Estimating direct and episodic atmospheric nitrogen deposition to a coastal waterbody

Direct deposition of atmospheric nitrogen to shallow coastal embayments is usually estimated, since insufficient field measurements are available. Using Waquoit Bay (Cape Cod, MA. USA) as a case study, and a recent review of literature, we determined reasonable bounds on wet and dry inputs of inorganic and organic N. Since precipitation and wind vary daily, we explored the potential of episodic events to stimulate phytoplankton blooms. Many coastal waterbodies like Waquoit Bay are small relative to their watersheds. Nevertheless, direct deposition of NH(3), NO(3)(-), and HNO(3) is significant in the loading budget. For Waquoit Bay, direct deposition was calculated to be 7-15.5 kg total N ha(-1)yr(-1), representing 70-150% of the atmospheric N reported to reach the bay via the watershed, and 20-45% of the total N reaching the bay from all land-based sources. Episodic events were estimated to deliver up to 65 mg N m(-2)day(-1), representing a phytoplankton stock of 12.3 mg Chl m(-2), an amount unlikely to stimulate dense blooms in shallow coastal waters in the northeastern United States.     

The problem of the future in postwar Anglo-American political philosophy

Among the conceptual problems raised by climate change is that of how to think about the future. Theories of intergenerational justice and other accounts of obligations to the future in Anglo-American philosophy tend to argue that the remote future matters morally. Where did these arguments come from? This essay explores the roots of contemporary ideas about the remote future in debates that took place among Anglophone philosophers in the 1970s.     

Salinity in Colonial Irrigation: British India and south-eastern Australia

Salinity is an environmental phenomenon that affects the world's arid and semi-arid regions, where it causes soil degradation and problems for agriculture. Salinity began to attract serious attention in the irrigated districts of the Murray Valley in south-eastern Australia in the 1960s. However, observations that the south-eastern Australian landscape was affected by naturally occurring salts predates this period of awareness by more than half a century. Drawing on documentary history, the present paper reveals what soil chemists in New South Wales in the 1890s already understood of the potential dangers of salinity. These scientists were aware of the experience of their colonial colleagues in British India, where the seriousness of the problem had been recognised by the 1870s. Using evidence from India and south-eastern Australia in the nineteenth and early-twentieth centuries, the paper outlines the opposing worldviews of scientists and engineers in New South Wales about the potential dangers of intensive irrigation. It offers an explanation as to why that understanding was insufficient to prevent the growth of the problem.     

Lateral and vertical juxtaposition of matrix‐rich and matrix‐poor lithologies caused by particle settling in mixed mud–sand deep‐marine sediment suspensions

Sandy sedimentary rocks rich in detrital matrix (>10% silt/clay) have long been recognized in the ancient sedimentary record, and nowhere more commonly than in deep‐marine turbidite systems. Despite this, their depositional mechanisms remain poorly understood, in part because these rocks, which are enriched in fine‐grained sediment, are often poorly exposed in outcrop or are confined to observation in core. Matrix‐rich strata in the Neoproterozoic Windermere Supergroup, in contrast, are very well‐exposed and show systematic changes in lithofacies over distances of several tens to a few hundreds of metres along‐strike. Notably, these strata are observed in both basin floor and continental slope deposits, suggesting that their occurrence and systematic lithological arrangement is related to mechanistic, rather than palaeogeographic, controls. Specifically, the facies transect consists of structureless, clayey sandstone that transforms along‐strike to a two‐layer deposit with the development of an upper, planar‐based, markedly more matrix‐rich layer. Further along‐strike, the basal clayey sandstone thins and eventually pinches out, leaving only the (upper) sandy claystone layer, which in turn thins along‐strike and then pinches out. These systematic changes in lithology, but more specifically the distribution of clay, is interpreted to form a depositional continuum related to particle settling in a horizontally advecting, high concentration particle suspension formed along the margins of an avulsion‐related high‐energy turbulent suspension.     

Authigenic replacement of cyanobacterially precipitated calcium carbonate by aluminium‐silicates in giant microbialites of Lake Van (Turkey)

Studies of modern cyanobacterial mats and biofilms show that they can precipitate minerals as a consequence of metabolic and degradational activities paired with ambient hydrochemical conditions. This study looked at modern microbial mats forming giant, tower‐like, groundwater‐fed, calcareous microbialites in the world's largest, highly alkaline lake; Van Gölü (Lake Van), East Turkey. Results show that microbial systems play a role not only in carbonate precipitation but also in the formation of siliceous mineral phases. Transmitted light microscopy, scanning electron microscopy and spectral observations revealed that, within the extracellular polymeric substances excreted by the mats abundant minute aragonite grains precipitated first in vivo. These minute grains were quickly succeeded and/or supplemented in the dead biomass of the cyanobacterial mat by authigenic Al–Mg–Fe siliceous phases. Silicon dioxide is available in large concentrations in the highly alkaline water of Lake Van. Divalent cations (Ca and Mg) are delivered to the microbialites mostly by groundwater springs. The precipitation of the fine‐grained siliceous phases is probably mediated by bacteria degrading the cyanobacterial biomass and complexing the excessive cations with their extracellular polymeric envelopes. The bacteria serve as nucleation centres for the subsequent precipitation of siliceous mineral phases. Generally, the biphasic (calcareous and siliceous) mineralization – characterizing Lake Van microbialites – is controlled by their interior highly dynamic hydrogeochemical situation. There, the dramatically different alkaline lake water and the Ca–Mg‐charged groundwater mix at various rates. The early diagenetic replacement of the in vivo aragonite by authigenic siliceous phases significantly increases the fossilization potential of the mat‐forming cyanobacteria. Lake Van and its giant microbialite tufa towers act as a model explaining the transformation of early diagenetic mineral phases observed in many modern and ancient carbonate marine deposits, particularly those influenced by diffusion of silica‐enriched and metal‐enriched pore waters from below the water–sediment interface.     

Tracing iron-fueled microbial carbon production within the hydrothermal plume at the Loihi seamount

The Loihi hydrothermal plume provides an opportunity to investigate iron (Fe) oxidation and microbial processes in a system that is truly Fe dominated and distinct from mid-ocean ridge spreading centers. The lack of hydrogen sulfide within the Loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano’s summit, results in a prolonged presence of reduced Fe within the dispersing non-buoyant plume. In this study, we have investigated the potential for microbial carbon fixation within the Loihi plume. We sampled for both particulate and dissolved organic carbon in hydrothermal fluids, microbial mats growing around vents, and the dispersing plume, and carried out stable carbon isotope analysis on the particulate fraction. The δ¹³C values of the microbial mats ranged from −23‰ to −28‰, and are distinct from those of deep-ocean particulate organic carbon (POC). The mats and hydrothermal fluids were also elevated in dissolved organic carbon (DOC) compared to background seawater. Within the hydrothermal plume, DOC and POC concentrations were elevated and the isotopic composition of POC within the plume suggests mixing between background seawater POC and a ¹³C-depleted hydrothermal component. The combination of both DOC and POC increasing in the dispersing plume that cannot solely be the result of entrainment and DOC adsorption, provides strong evidence for in-situ microbial productivity by chemolithoautotrophs, including a likelihood for iron-oxidizing microorganisms.     

Diel oxygen dynamics and anoxic events in an eutrophic estuary of Waquoit Bay,Massachusetts

As a result of nutrient loading from septic systems, a thick canopy of macroalgae covers the bottom of Waquoit Bay, an embayment on Cape Cod, Massachusetts. Using automated conductivity-temperature-oxygen recorders and manual profiles, we measured diel water column O₂ changes during summer in the Childs River, the estuary of the bay with the highest housing density. At dawn in midsummer, bottom waters in the Childs River are chronically hypoxic due to high rates of benthic respiration. On sunny days benthic photosynthesis drives bottom water O₂ to 10–15 mg l^?1 by afternoon. The extent of the daily O₂ excursion is directly proportional to daily irradiance. Large diel O₂ excursions in bottom water are due to limited mixing of surface and bottom water. Density stratification exceeded two sigma-t units 85% of the time during midsummer in the Childs River. Because of stratification, hypoxia and even anoxia occur in this estuary. The first of several anoxic events was observed in Waquoit Bay in 1988, and we have attempted to evaluate factors that trigger anoxia. High rates of benthic respiration result in anoxia when replenishment of O₂ during the day is limited by insufficient light. Our analysis of meteorological records during two recent anoxic events shows that anoxia develops overnight in midsummer during periods of peak summertime temperatures after several days of cloudy, moderately calm weather. Similarly critical conditions existed most summers since 1975, yet anoxic events in the bay have not been reported historically. If climatic warming occurs, anoxic events in the bay may occur more frequently even if algal stocks remain unchanged. Eutrophication of Waquoit Bay is similar to many other embayments in populated coastal areas, and anoxic events may indicate a chronic growing problem in these important ecosystems. However, in shallow, stratified embayments, anoxia may be transient and easily missed without frequent monitoring.     

Perceptions of Environmental Change and Climate Concern Among Idaho’s Farmers

Climate change public opinion research has identified conservative political ideology as the primary predictor of skepticism about climate change’s anthropogenic causes. Most farmers in Idaho are politically conservative, but they are also a unique group for whom observing their environment is part of daily life and work. We use data from in-depth interviews with 30 Idaho farmers to examine the relationship between observations of specific environmental changes and climate concern. We find that while most farmers report noticing changes in precipitation patterns, growing season length, and winter temperatures, few farmers connect these with long-term global climate change. These findings have two important implications: 1) direct experience, even in the form of disruption to an individual’s economic security, is not enough to overcome the influence of political ideology on climate change beliefs, and 2) acknowledging climate variation is not sufficient to convince individuals that the changes are produced by human activities.     

Catchment and in-stream influences on metal concentration and ochre deposit density in upland streams, Northern Ireland

Metal concentrations from stream waters in two geological blocks in Northern Ireland were compared to determine the contributions of catchment characteristics and in-stream conditions. One block is composed of metamorphosed schist and unconsolidated glacial drift with peat or peaty podzol (mainly humic) soils, while the other block consists of tertiary basalt with brown earth and gley soils. Water samples were collected from 52 stream sites and analysed for iron (Fe), manganese (Mn) and aluminium (Al) as well as a range of other chemical determinands known to affect metal solubility. Densities of metal-rich ochre deposit were determined for stream bed stone samples. Higher conductivities and concentrations of bicarbonate, alkalinity, calcium and magnesium occurred on basalt than on schist. Despite higher Fe and Mn oxide concentrations in basalt-derived non-humic soils, stream water concentrations were much lower and ochre deposit densities only one-third of those on schist overlain by humic soils. Neither rock nor soil type predicted Al concentrations, but pH and dissolved oxygen did. Peat-generated acidity and the limited acid neutralising capacity of base-poor metamorphosed schist have resulted in elevated concentrations of metals and ochre deposit in surface waters.     

Review of Acquisition and Signal Processing Methods for Electromagnetic Noise Reduction and Retrieval of Surface Nuclear Magnetic Resonance Parameters

Surveys in Geophysics - Surface nuclear magnetic resonance (sNMR) is an electromagnetic hydrogeophysical method directly sensitive to liquid phase water in the upper $$\approx $$ 100 m of the...