Lurralde :inv. espac. N. 3 (1980) p. 109-123 ISSN 1697-3070








© Miguel IBAÑEZ







The evolution of the nitrate, nitrite, phosphate and dissolved oxygen values in s ix stations off the Guipuzcoan coast and al so their possible relation with the development of mcrophytes from the intertidal fringe are commented on in the present work.

An increase in nutrients in the winter months in seen in the surface layers as well as a notable stratification and decrease of the same in the summer.

Some nitrophylic species such as Enteromorpha develop paradoxically in the summer months and disappear nearly totally in winter. On the other hand, the value of lm in long life species is actually less during the winter.



Se comenta en el presente trabajo la evolución de los valores de nitratos, nitritos, oxígeno disuelto y fosfatos en seis estaciones frente a la costa de Guipúzcoa, así como su posible relación con el desarrollo de las algas macrofitas de la franja intermareal.

Se observa un aumento de nutrientes en los meses invernales en las capas superficiales y una marcada estratificación y empobrecimiento de los mismos en el verano.

Algunas especies nitrófilas como Enteromorpha se desarrollan paradójicamente en los meses estivales y desaparecen casi completamente en invierno, mientras que en especies de ciclo largo el valor del lm es menor precisamente en la época invernal.



Ce travail aborde I'évolution des valeurs des nitrates, nitrites, oxygene dissous et phosphates dans s ix stations faisant face a la cate de Guipuzcoa, ainsi que leur rapport possible avec le développement des algues macrophytes de la frange intertidale.

On observe une augmentation des seis nutritifs aux moins d'hiver dans les couches superficielle$, ainsi que leur stratification et appauvrissement notoires en été.

Quelques es peces nitrophiles telles qu'Enteromorpha se développent paradoxalement aux mois d'été et disparaissent presque entierement en hiver, tandis que chez des especes au cycle long la valeur de l'lm est moindre justement a I'époque d'hiver.




In accordance with a Pilot programme "The Fight Against Littoral Pollution.', under the patronage of WHO (MANCY, 1975 & MACKAY, 1976) and carried out jointly by the "Ministerio de Obras Públicas" and "Jefatura Provincial de Sanidad de Guipúzcoa", a series of studies about nutrients, dissolved oxygen, temperature, salinity and pigments was worked on in 1976 and 1977 in nine stations just off the Guipuzcoan coast.

We trust that the complete study may be published by the competent organisms given that it constitutes the first serious contribution to the Oceanographic study of our little known coast.

In the present work we shall only comment on, and in summarised form, the principal characteristics of six stations situated off three coastal points (Jaizkibel, Mompás and Orio) of which three are near the coast (where the depth is 20 m). The other three are further away, where the depth is 100 m.

1ª: 43° 22' N; 2° 7' W  / 1 c: 43° 18' N; 2° 9' W 

2ª:43°24' N; 1°58'W  / 2c:43°20' N: 1°58'W 

3ª:43°25'20.'N; 1°54.W / 3c:43°22.30"N; 1°52'W

Material and methods

1.-Determination of dissolved oxygen

The method used is a modification of Winkler's classical procedure.

A solution of divalent manganese, followed by an alkaline iodide solution. is added to the sample. The manganous hydroxide formed disperses in the sea



water sample, which completely fills a flask of the kind used for BOD determinations.

The dissolved oxygen oxidises the divalent manganese to basic hydroxide of higher valency, which gives off a quantity of I2 equivalent to the dissolved oxygen, when the solution is acidified in the presence of KI. The I2 is titrated with a standardized Na2 S2 O3 using starch to detect the end result.

The samples were "pickled" as they were taken, by the addition of two solutions, manganous sulphate and alkaline iodide, and later analysed in the laboratory.

2.-Determination of Phosphates

The procedure followed consists in making the sea water sample react with a reactive mixture which contains molybdic acid, ascorbic acid and trivalent antimony.

The resulting complex heteropoly acid is reduced "in situ" giving a blue o solution, the extinction of which is read at 8850 A.

Once the samples were taken, they were refrigerated till the moment of analysis.

The extin¿tion of the samples was corrected subtracting the values given by turbidity and reactive blanks. 3.-Determination of Nitrites

The nitrites present in sea water react with sulphanilamide in an acid solution. The resulting diazo-compound reacts with N-naphthyl-etylendiamine and forms a highly coloured compound the extinction of which we measure at 5430 A using 10 cm cells.

The samples were refrigerated till the moment of analysis, and the values obtained were corrected considering the turbidity and reactive blanks. A solution of NaNO2 was used as pattern.

4.-Determination of Nitrates

The sea water nitrates are reduced q/Jantitatively to nitrites when the sample is passed through a reduction column full of Cd-Cu filings.

The nitrite from th,s way is determined using the method above but using 1 cm cells.

Synthetic sea water to which was added a solution of KNO3 was used as a pattern.



In figures 1,3 and 5" an evQ!ution in the depth is clearly seen in the course of time. In spring, summer and autumn, the surface values are small. A very accentuated stratification is observed in the summer months and the beginning of autumn.

I n November-December a mixture is produced which causes an enrichment of the surface waters which reaches a maximum value in February and which later diminishes.



In the coastal stations (figures 2,4 and 6) the same pattern is produced but with slightly higher surface values in spring, possibly due to fluvial waste.

In August 1977 there is an abnormally high value off Jaizkibel, perhaps due to a coastal current in a westerly direction and which transports the waste of the river Bidasoa without mixing them too much.

In figure 7 two maximums in the surface are observed in the coastal stations, one corresponding to the winter upwelling and the second to the spring fluvial wastes.


In general, the evolution of the phosphates is parallel to that of the nitrates. hqwever an enrichment of the surface (figs. 8-13) is manifest in the coastal stations between May and June, there also exists a maximum between January and March.

In the surface (fig. 14) we can see a winter maximum between January and March with another more accentuated in the coastal stations in the spring months. this latter is possibly also due to fluvial effluents.

In the coastal stations a third maximum is noticed in September. possibly also due to fluvial wastes.


The interpretation of the nitrites is more complex. A noticeable increase is manifest in April and October between a depth of 40-80 meters (fig. 15) with the observed values being greater in general in the coastal stations.

4.-Dissolved oxygen

The values of dissolved O2 are quite homogeneous in time and space, only that somewhat lower values are seen in August, coinciding with the elevation of temperature and maximum stratification of the layers of surfaces waters (figs. 17 and 18).

Two maximums are observed (fig. 19). the first being in September 1976 and the second between March and April 1977.


In general we can clearly differentiate two distribution patterns in the parameters studied. one in the summer months represented in the figure 20 and corresponding to the month of August. whit a thermocline at a depth of 30 m and oligotrophic characteristics in the surface layer.

The second pattern corresponds to February (fig. 21) and shows a homogeneous distributions of nutrients at all depths.

In view of these results. we see that. off the Basque coast in a certain way a "phenomenon occurs which is inverse to that produced off the NW coast of the Peninsula. In effect, while there is an upwelling of deep waters. which begins in May, caused by the prevailing winds from NE, a period of calm whit greater insolation (SERVAIN. 1978) begins in front of the Basque coast. This originates higher temperatures of the surface layers (SERVAIN. 1977) and a marked stratification and decrease of nutrients in the surface layers.

In November on the contrary, when this upwelling off the Galician coast



finishes, strong surface current, produced by winds from NW-W, are formed just off the Basque Coast and circulates parallel to the coast in a W -? E direction and S -> N off the French coast (IBAÑEZ, 1979).

AII this coincides with a mixture of both surface and deep waters off the Basque coast which produces an enrichment in nutrients in the surface layers.

(It would be interesting in later works to take samples from deeper waters, up to 1000 m, in order to establish the true magnitude of this upwelling.)

In October, according to MANRIQUEZ et al. (1978) the nitrate and phosphate values seem to be slightly higer still off Galicia, at least in the coastal area (1).

Whit reference to the effects which this cycle of nutrients may have on the intertidal benthic algae, there are some ephemeral algae (species which usually persist for only a few months) like Porphyra linearis which develops in the winter months in the upper mid-Iittoral or upper shore area (depending on the force of the waves at this time). There are also other long life species such as Corallina officinalis, Halopteris scoparia, C/adostephus spongiosus (var. spongiosus and verticillatus) and Bifurcaria rotunda, whose biomass per surface unit diminishes notably in the winter due to the storms, and which present a lower Margalef index precisely at this time (IRASTORZA & IBAÑEZ, in press).

It seems that the combined effect of the storms and an increase of nutrients favours the fall of the old part and the active growth of new branches, which produces a minimum value of Im.

However apparen contradictions are seen in some nitrophylic algae

Enteromorpha, which forms dense "grass" in the upper mid-Iittor~1 area and which reaches a maximum in the months of June-July, later disappearing in winter (fig. 22).

This disappearance is possibly due to the active '.grazing" by the moluscs Patella intermedia, Gibbula umbilicaris and Monodonta lineata, this last in lesser degree, in the community of green seaweeds.

Less insolation in the winter months, the force of storms etc... may also have an adverse effect on this time.

Indeed, a little sandy blanket which the algae grow on, develops on flat surfaces as in Zumaya. In December this blanket disappears completely leaving the bare rock and with it the community of Enteromorpha disappears too.

In Mompas we can see how the belt of Enteromorpha which completely covers the upper mid-Iittoral area ascends in the winter months. And the Enteromorpha disappears from the lowest levels and develops at the lower extreme of the upper shore.

Possibly adverse conditions such as absence of insolation cause a disequilibrium between the algae production and the grazing of the phito- phagous molluscs, so that they can only develop in areas where the molluscs have limited access (upper-shore) and where sufficient humidity exists in winter to permit the development of Enteromorpha in precarious conditions.

(1) According lo MILLOT (1979) and HUA & THOMASSET (1979), well localized coaslal upwellings are produced with different Iypes of wind depending on the coastaI geometry.



Figuras 1 to 3

Figuras 4 to 6

Figuras 8 to 10

Figuras 11 to 13

Figuras 19 - 14 - 7

Figuras 15 to 17

Figura 20 - 21

Figura 22



Fig 1-6 Monthly distribution of Nitrates.

Fig. 7. Surface and sea-bed distribution of Nitrates.

Fig.8-13: Monthly distribution of Posphates.

Fig. 14: Surface and sea-bed distribution of Phosphates.

Fig. 15 & 16. Monthly distribution of Nitrites.

Fig. 17 & 18. Monthly distribution of dissolved oxygen

Fig. 19 Surface and sea-bed distribution of dissolved oxygen Fig. 20: Distribution pattern of nutrients and dissolved oxygen in August.

Fig. 21. Distribution pattern of nutrients and dissolved oxygen in February.

Fig. 22. Monthly distribution of Enteromorpha biomass.





HUA L. & F. THOMASSET: Modélisation numerique de phénomen~s d"'upwelling" cDtiers pars une methode d'éléments finis non conformes. IRIA Rap. Rech. n.o 366 (1979) 48 pp.

IBAt'lEZ M.: Hydrological studies and suTface currents in the coastal area of the bay of Biscay. Lurralde 2 (1979): 37-75.

lRASTORZA A. J. & M. IBAÑEZ: Estudio de pigmentos en algas macrofitas de la zona inter- mareal de la costa vasca. (in press).

MACKA y D. W. : Report on a visit to Spain. Control of pollution in rivers and coastal waters 19-24 October 1976. WHO.

MANCY K. H.: Report on a visit to Spain. Control of pollution in rivers and coastal waters 27 Feb.-11 March 1975. WHO.

MANRIQUEZ M., C. MOURlt'lO & F. FRAGA: Campaña "Galicia [V". Datos básicos [. Res. Exp. Cient. B/O Comide 7 (1978): 195-240.

MILLOT L.: Wind induces upwellingin the Gulf of Lions. Oceanológica Acta (1979) 2 (3).

SERVAIN J.: Rapport preliminaire sur l'étude des donées climatologiques historiques du Proche Atlantique. Rapport n.o 5 Univ. Bretagne Occidentale (1977).

SERV AIN J.: Suite de l'étude des données climatologiques historiques du Proche Atlantique. Rapport n.O 6 Univ. Bretagne Occidentale (1978).

STRICKLAND J. D. H. & T. T. PARSON: A practical Handbook of Seawater Analysis. Fish. Res. Bd. Canada. Ottawa (1968) Bull. n. 168.