Sustainability of Mediterranean Deltaic and Lagoon Wetlands with Sea-Level Rise: The Importance of River Input

We report on a decadal trend of accretionary dynamics in the wetlands of several northwestern Mediterranean deltas and a lagoon system, all of them with high rates of wetland loss. Wetland vertical accretion and surface elevation change were measured at 55 riverine, marine, and impounded sites in four coastal systems: the Ebro delta, Spain; the Rhône delta, France; and the Po delta and Venice Lagoon, Italy. Vertical accretion and elevation change ranged between 0 and 25 mm year^?1 and were strongly correlated. The highest rates of elevation gain occurred at riverine sites where vertical accretion was highest. We conclude that areas with high sediment input, mainly riverine, are the only ones likely to survive accelerated sea-level rise, especially if recent higher estimates of 1 m or more in the twenty-first century prove to be accurate. This is the first study where the importance of river input on wetland survival has been demonstrated at a decadal time scale over a broad geographical area.     

Impact of an unsealed forest road stream crossing: water quality and sediment sources

Turbidity monitoring and rainfall and runoff simulation experiments were conducted at a newly constructed unsealed road stream crossing to determine the quantity and sources of sediment entering the stream. Continuous measurements of turbidity and estimation of total suspended solids (TSS) concentration upstream and downstream of the stream culvert were taken over a 5 month period. There was a statistically significant difference in turbidity and TSS downstream of the crossing during baseflow conditions, but the quality of the water column remained good during non‐rain periods. Rainfall events comprised around 20% of the observation period and led to decreases in water quality downstream of the crossing. Water quality could be considered as degraded for 10% of the observations. This was during a period when the rainfall was 65% of the long‐term average. Calculated suspended sediment loads were 0·78 t upstream and 2·77 t downstream, an increase of 3·5. It was estimated that at least 2–3 t of bedload material was also added to the stream during the crossing construction and from subsequent erosion. This material is a deposit on the cobble stream bed, and is most likely to degrade aquatic ecosystem values. Rainfall and runoff simulation revealed the principal sediment sources to be a fillslope that contributed coarse bedload material through rill erosion and unprotected toe scour, and the unmetalled road verge that provided fines. Although the quality of water column was good for the majority of the observations, the new Australian and New Zealand Water Quality Guidelines for Fresh and Marine Waters suggest this site exceeded ‘trigger levels’ that would warrant further investigation for both the water column and the bed deposits. Copyright © 2002 John Wiley & Sons, Ltd.     

Latitudinal Range Variation of Trees in the United States: A Reanalysis of the Applicability of Rapoport's Rule*

In 1975 E. H. Rapoport described a pattern of increasing latitudinal range sizes for organisms with increasing latitude, a pattern that is now known as Rapoport's rule. The universal applicability of Rapoport's rule has been long contested, making it one of the more controversial biogeographic “rules.” This study aims to reassess the applicability of Rapoport's rule to U.S. tree species. Data presented here suggest that Rapoport's rule does indeed apply to most tree taxa within the United States, but may be taxon specific. In addition, data presented here suggest that tree range patterns consistent with Rapoport's rule in the United States are not restricted to high latitudes and are not the result of a “boundedness effect” but may be intimately linked with the glacial history and physical geography of North America. The analyses conducted here are intended to emphasize the utility of such biogeographic rules even if they are not universally applicable and should, in turn, only be considered biogeographic patterns.     

High altitude Venus haze from Pioneer Venus limb scans

High vertical resolution scans of the Venus limb made by the Pioneer Venus Orbiter Cloud Photopolarimeter at 365 nm and 690 nm wavelengths are used to investigate the level of the haze top, and haze particle properties and scale height. Haze particle vertical optical depth 0.01 occurs at altitude 80 to 85 km based on knowledge of instrument pointing. The lowest haze tops were observed close to subsolar longitudes but the data set supports a longitude dependence no more than a temporal variation. Single scattering computations for a spherical shell atmosphere show good agreement with observed intensities for particles smaller than 0.3 μm radius and refractive index less than 1.7, consistent with, but not limited to, concentrated sulfuric acid. Particle scale height in the 0.5 to 2 mbar pressure regions varies between 1 and 3 km over the season (12 of 92 days), latitude (15–45°N), and local time (0900–1800) ranges of the observations. Detached layers of haze are sometimes present. An average particle scale height of 2.2 km at 84 km altitude yields an eddy diffusion coefficient of 1.3 × 10⁵ cm² sec^?1.     

Suspended sediment yield and metal contamination in a river catchment affected by El Niño events and gold mining activities: the Puyango river basin,southern Ecuador

The suspended sediment yield and the transfer of polluted sediment are investigated for the Puyango river basin in southern Ecuador. This river system receives metal (Cd, Cu, Hg, Pb and Zn) and cyanide pollution generated by mining, and is associated with large‐scale hydrological variability, which is partly governed by El Niño events. Field sampling and statistical modelling methods are used to quantify the amount of mine tailings that is discharged into the basin. Annual suspended sediment yields are estimated using a novel combination of the suspended sediment rating method and Monte Carlo simulations, which allow for propagation of the uncertainties of the calculations that lead to final load estimates. Geochemical analysis of suspended and river bed sediment is used to assess the dispersion and long‐term fate of contaminated sediment within the river catchment. Knowledge of the inter‐ and intra‐annual variation in suspended sediment yield is shown to be crucial for judging the importance of mining discharges, and the extent to which the resultant pollution is diluted by river flows. In wet years, polluted sediments represent only a very small proportion of the yield estimates, but in dry years the proportion can be significant. Evidence shows that metal contaminated sediments are stored in the Puyango river bed during low flows. Large flood events flush this sediment periodically, both on an annual cycle associated with the rainy season, and also related to El Niño events. Therefore, environmental impacts of mining‐related discharges are more likely to be severe during dry years compared with wet years, and in the dry season rather than the wet season. The hydrological consequences of El Niño events are shown to depend upon the extent to which these events penetrate inland. It is, thus, shown that the general conclusion that El Niño events can significantly affect suspended sediment yields needs evaluation with respect to the particular way in which those events affect a given catchment. Copyright © 2003 John Wiley & Sons, Ltd.     

Testing the influence of topography and material properties on catchment‐scale soil moisture patterns using remotely sensed vegetation patterns in a humid temperate catchment,northern Britain

In order to evaluate the relationship between the apparent complexity of hillslope soil moisture and the emergent patterns of catchment hydrological behaviour and water quality, we need fine‐resolution catchment‐wide data on soil moisture characteristics. This study proposes a methodology whereby vegetation patterns obtained from high‐resolution orthorectified aerial photographs are used as an indicator of soil moisture characteristics. This enables us to examine a set of hypotheses regarding what drives the spatial patterns of soil moisture at the catchment scale (material properties or topography). We find that the pattern of Juncus effusus vegetation is controlled largely by topography and mediated by the catchment's material properties. Characterizing topography using the topographic index adds value to the soil moisture predictions relative to slope or upslope contributing area (UCA). However, these predictions depart from the observed soil moisture patterns at very steep slopes or low UCAs. Copyright © 2012 John Wiley & Sons, Ltd.     

Urban fluvial flood modelling using a two‐dimensional diffusion‐wave treatment,part 2: development of a sub‐grid‐scale treatment

This paper develops and tests a sub‐grid‐scale wetting and drying correction for use with two‐dimensional diffusion‐wave models of urban flood inundation. The method recognizes explicitly that representations of sub‐grid‐scale topography using roughness parameters will provide an inadequate representation of the effects of structural elements on the floodplain (e.g. buildings, walls), as such elements not only act as momentum sinks, but also have mass blockage effects. The latter may dominate, especially in structurally complex urban areas. The approach developed uses high‐resolution topographic data to develop explicit parameterization of sub‐grid‐scale topographic variability to represent both the volume of a grid cell that can be occupied by the flow and the effect of that variability upon the timing and direction of the lateral fluxes. This approach is found to give significantly better prediction of fluvial flood inundation in urban areas than traditional calibration of sub‐grid‐scale effects using Manning's n. In particular, it simultaneously reduces the need to use exceptionally high values of n to represent the effects of using a coarser mesh process representation and increases the sensitivity of model predictions to variation in n. Copyright © 2005 John Wiley & Sons, Ltd.