Salinity and its variability in the Lagoon of Venice, 2000–2009

Abstract

Yearly averages computed from monthly and bimonthly salinity data collected between 2000 and 2009 from 13 broadly spaced stations in the Venice Lagoon were analysed in view of 30 min data collected semi-continuously during 2009 at nine similarly located stations. Data from all stations and all years indicate that, based on yearly averages, the lagoon may be divided along its major (long) axis into three areas: 1) a northern, freshwater impacted area (S = <28 PSU) of high, tidally-caused, variability, 2) a southern, marine, zone of S >32 PSU of low, tidally-caused, variability, and 3) an intermediate zone. Salinity changes are closely associated with rainfall events, and the incoming freshwater is consistently distributed throughout the lagoon by tidal action. Much variability is simply a result of the forward and backward motion of the tides and is not caused by a salinity change in the water itself. The consistency of the 2000–2009 data and the historical (to 1961) watershed record support the hypothesis that the Venice Lagoon has been and is currently at steady-state with respect to its salinity distribution. As such, it is conducive to the development of (at least) three separate ecosystems.

Keywords:

• Venice Lagoon
• salinity
• steady-state

Acknowledgements

The authors wish to acknowledge Drs. Andrea Berton and Cristian Badetti for carrying out the MELa programmes and sharing their knowledge and first-hand experience in the Venice Lagoon. We also thank Alberto Bernstein, Laura Montobbio, and Roberto Rosselli for their unfailing managerial support of MELa. Gianni Mazzacurati made it all possible.

Notes

¹ Temperature, salinity, dissolved oxygen, pH, Eh (redox potential), turbidity, chlorophyll-a and phaeopigments, total suspended solids, nitrogen as NH₄⁺, NO₂⁻, NO₃⁻, total inorganic nitrogen (TIN), total dissolved nitrogen (TDN) and dissolved organic nitrogen (DON), phosphorus (as PO₄³⁻), total dissolved phosphate (TDP), dissolved organic phosphate (DOP), and carbon as total organic carbon (TOC), particulate organic carbon (POC), and dissolved organic carbon (DOC).

² Cu, Hg, Pb, Zn, Cd, Cr, and Ni

³ Measurements made in 2010 also showed that evaporation and rainfall were nearly equal to each other (G. Cecconi, unpubl.)