Formation of humic-like substances by fungi epiphytic onSpartina alterniflora

In laboratory experiments, two fungi that commonly colonize leaves of Spartina aZterniJEoru(L oisel.) were studied to determine if they contribute to the formation of humic substances, which have been isolated earlier from salt marsh estuaries. In incubations of up to one year in duration, Phaeosphaeria spartinicola and Phaeosphaeria halima did not form dark pigments when grown in an artificial, full-nutrient medium. However, if the nutrient solution was enriched with a water extract of S. alterniJEoro, appreciable amounts of dark brown substances were produced. Elemental (C, H, N, 0) and spectral (ultraviolet, visible, and Fourier Transform Infrared) analyses of these dark brown substances show them to be similar to salt marsh humic substances.     

Aircraft observations in the planetary boundary layer under stable conditions

An analysis of observations of airflow over Lake Ontario in a stably stratified atmosphere is presented. The relationship with theory is mentioned only in terms of what may be important to future work. Detailed air motion, potential temperature and mixing-ratio measurements are presented which show pervasive variability in the horizontal. There is no evidence of gravity waves. It is suggested that vertical mixing of the atmosphere may occur in stable conditions by a mechanism quite apart from the usual concept of the small-scale random eddy motion usually associated with surface convection. Vertical soundings are analyzed as well as two long constant-height observational runs.     

The (re)making of the western 'geographical tradition': some missing links

Summary A brief investigation of certain missing links in the narration of the history of geography focuses on the need to consider the contribution of non-western geographical and scientific knowledges to the making of 'European discovery' and therefore to the development of a putatively western geographical tradition.     

Watershed-scale vegetation,water quantity,and water quality responses to wildfire in the southern Appalachian mountain region,United States

Wildfires are landscape scale disturbances that can significantly affect hydrologic processes such as runoff generation and sediment and nutrient transport to streams. In Fall 2016, multiple large drought-related wildfires burned forests across the southern Appalachian Mountains. Immediately after the fires, we identified and instrumented eight 28.4–344 ha watersheds (four burned and four unburned) to measure vegetation, soil, water quantity, and water quality responses over the following two years. Within burned watersheds, plots varied in burn severity with up to 100% tree mortality and soil O-horizon loss. Watershed scale high burn severity extent ranged from 5% to 65% of total watershed area. Water quantity and quality responses among burned watersheds were closely related to the high burn severity extent. Total water yield (Q) was up to 39% greater in burned watersheds than unburned reference watersheds. Total suspended solids (TSS) concentration during storm events were up to 168 times greater in samples collected from the most severely burned watershed than from a corresponding unburned reference watershed, suggesting that there was elevated risk of localized erosion and sedimentation of streams. NO₃-N concentration, export, and concentration dependence on streamflow were greater in burned watersheds and increased with increasing high burn severity extent. Mean NO₃-N concentration in the most severely burned watershed increased from 0.087 mg L⁻¹ in the first year to 0.363 mg L⁻¹ (+317%) in the second year. These results suggest that the 2016 wildfires degraded forest condition, increased Q, and had negative effects on water quality particularly during storm events.     

27Al, 29Si,and 23Na MAS NMR study of an Al,Si ordered alkali feldspar solid solution series

Solid-state ²⁷Al, ²⁹Si and ²³Na MAS NMR spectra have been obtained for an Al,Si ordered low albite to low microcline ion exchange series for which unit-cell parameters and ²⁹Si NMR data have previously been reported. ²⁷Al δ_i vary continuously with composition from 63.4 (±0.5) ppm for albite to 58.9 (±0.5) ppm for microcline, and parallel the ²⁹Si chemical shifts assigned to the T2m-site. The ²⁷Al and ²⁹Si chemical shifts for this series correlate well with composition-dependent lattice parameters, most notably cell volume and the angle [201]¹b. The linewidths of the ²⁹Si and ²⁷Al resonances indicate a significant amount of structural disorder in the intermediate compositions due to Na, K substitution. The 1 σ width of the distribution of average Si-O-T angles for each T-site is estimated to be about 1° for the Or33 sample. The average ²³Na δ_i varies monotonically from -8.5 (±1) ppm for albite to -24.3 (±1)ppm for Or83. Similarly, the average ²³Na nuclear quadrupole coupling constant decreases from 2.60 to 1.15 (±0.05) MHz and the asymmetry parameter of the electric field gradient increases from 0.25 to 0.6 with increasing K-content from albite to Or83. The observed variations in the quadrupole coupling parameters are consistent with simple electrostatic calculations. Higher resolution ²³Na spectra of the intermediate compositions obtained at 11.7 T indicate the presence of an inhomogeneous linebroadening which is related to the distribution of Na-environments. A model based on a random distribution of local compositions does not simulate the spectra, suggesting that the distribution of Na is skewed toward Na-rich clusters. Observation of the ²³Na NMR lineshape of Or49 after short periods of heat treatment indicate that ²³Na NMR is very sensitive to the changes in the Na, K distribution accompanying the early stages of exsolution. Reversible changes occur after heating at 530° C for 3 h, whereas heating at 600° C produces no changes, possibly bracketing the position of the coherent spinodal for Al, Si ordered alkali feldspars at this composition.     

The alluvial architecture of a suspended sediment dominated meandering river: the Río Bermejo,Argentina

The alluvial architecture of fine‐grained (silt‐bed) meandering rivers remains poorly understood in comparison to the extensive study given to sand‐bed and gravel‐bed channels. This paucity of knowledge stems, in part, from the difficulty of studying such modern rivers and deriving analogue information from which to inform facies models for ancient sediments. This paper employs a new technique, the parametric echosounder, to quantify the subsurface structure of the Río Bermejo, Argentina, which is a predominantly silt‐bed river with a large suspended sediment load. These results show that the parametric echosounder can provide high‐resolution (decimetre) subsurface imaging from fine‐grained rivers that is equivalent to the more commonly used ground‐penetrating radar that has been shown to work well in coarser‐grained rivers. Analysis of the data reveals that the alluvial architecture of the Río Bermejo is characterized by large‐scale inclined heterolithic stratification generated by point‐bar evolution, and associated large‐scale scour surfaces that result from channel migration. The small‐scale and medium‐scale structure of the sedimentary architecture is generated by vertical accretion deposits, bed sets associated with small bars, dunes and climbing ripples and the cut and fill from small cross‐bar channels. This style of alluvial architecture is very different from other modern fine‐grained rivers reported in the literature that emphasize the presence of oblique accretion. The Río Bermejo differs from these other rivers because it is much more active, with very high rates of bank erosion and channel migration. Modern examples of this type of highly active fine‐grained river have been reported rarely in the literature, although ancient examples are more prevalent and show similarities with the alluvial architecture of the Río Bermejo, which thus represents a useful analogue for their identification and interpretation. Although the full spectrum of the sedimentology of fine‐grained rivers has yet to be revealed, meandering rivers dominated by lateral or oblique accretion probably represent end members of such channels, with the specific style of sedimentation being controlled by grain size and sediment load characteristics.     

La–SiO<Subscript>2</Subscript> and Yb–SiO<Subscript>2</Subscript> systematics in mid-ocean ridge magmas: implications for the origin of oceanic plagiogranite

Analytical expressions for the variation in D _La and D _Yb with increasing liquid SiO₂ for olivine, plagioclase, augite, hornblende, orthopyroxene, magnetite and ilmenite (Brophy in Contrib Mineral Petrol 2008, online first) have been combined with numerical models of hydrous partial melting, of mid-ocean ridge (MOR) cumulate gabbro melting, and fractional crystallization of slightly hydrous mid-ocean ridge basalt (MORB) magma to assess a melting versus fractionation origin for oceanic plagiogranite. For felsic magmas (>63 wt.% SiO₂) the modeling predicts the following. MOR cumulate gabbro melting should yield constant or decreasing La and constant Yb abundances with increasing liquid SiO₂. The overall abundances should be similar to those in associated mafic magmas. MORB fractional crystallization should yield steadily increasing La and Yb abundances with increasing SiO₂ with overall abundances significantly higher than those in associated mafic magmas. Application to natural occurrences of oceanic plagiogranite indicate that both MOR cumulate gabbro melting and MORB fractionation are responsible. Application of the model results to Icelandic rhyolites strongly support a fractional crystallization rather than a crustal melting origin.     

An investigation of the controls on Irish precipitation δ18O values on monthly and event timescales

This two-year study investigates the relative influence of meteorological variables (precipitation amount and temperature), atmospheric circulation, air mass history, and moisture source region on Irish precipitation oxygen isotopes (δ¹⁸O_p) on event and monthly timescales. Single predictor correlations reveal that on the event scale, 20% of δ¹⁸O_p variability is attributable to the amount effect and 7% to the temperature effect while on the monthly timescale the North Atlantic Oscillation accounts for up to 20% of δ¹⁸O_p variability and the amount and temperature effects are not significant. In comparison, multivariate linear regression reveals that the interaction of temperature and precipitation amount explains up to 40% of δ¹⁸O_p variance at event and monthly timescales. Five-day kinematic back trajectories suggest that the amount-weighted mean δ¹⁸O_p value of southerly- and northerly-derived events are lower by 2‰ relative to events derived from the west. Because air mass history and atmospheric circulation appear to influence δ¹⁸O_p in Ireland, Irish paleo-δ¹⁸O_p proxy records are best interpreted as reflecting a combination of parameters, not just paleotemperature or paleorainfall.     

Nitrogen inputs to seventy-four southern New England estuaries: Application of a watershed nitrogen loading model

Excess nitrogen inputs to estuaries have been linked to deteriorating water quality and habitat conditions which in turn have direct and indirect impacts on aquatic organisms. This paper describes the application of a previously verified watershed loading model to estimate total nitrogen loading rates and relative source contributions to 74 small-medium sized embayment-type estuaries in southern New England. The study estuaries exhibited a gradient in nitrogen inputs of a factor of over 7000. On an areal basis, the range represented a gradient of approximately a factor of 140. Therefore, all other factors being equal, the study design is sufficient to evaluate ecological effects conceptually tied to excess nitrogen along a nitrogen gradient. In addition to providing total loading inputs rates to the study estuaries, the model provides an estimate of the relative contribution of the nitrogen sources from each watershed to each associated estuary. Cumulative results of this analysis reveal the following source ranking (means): direct atmospheric deposition (37%), ≈wastewater (36%), >indirect atmospheric deposition (16%) > fertilizer (12%). However, for any particular estuary the relative magnitudes of these source types vary dramatically. Together with scientific evidence on symptoms of eutrophication, the results of this paper can be used to develop empirical pressure-state models to determine critical nitrogen loading limits for the protection of estuarine water quality.