Fluvial transport of suspended sediment and organic carbon during flood events in a large agricultural catchment in southwest France

Water draining from a large agricultural catchment of 1 110 km² in southwest France was sampled over an 18‐month period to determine the temporal variability in suspended sediment (SS) and dissolved (DOC) and particulate organic carbon (POC) transport during flood events, with quantification of fluxes and controlling factors, and to analyze the relationships between discharge and SS, DOC and POC. A total of 15 flood events were analyzed, providing extensive data on SS, POC and DOC during floods. There was high variability in SS, POC and DOC transport during different seasonal floods, with SS varying by event from 513 to 41 750 t; POC from 12 to 748 t and DOC from 9 to 218 t. Overall, 76 and 62% of total fluxes of POC and DOC occurred within 22% of the study period. POC and DOC export from the Save catchment amounted to 3090 t and 1240 t, equivalent to 1·8 t km^?2 y^?1 and 0·7 t km^?2 y^?1, respectively. Statistical analyses showed that total precipitation, flood discharge and total water yield were the major factors controlling SS, POC and DOC transport from the catchment. The relationships between SS, POC and DOC and discharge over temporal flood events resulted in different hysteresis patterns, which were used to deduce dissolved and particulate origins. In both clockwise and anticlockwise hysteresis, POC mainly followed the same patterns as discharge and SS. The DOC‐discharge relationship was mainly characterized by alternating clockwise and anticlockwise hysteresis due to dilution effects of water originating from different sources in the whole catchment. Copyright © 2011 John Wiley & Sons, Ltd.     

Revisiting the Gow Lake impact structure,Saskatchewan, Canada

The ~5 km diameter Gow Lake impact structure formed in the Canadian Shield of northern Saskatchewan approximately 197 Myr ago. This structure has not been studied in detail since its discovery during a regional gravity survey in the early 1970s. We report here on field observations from a 2011 expedition that, when combined with subsequent laboratory studies, have revealed a wealth of new information about this poorly studied Canadian impact structure. Initially considered to be a prototypical central peak (i.e., a complex) impact structure, our observations demonstrate that Gow Lake is actually a transitional impact structure, making it one of only two identified on Earth. Despite its age, a well-preserved sequence of crater-fill impactites is preserved on Calder Island in the middle of Gow Lake. From the base upward, this stratigraphy is parautochthonous target rock, lithic impact breccia, clast-rich impact melt rock, red clast-poor impact melt rock, and green clast-poor impact melt rocks. Discontinuous lenses of impact melt-bearing breccia also occur near the top of the red impact melt rocks and in the uppermost green impact melt rocks. The vitric particles in these breccias display irregular and contorted outlines. This, together with their setting within crater-fill melt rocks, is indicative of an origin as flows within the transient cavity and not an airborne mode of origin. Following impact, a hydrothermal system was initiated, which resulted in alteration of the crater-fill impactites. Major alteration phases are nontronite clay, K-feldspar, and quartz.     

Regime shifts in the marine environment: the scientific basis and political context

Regime shifts in the marine environment have recently received much attention. To date, however, few large-scale meta-analyses have been carried out due to insufficient data coverage and integration between sustained observational datasets because of diverse methodologies used in data collection, recording and archival. Here we review the available data on regime shifts globally, followed by a review of current and planned policies with relevance to regime shifts.We then focus on the North and Baltic Seas, providing examples of existing efforts for data integration in the MarBEF Network of Excellence. Existing gaps in data coverage are identified, and the added value from meta-analyses of multiple datasets demonstrated using examples from the MarBEF integrated data project LargeNet. We discuss whether these efforts are addressing current policy needs and close with recommendations for future integrated data networks to increase our ability to understand, identify and predict recent and future regime shifts.     

Nitrogen functionality in “oil window” rank range vitrinite rich coals and chars

X-ray photoelectron spectroscopy (XPS) was used to characterize organic nitrogen species in coals and chars. The coals comprise a set of vitrinite-rich samples from the Penn State Coal Bank set, ranging from vitrinite reflectance (R_r) 0.42-1.60%. Chars were obtained after coal pyrolysis under an inert atmosphere at 800 °C and fast heating rate. In the coals, pyrrolic nitrogen was the predominant form, steadily decreasing with coal rank, while pyridinic and quaternary nitrogen showed pronounced variation with rank. In contrast to the coals, the chars show much less pyrrolic and pyridinic nitrogen, and more quaternary nitrogen. The chars were also characterized by having oxidized nitrogen and nitro sub-peaks, which were not observed for the coals. Apparently the occurrence of these forms is related to the decrease in the pyridinic nitrogen.     

Environmental controls on stable isotope precipitation values over Mali and Niger,West Africa

This study evaluated the effects of the environmental factors precipitation amount (P), temperature (T), and vapor pressure (V _p) on the stable isotope composition (δ) of precipitation and the excess-deuterium (d) parameter in Mali and Niger, West Africa. At both locations, δ values were greatly affected by seasonal climatic conditions and a statistically significant negative correlation was observed between δ and P. In Mali, a statistically significant negative correlation was also observed between δ and V _p. There was no statistically significant correlation between δ and T. Mean-weighting of δ values may be masking both dry-season and individual storm event precipitation phenomena, which are otherwise observed in arithmetically averaged δ values. Mean monthly d values for peak monsoonal months indicate that precipitation is first-fraction, gaining little recycled water on its journey inland from the Atlantic Ocean near the equator. Agreement between rainy-season precipitation and groundwater δ values, specifically peak monsoonal months, indicates that groundwater is being recharged by infiltration of current monsoonal rains and is not paleo-groundwater recharged under past climatic conditions. Similarity between rainy-season precipitation and groundwater d values provide another indication that monsoonal precipitation under current climatic conditions is the source of groundwater recharge. The knowledge that groundwater is recently recharged monsoonal rains, rather than paleo-groundwater, is important for evaluating groundwater sustainability and the effects that climate change will have on water resources. Understanding and predicting changes in precipitation amounts and intensities, which ultimately affect timing and amount of groundwater recharge, is critical for water resource management.     

Sub-recent nitrogen-isotope trends in sediments from Skagerrak (North Sea) and Kattegat: Changes in N-budgets and N-sources?

We determined ¹⁵N/¹⁴N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand (δ¹⁵N = 5‰) and the imprint of river-borne nitrogen input into the SE North Sea (δ¹⁵N up to 12‰ in estuaries of the SE North Sea) on the other hand. We compare the results with δ¹⁵N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of δ¹⁵N in cores from the Skagerrak – the largest sediment sink for nitrogen in the entire North Sea – was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow shallow-water sediments before reaching the main sedimentary basin of the North Sea.