Coefficients for Penman-based estimation of daily potential evapo-transpiration in Botswana

Reference potential evapo-transpiration (PET) for Botswana was estimated using a Penman-based equation in order to determine the appropriateness of five different sets of values for the 10 input coefficients. Calculated estimates were compared to the only existing set of observed PET values from two free drainage lysimeters at the headquarters of the Department of Meteorological Services (DMS) in Gaborone, Botswana. These values consisted of 36 five-day mean values of PET for grass cover during the period March 21, 1989–20 March, 1990 distributed as follows: fall 9, winter 8, spring 10, summer 9. Estimates were most sensitive to the wind coefficient in the aerodynamic term of the Penman-based equations. Analysis of the residual error between observed and estimated PET showed that the coefficients currently used by DMS best matched the lysimeter observations over the 4 seasons. However, only further comparisons between estimates and long-term, accurate, and multi-locational lysimeter measurements of reference crop PET would establish the set of coefficients appropriate for Penman-based PET estimation across Botswana.     

Relationships between body size and trophic position of consumers in temperate freshwater lakes

Animal body size is a driving force behind trophic interactions within biological communities, yet few studies have explored relationships between body size and trophic position (based on δ¹⁵N) at a broad-scale in freshwater lakes. Therefore, our goals were to (1) determine whether body size is a good predictor of trophic position for multiple pelagic zooplankton taxa and fish communities, and (2) examine how body size-trophic position relationships at the community level compare to species level for fish. Zooplankton and fish were collected from 12 and 7 lakes, respectively, located in the Kawarthas, southern Ontario, Canada. The results indicated that for zooplankton, significant positive but different relationships were found between body size and trophic position for cladocerans, in general, and Daphnia, but not Holopedium. For fish, at the lake community level six out of seven relationships were positive and significant, but again, different among lakes. In contrast, at the species level only three of eight species-specific relationships were significant. Furthermore, for two widespread species, Perca flavescens and Micropterus dolomieu, significant differences were found between community- and lake-specific species relationships. Our community-level models and most species-level models provide evidence that trophic interactions in freshwater lakes are size-based. These results demonstrate that general species models should be applied with caution when using body size to predict trophic position. Additionally, the predictive power of some relationships found here is questionable since, albeit significant, their strengths are generally low. Together, our results suggest that body size may have limited use in predicting trophic position of some biota in temperate freshwater lakes.     

Differences in zooplankton feeding rates and isotopic signatures from three temperate lakes

Bacteria and phytoplankton are integral in the mobilization and transfer of organic matter to higher trophic levels. Hence, we examined their role in zooplankton diets and assessed trends in their nitrogen isotopic variability. We performed feeding experiments with natural particulate organic matter (POM) and four zooplankton groups (Daphnia, Holopedium, large calanoids and small calanoids) to (1) examine whether there are differences in consumption (presented as clearance and ingestion rates) of phytoplankton and bacteria, and (2) determine whether differences in zooplankton clearance and ingestion rates are correlated with their δ¹⁵N isotopic signatures. In general, phytoplankton and bacteria clearance rates and biomass ingested per animal varied significantly among different zooplankton groups within lakes and between lakes for a given zooplankton group. Within a given lake, Daphnia and Holopedium had the highest phytoplankton and bacteria clearance and ingestion rates, followed by large calanoids, and then small calanoids. For a given zooplankton group, bacteria and phytoplankton clearance rates varied among lakes. In contrast, phytoplankton ingestion rates were consistently highest in Dickie Lake for all taxa, whereas bacteria ingestion rates were more variable among lakes for the different zooplankton taxa. The percentage contribution of different phytoplankton taxa to the biomass of phytoplankton ingested also varied significantly among lakes for a given taxa, but there were few differences within a given lake among zooplankton. Zooplankton δ¹⁵N_DOMC values were correlated with their size adjusted phytoplankton and bacteria clearance and ingestion rates. The correlations were stronger with (1) phytoplankton compared to bacteria, and (2) clearance rates compared to ingestion rates of biomass. Together our results suggest that zooplankton taxa with low phytoplankton and bacteria clearance and ingestion rates and higher δ¹⁵N_DOMC are likely exploiting food sources from higher trophic levels.     

Evaluating the suitability of three gridded-datasets and their impacts on hydrological simulation at Scotty Creek in the southern Northwest Territories,Canada

In the southern Northwest Territories (NWT), long time series of historical observations of climate and hydrology are scarce. Gridded datasets have been used as an alternative to instrumental observations for climate analysis in this area, but not for driving models to understand hydrological processes in the southern NWT. The suitability of temperature and precipitation from three-gridded datasets (Australian National University Spline [ANUSPLIN], ERA-Interim, and Modern-Era Retrospective Analysis for Research and Application, Version 2 [MERRA-2]) as forcings for hydrological modelling in a small subcatchment in the southern NWT are assessed. Multiple statistical techniques are used to ensure that structural and temporal attributes of the observational datasets are adequately compared. Daily minimum and maximum air temperatures in gridded datasets are more similar to observations than precipitation. The ANUSPLIN temperature time series are more statistically similar to observations, based on population statistics and temporal structure, than either of ERA-Interim or MERRA-2. The gridded datasets capture the seasonal and annual seasonal variability of precipitation but with large biases. ANUSPLIN precipitation compares better with observations than either ERA-Interim or MERRA-2 precipitation. The biases in these gridded datasets affect run-off simulations. The biases in hydrological simulations are predictable from the statistical differences between gridded datasets and observations and can be used to make informed choices about their use.     

Artisanal and Small-Scale Gold Mining in Senegal: Livelihoods,Customary Authority,and Formalization

In Sub-Saharan Africa, efforts to formalize the artisanal and small-scale gold mining (ASGM) sector under legal frameworks and to improve its environmental and health practices have largely failed as a result of top-down policy measures that make change complicated and burdensome for low-resource miners. Using evidence from a case study of the ASGM sector within areas of Senegal, this article demonstrates that ASGM has become an important source of income for many traditionally agricultural rural populations. The findings point toward the embedded nature of ASGM within customary management structures in Senegal, and demonstrate that customary authority is an important component of ASGM operations and development, and should be recognized and integrated into innovative formalization policies and better practices initiatives.     

Ten best practices to strengthen stewardship and sharing of water science data in Canada

Water science data are a valuable asset that both underpins the original research project and bolsters new research questions, particularly in view of the increasingly complex water issues facing Canada and the world. Whilst there is general support for making data more broadly accessible, and a number of water science journals and funding agencies have adopted policies that require researchers to share data in accordance with the findable, accessible, interoperable, reusable (FAIR) principles, there are still questions about effective management of data to protect their usefulness over time. Incorporating data management practices and standards at the outset of a water science research project will enable researchers to efficiently locate, analyse and use data throughout the project lifecycle, and will ensure the data maintain their value after the project has ended. Here, some common misconceptions about data management are highlighted, along with insights and practical advice to assist established and early career water science researchers as they integrate data management best practices and tools into their research. Freely available tools and training opportunities made available in Canada through Global Water Futures, The Gordon Foundation DataStream, the Digital Research Alliance of Canada Portage Network, Compute Canada, and university libraries, among others are compiled. These include webinars, training videos, and individual support for the water science community that together enable researchers to protect their data assets and meet the expectations of journals and funders. The perspectives shared here have been developed as part of the Global Water Futures programme's efforts to improve data management and promote the use of common data practices and standards in the context of water science in Canada. Ten best practices are proposed that may be broadly applicable to other disciplines in the natural sciences and can be adopted and adapted globally.     

Crustal thickness variations in the margins of the Gulf of California from receiver functions

Receiver functions (RFs) from teleseismic events recorded by the NARS-Baja array were used to map crustal thickness in the continental margins of the Gulf of California, a newly forming ocean basin. Although the upper crust is known to have split apart simultaneously along the entire length of the Gulf, little is known about the behaviour of the lower crust in this region. The RFs show clear P -to- S wave conversions from the Moho beneath the stations. The delay times between the direct P and P -to- S waves indicate thinner crust closer to the Gulf along the entire Baja California peninsula. The thinner crust is associated with the eastern Peninsular Ranges batholith (PRB). Crustal thickness is uncorrelated with topography in the PRB and the Moho is not flat, suggesting mantle compensation by a weaker than normal mantle based on seismological evidence. The approximately W–E shallowing in Moho depths is significant with extremes in crustal thickness of ∼21 and 37 km. Similar results have been obtained at the northern end of the Gulf by Lewis et al., who proposed a mechanism of lower crustal flow associated with rifting in the Gulf Extensional Province for thinning of the crust. Based on the amount of pre-Pliocene extension possible in the continental margins, if the lower crust did thin in concert with the upper crust, it is possible that the crust was thinned during the early stages of rifting before the opening of the ocean basin. In this case, we suggest that when breakup occurred, the lower crust in the margins of the Gulf was still behaving ductilely. Alternatively, the lower crust may have thinned after the Gulf opened. The implications of these mechanisms are discussed.     

Active deformation in the eastern Swiss Alps: post-glacial faults, seismicity and surface uplift

Post-glacial tectonic faults in the eastern Swiss Alps occur as single lineaments, clusters of faults or extensive fault zones consisting of several individual faults aligned along the same trend. The orientation of the faults reflects the underlying lithology and the pre-existing structures (joints, pervasive foliations) within these lithologies. Most post-glacially formed faults in the area around Chur, which undergoes active surface uplift of 1.6 mm/year, trend E–W and cut across Alpine and glacial features such as active screes and moraines. Additionally, there are NNW and ENE striking faults reactivating pervasive Alpine foliations and shear zones. Based on a comparison with the nodal planes of recent earthquakes, E–W striking faults are interpreted as active faults. Because of very short rupture lengths and mismatches of fault location with earthquake distribution, magnitude and abundance, the faults are considered to be secondary faults due to earthquake shaking, cumulative deformation in post- or interseismic periods or creep, and not primary earthquake-related faults. The maximum of recent surface uplift rates coincides with the youngest cooling of the rocks according to apatite fission-track data and is therefore a long-lived feature that extends well into pre-glacial times. Isostatic rebound owing to overthickened crust or to melting of glacial overburden cannot explain the observed surface uplift pattern. Rather, the faults, earthquakes and surface uplift patterns suggest that the Alps are deforming under active compression and that the Aar massif basement uplift is still active in response to ongoing collision.