Benthic nutrient cycling at the sediment-water interface in a lagoon fish farming system (northern Adriatic Sea, Italy)

Metabolism and carbon, oxygen, and nutrient fluxes (DIC, DOC, DO2, NO2 12, NO3 12, NH4+, PO4 3 12 and SiO4 4 12) were studied during three surveys at two sites (VN1 and VN3) located at a fish farm at theMarano and Grado Lagoon (northern Adriatic Sea), using an in situ benthic chamber. Field experimentswere conducted in July and October 2015 and March 2016 at a depth of approximately 2 m along the main channels of the fish farm.Water samples were collected by a scuba diver every 2 h in order to investigate daily fluxes of solutes across the sediment-water interface (SWI). Regarding the solid phase, Corg/Ntot and Corg/Porg molar ratios suggested an autochthonous marine origin of the organic matter and a minor preservation of P in the sediments, respectively; high values of sulphur (Stot) were also encountered (0.8\u20132%). The conditions at VN3 were mostly anoxic with high NH4 + levels (30\u20131027 \u3bcM) and the absence of NO3 12. Substantial daily patterns of all solutes occurred especially in autumn andwinter. On the contrary, fluxes at VN1were less pronounced. Usually, inverse correlations appeared between dissolved O2 and DIC trends, but in our systemthis was observed only at VN3 in autumn and accomplished by a parallel increase in NH4+, PO4 3 12 and SiO4 4 12 during intense nutrient regeneration. These results are significantly different than those reported for open lagoon environments,where nutrient regeneration at the SWI and in surface sediments is the primary source of nutrients available for assimilation processes, especially during the warmer period of the year when the natural nutrient input by fresh water inflows is limited. Due to the importance of this site for aquaculture, biodiversity and ecosystem services, useful suggestions have been provided from this study in order to improve the quality of this unique aquatic system

Panarea natural-lab: eight years of underwater research

The volcanic island of Panarea is characterized by the presence of continuous emission of volcanic gases from the seafloor. In November 2002 the system increased its flow of some order of magnitude and since then a steady release of gas is present generating bubble plumes that, in the shallowest points, reach the sea surface. Due to the environmental conditions, the area close to the shore and shallow water can be utilized as a “natural lab” to study the effect of high levels of CO2on the marine realm by surface techniques and directly by means of SCUBA diving. Since 2002, over one hundred hours of diving have been utilized to collect samples of fluids and sediments and to study the biota. After a first phase of volcanic surveillance, the island is more recently studied as a “natural analogue” for the development of reliable monitoring techniques for potential seepage from sub-seabed carbon storage sites. Hereby we present a synthesis of eight years of research in the area

Recent Trends Towards Oligotrophication of the Northern Adriatic: Evidence from Chlorophyll a Time Series

Abstract The results of the updated and quality-checked data base of field observations on chlorophyll a (Chl a) collected in the period 1970-2007 in the Northern Adriatic Sea are presented. From the last decade, SeaWiFS satellite information was also considered. Results demonstrate a global tendency towards Chl a reduction in the period of investigation, which is more marked in the eutrophic area under the influence of the Po River. In the rest of the basin, which presents meso- or oligotrophic characteristics, long-term changes are more difficult to detect. The long-term field dataset can be divided into two periods: the last decade characterized by the strong decrease observed in the whole northern Adriatic and the earlier period with no or slight increase. The recent substantial reduction of Chl a concentrations is confirmed all over the basin (−0.11 mg m−3 year−1) from satellite-derived information. Results are consistent with recently evidenced decrease in concentrations of phosphate and ammonia and point to the existence of oligotrophication in the Northern Adriatic. Results indicate forcefully that the still common perception of the Adriatic Sea as a very eutrophic basin is no longer appropriate, at least for its northern part and in recent years

Spiculosiphon oceana (foraminifera) and its affinity to intermediate stress conditions in the Panarea hydrothermal complex (Mediterranean Sea)

Spiculosiphon oceana Maldonado, L\uf3pez-Acosta, Sitj\ue0, Aguilar, Garc\ueda & Vacelet, 2013 is a Mediterranean endemic giant stalked foraminifer described as a potential bio-indicator of acidic environments, thanks to its ability to cope with stressful chemical conditions. Here, we present the first record and the first video images of living specimens of this giant foraminifera in the Panarea Volcanic Complex (PVC; southern Tyrrhenian Sea), representing the third discovery worldwide. Specimens of S. oceana were identified through microscopic and remotely operated vehicle (ROV) image analyses, in two different areas characterised by water column physico-chemical parameters typical of the non-vented areas, but with some evidence of hydrothermal alteration. This new finding enhances knowledge on the ecology of S. oceana, enlarges its known spatial distribution, and corroborates its affinity to intermediate stress conditions related to hydrothermal activity

Stable carbon isotopes of phytoplankton as a tool to monitor anthropogenic CO2 submarine leakages

This study aims to validate the stable carbon isotopic composition (d13C) of phytoplankton as a tool for detecting submarine leakages of anthropogenic CO2(g), since it is characterised by d13C values significantly lower than the natural CO2 dissolved in oceans. Three culture experiments were carried out to investigate the changes in d13C of the diatom Thalassiosira rotula during growth in an artificially modified medium (ASW). Three different dissolved inorganic carbon (DIC) concentrations were tested to verify if carbon availability affects phytoplankton d13C. Simultaneously, at each experiment, T. rotula was cultured under natural DIC isotopic composition (d13C DIC) and carbonate system conditions. The available DIC pool for diatoms grown in ASW was characterised by d13C DIC values (-44.2 ± 0.9‰) significantly lower than the typical marine range. Through photosynthetic DIC uptake, microalgae d13C rapidly changed, reaching significantly low values (until -43.4‰). Moreover, the different DIC concentrations did not affect the diatom d13C, exhibiting the same trend in d13C values in the three ASW experiments. The experiments prove that phytoplankton isotopic composition quickly responds to changes in the d13C of the medium, making this approach a promising and low-impact tool for detecting CO2(g) submarine leakages from CO2(g) deposits