LOSS, GROWTH AND TRANSPORT DYNAMICS OF CHAETOMORPHA-AEREA AND ULVA-RIGIDA IN THE LAGOON-OF-VENICE DURING AN EARLY SUMMER FIELD CAMPAIGN

The growth, the losses by grazing and sporulation and the advective tr ansport of benthic macrophytes, dissolved and particulate nutrients we re studied in the Lagoon of Venice during May-June 1995. The growth ra te of Ulva rigida was 0.043 d(-1) and the grazing rate found to be 0.0 1 d(-1). No sporulation was observed in the study period. The advectiv e transport of macrophytes was measured by catches in vertically expos ed nets during several tidal excursions and varied from 0 to 11 kg Cha etomorpha aerea, 10 kg Zostera sp. and 9 kg Ulva sp. wwt. hour(-1) per 2 m net length normalized to effective length perpendicular to the cu rrent direction. The transport of Chaetomorpha and Ulva was linearily correlated to the current velocity (r(2) = 0.80 and 0.88 respectively) . Vertically separated nets revealed that 89% of the Zostera sp. was t ransported in the top 30 cm of the water column and 65% of the Chaetom orpha sp. was transported in the deepest 30 cm of the column and the t ransport of Ulva sp. was dispersed over the 1 m water column. Automati cally taken water samples were analysed for dissolved inorganic nutrie nts (carbon, nitrogen and phosphorus) and particulate nutrients during the campaign periods together with nutrients bound in macroalgae and seagrasses. The advective transport of dissolved and non-macrophyte bo und, particulate nutrients were calculated by a 2-dimensional, hydrody namic model. Less than 1% of the nutrients were transported as dissolv ed inorganic nitrogen and phosphate, 3-4% was transported as non-macro phyte, particulate nitrogen and phosphorus and more than 90% of the nu trients were transported as macrophyte bound nutrients. It is therefor e obvious that mass balance calculations for shallow estuarine systems should include advective transport of dead and alive macrophytes. (C) 1997 Elsevier Science B.V.