An optimized method for automated analysis of algal pigments by HPLC

A recent development in algal pigment analysis by high-performance liquid chromatography (HPLC) is the application of automation. An optimization of a complete sampling and analysis protocol applied specifically in automation has not yet been performed. In this paper we show that automation can only be successful if the various methodological aspects of the sampling and analysis protocol are considered in coherence. We introduce an optimized protocol that involves freeze-drying of the sample, subsequent extraction in 90% acetone and the application of water-packing during analysis. The method was evaluated on both natural plankton populations and a broad spectrum of microalgal cultures: Thalassiosira weisflogii (Bacillariophyceae), Emiliania huxleyi (Prymnesiophyceae), Phaeocystis globosa and Phaeocystis antarctica (Prymnesiophyceae) and Pyramimonas sp. (Prasinophyceae). Whereas pigment extracts were unstable in methanol, with recorded chlorophyll a losses from 10% to 60% per day, pigment degradation rates in acetone were generally less than 1% over 18 h storage in the autosampler (4 °C). In addition, it was found that the extraction efficiency of acetone significantly increased upon freeze-drying prior to extraction. Increases as high as 50–60% were measured in P. antarctica. The application of water-packing of the sample during injection resulted in improved peak shape and peak separation, without diluting the pigment concentrations. Automation is especially beneficial for application in the field, when mixed algal assemblages and low biomass put a high demand on the sensitivity as well as reproducibility of the method.     

The effect of multiple stressors on salt marsh end-of-season biomass

It is becoming more apparent that commonly used statistical methods (e.g. analysis of variance and regression) are not the best methods for estimating limiting relationships or stressor effects. A major challenge of estimating the effects associated with a measured subset of limiting factors is to account for the effects of unmeasured factors in an ecologically realistic matter. We used quantile regression to elucidate multiple stressor effects on end-of-season biomass data from two salt marsh sites in coastal Louisiana collected for 18 yr. Stressor effects evaluated based on available data were flooding, salinity air temperature, cloud cover, precipitation deficit, grazing by muskrat, and surface water nitrogen and phosphorus. Precipitation deficit combined with surface water nitrogen provided the best two-parameter model to explain variation in the peak biomass with different slopes and intercepts for the two study sites. Precipitation deficit, cloud cover, and temperature were significantly correlated with each other. Surface water nitrogen was significantly correlated with surface water phosphorus and muskrat density. The site with the larger duration of flooding showed reduced peak biomass, when cloud cover and surface water nitrogen were optimal. Variation in the relatively low salinity occurring in our study area did not explain any of the variation inSpartina alterniflora biomass.     

Researching the South African tourism and development nexus

Under apartheid, tourism was essentially anti-developmental in focus and tourism research largely centred on the recreation of white South Africans. Since the 1994 democratic transition tourism has become recognised as an increasingly important sector for South Africa's economy and for achieving the government's goals for reconstruction and development. In this paper a review and critical analysis is presented of the changing directions and foci of tourism scholarship in South Africa. It is shown that South African scholars are beginning to respond to the challenges posed by tourism as a developmental focus. This revised version was published online in August 2006 with corrections to the Cover Date.     

From economic integration to socioeconomic inclusion: day labor worker centers as social intermediaries

Day labor worker centers have emerged as an important mode of regulatory action in the informal economy of major US cities. Research suggests that these organizations are beneficial in improving employment outcomes experienced by migrant workers engaged in this labor market sector. Yet, the extent to which these organizations impact the social integration of this working population remains relatively undeveloped in the literature. Using data from the National Day Labor Survey, we examine the impact of day labor worker centers on the level of social inclusion experienced by migrant day laborers. We find that worker centers have a modest, but statistically significant, impact on the levels of social integration experienced by this working population and that this varies from city to city. Ultimately we argue that the social intermediary role of these organizations may offer a type of counter mobilization necessary to promote the socioeconomic integration of this working population, but that issues of capacity remain.     

Identifying Key Sources of Uncertainty in Climate Change Projections

What sources of uncertainty shouldbe included in climate change projections and whatgains can be made if specific sources of uncertaintyare reduced through improved research?DIALOGUE, anintegrated assessment model, has been used to answerthese questions. Central in the approach of DIALOGUEis the concept of parallel modeling, i.e., for eachstep in the chain from emissions to climate change anumber of equivalent models areimplemented. The followingconclusions are drawn:The key source of uncertainty in global temperatureprojections appears to be the uncertainty inradiative forcing models. Within this group ofmodels uncertainty within aerosol forcing models isabout equal to the total forcing of greenhouse gasmodels. In the latter group CO₂ is dominant.The least important source of uncertainty appears tobe the gas cycle models. Within this group of modelsthe role of carbon cycle models is dominant.Uncertainty in global temperature projections hasnot been treated consistently in the literature.First, uncertainty should be calculated as a productof all uncertainty sources. Second, aparticular choice of a base year for global warmingcalculations influences the ranking of uncertainty.Because of this, a comparison of ranking resultsacross different studies is hampered. We argue that`pre-Industrial' is the best choice for studies onuncertainty.There is a linear relationship between maximumuncertainty in the year 2100 and cumulativeemissions of CO₂ over the period 1990–2100:higher emissions lead to more uncertainty.     

Northwest Africa 11024—A heated and dehydrated unique carbonaceous (CM) chondrite

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.     

The impact of vertebrate herbivores on wetland vegetation in Atchafalaya Bay, Louisiana

Delta islands in the Atchafalaya and Wax Lake deltas in Atchafalaya Bay, Louisiana, are in an extremely dynamic successional phase. These islands initially supported large marshes dominated by the pioneering plant species Sagittaria latifolia and Sagittaria platyphylla. A general decrease in vegetated areas has occurred in the delta island marshes in the Atchafalaya Delta since about 1980, while in the Wax Lake Delta portion of the complex the vegetation still flourished. The Atchafalaya Delta provides an interesting setting for the study of herbivory because of the complex interaction of biotic and physical factors operating in this delta. We hypothesized that grazing by herbivores has a marked effect on vegetation in these developing marshes. To test this hypothesis, exclosures were erected on islands in both deltas in September 1985 and January 1986. Each set of exclosure treatments included an openly-grazed control area, an ungrazed area, an area allowing nutria grazing, and one allowing waterfowl grazing in each site. Results of the experiment, based on field sampling of vegetation, indicated decreases in plant biomass and changes in plant species composition in grazed treatments. Waterfowl and nutria reduced biomass aboul equally, but there was a more marked effect in the openly grazed areas. These findings may be extrapolated to sediment diversion areas along the Mississippi River.     

Response of the barrier island coastal region of southwestern Nigeria to climate and non-climate forcing

Despite threats emanating from the influence of climate and non-climate forcing on the barrier island coastal region of southwestern Nigeria, the extent of the coastal erosion is poorly understood. We report evidence of coastal erosion and sediment accumulation in the region over a 34-year period (1973–2017), using Landsat imagery at intervals of approximately six years. Landsat image corrections and various water-extraction algorithms were used to systematically delineate coastal erosion and accumulation in the area. The region was subdivided into western and eastern subregions separated by Lagos Harbour. In the west, erosion took place during the periods 1973–1979, 1979–1984, 1990–1999 and 2005–2011, whereas in the east, erosion occurred during 1973–1979, 1990–1999 and 1999–2005. Coastal sediment accumulation occurred in the east during 1979–1984, 1984–1990, 2005–2011 and 2011–2017, whereas gains in the west occurred during 1984–1990, 1999–2005 and 2011–2017. The study revealed substantial net erosion of 1 228.1 ha in the region as a whole, over the full period. Sediment accumulation accompanying the coastal erosion appears to be linked to longshore drift. Erosion between 1973 and 2011 was probably attributable to climate change (storms and tidal conditions), longshore drift, the inflow and outflow of water at Lagos Harbour, coastal morphology and, possibly, human impacts. However, the coastal changes between 2011 and 2017 were more obviously associated with human activities, such as development of the Eko Atlantic construction project. Coastal surveillance, together with the use of environmentally sensitive protective measures, could possibly help to reduce coastal erosion in the region. Careful coastal management practices, including artificial nourishing and the installation of resilient structures (e.g. seawalls), should be undertaken to protect human settlements that are already at risk from sea-level rise.     

Tectonic control of Late Pliocene molasse sedimentation in a portion of the Jhelum Re-Entrant,Pakistan

A Late Pliocene interval of the Neogene Siwalik (Himalayan) molasse exposed in the Jhelum Re-entrant, Pakistan, is examined for lateral variations in the environment and rate of fluvial sedimentation. A correlative pair of volcanic ash horizons within the Upper Siwalik section defines an isochronous interval of fluvial deposition. Stratigraphic sections measured through the interval at various localities in the Jhelum Re-entrant are analyzed in terms of fluvial stratigraphy and interval thickness, or net sedimentation rate. The stratigraphy indicates a fluvial system of laterally migrating streams leaving behind fining upward sedimentary cycles of lateral and vertical accretion deposits. Fully developed sedimentary cycles display point bar sands (lateral accretion deposits) of the stream channel environment topped by mudstones (vertical accretion deposits) of the overbank (floodplain) environment. The detailed sequence of vertical accretion deposits in these cycles indicates that the floodplain environment consisted of a stream-proximal, sedimentation-dominant zone and a stream-distal, pedogenesis-dominant zone.Broad lateral variations in the rate of molasse sedimentation appear to be related to the large-scale syntaxial tectonics of the northwestern Himalaya. Sedimentation rate increases toward the apex of the re-entrant, indicating that the syntaxial structure controlled the focus of molasse sedimentation during the examined interval of Late Pliocene time. In addition, sedimentation may have been influenced by mild flexures within the molasse basin.

---

Zusammenfassung Im Gebiet von Jhelum (nördliches Pakistan) reicht das Vortief der neogenen Siwalik-Molasse als Sporn weit in den Faltenbogen des nordwestlichen Himalaya. Die Verfasser untersuchten hier einen Abschnitt des Spätpliozän mit besonderem Hinblick auf laterale Wechsel der fluviatilen Ablagerungen und Sedimentationsraten. Die Obere Siwalik-Molasse enthält hier zwei Leithorizonte mit Tuff, wodurch die Altersgleichheit der fluviatilen Zwischenlagerungen sichergestellt wird. Die Schichtfolge dieser Zwischenlagerungen ist an mehreren Lokalitäten in bezug auf Sedimentationstypen und-raten analysiert worden. Die vorgefundenen Ablagerungszyklen deuten auf ein System von seitlich wandernden Flußläufen. Vollständige Zyklen zeigen Flußbettsedimente (meist Ufersandbänke) gefolgt von feinkörnigen Überflutungssedimenten. Die Feingliederung der Überflutungsfazies zeigt stromnahe Ablagerungszonen einerseits und pedogenetische Randzonen andererseits.Über das gesamte Untersuchungsgebiet ergibt sich eine klare Abhängigkeit zwischen Raten der Molasseaufschüttung und der Faltenbogentektonik des nordwestlichen Himalaya. Die Ablagerungsraten nehmen in Richtung des Bogenscheitels deutlich zu. Daraus wird geschlossen, daß während des untersuchten Zeitabschnittes die regionale Bogentektonik den Schwerpunkt der Molassesedimentation maßgeblich beeinflußt hat. Flache Flexuren innerhalb des Molassebeckens sind ebenfalls in diesen Zusammenhang zu stellen.

---

Résumé Une avant-fosse de la molasse du néogène Siwalik (Himalayen), en éperon dans l'arc plissé du nord-ouest de l'Himalaya, dans la région du Jhelum, Pakistan, a été étudiée quant à ses variations latérales environnantes et son taux de sédimentation fluviale. Dans la section du Siwalik supérieur, deux horizons-repères de tuffs volcaniques délimitent une période isochronique du dépôt fluvial. Les séries stratigraphiques de cet intercalaire ont été analysées en divers points en fonction de la stratigraphie fluviale et de son épaisseur ou en fonction du taux de sédimentation. Les cycles de sédimentation indiquent un réseau fluvial à migration latérale avec dépôts latéraux et verticaux, de plus en plus fins vers le haut. Les cours semblent être en transition avec le type traditionnel de haute et basse sinuosité. On démontre que l'ensemble des dépôts verticaux sont différentiés selon une zone proximale où la sédimentation domine et une zone distale où la pédogenèse domine.De larges variations latérales dans le taux de sédimentation semblent dues à la tectonique globale de l'éperon associée à la syntexis du nord-ouest himalayen. Une tendance vers une augmentation du taux de sédimentation / subsidence en direction de l'axe de l'éperon délimite un lieu de sédimentation molassique pendant l'intervalle étudié. De plus, l'auteur suggère que la sédimentation du bassin de l'éperon ait été influencée par de légères flexures à la périphérie de la structure régionale.

---

, , - . , . , , . . , , . — — , — . , — . -. , . .