Organic Enrichment Of Sediments Research Articles

Restoration of Water Environment by Covering Granulated Coal Ash in Brakish-water Lake Nakaumi, Japan

Granulated coal ash was used to restore water environment in a brackish-water lake, Nakaumi, Japan, whose sediment was heavily deteriorated with organic substances. Number of bivalves, Tapes japonica and Scapharca subcrenata, which were important fisheries resources, were significantly recovered 2-3 years after the granulated coal ash covering. Oxydation-reduction potential of the amended sediment with the coal ash was significantly high compared to those with natural sand. Dissolved oxygen concentration in the overlying water was also high at the coal ash amendment site. This means, the sediment oxygen consumption was depressed by covering with the granulated coal ash. From these results, granulated coal ash can be effective to restore water environment and bivalve habitat by amending the organically-enriched sediments.

Effects of Hurricane Katrina on benthic macroinvertebrate communities along the northern Gulf of Mexico coast

The effects of Hurricane Katrina on benthic fauna and habitat quality in coastal waters of Louisiana, Mississippi, and Alabama, USA, were assessed in October, 2005, 2 months after the hurricane made landfall between New Orleans, LA and Biloxi, MS. Benthic macrofaunal samples, sediment chemical concentrations, and water quality measurements from 60 sites in Lake Pontchartrain and Mississippi Sound were compared with pre-hurricane conditions from 2000-2004. Post-hurricane benthic communities had significant reductions in numbers of taxa, H(') diversity, and abundance as well as shifts in composition and ranking of dominant taxa. These effects were not associated with changes in chemical contamination, organic enrichment of sediments, or hypoxia and were likely due to hurricane-related scouring and changes in salinity.

Influence of mussel aquaculture on sediment organic enrichment in a nutrient-rich coastal embayment

Effects of mussel Mytilus edulis aquaculture on benthic organic enrichment were deter- mined in Tracadie Bay, a shallow, nutrient-rich embayment in Prince Edward Island, Canada. Water content (WC), inorganic grain size (GS), organic matter (OM), redox potentials (EhNHE) and free sul- fides (S) in the upper 2 cm of sediment were measured at 58 stations throughout the inlet to evaluate spatial variations between lease and non-lease locations. MANOVA results showed that mean (±SD) values for WC (64.8 ± 12.7%), OM (9.8 ± 4.3%), and S (1794 ± 771 µM) were significantly (p < 0.005) higher and EhNHE lower (-51 ± 78 mV) within mussel leases (n = 24) vs. non-lease areas (n = 34). Negative regressions between S and GS and positive regressions between EhNHE and GS at lease and non-lease locations had similar slopes but intercept values were significantly higher for S and lower for EhNHE (p < 0.007) for lease locations. EhNHE and a Benthic Enrichment Index derived from EhNHE, OM and WC were inversely related to S. K-means clustering and multi-dimensional scaling showed that geochemical variables could be used to group stations into categories of benthic organic enrich- ment within mussel lease and non-lease areas characteristic of oxic-hypoxic sediments described by measures of S and EhNHE.

마산만 저서생태계를 중심으로 연안해역 건강성 평가를 위한 저서생물지수의 적용

In this work, we compared the characteristics of three benthic biotic indices (BPI, AMBI, BIBI) which indicates the health condition of benthic communities in Masan Bay, Korea where anthropogenic impacts have been concentrated. Also we evaluated the usefulness of these benthic indices and some problems if they were applied to the Korean coastal waters. For this we used the macrozoobenthos data collected using van Veen grab (<TEX>$0.1\;m^2$</TEX>) at 21 sites in Masan Bay in February and August 2004. Based on the BPI values, two stations in the inner bay were found in a very hard polluted condition and three stations in the middle bay were also in a highly polluted condition. Only one station located in the bay mouth was in a normal condition. The inner bay stations showed very high AMBI values (<TEX>${\geq}5.0$</TEX>), indicating a highly polluted condition. The bay mouth station was assessed in a moderately polluted condition. The overall BIBI values in Masan Bay were in the range between 1.0 and 3.0. The inner bay stations showed low BIBI values (<TEX>${\leq}2.0$</TEX>) in the severely degraded condition. The bay mouth station with high BIBI value over 3.0 was assessed as a normal condition. All three benthos indices showed that macrozoobenthic communities in the inner bay were in a seriously polluted condition all year round, and macrobenthic faunas in the bay mouth seemed in a bad healthy condition (slightly polluted) based on AMBI during summer season. These three benthic biotic indices showed the similar assessment result, and thus we consider that each of them is a useful tool for the assessment of coastal benthic ecosystems under the organic enrichment in sediment.

Occurrence of florfenicol resistance in bacteria associated with two Chilean salmon farms with different history of antibacterial usage

In Chile, the administration of florfenicol to control bacterial pathologies in freshwater salmon farms is a frequent practice, but no studies has been developed to evaluate the incidence of florfenicol-resistant bacteria in these cultures. This study was undertaken to obtain information on the occurrence of florfenicol-resistant bacteria in a farm (LF1) under florfenicol therapy two weeks before sampling date, located in the Rupanco Lake, and a farm (LF2) with no recent history of antibacterial therapy, located in the Llanquihue Lake. Samples from surface water, pellet, Salmo salar fingerlings and control and under-cage sediments were collected from each salmon farm. Total and florfenicol-resistant culturable counts were determined by a spread plate method, observing low (< 9%) proportions of florfenicol resistance in water and fingerling samples, whereas sediment samples from LF1 farm showed proportions ranging from 18.55 ± 2.85% (control) to 26.40 ± 1.56% (under-cage) and were significantly higher ( P < 0.05) than those from LF2 farm, with 0.29 ± 0.30% (control) and 0.69 ± 1.00% (under-cage) values, not observing a direct correlation with sediment organic enrichment. Also, unmedicated pelletized feed from LF1 farm showed high levels of resistance (34.79 ± 11.87%), and were significantly ( P < 0.05) higher than those from LF2 farm (< 0.001%). A number of 34 and 36 representative isolates recovered from LF1 and LF2 farms respectively, were selected and identified by using the Biolog Microbial ID System, observing that mainly belonged to Pseudomonas genus (67.65 and 66.67% in LF1 and LF2 farms) and the predominant species were P. putida and P. viridilivida (14.71%) in LF1 farm, and P. fluorescens (36.11%) in LF2 farm. Antibacterial susceptibility patterns of resistant strains from both Lakes were similar, showing important proportions of isolates resistance to ampicillin, erythromycin, furazolidone and cotrimoxazole and susceptibility to gentamicin, kanamycin and enrofloxacin. The minimum inhibitory concentration (MIC) of florfenicol against these selected bacteria were determined, observing MIC ranges of 256–> 1024 and 64–> 1024 μg ml − 1 for strains recovered from LF1 and LF2 farms, respectively. The important occurrence of florfenicol-resistant and antibacterial-multiresistant microorganisms in unpolluted and farm-impacted sites in Rupanco Lake suggests that use of florfenicol is not a necessary causal condition for the development of elevated frequencies of florfenicol resistance. Otherwise, considering that intrinsic resistance to many antibacterials has been extensively reported for Pseudomonas species, observed levels of resistance to florfenicol could be overestimated by the occurrence of innately resistant bacteria with multiple non-specific resistances. Our results prompt the necessity for maintaining a continuous surveillance of florfenicol resistance in salmon farms, as well as to characterize the molecular elements involved in these resistances to evaluate the feasibility of their dissemination among environmental microbiota.

Iron Additions Reduce Sulfate Reduction Rates and Improve Seagrass Growth on Organic-Enriched Carbonate Sediments

Here we demonstrate, through experimental iron additions to a Mediterranean seagrass meadow, that iron plays a pivotal role in seagrass systems on carbonate sediments, directly through its role as a limiting nutrient, and indirectly by stimulating phosphorus recycling through the activity of the enzyme alkaline phosphatase and by buffering the development of reduced conditions in sediments. Iron additions were performed throughout the active root zone (30 cm depth) to two Posidonia oceanica meadows, one on organic-enriched sediments and one on organic poor sediments (Reference). Seagrass growth, nutrient incorporation and sediment biogeochemical conditions were followed for four months. Iron additions had positive effects on seagrass growth (leaf production increased with 55%) and nutrient incorporation (increased 46–91%) in the organic-enriched site, increasing to levels found at the Reference site. There was no effect of iron additions in the Reference seagrass meadow suggesting that iron was not the most important controlling factor at this site. The iron pools were about two times higher compared to the organic-enriched site. The main effect on the sediment biogeochemical conditions at the organic-enriched site was a suppression of sulfate reduction activity to the levels encountered at the Reference site (6.7 mmol m−2d−1 vs. 4.7–5.9 mmol m−2d−1). This suggests that the sulfide stress on the seagrasses was removed and that the iron availability increased due to reduced precipitation of iron-sulfides and thus improving seagrass growth conditions in these organic-enriched sediments.

Acoustic detection of organic enrichment in sediments at a salmon farm is confirmed by independent groundtruthing methods

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 267:99-105 (2004) - doi:10.3354/meps267099 Acoustic detection of organic enrichment in sediments at a salmon farm is confirmed by independent groundtruthing methods D. J. Wildish1,*, J. E. Hughes-Clarke2, G. W. Pohle3, B. T. Hargrave4, L. M. Mayer5 1Biological Station, Fisheries & Oceans Canada, 531 Brandy Cove Road, St. Andrews, New Brunswick E5B 2L9, Canada 2Department of Geodesy & Geomatics Engineering, University of New Brunswick, PO Box 4400, Fredericton, New Brunswick E3B 5A3, Canada 3Huntsman Marine Science Centre, 1 Lower Campus Road, St. Andrews, New Brunswick E5B 2L7, Canada 4Bedford Institute of Oceanography, Fisheries & Oceans Canada, Dartmouth, Nova Scotia B2Y 4A2, Canada 5Darling Marine Center, University of Maine, 193 Clarks Cove Road, Walpole, Maine 04573, USA *Email: wildishd@dfo-mpo.gc.ca ABSTRACT: Acoustic backscatter contrast in depositional sediments under salmon farm cages in the Bay of Fundy, Canada, was correlated with localized changes in (unknown) sediment geotechnical properties, as indicated by 4 independent measures of organic enrichment. Sediment total sulfides and redox potentials, enzyme hydrolyzable amino acids, sediment profile imaging and macrofaunal samples, taken at mid-cage positions, each rejected the null hypothesis that salmon cage footprints, defined acoustically as high backscatter areas, were indistinguishable from nearby reference areas. Acoustic backscatter imaging appears capable of mapping organic enrichment in depositional sediments caused by excessive inputs of salmon farm wastes associated with intensive aquaculture. KEY WORDS: Organic enrichment · Multi-beam acoustics · Sedimentary sulfides · Sediment profile imaging · Aquaculture Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 267. Online publication date: February 19, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Organic enrichment of sediments from salmon farming in Norway: environmental factors, management practices, and monitoring techniques

Environmental impacts of salmon cage aquaculture resulting from deposition of organic-rich particulate matter to the sea bottom have been thought to be a function of the local environmental conditions and management practices. However, testing of these suppositions have been limited by (1) widely varying monitoring methods employed, and (2) lack of data comparability resulting from the absence of standardized national monitoring schemes. In order to determine the sensitivity of different monitoring methods in detecting benthic environmental effects, a comparative analysis was undertaken of four methods commonly employed in Norway that vary in cost and expertise required: (1) visual diver surveys, (2) faunal analysis, (3) sediment chemistry, and (4) Sediment Profile Imagery (SPI). Results indicate that all methods agreed in the common “impact zone” under and immediately next to the cages. However, each of the methods differed in their sensitivity in detecting more subtle effects at greater distances from the cages. Data from 168 environmental survey samples located at various distances from working Norwegian salmon cage farms collected using similar methodology between 1996 and 1998 were analyzed to determine the relationship between environmental variables, management regimes, and levels of environmental impact. Total organic carbon (TOC) levels in sediments were significantly higher immediately adjacent to cages compared to reference sites, and approximately 32% of the samples under the cages showed significant degradation. At intermediate distances (50–100 m), influences from fish farming are not clearly detected by TOC analysis. Further, while neither depth nor current speed alone are good predictors for environmental management, the results suggest recovery of sites by periodic abandonment (or fallowing) is one of the best management tools for sustainable salmon farming in cold-water environments.

Benthic microbial indicators of fish farm impact in a coastal area of the Tyrrhenian Sea

We studied the impact of organic loads due to the biodeposition of a fish farm in a non-impacted coastal area of the Tyrrhenian Sea (Western Mediterranean). Sediment chemistry and benthic microbial community were investigated from July 1997 to February 1998 on monthly basis at two stations: one was located under the fish farm, while the second was about 1 km away, and served as a reference site. The presence of the cage induced rapid changes in the benthic conditions: the sediments were rapidly (after 6 weeks) reduced. A significant accumulation of biopolymeric carbon was observed beneath the cage both 2 weeks after the initial cage deployment, on non-impacted sediments, and 5-7 months after, and appeared to be related to the fish farm production cycle. The density of microbial communities beneath the fish farm increased only during the first month of farming activity (July) and partially 7 months after cage disposal (i.e. in January), when there was a significant sediment organic enrichment. Additional evidence of rapid impact of the fish farm on the benthic bacterial communities is provided by the increase in the numbers of autofluorescent microbial cells. The photosynthetic eukaryotic cells displayed a highly reduced contribution to total autofluorescent microbial density, indicating that their decrease is related with biopolymeric carbon accumulation, and probably was due also to “shadow effect” induced by suspended material, coming from the fish farm, on the environment below. We propose here, to apply the ratio of culturable heterotrophic bacteria to microbial direct counts (CFU/MDC) to detect fish farm impact. In cage sediments, organic enrichment and the consequent modification of the characteristics of the benthic environment, determined an increase in aerobic heterotrophicbacteria and vibrio density indicating that they are efficient colonizers of organic-rich sediments. Densities of Escherichia coli and Enterococci were not significantly higher than in the reference site, and are likely of terrestrial origin. Thus they cannot be used as specific indicators of fish farm impact.

Sequential extraction of iron, manganese and related elements in S1 sapropel sediments, eastern Mediterranean

A detailed sequential extraction scheme (MESEX) was developed to distinguish Fe and Mn phases in eastern Mediterranean sediments. After calibration and validation using single natural minerals and a mixed mineral standard, MESEX was applied to Holocene eastern Mediterranean sediments from (1) a former brine basin, and (2) a normal setting, including the organic-rich sapropel S1. In both sediments the Mn(II)/Mn(III,IV) redox boundary is clearly distinguished with carbonate-related Mn being enriched below, and Mn oxides occurring only above it. A clear Fe(II)/Fe(III) redox boundary is present in the normal eastern Mediterranean sediments and is located just below the Mn(II)/Mn(III,IV) redox boundary. The Fe(II)/Fe(III) boundary closely coincides with the visible boundary between the lower unoxidised and the upper oxidised (burned-down) part of the original sapropel S1 interval. Pyrite is only present within the unoxidised interval, whereas Fe oxides are abundant above it. The Fe(II)/Fe(III) redox boundary in the former brine sediments resides on top of the organic-enriched sediments, as deduced from the distribution of Fe oxides and pyrite. As a result of burn-down of the sapropel S1 unit in the normal sediments, a vanadium peak has been formed below the oxidation front, whereas no such V peak was observed in the former brine sediments. This, together with the location of the Mn(II)/Mn(III,IV) redox boundary well above the organic-enriched sediments, suggests that no burn-down has taken place into the sapropelic sediments of the former brine basin, resulting in the preservation of the relationships of trace metal to organic carbon or pyrite. In these latter sediments, Mn and Co appear to be associated with pyrite, whereas Ni, Cu and Zn, as well as V, are more related to organic matter. On the basis of MESEX, variations have also been detected in the terrigenous component, i.e. aluminosilicates. (Fe/Al) clay, (Mg/Al) clay, and several trace metal to Al ratios are higher in sapropelic than in non-sapropelic sediments. These results indicate that sources of terrestrial material have been different during sapropel times compared to the period immediately after it. On the other hand, the fairly constant K/Al clay ratio suggests that no major changes may have occurred in the relative illite contribution.

Experimental evidence of polymorphysm of sexual development in &lt;i&gt;Capitella&lt;/i&gt; sp. B (Polychaeta: Capitellidae) from Barcelona, Spain

The development and growth of Capitella sp. B obtained from Barcelona were studied under culture conditions. Trochophore and metatrochophore larvae hatched non-simultaneously (two periods) from single brood tubes. This is the laboratory evidence of polymorphysm of sexual development in the Capitella capitata species-complex. During the first release period, only free swimming trochophores hatched. The females, still bearing larvae inside the brood tube, were transferred to another dish. After three days, ciliated metatrochophores hatched from 8.7% of the transferred broods. In a culture experiment, larvae maintained in sediment enriched with artificial food grew to immature and mature adults. In this condition, the larvae that hatched during the first release reached the immature adult stage, while the larvae derived from the release became mature adults. Oogenesis was observed three times in one female from the second release, though no spawning and fertilization occurred under incubation with sib mature males. Two different sizes of coelomic oocytes were observed. Polymorphysm of sexual development is discussed as an advantageous reproductive strategy enhancing survival in organic enriched sediments.

Community Experiments Using Benthic Chambers: Microbial Significance in Highly Organic Enriched Sediments

The structure of the benthic microbial loop was studied in order to understand heterotrophic pathways in the suboxic sediments of the Rapallo Harbour in autumn, 1996. Sediments were characterized by the large accumulation of organic detritus (17.2 – 21.4 μg chloroplastic pigment equivalents (CPE)g−1; carbohydrates and proteins: 7.8–16.7 and 6.7–7.5 mg g−1). Due to the high organic load, benthic bacteria and protozoa displayed extremely high densities (1.4 × 109 cells g−1 and 26.9 × 105 cells g−1). Meiofauna, protozoa and bacteria showed an approximate biomass ratio of 1:2:20. the presence of large amounts of organic matter appeared to determine a shift of the benthic size structure toward the increasing dominance of the smaller components of the benthic food webs. These data indicate that the sediments of the Rapallo Harbour were dominated by microbial biomasses to a larger extent than in non-food limited environments, characterized by a lower organic contamination. On the results presented in this study, the microbial dominance in highly organic enriched sediments can be explained with: (1) a reduction of the top-down control and grazing pressure of meio- and macrofauna on the microbial components; (2) the opportunistic composition and high metabolic activity of the microbial components.

Coprostanol levels and organic enrichment in sediments of the Bilbao estuary (north of Spain)

An assessment was made of the distribution of the faecal sterol coprostanol (COP) in sediments in the Bilbao estuary. Concentrations of COP ranged from 135.15 to 10.77 μg g −1 dry weight, from the inner to the open estuary, with a mean value of 51.43 μg g −1; the highest concentrations were found near the mouths of several tribularies flowing into the estuary. Comparisons with other published values indicate that sediments from the Bilbao estuary are affected by sewage pollution in a similar degree to that reported for other estuaries in the world. Organic enrichment and anaerobic sediment conditions prevail in three-fourths of its watercourse bed. Since the spatial distribution of several organic sedimentary parameters could be clearly correlated with COP levels, we can conclude the existence of major pollution by the addition of untreated sewage, coming from mainly domestic sources. The implementation of a sewerage treatment plan by the local water authority needs the monitoring of reliable sewage tracers, such as faccal sterols, to assess the effectiveness of the plan in reducing the effects of pollution.

Response of meiobenthic size-structure, biomass and respiration to sediment organic enrichment

Samples for benthic meiofauna were collected in the vicinity of a salmon aquaculture farm in Bliss Harbour, Bay of Fundy, Canada in early August 1990. Simultaneously, samples for water content, organic carbon, organic nitrogen were collected, and redox potential and benthic oxygen consumption were measured. Meiobenthic size-spectra of biomass and respiration (calculated using allometric equations) were examined at three locations along a gradient of sediment organic enrichment radiating from the farm. Neither biomass nor respiration size-spectra were significantly different between locations despite a decrease in taxon diversity with increasing sediment organic enrichment. Small nematodes were the single largest contributor to respiration and usually to biomass at all locations, particularly at the most organically enriched location directly under the salmon farm. Calculated meiofauna respiration accounted for a greater proportion of total benthic community respiration in organically enriched sediments than in less enriched sediments.

POPULATION DYNAMICS, LIFE HISTORY, AND PRODUCTION OF CYATHURA CARINATA (KRØYER) (ISOPODA: ANTHURIDAE) IN THE MONDEGO ESTUARY, PORTUGAL

ABSTRACT Previous studies of the benthic community in the Mondego estuary revealed that Cyathura carinata has spatially and temporally stable populations, has significant biomass throughout the year, and is one of the most abundant species in the estuary. The present work was carried out to study its population dynamics and life cycle in relation to physicochemical factors, and to estimate its productivity within intertidal mud flats. Cyathura carinata was sampled every two weeks from November 1990 to December 1991. It exhibited a contagious spatial distribution within the eulittoral zone, and its abundance changed seasonally, decreasing gradually from midfall to late spring, and increasing again from early summer to the following fall. Abundance appeared to be inversely related to emersion periods, and positively correlated with salinity and nitrate concentrations, while higher temperature and sediment organic enrichment appeared to have a negative effect on the abundance of organisms. Nevertheless, the correlations between abundance and environmental factors could not be considered as defining cause-andeffect, since environmental factors were also intercorrelated. Protogynous hermaphroditism was hypothesized, with males being present from March to September. Sexual activity began in early spring and recruitment took place through the summer. Two cohorts were produced, one in June and a second in August. Fecundity was significantly correlated with female size. In addition, higher salinities and pH favored higher fecundity. Although seasonal variations in growth rates were observed, growth was continuous through the life of the animal. Growth rates practically ceased during the winter, increased gradually from late winter to a maximum between early summer and midfall, and decreased again until the following winter. Life span was roughly estimated at 18-22 months. Sexual differentiation was estimated to occur within a period of 49-54 days from birth, for females, and 146-208 days for males. Sexual maturation in females was estimated to occur in 240-357 days (8-12 months). Cyathura carinata is a semiannual species in the Mondego estuary, with iteroparous females and an univoltine life cycle. Growth production (P) and elimination production (E) were estimated as, respectively, 5.6-9.9 and 11.8-22.3 g·m―2· year―1 ash-free dry weight. P/B and E/B ratios were estimated, respectively, as 1.65-2.03 and 3.74-4.37. Despite several differences with regard to the reproductive period, all populations of C. carinata studied along the European coasts show univoltine life cycles. Due to stable populations and life cycle characteristics, this species appears ideal for comparative ecophysiological and ecotoxicological studies in European estuaries.

Relationship between growth of Capitella sp. and organic enrichment of the sediment

Laboratory colonies of Capitella sp., which 1s found densely distributed in organically enriched or polluted areas, were cultured in sediments with various levels of organic matter to examine the relationship between level of sediment organic matter and growth of individuals. Growth was independent of absolute levels of sediment organic matter, but was significantly correlated with increases in the level of sediment organic matter on addition of algal powder to the sediment. These results indicate that Capitella species predominating in organically enriched areas have a physiological requirement for organic materials discharged from sources of organic enrichment, e.g, abundant growth of algae, fish farming, industrial effluent, sewage, if they are to grow normally. Although associat~on of some Capitella species with sediment organic enrichment has been previously recognized as a reflection of their opportunistic characteristics, a physiological requirement for organic materials discharged from sources of organic enrichment may be the single factor most responsible for the concentration of CapiteNa species in organically enriched areas. However, it is unlikely that they can directly ingest and assimilate such organic materials. Since the additional organic materials are easily decomposed in the sediment, Capitella species may require either (1) some specific microorganisms, the levels of which increase with levels of the organic materials, or (2) certain substance(s) produced during decomposition of the organic materials.

Effects of rhizosphere macronutrients and sulfide levels on the growth physiology of Halodule wrightii Aschers, and Ruppia maritima L. s.l.

Correlations were found between seasonal shoot production rates, tissue N and P contents, and stable S isotope ratios for co-occurring Halodule wrightii Aschers, and Ruppia maritima L.s.l. plants at a typical estuarine field site. Halodule growth rates correlated positively with elemental composition of root tissue while Ruppia growth correlated positively with leaf tissue elemental concentrations. Based on these field observations, controlled laboratory studies were conducted to compare growth responses of Halodule and Ruppia to selected sediment nutrient regimes. Ruppia grew readily on sediments enriched with low-to-moderate levels of inorganic nutrients (e.g., NO 3 − or NH 4 + and PO 4 3− ). In contrast, these inorganic nutrients were ineffective in supporting Halodule growth and sediment enrichment with organic N was specifically required for vigorous growth. Nitrate added to organic-enriched sediments was inhibitory to Halodule growth, most likely through its suppressive effect on SO 4 2− reduction activity. These data provide experimental evidence that differential responses to sediment sulfate reduction are involved in the competition between Halodule and Ruppia under polyhaline estuarine regimes.

Devonian lacustrine limestones at the margin of the Orcadian Basin, Scotland

A complex overlap of middle Old Red Sandstone occus in N. Caithness and Sutherland. The relief of the underlying surface of Moine metamorphics and intrusions is irregular. The facies variation of the sediments reflects lacustrine transgression and regression within the Orcadian Basin. When the lake level was high and the lake margin coincided with the basin margin, thick ( c. 4m) carbonates were deposited on the unconformity. Carbonate deposition was controlled by photosynthesizing algae. At such sites the depositional environment was oxygen-rich and the carbonates do not contain biotite, organic carbon or pyrite. The offshore facies was deposited in deeper stratified lakes, anoxic at depth, and comprises organically-enriched sediments (with pyrite and biotite). When the lake margin was not coincident with the basin margin alluvial sediments mantled the unconformity as rivers cut to a lower base level. At marginal sites compaction of the lacustrine sediments over the irregular basement during periods of low lake level, when no deposition occurred, produced local unconformities.