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     

Particulate Organic Matter Composition in A Semi-Enclosed Marine System

Spatial and temporal changes in the biochemical composition of particulate organic matter in a semi-enclosed marine system (Stagnone di Marsala, Mediterranean Sea) were studied, on a monthly basis, from January to December 1994, in order to assess nutritional value of suspended particles for benthic suspension feeders. According to previous findings, the study site displayed a strong oligotrophy. Chlorophyll-a accounted for a very low fraction of the total suspended matter pool (0.1%), whereas at least 75% of POC was of detrital/heterotrophic origin. POC: PON ratio values indicate that bacterioplankton biomass accounted for a significant fraction of the total POC pool, displaying values comparable to those of the phytoplankton biomass (phytoplankton to bacterial biomass ratio was about (1). Temporal and spatial changes in the biochemical composition of particulate organic matter were rather limited and related to its sources, the main of which is represented by detrital particles released by the Posidonia oceanica (L.) beds. the comparison between our results and those encountered in other coastal lagoons indicates that the low abundance of suspension-feeding organisms observed in the study area is related to the “quality depression” of particles due to the dilution of high quality compounds (i.e., biopolymeric carbon) in a largely inorganic matrix. This result leads us to conclude that, to reach the same amount of high quality particulate food, a suspension feeder mollusc in the Marsala lagoon would need to filter a sea water volume around 3 times higher than in other Mediterranean coastal lagoons.     

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     

Particulate Organic Matter Composition in A Semi-Enclosed Marine System

Spatial and temporal changes in the biochemical composition of particulate organic matter in a semi-enclosed marine system (Stagnone di Marsala, Mediterranean Sea) were studied, on a monthly basis, from January to December 1994, in order to assess nutritional value of suspended particles for benthic suspension feeders. According to previous findings, the study site displayed a strong oligotrophy. Chlorophyll-a accounted for a very low fraction of the total suspended matter pool (0.1%), whereas at least 75% of POC was of detrital/heterotrophic origin. POC: PON ratio values indicate that bacterioplankton biomass accounted for a significant fraction of the total POC pool, displaying values comparable to those of the phytoplankton biomass (phytoplankton to bacterial biomass ratio was about (1). Temporal and spatial changes in the biochemical composition of particulate organic matter were rather limited and related to its sources, the main of which is represented by detrital particles released by the Posidonia oceanica (L.) beds. the comparison between our results and those encountered in other coastal lagoons indicates that the low abundance of suspension-feeding organisms observed in the study area is related to the “quality depression” of particles due to the dilution of high quality compounds (i.e., biopolymeric carbon) in a largely inorganic matrix. This result leads us to conclude that, to reach the same amount of high quality particulate food, a suspension feeder mollusc in the Marsala lagoon would need to filter a sea water volume around 3 times higher than in other Mediterranean coastal lagoons.     

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     

Sources and biochemical composition of suspended particulate material in a submarine cave with sulphur water springs

Sources, biochemical composition and nutritional value of suspended particulate material were investigated from February 1994 to February 1995 in a submarine cave (Grotta Azzurra, Capo Palinuro, southwestern Italy) with hot sulphur springs and associated mats of chemolithoautotrophic bacteria in its innermost dark part (Snow Hall). Concentrations of total suspended material (TSM), particulate inorganic material (PIM), organic carbon (POC), organic nitrogen (PON), chlorophyll a (Chl a), phaeopigments (Phaeo), carbohydrates (TCH), proteins (TPR) and lipids (TLI) were measured at four stations along an outside–inside transect, in order to address whether the quantity and quality of suspended particles varied over time with increasing distance from the entrance of the cave and estimate the relative contribution of chemosynthesis versus photosynthesis in supplying POC to cave heterotrophs. The abundance and biochemical composition of suspended material available to filter-feeders varied over time, but no significant quantitative or qualitative differences were detected along the outside–inside transect. Concentrations of TSM and of its different compounds (PIM, POC, PON, Phaeo, TCH, TPR, TLI) were homogeneous among the four stations or fluctuated without any consistent trend, with no apparent ageing and degradation of organic material in the innermost dark station. Conversely, concentrations of Chl a significantly decreased from outside to inside the cave at all sampling periods. It is suggested that suspended POC in Grotta Azzurra consists of mixed assemblages of particles coming from advection of photosynthetic material from the open sea and local inputs of carbon by sulphur-oxidizing bacteria. Based on POC/Chl a ratios, the relative contributions of chemosynthesis versus photosynthesis in supplying POC to benthic heterotrophs was estimated to be 31 and 69%, respectively. Received: 9 December 1996 / Accepted: 14 January 1997     

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.     

Comparison of the sedimentation of a diatom spring bloom and of a subsurface chlorophyll maximum

The seasonal pattern of sedimentation was determined over a 8-mo investigation period covering the productive season at a permanent station in the Southern Kattegat (Denmark) in 1990. The phytoplankton succession was characterised by a 4-mo long subsurface maximum associated with the pycnocline which was entirely dominated by the dinoflagellate Gyrodinium aureolum. The bulk sedimentation of organic matter took place during this period and accounted for >60% of the annual particulate organic carbon (POC) and particulate organic nitrogen (PON) sedimentation. The spring bloom period contributed 60% of the sedimentation of intact phytoplankton cells, but only 20% of the POC and PON sedimentation. A minor fraction of the sedimenting matter from the subsurface phytoplankton maximum consisted of intact phytoplankton (<20%), suggesting that the phytoplankton was processed by heterotrophs and that it was mainly products from this activity which contributed to thevertical flux of organic matter. The variation in oxygen concentration below the pycnocline coincided with the pattern of sedimentation with a delay of 3 to 6 wk.     

Influence of hydrodynamic conditions on the production and fate of Posidonia oceanica in a semi-enclosed shallow basin (Stagnone di Marsala,Western Sicily)

An integrated approach using hydrodynamic and transport numerical models, lepidochronology and stable isotope analysis was used to investigate how local hydrodynamic conditions influence the primary production and fate of the seagrass Posidonia oceanica in a Mediterranean semi-enclosed marine system (Stagnone di Marsala). The water mass exchange aptitude of different sectors of the basin was analysed, and data collected were used to select two sectors (colonized by Posidonia oceanica showing the lowest and highest water exchange values) for biological analyses. According to the mean dispersal coefficient differences simulated by the hydrodynamic model, growth rate and primary production of P. oceanica differed between sectors, with average values lower in the central sector where water exchange is lower than in the southern sector. Although P. oceanica coverage and primary production were higher in the southern sector, carbon and nitrogen stable isotope analysis suggests that the transfer of seagrass organic matter to higher trophic levels of the food web was higher in the central sector. The possibility of a link between hydrodynamism, production and fate of organic matter is proposed to explain the observed patterns.     

High seasonal variation of atmospheric C and particle concentrations in Delhi,India

The highly populated Indian regions are currently in a phase of rapid economic growth resulting in high emissions of carbonaceous aerosols. This leads to poor air quality and impact on climate. The chemical composition of carbonaceous aerosols has rarely been studied in industrial areas of India. Here, we investigated carbonaceous aerosols in particulate matter (PM) monthly in the industrial area of Delhi in 2011. The concentrations of organic C and elemental C in PM₁₀ fraction were analyzed. Results show a clear seasonal variability of organic and elemental C. PM₁₀ ranged 95.9–453.5 μg m^?3, organic C ranged 28.8–159.4 μg m^?3, and elemental C ranged 7.5–44.0 μg m^?3; those values were higher than reported values. Organic and elemental C were correlated with each other in pre-monsoon and winter seasons, implying the existence of similar emission sources such as coal combustion, biomass burning and vehicular exhaust. The annual average contribution of total carbonaceous aerosols in PM₁₀ was estimated as 62 %.     

Restoration and sequestration of carbon and nitrogen in the degraded northern coastal area in Nile Delta,Egypt for climate change mitigation

Most of coastal area in Nile Delta, Egypt, is salt-affected soils and have low carbon (C) and nitrogen (N) inputs as a result of declining vegetation growth and low net primary production. Therefore, this study amid to compare between C and N pools in degraded (uncultivated and salt-affected soil) and restored (cultivated and reclaimed 20 years ago) locations in North Nile Delta. and to examine the impact of cultivation on sequestering C and N pools in this area as one of the most important methods for mitigating climate change impacts. C and N pools increased significantly in surface soil from 2.99 and 0.43 Mgh^?1 in uncultivated sites to 19.26 and 1.66 Mgh^?1 in cultivated ones as salinity was reduced and net primary production was increased due to leaching and reclamation. Particulate (associated with sand) and nonparticulate (associated with clay +silt) soil organic C or N was significantly higher cultivated sites. In addition, nonparticulate organic C or N was lower than particulate part indicating and supporting the strong relationship between organic matter and clay. The sequestration rate (in approximately 1 m profile) was 1.69 and 0.14 Mgh^?1 yr.^?1 C and N pools respectively. Although the cultivation is leading to loss of organic matter in some areas; C and N in this coastal area are partially restored and stored. Therefore, restoration and appropriate management practices will lead to mitigate the negative impacts of climate change in this area.     

Relationships between marine microorganisms and the wood-boring isopod Limnoria tripunctata

The quantities and the behavior of particulate proteinous carbon (PPC) were investigated at an experimental station in Funka Bay, southern Hokkaido from February 1974 to January 1975 using R. V. Ushio Maru. The amino acid composition of PPC, quantity of particulate organic carbon (POC), PPC:POC ratio, concentration of plant pigments and the primary productivity and heterotrophic activity in situ were measured to clarify PPC status. The net production was ca. 100 g C m^-2 year^-1. The inflow of Oyashio water and stagnation during early spring and summer may increase productivity. The net production during this period attained 70% of the net production for the whole year. The concentration of chlorophyll changed monthly parallel to changes in the primary production of the surface waters. The concentration of PPC and the PPC:POC ratio in the surface layer decreased gradually during the stagnation period of the Oyashio water. This implies that the PPC in the particulate organic matter was more easily consumed than the other organic constituents by the increased heterotrophic activity in summer. In contrast, low concentrations of PPC and high PPC:POC ratios were found during the stagnation period of Tsugaru warm water from autumn to winter. Concentrations of PPC and POC were not evenly distributed throughout the year; they decreased with depth during the stagnation period in summer. On the other hand, higher concentrations of PPC and POC, and an increased PPC:POC ratio were noted in samples collected near the sea bed, compared with the concentration and the ratio of the upper layer throughout the year. It seems likely that the particulate organic matter, originating from resuspension of bottom sediments containing proteins, was produced by the benthos. The turnover time of PPC in the upper layer was 7 to 11 days in summer and 45 to 100 days in winter; the turnover time for POC was 14 to 28 days in summer and 97 to 147 days in winter.     

Variability of particulate organic carbon and nitrogen in the Namibian upwelling system

Particulate organic carbon (POC) and nitrogen (PON) were analyzed during cruises undertaken in September 1985 and April 1986 along the Namibian upwelling system. The main objectives were to provide estimates of standing stocks of particulate organic matter (POM) and analyze its temporal and spatial variability. Average estimates of total carbon standing stock (0 to 100 m depth) accounted for 1.2 g-at C m^–2 during active and 1.32 g-at C m^–2 during abated upwelling. Zooplankton carbon was estimated as 0.22 and 0.27 g-at C m^–2, respectively, for both periods. POM was generally concentrated near the surface, especially during abated upwelling. During abated upwelling, POM was not only abundant inshore but also over the shelf, as a response of a more diffuse frontal system and a more strongly stratified water column. Cross-shelf gradients were more significant during active upwelling, while alongshore gradients accounted for most of the variance of particulate organic matter during abated periods. This result was a consequence of the seasonal intrusion of warm, Angolan water from the north during the period of minimum upwelling, and resulted in poorer POM concentrations and higher consumer: producer ratios (24.4%). Nevertheless, this last conclusion should be regarded with caution due to the lack of comparative interannual variability. A 48 h study at a fixed station permitted analysis of the daily variability in POM during the intrusion process. Changes in the thickness of the surface mixed layer due to irregular time-spaced pulses of non-homogeneous water masses resulted in sudden enrichments and renewals of phytoplankton and zooplankton populations in a matter of hours.     

Sexual and asexual reproduction in two species of Tethya (Porifera: Demospongiae) from a Mediterranean coastal lagoon

The sexual and asexual phases of reproductive cycles of two sponges, Tethya citrina and T. aurantium, living sympatrically in a Mediterranean coastal lagoon (Stagnone di Marsala, NW Sicily) were studied from samples collected over an 18-mo period. Both species are oviparous and gonochoric. They have a summer, partially overlapping, period of oocyte production, although T. citrina appear to mature earlier. No males were found, possibly due to the very short period of spermatogenesis. Both species produce asexual buds during the autumn/winter months. However, they seem to follow different reproductive strategies, with T. citrina showing a significantly lower production of buds than T. aurantium; by contrast, egg production is significantly lower in the latter species. The difference in the reproductive resource allocation is consistent with data reported in the literature on the anatomy features, genetic population structure and ecological distribution.     

Relationships between porewater nutrients and seagrasses in a subtropical carbonate environment

The feeding, diet and egg production of the copepod Acartia tonsa were dermined during ten experiments in Los Angeles Harbor, California, between November 1986 and October 1987. Copepods were incubated in situ, in quasi-natural food environments. Water temperatures ranged from 14.6 to 21.5°C. Particulate organic carbon and nitrogen (POC and PON) were high (534 to 3710 g Cl^-1, 51 to 459 Nl^-1) but dominated by small (<8 m diam) particles. Plankton (phytoplankton and microzooplankton) C-biomass composed about 10% of the total POC and was usually dominated by particles >8 m. Plankton biomass was always low. Daily ingestion rates ranged from 3 to 96% of body C; egg production ranged from 4 to 35% of body carbon. Mean ingestion and egg production rates during spring-summer were 1.9 and 1.5 times higher than average for the entire study, respectively. The average gross efficiency of egg production for the study was 80%; the spring-summer mean was 41%. Bivariate and multiple-regression analyses revealed that the ingestion rate was dependent upon both temperature and food availability, but that, below 21°C, egg production depended more upon temperature than upon food concentration. To detect dietary preferences, the composition of diet was compared with that of the food supply. Selective feeding was infrequent, but the diet was often dominated by dinoflagellates and ciliates. It would appear that within metabolic limits governed by temperature, the feeding response of A. tonsa is dependent upon food concentration, while egg production depends more on qualitative attributes of the food supply.     

Particulate DNA in subtropical oceanic and estuarine planktonic environments

Particulate DNA was measured in estuarine, coastal, and oligotrophic oceanic environments near the southwest coast of Florida and in the Gulf of Mexico. Particulate organic carbon and nitrogen (POC and PON), chlorophyll a, bacterial direct counts, DNA, and bacterial activity as determined by thymidine incorporation all showed a high degree of intercorrelation. Normalization of the data for offshore/onshore similarities by dividing by POC yielded significant correlations only for DNA, direct counts, and bacterial activity. Most (70–99%) of the particulate DNA in offshore samples was in the 0.2- to 1-m fraction, while DNA in nearshore and estuarine samples was associated with larger particles. Cellular DNA contents obtained by dividing DNA by direct counts in the 0.2- to 1-m fraction were in the range of reported bacterial genome weights. However, DNA nitrogen comprised a greater proportion of the PON than reported for microorganisms in culture. Collectively, these results suggest that (1) most of the particulate DNA in oceanic environments is contained in bacterioplankton; (2) DNA is a significant proportion of the cell biomass, possibly due to growth under nutrientlimiting conditions.     

The influence of macrofauna on estuarine benthic community metabolism: a microcosm study

Effects of benthic macrofauna (Corophium volutator, Hydrobia sp., Nereis virens) on benthic community metabolism were studied over a 65-d period in microcosms kept in either light/dark cycle (L/D-system) or in continuous darkness (D-system). Sediment and animals were collected in January 1986 in the shallow mesohaline estuary, Norsminde Fjord, Denmark. The primary production in the L/D-system after 10 d acted as a stabilizing agent on the O₂ and CO₂ flux rates, whereas the D-system showed decreasing O₂ and CO₂ flux throughout the period. Mean O₂ uptake over the experimental period ranged from 0.38 to 1.24 mmol m^–2 h^–1 and CO₂ release varied from 0.80 to 1.63 mmol m^–2 h^–1 in both systems. The presence of macrofauna stimulated community respiration rates measured in darknes, 1.4 to 3.0 and 0.9 to 2.0 times for O₂ and CO₂, respectively. In contrast, macrofauna lowered primary production. Gross primary production varied from 1.06 to 2.26 mmol O₂ m^–2 h^–1 and from 1.26 to 2.62 mmol CO₂ m^–2 h^–1. The community respiratory quotient (CRQ, CO₂/O₂) was generally higher in the begining of the experiment (0–20 d, mean 1.89) than in the period from Days 20 to 65 (mean 1.38). The L/D-system exhibited lower CRQ (ca. 1) than the D-system. The community photosynthetic quotient varied for both net and gross primary production from 0.64 to 1.03, mean 0.81. The heterotrophic D-system revealed a sharp decrease in the sediment content of chlorophyll a as compared to the initial content. In the autotrophic L/D-system, a significant increase in chlorophyll a concentration was observed in cores lacking animals and cores with C. volutator (The latter species died during the experiment). Due to grazing and other macrofauna activities other cores of the L/D-system exhibited no significant change in chlorophyll a concentration. Community primary production was linearly correlated to the chlorophyll a content in the 0 to 0.5 cm layer. Fluxes of DIN (NH₄ ⁺+NO₂ ^–+NO₃ ^–) did not reveal significant temporal changes during the experiment. Highest rates were found for the cores containing animals, mainly because of an increased NH₄ ⁺ flux. The release of DIN decreased significantly due to uptake by benthic microalgae in the L/D-system. No effects of the added macrofauna were found on particulate organic carbon (POC), particulate organic nitrogen (PON), total carbon dioxide (TCO₂) and NH₄ ⁺ in the sediment. The ratio between POC and PON was nearly constant (9.69) in all sediment dephts. The relationship between TCO₂ and NH₄ ⁺ was more complex, with ratios below 2 cm depth similar to those for POC/PON, but with low ratios (3.46) at the sediment surface.     

Spatial distribution of perfluorooctane sulfonate (PFOS) in major rivers in southwest Nigeria

Concentrations of perfluorooctane sulfonate (PFOS) were measured for the first time in major rivers within southwest, Nigeria. PFOS was concentrated from water and sediment using solid-phase extraction, identified and quantified with high-performance liquid chromatography coupled with tandem mass spectrometry. Concentrations of PFOS ranged from 1.71 to 16.19 ng L^?1 in water, and from 1.64 to 10.29 ng g^?1 in sediments across all locations. Comparatively, the concentrations of PFOS observed in this study were within the range ever measured in the environment. Field-based sediment water distribution coefficients (log K_d, L kg^?1) ranged from 2.08 to 3.56. While no correlation was observed between K_d and organic carbon contents, there was significant positive correlation between K_d and salinity (r² = 0.7867), which suggested that activities capable of increasing salinity can enhance PFOS removal from the environment.     

Influence of hydrodynamic conditions on the production and fate of Posidonia oceanica in a semi-enclosed shallow basin (Stagnone di Marsala, Western Sicily)

An integrated approach using hydrodynamic and transport numerical models, lepidochronology and stable isotope analysis was used to investigate how local hydrodynamic conditions influence the primary production and fate of the seagrass Posidonia oceanica in a Mediterranean semi-enclosed marine system (Stagnone di Marsala). The water mass exchange aptitude of different sectors of the basin was analysed, and data collected were used to select two sectors (colonized by Posidonia oceanica showing the lowest and highest water exchange values) for biological analyses. According to the mean dispersal coefficient differences simulated by the hydrodynamic model, growth rate and primary production of P. oceanica differed between sectors, with average values lower in the central sector where water exchange is lower than in the southern sector. Although P. oceanica coverage and primary production were higher in the southern sector, carbon and nitrogen stable isotope analysis suggests that the transfer of seagrass organic matter to higher trophic levels of the food web was higher in the central sector. The possibility of a link between hydrodynamism, production and fate of organic matter is proposed to explain the observed patterns.     

Scope for growth of Mytilus?galloprovincialis (Lmk., 1819) in oligotrophic coastal waters (Southern Tyrrhenian Sea, Italy)

The ‘scope for growth’ (SFG) tool was used to study the growth performance of cultivated populations of Mytilus galloprovincialis (Lmk., 1819) in an oligotrophic area of the Southern Mediterranean Sea. The study was carried out between 1993 and 1996 by using data from four seasonal oceanographic cruises and from growth experiments. Water samples were collected and analysed for total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PON), particulate lipids, proteins and carbohydrates and chloropigments. The sum of the carbon equivalents of carbohydrates, proteins and lipids is indicated as the total biopolymeric particulate organic carbon (BPC) and was converted into a unit of energy in order to calculate the SFG of a theoretical mussel of 5 cm length. In order to test the performance of mussel growth at two depths (5 and 15 m water depth), mussel body size [as ash free dry weight (AFDW)] and the actual concentrations of BPC were used to calculate the monthly SFG using the physiological energetic relationships suggested in the current literature. Data from the field cruises led us to characterise the study site as ultra-oligotrophic (annual average of chloropigment concentration approximately 0.5 μg L⁻¹). SFG calculations allowed us to identify a site where mussels grown successively were found to reach a commercial size in approximately 12 months. The good agreement obtained between energetic response and subsequent production response suggests that the available energy from particulate food could be fully available for organic production for maintaining “proportionate” growth trajectories, even in a ultra-oligotrophic system.