Stochastic processes of soil production and transport: erosion rates,topographic variation and cosmogenic nuclides in the Oregon Coast Range

Landscapes in areas of active uplift and erosion can only remain soil‐mantled if the local production of soil equals or exceeds the local erosion rate. The soil production rate varies with soil depth, hence local variation in soil depth may provide clues about spatial variation in erosion rates. If uplift and the consequent erosion rates are sufficiently uniform in space and time, then there will be tendency toward equilibrium landforms shaped by the erosional processes. Soil mantle thickness would adjust such that soil production matched the erosion. Previous work in the Oregon Coast Range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield. Here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported. We quantify how soil production varies with soil thickness in the southern Oregon Coast Range and explore further the issue of landscape equilibrium. Apparent soil production is determined to be an inverse exponential function of soil depth, with a maximum inferred production rate of 268 m Ma^?1 occurring under zero soil depth. This rate depends, however, on the degree of weathering of the underlying bedrock. The stochastic and large‐scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth; the spatial variation of soil depth neither supports nor rejects equilibrium morphology. Our observed catchment‐averaged erosion rate of 117 m Ma^?1 is, however, similar to that estimated for the region by others, and to soil production rates under thin and intermediate soils typical for the steep ridges. We suggest that portions of the Oregon Coast Range may be eroding at roughly the same rate, but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle. Copyright © 2001 John Wiley & Sons, Ltd.     

Torsion in two buildings—1987 whittier narrows earthquake

Study of the data from the extensively instrumented buildings in the 1987 Whittier Narrows earthquake suggests that torsional modes probably were excited in buildings that outwardly appear quite symmetric. Accordingly this study involves: (i) investigation of the observed response of two low-rise buildings in both the elastic and moderately inelastic domains, (ii) comparison of such behaviour with the results obtained from modelling studies, and (iii) examination of the possible effects arising from stronger shaking. The study was directed towards attempting to provide a partial answer to the critical question of whether or not the torsional response was important in the gross total response of these low-rise buildings, and to what extent torsional concepts should be considered in design. Also the numerical results were extrapolated to examine the survivability of the same buildings if subjected to a somewhat stronger earthquake. The ultimate goal was to contribute insight to the practical guidelines for design and analysis of low-rise buildings subjected to strong ground motion.     

Inverse modeling of dissolved O2 and δ18O-DO to estimate aquatic metabolism,reaeration and respiration isotopic fractionation: effects of variable light regimes and input uncertainties

A transient model, hereafter referred to as ROM-TM, was developed to quantify river ecosystem metabolic rates and reaeration rates from field observation of changes in dissolved O₂ (DO) and the ratio of ¹⁸O to ¹⁶O in DO (δ¹⁸O-DO). ROM-TM applies an inverse modeling approach and is programmed using MATLAB. Parameters describing photosynthesis, ecosystem respiration, gas exchange, and isotopic fractionation, such as maximum photosynthetic rate (P _m ), photosynthetic efficiency parameter (a), respiration rate at 20 °C (R ₂₀ ), gas exchange coefficient (K), respiration isotopic fractionation factor (a _R ), and photorespiration coefficient (β _R ), can be abstracted by minimizing the sum of square errors between the fitted data and the observed field data. Then DO and δ¹⁸O-DO time series can be reconstructed using estimated parameters and input variables. Besides being capable of teasing apart metabolic processes and gas exchange to provide daily average estimates of metabolic parameters at the ecosystem scale, ROM-TM can be used to address issues related to light including light saturation phenomena at the ecosystem level, the effect of cloud cover on the metabolic balance, and photorespiration. Error and uncertainty analysis demonstrates that ROM-TM is stable and robust for the random errors of DO time series. The photosynthetic parameters P _m and a are more sensitive than other parameters to lower-resolution time series data.     

On the Vp/Vs–Mg# correlation in mantle peridotites: Implications for the identification of thermal and compositional anomalies in the upper mantle

We use thermodynamically self-consistent and hybrid methods to analyze the correlation of important physical parameters (e.g. bulk density, elastic moduli) with bulk Mg# and modal composition in mantle peridotites at upper mantle conditions. Temperature (anharmonic and anelastic), pressure and compositional derivatives for all these parameters are evaluated. The results show that the widely used correlations between Vp/Vs and Mg# in peridotites are strictly valid only for garnet-bearing assemblages at temperatures < 900 °C. The correlation breaks down when: i) spinel is the stable Al-rich phase in the assemblage and ii) when anelastic attenuation of seismic velocities becomes important (T ? 900 °C). This implies that the range of applicability of published Vp/Vs–Mg# correlations for the upper mantle is limited to a depth interval between the spinel–garnet phase transition and the 900 °C isotherm. We use numerical simulations to show that this depth interval is virtually nonexistent in lithospheres thinner than ～ 140 km and can comprise up to ～ 50% of the lithospheric mantle in thick (> 220 km) lithospheric domains. In addition, we show that for most of the upper mantle the expected Δ(Vp/Vs) values associated with compositional variations are smaller than the resolution limit of current seismological methods. All these considerations suggest that the Vp/Vs ratio is not a reliable measure of compositional variations and that for large parts of the upper mantle compositional anomalies cannot be separated from thermal anomalies on the basis of seismological studies only. We further confirm that the only reliable indicator of compositional anomalies in a peridotitic mantle is the ratio of density to shear wave velocities (ρ/Vs). Our results demonstrate that geophysical–petrological models (forward or inverse) that model these two fields (i.e. density and Vs) self-consistently within a robust thermodynamic framework are necessary for characterizing the small-scale thermal and compositional structure of the lithosphere and sublithospheric upper mantle.     

Implications of ozone depletion for surface-water photochemistry: Sensitivity of clear lakes

Increased ultraviolet-B radiation (UV-B) in aquatic ecosystems brought about by stratospheric ozone depletion may result in increased formation rates of photochemical reaction products in the surface waters of aquatic ecosystems. In this study, the potential impact of increases in lower wave-length radiation on the formation of hydrogen peroxide (H₂O₂) and singlet oxygen (¹O₂) was modelled for lakes over a range of dissolved organic carbon (DOC) concentrations. The impact of increased UV-B radiation on the production of carbon monoxide (CO) was also calculated for two humic stained systems. The relative increases of H₂O₂ and¹O₂ production were greater in the clear lakes (70% increase in photochemical reaction rates near the surface) than the coloured systems (25%). Production of CO in the study sites also increased under depleted ozone conditions implying increased DOC losses to the overlying atmosphere.     

Model of particulate organic carbon transport in an agriculturally impacted stream

The present contribution focuses on modeling the total particulate organic carbon (POC) and benthic POC transport from a lowland stream impacted by agricultural land‐use. A mass balance, reach scale model is verified that accounts for water, sediment and POC transport, sediment and POC temporary storage and exchange with the streambed, and production and degradation of carbon pools in the benthos. We found that the POC load is highly variable during individual hydrologic events and is influenced by transport of mixed carbon sources including upland, streambank and benthic POC sources. Benthic POC stocks and transport were found to vary seasonally and annually but are in a state of long‐term equilibrium. Equilibrium is governed by negative feedback mechanisms whereby high POC export due to extreme hydrologic events and high‐frequency hydrologic events reduces benthic POC stocks and inhibits benthic POC growth. Benthic POC accounted for 4 tC y^?1 or 22% of the total annual POC loading in the stream's main stem and 8.9 tC y^?1 or 48% of the POC yield for the entire watershed. These results suggest that further attention should be given to benthic‐derived POC when budgeting stream ecosystem carbon for low‐order stream systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of antecedent soil moisture on hydraulic conductivity in a series of texture‐contrast soils

Antecedent soil moisture significantly influenced the hydraulic conductivity of the A1, A2e and B21 horizons in a series of strong texture‐contrast soils. Tension infiltration at six supply potentials demonstrated that in the A1 horizon, hydraulic conductivity was significantly lower in the ‘wet’ treatment than in the ‘dry’ treatment. However in the A2e horizon, micropore and mesopore hydraulic conductivity was lower in the ‘dry’ treatment than the ‘wet’ treatment, which was attributed to the precipitation of soluble amorphous silica. In the B21 horizon, desiccation of vertic clays resulted in the formation of shrinkage cracks which significantly increased near‐saturated hydraulic conductivity and prevented the development of subsurface lateral flow in the ‘dry’ treatment. In the ‘wet’ treatment, the difference between the hydraulic conductivity of the A1 and B21 horizons was reduced; however, lateral flow still occurred in the A1 horizon due to difficulty displacing existing soil water further down the soil profile. Results demonstrate the need to account for temporal variation in soil porosity and hydraulic conductivity in soil‐water model conceptualisation and parameterisation. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of open-marsh water management on summer bird populations on Topsail Island, North Carolina

Open-marsh water management (OMWM) manipulates selected areas of an estuarine marsh by constructing narrow, deep ditches that harbor resident populations of predators of mosquito larvae. It does not, however, alter the surrounding vegetation by deposition of spoil mounds. We censused the summer (breeding and nonbreeding) bird populations in two adjacent salt marsh sites on Topsail Island, North Carolina, for two summers before OMWM ditching occurred and for four seasons postditching. A total of 53 nonbreeding species and five breeding species of birds were encountered on the study sites. None of the interannual changes in bird populations can be attributed to OMWM.     

Neoliberalisation,rural land trusts and institutional blending

In the context of rural land conservation, neoliberalisation involves an increasingly wide range of changes in formal and informal institutional arrangements. These affect the relationship between the state and the market in a variety of ways and have different implications for the governance of rural land. In the context of rural land conservation in the UK, we identify a broad range of changes to policy that promote altered ownership and market related institutional forms, all of which might be seen as forms of neoliberalisation. In some instances these promote market forces and private ownership, while in others they push back the market and support collectivisation. We argue that the complex processes of the decomposition property and reassignment of property rights and the emergence of new forms of governance and partnership are better characterised in terms of institutional blending.