Nitrogen isotope ratios in estuarine biota collected along a nutrient gradient in Narragansett Bay, Rhode Island, USA

Stable nitrogen isotope ratios were used to study the incorporation of anthropogenically-derived nitrogen into the food webs of salt marsh systems along a contamination gradient in Narragansett Bay. Nitrogen isotope ratios (delta(15)N) were measured in six estuarine species collected from three marshes along this gradient, monthly from June to October between 1997 and 1999. A significant decrease in delta(15)N was found with distance along the estuary for four of the six species. Significant differences were found among monthly isotope ratios for some species. Nitrogen isotope ratios in sea lettuce (Ulva lactuca) increased during the summer season with highest delta(15)N values measured during September and October. This trend was most pronounced at the station receiving the highest nutrient inputs. Elevated delta(15)N values at this station appeared to correlate with seawater ammonia/nitrate concentration ratios. The temporal variations in delta(15)N suggest that care should be taken in species selection and the design of sampling schemes of studies using delta(15)N for monitoring anthropogenic nutrients in aquatic systems. Sampling programs designed to determine long-term trends should consider species that do not show rapid fluctuations in isotope ratios. The mud snail, Nassarius obsoletus, responded this way in the present study. Studies designed to measure short-term changes should include species such as U. lactuca, which rapidly respond to isotope changes. The results from this study also help to establish a baseline for nitrogen isotope values in Narragansett Bay. This information can be used to monitor future trends in nitrogen inputs to this estuary.     

On the application of turbulence theory to the determination of marine evaporation

Summary Simultaneous measurements of wind, air temperature, and humidity profiles as well as of evaporation, presented byTakahashi (1958), were compared with relevant formulae suggested by turbulence theory. Satisfactory agreement could be achieved if, near the sea surface, the influence of molecular diffusion and, at higher levels, the effect of thermal stratification on the profiles were taken into account in addition to a suitable reduction of the value of evaporation obtained by means of a floating pan.The chief results of this report have been presented on 27th April 1962 to the Tenth Yearly Meeting of theSocietà Italiana di Geofisica e Meteorologia (Genova: 26–28 April 1962).     

Ottant'anni di Osservazioni Meteorologiche a Moncalieri (Torino)

Riassunto Si espongono ed illustrano i valori medi dei principali elementi meteorologici osservati a Moncalieri senza alcuna interruzione nell'ottantennio 1865–1945 e durante il quarantennio 1907–1946 per il vento. L'analisi delle medie quinquennali ed annuali pone in luce qualche caratteristica della variazione secolare dei medesimi fattori.

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Zusammenfassung Die Mittelwerte der wichtigsten meteorologischen Elemente die in Moncalieri ohne Unterbrechung gesammelt worden sind, werden angegeben und zwar für den Zeitraum 1865–1945, ausgenommen für den Wind, deren Beobachtungen auf die Periode 1907–1946 sich beziehen. Die Gänge der fünfjährigen und jährlichen Mitteln zeigen einige Eigentümlichkeiten der sekularen Variation für denselben Elemente, die herausgehoben werden.

     

Betrachtungen über die Grundschicht

Zusammenfassung 1. Es werden die einzelnen Vorgänge besprochen, die das eigentümliche Verhalten der Veränderlichkeit von Druck und Temperatur in ihrer vertikalen Verteilung erklären sollen. Wenn ein unteres an der Erdoberfläche vorhandenes Druckausgleichsniveau vorhanden ist und ein weiteres in grösserer Höhe, so müssen Temperaturänderungen in dem einen Niveau durch solche eines anderen ausgeglichen, kompensiert werden. Es wird gezeigt, dass dem kompensierenden Einfluss der mittleren und oberen Troposphäre ein kompensierender Einfluss der Kälte- und Wärmewellen aus dem Bereiche der Grundschicht entgegenwirkt, sodass letzten Endes das Druckausgleichsniveau nicht mehr am Erdboden liegt, sondern in eine Höhe verschoben wird, die der ungefähren Höhe der Grundschicht entspricht. — 2. Der Einfluss von Reibung und Konvektion auf die Bildung der Grundschicht wird besprochen. Die Reibung wirkt langsam und immer schichtweise. Die Konvektion wirkt rascher, aber zunächst immer nur lokal. Im Verlaufe längerer Zeit kann aber auch die Konvektion eine Homogenisierung der unteren Luftschichten bewirken, also eine Luftschicht von einem einheitlichen Charakter schaffen. Dieser Prozess wird noch verstärkt, wenn die Konvektion mit Kondensation verbunden ist. Jetzt ist eine weitere Ueberhöhung der Grundschicht möglich. Da dieser Prozess aber über weite Räume nicht von gleicher Grösse ist, wird diese Ueberhöhung vielfach gebietsweise verschieden sein. Die Grundschicht vom Böenwettertyp hat daher gewöhnlich keine einheitliche Oberfläche über weite Gebiete hinweg. — 3. Ein weiterer Faktor, der für die Bildung der Grundschicht von Bedeutung ist, ist die Strahlung. Da der Beitrag, den jeder der drei Faktoren (Reibung, Konvektion, Strahlung) zur Bildung der Grundschicht beisteuert, nicht errechnet werden kann, muss man sich zunächst mit einer qualititativen Abschätzung der Einflüsse der einzelnen an der Bildung der Grundschicht beteiligten Faktoren begnügen. Ein entsprechendes Schema wird vorgelegt und besprochen.

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Summary 1. There are discussed individual proceedings which shall explain the characteristic behaviour of pressure, and temperature instability in their vertical distribution. When there exists equalization of pressure on a lower level near the ground, and again on a higher level, changes of temperature on one level will be compensated by such on another level. It is shown that the compensating influence of middle and upper troposphere is opposed by the compensating influence of cold, and heat waves from the ground layer, ultimately resulting in the removal of the level of pressure equalization from the ground to an altitude roughly corresponding to the height of ground layer. — 2. The influence of friction and convection on the formation of ground layer is discussed. While friction is acting slowly and by layers, convection is acting more rapidly, but only locally at first. In the long run however, also convection can produce homogeneity of the lower layers of the atmosphere, i. e. an atmospheric layer of uniform character. This process is being intensified when convection is associated with condensation. Then, another increase in height of the ground layer will be possible. However, as this process will not be of similar intensity over wide stages, the increase in height will vary locally. Therefore, generally the ground layer of the squally weather type will not possess a uniform surface extending over wide areas. — 3. Another important factor in the formation of ground layer is radiation. Since the share taken by each of the three factors (friction, convection, radiation) cannot be computed, one must be satisfied with qualitative valuation of the influence of the factors participating in the formation of ground layer. An appropriate scheme is submitted and discussed.

     

Last interglacial climates of south-eastern Australia: plant and beetle-based reconstructions from Yarra Creek,King Island,Tasmania

This paper explores the palaeoclimatic significance of a fossil plant and insect record from Yarra Creek, on King Island, between Tasmania and the Australian mainland. The record dates, based upon a thermoluminescence chronology and other evidence, to Marine Isotope Stage 5 (MIS 5); the exact timing is impossible to ascertain given the resolution of the thermoluminescence results and the presence of an unconformity in the dated section. The presence of a cool-temperate rainforest flora, outside its modern range, and other independent evidence, suggest the sequence may represent the last interglacial (MIS 5e) rather than a later MIS 5 substage. Using coexistence methods that compare modern climatic ranges of the taxa in the assemblage we reconstruct independent beetle and plant based annual and seasonal temperate and precipitation parameters. The results imply the assemblage was deposited under a wetter summer climate and suggest conditions of enhanced temperature seasonality. It is probable that enhanced temperature seasonality is a methodological artefact reflecting the rarity of extremely equable climates (like King Island) in modern climate space. This would indicate a limitation of most methods of palaeoclimatic reconstruction that rely on modern datasets – it is only possible to reconstruct past climates as being within the range of values in that currently exist in modern climate space.     

Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland

Sulfur biogeochemical cycling and associated Fe-S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine reduction rates and Fe-S mineralization at the tidal fringe, 7 years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS₂) oxidation, resulting in the drained soil layers being highly acidic and rich in -bearing Fe(III) minerals, including jarosite (KFe₃(SO₄)₂(OH)₆). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5-7. The fastest rates of in-situ reduction (up to ∼300 nmol cm⁻³ day⁻¹) occur within the inter-tidal zone in the near-surface soil layers (to ∼60 cm below ground surface). The reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H₂S and jarosite - a process that also contributed to enrichment in pore-water Fe²⁺ (up to 55 mM) and (up to 50 mM). The iron sulfide thiospinel, greigite (Fe₃S₄), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe-S mineralization pathways. Overall, this study highlights novel aspects of Fe-S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands.