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Background: Earthquake is one of the most destructive natural disasters, which cause immediate and long-term changes to the river systems. This research aimed to examine the immediate and five-year impacts of the 2015 Ranau Earthquake (6.0 Mw) on river systems in Malaysian state of Sabah, a region of low earthquake hazard. Methods: We used object-based classification on Landsat 8 (2014 and 2015) and Sentinel-2A (2020) satellite imageries to derive land cover time series for investigating the impacts on the riparian areas. Results: The earthquake removed vegetation in the riparian zones of four rivers, the highest being the Penataran River (69.21 ha). During the immediate impact period (2014–2015), river bar formation occurred in all rivers, with the largest increase occurring in the Kadamaian River (56.97 ha), followed by the Panataran River (54.36 ha), which had no river bar before the earthquake. The river bar of the Kadamaian River continued to increase, whereas the river bar of the Panataran River decreased five years after the earthquake. Land cover transition analysis revealed that 78.39 ha of vegetation, barren land, and river water areas changed to river bars in the Kadamaian riparian area during the immediate impact period. Except for 26.87% of river bars in the Kadamaian riparian area in 2015, most river bars transitioned to other land cover types five years later. During the period of immediate impact, 22.05 ha of vegetation and 10.71 ha of river water were transformed into river bars along the Penataran River. Five years later, except for 16.2 ha, all river bar areas had transitioned to other cover types. Additionally, 17.7 ha of new river bars were formed. This study provides crucial data on post-earthquake land cover changes, particularly river bar formation and changes, for assessing the earthquake impacts on the river systems and supporting impact mitigation. [ABSTRACT FROM AUTHOR]

Pristine tropical river systems are coming under increasing pressure from the development of economic resources such as forestry and mining for valuable elements. The Lebir catchment, north eastern Malaysia, is now under development as a result of unregulated tree felling and mining for essential and rare metals. Two sediment cores, one in the upstream reaches and the other from the downstream reaches, were taken from flood prone area of the Lebir River, Malaysia, and analysed for their elemental composition by XRF, specifically Al, Si, Fe, Ca, K, Mg, Mn, V, Cu, Ni, Pb, Cr, Zn, As, Th and U. Activities of fallout radionuclides, 137Cs and 210Pb were also determined to from a geochronological context. The elemental concentrations in the soils were assessed in terms of their enrichment factor and Si, Ca, K, Mg, Mn, V, Cu, Ni and Zn were found not to be enriched, whereas As, Th and U had elevated enrichment factors. The Th and U were particularly enriched in the downstream core indicating inputs from a tributary that drains a catchment with known deposits of Th and possibly U. The results suggest that the growth in economic development is fostering the transport of contaminants by the major rivers which, in turn, is contaminating the riverine floodplains. This points to the need for a more integrated and holistic approach to river basin management to maintain the environmental quality of these fragile aquatic systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Understanding baseline runoff characteristics is critical in any water balance study whether single- or multiple-catchment. As a product of interaction between many area-specific factors (scale, climate, geology, vegetation, land-use history), each catchment can only be well-understood through a reasonable period of baseline observation. In temperate regions, processes are complicated by a range of meteorological factors and plant phenological periods (growth and dormant) as well as the way vegetation reacts to these factors resulting in varying water uptake from soils. In the Inuyama Research Forest of the Ecohydrology Research Institute in Aichi prefecture, central Japan, streams in two small headwater catchments (cypress plantation, 2.2 ha; secondary mixed-broadleaf, 2.1 ha) were instrumented with 90° v-notch weirs and automatic data loggers that recorded water level at 5-minute intervals. These data were then converted to discharge via calibration. A weather station was also set up in the area to record rainfall and other meteorological data. After quality control and data filtering, 1,398 daily runoff and rainfall over five years (April 2013-April 2018) were computed and analysed. Data were separated according to plant phenology (growth period from 1st May to 31st October; dormant period from 1st November to 30th April) and explored via runoff coefficients (C) and rainfall-runoff regressions in two ways:- (i) growth vs. dormant periods within individual catchments (cypress and broadleaf); (ii) cypress vs. broadleaf forests within each phenological period (growth and dormant). C-values in the growth and dormant periods are 0.534 and 0.521 for cypress; and 0.506 and 0.525 for broadleaf respectively. Within individual catchments, the cypress catchment has a 2.5% higher C-value in the growth period (0.534) compared to in the dormant period (0.521) whilst the broadleaf catchment shows a 3.6% reduction instead (0.506 in growth; 0.525 in dormant). This suggests that during the warm and humid growth period, the increased water uptake by cypress trees does not offset the influence exerted by higher rainfall. However, the slopes of rainfall-runoff relationship are higher during the growth period in both catchments. For comparison between the two catchments within the same phenological period, the 5% lower C-value in broadleaf (0.506) compared to cypress (0.534) reflects higher water use by broadleaf trees during the growth season whereas similar values (0.521 in cypress, 0.525 in broadleaf) during the dormant season indicate continual rainfall interception by cypress even after leaf abscission in the broadleaf catchment. This is further supported by the higher slope of rainfall-runoff relationship in the broadleaf catchment during the dormant period. This study has shown that rainfall-runoff relationships in this area differ according to vegetation type and phenological periods. Hence, forthcoming catchment hydrological studies should be designed to control for these effects. [ABSTRACT FROM AUTHOR]

It is well known that a logging/harvesting practice in a forested catchment induces evapotranspiration (ET) decline and a subsequent runoff increase. In addition, most previous paired-catchment studies have revealed that, after re-planting the same tree species in the logged catchment, the post-logging runoff increase gradually diminished and returned to pre-logging level within short time period (typically 5-15 years), due to increasing water use by the planted trees with their growths. However, there is relatively little information on how longer-term catchment water balance changes with maturity of trees in the catchment. Marc and Robinson (2007) is one the few studies, in which, based on long-term catchment water balance data in UK, they reported that ET reduced by 140 mm per year in spruce/pine catchments with increasing forest ages. In order to fill the knowledge gap further, we revisited long-term water balance data for a Japanese catchment in which the soil and vegetation had been disturbed due to forest overuse, until its establishment in 1929 by University of Tokyo. Initially, the catchment was covered by young pines with scattered denuded ridges. After the catchment establishment, the poor vegetation had gradually been matured and the scattered denuded ridges had been decreased particularly after 1960s. Because the matured pine trees in the catchment had been largely declined due to an epidemic (pine wilt disease) during 1980s, we examined annual loss of the catchment from 1930s to 1970s. The result showed that the annual loss decreased with the decades, i.e., pine maturing, by about 100-150 mm per year. A further event-basis water balance analysis (Linsley et al. 1982) showed that the decline in the annual loss was caused by ET decline in the mid-growing season while ET in the dormant season exhibited almost no change throughout decades. Though, in order to draw a solid conclusion, a further investigation is still needed considering fluctuations in meteorological factors (such as air temperature) controlling ET, we currently attribute the ET decline in the mid-growing season to age-related transpiration decline, as was found for maritime pine stands in France (Delzon and Loustau 2005), because canopy interception would be augmented in later decades due to larger above-ground biomass and leave amount. [ABSTRACT FROM AUTHOR]