Sediment organic matter and meiofauna community response to long-term fish-farm impact in the Ligurian Sea (Western Mediterranean)

Quantitative and qualitative changes in meiofauna community structure were investigated to assess the impact of a fish farm, which was operating continuously for 15 years (La Spezia Gulf, W Mediterranean). Sediment samples were collected in June, July, September, October 2000 and February 2001 for the analysis of phytopigments (chlorophyll-a and phaeopigments), the biochemical composition of organic matter (proteins, carbohydrates and lipids) and related to meiofaunal parameters.

Sediment organic matter reached extremely high concentrations beneath the fish cages when compared to the control. Particularly lipids, carbohydrates and chlorophyll-a were significantly higher in fish-farm sediments. On a long-term basis meiofauna displayed adaptations in sediments beneath the cages resulting in an increase of density. Organic impact on meiofaunal community structure was evident in terms of an increase of the nematodes to copepods (Ne/Co) and nauplius to copepods (Na/Co) ratios in fish farm sediments. Cumaceans and kinorhynchs were encountered in control sediments, but disappeared in fish-farm samples. These data suggest that meiofauna is a sensitive tool for evaluating the effects of organic enrichment in fish farm impacted areas.     

Sediment organic matter and meiofauna community response to long-term fish-farm impact in the Ligurian Sea (Western Mediterranean)

Quantitative and qualitative changes in meiofauna community structure were investigated to assess the impact of a fish farm, which was operating continuously for 15 years (La Spezia Gulf, W Mediterranean). Sediment samples were collected in June, July, September, October 2000 and February 2001 for the analysis of phytopigments (chlorophyll-a and phaeopigments), the biochemical composition of organic matter (proteins, carbohydrates and lipids) and related to meiofaunal parameters.

Sediment organic matter reached extremely high concentrations beneath the fish cages when compared to the control. Particularly lipids, carbohydrates and chlorophyll-a were significantly higher in fish-farm sediments. On a long-term basis meiofauna displayed adaptations in sediments beneath the cages resulting in an increase of density. Organic impact on meiofaunal community structure was evident in terms of an increase of the nematodes to copepods (Ne/Co) and nauplius to copepods (Na/Co) ratios in fish farm sediments. Cumaceans and kinorhynchs were encountered in control sediments, but disappeared in fish-farm samples. These data suggest that meiofauna is a sensitive tool for evaluating the effects of organic enrichment in fish farm impacted areas.     

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.     

Contribution of salps to carbon flux of marginal ice zone of the Lazarev Sea, southern ocean

In order to estimate the in situ grazing rates of Salpa thompsoni and their implications for the development of phytoplankton blooms and for the sequestration of biogenic carbon in the high Antarctic, a repeat-grid survey and drogue study were carried out in the Lazarev Sea during austral summer of 1994/1995 (December/January). Exceptionally high grazing rates were measured for S. thompsoni at the onset of a phytoplankton bloom (0.2 to 0.8 μg chlorophyll a l⁻¹) in December 1994, with up to ≃160 μg of plant pigments consumed by an individual salp of 7 to 10 cm length per day. Dense salp swarms extended throughout the marginal ice zone, consuming up to 108% of daily phytoplankton production and 21% of the total chlorophyll a stock. Due to the much faster sinking rates and higher carbon content of salp faecal pellets, the efficiency of downward carbon flux through salps is much higher than through the other major grazers, krill and copepods. S. thompsoni can thus export large amounts of biogenic carbon from the euphotic zone to the deep ocean. With the observed ingestion rates during December 1994, this flux could have attained levels of up to 88 mg C m⁻² d⁻¹, accounting for the bulk of the vertical transport of carbon in the Lazarev Sea. However, in January 1995, when phytoplankton concentrations exceeded a threshold level of 1.0 to 1.5 μg chlorophyll a l⁻¹, salps experienced a drastic reduction in their feeding efficiency, possibly as a result of clogging of their filtering apparatus. This triggered a dramatic reversal in the relationship, during which a dense phytoplankton bloom developed in conjunction with the collapse of the salp population. Increases in the biomass and geographic range of the tunicate S. thompsoni have occurred in several areas of the southern ocean, often in parallel with a rise in sea-surface temperature during sub-decadal periods of warming anomalies. Received: 10 August 1997 / Accepted: 21 October 1997     

Seasonal changes of benthic bacteria in a seagrass bed (Posidonia oceanica) of the Ligurian Sea in relation to origin,composition and fate of the sediment organic matter

Variations in number and biomass of benthic bacteria were examined in the surface sediments of a Mediterranean seagrass bed [Posidonia oceanica (L.) Delile] in the Gulf of Marconi (northwestern Mediterranean Sea) from 1990 to 1991. The annual dynamics of benthic bacterial density and biomass were compared to changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter, as well as to microphytobenthic biomass, dissolved inorganic nutrients and ATP. Bacterial densities exhibited marked seasonal variations (5.12 to 322.7x10⁸ cells g^-1 sediment dry wt) with highest values in late spring. Bacterial standing stocks (15.8 to 882.33 g C g^-1 of sediment dry wt) were high. Bacterial biomass did not correlate with organic C, total N or to specific biochemical components, but correlated significantly with chlorophyll a, ATP and porewater phosphate concentrations. There is evidence that benthic bacteria were responding to variations of algal biomass. Bacterial biomass accounted, on average, for 30% of total living carbon (calculated on the basis of the ATP concentrations) and 8.4% of total organic carbon.     

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.     

Primary productivity and the flux of dissolved organic matter in several marine environments

Primary productivity and the flux of DO¹⁴C, dissolved saccharides (DSAC) and dissolved free primary amines (DFPA) were followed in the Sargasso Sea, Caribbean and upwelling waters of Peru. Average carbon fixation rates were 42.8, 292.8 and 4791.6 mg C m^-2 d^-1, respectively, with nocturnal respiration rates ranging from 9.8–16.3% of gross photosynthesis for the 3 areas. The release of DO¹⁴C, as a percentage of the total carbon fixed in photosynthesis, was non-detectable in the Sargasso Sea, and 3.2 and 4.4% for the Caribbean and Peruvian phytoplankton communities. Few significant changes in DSAC concentrations were recorded over a 36-h incubation period in the Sargasso Sea and Caribbean stations, whereas light-dependent accumulations of DSAC and DFPA were noted in Peruvian stations which were strongly correlated with total phytoplankton productivity. In the Peruvian stations, the average accumulation rate was 234 mg DSAC-C m^-2h^-1 while the average rate of nocturnal decomposition was 141 mg DSAC-C m^-2h^-1; diurnal and nocturnal rates of DFPA accumulation and decomposition were similar (2 mg DFPA-C m^-2h^-1). These data were used to calculate bacterial production in the upwelling waters of Peru. A general discussion of ¹⁴C-technique and routine analytical techniques for DSAC analysis is presented, as DSAC flux exceeded DO¹⁴C flux by 17-fold in coastal Peruvian stations.     

Supply of organic matter to the sediment in the northern North Sea during a spring phytoplankton bloom

Strings of moored sediment traps were deployed in a 150 m water column over a period covering the growth and collapse of the spring bloom (4 April–3 June 1976) in an area of the northern North Sea. The efficiency of collection of material in the moored traps was compared to collections in free-drifting traps in the same area of deployment. The ways in which the data from the trap collections may be interpreted was considered at some length and a best estimate of the flux of organic carbon and nitrogen to the sediment was made. For the period prior to the spring bloom (4–23 April) this flux was 50 mg C m^–2 d^–1 (about 20% of primary production). During the bloom (24 April–19 May) it was about 185 mg C m^–2 d^–1 (35% of production) and during early summer (20 May–3 June) it was 115 mg C m^–2 d^–1, about 25% of the overlying production. The organic carbon and nitrogen content of the material collected was measured and the material was examined microscopically. There was evidence of a large settlement of diatoms immediately after the spring bloom which was reflected in changes in the C:N and C:chlorophyll ratios of the material collected. This change in biochemical composition of the material may affect its nutritional quality and have a stimulatory effect on the growth and reproduction of the animals living in the sediment.     

Heavy Metals in Superficial Sediments from the Ligurian Sea,Italy

In this paper we are presenting the concentrations and the distributions of trace metals (Fe, Ni, Cr, Cu, Pb and Zn) in the coastal area of the Ligurian Sea between Capo Noli and Capo Mele. Fifty-six samples were subjected to textural, organic carbon and chemical analyses. Three different extraction methods were used: 1N NH₂OH.HCl plus 25% CH₃COOH, nitric acid solution, and total attack with HClO₄-HF mixture. The solutions were analysed by atomic absorption spectrophotometry. The results obtained confirm that the extraction methods which are most informative for environmental purposes are the cold or the easily extractable metal techniques. The results also show that for the study area the concentrations of Fe, Ni, Cr, Cu, Pb, and Zn do not indicate traces of anthropogenic inputs.     

Heavy Metals in Superficial Sediments from the Ligurian Sea, Italy

In this paper we are presenting the concentrations and the distributions of trace metals (Fe, Ni, Cr, Cu, Pb and Zn) in the coastal area of the Ligurian Sea between Capo Noli and Capo Mele. Fifty-six samples were subjected to textural, organic carbon and chemical analyses. Three different extraction methods were used: 1N NH₂OH.HCl plus 25% CH₃COOH, nitric acid solution, and total attack with HClO₄-HF mixture. The solutions were analysed by atomic absorption spectrophotometry. The results obtained confirm that the extraction methods which are most informative for environmental purposes are the cold or the easily extractable metal techniques. The results also show that for the study area the concentrations of Fe, Ni, Cr, Cu, Pb, and Zn do not indicate traces of anthropogenic inputs.     

Particulate Organic Matter and Heavy Metals in Ligurian Open Sea

Seven stations were sampled along a transect between Imperia and Cape Corso during the C.N.R. “Bannock” survey (8-10 October 1984).

The TSM, PC, PN, and chlorophyll-a concentrations are low and decrease with depth. The AOU values suggest that below 400 m the organic matter is completely inert to further oxidation. Heavy metals concentrations show marked differences in the surface water layer between coastal and offshore stations. The chemical characteristics of total suspended matter are more conservative as an index of waters of coastal origin than the quantity of particulate matter itself or metal concentrations. The Fe: Cd ratio in particles is of interest as an indicator of coastal waters.     

Turnover and vertical transport of zinc by the euphausiid Meganyctiphanes norvegica in the Ligurian Sea

Participatory turnover time is defined as the time required to cycle an element in a system through a given material in that system. The participatory turnover time of ionic zinc by the adult Meganyctiphanes norvegica population in the Ligurian Sea ranged between 498 and 1243 years, depending upon the available food supply, and considering the food chain as the only route for zinc accumulation by the population. A total-impact turnover time was calculated as the sum of the participatory turnover time for live individuals plus the time required for dead euphausiids to lose 90% of their zinc to the water. Carcasses lost zinc to the water slower than either feces or molts, and so established the maximum loss time for all particulate excretion products; nevertheless, total-impact turnover time for zinc did not differ significantly from the participatory turnover time. The net vertical transport of zinc by M. norvegica from the sea surface to any specified depth can be calculated as the sum of the dissolved zinc excreted below the depth plus the concentrations of zinc left in feces, molts, and carcasses after they have sunk to the specified depth. Carcasses sink the fastest and lose the smallest fraction of their zinc concentration during descent; fecal pellets sink the slowest and lose the greatest fraction of their zinc concentration, and molts are intermediate. Nevertheless, feces represents the major route for delivering zinc to the bottom of the Ligurian Sea (2500 m), because concentration of the element in the pellets is so much higher than in carcasses or molts. Excretion of dissolved zinc into the water at the vertical migration depth of the living population during daylight hours was also inconsequential. Feces zinc represented over 80% of the total zinc transported to the sea floor if only marginal food supplies were available to the euphausiids, and over 90% if food was in sufficient supply. M. norvegica can effect a net transport of about 98% of its body zinc concentration below 500 m daily, in conditions of sufficient food supply and assuming that no released products are eaten during descent. If the food supply in the Ligurian Sea is considered only marginal throughout the year, M. norvegica can still effect a daily net transport below 500 m of about 36% of its body concentration, and about 6% of its body concentration will reach 2500 m daily.     

Microbial activities as a function of water depth in the Ligurian Sea: an autoradiographic study

Fourteen species of sergestid shrimps were collected in the Sargasso Sea between the surface and 1500 m near Bermuda on 4 cruises. The vertical distribution and feeding activity of the most abundant species are discussed in relation to interspecific competition and the adaptive significance of vertical migration. Each species lives within a narrow depth range and exhibits a diel vertical migration. Sergestes splendens migrated as much as 825 m, while S. japonicus migrated less than 100 m. Neither the seasonal nor permanent thermocline influenced the migration range. The only species which occurred together both day and night were S. pectinatus with S. vigilax and S. pectinatus with S. sargassi. Morphological differences in the third maxillipeds of these species suggest differences in feeding. Although most species eat a variety of organisms, the foreguts of S. grandis, S. corniculum, and S. splendens contained euphausiids more often than those of other species, and S. grandis and S. robustus fed more frequently on fishes. In contrast, S. japonicus appears to feed on detritus. Food was found in the foreguts of most species less frequently during the day than night, but no species fed only at night. S. sargassi and S. pectinatus fed equally day and night.     

Quantity and biochemical composition of sedimentary organic matter around offshore gas extraction platforms of the Adriatic Sea

Gas platforms can exert relevant effects on various ecosystem properties of the hosting area, modifying patterns of productivity and particle sedimentation. We hypothesised that the presence of gas platforms is associated with higher organic matter (OM) contents and we tested the null hypothesis by which benthic trophic conditions do not vary significantly among gas structures with different architectural characteristics. To test these hypotheses, we investigated sedimentary OM contents and biochemical composition at increasing distance from two distinct structures: one subsea well-site and one four-leg platform (FLP). We found that sediments surrounding the structures were characterised by similar OM contents, but different biochemical compositions, and that sedimentary OM compositional change with increasing distance from the structure is confirmed only at the FLP. These results suggest that: (i) benthic eutrophication is not consistent among different structures; (ii) OM biochemical composition changes are more evident than those in OM quantity; and (iii) the effect, wherever present, disappears at a very narrow distance from the platform. As biochemical composition of OM reflects food availability for benthic organisms, our results suggest that the enrichment of macrozoobenthic communities around these structures could be the consequence of increased nutritional quality of resources.     

Estimating carbon flux to pelagic grazers in the ice-edge zone of the eastern Bering Sea

Zooplankton ingestion of phytoplankton carbon in the iceedge zone of the Eastern Bering Sea was measured using a deck incubation approach in 1982. Using further samples collected in 1983, the plant cell carbon to cell volume ratio was estimated at 0.0604 pg m^–3 from an experimentally determined particulate carbon to seston volume relationship. The application of this conversion to the results of experimental incubations of natural plant stocks with net-caught zooplankton produced ingestion rates of 68.8 and 10.26 mg C g^–1 grazer d^–1 for copepods and euphausiids, respectively. Extrapolating these rates to in situ zooplankton biomass at the edge of the seasonal ice pack yielded carbon flux rates through the zooplankton community ranging between 6.5 and 32.8 mg C m^–2 d^–1. This consumption amounted to less than 2% of the daily phytoplankton production in the ice-edge zone.     

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.     

Carbon flux to seabirds in waters with different mixing regimes in the southeastern Bering Sea

The southeastern Bering Sea is characterized by three mixing regimes, separated by fronts associated with the 50, 100, and 200 m isobaths. Phytoplankton to zooplankton transfer-rates are high in waters over the outer shelf and slope (seaward of the 100 m front) relative to transfer in waters over the middle shelf (between the 50 and 100 m fronts). To see whether this difference is reflected at a higher trophic level, we computed carbon flux to the 11 commonest seabird species. Bird-density data (for the period 1975 through 1979) were combined with daily caloric requirement, which is an allometric function of body size in this endothermic group. Minimum transfer to seabirds over a 153 d period (April–August) was 30 mg C m^-2 for the middle shelf and 48 mg C m^-2 for outer shelf and slope waters. Trophic transfer to subsurface-feeding birds (shearwaters, murres and auklets) differed little between regions. In contrast, trophic transfer to surface-feeding birds (fulmars, petrels, and kittiwakes) in the outer shelf and slope waters was 3 times greater than in the waters of the middle shelf. Thus, for seabirds as a whole, pathways of energy transfer differed more between regions than did total carbon flux.     

Road-deposited sediments mediating the transfer of anthropogenic organic matter to stormwater runoff

Environmental Geochemistry and Health - It has been regarded that road-deposited sediment (RDS) is one of the important sinks of anthropogenic pollutants as well as the major source of pollutants...     

土壤有机质对宁夏农业综合开发活动的响应

为深入分析宁夏农业综合开发活动对土壤有机质的影响,认识其对气候变化的适应意义,分别于北部平原灌区、中部干旱带和南部黄土丘陵区的3个农发项目典型示范点,选取典型用地、玉米地、未利用地3种土地利用类型,分析表层10～20 cm土壤有机质的变化规律。研究发现,生态区和土地利用类型是影响土壤有机质的重要因素,并存在极显著的交互作用。研究区土壤有机质在4.53～14.70 g·kg-1范围内变化,典型用地有显著改善,平均质量分数达10.40 g·kg-1。限定生态区条件下,北部平原灌区无论水稻还是玉米利用方式下,土壤有机质含量相对未利用地都出现显著提升,但是南部黄土丘陵区3种土地利用类型间并无显著差异,中部干旱带只有甘草地土壤有机质含量显著提升,幅度高达145%。限定土地利用类型条件下,3个生态区间典型用地土壤有机质出现显著差异,但是北部平原灌区和南部黄土丘陵区间未利用地以及玉米地表层土壤有机质差异并不显著。研究区农业综合开发活动对土壤有机质储存的作用以正效应为主,但是不同农业土地利用类型在不同生态区对土壤有机质的作用不尽相同。宁夏农业综合开发活动需要综合考虑生态区水土资源特征,选取适宜的农业土地利用类型,有效提升土壤有机质含量,积极应对气候变化。     

河流有机质生物地球化学研究进展

探讨了近年来河流中有机质的生物地球化学研究状况。大多数河流有机质的来源主要是外源即流域侵蚀而来的,经过河流的新陈代谢过程,把河流中的悬浮物分解为不同类型的有机质。在有机质分解过程中由于外部条件的差异,形成粒径大小不同的颗粒物和溶解有机质、无机质等。河流水体中的溶解有机碳(DOC)在全球不同纬度、不同区域,其含量差异较大,但目前对其生物地球化学控制的量级缺乏足够的理解和认识。另外碳氮同位素及其比值在当前的河流有机质生物地球化学研究中仍起着非常重要的示踪作用。