Are seagrass beds indicators of anthropogenic nutrient stress in the rocky intertidal?

It is well established that anthropogenic nutrient inputs harm estuarine seagrasses, but the influence of nutrients in rocky intertidal ecosystems is less clear. In this study, we investigated the effect of anthropogenic nutrient loading on Phyllospadix spp., a rocky intertidal seagrass, at local and regional scales. At sites along California, Washington, and Oregon, we demonstrated a significant, negative correlation of urban development and Phyllospadix bed thickness. These results were echoed locally along an urban gradient on the central California coast, where Phyllospadix shoot δ¹⁵N was negatively associated with Phyllospadix bed thickness, and experimentally, where nutrient additions in mesocosms reduced Phyllospadix shoot formation and increased epiphytic cover on Phyllospadix shoots. These findings provide evidence that coastal development can threaten rocky intertidal seagrasses through increased epiphytism. Considering that seagrasses provide vital ecosystem services, mitigating eutrophication and other factors associated with development in the rocky intertidal coastal zone should be a management priority.     

The sea level at Port-aux-Français,Kerguelen Island,from 1949 to the present

Relative sea level rise at Kerguelen Island over the last 55 years has been investigated using a combination of historical and recent tide gauge data. The best estimate of relative sea level trend from data sets spanning 38 years is estimated to be 1.1±0.7 mm year^?1. We have tried to quantify the error budget due to some of the possible sources of uncertainty. As expected, the main source of uncertainty comes from oceanic interannual variability, preventing an accurate estimate of sea level trend over short record lengths. However, our values are reasonably consistent with other reported southern hemisphere sea level trends for similar time periods.     

Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?

We evaluated the alterations of organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) on the thyroid in wild and cultured sea bass (Dicentrarchus labrax) at environmental concentrations. These compounds influence the endocrine system of many fish species and are qualified as endocrine disruptors. The thyroid seems to be a target organ. Two alteration endpoints: the thyroid histology and the muscular thyroid hormone concentrations, were used simultaneously.High concentrations in PCBs and DDT were detected in muscles, supporting the idea that the Mediterranean fauna could be more polluted than the Atlantic fauna. The high abundance of DDE indicates a progressive degradation of remnant DDT load and the absence of new inputs in this area. Aquaculture sea bass shows a significant higher amount of pollutants on fresh weight basis (especially PCBs) in their muscles compared to the wild sea bass. Those differences may be related mainly to the contaminations of diet.Thyroid parameters vary between wild and aquaculture sea bass, wild sea bass were characterized by higher follicle diameters, epithelial cell heights and muscular T₄ concentrations. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T₄ levels) could be observed, which support the hypothesis that these compounds have an adverse impact on thyroid morphometry and function.     

Are marine plastic particles transport vectors for organic pollutants to the Arctic?

Plastic litter accounts for 50-80% of waste items stranded on beaches, floating on the ocean surface and lodged in the seabed. Organic pollutants can be absorbed onto plastic particles from sea water, attached to their surfaces or included in the plastic matrix as additives. Such chemicals may be transported to remote regions by buoyant plastics and ocean currents. We have estimated mass fluxes of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and perfluorooctanoic acid (PFOA) to the Arctic via the main ocean currents and compared them to those in the dissolved state and in air. Substance fluxes with atmospheric or sea water currents account for several tons per year, whereas those mediated by plastics are four to six orders of magnitude smaller. However, the significance of various pollutant transport routes does not depend only on absolute mass fluxes but also on bioaccumulation in marine food chains.     

Letter to the editor Are the North Atlantic Oscillation and the Southern Oscillation related in any time-scale?

The North Atlantic Oscillation (NAO) and the Southern Oscillation (SO) are compared from the standpoint of a possible common temporal scale of oscillation. To do this a cross-spectrum of the temporal series of NAO and SO indices was determined, finding a significant common oscillation of 6/8 years. To assure this finding, both series were decomposed in their main oscillations using singular spectrum analysis (SSA). Resulting reconstructed series of 6/8 years oscillation were then cross-correlated without and with pre-whitened, the latter being significant. The main conclusion is a possible relationship between a common oscillation of 6/8 years that represents about 20% of the SO variance and about 25% of the NAO variance.     

Are temporal variations in the nitrate content of UK upland freshwaters linked to the North Atlantic Oscillation?

Synchronous patterns of variation in NO₃ concentration, observed in upland lakes and streams across gradients of climate, altitude, land use and nitrogen deposition over the last decade, show a strong negative correlation with winter values for the North Atlantic Oscillation Index and mean winter temperature. Variations in a longer term stream NO₃ record validate this relationship, and although mechanisms are yet unclear, may be linked to the length of time the soil profile remains frozen during the winter. These findings are of particular significance to our understanding of the relationship between atmospheric N deposition and concentrations and fluxes of NO₃ in runoff, and the potential response to future climatic changes. Copyright © 2000 John Wiley & Sons, Ltd.     

Suspended sediment delivery from small catchments to the Bay of Biscay. What are the controlling factors?

The transport and yield of suspended sediment (SS) in catchments all over the world have long been topics of great interest. This paper addresses the scarcity of information on SS delivery and its environmental controls in small catchments, especially in the Atlantic region. Five steep catchments in Gipuzkoa (Basque Country) with areas between 56 and 796 km² that drain into the Bay of Biscay were continuously monitored for precipitation, discharge and suspended sediment concentration (SSC) in their outlets from 2006 to 2013. Environmental characteristics such as elevation, slope, land‐use, soil depth and erodibility of the lithology were also calculated. The analysis included consideration of uncertainties in the SSC calibration models in the final suspended sediment yield (SSY) estimations. The total delivery of sediments from the catchments into the Bay of Biscay and its standard deviation was 272 200 ± 38 107 t yr.^?1, or 151 ± 21 t km^?2 yr.^?1, and the SSYs ranged from 46 ± 0.48 to 217 ± 106 t km^?2 yr.^?1. Hydroclimatic variables and catchment areas do not explain the spatial variability found in SSY, whereas land‐use (especially non‐native plantations) and management (human impacts) appear to be the main factors that control this variability. Obtaining long‐term measurements on sediment delivery would allow for the effects of environmental and human induced changes on SS fluxes to be better detected. However, the data provided in this paper offer valuable and quantitative information that will enable decision‐makers to make more informed decisions on land management while considering the effects of the delivery of SS. Copyright © 2016 John Wiley & Sons, Ltd.     

Can tidal perturbations associated with sea level variations in the western Pacific Ocean be used to understand future effects of tidal evolution?

This study examines connections between mean sea level (MSL) variability and diurnal and semidiurnal tidal constituent variations at 17 open-ocean and 9 continental shelf tide gauges in the western tropical Pacific Ocean, a region showing anomalous rise in MSL over the last 20 years and strong interannual variability. Detrended MSL fluctuations are correlated with detrended tidal amplitude and phase fluctuations, defined as tidal anomaly trends (TATs), to quantify the response of tidal properties to MSL variation. About 20 significant amplitude and phase TATs are found for each of the two strongest tidal constituents, K₁ (diurnal) and M₂ (semidiurnal). Lesser constituents (O₁ and S₂) show trends at nearly half of all gauges. Fluctuations in MSL shift amplitudes and phases; both positive and negative responses occur. Changing overtides suggest that TATs are influenced by changing shallow water friction over the equatorial Western Pacific and the eastern coast of Australia (especially near the Great Barrier Reef). There is a strong connection between semidiurnal TATs at stations around the Solomon Islands and changes in thermocline depth, overtide generation, and the El Niño Southern Oscillation (ENSO). TATs for O₁, K₁, and M₂ are related to each other in a manner that suggests transfer of energy from M₂ to the two diurnals via resonant triad interactions; these cause major tidal variability on sub-decadal time scales, especially for M₂. The response of tides to MSL variability is not only spatially complex, it is frequency dependent; therefore, short-term responses may not predict long-term behavior.     

Is there an active subduction beneath the Gibraltar orogenic arc? Constraints from Pliocene to present-day stress field

We present a new set of brittle microtectonic measurements carried out in the Pliocene and Quaternary rocks outcropping in several key sectors of the western Betic and Rif orogen, the so-called Gibraltar orogenic arc. This data set, along with available earthquake focal mechanisms and borehole breakouts, allowed us to compile the Pliocene and Quaternary stress map of this area. This map provides new constraints for tectonic models and the present-day tectonic activity of the proposed active eastward subduction of oceanic lithosphere beneath the Gibraltar Arc and roll-back. The horizontal maximum compressive stress (S_Hmax) is NW-SE in the Betic Orogen and N-S/NNW-SSE in the southern Rif Cordillera. There is a significant consistency between S_Hmax and the displacement field deduced from GPS measurements with respect to the African plate: both appear to reflect the NW-SE convergence between the African and the European plates that is perturbed in the Rif. We propose that part of the eastern Rif behaves as a quasi-rigid block welded to the stable African plate. This block is bounded by important faults that localized most of the deformation disturbing the stress and surface displacement field. Pliocene to Quaternary N-S to NW-SE Africa-Europe plate convergence seem to be associated to the reorganization of the remnant Early Miocene subduction system in a continental–continental collision framework. Three-dimensional reconstruction of available seismic tomography plotted against the intermediate seismicity shows that only part of the old subduction system, whose orientation ranges from N20°E to N100°E, remains active: the portion ranging from N30°E to N40°E, orthogonal to the regional convergence.     

Is proximity to land-based sources of coral stressors an appropriate measure of risk to coral reefs? An example from the Florida Reef Tract

Localized declines in coral condition are commonly linked to land-based sources of stressors that influence gradients of water quality, and the distance to sources of stressors is commonly used as a proxy for predicting the vulnerability and future status of reef resources. In this study, we evaluated explicitly whether proximity to shore and connections to coastal bays, two measures of potential land-based sources of disturbance, influence coral community and population structure, and the abundance, distribution, and condition of corals within patch reefs of the Florida Reef Tract. In the Florida Keys, long-term monitoring has documented significant differences in water quality along a cross-shelf gradient. Inshore habitats exhibit higher levels of nutrients (DIN and TP), TOC, turbidity, and light attenuation, and these levels decrease with increasing distance from shore and connections to tidal bays. In clear contrast to these patterns of water quality, corals on inshore patch reefs exhibited significantly higher coral cover, higher growth rates, and lower partial mortality rates than those documented in similar offshore habitats. Coral recruitment rates did not differ between inshore and offshore habitats. Corals on patch reefs closest to shore had well-spread population structures numerically dominated by intermediate to large colonies, while offshore populations showed narrower size-distributions that become increasingly positively skewed. Differences in size-structure of coral populations were attributed to faster growth and lower rates of partial mortality at inshore habitats. While the underlying causes for the favorable condition of inshore coral communities are not yet known, we hypothesize that the ability of corals to shift their trophic mode under adverse environmental conditions may be partly responsible for the observed patterns, as shown in other reef systems. This study, based on data collected from a uniform reef habitat type and coral species with diverse life-history and stress-response patterns from a heavily exploited reef system, showed that proximity to potential sources of stressors may not always prove an adequate proxy for assigning potential risks to reef health, and that hypothesized patterns of coral cover, population size-structure, growth, and mortality are not always directly related to water quality gradients.     

To what extent have laterites contributed to the geochemical,surface reflectance and magnetic properties of adjacent tropical soils? Evidence from Niger and Burkina Faso

The present study is based on a suite of surface samples from exposures of eroded laterite, considered to be Tertiary in age, and nearby soils in the Sahelian region of SW Niger and Burkina Faso. X‐ray fluorescence, X‐ray diffraction, computer‐controlled scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, diffuse UV–visible reflectance spectroscopy and a suite of magnetic measurements have been used to shed light on the origin of the soils and their possible derivation from the adjacent, eroded laterite outcrops. On the basis of the wide range of data obtained, we conclude that the mineralogy and magnetic properties of the soils preclude direct derivation from the laterites without further weathering and modification. Nor does the evidence support the view that the soils have evolved entirely independently, uninfluenced by input from the laterites. The only conclusion that is consistent with all the lines of evidence is that the erosion of the laterites provided at least a significant part of the material upon which soil formation took place. This must have occurred at a time early enough to permit a long period of subsequent soil development during which the iron oxides, specifically haematite and ferrimagnetic minerals, were significantly modified. From this, we infer that eroded material from discontinuous laterite exposures has contributed significantly to the remotely sensed, distinctive reflectance characteristics of the Sahel surfaces. The magnetic properties of the soils provide evidence for the in situ neo‐formation of fine, secondary, pedogenic magnetite/maghemite grains typical of those found in many soils across the Sahel region and elsewhere in both temperate and tropical environments. Copyright © 2017 John Wiley & Sons, Ltd.     

Trends in annual discharge from the Yangtze River to the sea (1865–2004) / Tendances et épisodes extrêmes dans les débits annuels du Fleuve Yangtze débouchant dans la mer (1865–2004)

Abstract

Uninterrupted records of annual discharge from the Yangtze River to the sea (at Datong Hydrographical Station) began in the 1950s. This series shows no significant trend. However, at Hankou, a station upstream from Datong, annual discharges have been observed since 1865 almost without gaps. The annual discharges at Datong and Hankou were found to be closely correlated. Based on the regression equation, the missing annual discharges at Datong were estimated and a time series from 1865 to 2004 was established. Although the annual discharge has varied greatly, it shows a significant decreasing trend. The trendline revealed an 8.2% decrease from 1865 to 2004. The decrease in discharge was attributed to increases in water consumption and reservoir construction, while the interannual variations were related to climate variability. The decreasing trend in discharge is expected to continue in the coming decades due to human activities. This decreasing trend should be taken into account in the decision making on the South-to-North-Water Diversion projects.     

Imprudent fishing harvests and consequent trophic cascades on the West Florida shelf over the last half century: A harbinger of increased human deaths from paralytic shellfish poisoning along the southeastern United States, in response to oligotrophication?

Within the context of ubiquitous overfishing of piscivores, recent consequent increments of jellyfish and clupeids have occurred at the zooplanktivore trophic level in the eastern Gulf of Mexico (GOM), after overfishing of one of their predators, i.e. red snapper. Initiation of a local trophic cascade thence led to declines of herbivore stocks, documented here on the West Florida shelf. These exacerbating world-wide trophic cascades have resulted in larger harmful algal blooms (HABs), already present at the base of most coastal food webs. Impacts on human health have thus far been minimal within nutrient-rich coastal regions. To provide a setting for past morbidities, consideration is given to chronologies of other trophic cascades within eutrophic, cold water marine ecosystems of the Scotian Sea, in the Gulf of Alaska, off Southwest Africa, within the Barents, White, and Black Seas, in the Gulf of Maine, and finally in the North Sea. Next, comparison is now made here of recent ten-fold increments within Florida waters of both relatively benign and saxitoxic HABs, some of which are fatal to humans. These events are placed in a perspective of other warm shelf systems of the South China and Caribbean Seas to assess prior and possible future poison toxicities of oligotrophic coastal habitats. Past wide-spread kills of fishes and sea urchins over the Caribbean Sea and the downstream GOM are examined in relation to the potential transmission of dinoflagellate saxitoxin and other epizootic poison vectors by western boundary currents over larger “commons” than local embayments. Furthermore, since some HABs produce more potent saxitoxins upon nutrient depletion, recent decisions to ban seasonal fertilizer applications to Florida lawns may have unintended consequences. In the future, human-killing phytoplankton, rather than relatively benign fish-killing HABs of the past, may be dispersed along the southeastern United States seaboard.