Inverse modeling for seawater intrusion in coastal aquifers: Insights about parameter sensitivities,variances, correlations and estimation procedures derived from the Henry problem

Inverse modeling studies employing data collected from the classic Henry seawater intrusion problem give insight into several important aspects of inverse modeling of seawater intrusion problems and effective measurement strategies for estimation of parameters for seawater intrusion. Despite the simplicity of the Henry problem, it embodies the behavior of a typical seawater intrusion situation in a single aquifer. Data collected from the numerical problem solution are employed without added noise in order to focus on the aspects of inverse modeling strategies dictated by the physics of variable-density flow and solute transport during seawater intrusion. Covariances of model parameters that can be estimated are strongly dependent on the physics. The insights gained from this type of analysis may be directly applied to field problems in the presence of data errors, using standard inverse modeling approaches to deal with uncertainty in data.     

The 2012 Olympic Learning Legacy Agenda – the intentionalities of mobility for a new London model

This paper investigates the emergence of a Learning Legacy Agenda (LLA) in the wake of the London 2012 Olympic Games as a governmental tool for the dissemination of urban development and infrastructure project delivery best practice. Focusing on the inception, coordination and implementation of the LLA we outline the intentionalities of mobility that underpin its formation and appropriation and suggest how this points to the emergence of a new “London model” of development and governance. Three intentionalities of knowledge capture, public duty and extra-local salience are unpacked to demonstrate the range of ways in which the bureaucratically initiated LLA banner has been used by various development actors and organisations to validate their existing practices. The case study of the LLA as an institutionalised governance apparatus is used to analyse the impact of specific forms of social relations on the ways in which “models” are produced, what their content consists of, how dominant agendas and narratives co-evolve with the priorities of an assemblage of actors and the processes of selective abstraction used to curate particular messages and forms of fixed and potentially mobile knowledge, yet dubious claims of “learning”.     

Long-term rates of chemical weathering and physical erosion from cosmogenic nuclides and geochemical mass balance

Quantifying long-term rates of chemical weathering and physical erosion is important for understanding the long-term evolution of soils, landscapes, and Earth's climate. Here we describe how long-term chemical weathering rates can be measured for actively eroding landscapes using cosmogenic nuclides together with a geochemical mass balance of weathered soil and parent rock. We tested this approach in the Rio Icacos watershed, Puerto Rico, where independent studies have estimated weathering rates over both short and long timescales. Results from the cosmogenic/mass balance method are consistent with three independent sets of weathering rate estimates, thus confirming that this approach yields realistic measurements of long-term weathering rates. This approach can separately quantify weathering rates from saprolite and from overlying soil as components of the total. At Rio Icacos, nearly 50% of Si weathering occurs as rock is converted to saprolite; in contrast, nearly 100% of Al weathering occurs in the soil. Physical erosion rates are measured as part of our mass balance approach, making it particularly useful for studying interrelationships between chemical weathering and physical erosion. Our data show that chemical weathering rates are tightly coupled with physical erosion rates, such that the relationship between climate and chemical weathering rates may be obscured by site-to-site differences in the rate that minerals are supplied to soil by physical erosion of rock. One can normalize for variations in physical erosion rates using the “chemical depletion fraction,” which measures the fraction of total denudation that is accounted for by chemical weathering. This measure of chemical weathering intensity increases with increasing average temperature and precipitation in data from climatically diverse granitic sites, including tropical Rio Icacos and six temperate sites in the Sierra Nevada, California. Hence, across a wide range of climate regimes, analysis of chemical depletion fractions appears to effectively account for site-to-site differences in physical erosion rates, which would otherwise obscure climatic effects on chemical weathering rates. Our results show that by quantifying rates of physical erosion and chemical weathering together, our mass balance approach can be used to determine the relative importance of climatic and nonclimatic factors in regulating long-term chemical weathering rates.