Diatoms and sockeye salmon (Oncorhynchus nerka) population dynamics: Reconstructions of salmon-derived nutrients over the past 2,200 years in two lakes from Kodiak Island, Alaska

The return of hundreds to millions of adult sockeye salmon (Oncorhynchus nerka), which have returned from the ocean to their natal nursery lake environment to spawn, can result in significant nutrient loading. By analyzing sedimentary diatom assemblages from nursery lakes, we demonstrated that a salmon-derived nutrient signal could be traced over time and be used to infer past sockeye salmon population dynamics. We conducted a 2,200 year paleolimnological study of two Alaskan sockeye salmon nursery lakes, Karluk and Frazer lakes. The two lakes are very similar, except that sockeye salmon were only introduced into Frazer Lake in 1951 (first spawners returned in 1956). In both lakes we found a strong correspondence between diatom assemblages and the number of adult salmon spawners recorded in the historical data (40 and 70 years for Frazer and Karluk lakes, respectively). Given this robust relationship, we then used our analyses of diatoms from Karluk Lake over the past 2,200 years to gain insight into salmon-derived nutrient loading changes (which are directly related to the number of sockeye salmon spawners). The diatom record from Karluk Lake recorded dramatic species changes on both decadal and century timescales, and was strongly correlated with an independent indicator of sockeye salmon abundances, ¹⁵N. Together, these data suggest pronounced variability in sockeye salmon abundances at Karluk Lake over the past 2,200 years. The direct impacts of regional environmental variability were not likely responsible for the patterns apparent in Karluk Lake, as the diatom and ¹⁵N profiles from Frazer Lake were relatively stable prior to the introduction of sockeye salmon. Application of total phosphorus transfer functions to the Karluk and Frazer lakes' diatom records revealed that sockeye salmon carcasses substantially increased the trophic status in these lakes, which has important implications for the health of juvenile salmon that rear in nursery lakes. Overall, this paper illustrates the potential use of diatoms in reconstructing past sockeye salmon population dynamics, which in turn can lead to a greater understanding of the mechanisms influencing abundances of sockeye salmon.     

Evidence for recent warming from perturbed geothermal gradients: examples from eastern Canada

Recent variations of the surface temperature of the Earth can be inferred from borehole temperature measurements. Generalized inversion is used to extract the information from the data; the potential of the method is evaluated. Tests were performed with synthetic data to demonstrate the effectiveness of the inversion to recover the gross features of the surface temperature history even when the data are affected by noise and errors. The tests show that it is possible to reconstruct the long term changes in ground temperature during the past 300 years; the resolution decreases with time, in particular if noise and errors must be filtered. Temperature logs, obtained in eastern Canada, and not suspected of being affected by non-climatic factors, have been inverted. The analysis confirms that eastern Canada has experienced warming by 1 to 2°C over the past 100–200 years. The relationship between air and ground temperatures has been examined. In eastern Canada ground temperature follows air temperature closely in summer but stays well above air temperature in winter. The number of days with snow on the ground correlates with the difference between annual mean ground and air temperature.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate-Program     

A magnetotelluric investigation of the structural geology beneath Charlevoix Crater, Quebec

The results of ten tensor magnetotelluric soundings recorded within the Charlevoix crater are presented. The geological complexity of the region (the crater is located at the junction of two major geological provinces, i.e. the crystalline basement of the Canadian shield and the more conductive sediments of the Appalachian system) and the amount of cultural noise present in our data prevent a highly definitive interpretation of the shallow structure. A subhorizontal conductive fault related to Rondot's (1971) structural sketch of the original impact structure may exist within the upper 5 km, but it is not completely constrained by the data. Pseudo 3D modelling using stacked thin sheets indicates that superficial patches of high conductivity may explain the large anisotropy observed at the long periods and suggests that our deeper structures fit well with the 2D model previously proposed by Kurtz (1982) for the region.     

A general model for Mt. Ruapehu lahars

A mathematical model of the motion of lahars is presented. Lahar flows and travel speeds are calculated using a kinematic wave model which equates gravitational accelerations to frictional losses. A chezyor Manning-type law of friction is assumed, in which lahar flow rate is a simple power function of lahar depth, multiplied by another simple power of the chanel slope. Use of the model requires knowledge of essentially only one parameter which appears to be relatively insensitive for flows down a given channel. Variable channel slope effects are removed by a longitudinal scaling which applies to all flows down a given channel. For lahars generated by a single explosive event it is unnecessary to perform numerical calculations to predict lahar flow and travel time, but for lahnars produced by multiple sources in which different lahar flows are interacting, numerical calculations appear necessary. The model is applied to all recorded lahar flows from Mt. Ruapehu, and satisfactorily described all lahar flows generated by a single explosive mechanism. Such flows depend essentially only on total lahar volume. The 1968 Mt. Ruapehu lahar, generated by a series of smaller eruptive mechanisms, was modelled as the interaction of seven point sources of fluid originating from positions mathematically extrapolated up the mountain. Good agreement was obtained between the predicted times of formation of these 1968 lahars, and the times of greatest seismic amplitude.     

Mapping and measuring the ecological embeddedness of food supply chains

The status of nature in food systems is the subject of this paper, which looks into the ecological embeddedness of the Austrian food system both on the national level and in a regional case study. By a first attempt to measure and map ecological embeddedness, the author intends to contribute to the operationalisation of the embeddedness concept, which is characterised as ambivalent, fuzzy and dynamic (see e.g., [Goodman, D., 2003. The quality ‘turn’ and alternative food practices: reflections and agenda. Editorial. Journal of Rural Studies 19 (1), 1-7; Markusen, A., 1999. Fuzzy concepts, scanty evidence, policy distance: the case for rigour and policy relevance in critical regional studies. Regional Studies 33, 869-884; Hess, M., 2004. ‘Spatial’ relationships? Towards a reconceptualization of embeddedness. Progress in Human Geography 28 (2), 165-186]). The paper starts with a critical outline of the academic discourse on embeddedness in food chain studies. In the second section, general developments in the Austrian food system and their ecological implications are illustrated for the national level. Thereafter in a case study, the author tries to map and measure the ecological embeddedness of two conventional bread chains. The focus on conventional food chains provides a contrast with the growing body of embeddedness studies concentrating on alternative food chains. The author concludes that for both conventional as well as alternative food chains, the mode of ecological embeddedness or the degree of a food chain’s commitment to particular landscapes could become important factors for the maintenance, enhancement and capture of ecological value.