Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.     

Mapping conservation priorities and connectivity pathways under climate change for tropical ecosystems

Climate change and land use conversion are global threats to biodiversity. Protected areas and biological corridors have been historically implemented as biodiversity conservation measures and suggested as tools within planning frameworks to respond to climate change. However, few applications to national protected areas systems considering climate change in tropical countries exist. Our goal is to define new priority areas for biodiversity conservation and biological corridors within an existing protected areas network. We aim at preserving samples of all biodiversity under climate change and facilitate species dispersal to reduce the vulnerability of biodiversity. The analysis was based on a three step strategy: i) protect representative samples of various levels of terrestrial biodiversity across protected area systems given future redistributions under climate change, ii) identify and protect areas with reduced climate velocities where populations could persist for relatively longer periods, and iii) ensure species dispersal between conservation areas through climatic connectivity pathways. The study was integrated into a participatory planning approach for biodiversity conservation in Costa Rica. Results showed that there should be an increase of 11 % and 5 % on new conservation areas and biological corridors respectively. Our approach integrates climate change into the design of a network of protected areas for tropical ecosystems and can be applied to other biodiversity rich areas to reduce the vulnerability of biodiversity to global warming.     

Common cause or common concern? The role of common lands in the post-productivist countryside

Summary The aim of this paper is to contribute towards a better understanding of the contemporary position of commons as a land resource, and to evaluate whether commons have a distinct role to play in today's 'post-productivist' countryside. Following the government's recent recognition of the multi-functional role of commons, the paper sets out to investigate whether this can be achieved through existing agri-environmental schemes. A case study of commons in the Cambrian Mountains (Wales) enables an assessment of the compatibility of one recent agri-environmental scheme, the ESA scheme, with commons management. It is concluded that new legislation and policy are needed, and that agri-environmental policy may provide an opportunity to develop a framework within which the management of common land can be improved to meet conservation and amenity as well as farming objectives.     

Inserting scales of urban politics: the possibilities of meso-urban governance shims

This article explores the geographic literature on governance at smaller-than-urban but larger-than-household scales, identifying a relative inattention to neighborhood and other partial-city scales of governance. Hegemonic power relationships are institutionalized at particular scales of state government (e.g. national, regional, municipal) and state-sanctioned governing units (e.g. jurisdictional districts or supranational bodies), which in turn shapes urban research. We propose a new analytical term, governance shims, to describe the insertion of new scales of governance between those already reified and reproduced; institutions at such scales may be unusually grounded in authority beyond the state. Geographers seem well positioned to explore the characteristics of governance shims at the meso-urban scale. We illustrate this by briefly tracing how common interest communities (CICs), housing cooperatives, and community land trusts (CLTs) might be analyzed through a shims approach. Provocatively, emergent governance at the meso-urban scale often leverages idiosyncratic structures of property ownership to produce institutional authority.     

The Loncopué Trough: A Cenozoic basin produced by extension in the southern Central Andes

The Loncopué Trough is located in the hinterland Andean zone between 36°30′ and 39°S. It constitutes a topographic low bounded by normal faults and filled by lavas and sediments less than 5 Ma old. Reprocessed seismic lines show wedge-like depocenters up to 1700 m deep associated with high-angle faults, correlated with the 27–17 Ma Cura Mallín basin deposits, and buried beneath Pliocene to Quaternary successions and Late Miocene foreland sequences. The southern Central Andes seem to have been under extension in the hinterland zone some 27 Ma ago and again at approximately 5 Ma ago. This last extensional period could have been the product of slab steepening after a shallow subduction cycle in the area, although other alternatives are discussed. Orogenic wedge topography, altered by the first extensional stage in the area, was recovered through Late Miocene inversion, and was associated with foreland sequences. However, since the last extension (<5 Ma) the Andes have not recovered their characteristic contractional behavior that controlled past orogenic growth.     

Defining communities of interest: political self-definition in Los Angeles County during the first California Citizen’s Redistricting Commission

GeoJournal - This study analyzes how the 2010 establishment of the California Citizen’s Redistricting Commission allowed communities to assert their presence and define their borders in order...     

Sedimentology of a debris‐rich,perhumid valley glacier margin in the Rakaia Valley,South Island,New Zealand

The sedimentology and stratigraphy of a multi‐phase glaciation sequence dating to Marine Isotope Stage 6 in the Rakaia Valley, South Island, New Zealand, is presented. This outcrop presents an example of the depositional signature of an end member of temperate valley glaciation, where voluminous sediment supply in a tectonically active setting combines with high annual temperatures and low seasonality to generate significant year‐round glacifluvial activity. Such glacial systems produce geological–climatic units that are dominated by thick sequences of aggradational gravels and proglacial lake sediments trapped behind outwash heads during deglaciation. At Bayfields Cliff, outwash sequences record an oscillating glacier margin marked by a sequence of glacier‐fed, Gilbert‐type deltas. The deltas are cut by numerous small‐scale, syndepositional, normal faults indicating both loss of glacier support and melt‐out of buried ice. A larger‐scale thrust fault system reflects late‐stage ice overrun. Braid plain gravels and chaotic disturbed glacial lake sediments are also recorded. A notable feature of these systems is the virtual absence of till in an environment with much other evidence for proximal ice. Cumulatively we regard these sediment–landform associations as diagnostic of debris‐laden, perhumid, temperate valley glacier systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Nutrient inputs from submarine groundwater discharge on the Santiago reef flat, Bolinao, Northwestern Philippines

Submarine groundwater discharge (SGD) on the reef flat of Bolinao, Pangasinan (Philippines) was mapped using electrical resistivity, 222Rn, and nutrient concentration measurements. Nitrate levels as high as 126 μM, or 1-2 orders of magnitude higher than ambient concentrations, were measured in some areas of the reef flat. Nutrient fluxes were higher during the wet season (May-October) than the dry season (November-April). Dissolved inorganic nitrogen (DIN=NO3+NO2+NH4) and soluble reactive phosphorus (SRP) fluxes during the wet season were 4.4 and 0.2 mmoles m(-2) d(-1), respectively. With the increase population size and anthropogenic activities in Bolinao, an enhancement of SGD-derived nitrogen levels is likely. This could lead to eutrophic conditions in the otherwise oligotrophic waters surrounding the Santiago reef flat.