Effects of freshwater inputs on the lower trophic levels of a temperate estuary: physical, physiological or trophic forcing?

The aim of this 6?year study was to assess whether freshwater inputs (rainfall and dam discharges) were acting as physical, physiological or trophic forcing factors on phytoplankton pigment concentrations and the dominant mysids of a temperate estuary (Guadalquivir estuary; SW, Spain). The effects of natural and human-controlled freshwater inputs modified the physico-chemical conditions and consequently biological production (bottom up control). Nutrient (nitrogen hypernutrification), suspended particulate matter and allochthonous photosynthetic pigment imports linked to freshwater inputs from adjacent habitats were observed, as well as light-limited autochthonous primary production. Seasonal and/or spatial patterns were shown by all study variables, including mysids. Freshwater management effects on dominant mysids differed depending on the species?? salinity tolerance (physiological forcing) and preferred prey availability (trophic forcing). Moreover, high inorganic matter content had a negative effect on the density of Mesopodopsis slabberi (physical forcing), which led to an increased detritivory/herbivory ratio (Neomysis integer/M. slabberi ratio). In conclusion, freshwater inputs appeared to effect estuarine lower trophic levels via a combination of different forcing mechanisms. Although several general patterns can be derived, the response of the system to freshwater inputs was not always univocal.     

Comparison of metal accumulation in the azooxanthellate scleractinian coral (Tubastraea coccinea) from different polluted environments

The response of metal accumulation in coral Tubastraea coccinea to various degrees of metal enrichment was investigated from the Yin-Yang Sea (YYS) receiving abandoned mining effluents, the Kueishan Islet (KI) hydrothermal vent field, and the nearshore area of remoted Green Island (GI). The concentrations of most dissolved metals were highest in seawater at YYS, followed by KI, and then GI, showing the effects of anthropogenic and venting inputs on metal levels. Five metals (Co, Fe, Mn, Ni, and Zn) yielded significant differences (p < 0.05) among the skeleton samples. We identified similar patterns in the metal–Ca ratios, indicating that the elevated metals in skeletons was a consequence of external inputs. The coral tissues were relatively sensitive in monitoring metal accumulation, showing significant differences among three locations for Cd, Co, Cu, Fe, Pb, Ni, and Zn. Specific bioconcentration factors provided strong support for the differential metal accumulation in skeletons and tissues.     

Aerial flux of particulate hydrocarbons to the Chesapeake Bay Estuary

Bulk hydrocarbon deposition rates have been measured over a 15 month period at four stations in south-eastern Virginia surrounding the lower Chesapeake Bay. A nearly linear trend of atmospheric particulate deposition was recorded. Deposition rates at the urban station (195 μg m^?2 day^?1) were aproximately three times greater than those recorded for nonurban and coastal locations (mean value 69 μg m^?2 day^?1). The increased levels at the urban location were attributed to localized source inputs. Anthropogenic hydrocarbons accounted for approximately 50% of the total deposition at all stations. Significant biogenic inputs were indicated by the odd/even n-alkane distribution. A minimum flux to the water surface, based on mean nonurban deposition rates (24 mg yr^?1), indicated an annual particulate hydrocarbon flux of +275 metric tons. Little information is available for the comparison of additional source inputs; however, the data reported here indicate that the aerial deposition of hydrocarbons is of the same order of magnitude as the input from municipal wastewater facilities and accidental discharge and is a potentially significant source of hydrocarbon pollution to the Chesapeake Bay Estuary.     

Modelling the spatial and temporal variability of the SW lagoon of New Caledonia II: Realistic 3D simulations compared with in situ data

Coral reef lagoons are under the growing influence of anthropogenic activities, leading to increasing loads of nutrients and various contaminants. Modelling approaches are a useful tool for studying such a complex coastal environment. In this study, we carried out the development of a three-dimensional coupled hydrodynamical-biogeochemical model of the south-west lagoon of New Caledonia. The biogeochemical model presented in Faure et al., 2006, Faure et al., 2010 was dynamically coupled with a hydrodynamical model (MARS3D) in order to study the short-term variability of the ecosystem. Two simulations (in winter and summer) were then performed from measured initial conditions using realistic wind and irradiance conditions and river inputs. Examinations of the biogeochemical response to these transient meteorological conditions were presented and compared with temporal field data corresponding to the considered periods. Results highlighted the ecosystem functioning, based on the balance of hydrodynamical and biogeochemical processes. Influence of urban and terrigeneous inputs were limited to the coastal zone. The model accurately reproduced the measured Chl.a and bacterial production, highlighting the improvement made on the biogeochemical model. However, the underestimation of some variables in model outputs, in particular nutrients, led us to focus on different inputs, such as sediment inputs which were not taken into account or properly estimated. Moreover, the role of boundary waters appeared crucial and suggested a calibration effort. Last, the final aim of our modelling study will help the development of a useful tool for studying the key processes of the ecosystem of the south-west lagoon of New Caledonia, as well as the examination of the biogeochemical response under different scenarios.     

Assessment of the distribution and risks of organochlorine pesticides in core sediments from areas of different human activity on Lake Baiyangdian,China

Burial characteristics and risks associated with 13 organochlorine pesticides (OCPs; α-HCH, β-HCH, γ-HCH, δ-HCH, p,p′-DDE, p,p′-DDD, p,p′-DDT, heptachlor, aldrin, dieldrin, endrin, α-endosulfan and β-endosulfan) in core sediments of Lake Baiyangdian were investigated. The core sediments were taken from areas of different anthropogenic activity along the lake. Concentrations of hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT), heptachlor, aldrin, and endosulfan ranged from 0.64 to 2.72, nd (undetectable levels) to 2.79, 0.29 to 1.37, nd to 2.62, and nd to 1.76 ng g^?1, respectively. Concentrations of OCPs in the core sediments exhibited the following spatial trend: Dongtianzhuang > Shaochedian > Zaolinzhuang. Concentrations in the surficial layer were also found to be greater than those in the bottom layer. OCPs were dominated by HCH. β-HCH was found in the greatest concentrations, indicating that the majority of HCH came from older inputs to the area. The ratio of DDT and its metabolites (DDD and DDE) also suggested a lack of recent inputs to the lake environment. The residues of heptachlor, aldrin, and endosulfan in core sediments indicated that cyclodienes were historically applied in the area. The OCP risk assessment, which was based on effect range low and threshold effect level values, suggested that the top layer of sediment in Dongtianzhuang cores had a relatively high toxicity to human health and the environment.     

Modelling the relative impact of rivers (Scheldt/Rhine/Seine) and Western Channel waters on the nutrient and diatoms/Phaeocystis distributions in Belgian waters (Southern North Sea)

The coastal areas of the Southern North Sea (SNS) experience eutrophication problems resulting from freshwater nitrogen (N) and phosphorus (P) inputs from rivers. In particular, massive blooms of Phaeocystis colonies occur in Belgian waters. In this region, water masses result from the mixing of Western Channel (WCH) waters transported through the Straits of Dover with nutrient-rich freshwater from the Scheldt, the Rhine and Meuse, the Seine, the Thames and other smaller rivers. However, the relative contribution of the WCH and each river to the inorganic nutrient pool and the impact on the phytoplankton community structure (diatoms and Phaeocystis) are not known. In order to effectively manage the eutrophication problems, it is necessary to know: (i) the relative contribution of the WCH and of each river impacting the region and (ii) the relative effect of a N and/or P nutrient reduction on the Phaeocystis blooms. To answer these questions, sensitivity tests (1% nutrient reduction) and nutrient reduction scenarios (50% nutrient reduction) have been performed with a three-dimensional (3D) coupled physical–biogeochemical model (MIRO&CO-3D).MIRO&CO-3D results from the coupling of the COHERENS 3D hydrodynamic model with the ecological model MIRO. The model has been set up for the region between 48.5°N, 4°W and 52.5°N, 4.5°E and run to simulate the annual cycle of carbon, inorganic and organic nutrients, phytoplankton (diatoms and Phaeocystis), bacteria and zooplankton (microzooplankton and copepods) in the SNS under realistic forcing (meteorology and river inputs) for the period 1991–2003. The relative contribution of the WCH waters and of the different rivers on the inorganic nutrient pool available for phytoplankton (diatoms and Phaeocystis) growth is assessed by decreasing by 1% the nutrient (dissolved inorganic nitrogen, DIN and inorganic phosphate, PO₄) inputs from the WCH and from, respectively, the Scheldt (and smaller Belgian rivers), the Rhine/Meuse and the Seine (and smaller French rivers) [sensitivity tests]. The relative role of N and P reduction on the diatoms/Phaeocystis distribution is further explored by simulations with 50% reduction of the total (inorganic and organic) N and total P river inputs [nutrient reduction scenarios]. These scenarios allow assessing the impact of the expected 50% reduction of river nutrient inputs resulting from the implementation of nutrient reduction policy.Results of the sensitivity tests suggest that the impact of a 1% reduction of river nutrient inputs on surface nutrients (DIN and PO₄) over the Belgian Exclusive Economic Zone (EEZ) area is similar for the Seine and the Scheldt, which are in turn greater than for the Rhine. However, a hypothetical 1% reduction of nutrient input from the WCH boundary would have a higher impact than for the Scheldt. The impact of nutrient reduction is higher for DIN than for PO₄ whatever the river (contrary to the WCH). DIN is more sensitive to riverine nutrient reduction because the rivers are over enriched in DIN compared to PO₄. The sensitivity tests suggest also that a PO₄ river input reduction would result in a N:P increase and a DIN river input reduction would result in a N:P decrease but that a combined (PO₄ and DIN) input reduction would reduce the N:P ratio at sea.From 50% nutrient reduction scenarios, model results suggest that a total P reduction would induce a significant decrease of diatoms and a small (coast) to negligible (offshore) decrease of Phaeocystis biomass. On the contrary, a total N reduction would induce a significant decrease of Phaeocystis biomass and a moderate increase of diatoms. When N and P river input reductions are combined, the model predicts a significant decrease of Phaeocystis biomass in Belgian waters and a significant decrease of diatom biomass in the coastal waters and a small increase offshore. A future management plan aiming at Phaeocystis reduction should thus prioritise N reduction.     

Uptake and resource allocation of ammonium and nitrate in temperate seagrasses Posidonia and Amphibolis

Ecologically relevant estimates of seasonal variability in nitrogen uptake and allocation in two species of temperate seagrasses were obtained using in situ isotope-labelling approach. Significantly higher uptake rates of ammonium by leaves, roots and epiphytes of Amphibolis than Posidonia were observed. Overall, root uptake rates were lower than other components. Effect of season was not significant for leaves, roots or epiphytes of the two species. However, plankton uptake varied seasonally with higher rates in winter (0.98 mg N g⁻¹ DW h⁻¹). In contrast, nitrate uptake rates for various components were significantly affected by seasons. Uptake rates by plankton were highest ranging from 0.003 mg N g⁻¹ DW h⁻¹ (summer, Amphibolis) to 0.69 mg N g⁻¹ DW h⁻¹ (winter, Posidonia). Uptake of nitrate by roots was negligible. Biotic uptake rates for nitrate were an order of magnitude slower than ammonium, demonstrating an affinity for ammonium over nitrate as a preferred inorganic nitrogen source. Adelaide coastal waters have lost over 5000 ha of seagrasses, much of this attributed to nutrient inputs from wastewater, industrial and stormwater. Managing these inputs into future requires better understanding of the fate of nutrients, particularly biological uptake. This study attempts to quantify uptake rates of nitrogen by seagrasses.     

Input variable selection for water resources systems using a modified minimum redundancy maximum relevance (mMRMR) algorithm

Input variable selection (IVS) is a necessary step in modeling water resources systems. Neglecting this step may lead to unnecessary model complexity and reduced model accuracy. In this paper, we apply the minimum redundancy maximum relevance (MRMR) algorithm to identifying the most relevant set of inputs in modeling a water resources system. We further introduce two modified versions of the MRMR algorithm (α-MRMR and β-MRMR), where α and β are correction factors that are found to increase and decrease as a power-law function, respectively, with the progress of the input selection algorithms and the increase of the number of selected input variables. We apply the proposed algorithms to 22 reservoirs in California to predict daily releases based on a set from a 121 potential input variables. Results indicate that the two proposed algorithms are good measures of model inputs as reflected in enhanced model performance. The α-MRMR and β-MRMR values exhibit strong negative correlation to model performance as depicted in lower root-mean-square-error (RMSE) values.     

Organic sources and carbon sequestration in Holocene shelf sediments from the western Arctic Ocean

To quantify changes in organic carbon inputs and preservation, sediments from the Northern Chukchi Sea spanning the last 9000 years of the Holocene period were collected during the HOTRAX expedition and analyzed. The multi-proxy approach included molecular organic markers, bulk carbon and isotope measurements plus more recent approaches to terrestrial carbon estimation (the BIT index of Branched and Isoprenoid Tetraethers). The upper 1100 cm of the core, corresponding to the last 7.4 ka, showed a relatively stable total organic carbon content of 1.13-1.38% which decreased below 1100 cm to 0.6%. C:N ratios ranged from 8.4 to 10.83 over the Holocene time period examined. The distribution of n-alcohols and n-alkanes revealed major contributions from long-chain n-alcohols and n-alkanes while minimal contributions were seen from short-chain n-alkanes. The majority of the total fatty acids was comprised of saturated and monounsaturated fatty acids with short-chain and long-chain saturated fatty acids present in similar concentrations throughout most of the core and monounsaturated fatty acids decreasing down-core. Total sterol concentrations showed considerable inputs from marine sterols, C₂₈Δ^5,22, C₂₈Δ^5,24(28) and dinosterol, as well as C₂₉Δ⁵, typically considered a terrestrial marker. The BIT indices for core sediments ranged from 0.021 to 0.216 with minor changes seen in older sequences. Overall, organic biomarkers indicate marine sources as the more dominant input of organic matter with lower but continual contributions from terrestrial sources at this location during the Holocene. The remarkable consistency among multiple molecular organic markers of both marine and terrestrial origin over the Holocene period encompassed by the core suggests that sinking material or surface sediments were heavily influenced by bottom currents or other mixing processes prior to their deposition.     

Tracing sewage and natural freshwater input in a Northwest Mediterranean bay: Evidence obtained from isotopic ratios in marine organisms

Elemental carbon and nitrogen levels and isotope ratios were assessed in different biological compartments of a Northwest (NW) Mediterranean bay to trace the various sources of nutrient input from natural (river runoffs) and anthropogenic (harbor outflows, fish farms and urban sewage outfall) sources. Samples from transplanted mussels and natural sea grass communities (Posidonia oceanica leaves and epiphytes) were harvested from different locations throughout the bay during the touristic summer and rainy seasons. The results from the nitrogen analysis revealed that sewage and harbor outflow promote higher nitrogen levels, enrichment of ¹⁵N in the tissues, and a higher seasonal variability in sea grass and epiphytes. In mussel tissues, the δ¹⁵N was also influenced by sewage and harbor outflow, whereas δ¹³C was influenced by terrestrial inputs. These results suggest that natural and anthropogenic nutrient inputs have a temporary and localized influence and affect the sensitivity of natural isotopic ratios to changes in hydrologic conditions, especially to rain and tourism.     

Distribution of the surface partial pressure of CO2 in the southern Yellow Sea and its controls

Surface partial pressure of CO₂ (pCO₂), dissolved inorganic carbon (DIC), temperature, salinity and chlorophyll a (Chl a) at grid stations were measured in the southern Yellow Sea (SYS; 32–37°N to 120–125°E) during four cruises conducted in March 2005 (winter), April 2006 (spring), May 2005 (late spring), and July 2001 (summer). Factors influencing pCO₂ spatial and seasonal variations are explored.Surface seawater pCO₂ during winter was oversaturated with respect to the atmosphere in the entire study area (380–606 μatm), primarily due to the complete mixing of the water column in winter which brought CO₂-enriched bottom water to the surface. However, during spring, surface pCO₂ in the central SYS was undersaturated relative to the atmosphere with a low range between 274 and 408 μatm. The net CO₂ sink in the central SYS was mainly due to the consumption of CO₂ by the strong phytoplankton activity and to the weak water stratification, whereas surface pCO₂ in the nearshore area was oversaturated for the atmosphere owing to vertical mixing and terrestrial inputs. During summer, surface pCO₂ varied between 125 and 599 μatm over the entire sampling area. In the Changjiang (Yangtze River) Diluted Water (CDW) area, surface pCO₂ was undersaturated because of the nutrient inputs via the Changjiang, triggering strong phytoplankton activity, whereas surface pCO₂ was oversaturated in other areas. We conclude that the nearshore area behaves as a source of atmospheric CO₂ during the entire investigated periods owing to vertical mixing and terrestrial inputs as well as upwelling, whereas the central region generally shifts from a source of CO₂ in March to a sink in the remaining time of the investigation.     

Link between sewage-derived nitrogen pollution and coral disease severity in Guam

The goals of this study were to evaluate the contribution of sewage-derived N to reef flat communities in Guam and to assess the impact of N inputs on coral disease. We used stable isotope analysis of macroalgae and a soft coral, sampled bimonthly, as a proxy for N dynamics, and surveyed Porites spp., a dominant coral taxon on Guam’s reefs, for white syndrome disease severity. Results showed a strong influence of sewage-derived N in nearshore waters, with δ¹⁵N values varying as a function of species sampled, site, and sampling date. Increases in sewage-derived N correlated significantly with increases in the severity of disease among Porites spp., with δ¹⁵N values accounting for more than 48% of the variation in changes in disease severity. The anticipated military realignment and related population increase in Guam are expected to lead to increased white syndrome infections and other coral diseases.     

Driving the high-latitude ionosphere with variable time resolution “K-like” geomagnetic indices

The 3-h K_p index is widely used as a measure of geomagnetic activity for ionospheric studies. Specifically, it is the planetary index used to determine the geomagnetic dependence of statistical auroral patterns and the convection electric field for certain models. Its quasi anti-logarithm, the A_p index, is similarly used in statistical models of the neutral atmosphere and neutral wind. Physics-based ionospheric models, such as the Utah State University (USU) Time-Dependent Ionospheric Model (TDIM), use these statistical models as magnetospheric and thermospheric inputs. However, the 3-h time interval between index computations is now considered a shortfall with regard to specifying and forecasting phenomena known to have faster time constants, e.g., auroral electrojet variations during a substorm. Therefore, these indices have been targeted for high-time resolution development; we have developed such indices in Della-Rose et al. (1999). We now use our 15-minute station “K-like” index to determine the effect of introducing high-time resolution magnetic fluctuations into the TDIM inputs. This study represented the high-latitude ionosphere by a grid of 1484 locations, and was carried out for a geomagnetic storm period during solar maximum and “simulated” winter solstice conditions. We found that, for fixed Interplanetary Magnetic Field (IMF) B_y/B_z ratio, driving the TDIM with our 15-minute “K-like” index altered the average high-latitude N_mF₂ value by as much as 8% (vs. the average N_mF₂ obtained using a 3-h index to drive the TDIM). More significantly, the standard deviation of the N_mF₂ variations was up to 35%. Under some conditions, the average N_mF₂ was changed by up to 30% with a standard deviation of over 60%. However, the effect of selecting different convection patterns that represented three southward IMF B_z orientations led to larger effects. The high-latitude average N_mF₂ changed by 10% or less, but the spread in the distribution always ranged from standard deviations of 29 to 68%. These results indicate that there is a substantial need to consider both short-term magnetic fluctuations and inclusion of real-time IMF data in the inputs to ionospheric models.     

Bias and uncertainty in regression-calibrated models of groundwater flow in heterogeneous media

Groundwater models need to account for detailed but generally unknown spatial variability (heterogeneity) of the hydrogeologic model inputs. To address this problem we replace the large, m-dimensional stochastic vector β that reflects both small and large scales of heterogeneity in the inputs by a lumped or smoothed m-dimensional approximation γθ_∗, where γ is an interpolation matrix and θ_∗ is a stochastic vector of parameters. Vector θ_∗ has small enough dimension to allow its estimation with the available data. The consequence of the replacement is that model function f(γθ_∗) written in terms of the approximate inputs is in error with respect to the same model function written in terms of β, f(β), which is assumed to be nearly exact. The difference f(β) − f(γθ_∗), termed model error, is spatially correlated, generates prediction biases, and causes standard confidence and prediction intervals to be too small. Model error is accounted for in the weighted nonlinear regression methodology developed to estimate θ_∗ and assess model uncertainties by incorporating the second-moment matrix of the model errors into the weight matrix. Techniques developed by statisticians to analyze classical nonlinear regression methods are extended to analyze the revised method. The analysis develops analytical expressions for bias terms reflecting the interaction of model nonlinearity and model error, for correction factors needed to adjust the sizes of confidence and prediction intervals for this interaction, and for correction factors needed to adjust the sizes of confidence and prediction intervals for possible use of a diagonal weight matrix in place of the correct one. If terms expressing the degree of intrinsic nonlinearity for f(β) and f(γθ_∗) are small, then most of the biases are small and the correction factors are reduced in magnitude. Biases, correction factors, and confidence and prediction intervals were obtained for a test problem for which model error is large to test robustness of the methodology. Numerical results conform with the theoretical analysis.     

Comparison of C and N stable isotope ratios between surface particulate organic matter and microphytoplankton in the Gulf of Lions (NW Mediterranean)

Carbon and nitrogen stable isotope ratios of particulate organic matter (POM) in surface water and 63–200 μm-sized microphytoplankton collected at the fluorescence maximum were studied in four sites in the Gulf of Lions (NW Mediterranean), a marine area influenced by the Rhone River inputs, in May and November 2004. Some environmental (temperature, salinity) and biological (POM, Chlorophyll a and phaeopigments contents, phytoplankton biomass and composition) parameters were also analysed. Significantly different C and N isotopic signatures between surface water POM and microphytoplankton were recorded in all sites and seasons. Surface water POM presented systematically lower δ¹³C (∼4.2‰) and higher δ¹⁵N (∼2.8‰) values than those of microphytoplankton, due to a higher content of continental and detrital material. Seasonal variations were observed for all environmental and biological parameters, except salinity. Water temperature was lower in May than in November, the fluorescence maximum was located deeper and the Chlorophyll a content and the phytoplankton biomass were higher, along with low PON/Chl a ratio, corresponding to spring bloom conditions. At all sites and seasons, diatoms dominated the phytoplankton community in abundance, whereas dinoflagellate importance increased in autumn particularly in coastal sites. C and N isotopic signatures of phytoplankton did not vary with season. However, the δ¹⁵N of surface water POM was significantly higher in November than in May in all sites likely in relation to an increase in ¹⁵N/¹⁴N ratio of the Rhone River POM which influenced surface water in the Gulf of Lions. As it is important to determine true baseline values of primary producers for analysing marine food webs, this study demonstrated that C and N isotopic values of surface water POM cannot be used as phytoplankton proxy in coastal areas submitted to high river inputs.     

Relationship between dynamics of litterfall and riparian plant species in a tropical stream

We investigated the dynamics of organic matter and type of detritus in a riparian zone of the Atlantic Rain Forest domain, and specifically determined the inputs and stock of detritus contributed by plant species, and their relationship to temperature and precipitation. Our hypotheses tested were: (1) the species composition of riparian vegetation influences the amount and type of detritus delivered to a stream in an Atlantic Rain Forest, and (2) the dynamics of litterfall in the riparian zone is influenced by climate factors. The plant community was formed principally by pioneer and early successional species such as Apuleia leiocarpa, Erytrina velutina, Erytrina verna, Eucalyptus torelliana, Ficus glabra, Ficus insipida, Guarea guidonea, Guarea guidonia, Maprounea guianensis and Psidium guajava. There was a large number of G. guidonea (318 individuals/ha), followed by Cupania oblongifolia (91), Trichilia pallida (52), Piptadenia gonoacantha (26) and E. torelliana (14). G. guidonea contributed >50% of the total litterfall; however, some species which were present in high density in the plant community and did not yield significant biomass, indicating that detritus production was based on the contribution of a few species. We found 697, 856 and 804 g/m²/year from vertical, terrestrial, and lateral inputs, respectively, whereas to the annual benthic standing stock was 3257 g/m². Detritus was formed by leaves (60%), branches (32%), reproductive parts (3%), and unidentifiable fragments of organic-matter (5%). Inputs and benthic stock were markedly seasonal, with an increase of leaf litter during the dry season. Our results indicate that litterfall dynamics is basically composed of a few species that contribute with higher values of biomass. Moreover, ecological characteristics together with environmental factors can be viewed as the principal factors determining the energy balance of riparian ecosystems. The biological implications of the dynamics of organic matter have high importance for the maintenance and restoration of riparian zones. However, the amount of litterfall required to maintain the balance of the riparian community remains unclear in the tropical zone.     

Determination of Q β(f) in Different Parts of Kumaon Himalaya from the Inversion of Spectral Acceleration Data

This paper presents the results of a modified two-step inversion algorithm approach to find S wave quality factor Q _β(f) given by Joshi (Bull Seis Soc Am 96:2165–2180, 2006). Seismic moment is calculated from the source displacement spectra of the S wave using both horizontal components. Average value of seismic moment computed from two horizontal components recorded at several stations is used as an input to the first part of inversion together with the spectra of S phase in the acceleration record. Several values of the corner frequency have been selected iteratively and are used as inputs to the inversion algorithm. Solution corresponding to minimum root mean square error (RMSE) is used for obtaining the final estimate of Q _β(f) relation. The estimates of seismic moment, corner frequency and Q _β(f) from the first part of inversion are further used for obtaining the residual of theoretical and observed source spectra which are treated as site amplification terms. The acceleration record corrected for the site amplification term is used for determination of seismic moment from source spectra by using Q _β(f) obtained from first part of inversion. Corrected acceleration record and new estimate of seismic moment are used as inputs to the second part of the inversion scheme which is similar to the first part except for use of input data. The final outcome from this part of inversion is a new Q _β(f) relation together with known values of seismic moment and corner frequency of each input. The process of two-step inversion is repeated for this new estimate of seismic moment and goes on until minimum RMSE is obtained which gives final estimate of Q _β(f) at each station and corner frequency of input events. The Pithoragarh district in the state of Uttarakhand in India lies in the border region of India and Nepal and is part of the seismically active Kumaon Himalaya zone. A network of eight strong motion recorders has been installed in this region since March, 2006. In this study we have analyzed data from 18 local events recorded between March, 2006 and October, 2010 at various stations. These events have been located using HYPO71 and data has been used to obtain frequency-dependent shear-wave attenuation. The Q _β(f) at each station is calculated by using both the north-south (NS) and east-west (EW) components of acceleration records as inputs to the developed inversion algorithm. The average Q _β(f) values obtained from Q _β(f) values at different stations from both NS and EW components have been used to compute a regional average relationship for the Pithoragarh region of Kumaon Himalaya of form Q _β(f)?=?(29?±?1.2)f ^{(1.1 ± 0.06)}.     

A climatic dataset of ocean vertical turbulent mixing coefficient based on real energy sources

Using data on wind stress, significant height of combined wind waves and swell, potential temperature, salinity and seawater velocity, as well as objectively-analyzed in situ temperature and salinity, we established a global ocean dataset of calculated wind- and tide-induced vertical turbulent mixing coefficients. We then examined energy conservation of ocean vertical mixing from the point of view of ocean wind energy inputs, gravitational potential energy change due to mixing (with and without artificially limiting themixing coefficient), and K-theory vertical turbulent parameterization schemes regardless of energy inputs. Our research showed that calculating the mixing coefficient with average data and artificial limiting the mixing coefficient can cause a remarkable lack of energy conservation, with energy losses of up to 90% and changes in the energy oscillation period. The data also show that wind can introduce a huge amount of energy into the upper layers of the Southern Ocean, and that tidesdo so in regions around underwater mountains. We argue that it is necessary to take wind and tidal energy inputs into account forlong-term ocean climate numerical simulations. We believe that using this ocean vertical turbulent mixing coefficient climatic dataset is a fast and efficient method to maintain the ocean energy balance in ocean modeling research.     

What factors drive seasonal variation of phytoplankton,protozoans and metazoans on leaves of Posidonia oceanica and in the water column along the coast of the Kerkennah Islands,Tunisia?

A hierarchical sampling design was used during two seasons (spring (May) and summer (August) 2006). Using this design, three regions of the Kerkennah Islands (Tunisia) were analyzed for the distribution of microalgal, protozoan and metazoan assemblages in two different habitats: (1) the water column; and (2) on Posidonia oceanica (L.) Delile (P. oceanica) leaves in shallow meadows. A total of 85 species were obtained. In particular, the diatom family Naviculacea consistently dominated (both numerically and in their diversity) the micro-algae in all regions for the two seasons of the study and in both habitats. In the Chergui region, which is the closest area to a source of impact, fast growing centric diatoms (such as Thalassionema, Rhizosolenia, Striatella, and Skeletonema) were identified as indicators of high organic matter and nutrient enrichment in water bodies. Protozoan and metazoan species abundance in the different regions indicate a non-random spatial and temporal distribution of the epiphytic organisms on leaves of P. oceanica that correlated with phytoplankton. The results also indicate that (1) the abundance of micro- and macroorganisms in the three regions were higher on P. oceanica leaves than in the water column for the two seasons; (2) environmental factors such as currents and tide influenced assemblages; and (3) the highest abundance was due to direct exposure to the polluted coast of Sfax and the effect of tidal asymmetries generating nutrient-rich inputs from the city.