Changes in nutrient concentrations and ratios during mucilage events in the period 1999-2002.

Rudjer Bosković Institute, Center for Marine Research (CMR), G. Paliaga 5, 52210 Rovinj, Croatia.
Science of The Total Environment (Impact Factor: 3.26). 01/2006; 353(1-3):103-14. DOI: 10.1016/j.scitotenv.2005.09.010
Source: PubMed

ABSTRACT Nutrient and chlorophyll a concentrations and salinity were measured, approximately monthly, from June 1999 to July 2002 at 20 stations along three transects in the northern Adriatic Sea, north of the line Susak Island-Senigallia, with the aim of confirming or rejecting the hypothesis that changes in nutrient ratios may have an important role in the mucilage phenomenon. The data analyses were focused on the two major water types identified in the region: lower salinity (32-37) and oxygenated surface waters (type 1) in which the mucilage phenomenon primarily developed, and high salinity water originating from other parts of the Adriatic (type 4). Marked variability of dissolved inorganic nitrogen (DIN) in type 1 waters was roughly correlated with extreme fluctuations of the Po River flow rate during the investigated period. In contrast, the orthophosphate (PO4) concentration was primarily controlled by phytoplankton assimilation. The nutrient discharges and DIN/PO4 ratios (median 120) in the freshened surface layer were much higher and more variable in the period before the mucilage event in 2001 than in 2000 (median 75), and particularly in 2002 (median 30), although intensity and duration of the 2001 event were the lowest. However, in that period of 2000 and 2002 significant transversal transport of freshened waters occurred, despite the unusually low Po flow rates. In summer, in conditions of low freshwater discharge and the prevailing of semi-enclosed circulation in the region, more efficient DIN assimilation by phytoplankton occurred, probably due to a faster recycling of PO4. However, in 2002 this process appeared to have already started in March. Changes of the orthosilicate (SiO4)/DIN ratio were mainly dependent on DIN concentrations. In the more saline waters (type 4) the nutrient concentrations, particularly DIN, were much lower and no significant relationships were noticed among the studied parameters. Nutrient concentration and ratio changes do not trigger mucilage events, although very probably they have an essential role in combination with several other physical (pulsing freshwater discharge, marked stratification, minimal water exchange) and biological (e.g., increased plankton excretion, limited bacterial degradation) factors.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Parameters relevant to the study of eutrophication processes in the northeastern Adriatic (NEA) during the period 2000–2009 were analysed and compared with a previous period (1972–1999). The data used in this study were collected at two stations in the coastal zone up to 13 NM off Rovinj (western Istria). The more recent period was characterised by a strong reduction of the Po River flow rate and different circulation regime with the more frequent inflow of high salinity and oligotrophic water from the central Adriatic. Change in the circulation was evidenced by lower frequencies of the Istrian Coastal Countercurrent (ICCC) as compared to the Eastern Adriatic Current (EAC) after 2000, particularly in spring. As a consequence, a marked increase in surface salinity and decrease in orthophosphate and chlorophyll a concentrations at two stations in the period 2000–2009 occurred. In contrast, during late winter and in spring of the more recent period, dissolved inorganic nitrogen (DIN) concentrations were higher, despite the lower freshwater discharge and increased inflows on nutrient-poorer water. This DIN increase was very probably due to an enhanced reduction of orthophosphate concentration after 2000, limiting further the phytoplankton growth, resulting in a more marked accumulation of unused DIN. The obtained results showed that the eutrophication pressure was markedly reduced in the NEA during 2000–2009 in respect to the previous period.
    Estuarine Coastal and Shelf Science 12/2012; 115:25–32. · 2.32 Impact Factor
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: a b s t r a c t Benthic metabolism and carbon and nutrient cycling at the sedimentewater interface were studied seasonally in the Marano (sites MB and MC) and Grado Lagoon (sites ART and BAR), northern Adriatic Italy, using porewater vertical profiles and daily fluxes of O 2 , DIC, DOC, NO 3 À , NH 4 þ , PO 4 3À and SiO 4 4À measured in situ deployed transparent and dark benthic chambers. Diffusive and benthic fluxes of solutes were eval-uated on a seasonal basis. Sites MC and ART were characterized by higher C org. contents due to input of riverine organic matter and mariculture, respectively. The C org. , N tot. , P tot. , P org. and Si biog. contents decreased along the sediment cores while porewater concentrations of DIC, DOC, NO 3 À , NH 4 þ , PO 4 3À and SiO 4 4À increased along the sediment cores at all study sites due to the degradation of labile sedimentary matter. Higher concentrations of all porewater solutes and higher diffusive fluxes were observed in warmer periods. Benthic fluxes of O 2 , DIC, NO 3 À , NH 4 þ , PO 4 3À and SiO 4 4À showed intensive seasonal variations. Based on O 2 and DIC metabolism, the lagoon sediments were highly heterotrophic except at BAR being in trophic balance or weakly heterotrophic. NO 3 À and SiO 4 4À exhibited influxes due to intense microphytobenthic assimilation, mostly by diatoms, and denitrification while extremely low PO 4 3À fluxes suggest P as a limiting factor. The great difference observed between the diffusive and the in situ benthic fluxes suggests the importance of bioturbation and that the pertinent processes occur at the sedimentewater interface. Tentative annual budgets of carbon and nutrients in surface sediments of studied sites indicate that their cycling, compared to burial flux, is more intensive at the sedimentewater interface. These basic benthic biogeochemical processes can be important to better understand the trace metal cycling, especially Hg mobilization and sequestration, in the lagoon environment.
    Estuarine Coastal and Shelf Science 11/2012; 113:57-70. · 2.32 Impact Factor


1 Download
Available from
Jun 24, 2014