Phytoplankton responses to freshwater inputs in a small semi-enclosed gulf (Gulf of Trieste, Adriatic Sea)

Abstract

Phytoplankton variations in response to freshwater inputs and water column structure in a shallow (c25 m) semi-enclosed Mediterranean gulf (Gulf of Trieste, Adriatic Sea) are described. Hydrographic profiles and In situ fluorescence were recorded at high resolution, while nutrients and phytoplankton were analysed at 5 pre-set depths. Analyses of the phytoplankton community structure were completed by determinations of the pigment pool using reverse-phase high-performance liquid chromatography and size-fractionated primary production. The phytoplankton standing crop, community structure and primary production were profoundly influenced by freshwater inputs and water column stratification. The water column was well mixed and supported modest phytoplankton concentrations during winter. A spring diatom bloom (Skeletonema costatum, Nitzschia spp., Chaetoceros spp.) developed in response to major freshwater input to the surface layer; a similar increase in diatoms (Rhizosolenia delicatula, R. fragilissima) followed October-November freshets. A shift from diatomdominated winter-spring phytoplankton to a flora wlth increased numbers of flagellates in the stratified water column during late spring-summer was reflected in the composition of accessory pigments [lower fucoxanthin : 19'-hexanoyloxyfucoxanthin ratio, an increase of chlorophyll b (chl b) and peridinin concentration]. Primary productivity was correlated with chl a biomass and showed surface peaks in April and June. The 2 to 10 pm phytoplankton contributed significantly to the total productivity in January and June, while on an annual basis the most important producers were > l 0 pm. The smallest fraction (<2 pm) seemed to contribute little, except in July. Our data indicate that the new production resulting from land-born nutrient inputs was the main cause of major phytoplankton blooms, while the nutrient supply from the bottom became comparatively more important during dry summer months.

Pelagic metabolism of the Douro estuary (Portugal) – Factors controlling primary production

“…From the PCA analysis, it is clear that spatial differences arose mostly along PC2, contrasting mostly larger nitrate þ nitrite concentrations and N:P ratios (upper station) to higher salinities, TPM and POM concentrations (lower station). This suggests that the upper estuary is more productive than the lower estuary as a result of higher nitrogen concentrations from riverine origin (Mallin et al, 1993;Malej et al, 1995). Also, higher chlorophyll biomass from the reservoir (Bordalo and Vieira, 2005) may help to explain these trends, but to a lesser extent (Table 5).…”

Variability of environmental factors of an eastern Mediterranean Sea river influenced coastal system

“…With such contribution, the effect of the river would be expected to be obvious. Many authors (LEVEAU et al, 1990;JORDAN et al, 1991a;HAMA & HADA 1994;MALEJ et al, 1995;SHIAH et al, 1996) have found that even shortterm nutrient inputs from rivers to coastal waters can cause the development of phytoplankton bloom.…”

Seasonal evolution of the nutrient pattern on Biscay Bay continental shelf over the years 1999-2000

“…Therefore, they can enhance the primary production in coastal areas (Lancelot et al, 1987;Radach, 1991;Turner and Rabalais, 1991;De Jonge et al, 1994;Peperzak et al, 1996;Harding and Perry, 1997). In the same way, the physical regulation of phytoplankton blooms by haline stratification has already been shown in coastal waters (Morin et al, 1991;Malej et al, 1995;Yin et al, 1996).…”