Global Radiation and Onset of Stratification as Forcing Factors of Seasonal Carbonate and Organic Matter Flux Dynamics in a Hypertrophic Hardwater Lake (Sacrower See,Northeastern Germany)

A 2-year (October 2003–October 2005) high-resolution sediment trap study was conducted in Sacrower See, a dimictic hardwater lake in northeastern Germany. Geochemical and diatom data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to quantify the impact of single parameters on biochemical calcite precipitation and organic matter production. Our goals were to disentangle how carbonaceous varves and their sublaminae form during the annual cycle to better understand the palaeorecords and to detect influences of dissolution, resuspension as well as of global radiation and stratification on lake internal particle formation. Total particle fluxes in both investigated years were highest during spring and summer. Sedimentation was dominated by autochthonous organic matter and biochemically precipitated calcite. Main calcite precipitation occurred between April and July and was preceded and followed by smaller flux peaks caused by resuspension during winter and blooms of the calcified green algae Phacotus lenticularis during summer. In some of the trap intervals during summer up to 100% of the precipitated calcite was dissolved in the hypolimnion. High primary production due to stable insolation conditions in epilimnic waters began with stratification of the water column. Start and development of stratification is closely related to air and water surface temperatures. It is assumed that global radiation influences the onset and stability of water column stratification and thereby determining the intensity of primary production and consequently of timing and amount of calcite precipitation which is triggered by phytoplanktonic CO₂ consumption. Sediment fluxes of organic matter and calcite are also related to the winter NAO-Index. Therefore these fluxes will be used as a proxy for ongoing reconstruction of Holocene climate conditions.     

A 1000-yr record of environmental change in NE China indicated by diatom assemblages from maar lake Erlongwan

Past environmental changes based on diatom relative abundances have been inferred from the maar Lake Erlongwan in northeast China. The limnology of Lake Erlongwan is affected by the strongly seasonal regional climate. The composition of diatom assemblages, in turn, responds to changes in the seasonal duration of ice cover in winter, water-column turnover in spring and autumn, and thermal stratification in summer. Statistical analysis of the sedimentary diatom assemblages reveals three significant stratigraphic zones over the past 1000 yr. The highest abundance of the planktonic species Discostella species occurs between AD 1050 and 1400 and suggests an annual ice-free period of long duration and well-developed summer stratification of the water column. This planktonic diatom peak between ca. AD 1150 and 1200 suggests that this period was the warmest over the past 1000 yr. The interval between AD 1400 and 1800 is marked by a decline in planktonic diatoms and suggests shorter duration of the ice-free season, weaker water stratification and possibly generally cold conditions. After AD 1800 relative abundances of planktonic diatoms, including Puncticulata praetermissa and Asterionella formosa, increase again, which indicates lengthening of the duration of the annual ice-free period and a stronger overturn of the water column. All these data imply that the pattern of the seasons is different between the MWP and the 20th century.     

Blooms of Dinoflagellate Mixotrophs in a Lower Chesapeake Bay Tributary: Carbon and Nitrogen Uptake over Diurnal,Seasonal, and Interannual Timescales

A multi-year study was conducted in the eutrophic Lafayette River, a sub-tributary of the lower Chesapeake Bay during which uptake of inorganic and organic nitrogen (N) and C compounds was measured during multiple seasons and years when different dinoflagellate species were dominant. Seasonal dinoflagellate blooms included a variety of mixotrophic dinoflagellates including Heterocapsa triquetra in the late winter, Prorocentrum minimum in the spring, Akashiwo sanguinea in the early summer, and Scrippsiella trochoidea and Cochlodinium polykrikoides in late summer and fall. Results showed that no single N source fueled algal growth, rather rates of N and C uptake varied on seasonal and diurnal timescales, and within blooms as they initiated and developed. Rates of photosynthetic C uptake were low yielding low assimilation numbers during much of the study period and the ability to assimilate dissolved organic carbon augmented photosynthetic C uptake during bloom and non-bloom periods. The ability to use dissolved organic C during the day and night may allow mixotrophic bloom organisms a competitive advantage over co-occurring phytoplankton that are restricted to photoautotrophic growth, obtaining N and C during the day and in well-lit surface waters.     

Taxonomic composition,paleoecology and biostratigraphy of Late Cretaceous diatoms from Devon Island,Nunavut, Canadian High Arctic

Upper Cretaceous sediments of the Kanguk Formation exposed in Eidsbotn and Viks Fiord grabens on Devon Island, Nunavut, Canadian High Arctic, yielded 91 fossil marine diatom species and varieties (including indeterminate taxa), representing 41 genera. Excellent preservation of the assemblages was aided by shallow burial, protection in downfaulted linear grabens, and the presence of abundant volcanic material. Planktonic species and resting spores comprise nearly 70% of the diatom assemblage, and provided abundant food resources for the Late Cretaceous Arctic ecosystem. Deposition of the approximately 225 m-thick stratigraphic sequence was predominantly in a shallow marine neritic setting, with an upward progression to interbedded terrestrial deposits of the Expedition Fiord Formation, reflecting a regression and eventual persistence of terrestrial facies into the Early Cenozoic. The Kanguk Formation is widespread across the Canadian Arctic, and diatom biostratigraphy indicates a Santonian–Campanian age for the sequences reported herein, based on the presence of Gladius antiquus in the lowermost strata and occurrence of Costopyxis antiqua throughout the succession. However, Amblypyrgus sp. A and Archepyrgus sp. aff. A. melosiroides, encountered in the lower part of the succession, are known exclusively from the Lower Cretaceous. This may suggest a slightly older age. New information on shallow shelf diatom assemblages from this study is compared to reports on two other Late Cretacous Arctic diatom assemblages. These three sites represent an environmental transect from shallow to distal shelf settings and into the oceanic realm.     

The annual cycle of kiel bight plankton: A long-term analysis

Over the past decade, the annual cycle of the major pelagic processes in relation to environmental factors and species composition of the plankton has been studied intensively at a fixed station in Kiel Bight. A series of sequential phases, differentiated according to characteristic properties, succeed each other in a recurring pattern each year. The following phases have been differentiated: the spring diatom bloom, the late spring copepod maximum, the summer stratification, the fall blooms and the winter dormancy. Each phase represents a particular pattern of biogenous element cycling, both within the pelagic system and between the pelagic and benthic systems. Each phase is also characterized by a spectrum of dominant species, many of which do not recur each year. Greatest variation is found amongst bloom diatoms, whereas large, slow-growing species such as the Ceratia and most metazooplankton are highly recurrent. Variation in species composition is not related to long-term trends since the past century, in spite of the considerable increase in anthropogenic nutrient input to the Bight. Short-term events appear to determine occurrence of fast-growing species, many of which have benthic resting stages in their life histories. It is concluded that more attention should be paid to life history strategies of species if the mechanisms of seasonal succession are to be elucidated. Long-term observations on appearance or absence of the various species in relation to environmental properties can provide clues as to the nature of these life history strategies.     

Feeding ecology of the northern pipefish,Syngnathus fuscus,in a seagrass community of the lower Chesapeake Bay

Examination of gut contents of the northern pipefish,Syngnathus fuscus, revealed that gammarid amphipods, caprellid amphipods, isopods, and calanoid copepods were the dominant food items during the sevenmonth study period.Gammarus mucronatus, calanoid copepods, andErichsonella attenuata were the seasonally dominant prey items in the spring, summer, and fall, respectively.G. mucronatus and calanoid copepods were consumed in approximate proportion to their numerical abundance in the environment, whileE. attenuata, present in rather uniform densities throughout the study period, was extensively consumed only in the late summer and fall. An ontogenetic pattern of prey consumption was evident, in addition to the seasonal pattern. Comparison ofG. mucronatus andE. attenuata size ranges from the field and in pipefish guts revealed thatS. fuscus preyed upon the smaller size classes of each species, and that mean size of prey consumed was positively related to fish size.     

Short-term biogeochemical influence of a diatom bloom on the nutrient and trace metal concentrations in South San Francisco Bay microcosm experiments

Two laboratory microcosm experiments were conducted to mimic an annual spring diatom bloom in South San Francisco Bay by isolating the phytoplankton community from the benthic grazing pressure to induce a phytoplankton bloom. The purpose of these experiments was to isolate the impact of a spring diatom bloom on the nutrient and trace metal geochemical cycling. Microcosms were created in 2.5 L incubation bottles and subjected to one of 4 treatments (control, copper [Cu] addition, manganese [Mn] addition, and both Cu and Mn addition) to investigate the toxicity of Cu on the resident plankton and the potential antagonistic effects of Mn on reducing Cu toxicity. Dissolved macronutrient (nitrate + nitrite, phosphate, and silicate), and dissolved and particulate trace metal (Cu, Ni, Mn) concentrations were monitored in the grow-out incubations on a daily basis. Chlorophylla concentrations were also monitored over the course of the experiment and used to calculate diatom-specific growth rates. In the experiments containing ambient South San Francisco Bay surface waters, average specific growth rates were on the order of 1.1 d^?1. The induced diatom blooms resulted in significant removal of macronutrients from the microcosms over the course of the experiments. Our research supports previous suggestions that dissolved Ni and Cu concentrations in South San Francisco Bay have a very low biological availability as a result of organic chelation. Ni(EDTA)^2? has been found to be the dominant dissolved Ni species by other researchers and Cu speciation analyses from this study and others indicate that > 99% of the dissolved Cu in South San Francisco Bay is strongly chelated as CuL₁. The free cupric ion concentration was on the order of 10^?12 M. Marked removal of dissolved Mn was observed in the control treatments, well exceeding expected dissolved Mn removal by diatom uptake. Additions of 375 nM Cu resulted in the complete titration of the chelating ligand (L₁) concentrations. The elevated [Cu²⁺] (≈10^?8MM) appeared to have a toxic effect on the diatom community observed in the significant decreases in their specific growth rates (μ=0.4 d^?1). The suppression of dissolved Mn removal from solution was also observed in treatments spiked with high levels of dissolved Cu, providing support that Mn precipitation was due to biologically mediated oxidation not phytoplankton assimilation. The observed geochemical behavior in the concurrent Cu and Mn addition treatments provide evidence in support of Mn alleviation of Cu toxicity. The biological role in the ambient short-term biogeochemical cycling of Cu and Ni in South San Francisco Bay appears to be minimal due to the inert character of the organic ligand-metal complexes. A significant portion of the annual macronutrient and Mn cycling occurs as a result of spring diatom blooms in South San Francisco Bay.     

Diatom responses to limnological and climatic changes at Ribains Maar (French Massif Central) during the Eemian and Early Würm

High-resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at Ribains maar (French Massif Central) during the Late Pleistocene (∼131–∼105 ka BP), with a focus on the Eemian interglacial in particular. Numerical analyses were used to show that most of the variability in the fossil diatom assemblages was due to climate independently from the changes in the lake catchment vegetation (as represented by pollen data). Diatom-based quantitative reconstructions of the past limnological conditions, as well as a comprehensive literature review on the auto-ecological requirements for the principal diatom taxa, were used to interpret the record. An absolute time-scale for the sequence was derived by matching the major pollen shifts with the radiometrically dated changes in oxygen isotopes observed in Italian stalagmites. This study shows that at Ribains maar, the transition from the Riss (=Saalian) Glacial to the Eemian interglacial was marked by a gradual increase in the contribution of spring-blooming diatom species, indicating a longer growing season and milder winter/spring conditions at that time. A short cooling event interrupts this trend and may correspond to a stadial. At the start of the Eemian a peak in benthic taxa and the suppression of spring-blooming flora probably reflects the effects of deglaciation on the catchment. During the Eemian interglacial itself three main phases were distinguished within the diatom record. The first phase (∼8000 years in duration) was dominated by Stephanodiscus minutulus, which suggests that intense mixing in the water-column took place during spring. The pollen record was simultaneously dominated by Quercus and Corylus that typify this phase as the climatic optimum of the Eemian. The second phase, almost equal in duration to the first phase (∼7000 years), is generally dominated by Cyclotella taxa and suggests a less productive lake and much reduced period of spring mixing compared with the first phase. In the pollen diagram this corresponds to an interval dominated by Carpinus–Picea–Abies that indicates a cooler and wetter climate. The third and last phase of the Eemian, ∼2000 year long, saw the return to Stephanodiscus-dominated assemblages, indicating a warming that may correspond to the Dansgaard–Oeschger event 25 identified in the Greenland ice-core record. In the early stage of the Würm Glacial (=Weichselian), assemblages in the Melisey I stadial (∼3000 year long) were dominated by either Aulacoseira subarctica or Asterionella formosa, which suggest colder spring conditions than during the late Eemian, but not as cold as the ones indicated by the pollen record. Stephanodiscus spp. again dominate during the Saint-Germain Ia interstadial (∼5000 year long) suggesting a return to the conditions that prevailed before the Melisey stadial, in agreement with the pollen record. The record ends with the Montaigu cold event, which is characterised by a Pinus peak in the pollen record, and corresponds to a large abundance of A. subarctica in the diatom sequence. Throughout the Eemian the abundance of Stephanodiscus spp., which is thought to be driven by winter conditions, show cyclic fluctuations that most likely match the cooling events identified in a pollen record from Germany. Variation in insolation throughout the Eemian may have been the driving factor behind the species succession observed in the diatom sequence. While this study demonstrates that diatom analysis of lake sediment can provide very detailed information on long-term climate change, a review of the few other diatom investigations published on European Eemian deposits shows that this technique has been so far seldom used to its full potential in this context in central and southern Europe.     

Pithonellid blooms in the Chalk of the Isle of Wight and their biostratigraphical potential

Five pithonellid blooms recognised in the Chalk Group of the Isle of Wight are correlated via foraminiferal biostratigraphy to regional and global events. Blooms were recognised in the Holywell Nodular Chalk to basal New Pit Chalk formations (foraminiferal zones BGS7 to BGS9); M. guerangeri to Mytiloides standard (macrofaunal zones); middle Lewes Chalk (questionably foraminifera Zone BGS12; S. plana standard macrofaunal Zone); basal Seaford Chalk (BGS14; base M. coranguinum standard macrofaunal Zone); lower Newhaven Chalk (base BGS18; base U. socialis standard macrofaunal Zone); and uppermost Newhaven to basal Culver formations (BGS19-20; O. pilula to low G. quadrata standard macrofaunal zones). The blooms appear to be coeval with oceanographic change and the general trend towards an increase in the proportion of planktonic taxa may suggest upwelling and/or dysaerobic bottom waters.     

Phytoplankton ecology of North Carolina estuaries

Numerous phytoplankton-oriented ecological studies have been conducted since 1965 in the extensive North Carolina estuarine system. Throughout a range of geomorphological estuarine types, a basic underlying pattern of phytoplankton productivity and abundance following water temperature seasonal fluctuations was observed. Overlying this solar-driven pattern was a secondary forcing mechanism consisting of a complex interaction between meteorology and hydrology, resulting in periodic winter or early spring algal blooms and productivity pulses in the lower riverine estuaries. Wet winters caused abundant nitrate to reach the lower estuaries and stimulate the blooms, whereas dry winters resulted in low winter phytoplankton abundance and primary production. Dinoflagellates (Heterocapsa triquetra, Prorocentrum minimum, Gymnodinium spp.) and various cryptomonads dominated these cool-weather estuarine blooms. Sounds were less productive than the riverine estuaries, and were dominated by diatoms such asSkeletonema costatum, Thalassiosira spp.,Melosira spp., andNitzschia spp., as were the most saline portions of riverine estuaries. Nutrient-limitation studies found that nitrogen was the principal limiting nutrient in these estuarine systems over a range of trophic states, with phosphorus occasionally co-limiting. Freshwater and oligohaline portions of large coastal plain rivers were often subject to summer blue-green algal blooms. Formation of these blooms on a year-to-year basis was also determined by meteorology and hydrology: wet winters or springs and consequent nutrient loading, coupled with low summer flow conditions and regeneration of nutrients from the sediments. Dry winters or springs resulted in less available nutrients for subsequent summer regeneration, and high flow conditions in summer flushed out the blooms. In recent years, there has been a dramatic increase in reported fish kills attributed to toxic dinoflagellate blooms, particularly in nutrient-enriched estuarine areas. This issue has become a major coastal ecological and economic concern.     

北极地区地面辐射量和云辐射强迫特征

In this paper the characteristics of surface radiative fluxes and cloud-radiative forcing are reviewed with a focus on the Arctic. Three aspects are addressed, including (i) changes in radiation flux over the global surface; (ii) characteristics of surface fluxes in the Arctic; and (iii) characteristics of cloud-radiative forcing in the Arctic. The clouds not only significantly reduce the peak summer radiative heating of the surface but also reduce the wintertime radiative cooling at the surface in　higher latitudes. The downward longwave fluxes dominates the incident radiative fluxes in the Arctic during most of the year. Incoming shortwave fluxes are negligible during late fall, winter and early spring, and even during the midsummer the incoming shortwave fluxes are only slightly greater than the downward longwave fluxes. The total net surface radiative flux is negative for most of the year and only positive during midsummer in the Arctic. The global net cloud-radiative forcing is negative, but the cloud-radiative forcing is positive in the Arctic, showing a warming effect, except for a short period in mid-summer. Positive cloud-radiative forcing in the Arctic is attributed　to the presence of snow and ice with high albedo and the absence of solar radiation during the polar night.     

Mercury speciation and distribution in Aha Reservoir which was contaminated by coal mining activities in Guiyang, Guizhou, China

Two sampling campaigns were carried out in March and August 2005 representing dry and wet seasons, respectively, to investigate the distribution patterns of Hg species in the water column and sediment profiles at two sampling stations in Aha Reservoir located in Guiyang, Southwestern China. Aha Reservoir has been contaminated by Hg due to small scale coal mining activities. Mercury concentrations in both water and sediment were elevated. A clearly seasonal variation of dissolved Hg (DHg), particulate Hg (PHg) and total Hg (THg) concentrations in the water column was observed. The concentrations of these Hg species in the wet season were significantly higher than in the dry season. Runoff input and diffusion of Hg from sediments could be the reasons for elevated concentrations of these Hg species in the wet season. The contaminated sediment is acting as a secondary contamination source for both inorganic Hg (IHg) and methylmercury (MeHg) to the overlying water. The cycling of Mn in the sediment governs the diffusion process of IHg to the water column. In the dry season (winter and spring), Mn occurs as MnO₂ because the uppermost part of sediment is in an oxic condition and Hg ions are absorbed by MnO₂. In the wet season (summer and fall), the uppermost part of the sediment profile is in a reduced condition because of stratification of the water column and MnO₂ is reduced to Mn²⁺, which results in transformation of Hg²⁺ into porewater as Mn²⁺ became soluble. This causes a higher diffusive flux of IHg from sediment to overlying water in the wet season. Both sampling stations showed a consistent trend that THg concentrations decreased in the uppermost part of sediment cores. This demonstrated that the measures taken to reduce ADM contamination to Aha Reservoir also reduced Hg input to the reservoir. Methyl Hg diffusive fluxes from sediment to overlying water were higher in the wet season than the dry season demonstrating that high temperatures favor Hg methylation processes in sediment.     

Environmental Forcing of Phytoplankton in a Mediterranean Estuary (Guadiana Estuary,South-western Iberia): A Decadal Study of Anthropogenic and Climatic Influences

Phytoplankton seasonal and interannual variability in the Guadiana upper estuary was analyzed during 1996–2005, a period that encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton succession, with early spring diatom blooms and summer–early fall cyanobacterial blooms, was apparently driven by changes in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited mode in the near future.     

Chesapeake Bay nutrient and plankton dynamics: III. The annual cycle of dissolved silicon

Silicic acid (H₄SiO₄) flux from the sediment, H₄SiO₄ concentration and river flow were used to obtain an annual dissolved silicon budget for Chesapeake Bay. H₄SiO₄ concentrations vary seasonally in the estuary: for a 12-year period, mean H₄SiO₄ concentrations in the mesohaline region were high both in spring and in late summer to early fall, and were low in late spring—occasionally approaching levels potentially limiting to diatom growth. Most of the annual allochthonous H₄SiO₄ supply to the estuary derives from the three major rivers, but regenerative H₄SiO₄ flux from the sediment to the water column exceeds the total riverine input by a factor of at least five. Sediment H₄SiO₄ efflux exhibits seasonality and averages approximately 2–3 mol Si m^?2 yr^?1. The high rates of sediment dissolution and efflux appear to maintain high levels of H₄SiO₄ in the mesohaline region, and Si-limitation of diatom growth there seems unlikely. The relative rates of biogenic silica formation and dissolution do not vary synchronously: seasonal variations in diatom productivity, sedimentary release of H₄SiO₄ and river flow all contribute to the observed late winter and late summer seasonal maxima and late spring minimum in water column H₄SiO₄ concentrations. If the only source of Si to support sedimentary H₄SiO₄ efflux is biogenic particulate silica recently deposited from the water column and this silica in turn was produced by diatoms in a ratio of 8C:1 Si, the minimum annual primary production by diatoms is at least 260 g C m^?2, approximately half of annual total plankton primary production. This estimate would be revised upwards according to the amount of particulate biogenic silica dissolving in the water column. Burial of biogenic silica amounts to from 2 to 84% of the sediment efflux of H₄SiO₄, depending on location in the bay. On an annual basis, burial represents from 60 to 100% of fluvial H₄SiO₄-Si inputs.     

The Influence of Coastal Nutrients on Phytoplankton Productivity in a Shallow Low Inflow Estuary,Drakes Estero,California (USA)

Seasonal wind-driven upwelling along the U.S. West Coast supplies large concentrations of nitrogen to surface waters that drives high primary production. However, the influence of coastal upwelled nutrients on phytoplankton productivity in adjacent small estuaries and bays is poorly understood. This study was conducted in Drakes Estero, California, a low inflow estuary located in the Point Reyes National Seashore and the site of an oyster mariculture facility that produces 40 % of the oysters harvested in California. Measurements of nutrients, chlorophyll a, phytoplankton functional groups, and phytoplankton carbon and nitrogen uptake were made between May 2010 and June 2011. A sea-to-land gradient in nutrient concentrations was observed with elevated nitrate at the coast and higher ammonium at the landward region. Larger phytoplankton cells (>5 μm diameter) were dominant within the outer and middle Estero where phytoplankton primary productivity was fueled by nitrate and f-ratios were >0.5; the greatest primary production rates were in the middle Estero. Primary production was lowest within the inner Estero, where smaller phytoplankton cells (<5 μm) were dominant, and nitrogen uptake was dominated by ammonium. Phytoplankton blooms occurred at the outer and middle Estero and were dominated by diatoms during the spring and dry-upwelling seasons but dinoflagellates during the fall. Small flagellated algae (>2 μm) were dominant at the inner Estero where no blooms occurred. These results indicate that coastal nitrate and phytoplankton are imported into Drakes Estero and lead to periods of high new production that can support the oyster mariculture; a likely scenario also for other small estuaries and bays.     

Climate change in Lake Baikal: diatom evidence in an area of continuous sedimentation

The presence of inhomogeneous sedimentation is acknowledged as being an important problem in palaeolimnological studies. Sediment records can be disturbed by erosional and redepositional events, which redeposit microfossils within a basin and may then lead to misinterpretations of fossil diatom assemblages. This study uses a combination of sedimentological tools, magnetic susceptibility measurements and high-resolution diatom analysis to show that a sediment core, BAIK80, taken in 345 m water depth from a shoulder region in the North Basin of Lake Baikal, is free of disturbances. Our results confirm that the sediment record is consistent and continuous for the uppermost sediment. Consequently, the fossil diatom data can be used to establish a continuous record of past climate variability over approximately the past 1300 years. Distinct changes occur in downcore abundances of endemic taxa Aulacoseira baicalensis and Cyclotella minuta, and principal components analysis (PCA) indicates a gradual transformation of taxa over the past 1300 years. These changes are likely to be related to climate, although definite links still have to be established. Received: 15 December 1998 / Accepted: 13 September 1999     

The cyclopoid copepods,Hemicyclops adhaerens andSaphirella sp., in the Damariscotta River estuary,maine, with a note to their possible relationship

During the 14-month collection period,Hemicyclops always appeared as naupliar stages andSaphirella as immature copepodite stages at 3 stations in the middle and lower estuary.Hemicyclops nauplii were abundant during late spring and summer, with a seasonal maximum of 7448/m³ in late spring at the upstream station.Saphirella stages were observed throughout the year, but higher population densities generally occurred in the summer and fall; the highest density was 3413/m³. Both species were usually more abundant upstream than downstream. The larvae may be life stages of a single bottom-dwelling species,Hemicyclops adhaerens.     

Quantitative measurement of the sea ice diatom biomarker IP25 and sterols in Arctic sea ice and underlying sediments: Further considerations for palaeo sea ice reconstruction

The lipid content of sea ice samples collected in 2011 and 2012 from Resolute Passage in the Canadian Arctic Archipelago was measured and compared with related samples obtained from the Amundsen Gulf in 2008. The highly branched isoprenoid (HBI) sea ice biomarker, IP₂₅, was found in sea ice samples from each study, consistent with its formation by diatoms during the spring bloom. Our analysis also revealed the occurrence of a number of sterols in Arctic sea ice and these were rigorously identified and quantified for the first time. Concentrations of IP₂₅ and sterols exhibited some variability between sampling studies, with somewhat higher values in samples from Resolute in 2012 than for the other two datasets, consistent with a general increase in biomass; however, major differences in biomarker concentration between sampling studies were not observed. An estimate of the proportion of Arctic sea ice diatoms that produce IP₂₅ (ca. 1–5%) was obtained by comparison of the concentration of IP₂₅ in the samples with those in laboratory cultures of known HBI-producing diatoms and cell enumeration in selected sea ice samples. The estimate is similar to the proportion of Haslea spp. in the same samples, providing further support to the suggestion that at least some species of the Haslea genus may be responsible for the biosynthesis of IP₂₅ and related HBI diatom lipids in Arctic sea ice and that IP₂₅ is made by a relatively small proportion of sea ice diatoms. In contrast, median sterol/IP₂₅ values were all substantially higher than those in cultures of HBI-producing diatoms, suggesting that sterols are made by the majority of sea ice diatoms. The sterol/IP₂₅ ratio was quite variable between locations and samples, likely as a result of differences in diatom assemblage; however, a comparison of individual and median sterol/IP₂₅ values in sea ice with those from surface sediments from different Arctic regions demonstrated that sterols from sea ice diatoms may, in some cases, have a significant impact on the sedimentary budget. This should be considered carefully for quantitative estimates of palaeo sea ice reconstruction using methods such as the PIP₂₅ index, which are based on the relative concentrations of IP₂₅ and sterols in Arctic marine sediment cores.     

Algal blooms: a perspective from the coasts of India

Algal blooms have been documented along the west and east coasts of India. A review of bloom occurrences in Indian waters from 1908 to 2009 points out that a total of 101 cases have been reported. A comparison of the bloom cases reported before and after the 1950s reveals that there is an increase in the number of bloom occurrences. The reports of algal blooms indicate their predominance along the west coast of India especially the southern part. Majority of the blooms reported along the west coast of India are caused by dinoflagellates, whereas diatom blooms prevail along the east coast. There have been 39 causative species responsible for blooms, of which Noctiluca scintillans and Trichodesmium erythraeum are the most common. Reporting of massive fish mortality in Indian waters has been associated with the blooming of Cochlodinium polykrikoides, Karenia brevis, Karenia mikimotoi, N. scintillans, T. erythraeum, Trichodesmium thiebautii and Chattonella marina. Most of the blooms occurred during withdrawal of the south-west monsoon and pre-monsoon period. In Indian waters, this process is mainly influenced by seasonal upwelling and monsoonal forcing that causes high riverine discharge resulting in nutrient-enriched waters that provides a competitive edge for blooming of phytoplankton species.     

Distribution of Diatoms Along Environmental Gradients in the Charlotte Harbor,Florida (USA), Estuary and Its Watershed: Implications for Bioassessment of Salinity and Nutrient Concentrations

The relative abundance of diatom species in different habitats can be used as a tool to infer prior environmental conditions and evaluate management decisions that influence habitat quality. Diatom distribution patterns were examined to characterize relationships between assemblage composition and environmental gradients in a subtropical estuarine watershed. We identified environmental correlates of diatom distribution patterns across the Charlotte Harbor, Florida, watershed; evaluated differences among three major river drainages; and determined how accurately local environmental conditions can be predicted using inference models based on diatom assemblages. Sampling locations ranged from freshwater to marine (0.1–37.2 ppt salinity) and spanned broad nutrient concentration gradients. Salinity was the predominant driver of difference among diatom assemblages across the watershed, but other environmental variables had stronger correlations with assemblages within the subregions of the three rivers and harbor. Eighteen indicator taxa were significantly affiliated with subregions. Relationships between diatom taxon distributions and salinity, distance from the harbor, total phosphorus (TP), and total nitrogen (TN) were evaluated to determine the utility of diatom assemblages to predict environmental values using a weighted averaging-regression approach. Diatom-based inferences of these variables were strong (salinity R ²?=?0.96; distance R ²?=?0.93; TN R ²?=?0.83; TP R ²?=?0.83). Diatom assemblages provide reliable estimates of environmental parameters on different spatial scales across the watershed. Because many coastal diatom taxa are ubiquitous, the diatom training sets provided here should enable diatom-based environmental reconstructions in subtropical estuaries that are being rapidly altered by land and water use changes and sea level rise.