o an in e se dis ance in e pola ion me hod.
The ho izon al lux o any ni ogen species (FX, in µmol
m–2 d–1) was calcula ed as ollows:
FX= VXCXρX(5)
whe e VXis he ho izon al eloci y, and CXand ρXa e
he a e age concen a ion and densi y, espec i ely, a
each o 5 sec o s de ined abo e.
Ve ical con ec i e luxes (FZ, in µmol m–2 d–1) we e
ob ained as ollows:
FZ= VZCZρZ(6)
whe e VZis he e ical con ec i e eloci y, and CZ
and ρZa e he dep h-a e age concen a ion and den-
si y, espec i ely, in he s udy sec ion.
Ri=−
⋅∂
∂
∂
∂
()
g
z
u
z
ρ
ρ
2
30
Pied acoba e al.: Physical–biological coupling in Ría de Vigo. I
Finally, e ical di usi e luxes (MZ, in µmol m–2 d–1),
we e ob ained as:
(7)
whe e CSand CBa e he a e age concen a ions o any
species in he su ace and bo om laye , espec i ely.
Geochemical budge . The ne budge o inpu s
minus ou pu s, i – o, o any species (C)in o a gi en ol-
ume (in µmol C m–2 d–1) esul s om he accumula ion,
Δ(C⋅V)兾Δ , and ne ecosys em p oduc ion, NEPC, e ms:
(8)
The accumula ion e m (in µmol C m–2 d–1) can be sep-
a a ed in 2 e ms:
(9)
The i s e m on he igh o Eq. (9) indica es he ne
accumula ion due o changes in concen a ion and
he second e m due o changes in olume. The a e -
age NEPCbe ween 2 consecu i e su eys can be es i-
ma ed as:
(10)
whe e he balance o o – i (in mol C m–2 d–1) is calcu-
la ed as:
o – i = (FS⋅AS– FB⋅AS)兾A(11)
FSand FBa e he a e age su ace and bo om ho izon-
al luxes (in µmol m–2 d–1); ASand ABa e he a eas o
he su ace and bo om laye o he ans e se sec ion
(in m2); and Ais he ee su ace a ea o he ía
bounded by he ans e se sec ion (35.6 ×106m2).
RESULTS
Wa e lows
No he ly winds p e ailed o e he shel in July
(Fig. 2a), while sou he ly winds we e dominan in Sep-
embe (Fig. 3a). Since con inen al uno was e y low
in July (<9 m3s–1; Fig. 2b) and Sep embe ( om 5.7 o
14.5 m3s–1; Fig. 3b), 6 pe iods we e de ined acco ding
o he dominan shel wind. The i s , om 15 o
18 July, was cha ac e ized by an in ense upwelling
episode ha eached a maximum on 15 July. A posi i e
esidual ci cula ion pa e n wi h a s ong su ace ou -
low o –12 cm s–1 was eco ded (Fig. 2d). Du ing he
second pe iod, om 18 o 22 July, no he ly winds
aba ed, p oducing a e e sal o he esidual ci cula ion
pa e n (su ace in low and bo om ou low; Fig. 2d).
The hi d pe iod (22 o 26 July) was domina ed by
no he ly winds ha p omo ed an in ense upwelling
on 26 July. A posi i e esidual ci cula ion pa e n
esumed (Fig. 2d), wi h su ace and bo om cu en s
simila o he i s pe iod. The ou h pe iod, om 17 o
19 Sep embe , was domina ed by sou heas e ly winds
ha dec eased g adually and caused a nega i e esid-
ual cu en pa e n wi h a maximum su ace in low o
10 cm s–1 and bo om ou low o –10 cm s–1 (Fig. 3d).
The i h pe iod, om 19 o 23 Sep embe , was cha ac-
e ized by he ansi ion om sou he ly o no he ly
winds (Fig. 3a), when he e e sal o he esidual pa -
e n pe sis ed bu cu en eloci ies diminished. On 23
Sep embe , a 3-laye ci cula ion de eloped, wi h ou -
low h ough he su ace and bo om laye s and in low
h ough he in e media e laye . Finally, he six h
pe iod, om 23 o 26 Sep embe , was cha ac e ized by
mode a e no heas e ly winds blowing o e he shel
wi h lowe in ensi y han in July (Figs. 2a, 3a). As a
esul , he 2-laye posi i e ci cula ion pa e n was e-
es ablished.
On 15 July, he salini y and empe a u e dis ibu-
ions showed he ypical esponse o an upwelling
e en . Despi e he subsequen elaxa ion o shel
winds, he e ec o coas al upwelling s ill emained in
he bo om laye 3 d la e (Fig. 2e, ). The e e sal o he
ci cula ion in esponse o he wind calm (Fig. 2a)
a ec ed he wa e column s a i ica ion: salini y was
mo e homogeneous and he halocline was di icul o
dis inguish, while su ace empe a u e inc eased and
he he mocline was ound a 20 m dep h. The he mo-
haline s uc u e ound on 17 Sep embe co esponded
o a ypical au umn downwelling, wi h wa m (>17°C)
and ela i ely sal y (>34.8) shel su ace wa e s in he
su ace laye (Fig. 3e, ). The pe sis ence o shel
sou he ly winds p oduced a deepening o he su ace
salini y and empe a u e as a consequence o down-
welling. Sou he ly winds changed o no heas e ly on
22 Sep embe (Fig. 3a), p oducing a sligh upli o
he isohalines and iso he ms, sugges ing he en y
o oceanic ENACW h ough he bo om laye s on
26 Sep embe .
The analysis o he longi udinal componen o he
esidual cu en shows ypical 2-laye ed posi i e and
nega i e ci cula ion pa e ns unde upwelling condi-
ions on 15 July (Fig. 4a) and downwelling condi ions
on 19 Sep embe (Fig. 4 ), espec i ely. A a ie y o
in e media e cases we e obse ed on he o he sam-
pling da es, showing he complexi y o he la e al
esidual ci cula ion o he ía.
Ve ical con ec i e eloci ies we e upwa ds du ing
he upwelling e en s o 15 and 26 July (Fig. 4a,d) and
23 and 26 Sep embe (Fig. 4g,h). They we e nea ly
ze o du ing he elaxa ion o upwelling (Fig. 4b) and
e e sed o downwa ds on 22 July (Fig. 4c), and on 17
and 19 Sep embe (Fig. 4e, ). In July, mixing eloci ies
NEP o i (V )
C=−+ ⋅Δ
Δ
C
Δ
Δ
Δ
Δ
Δ
Δ
(V)V VC
C
C
⋅=+⋅
io (V)
NEPC
−= ⋅−
Δ
Δ
C
MKCC
ZZBS
z
=−
()
Δ
31

Ma Ecol P og Se 353: 27–40, 2008
eached a maximum du ing upwelling e en s, being
wice he e ical con ec i e eloci y on 15 July
(Fig. 4a). Th oughou Sep embe , mixing eloci y was
highe han he con ec i e e ical eloci y, excep on
17 Sep embe , and i eached a maximum on 19 Sep-
embe (Fig. 4 ). The s a i ica ion ha ook place du -
ing he elaxa ion a e he i s upwelling episode
caused mixing eloci y ha was hal he e ical con-
ec i e eloci y on 26 July (Fig. 4d). The e ical dis-
placemen s o he LNM we e negligible compa ed o
he e ical con ec i e and mixing eloci ies in July
and Sep embe .
Acco ding o ou p e ious hyd og aphic and dy-
namic desc ip ion, he 6 pe iods we e named as ol-
lows: (i) spin-down o s ong summe upwelling (15 o
18 July), (ii) summe elaxa ion (18 o 22 July), and
(iii) spin-up o weak summe upwelling (22 o 26 July),
(i ) au umn downwelling (17 o 19 Sep embe ),
( ) au umn ansi ion (19 o 23 Sep embe ), and
( i) au umn upwelling (23 o 26 Sep embe ).
Ni ogen luxes
NO3–(Fig. 2k), he mos abundan N-nu ien in July
(69% o NT= NO3–+ NO2–+ NH4+), was a a maximum
a he bo om laye du ing he spin-down o he s ong
summe upwelling (15 o 18 July) because o he en y
o ENACW. In he su ace laye , maximum concen a-
ions o chl a(Fig. 2i) and PON (Fig. 2j) we e eco ded.
Du ing he summe elaxa ion (18 o 22 July), lowe
chl aand PON concen a ions we e eco ded a he
su ace compa ed wi h he p e ious pe iod (15 o
18 July) and a subsu ace chl amaximum de eloped a
20 m dep h ( he nu icline). DON (Fig. 2g) accumula-
ion in he su ace laye ook place a he end o he
32
–10
–20
–30
–2
–2
2
2
0
2
4
4
0
0
0
0
d
–40
–30
–20
–10
35.6
35.6
35.5
e
–40
–30
–20
–10
15/7
18/7
22/7
26/7
12
12
14
16
–40
–30
–20
–10
6
4
g
–40
–30
–20
–10
15/7
18/7
22/7
26/7
2
4
6
10
12
8
i
–40
–30
–20
–10
2
4
4
h
–40
–30
–20
–10
2
4
6
j
–40
–30
–20
–10
2
4
8
10
6
k
–40
–30
–20
–10
15/7
18/7
22/7
26/7
0.1
0.2
0.3
l
16/7
18/7
20/7
22/7
24/7
26/7
Q -P-E
Q
P
E
–2
0
2
4
6
8
10
12
14
b
H
16/7
18/7
20/7
22/7
24/7
26/7
0
–200
–100
100
200
300
400
c
Dep h (m)
16/7
18/7
20/7
22/7
24/7
–12
–6
0
6
12
m/s a
Fig. 2. July 2002. (a) Time cou se o shel winds, in m s–1; (b) con inen al uno (Q ), p ecipi a ion (P) and e apo a ion (E), in m3s–1;
(c) hea balance (H), in cal cm–2 d–1; (d) esidual cu en s, in cm s–1; dashed line ep esen s he pycnocline; (e) salini y; ( ) empe a-
u e, in °C; (g) dissol ed o ganic ni ogen, in µmol l–1; (h) ammonium, in µmol kg–1; (i) chl a, in µg l–1; (j) pa icula e o ganic ni o-
gen, in µmol l–1; (k) ni a e, in µmol kg–1; and (l) ni i e, in µmol kg–1. Hea and eshwa e luxes aken om Pied acoba e al. (2005)
Pied acoba e al.: Physical–biological coupling in Ría de Vigo. I
summe elaxa ion, eaching concen a ions >7 µmol
kg–1. Du ing he spin-up o weak summe upwelling
(22 o 26 July), nu ien - ich wa e en e ed h ough he
bo om laye s, bu his inpu was weake compa ed
wi h he i s upwelling pe iod (bo om NO3–< 11 µmol
kg–1). In con as wi h July, N-nu ien s le els we e
educed by hal du ing Sep embe and NH4+(Fig. 3h)
was he mos abundan o m, ep esen ing 72% o NT.
Du ing he au umn downwelling (17 o 19 Sep embe ),
nu ien -poo wa e s en e ed om he shel . Concomi-
an ly, lowe PON (~4 µmol kg–1) and chl a(~4 µg kg–1)
concen a ions we e measu ed a he su ace laye
compa ed o July (Fig. 3i,j). DON was highe han PON
du ing his pe iod and p esen ed a homogeneous dis-
ibu ion h oughou he wa e column (Fig. 3j). A he
beginning o he au umn ansi ion (19 o 23 Sep em-
be ), nu ien s le els we e s ill e y low in he su ace
laye (NH4+< 1.6 µmol l–1 and NO3–< 0.5 µmol l–1), bu
he wind change caused a p og essi e en y o
ENACW in he bo om laye . The le els o NO3–and
NH4+(Fig. 3h,k) inc eased especially a he beginning
o he au umn upwelling (23 o 26 Sep embe ),
al hough he concen a ion o NO3–a he bo om was
5 imes lowe han he le els measu ed du ing he
weakes summe upwelling (22 o 26 July). As a conse-
quence o inc easing nu ien le els, high su ace chl a
(>8 µg l–1) and PON (>7 µmol kg–1) concen a ions
we e measu ed (Fig. 3i,j). As o July, he DON maxi-
mum (Fig. 3g) was delayed 3 o 4 d compa ed wi h he
chl aand PON maxima.
In July, no signi ican di e ences in ei he nu ien
s ocks o luxes we e obse ed be ween he 2 bo om
sec o s. By con as , signi ican di e ences (p < 0.05) in
nu ien luxes be ween he 3 su ace sec o s we e
obse ed on mos sampling da es (Table 2). DON and
PON s ocks we e e y homogeneous h ough he su -
33
1
1
2
–40
–30
–20
–10
k
0.4
0.2
0.3
0.3
6
7
7
9
8
–40
–30
–20
–10
g
2
3
4
6
7
–40
–30
–20
–10
j
17
17
14
16
16
15
–40
–30
–20
–10
17/9
19/9
23/9
26/9
35
35.2
34.8
35.4
–40
–30
–20
–10
e
2
2
4
6
8
–40
–30
–20
–10
17/9
19/9
23/9
26/9
i
2
6
4
–40
–30
–20
–10
h
2
–6
–2
2
4
4
–4
0
0
–10
–20
–30
d
16/9
18/9
20/9
22/9
24/9
26/9
H
0
–200
–100
100
200
300
400
–40
–30
–20
–10
17/9
19/9
23/9
26/9
l
16/9
18/9
20/9
22/9
24/9
26/9
Q -P-E
Q
P
E
–2
0
2
4
6
8
10
12
14
b
c
17/9
19/9
21/9
23/9
25/9
–12
–6
0
6
12
m/s a
Dep h (m)
Fig. 3. Sep embe 2002. (a) Time e olu ion o shel winds, in m s–1; (b) con inen al uno (Q ), p ecipi a ion (P) and e apo a ion (E), in
m3s–1; (c) hea balance (H), in cal cm–2 d–1; (d) esidual cu en s, in cm s–1 (dashed line: pycnocline); (e) salini y; ( ) empe a u e, in °C;
(g) dissol ed o ganic ni ogen, in µmol l–1; (h) ammonium, in µmol kg–1; (i) chl a, in µg l–1; (j) pa icula e o ganic ni ogen, in µmol l–1;
(k) ni a e, in µmol kg–1; and (l) ni i e, in µmol kg–1. Hea and eshwa e luxes aken om Pied acoba e al. (2005)
Ma Ecol P og Se 353: 27–40, 2008
ace and bo om laye s, whe eas DON and PON luxes
equen ly exhibi ed signi ican di e ences (p < 0.05)
be ween he 3 su ace sec o s, especially on 26 July. In
Sep embe , mos o he concen a ion di e ences
along he ans e se sec ion occu ed in o ganic ni o-
gen. As in July, he luxes o ino ganic and o ganic
species we e signi ican ly di e en be ween sec o s
(p < 0.05), especially on 17 Sep embe (Table 3).
Ni ogen budge
A budge o o – i (in mg N m–2 d–1) o NT, PON and
DON was es ima ed conside ing he luxes pe m2o
ee su ace a ea om he middle sec ion o he inne
eaches o he ía (Table 4). The la e al a iabili y
epo ed in bo h he N species concen a ions and he
longi udinal componen o he esidual cu en was
conside ed in he calcula ion o N-nu ien s, PON and
DON luxes and, he e o e, in he co esponding i – o
balances. In addi ion, he accumula ion e ms o all
ni ogen species we e also calcula ed (V · ΔNT兾Δ ),
assuming ha he concen a ions o NT, PON and DON
in he olume o he ía bounded by he middle sec ion
do no di e om he concen a ions in he middle sec-
ion. NEP was ob ained by summing up o – i and
V·ΔNT兾Δ (see Eq. 10) o NT(NEPT), DON (NEPD) and
PON (NEPP) be ween 2 consecu i e su eys.
Du ing he s ong summe upwelling, he olume o
he ía bounded by he middle sec ion apped –289 ±
17 mg N m–2 d–1, i.e. 62% o he NTen y, bu only 44%
o –289 ± 17 mg N m–2 d–1 we e ans o med in o
o ganic ma e (NEPT= –127 ± 37 mg N m–2 d–1), while
162 mg N m–2 d–1 accumula ed in o he olume. By
con as , he ía was a nu ien sou ce du ing he sub-
sequen upwelling elaxa ion (o – i = 101 ± 5 mg N m–2
d–1) a he expense o he nu ien s accumula ed du ing
he p e ious pe iod. Du ing he ollowing weak up-
welling episode, nu ien sal s we e apped again,
wi h 57% u ilized o o ganic ma e p oduc ion and
43% accumula ed in o he s udy olume. Du ing he
au umn downwelling he ía ac ed as a nu ien sou ce
(o – i = 119 ± 9 mg N m–2 d–1) a he expense o he
nu ien s p e iously accumula ed in he sys em,
whe eas NEPTwas balanced (–18 ± 12 mg N m–2 d–1).
Howe e , du ing he subsequen elaxa ion pe iod, he
ía showed a he e o ophic me abolism (NEPT> 0),
expo ing 28% o he egene a ed NT o he shel (o – i
= 19 ± 1) and accumula ing he emaining 72% in o he
ía. Finally, du ing he weak au umn upwelling, he ía
ac ed as a nu ien ap, –96 ± 8 mg N m–2 d–1, one hi d
lowe han du ing he weak summe upwelling. Only
27% o NTwas consumed o p oduce o ganic ni ogen
and he emaining 73% accumula ed in o he sys em.
As a esul , he sys em changed om he e o ophic
o balanced condi ions (NEPT~ 0). Du ing July, he
p opo ion o NEPTdue o NO3–and NH4+was 67%
and 33% espec i ely, whe eas du ing Sep embe , he
alues we e 45% and 55% espec i ely.
The ac ion o NEPT ans e ed o he sedimen s
(NEPSED) can be in e ed indi ec ly om he ollowing
mass balance equa ion:
NEPT+ NEPD+ NEPP+ NEPSED = 0 ± δ(12)
NEPSED is he balance be ween PON sedimen a ion
and PON esuspension + NTdi usion om he sedi-
men (Ál a ez-Salgado e al. 1996a). I should be no ed
ha NEPSED is calcula ed wi h a la ge unce ain y (±δ),
esul ing om he indi idual unce ain ies associa ed
wi h he calcula ion o NEPT, NEPDand NEPP. Du ing
he s ong and weak upwelling pe iods, a la ge ac-
34
1.7±0.1
–0
–0.
6±
6±0.5
–0
–0.
1±
1±0.3
0.
1±
1±0.3
0.
0±
0±0.3
0
.4±0.1
.4±0.1
–0.6±0.5
–3.0±0.1
17/09/02
–0.6±0.2 0.2±0.0 0.6±0.2
0.5±0.1 0.1±0.0
3.8±0.1
0.
8±
8±0.3
0.8±0.3
2.2±0.4
23/09/02
–0.8±0.2 –0.7±0.2 –0.7±0.2
–0.7±0.2 –0.5±0.1
2.1±0.1
0
.0±0.3
.0±0.3
0.0±0.3
1.2±0.2
26/09/02
–1.1±0.3 –1.0±0.3 0.3±0.1
0.3±0.1 0.5±0.1
19/09/02
1.1±1.0 1.8±0.8 4.1±1.2
–4.8±0.9 –4.4±0.7
5.3±0.2
0.5±0.6
–3.7±0.1
SNSN
1.7±1.3 –2.9±1.5 –7.0±1.6
2.9±0.4 3.4±0.3
18/07/02
0.7±0.1
–0.1±0.3
0.0±0.5
22/07/02
9.7±1.6 9.3±0.5 7.3±1.8
8.4±0.9 6.6±0.6
1.5±0.1
0.1±0.3
–1.0±0.1
8.2±0.2
0.0±0.3
3.7±0.5
15/07/02
–4.5±1.4 –4.0±1.2 –3.7±1.1
2.3±0.7 1.7±0.5
2.4±0.1
0.4±0.1
4.6±1.4
26/07/02
–1.3±0.4 –2.1±0.6 –3.0±0.9
–0.5±0.1 2.1±0.6
SNSN
ab
cd
e
gh
Fig. 4. Time cou se o ho izon al (km d–1) and e ical (m d–1)
eloci ies o each sampling da e (dd/mm/yy). Solid ci cle,
ou low (V < 0 o wes wa ds) and c ossed ci cle, in low (V > 0
o eas wa ds) in o he ía; solid a ow, e ical ad ec i e e-
loci y (upwa d, >0; downwa d, <0); zigzag a ow, e ical
mixing eloci y (KZ兾Δz); whi e a ow, e ical displacemen
o he LNM. Sec o s a e desc ibed in Fig. 1b
Pied acoba e al.: Physical–biological coupling in Ría de Vigo. I
ion o NEPTsank o he bo om (75 ± 35% on 15 o
18 July and 97 ± 27% on 22 o 26 July). Du ing he
au umn downwelling, he ne sedimen a ion (NEPSED)
es ima ed wi h Eq. (12) is balanced by he loss o he
DON p e iously accumula ed in he sys em, since
NEPTwas nea ly ze o. T ans o ma ion o DON in o
sinking pa icles implies he use o DON as a nu ien
sou ce o mic ohe e o ophs (mainly bac e ioplank-
on) and i s ans e ence o highe ophic le els (zoo-
plank on, hanging mussels) o become sinking pa i-
cles. The au umn ansi ion was he only pe iod when
NEPSED was <0, which means ha esuspension o
PON and/o di usion o NT om he sedimen s was
la ge han POM deposi ion o e he bo om.
The ela i e impo ance o accumula ion e sus ex-
po o DON and PON was also assessed in each pe iod.
35
Da e Sec o s Concen a ions Fluxes
NTDON PON NO3–NO2–NH4+NTDON PON NO3–NO2–NH4+
15 July SS-CS **ns ns *ns *ns ns *ns *
CS-NS ***ns ns ***ns *ns *
SS-NS **ns ns ** **ns ns ns *
NB-SB *ns ns ns ns ns ns ns ns ns ns ns
18 July SS-CS *ns **ns * ******
CS-NS *ns ns *** ******
SS-NS *ns **** ******
NB-SB nsnsnsnsnsns nsnsnsnsnsns
22 July SS-CS *ns ns *ns * ******
CS-NS *ns ns *ns **ns ns ***
SS-NS ns ns ns ns ns ns ns **ns ns ns
NB-SB *ns ns ns ns ns ****ns *
26 July SS-CS ns ns ns *** ***ns ns *
CS-NS *ns ns ns ** ******
SS-NS *ns ns ns ** ******
NB-SB nsnsnsnsnsns ******
Table 2. - es o he concen a ions and ho izon al luxes o NT, DON, PON, NO3 –, NO2–and NH4+be ween he 3 su ace (NS, CS
and SS) and he 2 bo om (NB and SB) sec o s, o each sampling da e in July 2002. The p-le el was calcula ed as ollows: i
> 2.015, he di e ences be ween 2 sec o s a e signi ican a p < 0.05 (indica ed by *), whe eas i
< 2.015, he di e ence is nonsigni ican (indica ed by ns). x
_,σ2
Xand y
_,σ2
Y he mean and a iance o he concen a ions o luxes
in 2 sec o s espec i ely
xy X
2Y
2
−
()
+σσxy X
2Y
2
−
()
+σσ
Da e Sec o s Concen a ions Fluxes
NTDON PON NO3–NO2–NH4+NTDON PON NO3–NO2–NH4+
17 Sep SS-CS ***ns *ns ******
CS-NS ***ns ns ns ******
SS-NS *ns ns ns ns ns ******
NB-SB ns *ns ns ns ns ******
19 Sep SS-CS ns **ns ns ns ***ns **
CS-NS ns *ns ns ns ns ns ns ns *ns ns
SS-NS ns **ns *ns ******
NB-SB ns **ns ns ns ns ns **ns ns
23 Sep SS-CS ns ns ns ns ns ns ns ns ns ns ns ns
CS-NS nsnsnsns *ns ns ns ns *ns *
SS-NS ns ns ns ns ns ns *ns ns *ns *
NB-SB *ns *ns ns ns *ns ns ***
26 Sep SS-CS ns **ns ns ns ******
CS-NS ns **ns ns ns ns ns ns ns ns ns
SS-NS ns *ns ns ns ns ******
NB-SB nsnsnsnsnsns nsnsns **ns
Table 3. - es o he concen a ions and ho izon al luxes as in Table 2, bu o Sep embe 2002