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This paper explores the potential for using multiple particle size fractions in a hierarchical geochemical sediment fingerprinting approach to the assessment of changes in sediment sources through time within a small Mediterranean peri-urban catchment. Conventional sediment fingerprinting has focussed on the This study explores this approach using 2), on the outskirts of Coimbra in central Portugal. The climate is humid Mediterranean. Catchment geology is 56% sandstone (in the east), 41 % marly limestone (in the west) and 3 % alluvium. Current land-use is 56% woodland, 4 % agricultural and 40% urban (mainly residential, but also including a recently constructed enterprise park (5%) and major highway (1%)). Recent urbanization has largely occupied former agricultural land. The study adopts a multi-proxy sediment fingerprinting approach to assessment of changes in sediment sources, based on geochemical (elemental) characterization of the four different size fractions of fluvial bed-sediment and soil samples, using a Niton x-ray fluorescence (XRF) elemental analyser. Sampling of fluvial sediment was carried out at 33 sites within the stream network (including all significant tributaries, downstream sites and the catchment outlet). Samples were collected in July 2018 and November 2018 following contrasting ‘late-wet-season’ and ‘end-of-dry-season’ events. In July 2018, samples of potential sediment sources were collected including: (i) soil surface (0-2cm) samples at 64 locations, (ii) 17 samples from eroding channel margin sites, and (iii) 15 samples of road sediment. All fluvial and soil samples were sieved to obtain the four target size fractions. The elemental geochemistry of each sample fraction at all fluvial and source sites was derived using the XRF analyser. (These results were added to similar datasets previously obtained on three occasions in 2012-15 in a period of enhanced urban constructional disturbance). Differences (and similarities) in geochemical signatures between the different size fractions at each survey date at and between each tributary and potential source site were assessed using a range of statistical techniques. Messages arising are discussed. For each size fraction and survey date, Bayesian unmixing models were used in a hierarchical (confluence-based) fashion to assess the contributions of sub-catchments to downstream sites and the catchment outlet. Modelling results for the two 2018 events were validated by comparing them with suspended sediment records collected at five tributary locations and at the catchment outlet. Although overall, the modelling was successful in indicating and quantifying significant changes in sediment sources through time within the catchment, uncertainties in interpretation of the multiple fractions are identified and discussed.

Understanding sediment dynamics in peri-urban catchments constitutes a research challenge because of the spatiotemporal complexity and variability of land-uses involved. This study investigates differences in the concentration of total sediments (TSC) and suspended sediments (SSC) in the small peri-urban Mediterranean Ribeira dos Cov&otilde, es catchment (40% urban area) in central Portugal. Suspended sediment responses at the catchment outlet (E) and in three upstream sub-catchments, during periods of urbanization (2011&ndash, 2013) and stabilizing land-use (2017&ndash, 2018) are compared for storm-event datasets encompassing similar ranges of rainstorm sizes and antecedent rainfall condition. The Quinta sub-catchment, with the lowest urban area (22%) but subject to major construction activities affecting 17% of its area, led to highest TSC and SSC during urbanization (attaining 4320 mg/L and 4184 mg/L, respectively), and a median reduction of 38% and 69%, respectively, during stabilization. Esp&iacute, rito Santo sub-catchment, with highest urban area (49%) and minor construction activities, displayed similar median TSC in both periods (258&ndash, 240 mg/L) but highest SSC reduction (76%), highlighting the impact of the anthropogenic disturbance mainly on fine-particle sediments and a good connectivity with the stream. Porto Bordalo sub-catchment, with 39% urban area and subject to the construction of a four-line road covering 1.5% of its area, showed the lowest TSC and SSC concentrations and the lowest median reductions in both periods (31% and 64%, correspondingly), mainly because of the impact of an unplanned retention basin established with soil from the construction site. Overall, median TSC and SSC reduced 14% and 59% at E, from urbanization to stabilization. Information about sediment dynamics should guide stakeholders in establishing strategies to reduce sediment loads and mitigate the impacts on urban aquatic ecosystems.

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.

The identification of sediment sources is important for catchment management, but few studies have been performed in Mediterranean areas. This study uses a multi-proxy sediment fingerprinting approach to explore sources and dynamics of fluvial sediments in a rapidly urbanizing Portuguese peri-urban catchment. X-Ray Fluorescence was used to characterize the elemental geochemistry of sediments collected within the stream network after three storm events in 2012 and 2015. A range of statistical techniques, including hierarchical cluster analysis, was used to identify discriminant sediment properties and similarities between fine bed-sediment samples of tributaries and downstream sites. Quantification of sediment supply from upstream sub-catchments was undertaken using established sediment fingerprinting approaches. The geochemistry of the sediments was found to be influenced by both lithology and land-use changes. In 2012 the sandstone sub-catchment provided 75% of the

Although there have been extensive studies on the hydrological and erosional impacts of logging, relatively little is known about the impacts of conversion into agricultural plantation (namely rubber and oil palm). Furthermore, studies on morphological impacts, sediment-bound chemistry and forensic attribution of deposited sediment to their respective sources are scarcer. This chapter introduces the potential for using the multi-proxy sediment fingerprinting technique in this context. Featuring pilot projects in two major flood-prone river systems in Malaysia, the studies explore application of geochemistry-based sediment source ascription. The geochemical signatures of sediment mixtures on floodplains were compared to sediments from upstream source tributaries. The tributaries were hypothesised to have different geochemical signatures in response to dominant land management. The first case study took place in the Segama River system (4,023 km2) of Sabah, Malaysian Borneo where a mixture of primary forest, logged-forests and oil palm plantations were predominant. The second case study was in the Kelantan River Basin (13,100 km2) with two major tributaries (Galas River and Lebir River) where logged-forests and rubber and oil palm plantations are dominant land-uses. Both case studies demonstrated the applicability of this method in ascribing floodplain deposited sediment to their respective upstream sources. Preliminary results showed that trace elements associated with fertilisers (e.g. copper and vanadium) contribute to agricultural catchment signatures. Alkaline and alkaline-earth elements were linked to recently established oil palm plantations due to soil turnover. Mixing model outputs showed that contributions from smaller, more severely disturbed catchment are higher than those from larger but milder disturbed catchments. This method capitalises on flood events to counter its adverse impacts by identifying high-priority sediment source areas for efficient and effective management.

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.

Freshwaters provide valuable habitat and important ecosystem services but are threatened worldwide by habitat loss and degradation. In Southeast Asia, rainforest streams are particularly threatened by logging and conversion to oil palm, but we lack information on the impacts of this on freshwater environmental conditions, and the relative importance of catchment versus riparian‐scale disturbance. We studied 16 streams in Sabah, Borneo, including old‐growth forest, logged forest, and oil palm sites. We assessed forest quality in riparian zones and across the whole catchment and compared it with stream environmental conditions including water quality, structural complexity, and organic inputs. We found that streams with the highest riparian forest quality were nearly 4 °C cooler, over 20 cm deeper, had over 40% less sand, greater canopy cover, more stored leaf litter, and wider channels than oil palm streams with the lowest riparian forest quality. Other variables were significantly related to catchment‐scale forest quality, with streams in the highest quality forest catchments having 40% more bedrock and 20 times more dead wood, along with higher phosphorus, and lower nitrate‐N levels compared to streams with the lowest catchment‐scale forest quality. Although riparian buffer strips went some way to protecting waterways, they did not maintain fully forest‐like stream conditions. In addition, logged forest streams still showed signs of disturbance 10–15 years after selective logging. Our results suggest that maintenance and restoration of buffer strips can help to protect healthy freshwater ecosystems but logging practices and catchment‐scale forest management also need to be considered.

Although the influences of urban land use on water quality have been widely investigated, the impacts of different urbanization patterns, particularly in Mediterranean environments, are not well understood. Focussing on a Portuguese peri-urban catchment with 40 % urban cover, this paper explores (1) the impact of areas with differing urban extent and storm drainage system on streamwater quality and (2) temporal variations driven by season and storm events of differing magnitude, intensity and antecedent weather. Water quality was assessed at the catchment outlet (E) and for three upstream tributaries: (1) Porto Bordalo (PB), 39 % urban with a new major road and piping of some overland flow from impervious surfaces directly into the stream; (2) Espirito Santo (ES), 49 % urban, mostly comprising detached houses surrounded by gardens, and with overland flow infiltrating into downslope pervious soils; and (3) Quinta (Q), 22 % urban with partial piping of overland flow from a recent enterprise park area. Water samples were collected at different stages in storm hydrograph responses to ten rainfall events from October 2011 to March 2013. The water quality variables analysed included chemical oxygen demand (COD), nutrients (Kjeldahl nitrogen [Nk-N], ammonium [NH4–N], nitrate [NO3–N] and total dissolved phosphorus (TDP) and heavy metals (Zn and Cu). Urban areas had great impact on COD, with the highest median concentrations in ES and the lowest in Q. In ES, fertilizing lawns and gardens may have been responsible for its higher median NO3–N concentrations. High concentrations of heavy metals were recorded in PB and Q, probably due to the piping of road runoff directly into the stream. Generally, higher pollutant concentrations were recorded in the first storm events after the summer drought due to the flushing of accumulated solutes and a lower dilution effect, with Nk-N and NH4–N exceeding water quality standards. Over the wet season, increasing soil moisture favoured greater flow connectivity between runoff processes from pollutant sources and the stream network, leading to a higher proportion of samples exceeding pollution thresholds. No direct relationship was identified between urban extent and water quality, possibly due to the overriding impact of different storm drainage systems and flow connectivities of different urban patterns. Hydrological regime, linked to seasonal changes, also exerted a major influence on the water quality dynamics. Information on the spatiotemporal dynamics of pollutants, linked to different urban patterns and storm drainage systems, should help enable urban planners to minimize the adverse impacts of urbanization on aquatic ecosystems.

Summary Forest hydrology has been widely investigated, but the impacts of different woodland types on hydrological processes within a peri-urban catchment mosaic are poorly understood. This paper investigates overland flow generation processes in three different types of woodland in a small (6.2 km2) catchment in central Portugal that has undergone strong urban development over the past 50 years. A semi-natural oak stand and a sparse eucalyptus stand on partly abandoned peri-urban land and a dense eucalyptus plantation were each instrumented with three 16 m2 runoff plots and 15 throughfall gauges, which were monitored at c. 1- to 2-week intervals over two hydrological years. In addition, surface soil moisture content (0–5 cm) and hydrophobicity (0–2 cm, 2–5 cm and 5–7 cm) were measured at the same time as overland flow and throughfall. Although all three woodland types produced relatively little overland flow (

Stable carbon isotope ( δ 13 C) series were developed from analysis of sequential radial wood increments from AD 1850 to AD 2009 for four mature primary rainforest trees from the Danum and Imbak areas of Sabah, Malaysia. The aseasonal equatorial climate meant that conventional dendrochronology was not possible as the tree species investigated do not exhibit clear annual rings or dateable growth bands. Chronology was established using radiocarbon dating to model age–growth relationships and date the carbon isotopic series from which the intrinsic water-use efficiency (IWUE) was calculated. The two Eusideroxylon zwageri trees from Imbak yielded ages of their pith/central wood (±1 sigma) of 670 ± 40 and 759 ± 40 years old; the less dense Shorea johorensis and Shorea superba trees at Danum yielded ages of 240 ± 40 and 330 ± 40 years, respectively. All trees studied exhibit an increase in the IWUE since AD 1960. This reflects, in part, a response of the forest to increasing atmospheric carbon dioxide concentration. Unlike studies of some northern European trees, no clear plateau in this response was observed. A change in the IWUE implies an associated modification of the local carbon and/or hydrological cycles. To resolve these uncertainties, a shift in emphasis away from high-resolution studies towards long, well-replicated time series is proposed to develop the environmental data essential for model evaluation. Identification of old (greater than 700 years) ringless trees demonstrates their potential in assessing the impacts of climatic and atmospheric change. It also shows the scientific and applied value of a conservation policy that ensures the survival of primary forest containing particularly old trees (as in Imbak Canyon and Danum).

Prescribed (controlled) fire has recently been adopted as an important wildfire-fighting strategy in the Mediterranean. Relatively little research, however, has assessed its impacts on soil erosion and soil quality. This paper investigates hillslope-scale losses of soil, organic matter and selected nutrients before and after a ‘worst-case scenario’ prescribed fire in a steep, shrub-vegetated catchment with thin stony soil in central Portugal. Comparison is made with soil erosion measured: (1) on a nearby hillslope burned by wildfire and monitored at the hillslope scale; and (2) on long-unburned terrain at small-plot, hillslope- and catchment-scales. Hillslope-scale pre- and post-fire soil erosion was recorded over periods of 6 weeks to 5 months for (1) 9.5 months pre-fire and 27 months post-fire in the prescribed fire catchment, and (2) c. 3 years post-fire at the wildfire site. Organic matter content, pH, total N, K2O, P2O5, Ca2 + and Mg2 + were measured in the eroded sediment and in pre- and post-prescribed fire surface soil. Results indicate that: (1) both the prescribed fire and the wildfire caused expected marked increases in erosion compared with unburned terrain; and (2) the hillslope-scale post-prescribed fire soil losses (up to 2.41 t ha− 1 yr− 1) exceeded many reported plot-scale post-prescribed fire and post-wildfire erosion rates in the Mediterranean. As a comparison, post-fire erosion for both fire types was less than that caused by some other forms of common soil disturbance (e.g. types of tillage) and even that on undisturbed shrubland in low rainfall areas of the region. Total estimated post-prescribed fire particulate losses of organic matter and nutrients represent only 0.2–2.9% of the content in the upper 2 cm of soil, suggesting only a modest fire effect on soil quality, although this may reflect in part a lack of extreme rainfall events following the fire. The longer-term implications for soil conservation of repeated prescribed fire in the Mediterranean are explored and future research priorities identified.

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.

Increased attention has focussed on using mineral magnetic measurements as a proxy for heavy metal related sediment quality since magnetic concentration often correlates with total heavy metal concentrations, thus providing rapid and non-destructive screening of contaminated samples. Mineral magnetic measurements are being used in the assessment of sediment quality in the Lower Swansea Valley (South Wales, UK) a uniquely contaminated environment with a legacy of 250 years of non-ferrous smelting. Fendrod Lake is an in-line flood detention lake (created in the mid-1980s) on the polluted Nant-y-Fendrod stream, which drains an area contaminated by atmospherically deposited heavy metals and metal-rich smelter waste buried within the reclaimed and remediated valley floor. Heavy metals are accumulating in the lake sediment column. Positive correlations found between heavy metal (Zn and Pb) concentrations and magnetic susceptibility (x) in contaminated soils (mineral waste and aerial fallout) are not clearly observed in the lake sediment column (where the use of proxy measures of sediment quality is of greatest interest). Downcore profiles of X and major and minor elements, and information on metal speciation, indicate two controlling factors: (1) sediment source and contaminant delivery mode and (2) water column sediment/contaminant interaction dynamics linked to lake productivity.

event, yielding clockwise and anticlockwise hysteretic loops respectively. In contrast, metal concentrations, although high throughout the winter storm event, were diluted somewhat during the storm peak itself. The Pb and Cu appear to be supplied by quickflow processes and transported in close association with fine sediment, whereas Zn and Cd are delivered to the channel and lake by slower subsurface seepage in dissolved form. In the winter 2001 event, antecedent soil moisture and shallow groundwater levels were anomalously high and seepage sources of dissolved metals dominated. Downstream of the lake, Pb and Cu levels and suspended sediment were high in the summer storm, but low in the winter storm, suggesting retention with deposition of fine sediment in the lake during the latter. In the winter storm, Zn and Cd levels were higher downstream than upstream of the lake, perhaps because of additional seepage inputs from the surrounding slopes, which failed to have an impact during summer. An understanding of the complex interplay of antecedent soil moisture and the dynamics of subsurface seepage pathways in relation to the three-dimensional distribution of sources is important in modelling heavy metal fluxes and levels in contaminated urban catchments. Copyright  2003 John Wiley & Sons, Ltd.

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.

Archival rainfall data are used to investigate changes in drought frequency and severity in Sabah and other parts of northern Borneo since the late nineteenth century. Two measures of drought severity are used: drought duration (given by the number of consecutive months with less than 100 mm rain); and drought intensity (indexed by the cumulative rainfall deficit below 100 mm per month of a drought sequence). Within northern Borneo dry periods are very short (>3 months) and infrequent in Sarawak, south-western Sabah, Brunei and central and western Kalimantan; droughts occur seasonally, but are comparatively short in north-western Sabah; droughts are less frequent) but more severe in eastern Sabah and parts of eastern Kalimantan. In coastal Sabah and Brunei, there has been a statistically significant increase in the frequency and severity of droughts since the late 1960s. At Sandakan, two drought-prone epochs in 1877–1915 and 1968–92 (each experiencing five droughts of at least 4 months duration) are identified, separated by a 52-year period that was nearly drought-free. At Sandakan also, the ecologically damaging 1982–3 drought was neither as long or severe as those of 1903 and 1915. Links with El Niño-Southern Oscillation events are found to be not as strong as previous studies have suggested. Possible implications of the spatial and temporal patterns in drought magnitude-frequency for differences in tropical rain forest character within the region are discussed.

In an earlier special issue of this journal, Marsh & Greer summarized forest land use in Sabah at that time and gave an introduction to the Danum Valley Conservation Area. Since that assessment, during the period 1990–2010, the forests of Sabah and particularly those of the ca 10 000 km 2 concession managed on behalf of the State by Yayasan Sabah (the Sabah Foundation) have been subject to continual, industrial harvesting, including the premature re-logging of extensive tracts of previously only once-logged forest and large-scale conversion of natural forests to agricultural plantations. Over the same period, however, significant areas of previously unprotected pristine forest have been formally gazetted as conservation areas, while much of the forest to the north, the south and the east of the Danum Valley Conservation Area (the Ulu Segama and Malua Forest Reserves) has been given added protection and new forest restoration initiatives have been launched. This paper analyses these forest-management and land-use changes in Sabah during the period 1990–2010, with a focus on the Yayasan Sabah Forest Management Area. Important new conservation and forest restoration and rehabilitation initiatives within its borders are given particular emphasis.

R.P.D. Walsh1, M.A. Clarke2, K. Bidin3, W.H. Blake4, N.A. Chappell5, I. Douglas6, N. Ramli3, A.M. Sayer1, W. Sinun7, J. Larenus8 and J. Hanapi8 1University of Wales Swansea, UK; 2National Soils Research Institute, UK; 3Universiti Malaysia Sabah, Malaysia; 4University of Plymouth, UK; 5Lancaster University, UK; 6Manchester University, UK; 7Innoprise Corporation Sdn. Bhd., Malaysia; 8Danum Valley Field Centre, Malaysia

Despite soil piping being increasingly reported from the humid tropics, quantitative assessments of the role of pipeflow in runoff generation and sediment supply in humid tropical catchments remain lacking. This paper assesses pipeflow and streamflow suspended sediment dynamics in small humid tropical rainforest catchments in Danum Valley, Sabah, Malaysian Borneo. Pipeflow and streamflow in two small catchments were continuously monitored between December 2002 and June 2004 using pressure-transducer probes behind V-notch weirs; suspended sediment was continuously monitored with turbidity probes. Monthly flow and sediment load data show that a single monitored pipe in one catchment accounted for 47.2% of a stream's discharge and 21.6% of the suspended sediment load over the monitoring period. Anecdotal evidence from unmonitored pipes suggests the total contribution from pipes to streamflow discharge and sediment loads may be much higher. In general, absolute monthly pipe and stream sediment yields increase with monthly rainfall and pipe or stream discharge. Fourteen storm event responses are considered in detail. Pipe and stream discharge-suspended sediment responses to storm events are rapid and are characterised by clockwise hysteresis. An inverse relationship between the percent contribution of sediment to streamflow from a monitored pipe and rainfall intensity was identified, indicating that in large, intense rainstorms other sediment sources (including slopewash and unmonitored pipes) become more important. Mechanisms of pipe discharge and suspended sediment generation are discussed and implications for future runoff, sediment and channel development models are briefly outlined.

Soil water repellency is generally thought to enhance runoff responses, thus representing a potentially important factor in hydrological modelling. Attempts to quantify its impacts have, however, either focused on soil profiles or plot scales and/or have been unable unequivocally to isolate repellency effects from other hydrologically important parameters. This research gap is addressed here by comparing responses of the same soil or terrain at a range of scales in highly repellent and wettable states, thereby limiting the impact of other variables. Hydrological responses of forest soils in north-central Portugal are assessed using laboratory wetting and rainfall simulation experiments at the point (0.002 m 2 ) and microplot scales (0.12 m 2 ), and field runoff responses from plot (16 m 2 ) and catchment scales (0.33 km 2 ). At the point scale, water repellency reduced soil wetting by a factor of >700 and increased mean runoff for a microplot from 1.5 to 53% during the first 9 min of a simulated rainstorm. At the field-plot scale impacts are evident, but less dramatic, with 16 of 45 of storms following dry, repellent conditions producing >3% overland flow compared with only one of 60 storms following moist, wettable conditions. In contrast, at the catchment scale, storm runoff responses were lower following dry, repellent, conditions than with moist, wettable conditions, although the time-to-peak was on average 62% shorter for the former compared with the latter conditions. The reduced correspondence between the scales is attributed mainly to increased capture of locally generated overland flow at the catchment scale by bypass routeways that are under-represented at point and plot scales. It is concluded that addressing water repellency in distributed hydrological modelling has considerable potential for improving predictions for affected regions, but that impacts may vary considerably from those found in the Portuguese case example. Key parameters for determining its impacts are its severity, spatial distribution, transient characteristics, and the character and spatial distribution of any bypass routeways and wettable subsoil.

The /// and //// montados of Spain and Portugal cover about 6 million ha and form open savannah-type woodland comprising cork (Quercus suber) and holm (Q. rotundifolia and Q. ilex) oaks. Following their decline until the 1960s, these land management practices have become valued at national and international policy-making levels for their biodiversity, aesthetic qualities and potential for tourism and recreation, but comparatively little attention has been given to consequences for soil conservation. In this paper, the soil erosion risks associated with these land uses are compared with those of selected alternative forestry and agroforestry land uses. Selected soil properties, results of rainfall simulation experiments and field observations of erosion features for (a) two //// montado and three /// dehesa sites differing in terms of grazing pressure and tree type, (b) six alternative forestry plantations of various ages and (c) an olive grove are ranked according to relative erosion risk. None of the /// dehesa or //// montado sites has an overall mean rank indicating an erosion risk as low as that in established forestry plantations (at least four-five years old). One (heavily grazed) /// dehesa has a relatively high overall mean rank indicating a relative erosion risk only slightly lower than that obtained for an erosion-prone, newly ploughed and planted eucalyptus plantation. It is concluded that present day /// dehesa and //// montado variants can be prone to severe erosion if stocking rates and/or tillage frequency become excessive. The advantages and limitations of the ranking methodology used are discussed. Copyright # 2002 John Wiley & Sons, Ltd.

Climatic records for Danum for 1985 to 1998, elsewhere in Sabah since 1879, and long monthly rainfall series from other rainforest locations are used to place the climate, and particularly the dry period climatology, of Danum into a world rainforest context. The magnitude frequency and seasonality of dry periods are shown to vary greatly within the world's rainforest zone. The climate of Danum, which is aseasonal but subject, as in 1997 to 1998, to occasional drought, is intermediate between less drought–prone north–western Borneo and the more drought–prone east coast. Changes through time in drought magnitude frequency in Sabah and rainforest locations elsewhere in South–East Asia and in the Neotropics are compared. The 1997 to 1998 ENSO–related drought event in Sabah is placed into a historical context. The effects of drought on tree growth and mortality in the tropics are assessed and a model relating intensity and frequency of drought disturbance to forest structure and composition is discussed.