Beneficial use of municipal sludge in the ocean

The micronutrients in municipal sludge enhance ocean productivity in much the same way as they enhance plant productivity when applied to the land. The organic solids of municipal sludge can also directly enhance production of valuable biomass in the ocean, particularly benthic biomass. Studies of municipal sludge and wastewater discharge into marine waters throughout the world have demonstrated that, if the application rate of municipal sludge or wasterwater was optimized by utilizing larger sites, beneficial enhancement of marine production could be achieved without the adverse effects associated with excessive application rates and overfertilization. Existing evidence indicates that, although not risk- or disadvantage-free, beneficial use of municipal sludges in the ocean is a viable management option which, in some instances, is likely to have fewer negative environmental side effects than other feasible beneficial use options.     

Stone line profiles: Importance in geochemical exploration

In vast tropical rain forest areas, weathering profiles are commonly characterized by a “stone line” overlain by a brown-yellow loose-clay horizon. Concordant with the topographic surface, such a stone line may be traced continuously over considerable distances. It is typically composed of coarse fragments of lithorelics, debris of laterite as Fe-oxides nodules, corroded quartz, gibbsitic aggregates, …, embedded in a clayey matrix. These materials cover the saprolitic weathering profile which is typically a few tens of metres thick.The origin of stone lines has given rise to much controversy and are still widely misunderstood. A broad range of processes, allochthonist or autochthonist, have been put forward in the literature. The findings in this paper conclude that these weathering profiles result from chemical leaching and differential movement between the matrix and the coarse fragments which accumulate by downward migration. Accumulation takes place at the lower limit of rain water impregnation and forms the stone line, whereas leaching and homogenization of fine material occur throughout the upper water-impregnated horizon. Although the materials of the loose-clay horizon and of the stone are extensively altered, the relics are chemically rather well recognizable.According to the above hypothesis, stone line weathering profiles should thus be mostly residual. The main aspects of geochemical dispersion processes of some stone line profiles in Gabon are presented as examples. These show that:

1. (a) The vertical redistribution of some major elements in the profiles, accumulation (Fe₂O₃, Al₂O₃, SiO₂) or leaching (K₂O, MgO, CaO, SiO₂,..) are different from the bedrock composition;

2. (b) In some situations, it is possible to characterize the bedrock by using groups of trace elements such as V, Ni,.. for basic rocks or Ba, Sr,.. for gneisses for instance; the contrasts obtained can be smoothed in comparison with results from deeper in the profile.

3. (c) The persistence of geochemical anomalies arising from mineralization, throughout the weathering profile, up to the main sampling media, the surface soil. A “mushroom” dispersion pattern can be recognized where the foot of the mushroom corresponds to the element dispersion pattern can be recognized where the foot of the mushroom corresponds to the element dispersion in the saprolite and the bedrock, with the top of the mushroom being partly in the stone line and partly in the loose clay horizon.

Such a dispersion pattern has two consequences on exploration: (1) the spreading out of the surficial signal favoring the identification of anomalies during follow-up on a relatively wide spaced grid; and (2) at the same time, a reduction of the extension of the signals by dilution and leaching according to the weathering process; therefore, relatively low anomaly contents must be taken into account in exploration.Thus, anomalies arising from stone line profiles tend to be well-dispersed, but of weak magnitude, and represent in situ transfer from the parent rock.     

Surface-wave analysis for static corrections in mineral exploration: A case study from central Sweden

In mineral exploration, increased interest towards deeper mineralizations makes seismic methods attractive. One of the critical steps in seismic processing workflows is the static correction, which is applied to correct the effect of the shallow, highly heterogeneous subsurface layers, and improve the imaging of deeper targets. We showed an effective approach to estimate the statics, based on the analysis of surface waves (groundroll) contained in the seismic reflection data, and we applied it to a legacy seismic line acquired at the iron-oxide mining site of Ludvika in Sweden. We applied surface-wave methods that were originally developed for hydrocarbon exploration, modified as a step-by-step workflow to suit the different geologic context of hard-rock sites. The workflow starts with the detection of sharp lateral variations in the subsurface, the existence of which is common at hard-rock sites. Their location is subsequently used, to ensure that the dispersion curves extracted from the data are not affected by strong lateral variations of the subsurface properties. The dispersion curves are picked automatically, windowing the data and applying a wavefield transform. A pseudo-2D time-average S-wave velocity and time-average P-wave velocity profile are obtained directly from the dispersion curves, after inverting only a reference curve. The time-average P-wave velocity profile is then used for the direct estimation of the one-way traveltime, which provides the static corrections. The resulting P-wave statics from the field data were compared with statics computed through conventional P-wave tomography. Their difference was mostly negligible with more than 91% of the estimations being in agreement with the conventional statics, proving the effectiveness of the proposed workflow. The application of the statics obtained from surface waves provided a stacked section comparable with that obtained by applying tomostatics.     

Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna

In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m² plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.     

Climate-induced boreal forest change: Predictions versus current observations

For about three decades, there have been many predictions of the potential ecological response in boreal regions to the currently warmer conditions. In essence, a widespread, naturally occurring experiment has been conducted over time. In this paper, we describe previously modeled predictions of ecological change in boreal Alaska, Canada and Russia, and then we investigate potential evidence of current climate-induced change. For instance, ecological models have suggested that warming will induce the northern and upslope migration of the treeline and an alteration in the current mosaic structure of boreal forests. We present evidence of the migration of keystone ecosystems in the upland and lowland treeline of mountainous regions across southern Siberia. Ecological models have also predicted a moisture-stress-related dieback in white spruce trees in Alaska, and current investigations show that as temperatures increase, white spruce tree growth is declining. Additionally, it was suggested that increases in infestation and wildfire disturbance would be catalysts that precipitate the alteration of the current mosaic forest composition. In Siberia, 7 of the last 9 yr have resulted in extreme fire seasons, and extreme fire years have also been more frequent in both Alaska and Canada. In addition, Alaska has experienced extreme and geographically expansive multi-year outbreaks of the spruce beetle, which had been previously limited by the cold, moist environment. We suggest that there is substantial evidence throughout the circumboreal region to conclude that the biosphere within the boreal terrestrial environment has already responded to the transient effects of climate change. Additionally, temperature increases and warming-induced change are progressing faster than had been predicted in some regions, suggesting a potential non-linear rapid response to changes in climate, as opposed to the predicted slow linear response to climate change.     

Postglacial rebound and fault instability in Fennoscandia

The best available rebound model is used to investigate the role that postglacial rebound plays in triggering seismicity in Fennoscandia. The salient features of the model include tectonic stress due to spreading at the North Atlantic Ridge, overburden pressure, gravitationally self-consistent ocean loading, and the realistic deglaciation history and compressible earth model which best fits the sea-level and ice data in Fennoscandia. The model predicts the spatio-temporal evolution of the state of stress, the magnitude of fault instability, the timing of the onset of this instability, and the mode of failure of lateglacial and postglacial seismicity. The consistency of the predictions with the observations suggests that postglacial rebound is probably the cause of the large postglacial thrust faults observed in Fennoscandia. The model also predicts a uniform stress field and instability in central Fennoscandia for the present, with thrust faulting as the predicted mode of failure. However, the lack of spatial correlation of the present seismicity with the region of uplift, and the existence of strike-slip and normal modes of current seismicity are inconsistent with this model. Further unmodelled factors such as the presence of high-angle faults in the central region of uplift along the Baltic coast would be required in order to explain the pattern of seismicity today in terms of postglacial rebound stress. The sensitivity of the model predictions to the effects of compressibility, tectonic stress, viscosity and ice model is also investigated. For sites outside the ice margin, it is found that the mode of failure is sensitive to the presence of tectonic stress and that the onset timing is also dependent on compressibility. For sites within the ice margin, the effect of Earth rheology is shown to be small. However, ice load history is shown to have larger effects on the onset time of earthquakes and the magnitude of fault instability.