Tag: hydrology
Evidence of a water δ18O negative shift driven by intensive deep CO2 upflow at Shiwaga gas field (Rungwe, Tanzania)
Located on the flank of Ngozi volcanoes (Tanzania), the Shiwaga gas field is a spot of intense CO2(g) emanations. Physico-chemical measurements on different types of waters (rivers, puddles, and springs) as water and gas sampling were discontinuously performed over 10 years for equilibrated partial CO2 pressure calculations and stable isotopic analyses. The most striking result shows that meteoric H2O and deep originated CO2(g) exchanges are responsible for a negative 18O-shift of the studied waters in relation with waters electrical conductivity, pH, and pCO2eq changes. In spring waters, a maximum shift of − 11.2‰ in δ18O was observed and pCO2eq values up to 1196 mbar were computed. Although this trend has already been reported around the world, such extended shift is rarely measured and requires an important amount of CO2(g), with a CO2(g)/H2O ratio up more than 0.5 mol/mol. This approach is useful to better understand the hydro-geochemical processes involved in such environments. Moreover, this study evidences that an inventory as a monitoring of these gas fields are needed for the management of natural hazards and local resources.
Changes in the landscape pattern of the La Mesa Watershed – The last ecological frontier of Metro Manila, Philippines
Spatial groundwater recharge estimation in Raya basin, Northern Ethiopia: an approach using GIS based water balance model
Understanding the spatial variability of groundwater recharge in response to distributed Land-use, soil texture, topography, groundwater level, and hydrometeorological parameters is significant when considering the security of groundwater resource development. Thus, this study was aimed at estimating the spatial groundwater recharge of Raya valley, northern Ethiopia using spatially distributed water balance model (WetSpass). Input data for the model were prepared in the form of grid maps using 90 m grid size and the parameter attribute tables were adjusted to represent the Raya valley condition using expert knowledge and scientific literatures. The results of the model indicated that the long-term temporal and spatial average annual rainfall of 710 mm was partitioned as 57 mm (8%) of surface runoff, 598 mm (84%) of evapotranspiration, and 55 mm (8%) of recharge. The recharge corresponds to 137 million cubic meters (Mm3) for the Raya basin (with area of about 2500 km2) from which 84% of the recharge takes place during summer season, while the remaining 16% takes place during the winter (dry) season. The analysis of the simulated result showed that WetSpass works well to simulate water balance components of Raya valley and is especially suitable for studying the effects of Land-use changes on the water regime in the basin.
An Outline of requirements for a spatial information and negotiation support system
This report describes the outcomes of a 45-day consultancy undertaken for RUPES, from August to November 2003. The purpose of the consultancy was to investigate the design requirements for a RUPES spatial information and negotiation support system (SINSS). Such a system would allow standardized and consistent assessment of RUPES action research sites and outcomes, and promote transparent and informed negotiation between stakeholders involved in the development of environmental service rewards schemes (ESRSs). It would also establish an important baseline for spatial targeting, impact monitoring and adaptive management.
Leaf area index as an indicator of ecosystem services and management practices: An application for coffee agroforestry
Scalable indicators are promising to assess ecosystem services. In a large (660 ha) coffee agroforestry farm,we calibrated the relationship between the Normalized Difference Vegetation Index (NDVI), calculatedon a High Resolution (HR) satellite image and ground-truth LAI, providing a 2-layer (shade trees andcoffee) LAI calibration with LAI 2000 and a new technique based on the cumulative distribution of LAIalong transects. The effective and apparent clumping of coffee leaves were computed (0.76 and 0.89,respectively). We also calibrated the relationship between the derived HR-LAI farm map and NDVI fromthe Moderate Resolution Imaging Spectroradiometer (MODIS) in order to re-construct LAI time-series(2001-2011).Coffee LAI, as derived from MODIS after substracting the contribution of shade tree LAI varied seasonallybetween 2.4 and 4.4 m2m-2, with a maximum by the end of wet season (peak of harvest), steep declineduring the drier-cooler season, minimum after annual coffee pruning, recovery during the next rainyseason and pause during the grain filling period. MODIS also detected significant inter-annual variationsin LAI originating from annual pruning, or plot renovation followed by a progressive LAI recovery duringup to 4 years.We related the coffee-LAI time-series with farm registries to examine the impacts of management onLAI and on selected ecosystem services, namely yield and hydrological services. Nitrogen fertilizationwas adjusted annually by the farmer and appeared as the best yield predictor (R2= 0.53). CombiningN-fertilization with LAI from 6 significant months of the year, the prediction was improved (R2= 0.74),confirming LAI as an important co-predictor of yield. We ended up with a yield prediction model includingalso the percentage of pruned resprouts (R2= 0.79), with potential uses for regional yield mapping orreconstruction of historical yield time-series.
Assesing conservation value of rubber agroforest in the Sumatra lowlands: a landscape level assessment of plant diversity
In order to make robust predictions about biodiversity levels at landscape scale there is a need to shift attention from simple species count to ecological processes. In this project which focuses on tree species, plant community data will be assessed both in terms of species composition and functional group composition
Sensitivity of groundwater recharge under irrigated agriculture to changes in climate, CO2 concentrations and canopy structure
Estimating groundwater recharge in response to increased atmospheric CO2 concentration and climate change is critical for future management of agricultural water resources in arid or semi-arid regions. Based on climate projections from the Intergovernmental Panel on Climate Change, this study quantified groundwater recharge under irrigated agriculture in response to variations of atmospheric CO2 concentrations (550 and 970 ppm) and average daily temperature (+1.1 and +6.4 C compared to current conditions). HYDRUS 1D, a model used to simulate water movement in unsaturated, partially saturated, or fully saturated porous media, was used to simulate the impact of climate change on vadose zone hydrologic processes and groundwater recharge for three typical crop sites (alfalfa, almonds and tomatoes) in the San Joaquin watershed in California. Plant growth with the consideration of elevated atmospheric CO2 concentration was simulated using the heat unit theory. A modified version of the Penman-Monteith equation was used to account for the effects of elevated atmospheric CO2 concentration. Irrigation amount and timing was based on crop potential evapotranspiration. The results of this study suggest that increases in atmospheric CO2 and average daily temperature may have significant effects on groundwater recharge. Increasing temperature caused a temporal shift in plant growth patterns and redistributed evapotranspiration and irrigation water use earlier in the growing season resulting in a decrease in groundwater recharge under alfalfa and almonds and an increase under tomatoes. Elevating atmospheric CO2 concentrations generally decreased groundwater recharge for all crops due to decreased evapotranspiration resulting in decreased irrigation water use. Increasing average daily temperature by 1.1 and 6.4 C and atmospheric CO2 concentration to 550 and 970 ppm led to a decrease in cumulative groundwater recharge for most scenarios. Overall, the results indicate that groundwater recharge may be very sensitive to potential future climate changes.
Agroforestry: hydrological impacts
In addition to their social and economic value, forests and agroforestry (AF) have been widely promoted as a viable solution to overcome the loss of ecosystem functions associated with the conversion of natural landscapes for human use (Jose,2009). AF systems vary in the density and configuration of trees in farming landscapes from a few scattered trees or line plantings to dense and complex agro forests. However, the relationship between tree cover and water supply is not straightforward and forest/agriculture policies are often at odds with scientific understanding. In the tropics, forest/farming and water policies were often based on the assumption that tree-covered landscapes are the most appropriate way to maximize water yield, regulate seasonal flows, and ensure high water quality under all hydrological and ecological situations (Calder et al., 2007). According to this assumption, conserving or extending tree cover in upstream watersheds is the most effective way to enhance water availability for agricultural, industrial, and domestic use and prevent floods in downstream areas. Various national agencies, often with international confounding, are spending vast sums of money on tree planting and soil conservation efforts based on the belief that ‘more trees mean more water’.
Water productivity in forestry and agroforestry
Forests are the biggest users of water worldwide and extensive forested areas have been lost or are undergoing conversion to agriculture, creating concerns about loss of hydro logical functions and increasing the competition for scarce water between agriculture, urban centers, industries and wildlife. The challenge is to improve the sustainability and productivity of land and water use, especially for the growing populations of many developing countries. In this chapter we review recent findings on the hydrology of forests and agroforestry systems and indicate how modifications in tree-based systems might increase water productivity. In forestry, the focus of research has moved from the hydro logical functions of upland forest reserves that are close to settlements to a greater recognition of the roles played by upland communi-ties in the management of water resources. A major source of conflict over water resources is the con-trasting perceptions of ‘watershed functions’ between forest managers and local people, which are often based more on myths of forest functions than on science – for example, the idea that forests increase rainfall. These myths continue to dominate the views of policy makers and institutions and should be revised. The challenge is to gain a better insight into how farmer-developed land-use mosaics have modified watershed-protection functions. Priority must be given to the perceptions,experiences and strategies of local communities.Trees on farms have the potential for improving productivity in two ways. Trees can increase the amount of water that is used on farm as tree or crop transpiration. Trees can also increase the produc-tivity of the water that is used by increasing biomass of trees or crops produced per unit of waterused. Plot-level evidence shows that improvements in water productivity as a consequence of modifi-cations to the microclimate of the crop are likely to be limited. Instead, evidence from semi-arid India and Kenya showed that the greater productivity of agroforestry systems is primarily due to the higher amount of water used. Almost half of the total water use occurred during the dry season,when cropping was impossible, and the rest was extracted from soil reserves. This implies a high temporal complementarity between the crop and tree components of the landscape mosaic. Research is needed to examine the impact of the increased water use on the drainage and base flow at the land-scape level. This chapter also describes some of the technical approaches that can be used to improve land and water management, the role of trees and its relation to hydrology and the challenges for rational land-use decision-making.