MESOSCALE VARIABILITY OF ORGANIC MATTER COMPOSITION IN NW ADRIATIC SEDIMENTS

We investigated the spatial variability of sediment organic matter content and composition in three areas (A, B and C) of the Northwestern Adriatic Sea, subjected to a putative gradient of trophic state ( i.e. , increasing distance from the Po river outflow) in order to determine the appropriate sample size and replication. The analysis of the mesoscale variability was carried out comparing variability on the scale of meters ( i.e. among different deployments) with the variability observed on a scale of several kilometres ( i.e. among different sampling areas). Sediment samples, collected on April 1999, October 1999, April and October 2000, were analysed for chloropigment content (chlorophyll-a and phaeopygments) and protein, carbohydrate and lipid concentrations. Chloropigment, protein, carbohydrate and lipid concentrations were high, indicating that this system shares trophic conditions typical of highly productive environments. All organic matter components displayed a distribution independent from the increasing distance from the Po river outflow and a clear spatial variability, characterised by significant differences among different areas, but not among deployments. Carbohydrates were the biochemical compound displaying the highest spatial variability among the three areas. Chloropigment, protein, carbohydrate and lipid concentrations displayed also significant temporal changes. When spatial and temporal variability were compared, chlorophyll-a, phaeopigment and protein concentrations displayed a higher temporal than spatial variability. Conversely, for carbohydrates and lipids spatial and temporal variability was of the same order of magnitude. Organic matter composition displayed limited changes among areas, but a strong temporal variability. The results from the Adriatic sea suggest that analyses from sediments collected from a single deployment are sufficient for assessing organic matter concentration and composition over areas of several hundreds of square meters. However, for estimating organic matter composition over larger spatial scales ( i.e. miles) the identification of different sampling areas is needed.     

Biochemical composition and early diagenesis of organic matter in coastal sediments of the NW Adriatic Sea influenced by riverine inputs

River inputs influence trophodynamic and biogeochemical processes of adjacent continental shelves. In order to provide new insights on the influence of continental inputs on the benthic trophic state and early diagenesis of sediment organic matter we collected surface sediments in the NW Adriatic Sea at three stations located at increasing distance from the Po River. Sediment samples were collected in four periods characterized by different river outflows and analysed for chloropigment content (chlorophyll-a and phaeopygments), protein, carbohydrate and lipid concentrations, prokaryote abundance and aminopeptidase activity. Sediments of the NW Adriatic Sea displayed high organic loads, tightly coupled with the outflow dynamics of the Po River. A major flooding event was responsible of an enhanced accumulation of organic material on the sea bottom. The resulting increased nutrient load in the sediment impaired organic matter degradation processes. The results of the present study suggest that the enhanced trophic state of marine coastal sediments subjected to riverine inputs are related not only to the increased nutrient inputs, but that they may be amplified by impaired degradation processes.     

Benthic Response to Mucilaginous Aggregates in the Northern Adriatic Sea: Biochemical Indicators of Eutrophication

Abstract

In summer 1997, gelatinous aggregates appeared in the Adriatic Sea, covering large areas of the northern basin. This study deals with the comparison between the biochemical composition of the sedimentary organic matter in summer, 1996 (when no aggregates appeared), and in summer, 1997 (during the appearance of aggregates). the biochemical composition of organic matter in surface sediments (determined in terms of proteins, carbohydrates, lipids, phytopigments and nucleic acids) has been investigated in two areas along the coast of the NW-Adriatic Sea in order to characterize benthic processes during aggregate deposition on the sea floor. During mucilage accumulation, a significant increase of biochemical compounds was observed, and chlorophyll-a and carbohydrate concentrations doubled their concentrations. in contrast, protein concentrations decreased, so that overall biopolymeric carbon content (expressed as the sum of lipid, protein and carbohydrate carbon equivalents) did not display significant differences between sampling periods (1579.3 in June, 1996 1678.8 μgCg^?1 and June, 1997). the protein to carbohydrate ratio decreased from 4.9 in June, 1996 to 1.8 in June, 1997. Mucilage production in June, 1997, modified significantly the biochemical composition of the sedimentary OM, thus affecting the potential availability of OM to benthic consumers. We hypothesise that the production of highly refractory composition of the sedimentary OM during mucilage accumulation might have an important biogeochemical implications.     

Benthic Response to Mucilaginous Aggregates in the Northern Adriatic Sea: Biochemical Indicators of Eutrophication

In summer 1997, gelatinous aggregates appeared in the Adriatic Sea, covering large areas of the northern basin. This study deals with the comparison between the biochemical composition of the sedimentary organic matter in summer, 1996 (when no aggregates appeared), and in summer, 1997 (during the appearance of aggregates). the biochemical composition of organic matter in surface sediments (determined in terms of proteins, carbohydrates, lipids, phytopigments and nucleic acids) has been investigated in two areas along the coast of the NW-Adriatic Sea in order to characterize benthic processes during aggregate deposition on the sea floor. During mucilage accumulation, a significant increase of biochemical compounds was observed, and chlorophyll-a and carbohydrate concentrations doubled their concentrations. in contrast, protein concentrations decreased, so that overall biopolymeric carbon content (expressed as the sum of lipid, protein and carbohydrate carbon equivalents) did not display significant differences between sampling periods (1579.3 in June, 1996 1678.8 μgCg^-1 and June, 1997). the protein to carbohydrate ratio decreased from 4.9 in June, 1996 to 1.8 in June, 1997. Mucilage production in June, 1997, modified significantly the biochemical composition of the sedimentary OM, thus affecting the potential availability of OM to benthic consumers. We hypothesise that the production of highly refractory composition of the sedimentary OM during mucilage accumulation might have an important biogeochemical implications.     

Benthic-pelagic coupling in frontal system areas of the Northern Adriatic Sea: Analysis of the carbon budgets

Sediment samples were collected between 1996 and 1998 during 4 cruises in the northern sector of the Adriatic Sea, facing the Po River outflow. In each sampling period, after identification of the front line, a grid of 6 sampling stations was selected in order to cover: the coastal area (largely affected by river waters), the inner and outer front areas, and the offshore waters. The biochemical composition of sedimentary organic matter (OM, lipids, proteins, carbohydrates and photosynthetic pigments) and enzymatic activity rates were studied to provide information on the potential organic matter turnover. Tentative estimates of the organic carbon budgets (input/production versus requirement by benthic consumers) are presented. Benthic carbon requirements, estimated from bacterial plus meiofaunal secondary production, was high (897 r mg r C r m m 2 r d m 1 ). OM concentrations in the Northern and Middle Adriatic Sea displayed high values, proteins being dominant, thus suggesting inputs of freshly produced material to the sea floor. OM turnover was generally rapid (11-30 r d m 1 ) and higher during summer. The uncoupled enzymatic rates ( i.e. faster protein than carbohydrate mobilisation in February, 1997) determined a decrease of the OM quality that plays an important role in biogeochemical cycles and OM diagenesis, limiting bacterial secondary production and sedimentary organic carbon utilisation. These data suggest that the efficiency of the system in the transfer of energy through the food web is generally higher in summer, especially during mucilage production.     

Spatial and Temporal Changes of Suspended Matter in Relation to Wind and Vegetation Cover in A Mediterranean Shallow Coastal Environment

Seasonal and spatial changes in seston, (POC), particulate organic carbon, (PON) particulate organic nitrogen and chlorophyll-a concentrations were studied on a monthly basis in a Mediterranean shallow coastal area (Stagnone di Marsala, Western Sicily) in order to gather information on factors controlling particulate organic matter distribution and composition. Seston concentration and composition were connected to the main physicochemical and biological driving factors, such as temperature, salinity, dissolved oxygen, wind-speed and biomass of submerged vegetation. the Stagnone di Marsala is characterized by high temperatures with strong seasonality (range: 11-28°C), while values ranged from 33 to 45 salinity. Total suspended organic matter concentrations (by ignition loss) ranged from 2 mg l^-1 (in summer) to 12mgl^-1 (in winter) and chlorophyll-a concentrations from 0.02 to 2 μgl^-1. Despite a low POC/PON ratios (ranging from 5 to 11), the ratio of POC to chlorophyll (CHL-a) displayed very high values (annual average of 647). the data reported in this study, highlighting the oligotrophy of the Stagnone di Marsala area, indicate that the trophic state of the basin was controlled by different degrees of wind exposure (mean monthly wind velocity at exposed sites ranged between 4.2 and 6.7 m s^-1) and by gradients in vegetation cover. These two factors induced clear changes in the concentration and composition of the suspended particles, but played a different role in exposed and sheltered areas. Exposed areas with limited vegetation were characterized by large resuspension processes and wide temperature and salinity fluctuations caused by wind induced turbulence. in these areas, autotrophic biomass (as chlorophyll-a), due to phytoplankton and/or re-suspended microphytobenthos, appeared to play an important     

Spatial and Temporal Changes of Suspended Matter in Relation to Wind and Vegetation Cover in A Mediterranean Shallow Coastal Environment

Abstract

Seasonal and spatial changes in seston, (POC), particulate organic carbon, (PON) particulate organic nitrogen and chlorophyll-a concentrations were studied on a monthly basis in a Mediterranean shallow coastal area (Stagnone di Marsala, Western Sicily) in order to gather information on factors controlling particulate organic matter distribution and composition. Seston concentration and composition were connected to the main physicochemical and biological driving factors, such as temperature, salinity, dissolved oxygen, wind-speed and biomass of submerged vegetation. the Stagnone di Marsala is characterized by high temperatures with strong seasonality (range: 11–28°C), while values ranged from 33 to 45 salinity. Total suspended organic matter concentrations (by ignition loss) ranged from 2 mg l^?1 (in summer) to 12mgl^?1 (in winter) and chlorophyll-a concentrations from 0.02 to 2 μgl^?1. Despite a low POC/PON ratios (ranging from 5 to 11), the ratio of POC to chlorophyll (CHL-a) displayed very high values (annual average of 647). the data reported in this study, highlighting the oligotrophy of the Stagnone di Marsala area, indicate that the trophic state of the basin was controlled by different degrees of wind exposure (mean monthly wind velocity at exposed sites ranged between 4.2 and 6.7 m s^?1) and by gradients in vegetation cover. These two factors induced clear changes in the concentration and composition of the suspended particles, but played a different role in exposed and sheltered areas. Exposed areas with limited vegetation were characterized by large resuspension processes and wide temperature and salinity fluctuations caused by wind induced turbulence. in these areas, autotrophic biomass (as chlorophyll-a), due to phytoplankton and/or re-suspended microphytobenthos, appeared to play an important     

Biodiversity and trophic structure of nematode assemblages in seagrass systems: evidence for a coupling with changes in food availability

Nematode assemblage composition, trophic structure and biodiversity were followed over an annual cycle in a Posidonia oceanica bed of the NW Mediterranean to test the response to temporally changing food availability (sediment organic matter, bacterial and microphytobenthic biomass). The sediment-water interface of the seagrass meadow was characterised by high particulate organic matter concentrations. Also, seagrass sediments had high organic matter content, chloropigment concentrations and bacterial biomass. All organic matter components (i.e. carbohydrates, proteins and lipids) changed temporally, with higher concentrations in winter and spring and lower concentrations in summer; however, overall, large amounts of organic compounds were potentially available for (seagrass) benthic consumers throughout the year. Nematode assemblage in the P. oceanica bed maintained a high genus number (88 genera), and a trophic structure tightly coupled with the composition of the potential food sources. In agreement with the relevance of microphytobenthos, epigrowth-feeder nematodes (2A) represented the dominant trophic guild. The biomass of predator nematodes (2B) was significantly correlated with the biomass of other nematodes. Non-selective deposit feeders (1B) displayed a close relationship with the concentration of proteins, carbohydrates and biopolymeric carbon (i.e. labile organic detritus). Conversely to what was expected, epigrowth feeders were not correlated with chloropigment concentrations, but showed a significant relationship with the number of dividing bacteria, possibly suggesting a trophic plasticity of the 2A feeding guild. The coupling between temporal changes in food sources and temporal variability of the nematode trophic structure was highlighted by a CANOCO analysis, which allowed us to identify and associate, at each sampling time, nematode genera and their feeding habits, with specific environmental variables and food indicators. Furthermore, species diversity (H') and evenness (J) calculated on nematodes identified to the genus level displayed evident temporal changes, also reflected by the index of trophic diversity (ITD). Both structural and functional diversity were coupled with high concentration and highly heterogeneous composition of the food sources (including organic detritus, microphytobenthic algae and bacteria) potentially available to nematodes. These data suggest that temporal changes in quantity and quality of food sources do not only influence nematode dynamics and trophic composition, but also influence nematode structural and functional diversity.     

Meiofauna response to a dynamic river plume front

 The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g⁻¹ for chlorophyll a and 1.2 to 17.7 μg g⁻¹ for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g⁻¹). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541 ind. 10 cm⁻²) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector, the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath, their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages. Received: 30 November 1999 / Accepted: 24 May 2000     

Sedimentary organic matter and bacterial community in microtidal mixed beaches of the Ligurian Sea (NW Mediterranean)

The quantity and quality of organic matter, and bacterial density and frequency of dividing cells were investigated in six microtidal mixed beaches of the Ligurian Sea (NW Mediterranean) to evaluate their main trophodynamic features. Concentrations of biopolymeric carbon (average 88.5?±?89.0 µgC/g) and the protein:carbohydrate ratio (on average lower than 1) were very low and classified these beaches as highly oligotrophic. The study of biochemical composition highlighted the nature of organic matter as being mainly refractory; furthermore, the quantitative differences observed along the across-beach gradient together with the unchanged pattern in qualitative features suggest that the organic matter in Ligurian beaches is prevalently of marine origin. This implies a negligible contribution of allochtonous and anthropogenic terrestrial input or in situ autochthonous production. Bacterial density displayed values ranging from 0.1–9.0 cell?×?10⁸/g DW in the top 2?cm layer and showed a significant correlation with the quantity of organic matter. In addition, the frequency of dividing cells showed a positive correlation with the protein:carbohydrate ratio, suggesting that the biochemical composition of organic matter also has an influence on the active bacterial fraction. Because of the exposed nature, a strong coupling was found between the beach and the marine systems, and this seems to be of fundamental importance in terms of material and energy supply for the beach ecosystem. A shortage within this linkage was observed in summer owing to the strong environmental constrains leading to a sort of “beach desertification” and to a marked oligotrophy. Summer also has an effect of smoothing for spatial variability occurring within the biochemical and microbiological variables among the different beaches. The linkage observed between the sea and the land is the main factor controlling the origin and nature of sediment organic matter in these beaches also regulating bacterial abundances and the frequency of dividing cells.     

Particulate matter and downward flux in the Northern and Central Adriatic Sea

During four oceanographic cruises carried out in June 1996, February and June 1997, and February 1998, particulate matter characteristics and short-term downward fluxes measured with drifting sediment traps were studied in two areas of the Adriatic Sea. The investigated areas were located one south of the Po River delta, and the other in the central Adriatic between Pesaro and Ancona. In each area, a frontal system was detected and two stations inside and outside the front, i.e . in coastal and offshore areas, were selected. The particulate and dissolved matter revealed a higher concentration in the coastal areas with the highest values in the central Adriatic coastal zone in both February surveys. Total mass fluxes ranged within two orders of magnitude from 11 to 3139 r mg m d in the northern area and similarly from 20 to 3864 r mg r m r d in the southern one, with higher values in the coastal stations. The organic carbon accounted for 3-30% of total flux in the northern coastal station with higher values in June, whereas at the offshore station it ranged from 6 to 39% in summer, decreasing to values lower than 10% in February. In the southern zone the organic carbon content was less than 2% in winter and from 3 to 33% in summer. The organic carbon fluxes (1-82 and 6-71 r mg C m d in the northern and southern area) were comparable with others measured with drifting sediment traps in the same area, though much lower with respect to those measured with long-term moored sediment traps. The export of organic carbon from the photic layer (expressed as the percentage of primary production) in the northern area was less than 10% at the coastal station, reaching a maximum of 12% in the offshore area. In the central Adriatic area it was greater, with values reaching up to 66% at the coastal station in June 1996. The organic carbon loss via sedimentation from the POC pool was low ( i.e. <1.5% per day) at both stations in the northern zone, while in the southern area the export was generally greater, exceeding 10% in the offshore area.     

Metal distribution in sediments from the Adriatic Sea

Total metal concentrations (Cu, Ni, Pb, Zn, Fe, and Mn) and their distribution in different chemical forms (speciation) were determined in sediments from the Adriatic Sea in order to evaluate contamination and mobility of metals. The study was carried out on marine sediments collected in two areas of the Adriatic Sea differently influenced by Po river waters. Metal distribution in the study area depends prevalently on water circulation and on organic matter distribution. Among metal levels, significant correlations between copper and zinc and between lead and nickel were found, suggesting common and specific sources. As regards metal speciation, the distribution of different chemical forms changes with the metal. The prevailing zinc phases, for example mobile forms, and sulphide together are greater than 50% of total metal. Nickel is mainly present in sediments as sulphide, and the preferential association of copper with organic matter is evident. Lead and manganese are preferentially found as mobile forms (more of 30% for lead, 40% or more for manganese).     

Distribution and behaviour of polycyclic aromatic hydrocarbons in subtropical river estuary,Okinawa, Japan

Surface water samples were collected along the salinity gradient of Manko estuary in Okinawa, Japan, between January and November 2012, to examine spatial and temporal variability in the distribution, composition, behaviour, and sources of particulate polycyclic aromatic hydrocarbons (PAHs). Concentrations of total particulate PAHs ranged from 169.7?ng?g^?1 at riverine station (N1) in November 2012 to 922?ng?g^?1 at another riverine station (K3) in May 2012. Based on observed environmental behaviour, particularly relationships to organic matter, the PAHs appear divisible into two groups: group I (low molecular weight) PAHs were characterised by low particles affinity and strong correlations with a pool of autochthonous organic matter (e.g. high concentrations of polyunsaturated fatty acids), reflecting processes controlling their delivery to the estuary; and, in contrast, group II (high molecular weight) PAHs were characterised by high particles affinity and exhibited estuarine distribution primarily controlled by suspended solid load and inputs from terrigenous sources through river inflows. This relationship, coupled with isomer ratios indicative of combined mixed sources from petroleum and petroleum combustions, indicates that terrestrial run-off is the dominant mode of delivery of particulate PAHs in the estuary. The relationships between distinct groups of PAHs and lipid biomarkers demonstrated in this study suggest that very specific pools of particulate organic matter, as opposed to concentrations of particulate organic carbon alone, can be important in the transport and fate of hydrophobic contaminants.     

Suspended particulate organic matter in a Mediterranean submarine cave

Submarine caves display a paucity of benthic density and biomass that may be related to low trophic resources. Analysis of organic carbon, organic nitrogen, carbohydrate, protein and lipid content of suspended particulate matter was made during the period July 1985–July 1987 in a Mediterranean cave (Marseille, France) in order to determine any differences in the particulate organic matter composition along an horizontal transect. Particulate organic matter content clearly declined from the entrance of the cave to the dark inner area. This impoverishment could not be explained by a simple decrease in a few organic compounds, but appeared to be related to the combination of a decrease in both the amount and the composition of the suspended particles. Three progressive levels of impoverishment were identified towards the dark inner area of the cave: (i) decreasing amounts of seston; (ii) decreasing organic content of particles; (iii) increasing proportions of the geopolymeric (i.e., humic) components in the remaining organic matter, indicating increased degradation. The cave appeared to be sharply divided into two distinct sections — a twilight outer section whose waters contained slightly lower amounts of particulate organic matter than the open sea, and a dark inner section, 8 to 10 m higher, separated from the outer section by a steep rise and with waters of low organic matter content. The water in the twilight section appeared to be in thermal equilibrium with the open sea, and that in the dark inner section displayed thermal stratification. These differences indicated the presence of two distinct water bodies with contrasting average residence times, estimated as 1 d in the outer twilight section and 8 d in the dark inner section. The joint action of sedimentation and degradation resulted in an abrupt depletion of particulate organic matter in the dark inner section accompanied by a decrease in the benthic fauna. The decline in benthic heterotroph populations is probably related to the abrupt transition to oligotrophic conditions.     

Origin and Distribution of Suspended Organic Matter As Inferred From Carbon Isotope Composition in A Mediterranean Semi-Enclosed Marine System

The origin and distribution of suspended organic matter, the trophic features and the stable carbon isotopic composition of particulate organic carbon (POC) were studied monthly in a Western Mediterranean semi-enclosed basin. Sampling stations were selected as a function of wind-exposure and the degree of vegetation cover and then compared with an adjacent unvegetated site. the predominant vegetation was seagrass (Posidonia oceanica and Cymodocea nodosa) and Caulerpa prolifera. Water samples were analyzed for total suspended matter (inorganic and organic fractions), photosynthetic pigments (chlorophyll-a and phaeopigments), dissolved organic carbon, particulate organic carbon and their isotopic composition. Temperature and salinity were also measured at the same sampling sites within range of Mediterranean limits. the suspended organic matter concentration was 1.77 ± 1.55 mg l^-1; the chlorophyll-a concentration was low (0.35 ± 0.24 μg l^-1); the disolved organic carbon concentration was 2,140 ± 2,010 μg l^-1; the particulate organic carbon concentration was 212 ± 106 μg l^-1 and the isotopic composition was 18.77 ± 2.51%_°. There were significant temporal differences except for phaeopigments, POC and its POC isotopic composition, and there were no spatial differences other than for δ¹³C. This picture highlighted a general seasonal trend and trophical features similar to adjacent sea.

Spatial differences in δ¹³C showed that the source of suspended organic matter was different between stations as that between sources and wind-hydrodynamic constraints. In     

Origin and Distribution of Suspended Organic Matter As Inferred From Carbon Isotope Composition in A Mediterranean Semi-Enclosed Marine System

Abstract

The origin and distribution of suspended organic matter, the trophic features and the stable carbon isotopic composition of particulate organic carbon (POC) were studied monthly in a Western Mediterranean semi-enclosed basin. Sampling stations were selected as a function of wind-exposure and the degree of vegetation cover and then compared with an adjacent unvegetated site. the predominant vegetation was seagrass (Posidonia oceanica and Cymodocea nodosa) and Caulerpa prolifera. Water samples were analyzed for total suspended matter (inorganic and organic fractions), photosynthetic pigments (chlorophyll-a and phaeopigments), dissolved organic carbon, particulate organic carbon and their isotopic composition. Temperature and salinity were also measured at the same sampling sites within range of Mediterranean limits. the suspended organic matter concentration was 1.77 ± 1.55 mg l^?1; the chlorophyll-a concentration was low (0.35 ± 0.24 μg l^?1); the disolved organic carbon concentration was 2,140 ± 2,010 μg l^?1; the particulate organic carbon concentration was 212 ± 106 μg l^?1 and the isotopic composition was 18.77 ± 2.51%_°. There were significant temporal differences except for phaeopigments, POC and its POC isotopic composition, and there were no spatial differences other than for δ¹³C. This picture highlighted a general seasonal trend and trophical features similar to adjacent sea.

Spatial differences in δ¹³C showed that the source of suspended organic matter was different between stations as that between sources and wind-hydrodynamic constraints. In     

Meio- and macrofauna communities in three sandy beaches of the northern Adriatic Sea protected by artificial reefs

Interactions between meio- and macrofaunal assemblages and food availability were investigated in relation to tourism pressures on three beaches of the northern Adriatic Sea. All beaches were characterised by the presence of artificial reefs, freshwater inputs and tourism pressures. Beach sediments displayed high organic loads and low protein and chlorophyll a contributions to the bulk of the organic matter. Consequently, the organic matter was of mostly refractory composition and, thus, of scarce nutritional quality. Macrofaunal community structure and biomass were related to the quantity and nutritional quality of sedimentary organic matter, whereas meiofauna was apparently not. No relationships were found between physical variables and the metazoan communities. Most likely, the presence of artificial reefs reduced the physical impact of waves on the beach assemblages, whereas the presence of synergistic human impacts, including freshwater inputs and the tourism pressure, negatively influenced both the meio- and the macrofaunal assemblages.     

Mechanisms of production and fate of organic phosphorus in the northern Adriatic Sea

In the period from 1980 to 1984 organic phosphorus, nutrients, primary production rates (¹⁴C), chlorophyll a (chl a) standing crops, and basic oceanographic parameters were measured during 23 cruises at six stations in the open waters of the northern Adriatic Sea. These waters are significantly influenced by polluted Po River discharge. Organic phosphorus was correlated with several parameters which characterize phytoplankton activity and organic matter decomposition processes. In the late winter-spring period, organic phosphorus is produced during phytoplankton blooms. It is hypothesized that microzooplankton grazing is the main factor increasing the organic phosphorus concentrations in summer (up to 1.1 mol 1^-1). Fall and winter had much lower values (below 0.3 mol 1^-1) due to remineralization processes and an increased water mass exchange between the northern and central Adriatic regions. The direct contribution of organic phosphorus by freshwater discharge was not found to be significant. The higher organic phosphorus concentrations that can occur in low salinity waters are most likely due to their increased capability to support primary production.     

HEAVY METAL DISTRIBUTION AND SPECIATION IN THE NORTHERN ADRIATIC SEA

In the present study the concentrations of cobalt, copper, iron, manganese, zinc were analysed and the speciation of copper and zinc performed, with a summer and winter sampling, for two areas in the Northern Adriatic Sea and crossing at the farthest zones of the Po river-sea water interface. Results show that when salinity increases the concentrations of all investigated metals (with the exception of cobalt) present some degree of biogeochemical cycling. Copper is the element whose dissolved phase has the highest importance in metal transport across the salinity gradient. Results of speciation analysis demonstrate that the presence of excess amounts (5-8 fold) of unbound ligands confers a buffering capacity for potential inputs of dissolved metals into the Northern Adriatic Sea. The speciation of both copper and zinc in the dissolved phase was dominated by organic complexation.     

Heavy metal distribution and speciation in the Northern Adriatic Sea

In the present study the concentrations of cobalt, copper, iron, manganese, zinc were analysed and the speciation of copper and zinc performed, with a summer and winter sampling, for two areas in the Northern Adriatic Sea and crossing at the farthest zones of the Po river-sea water interface. Results show that when salinity increases the concentrations of all investigated metals (with the exception of cobalt) present some degree of biogeochemical cycling. Copper is the element whose dissolved phase has the highest importance in metal transport across the salinity gradient. Results of speciation analysis demonstrate that the presence of excess amounts (5-8 fold) of unbound ligands confers a buffering capacity for potential inputs of dissolved metals into the Northern Adriatic Sea. The speciation of both copper and zinc in the dissolved phase was dominated by organic complexation.