Reflections on participatory research

Participatory research approaches are increasingly popular with geographers in developed as well as developing countries, as critical qualitative methodologies which at their best work with participants to effect change. This paper adds to recent debates over the methodologies, practices, philosophical and political issues involved. Drawing on a project on young people, exclusion and crime victimization in Newcastle upon Tyne, England, we discuss the limitations of participatory diagramming and illustrate some of the social and political barriers to meaningful participation in, and action from, this type of research.     

Subsolidus physical and chemical mixing of granite and gabbro during mylonitization, South Victoria Land, Antarctica

At Dromedary Massif, Southern Victoria Land, Antarctica, a suite of coarse-grained granite dykes cross-cuts a gabbro pluton which has been partially metamorphosed at amphibolite facies. During regional deformation, strain has been inhomogeneously distributed through the gabbro pluton and has been concentrated in granite dykes. In zones of relatively high strain, the granite dykes have developed a mylonitic fabric. A high strain gradient between granitic mylonite and metagabbroic host rock has induced isochemical mylonitization of the margin of the host. This grain size reduction allowed chemical diffusion between granitic and metagabbroic mylonites, resulting in a marginal zone of biotite-rich mylonite with intermediate composition. Biotite-rich mylonite decoupled from metagabbroic mylonite and flowed with granitic mylonite. Continued folding and transposition of granitic mylonite and biotite-rich mylonite has produced compositionally banded mylonite zones through thorough and irreversible mixing of the two lithologies.     

A 24,700-yr paleolimnological history from the Peruvian Andes

A new paleolimnological dataset from Lake Pacucha (13 °S, 3095 m elevation) in the Peruvian Andes provides evidence of changes in lake level over the past 24,700 yr. A late-glacial highstand in lake level gave way to an early-Holocene lowstand. This transition appears to have paralleled precessional changes that would have reduced insolation during the wet-season. The occurrence of benthic/salt-tolerant diatoms and CaCO₃ deposition suggest that the lake had lost much of its volume by c. 10,000 cal yr BP. Pronounced Holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c. 8300 to 5000 cal yr BP. While a polymictic lake formed at c. 5000 cal yr BP. These relatively wet conditions were interrupted by a series of drier events, the most pronounced of which occurred at c. 750 cal yr BP. Paleolimnological changes in the Holocene were more rapid than those of either the last glacial maximum or the deglacial period.     

Recapturing quality field experiences and strengthening teaching–research links

Because of unwieldy numbers, and in an attempt to strengthen teaching–research links, the teaching team of 'Field Research Methods' discarded a class fieldtrip in favour of more flexible fieldwork. The new approach continues to use inquiry-based learning but has research problems more closely linked to staff interests. Students are responsible for most aspects of the research process including some logistical planning of fieldwork. Although often anxious at first, students welcomed this approach and appreciated the host of transferable and research skills they developed. Tutors benefited from the enhanced learning outcomes for students and a strengthening of teaching–research links.     

Universality and variability in basin outlet spacing: implications for the two-dimensional form of drainage basins

It has been observed that the distance between the outlets of transverse basins in orogens is typically half of the distance between the main divide and the range front irrespective of mountain range size or erosional controls. Although it has been suggested that this relationship is the inherent expression of Hack's law, and/or possibly a function of range widening, there are cases of notable deviations from the typical half‐width average spacing. Moreover, it has not been demonstrated that this general relationship is also true for basins in morphologically similar nonorogenic settings, or for those that do not extend to the main drainage divide. These issues are explored by investigating the relationship between basin outlet spacing and the 2‐dimensional geometric properties of drainage basins (basin length, main valley length and basin area) in order to assess whether the basin outlet spacing‐range width ratio is a universal characteristic of fluvial systems. We examined basins spanning two orders of magnitude in area along the southern flank of the Himalayas and the coastal zone of southeast Africa. We found that the spacing between basin outlets (L_os) for major transverse basins that drain the main divide (range‐scale basins) is approximately half of the basin length (L_b) for all basins, irrespective of size, in southeast Africa. In the Himalayas, while this ratio was observed for eastern Himalayan basins (a region where the maximum elevations coincided with the main drainage divide), it was only observed in basins shorter than ～30 km in the western and central Himalayas. Our analysis indicates that basin outlet spacing is consistent with Hack's law, apparently because the increase in basin width (represented by outlet spacing) with basin area occurs at a rate similar to the increase in main stream length (L_v) with basin area. It is suggested that most river systems tend towards an approximately diamond‐shaped packing arrangement, and this applies both to the nonorogenic setting of southeast Africa as well as most orogenic settings. However, in the western Himalayas shortening associated with localised rock uplift appears to have occurred at length scales smaller than most the basins examined. As a result rivers in basins longer than ～30 km have been unable to erode in a direction normal to the range front at a sufficiently high rate to sustain this form and have been forced into an alternative, and possibly unstable, packing arrangement.     

Assessment of oxygen plasma ashing as a pre-treatment for radiocarbon dating

This study investigates the potential of low-temperature oxygen plasma ashing as a technique for decontaminating charcoal and wood samples prior to radiocarbon dating. Plasma ashing is demonstrated to be rapid, controllable and surface-specific. Different organic materials clearly ash at different rates, however, the ability of plasma ashing to selectively ash different organic components is limited in heterogeneous sample matrices. This is because oxidation is confined to the immediate sample surface. Comparison of radiocarbon dates obtained from identical aliquots of contaminated ancient charcoal pre-treated by acid–base–acid (ABA), acid–base-oxidation-stepped combustion (ABOx-SC) and plasma ashing suggests that the technique performs as well as the ABA pre-treatment but does not remove as much contamination as the ABOx-SC technique. Plasma ashing may be particularly useful in cases where sample size is limiting.     

The effect of nitrogen loading on a brackish estuarine faunal community: A stable isotope approach

Coastal ecosystems worldwide face increased nutrient enrichment from shoreline and watershed development and atmospheric pollution. We investigated the response of the faunal community of a small microtidal estuary dominated byRuppia maritima (widgeon grass) in Maine, United States, to increased nitrogen loading using an in situ mesocosm enrichment experiment. Community response was characterized by assessing quantitative shifts in macroinvertebrate community composition and identifying changes in food web structure using stable carbon and nitrogen isotope ratios of producers and consumers. The community was dominated by brackish water invertebrates including midge larvae, oligochaetes, damselfly larvae, amphipods, and ostracods. Experimental nutrient additions resulted in significantly lower densities of herbivorous chironomids and predatory damselflies and greater densities of deposit feeding oligochaetes. Grazing midge larvae (Chironomidae:Dicrotendipes, Cricotopus) consumed epiphytic algae under both natural and enriched conditions. Deposit feedingChironomus was dependent on allochthonous sources of detritus under natural conditions and exhibited a shift to autochthonous sources of detritus under enriched conditions. PredatoryEnallagma primarily consumed grazing chironomids under all but the highest loading conditions. Experimental nutrient loading resulted in an increase in generalist deposit feeders dependent on autochthonous sources of detritus.     

High-pressure phase equilibria and element partitioning experiments on Apollo 15 green C picritic glass: Implications for the role of garnet in the deep lunar interior

We report results of nominally anhydrous near-liquidus experiments on a synthetic analog to very low-titanium Apollo 15 green C lunar picritic glass from ∼2 to 5 GPa. Apollo 15 green C glass (A15C) is saturated with garnet and pyroxene on the liquidus at ∼3 GPa. However, such an assemblage is unlikely to represent the lunar-mantle source region for this glass, and instead an olivine + orthopyroxene-dominated source is favored, in accord with earlier lower-pressure experiments on A15C. Near-liquidus garnet has a slight but significant majorite component at ∼5 GPa in this iron-rich bulk composition, as expected from our previous work in ordinary-chondritic bulk compositions. Ion microprobe measurements of partitioning of Sr, Ba, Sc, Nd, Sm, Dy, Yb, Y, Zr, Hf, and Th between garnet and coexisting melt in these experiments are the first garnet partition coefficients (D values) available that are directly relevant to lunar compositions. D values for these garnets differ significantly compared to D values for garnets grown in more magnesian, terrestrial bulk compositions, which until now are all that have been available in modeling the possible role of garnet in the lunar interior. For example, D values for heavy rare earth elements are lower than are those from terrestrial basaltic systems. These partitioning values are well-described by the lattice-strain partitioning model, but predictive relationships for garnet partitioning using that model fail to match the measured values, as was the case in our earlier work on chondritic compositions. Using our new D values in place of the “terrestrial” values in a variety of models of lunar petrogenesis, we suggest that garnet is unlikely to be present in the source regions for very titanium-poor lunar liquids despite its appearance on the liquidus of A15C.     

Temporal variability in the isotopic niches of rocky shore grazers and suspension‐feeders

Carbon and nitrogen stable isotope ratios were measured in rocky inter‐tidal suspension‐feeders (brown mussels and cape reef worms) and grazers (goat's eye limpets and cape sea urchins) to determine the influences of lifestyle and time on the diets of consumers. Niche partitioning between consumer species within the same feeding guild was assessed using isotopic niche area (a proxy for trophic niche). Specimens were collected monthly at a single site in Southeastern South Africa from July 2010 to June 2011. Temporal variations in isotopic signatures were generally greater in the suspension‐feeders compared with the grazers, isotopic niche widths were smaller in the suspension‐feeders and intra‐population variations in isotope signatures were larger in the grazers. No inter‐specific niche overlap (according to standard ellipse areas) was observed within either feeding guild unless standardization calculations were used. Temporal variations in the diets of all the consumers appeared uncoupled from temporal variability in the isotopic signatures of basal resources in the region; as such, shifts in the consumer diets most likely pertained to feeding behaviour and food preferences. Our data provide new insights into how syntopic rocky shore consumers coexist by partitioning their temporally variable food environment.