Controls on stable isotopic characteristics of water vapour over Thailand

This study examined the weekly water vapour isotopic composition (δ¹⁸O_v) in Thailand. The water vapour was cryogenically collected from eight sites across the country. Two observational samples were collected over one 24-h period each week (a daytime and a night-time sample), from September 2013 to September 2014. The primary aim was to investigate the environmental factors influencing water vapour isotopes. The results revealed differences in water vapour isotopic values between day and night samples. Three periods of depleted δ¹⁸O_v were associated with large-scale convective systems in September, December, and May. The statistical relationship between the climate variables and water vapour isotopes indicated that the amount of precipitation and relative humidity were the primary controls on both diurnal and seasonal isotopic variability. The temperature did not affect the δ¹⁸O_v, mainly because the atmospheric processes are a function of vertical convection rather than temperature in tropical regions. The water vapour deuterium excess (d-excess) showed greater variability in 2013 than in 2014. The d-excess variation reflected the differences in convection occurring in the day and night. In addition, the vapour phase data were combined with the local meteoric water line to identify the local water vapour line and the interaction between the isotopic composition of water vapour and liquid water. The water vapour isotopic patterns paralleled the precipitation isotopes on rainy days because of equilibrium isotopic exchange. Water vapour and precipitation were isotopically similar under low humidity but showed greater differences from each other under wetter conditions. The study results provide insight into water vapour isotopic characteristics in tropical regions and constrain the role of large-scale atmospheric processes relative to isotopic variability of water vapour in Thailand and nearby countries.     

Contribution of intercepted subsurface flow to road runoff and sediment transport in a logging‐disturbed tropical catchment

Hydrological and sediment fluxes were monitored for a 1 yr period in a tropical headwater catchment where a 3 yr old logging road caused substantial Hortonian overland flow (HOF) and intercepted subsurface flow (ISSF). On a 51·5 m road section, ISSF became an increasingly important component of total road runoff, up to more than 90% for large storms. The proportion of ISSF contributed by road cuts along more or less planar slopes compared with ISSF from a zero‐order basin (convergent slopes) truncated by the road declined with increasing rainfall. During the monitored storms that generated ISSF along the road, on average, 28% of sediment export and 79% of runoff from the road section were directly attributable to ISSF. Estimates of total sediment export from the road surface (170 t ha^?1 yr^?1) and suspended sediment export from the logging‐disturbed catchment (4 t ha^?1 yr^?1) were exceptionally high despite 3 yr of recovery. ISSF caused not only additional road‐generated sediment export, but also exacerbated HOF‐driven erosion by creating a poor foundation for vegetation recovery on the road surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Soil pipes and their role in runoff generation and chemical denudation in a humid tropical catchment in dominica

Numerous soil pipes are reported from a small catchment in an area of kandoid (kaolin-rich) soils and 2375 mm annual rainfall in the humid tropical volcanic island of Dominica, West Indies. Two spot surveys in August 1982 at baseflow during the wet season indicated that pipes contributed at least 14–16 per cent of streamflow. Sampled pipeflow was of similar chemical composition to the baseflow-dominated streamwater. Specific conductance (249–420 μS cm^?1) and silica (75 mg l^?1) levels of pipeflow were high and suggested that the pipes tapped solute-rich water close to the soil-rock interface. The principal pipes flow perennially and showed little response to daily rainfalls of up to 43 mm during the monitoring period.     

Land cover effects on soil infiltration capacity measured using plot scale rainfall simulation in steep tropical lowlands of Central Panama

Understanding land use/land cover (LULC) effects on tropical soil infiltration is crucial for maximizing watershed scale hydro-ecosystem services and informing land managers. This paper reports results from a multiyear investigation of LULC effects on soil bulk infiltration in steep, humid tropical, and lowland catchments. A rainfall simulator applied water at measured rates on 2 × 6 m plots producing infiltration through structured, granulated, and macroporous Ferralsols in Panama's central lowlands. Time-lapse electrical resistivity tomography (ERT) helped to visualize infiltration depth and bulk velocity. A space-for-time substitution methodology allowed a land-use history investigation by considering the following: (a) a continuously heavy-grazed cattle pasture, (b) a rotationally grazed traditional cattle pasture, (c) a 4-year-old (y.o.) silvopastoral system with nonnative improved pasture grasses and managed intensive rotational grazing, (d) a 7 y.o. teak (Tectona grandis) plantation, (e) an approximately 10 y.o. secondary succession forest, (f) a 12 y.o. coffee plantation (Coffea canephora), (g) an approximately 30 y.o. secondary succession forest, and (h) a >100 y.o. secondary succession forest. Within a land cover, unique plot sites totalled two at (a), (c), (d), (e), and (g); three at (b); and one at (f) and (h). Our observations confirmed measured infiltration scale dependency by comparing our 12 m² plot-scale measurements against 8.9 cm diameter core-scale measurements collected by others from nearby sites. Preferential flow pathways (PFPs) significantly increased soil infiltration capacity, particularly in forests greater than or equal to 10 y.o. Time-lapse ERT observations revealed shallower rapid bulk infiltration and increased rapid lateral subsurface flow in pasture land covers when compared with forest land covers and highlighted how much subsurface flow pathways can vary within the Ferralsol soil class. Results suggest that LULC effects on PFPs are the dominant mechanism by which LULC affects throughfall partitioning, runoff generation, and flow pathways.     

Modelling the impacts of land-cover change on streamflow dynamics of a tropical rainforest headwater catchment

Abstract

A modelling experiment is used to examine different land-use scenarios ranging from extreme deforestation (31% forest cover) to pristine (95% forest cover) conditions and related Payment for Ecosystem Services (PES) schemes to assess whether a change in streamflow dynamics, discharge extremes and mean annual water balance of a 73.4-km² tropical headwater catchment in Costa Rica could be detected. A semi-distributed, conceptual rainfall–runoff model was adapted to conceptualize the empirically-based, dominant hydrological processes of the study area and was multi-criteria calibrated using different objective functions and empirical constraints on model simulations in a Monte Carlo framework to account for parameter uncertainty. The results suggest that land-use change had relatively little effect on the overall mean annual water yield (<3%). However, streamflow dynamics proved to be sensitive in terms of frequency, timing and magnitude of discharge extremes. For low flows and peak discharges of return periods greater than one year, land use had a minor influence on the runoff response. Below these thresholds (<1-year return period), forest cover potentially decreased runoff peaks and low flows by as much as 10%, and non-forest cover increased runoff peaks and low flows by up to 15%. The study demonstrated the potential for using hydrological modelling to help identify the impact of protection and reforestation efforts on ecosystem services.

Editor Z.W. Kundzewicz

Citation Birkel, C., Soulsby, C., and Tetzlaff, D., 2012. Modelling the impacts of land-cover change on streamflow dynamics of a tropical rainforest headwater catchment. Hydrological Sciences Journal, 57 (8), 1543–1561.     

中国热带琼雷生态经济区的建设构想

生态经济区克服了传统经济区生态环境约束下的经济增长瓶颈,是区域经济发展的重要内容和方向。目前黄河三角洲高效生态经济区和鄱阳湖生态经济区的建设都已引起国家的高度关注。琼雷生态经济区是在充分考虑了湛江市(雷州半岛)和海南省(海南岛)地区热带资源禀赋、生态环境脆弱性及经济空间紧密性的基础上提出来的战略构想。琼雷地区生态本底较好;热带作物资源、海洋资源及港口资源十分丰富,热带特色显著;经济结构以一、三产业为主,生态恢复与维护成本较小;存在地缘一致性和经济紧密性,有一定区域联系基础。但同时本区域存在生态环境的脆弱性,影响区域生态安全的因素较多,因此必须坚持生态主导下的经济发展原则。为此,建立中国热带琼雷生态经济区是必要的和及时的。本文从宏观的角度,详细分析了琼雷生态经济区的功能定位和建设的主要内容,以期在中国的典型热带区域打造生态经济区发展平台,构筑中国热带生态经济发展高地。     

THE LAPWING IN ANDEAN ETHNOECOLOGY: PROXY FOR LANDSCAPE TRANSFORMATION*

The Andean lapwing (Vanellus resplendens Tschudi) prompts rethinking of ethnoecology in neotropical cloud forests and páramos and challenges notions about conservation in mountain protected areas. Using archaeological, historical, and current evidence, I argue that the role of humans in shaping viable high‐mountain bird populations is an important factor in the conservation priorities of tropandean landscapes, particularly in the mountains. The presence of the Andean lapwing demonstrates the intricate linkages between culture and nature in the Andean region. I highlight a paradox of conservation, using the Andean lapwing as the avian indicator of global environmental change as an example of the contest between landscape change, biodiversity, and ethnoecological insights. Landscape stewardship, conservation easements, and cultural landscapes are options for inclusion in the repertoire of scenarios for the survival of healthy avifaunal assemblages in high‐mountain environments that have evolved in synchrony with humans, such as in páramos, cultural landscapes worth protecting in the tropical Andes.     

中国热带珊瑚礁的第四纪气候记录

The coral reef in China’s tropics can be divided into three regions, namely, the South China Sea Islands, Hainan Island and the Leizhou Peninsula as well as Taiwan Island. There are 34 islands of coral reef which are named in the South China Sea Islands …     

Measurement and prediction of sediment production from unpaved roads,St John,US Virgin Islands

Excess delivery of land‐based sediments is an important control on the overall condition of nearshore coral reef ecosystems. Unpaved roads have been identified as a dominant sediment source on St John in the US Virgin Islands. An improved understanding of road sediment production rates is needed to guide future development and erosion control efforts. The main objectives of this study were to: (1) measure sediment production rates at the road segment scale; (2) evaluate the importance of precipitation, slope, contributing area, traffic, and grading on road sediment production; (3) develop an empirical road erosion predictive model; and (4) compare our measured erosion rates to other published data. Sediment production from 21 road segments was monitored with sediment traps from July 1998 to November 2001. The selected road segments had varying slopes, contributing areas, and traffic loads. Precipitation was measured by four recording rain gauges. Sediment production was related to total precipitation and road segment slope. After normalizing by precipitation and slope, the mean sediment production rate for roads that had been graded within the last two years was 0·96 kg m^?2 cm^?1 m m^?1 or approximately 11 kg m^?2 a^?1 for a typical road with a 10 per cent slope and an annual rainfall of 115 cm a^?1. The mean erosion rate for ungraded roads was 42 per cent lower, or 0·56 kg m^?2 cm^?1 m m^?1. The normalized mean sediment production rate for road segments that had been abandoned for over fifteen years was only about 10 per cent of the mean value for ungraded roads. Sediment production was not related to traffic loads. Multiple regression analysis led to the development of an empirical model based on precipitation, slope to the 1·5 power, and a categorical grading variable. The measured and predicted erosion rates indicate that roads are capable of increasing hillslope‐scale sediment production rates by up to four orders of magnitude relative to undisturbed conditions. The values from St John are at the high end of reported road erosion rates, a finding that is consistent with the high rainfall erosivities and steep slopes of many of the unpaved roads on St John. Other than paving, the most practical methods to reduce current erosion rates are to minimize the frequency of grading and improve road drainage. Copyright © 2005 John Wiley & Sons, Ltd.