Climate variability and maize production in Cameroon: Simulating the effects of extreme dry and wet years

The effects of interyear variability of extreme rainfall events on maize yields at locations in Cameroon, in central‐west sub‐Saharan Africa were investigated through a simulation assessment combining a weather generator with a crop growth model. This study analyzes the potential of using dry/wet year predictions to reduce risk in subsistence agricultural production associated with climate variability at the site level. Weather data sets from eight provincial study localities were classified into three precipitation scenarios – dry (lower threshold), normal and wet (upper threshold) years. According to the modelling results, there is a less than 12 per cent variance in mean maize yields across six out of the eight localities when planting occurs in March, May and August. The variance is equivalent to approximately 100–300 kg per ha, which represents a significant amount of food in the household security of the majority impoverished sectors of rural and urban society, and which could greatly impact the socioeconomic activities of the entire populace. The results lead to the conclusion that all extreme dry and wet years are not equal in terms of their regional manifestation. This calls for precise monthly and sub‐seasonal local level forecasts and the effective dissemination of this information to farming communities in Cameroon, thereby facilitating the adaptive management of indigenous cropping practices and reducing their vulnerability to climate related disasters.     

The metabolism of aquatic ecosystems: history,applications, and future challenges

Measurements of the production and consumption of organic material have been a focus of aquatic science for more than 80 years. Over the last century, a variety of approaches have been developed and employed for measuring rates of gross primary production (P_g), respiration (R), and net ecosystem production (P_n = P_g − R) within aquatic ecosystems. Here, we reconsider the range of approaches and applications for ecosystem metabolism measurements, and suggest ways by which such studies can continue to contribute to aquatic ecology. This paper reviews past and contemporary studies of aquatic ecosystem-level metabolism to identify their role in understanding and managing aquatic systems. We identify four broad research objectives that have motivated ecosystem metabolism studies: (1) quantifying magnitude and variability of metabolic rates for cross-system comparison, (2) estimating organic matter transfer between adjacent systems or subsystems, (3) measuring ecosystem-scale responses to perturbation, both natural and anthropogenic, and (4) quantifying and calibrating models of biogeochemical processes and trophic networks. The magnitudes of whole-system gross primary production, respiration and net ecosystem production rates vary among aquatic environments and are partly constrained by the chosen methodology. We argue that measurements of ecosystem metabolism should be a vital component of routine monitoring at larger scales in the aquatic environment using existing flexible, precise, and durable sensor technologies. Current and future aquatic ecosystem studies will benefit from application of new methods for metabolism measurements, which facilitate integration of process measurements and calibration of models for addressing fundamental questions involving ecosystem-scale processes.     

Sediment colour reflectance spectroscopy as a proxy for wet/dry cycles at Lake El'gygytgyn,Far East Russia,during Marine Isotope Stages 8 to 12

Marine Isotope Stage 11 has been proposed as an analogue for the present interglacial interval; yet, terrestrial climate records from both this region and time interval are rare. The sediments deposited at Lake El'gygytgyn (67°30′N, 172°5′E) in Far East Russia contain a 3·56 Ma record of climate variability. This study presents a high‐resolution record of sediment colour change from Marine Isotope Stage 8 to 12 (ca 275 to 475 ka) and demonstrates the link between lake catchment processes and climate variability. The hue colour parameter, calculated from data collected via colour reflectance spectroscopy in the visible spectrum (380 to 720 nm), exhibits correspondence with global climate records. Determining the source of sediment colour changes was achieved through detailed mineralogical and sedimentological methods, and linked to colour changes through a series of colour sensitivity tests. Mineralogical data, measured by X‐ray diffraction, reveal fluctuations in concentrations of clay minerals corresponding to colour changes. Further analyses of the clay mineral assemblages show no change in relative clay mineral abundances, yet demonstrate a lake catchment dominated by physical weathering processes. Using measured mineral abundances, reconstructions of sediment colour based on colour reflectance mineral standards link mineral and clay mineral content to overall sediment colour. Colour sensitivity tests demonstrate the ability of iron oxide minerals to stain sediments red. Additionally, colour sensitivity to organic matter content was tested, suggesting that organic content drives variability in the red portion of the spectrum and darkens the overall colour signal. Sediment colour is then ultimately linked to physical weathering of bedrock minerals, with small amounts of chemical weathering producing iron oxides during wet intervals. Fluctuations in the sediment colour reveal a high‐resolution record of wet/dry cycles, and provide new information about wet periods for the Russian Arctic region not yet understood from other lake proxy records.     

The structure of hematite (α-Fe2O3) (001) surfaces in aqueous media: scanning tunneling microscopy and resonant tunneling calculations of coexisting O and Fe terminations

The iron oxide-water interface is of interest not only in geochemical and environmental processes, but also in fields ranging from corrosion to photocatalysis. The structure of α-Fe₂O₃ (001) surfaces is not fully understood, and questions have arisen recently concerning different terminations of (001) terraces; a so-called Fe-termination is expected, but under some conditions an O-termination may also be possible. Ultra-high vacuum (UHV) scanning tunneling microscope (STM) studies report evidence for an O-termination in coexistence with an Fe-termination, but other studies find no evidence for an O-termination. Molecular mechanics studies suggest that an O-termination should be possible in an aqueous environment. An O-termination could result from dissolution; if Fe atoms were to dissolve from an Fe-termination, an O-termination would presumably result (and vice-versa). We imaged hematite (001) surfaces in air and aqueous solution using STM. To aid interpretation of the images, we use a resonant tunneling model (RTM) parameterized using ab initio calculations.Our STM and RTM results are consistent with mixed O- and Fe-terminated (001) surfaces. For acid-etched surfaces we find evidence for a periodic (with wavelength of 2.2 ± 0.2 nm) arrangement of nominal O- and Fe-terminated domains. Two different borders between domains should occur, one in which the Fe-termination is high relative to the O-termination, and the reverse. The different domain borders have significantly different heights, consistent with RTM calculations. This agreement allows us to conclude that the Fe-termination is topographically high on most terraces. Surface domains are observed in aqueous solutions at the atomic scale, and appear to be very unreactive on tens-of-seconds time scales at pH 1.     

Predicting road system speeds using spatial structure variables and network characteristics

Spatial regression is applied to GPS floating car measurements to build a predictive model of road system speed as a function of link type, time period, and spatial structure. The models correct for correlated spatial errors and autocorrelation of speeds. Correlation neighborhoods are based on either Euclidean or network distance. Econometric and statistical methods are used to choose the best model form and statistical neighborhood. Models of different types have different coefficient estimates and fit quality, which might affect inferences. Speed predictions are validated against a holdout sample to illustrate the usefulness of spatial regression in road system speed monitoring.      

Upper Yellowstone River Flow and Teleconnections with Pacific Basin Climate Variability during the Past Three Centuries

Climate variability, coupled with increasing demand is raising concerns about the sustainability of water resources in the western United States. Tree-ring reconstructions of stream flow that extend the observational record by several centuries provide critical information on the short-term variability and multi-decadal trends in water resources. In this study, precipitation sensitive Douglas-fir (Pseudotsuga menzeisii) tree ringrecords are used to reconstruct annual flow of the Yellowstone River back to A.D. 1706. Linkages between precipitation in the Greater Yellowstone Region and climate variability in the Pacific basin were incorporated into our model by including indices Pacific Ocean interannual and decadal-scale climatic variability, namely the Pacific Decadal Oscillation and the Southern Oscillation. The reconstruction indicates that 20th century streamflow is not representative of flow during the previous two centuries. With the exception of the 1930s, streamflow during the 20th century exceeded average flows during the previous 200 years. The drought of the 1930s resulted in the lowest flows during the last three centuries, however, this probably does not represent a worst-case scenario for the Yellowstone as other climate reconstructions indicate more extreme droughts prior to the 18th century.