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Nitrogen, phosphorus, and biogenic silicon budgets for the northern adriatic sea
| Content Provider | Semantic Scholar |
|---|---|
| Author | Degobbis, Danilo Gilmartin, Malvern |
| Copyright Year | 1990 |
| Abstract | RESUME Danilo DEGOBBIS a, Malvern GILMARTIN b a "Rudjer Boskovie" Institute, Center for Marine Research, 52210 Rovinj, Yugoslavia. b University of Maine at Orono, Department of Zoology, Orono, Maine 04469, USA. Received 3/2/89, in revised forrn 31/7/89, accepted 11/8/89. Proximate nitrogen, phosphorus and biogenic silicon budgets were calculated for the northem Adriatic, one of the most productive subregions of the Mediterranean Sea, and the main processes driving the biogeochemical cycle of these biogenic elements were ranked as to their relative importance. The calculations were based on an extensive data set (n = 20 000) collected since 1966, and from results reported in the litera ture. Contributions (N: 23,640x 10 , P: 910x 10 , and Si: 8,400x 10 mol y) and !osses (N: 17,150x 10 , P: 750x 10 , and Si: 5,460x 10 mol y) were of the same order of magnitude. The results support the assumed importance of the nu trient contribution by the Po River (at !east 50% of the inputs) whose waters thereby influence a large part of the northem Adriatic. The loss by water mass transport is the principal mechanism balancing the nutrient budget in the northem Adriatic, although !osses by denitrification in sediments account for a large part (about 40 %) of the nitrogen output. Atmospheric contributions are relatively minor, particularly for total phosphorus and orthosilicate, and nitrogen fixation does not contribute significantly to the total nitrogen budget. Phosphorus and silicon burial in the sediments represents a significant Joss for these elements. Other !osses (fish catches and production of nitrogen oxides) were not significant on the scale of these calculations. Nutrient quantities equal to or higher than the yearly external input are biologically recycled annually in the northern Adria tic (N: 38,400 x 106 , P: 1,065 x 106 , and Si: 12,800 x 10 mol y). The results quantify the importance of water column microheterotrophic activity as the principal mechanism of nitrogen and phosphorus regeneration in the northern Adriatic. Macrozooplankton and nekton excretion and benthic release together con tri bute Jess than 10 % of the total nitrogen and phosphorus remineralization. In contrast, the bulk of orthosilicate regeneration occers in the sediments. The high ratio of externat contribution to regenerated nutrients clearly establishes that the former nu trient input is supporting a large part of the relatively high biological productivity of the region. This indicates that the northern Adriatic ecosystem is sensitive to further increases of anthropogenic nutrient load. The eutrophie impact of such loading could be critical during spring and early summer, when biological activity is the highest and the northern Adriatic behaves as a semienclosed sea due to eddy circulation. Oceanologica Acta, 1990. 13, 1, 31-45. · Les bilans en azote, phosphore et silicium biogenique de la mer Adriatique septentrionale Les bilans en azote, phosphore et silicium biogenique sont etablis pour l'Adriatique septentrionale, l'une des regions les plus productives de la mer Mediterranee. Les principaux phenomenes entrant dans le cycle biogeochimique de ces elements biogeniques ont ete classes selon leur importance relative en utilisant les nombreux 0399-1784/90/01 31 15/$ 3.50/© Gauthier-Villars 31 D. DEGOBBIS. M. GILMARTIN INTRODUCTION resultats (20 000) des analyses effectuees depuis 1966 et des resultats ci tes dans la litterature. Les apports (N : 23 640. 106 ; P : 910. 106 ; Si : 8 400. 10 mol. a 1) et les pertes (N : 17150. 106 ; P : 750. 106 ; Si : 5 460. 106 mol. a ) sont du meme ordre de grandeur. Les resultats confirment l'importance de l'apport de sels nutritifs par les eaux du Po (au moins 50% du total) dont l'effet s'etend a une grande partie de l'Adriatique septentrionale. La perte par transport de masse est le terme principal du bilan en elements nutritifs, bien que la denitrification soit importante dans les sediments (environ 40% des pertes d'azote). La contribution de l'atmosphere est relativement modeste, en particulier pour le phosphore total et l'orthosilicate; la fixation de l'azote elementaire n'est pas significative. Les pertes de phosphore et de silicium sont importantes dans les sediments; les autres pertes, dues a la peche et a la production des oxydes d'azote, ne sont pas significatives dans les bilans etablis ici. Des quantites d'elements nutritifs egales ou superieures aux apports externes sont recyclees chaque annee par des phenomenes biologiques (N: 38400.10 ; P: 1 065. 10 ; Si : 12 800.10 mol. a ). Les resultats montrent que l'activite microheterotrophique dans la colonne d'eau est le principal mecanisme de regeneration de l'azote et du phosphore. L'excretion du macrozooplancton et du necton, ainsi que la remineralisation dans les sediments, contribuent pour moins de 10% a la remineralisation totale de l'azote et du phosphore. Au contraire, la regeneration de l'orthosilicate se produit surtout dans les sediments. Le rapport eleve entre la quantite d'elements nutritifs d'origine externe et celle qui est regeneree montre que l'apport externe joue un role important dans la forte productivite biologique de cette region. L'Adriatique septentrionale est donc un ecosysteme sensible aux eventuelles augmentations de la charge anthropogenique en elements nutritifs. L'impact eutrophisant de cette charge pourrait devenir critique au printemps et au debut de l'ete lorsque l'activite biologique est maximale, la circulation dans l'Adriatique etant alors celle d'une mer semi-fermee. Oceanologica Acta, 1990. 13, 1, 31-45. The computation of a nutrient budget is the basic step in the study of the relative importance of the processes controlling the biogeochemical cycles of major plant nutrients. There are only a few coastal marine regions in the world for which budget calculations have been attempted: for example the Baltic Sea (Larsson et al., 1985), the Gulf of Maine and Georges Banks, USA (e.g. Schlitz and Cohen, 1984), the Gulf of St. Lawrence, Canada (Coote and Yeats, 1979), Narragansett Bay, Rhode Island, USA (Nixon and Pilson, 1983), and the Mediterranean Sea as a whole (Bethoux and Copin-Montegut, 1986). Partial calculations have been made for sorne other coastal and estuarine areas (see Nixon and Pilson, 1983 for review). However, there are no regions where complete and fully reliable nutrient budgets are available. The northern Adriatic Sea (18 900 km2 ) represents a small portion of the total area (139 000 km) of the Adriatic Sea (Fig.), but it is one of, if not the most, productive regions in the Mediterranean (Sournia, 1973). The Po River (ltaly), one of the largest in the Mediterranean, as well as various minor rivers, discharge their waters into the northern Adriatic. It was often assumed, but never quantified, that the Po River is the most important source of nutrients for the northern Adriatic. A preliminary budget calculation for |
| Starting Page | 31 |
| Ending Page | 45 |
| Page Count | 15 |
| File Format | PDF HTM / HTML |
| Volume Number | 13 |
| Alternate Webpage(s) | https://archimer.ifremer.fr/doc/00103/21404/18989.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
