Evolution of the Trophic Conditions and Dystrophic Outbreaks in the Sacca di Goro Lagoon (Northern Adriatic Sea)

  • P. Viaroli
  • R. Azzoni
  • M. Bartoli
  • G. Giordani
  • L. Tajé


Dystrophy and vulnerability have been analysed in the Sacca di Goro lagoon (Po river Delta, Italy), where long term research was started in 1989 with respect to the abnormal growth and decomposition of the seaweed Ulva rigida.The research addresses: (1) trends in hydrochemical variables; (2) biomass, growth rates and the elemental composition of the dominant macroalgae; (3) nutrient uptake and retention within the macroalgal biomass; (4) oxygen metabolism; (5) decomposition processes and their effects on benthic fluxes of nitrogen, phosphorus and sulphide; (6) iron buffering of the phosphorus and sulphur cycles.

In the last decade, annual patterns have been observed with the abnormal spring growth of the seaweed Ulva rigida, which is usually followed by a sudden collapse and a prolonged oxygen deficiency in early summer. Nitrates are the most important nitrogen source for the macroalgae. Soluble reactive phosphorus concentrations attain significant peaks only during summer anoxia. In the worst years (1989–92 and 1997), Ulva growth commences in early Spring at temperatures above 10°C. The biomass increases at high rates (0.10–0.25 d−1) and reaches the highest standing crop (103 g dw m−2) and the maximum spreading (10 km2) at the end of May. From mid June, the macroalgal biomass starts to decompose causing anoxia and sulphide production. The biomass accumulation results in the temporary nitrogen retention within the organic pool leading to a prolonged nitrogen deficiency in the water column which allows only Ulva to grow. The impact of the dystrophy is related to the sedimentary cycles of sulphur and iron. Microbiologically reducible iron seems to buffer against free sulphide, precipitating it as insoluble iron monosulphide and pyrite. However, a considerable production of sulphide may occur in the water column associated with the decomposition of the thick floating macroalgal mats, where its concentration is independent of the potential iron buffering capacity of the sediment. In conclusion, the vulnerability (or buffer capacity) of such coastal systems seems to depend on the extent of the macroalgal blooms, amplitude of dissolved oxygen fluctuations at different time scales (from days to weeks), and sedimentary iron availability.


Acid Volatile Sulphide Sulphate Reduction Rate Soluble Reactive Phosphorus Concentration Benthic Flux Macroalgal Biomass 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. APHA, AWWA, WPCF (1975) Standard methods for die examination of water and wastewaters. 14th edn. APHA, WashingtonGoogle Scholar
  2. Atkinson MJ, Smith SV (1983) C:N:P ratios of benthic marine plants. Limnol Oceanogr 28: 568–574CrossRefGoogle Scholar
  3. Bartoli M, Cattadori M, Giordani G, Viaroli P (1996) Benthic oxygen respiration, ammonium and phosphorus regeneration in surficial sediments of the Sacca di Goro (Northern Italy) and two French coastal lagoons: a comparative study. Hydrobiologia 329: 143–159CrossRefGoogle Scholar
  4. Bartoli M, Castaldelli G, Nizzoli D, Gatti LG, Viaroli P (2000) Benthic fluxes of oxygen, ammonium and nitrate and coupled and uncoupled denitrification rates in two eutrophic coastal lagoons with different primary producer communities. (this volume)Google Scholar
  5. Borum J (1996) Shallow waters and land/sea boundaries. In: Jørgensen BB, Richardson K (eds) Eutrophication in coastal marine ecosystems: coastal and estuarine studies. Am Geophys Union 52: 179–203Google Scholar
  6. Castel J, Caumette P, Herbert R (1996) Eutrophication gradients in coastal lagoons as exemplified by the bassin d’Arcachon and the étang du Prévost. Hydrobiologia 329: ix–xxviiiCrossRefGoogle Scholar
  7. Cline JD (1969) Spectrophotometric determination of hydrogen sulphide in natural waters. Limnol Oceanogr 14: 454–459CrossRefGoogle Scholar
  8. DeBoer JA, Guigli HJ, Israel TL, D’Elia CF (1978) Nutritional studies of two red algae. I. Growth rate as a function of nitrogen source and concentration. J Phycol 14: 261–266CrossRefGoogle Scholar
  9. Flecht RL (1996) The ocurrence of “green tides” — a review. In: Schramm W, Nienhuis PH (eds) Marine benthic vegetation: recent changes and the effect of eutrophication. (Ecological studies, 123), Springer, Berlin Heidelberg New York Tokyo, pp 7–43Google Scholar
  10. Fossing H, Jorgensen BB (1989) Measurement of bacterial sulphate reduction in sediment: evaluation of a single-step chromium reduction method. Biogeochemistry 8: 205–222CrossRefGoogle Scholar
  11. Fujita RM, Wheeler PA, Zedler JB (1989) Assessment of macroalgal nitrogen limitation in a seasonal upwelling region. Mar Ecol Prog Ser 53: 293–303CrossRefGoogle Scholar
  12. Giordani G, Cattadori M, Bartoli M, Viaroli P (1996) Sulphide release from anoxic sediments in relation to iron availability and organic matter recalcitrance and its effects on inorganic phosphorus recycling. Hydrobiologia 329: 211–222CrossRefGoogle Scholar
  13. Giordani G, Azzoni R, Bartoli M, Waroli P (1997) Seasonal variations of sulphate reduction rates, sulphur pools and iron availability in the sediment of a dystrophic lagoon (Sacca di Goro, Italy). Water Air Sou Pollut 99: 363–371Google Scholar
  14. Howarth RW, Stewart JWB (1992) The interactions of sulphur with other element cycles in ecosystems. In: Howart RW, Stewart JWB, Ivanov MU (eds) Sulphur cycling on the continents: wetlands, terrestrial ecosystems and associated water bodies: SCOPE 33. J Wiley and Sons, New York, pp 67–84.Google Scholar
  15. Jensen A (1978) Chlorophylls and carotenoids. In: Hellebust JA, Craigie JS (eds) Handbook of phycological methods. Physiological and biochemical methods. Cambridge Univ Press, Cambridge, pp 59–70.Google Scholar
  16. Lapointe BE (1997) Nutrient thresholds for bottom-up control of macroalgal blooms on coral reefs in Jamaica and southeast Florida. Limnol Oceanogr 42: 1119–1131CrossRefGoogle Scholar
  17. Lavery PS, McComb AJ (1991) The nutritional eco-physiology of Chaetomorpha linul and Ulva rigida in Peel Inlet, Western Australia. Estuarine Coast Shelf Sci 33: 1–22CrossRefGoogle Scholar
  18. Lovley DR, Phillips EJP (1987) Rapid assay for reducible ferric iron in aquatic sediments. Appl Environ Microbiol 53: 1536–1540PubMedGoogle Scholar
  19. O’Kane JP, Suppo M, Todini E, Turner J (1992) Physical intervention in the lagoon of Sacca di Goro: an examination using a 3-D numerical model. Sci Total Environ 1992, pp 459–510 (Suppl)Google Scholar
  20. Pedersen MF, Borum J (1997) Nutrient control of estuarine macroalgae: growth strategy and the balance between nitrogen requirements and uptake. Mar Ecol Prog Ser 161: 155–163CrossRefGoogle Scholar
  21. Piccoli F, Godini E (1994) Ricerche qualitative e quantitative sulla vegetazione della Sacca di Goro: anni 1989–90. In Bencivelli S, Castaldi N, Finessi D (eds) Sacca di Goro: studio integrate sull’ecologia. Franco Angeli, Milano. I. pp 227–243Google Scholar
  22. Raffaelli DG, Raven JA, Poole LJ (1998) Ecological impact of green macroalagal blooms. Oceanogr Mar Biol Annu Rev 36: 97–125Google Scholar
  23. Ruttemberg KC (1992) Development of a sequential extraction method for different forms of phosphorus in marine sediments. Limnol Oceanogr 37: 1460–1482CrossRefGoogle Scholar
  24. Sand-Jensen K, Borum J (1991) Interactions among phytoplankton, periphyton, and macrophytes in temperate freshwaters and estuaries. Aqat Bot 41: 137–175CrossRefGoogle Scholar
  25. Smolders A, Nijboer RC, Roelofs JGM (1995) Prevention of sulphide accumulation and phosphate mobilization by the addition of iron (II) chloride to a reduced sediment: an enclosure experiment Fresh Water Biol 34: 559–568Google Scholar
  26. Valderrama JC (1977) Methods used by the Hydrographic Department of National Board of Fisheries, Sweden. In: Grasshoff K (ed) Report of the Baltic Intercalibration Workshop. Annex Interim Comm Protection Environ Baltic Sea, pp 14–34Google Scholar
  27. Valiela I, McLelland J, Hauxwell J, Behr PJ, Hersh D, Foreman K (1997) Macroalgal blooms in shallow estuaries: controls and ecophysiological and ecosystem consequences. Limnol Oceanogr 42: 1105–1118CrossRefGoogle Scholar
  28. Viaroli P, Pugnetti A, Ferrari I (1992) Ulva rigida growth and decomposition processes and related effects on nitrogen and phosphorus cycles in a coastal lagoon (Sacca di Goro, Po River Delta). In: Colombo G, Ferrari I, Ceccherelli VU, Rossi R (eds) Marine eutrophication and population dynamics. Olsen and Olsen, Fredensborg, pp 77–84.Google Scholar
  29. Viaroli P, Naldi M, Christian R, Fumagalli I (1993) The role of macroalgae and detritus in the nutrient cycles in a shallow-water dystrophic lagoon. Verh Int Ver Limnol 25: 1048–1051Google Scholar
  30. Viaroli P, Bartoli M, Bondavalli C, Naldi M (1995) Oxygen fluxes and dystrophy in a coastal lagoon colonized by Ulva rigida (Sacca di Goro, Po River Delta, Northern Italy). Fresenius Environ Bull 4: 381–386Google Scholar
  31. Viaroli P, Naldi M, Bondavalli C, Bencivelli S (1996) Growth of the seaweed Ulva rigida C. Agardh in relation to biomass densities, internal nutrient pools and external nutrient supply in the Sacca di Goro lagoon (Northern Italy). Hydrobiologia 329: 93–103CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Italia 2001

Authors and Affiliations

  • P. Viaroli
    • 1
  • R. Azzoni
    • 1
  • M. Bartoli
    • 1
  • G. Giordani
    • 1
  • L. Tajé
    • 1
  1. 1.Dipartimento di Scienze AmbientaliUniversità degli Studi di ParmaParmaItaly

Personalised recommendations