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Although erosional impacts of rainforest logging are well established, changes in hydrological dynamics have been less explored especially in the post-logging recovery phase following repeat-logging cycles and mature phase of oil palm plantation cycles. This study addresses this gap by comparing hydrological characteristics of five catchments in a steep land area of Sabah, Malaysian Borneo on a gradient of disturbance and recovery – twice-logged forest, 22 years recovery (LF2); multiple-logged forest, 8 years recovery (LF3); mature oil palm, 20 years old (OP); and two primary forests (PF and VJR) as controls. Each catchment was instrumented with water depth (converted to discharge), conductivity, temperature, and turbidity sensors, and a raingauge connected to a solar-powered datalogger recording data at 5-minute intervals from November 2011 to August 2013. Data were analysed via the flow-duration curve (FDC) supplemented by the runoff coefficient (RR) and coefficient of variation in discharge (QVAR) for aggregated characteristics, as well as via a combination of the Dunn's test and multiple-regression at the storm event scale for focused hydrological dynamics. Results show that OP is characterised by a relatively low RR (0.357) but with high responsiveness during storm events and very low baseflow (38.4% of total discharge). Discharge in the LF3 (RR = 0.796) is always the highest while having an intermediate level of responsiveness. LF2 with longer-term recovery shown a reduction in terms of discharge (RR = 0.640). Being the benchmark, the undisturbed forest (PF) has the most buffered storm response with the highest baseflow (67.9% of total discharge). Stormflow and baseflow are anomalously high and low respectively in the near-primary VJR catchment, but this probably reflects the shallow soils and short-stature rainforest associated with its igneous and metamorphic lithology. From a management aspect, although hydrological recovery is more advanced in the 22 years than in the 8-years post-logging catchment, full recovery is yet to be achieved and might be hastened by enrichment planting of the degraded forest. The low baseflow and flashy nature of the mature oil palm have major implications for downstream water supply in ENSO periods and flooding in La Nina periods. Steep lands in the humid tropics are best avoided from any form of landscape disturbance.

One of the greatest challenges to developing time series from non-annual ring forming tropical trees arises before a sampling campaign can begin. Tropical trees can be exceptionally hard, often containing chemicals and minerals which make the wood near non-biodegradable. Such trees have considerable palaeoclimatic potential due to their longevity and landscape survival times, but are challenging to sample non-destructively. The hardest of these trees, the Ironwoods, are often the target of sampling campaigns as their properties are associated with longevity. Our objective was to develop a low-technology drill-borer capable of extracting cores from the Borneo Ironwood (Eusideroxylon zwageri Teijsm and Binn) of a suitable diameter for carrying out stable isotopic analysis and radiocarbon analysis (necessary for chronology development in non-annual ring forming trees). Due to the inaccessibility of tropical sampling field sites our criteria for development included: construction to be from readily available and replaceable parts; power to be derived from batteries; the main body [drill] to be of a weight and size appropriate to sampling in remote locations; a system operable with minimal training by a non-expert. The cores produced by our drill system were of high quality, and samples could successfully be taken from extremely hard trees without charring. The biggest limitation to the operation of our system was that core segments snapped and had to be sequentially removed from the tree and stored separately. This trial is the first successful non-destructive sampling of living E. zwageri, a species which has considerable palaeoclimatic potential.

Summary Planning of semi-urban developments is often hindered by a lack of knowledge on how changes in land-use affect catchment hydrological response. The temporal and spatial patterns of overland flow source areas and their connectivity in the landscape, particularly in a seasonal climate, remain comparatively poorly understood. This study investigates seasonal variations in factors influencing runoff response to rainfall in a peri-urban catchment in Portugal characterized by a mosaic of landscape units and a humid Mediterranean climate. Variations in surface soil moisture, hydrophobicity and infiltration capacity were measured in six different landscape units (defined by land-use on either sandstone or limestone) in nine monitoring campaigns at key times over a one-year period. Spatiotemporal patterns in overland flow mechanisms were found. Infiltration-excess overland flow was generated in rainfalls during the dry summer season in woodland on both sandstone and limestone and on agricultural soils on limestone due probably in large part to soil hydrophobicity. In wet periods, saturation overland flow occurred on urban and agricultural soils located in valley bottoms and on shallow soils upslope. Topography, water table rise and soil depth determined the location and extent of saturated areas. Overland flow generated in upslope source areas potentially can infiltrate in other landscape units downslope where infiltration capacity exceeds rainfall intensity. Hydrophilic urban and agricultural-sandstone soils were characterized by increased infiltration capacity during dry periods, while forest soils provided potential sinks for overland flow when hydrophilic in the winter wet season. Identifying the spatial and temporal variability of overland flow sources and sinks is an important step in understanding and modeling flow connectivity and catchment hydrologic response. Such information is important for land managers in order to improve urban planning to minimize flood risk.

Heavy metal concentrations and potential bioavailability are reported for sediment in a shallow flood detention lake surrounded by reclaimed, smelter-contaminated land. A range of sediment column proxy indicators is used to explore changes in pollution dynamics with remediation. Sediment concentrations of Pb and Zn are high at approximately 600 and 20,000 mg kg(-1), respectively. Less than 7% of total Pb is potentially bioavailable following sequential extraction as opposed to 47% of Zn. Metal transfer mechanisms to lake sediment include detrital inputs, scavenging by particulates and biogeochemical precipitation. Sedimentary evidence indicates that detrital inputs to the lake declined following land reclamation after which it is proposed that dissolved inputs increased with leaching of reworked waste material. Whilst downcore metal profiles may be subject to post-depositional change, diatom analysis suggests more recent improvements in water quality. The potential for post-remediation pollution episodes relating to metal release from historic sedimentary stores should be considered in future remediation strategies.

When rain forest is logged, rills and gullies are often initiated on heavily disturbed and compacted terrain components; whether and for how long they continue to enlarge following logging is critical as regards the recovery and sustainability of the regenerating forest. This paper examines these two issues in logged rain forest in northeastern Borneo. Results are presented of an investigation into how soil erosion rates and surface topography varies in selectively logged forests at different stages of regeneration (up to 15 years after logging) in Danum Valley, eastern Sabah, Malaysia. Measurements were made of changes in ground level and surface roughness at over 100 transect sites over periods of 1–15 years using the erosion bridge (microprofiler) technique. In the complex mosaic of the post-logging regenerating forest, attention focused on key features, notably abandoned logging tracks, gullies, heavily disturbed or compacted areas and road-related landslides and comparisons are made with primary forest terrain. The role of extreme rainstorms in controlling the temporal pattern of post-logging erosion in both regenerating and primary forest is demonstrated. The different situations in which rills and gullies initiated during or following logging enlarge or disappear in post-logging terrain are highlighted. The implications of the results for slope evolution and sustainable rain-forest management policies are briefly considered.

Water repellency (hydrophobicity) of soils is a property with major repercussions for plant growth, surface and subsurface hydrology, and for soil erosion. Important advances have been made since the late 1980s in identifying the range of environments affected by water repellency, its characteristics and its hydro-geomorphological impacts. This review summarises earlier work, but focusses particularly on these recent advances and identifies remaining research gaps. The associations of water repellency with (a) soils other than coarse-textured ones, (b) an expanding list of plant species, and (c) a widening range of climates other than seasonally dry types have been recurrent themes emphasised in recent literature. Nevertheless, knowledge about the extent of water repellency amongst world soils is still comparatively sparse. Its origin by the accumulation of long-chained organic compounds on or between soil particles is now widely accepted, but understanding of their exact chemical composition and means of attachment to particle surfaces remains incomplete. The transient nature of water repellency has been found to be mainly associated with fluctuations in soil moisture, but the precise processes and required conditions for the changes from hydrophobic to hydrophilic and vice versa are so far only poorly understood. Significant advances relating to the hydro-geomorphological impacts of hydrophobic layers have been made since the late 1980s in identifying and separating the various effects of such layers on surface and subsurface water flow. It has become evident that these effects in turn are influenced by variables such as the frequency and effectiveness of flow pathways through hydrophobic layers as well as their position and transitory behaviour. Recent literature has continued to highlight the role of water repellency in promoting soil erosion and it is now recognised that it can promote rainsplash detachment and soil loss not only by water, but also by wind. Major research gaps, however, remain in (a) isolating the erosional impact of water repellency from other factors, and (b) identifying the exact role of, and the interactions between the different variables controlling development and effectiveness of flow pathways through hydrophobic soil. Improved understanding of the effects of soil water repellency will enable its overall role in surface and subsurface hydrological and erosional processes to become more clearly defined.

Soil hydrophobicity affects the susceptibility of soils to erosion in a variety of ways (e.g. increased aggregate stability, reduced infiltration capacity, enhanced overland flow), but there are problems concerning the overall assessment of its erosional impact. Three current problems are discussed: (1) poor isolation of hydrophobicity from other effects; and poor understanding of its overall impact; (2) areally, at slope and catchment scales; and (3) temporally, over periods of months or years rather than on a storm basis. These problems are highlighted with reference to the literature and to research in Portugal on highly hydrophobic forest soils. A conceptual model relating erosion risk to three key aspects of soil hydrophobicity (temporal contiguity, spatial contiguity and the thickness of any overlying hydrophilic soil) is presented in order to provide a framework for future research into hydrophobicity–soil erosion links.

In the last two decades, Portuguese forests have undergone important changes in land use and management practices, some of which are posing significant problems as regards long-term sustainability of forestry. This paper examines the degradation processes associated with two events: deep ploughing prior to planting (termed ‘ripploughing’) and forest fire. The research design comprised plot and catchment approaches in which fluxes of water, sediment and solutes for rip-ploughed and burnt pine forest were monitored for the first year after ploughing and fire respectively. Although rip-ploughed areas experienced very high erosion rates at the plot scale (up to 51 t ha−1 yr−1) and enhanced catchment runoff due to increased overland flow (up to 50% of rainfall), catchment sediment yield was small because of sediment storage at the bases of slopes and in channel heads. For burned pine, the destruction of the vegetation and litter layer led to sharp increases in catchment runoff and nutrient losses both as dissolved and suspended sediments. Despite sediment loss at the plot scale being below 3 t ha−1 in the first year after the fire, the catchment suspended sediment loss in storm events was several orders of magnitude higher than for the partly rip-ploughed catchment.

In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.

A laboratory programme of water drop penetration tests is used to investigate the nature of hydrophobicity of soils in burnt and unburnt Eucalyptus globulus and Pinus pinaster forest areas of northern Portugal. Variations in hydrophobicity of air-dried soil with soil depth, soil particle size fraction, land use and burn history are assessed. Results differ from those found by many other studies in several respects: (1) fire was not found to enhance hydrophobicity, as unburnt and old-burn soils are as hydrophobic as newly-burnt ones; (2) hydrophobicity was found to be characteristic of soils from the surface down to the weathered (Cw) horizon rather than confined to a near-surface layer, (3) it is also associated with the finer rather than the coarser size fractions of the soils. Soils under E. globulus are distinctly more hydrophobic than those under P. pinaster. Implications for the generation of overland flow are briefly explored.