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Santa Giusta Lagoon (Sardinia): phytoplankton and nutrients before and after waste water diversion

Sechi, Nicola and Fiocca, Fatima and Sannio, Antonietta and Lugliè, Antonella Gesuina Laura (2001) Santa Giusta Lagoon (Sardinia): phytoplankton and nutrients before and after waste water diversion. Journal of Limnology, Vol. 60 (2), p. 194-200. ISSN 1723-8633. Article.

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Abstract

The purpose of this paper was to assess the effect of the diversion of waste water on the trophic status of the Stagno di Santa Giusta, a hypertrophic lagoon on the centre-western coast of Sardinia. The data available (1990, 1992-1994) before the diversion (1995) were compared with those collected from 1995 to 1999. The lagoon has an area of about 8 km2; its mean depth is about 1 m and is well mixed as regards circulation and stratification. This study examined temperature, salinity, pH, main nutrients (reactive and total phosphorus, nitrate and ammonium nitrogen, reactive silica), chlorophyll-a, phytoplanktonic density and phytobenthic biomass. A comparison of the condition of the water before and after the diversion showed that there was an insufficient reduction in nutrient concentrations. The mean concentrations of nitrate nitrogen and ammonium nitrogen fell from 33 and 87 mg N m-3, respectively, to 28 and 66 mg N m-3, respectively. There was a more marked reduction in phosphorus (from 107 mg P m-3 as reactive phosphorus and from 190 mg P m-3 as total phosphorus to 77 and 127 mg P m-3, respectively), and in reactive silica, from 3 to 1.7 mg l-1. Chlorophyll-a decreased from 11.3 to 10.2 mg m-3; the total density of phytoplankton dropped considerably, but this was due to a different species composition. Phytobenthic biomass showed no particular variations. There were no changes in trophic level, so that dystrophic crises still occurred after the diversion. The results showed that there were no substantial improvements in the trophic status of the lagoon during the years after the diversion, except for some months in 1995. A possible explanation may lie in the structure of the diversion system, which does not completely stop the inflow of sewage into the lagoon.

Item Type:Article
ID Code:279
Status:Published
Refereed:Yes
Uncontrolled Keywords:Coastal lagoons, eutrophication, Sardinian lagoons, long-term monitoring, waste diversion, Oristano, Sardinia
Subjects:Area 05 - Scienze biologiche > BIO/07 Ecologia
Divisions:001 Università di Sassari > 01 Dipartimenti > Scienze botaniche, ecologiche e geologiche
Publisher:CNR, Istituto per lo studio degli ecosistemi
ISSN:1723-8633
Publisher Policy:Documento open access
Deposited On:18 Aug 2009 10:01

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