Intense drought and flooding events in the Rio Negro and relation with the tropical Pacific and Atlantic variability modes

The relationship of the hydrological variability of the Rio Negro in Manaus and the dominant large-scale climate variability patterns for the 1902–2007 period is investigated using the quantile method and composite analyses. Variations of the Rio Negro Level (RNL) during its 3-month high (May to July—MJJ) and low (October to December—OND) phases are examined separately. The El Niño (La Niña) related maximum warming (cooling) in the central tropical Pacific during its mature and decaying stages modulates the atmospheric circulation in the tropics and displaces the Walker circulation cell eastward (westward), so that its sinking (rising) branch occurs over western Amazon and causes negative (positive) precipitation anomalies in this region. These anomalous climate conditions occur before the Rio Negro high phase (MJJ) and contribute to reduce (increase) the RNL and lead to a very low (very high) event in the river. On the other hand, the SST variability modes in the tropical Atlantic mainly during the transition from wet to dry season modulate the precipitation variations over western Amazon in OND. The very high events are more frequent after the 1960’s decade and the very low events, before the 1930’s decade. Therefore, the occurrence of these events contains a multidecadal scale variability. The results also indicate that the variations in the rainfall in western Amazon occur up to 9 months in advance and modulate the RNL in Manaus. The results presented here might be useful for monitoring purposes of the RNL.

     

New production in the subarctic Pacific Ocean: Net changes in nitrate concentrations, rates of nitrate assimilation and accumulation of particulate nitrogen

Changes in water column nitrate and particulate nitrogen (PN) concentrations and rates of nitrate assimilation at 50°N 145°W were measured over a four-month interval for 1984, 1987 and 1988. Rates of nitrate depletion in the upper 80m of the water column averaged 12mg N m⁻²d⁻¹, but most of the net depletion occurred during May when rates were high (75mg N m⁻²d⁻¹) compared to later in the year. Particulate nitrogen (collected on GF/F filters) increased 2- to 3-fold during the month of May and accounted for 30–60% of the net nitrate depletion for May. Mean rates of PN accumulation for the 4-month intervals were 2.4mg N m⁻²d⁻¹ and accounted for about 20% of the net nitrate depletion. Rates of nitrate assimilation (measured in incubation bottles with ¹⁵N) averaged 45.0±4.5mg N m⁻²d⁻¹ (mean±SD), and appeared to decrease between May and September. A good correspondence between in situ and incubation estimates of nitrate assimilation was found for the 4-month comparison, but not for the month of May when net changes in nitrate concentrations were greatest. Vertical and horizontal inputs of nitrate are about the same order of magnitude as biological removal, thus the high inout of nitrate into the euphotic zone contributed to the continuously high nitrate concentrations in this region. Seasonal changes in nitrate and PN were significant and need to be considered in comparisons of new and export production.     

Ubuntu nests and the emergence of an African metropolis

Cities are not homogenous sociocultural entities. The city of Nairobi exhibits the phenomena of ‘cities within cities’ and ‘African city forms’. Social and economic forms of African, western and Asian cities compete for space within Nairobi. This paper refers to the African city form as the ‘African metropolis’, which exhibits the African logic, norms and values in its architecture and human social relations. The African metropolis is made up of slums, urbanized villages, self‐developed urban fringes and indigenous markets. In urban literature, these spaces are referred to as informal or unplanned settlements. As drivers of this African form of urbanism, traders and artisans use the African logic, norms and values in the construction of the African metropolis. The traders and artisans contribute to the African metropolis, by hiring labour and investing surplus earnings, and are bonded into Ubuntu communities of family, friendship and ethnicity. The paper is based on data gathered through a questionnaire survey of traders and artisans. It contributes to urban theory, by showing how less dominant and subtle forces contribute to city‐forming processes. I propose the concept of cultural villages as a strategy for blending African logic, norms and values with those of global urban planning.     

It takes a garden: Cultivating citizen-subjects in organized garden projects

Since the 1980’s organized garden projects have proliferated in a institutional settings associated with the “roll-out” neoliberal state and the sad consequences of neoliberalism more generally: jails, schools, hospitals and other clinical settings for “at-risk” populations. This article advances the concept “organized garden project” over the richly connotative, but inchoate term “community garden,” and links the long episodic history of garden projects with changing discourses about the supposedly transformative power of gardening practice for individual and social transformation. The article highlights two organized garden projects within the San Francisco Bay area, a chief locus in the movement to using organized garden projects to produce new individual and collective subjectivities. The case studies assess, from the typically unambiguous standpoint of the garden organizers, the nature of the subjectivity that gardening practice is supposed to produce, the need for such alternative subjectivity and the “difference” such alternatives are believed to make for the individual and in the wider social, political and economic milieu.     

Differential Late Paleozoic active margin evolution in South-Central Chile (37°S–40°S) – the Lanalhue Fault Zone

The N–S oriented Coastal Cordillera of South Central Chile shows marked lithological contrasts along strike at 38°S. Here, the sinistral NW–SE-striking Lanalhue Fault Zone (nomen novum) juxtaposes Permo-Carboniferous magmatic arc granitoids and associated, frontally accreted metasediments (Eastern Series) in the northeast with a Late Carboniferous to Triassic basal-accretionary forearc wedge complex (Western Series) in the southwest. The fault is interpreted as an initially ductile deformation zone with divergent character, located in the eastern flank of the basally growing, upwarping, and exhuming Western Series. It was later transformed and reactivated as a semiductile to brittle sinistral transform fault. Rb–Sr data and fluid inclusion studies of late-stage fault-related mineralizations revealed Early Permian ages between 280 and 270 Ma for fault activity, with subsequent minor erosion. Regionally, crystallization of arc intrusives and related metamorphism occurred between 306 and 286 Ma, preceded by early increments of convergence-related deformation. Basal Western Series accretion started at >290 Ma and lasted to 250 Ma. North of the Lanalhue fault, Late Paleozoic magmatic arc granitoids are nearly 100 km closer to the present day Andean trench than further south. We hypothesize that this marked difference in paleo-forearc width is due to an Early Permian period of subduction erosion north of 38°S, contrasting with ongoing accretion further south, which kinematically triggered the evolution of the Lanalhue Fault Zone. Permo-Triassic margin segmentation was due to differential forearc accretion and denudation characteristics, and is now expressed in contrasting lithologies and metamorphic signatures in todays Andean forearc region north and south of the Lanalhue Fault Zone.     

Cryptic Blooms: Are Thin Layers the Missing Connection?

Harmful algal blooms (HABs) are common in Monterey Bay, CA, and have resulted in repeated closures of shellfish fisheries and the poisoning and death of marine mammals. In the majority of instances, HAB events in this region are first detected by the presence of sick or dying animals. The phrase “cryptic blooms” was adopted to denote the appearance of poisoning at higher trophic levels with no prior evidence of a large phytoplankton bloom. We hypothesize that the onset of many HAB events goes undetected because the bloom is initially concentrated in discrete thin subsurface layers in the water column that are easily missed by conventional sampling and monitoring methods. In this paper, we report on the detection and monitoring of a subsurface layer of phytoplankton in northern Monterey Bay, CA, using a high-resolution, autonomous profiler. This ‘thin layer,’ which measured from 10 cm to 3 m in thickness (85% < 2 m; 54% < 1 m), persisted over a 7-day period near the base of the pycnocline. The phytoplankton assemblage in the layer was primarily composed of a multi-species assemblage of Pseudo-nitzschia including the toxin-producing species Pseudo-nitzschia australis. Concentrations of toxic phytoplankton (P. australis), cyanobacteria, and bacteria in the layer were significantly higher than outside the layer (P < 0.05). Counts of total Pseudo-nitzschia spp. showed similar levels of enrichment in the layer compared to outside the layer. Our findings indicate that, when monitoring for HABs, it is critical to sample at scales appropriate to resolve thin layers. Thin layers have been identified as a common recurrent feature in a variety of coastal systems, suggesting that the use of autonomous high-resolution vertical profilers coupled with targeted sampling, could allow more timely detection of HABs in many coastal environments.     

The self-organising of youth volunteers during the Rena oil spill in New Zealand

ABSTRACT

This study explores the communication and organising of youth volunteers during a crisis, focusing on how they conceived, framed, and executed self-organising efforts during the 2011 Rena oil spill in New Zealand. It offers insights into the intersections of self-organising, youth volunteering and crisis events which have not been researched before. The study addresses two core research questions: 1. how was ‘volunteering’ conceptualised by youth volunteers involved in the Rena crisis; and 2. how did these volunteers communicate and self-organise during this crisis? The findings indicate that self-organising emerged out of a resistance towards structured responses and as a reaction to the inability of the official volunteer response to meet the needs of the community. Self-organised efforts were particularly attractive among youth volunteers because they offered flexibility, required minimal administrative processes, and fostered an environment of innovation and creativity. The volunteers’ youthful energy and technological aptitude additionally drove their self-organised responses. The study identifies the considerable challenges that crisis officials faced in utilising youth volunteers despite the significant advantages of self-organising.     

Parameterization,sensitivity analysis,and inversion: an investigation using groundwater modeling of the surface-mined Tivoli-Guidonia basin (Metropolitan City of Rome,Italy)

With respect to model parameterization and sensitivity analysis, this work uses a practical example to suggest that methods that start with simple models and use computationally frugal model analysis methods remain valuable in any toolbox of model development methods. In this work, groundwater model calibration starts with a simple parameterization that evolves into a moderately complex model. The model is developed for a water management study of the Tivoli-Guidonia basin (Rome, Italy) where surface mining has been conducted in conjunction with substantial dewatering. The approach to model development used in this work employs repeated analysis using sensitivity and inverse methods, including use of a new observation-stacked parameter importance graph. The methods are highly parallelizable and require few model runs, which make the repeated analyses and attendant insights possible. The success of a model development design can be measured by insights attained and demonstrated model accuracy relevant to predictions. Example insights were obtained: (1) A long-held belief that, except for a few distinct fractures, the travertine is homogeneous was found to be inadequate, and (2) The dewatering pumping rate is more critical to model accuracy than expected. The latter insight motivated additional data collection and improved pumpage estimates. Validation tests using three other recharge and pumpage conditions suggest good accuracy for the predictions considered. The model was used to evaluate management scenarios and showed that similar dewatering results could be achieved using 20 % less pumped water, but would require installing newly positioned wells and cooperation between mine owners.     

Assessing urban rainfall-runoff response to stormwater management extent

We report an empirical analysis of the hydrologic response of three small, highly impervious urban watersheds to pulse rainfall events, to assess how traditional stormwater management (SWM) alters urban hydrographs. The watersheds vary in SWM coverage from 3% to 61% and in impervious cover from 45% to 67%. By selecting a set of storm events that involved a single rainfall pulse with >96% of total precipitation delivered in 60 min, we reduced the effect of differences between storms on hydrograph response to isolate characteristic responses attributable to watershed properties. Watershed-average radar rainfall data were used to generate local storm hyetographs for each event in each watershed, thus compensating for the extreme spatial and temporal heterogeneity of short-duration, intense rainfall events. By normalizing discharge values to the discharge peak and centring each hydrograph on the time of peak we were able to visualize the envelope of hydrographs for each group and to generate representative composite hydrographs for comparison across the three watersheds. Despite dramatic differences in the fraction of watershed area draining to SWM features across these three headwater tributaries, we did not find strong evidence that SWM causes significant attenuation of the hydrograph peak. Hydrograph response for the three watersheds is remarkably uniform despite contrasts in SWM, impervious cover and spatial patterns of land cover type. The primary difference in hydrograph response is observed on the recession limb of the hydrograph, and that change appears to be associated with higher storm-total runoff in the watersheds with more area draining to SWM. Our findings contribute more evidence to the work of previous authors suggesting that SWM is less effective at attenuating urban hydrographs than is commonly assumed. Our findings also are consistent with previous work concluding that percent impervious cover may have greater influence on runoff volume than percent SWM coverage.     

The late Pleistocene environment of the Eastern West Beringia based on the principal section at the Main River,Chukotka

Chukotka is a key region for understanding both Quaternary environmental history and transcontinental migrations of flora and fauna during the Pleistocene as it lies at the far eastern edge of Asia bordering the Bering Sea. The now submerged land bridge is the least understood region of Beringia yet the most critical to understanding migrations between the Old and New Worlds. The insect fauna of the Main River Ledovy Obryv (Ice Bluff) section, which is late Pleistocene in age (MIS 3-2), is markedly different from coeval faunas of areas further to the west, as it is characterized by very few thermophilous steppe elements. From the fauna we reconstruct a steppe-tundra environment and relatively cold conditions; the reconstructed environment was moister than that of typical steppe-tundra described from further west. The data from this locality, if typical of the Chukotka Peninsula as a whole, may indicate that a barrier associated with the environments of the land bridge restricted trans-Beringian migrations, particularly the more thermophilous and xeric-adapted elements of the Beringian biota, supporting the hypothesis of a cool but moist land-bridge filter inferred from evidence from several other studies.