Sap flow and water transfer in the Garonne river riparian woodland, France : first results on poplar and willow

This work is the first attempt at using Granier sap sensors on Populus nigra, Populus x euramericana cv I45/51 and Salix alba for the monitoring of sap flows in an active floodplain over two consecutive years. The main characteristic of these diffuse porous trees is their capacity to use several tree rings for xylem sap transfer. Results showed that the sap flux densities remained homogeneous on the external 4 cm of the trunk, then decreased with depth. For young trees, the active sapwood can represent half of the trunk. Results indicated that in the same environment and at the same age, daily differences existed between the two major native riparian tree species, the black poplar and the white willow. Their maximal sap flux density (2.6-3.6 dm 3 dm -2 h -1) was similar to other fast growing trees. The influence of age was the third important screened factor. Sap flow measurements over several months indicated that water uptake was variable throughout the season, depending on water availability, and was more pronounced for older trees. The sap flux densities for the planted poplar (I45/51) ranged from 2.2-2.6 dm 3 dm -2 h -1 (about 90 dm 3 day -1) in the wetter spring conditions and dropped to 1.6-1.7 dm 3 dm -2 h -1 (about 60 dm 3 day -1) in less favourable conditions. Under the worst conditions, e.g., the especially long drought in the summer of 1998, these values dropped to 1.0-1.2 (about 40 dm 3 day -1), and even to 0.35 dm 3 dm -2 h -1 (about 12 dm 3 day -1) for a few days. Complementary long-term studies are needed to better understand the complex sap flow changes and to be able to relate them to significant environmental factors. Priority should be given to the long-term monitoring of sap flows at different depths for a correct estimation of actual daily water uptakes by riparian softwood trees

The Guianese paradox: How can the freshwater outflow from the Amazon increase the salinity of the Guianan shore?

French Guiana is notable for the extent of its rain forests, which occupy 97% of the country, and the influence of the Amazon along its shores. In fact, the shores and estuaries support a mangrove forest typical of saline conditions. This paper reports the chemical characteristics, conductivity and salinity and the stable isotopes (oxygen and deuterium) of the rivers and shores between the Cayenne area and the border with Surinam. The results show a quite homogenous freshwater pool over the country. However, the low slope of the coast, a result of the wide mud banks deposited by the Amazonian plume, have turned the mouths of the smaller rivers to the northwest, creating large salty areas where mangroves grow several kilometers inland. Despite the large amount of Amazonian water, the Guianan coast exhibits high salinity. In fact, the freshwater itself remains far from the shore, following the north Brazilian current, while only the mud plume arrives at the coast, creating this paradox

Mapping riparian vegetation along rivers : old concepts and new methods

Several objections have been made to the approach of a sliced environment introduced by the Remote Sensing (RS) and Geographic Information System (GIS) tools. There is no evidence that each discipline can be reduced to a set of layers of spatial information. For most botanists, the quality and hence the value of a vegetation map rests more heavily on the selected system of classification than on any other feature. This paper assumes that the knowledge of the historical trends in vegetation mapping concepts may provide useful insights for improving the GIS approach of vegetation. In the first part, a summary of the debates in the scientific community is presented. First taxonomists were opposed to physiognomists. Then, with the development of the ecosystem concept and the landscape concept new questions arose in the debate: what should be mapped, vegetation, ecosystems or landscapes? Controversies opposed botanists to geomorphologists. Today, patterns as well as processes have to be mapped. However, little has been done on riparian vegetation. The second part of the paper focuses on two specific requirements for RS of riparian vegetation, namely high spatial resolution and spatially-oriented classification algorithms. Both have been neglected in the past. By 1998, improvements in satellite data should stimulate studies on riparian vegetation. However, aerial photographs will remain the best medium for analysing riparian vegetation in detail. In the third part, the discussion focuses on the use of GIS for riparian vegetation studies. Obviously, a vegetation layer cannot show the vegetation in all its aspects. However, if it is based on a sound scientific method, much of the information which is stored in an implicit form can be exploited for broader application. Mapping vegetation can be considered as a driving element in research, a mean to moderate the subjectivity of conceptual statements and to validate ecological theories. On floodplains the major problem is a lack of useful data and the high cost for obtaining such data. The challenge is to map flood disturbances and the vegetation dynamic

Daily variations of water use with vapor pressure deficit in a plantation of I214 poplars.

Daily rates of whole tree water use were measured in a homogeneous 7-year-old plantation over 84 days. Two trees were selected in the two most contrasting ends, i.e., with mean water table at -1.5 m and -3.5 m. Results showed that the mean tree water use was close to 80 dm3 day–1 with a small mean difference between the two sites (5.4 dm3 day–1, about 7%). Higher daily variations were observed on a single tree over the season (from 17 to 138 dm3 day–1). These fluctuations could be modeled using linear regressions on the vapor pressure deficit (VPD). Results also indicated decreasing sap flux densities with radial sapwood depth and that the whole tree water use could be estimated from the sap flux densities measured at the 0–2 cm depth

Modeling soil moisture-reflectance

Spectral information on soil is not easily available as vegetation and farm works prevent direct observation of soil responses. However, there is an increasing need to include soil reflectance values in spectral unmixing algorithms or in classification approaches. In most cases, the impact of soil moisture on the reflectance is unknown and therefore ignored. The objective of this study was to model reflectance changes due to soil moisture in a real field situation using multiresolution airborne Spot data. As the direct observation of soils is only possible in the absence of vegetation, the effective remote sensing of soil moisture is limited to a few days each year. In such a favorable time window, modeling the soil moisture- reflectance relationships was found possible. The proposed exponential model was not valid when all soil categories were considered together. However, when fitted to each category, the RMS error on moisture estimates ranged from 2.0% to 3.5% except for silty soils with crusting problems (6%). Results also indicated that, when the soils have similar colors (i.e. same hue), soil categories can be partly grouped and the model can be simplified, using the same intercept coefficients. This study has potential application for the definition of a more generalized model of the soil reflectance. It shows that the impact of soil moisture on reflectance could be higher than differences in reflectance due to the soil categories

Characterizing the complexity of landscape boundaries by remote sensing

This paper presents a method for characterizing the complexity of landscape boundaries by remote sensing. This characterization is supported by a new boundary typology, that takes into account points where three or more landcovers converge (i.e., convergency points or coverts). Landscape boundary richness and diversity indices were proposed and calculated over 19 landscapes in South-East Brazil. Results showed that landscape boundaries, especially convergency points, provided an enrichment in landscape pattern analysis. Landcover boundary diversities were significantly related to landcover shape: elongated riparian units had the highest values for boundary diversity and coverts proportion indices. On the other hand, landscape analysis showed that indices of shape, richness, diversity and coverts proportion provided an additional evaluation of landcover spatial distribution within the landscape

Evaluation and correction of angular anisotropic effects in multidate SPOT and Thematic Mapper data

SPOT XS oblique data are compared with Landsat Thematic Mapper (TM) vertical data at two different times. Under the assumption that analogous spectral bands are equivalent, the differences in spectral responses observed over land cover classes are attributed to the effects of angular anisotropic reflection. This article shows that land cover classes cannot easily be characterized by their anisotropy. The magnitude of anisotropy varies strongly with the radiometric processing levels (i.e., absolute calibration or normalization) but has no significant impact on the overall classification results. The normalization method based on the use of pseudoinvariant objects is sufficiently effective as to correct most anisotropic disturbances and should facilitate an alternative use of SPOT and TM data

Facilitators and barriers to the implementation of a Mobile Health Wallet for pregnancy-related health care: A qualitative study of stakeholders’ perceptions in Madagascar

Financial barriers are a major obstacle to accessing maternal health care services in low-resource settings. In Madagascar, less than half of live births are attended by skilled health staff. Although mobile money-based savings and payment systems are often used to pay for a variety of services, including health care, data on the implications of a dedicated mobile money wallet restricted to health-related spending during pregnancy–a mobile health wallet (MHW)–are not well understood. In cooperation with the Madagascan Ministry of Health, this study aims to elicit the perceptions, experiences, and recommendations of key stakeholders in relation to a MHW amid a pilot study in 31 state-funded health care facilities. We conducted a two-stage qualitative study using semi-structured in-depth interviews with stakeholders (N = 21) representing the following groups: community representatives, health care providers, health officials and representatives from phone provider companies. Interviews were conducted in Atsimondrano and Renivohitra districts, between November and December of 2017. Data was coded thematically using inductive and deductive approaches, and found to align with a social ecological model. Key facilitators for successful implementation of the MHW, include (i) close collaboration with existing communal structures and (ii) creation of an incentive scheme to reward pregnant women to save. Key barriers to the application of the MHW in the study zone include (i) disruption of informal benefits for health care providers related to the current cash-based payment system, (ii) low mobile phone ownership, (iii) illiteracy among the target population, and (iv) failure of the MHW to overcome essential access barriers towards institutional health care services such as fear of unpredictable expenses. The MHW was perceived as a potential solution to reduce disparities in access to maternal health care. To ensure success of the MHW, direct demand-side and provider-side financial incentives merit consideration

Arctic Navigation: Stakes, Benefits and Limits of the Polaris System

Ensuring safe navigation is paramount for the economic development of the Arctic. Aware of this strategic issue, the International Maritime Organization (IMO), supported by the Arctic coastal states, adopted the International Code for Ships Operating in Polar Waters (Polar Code) with a set of navigation tools including the well-known Polar Operational Limit Assessment Risk Indexing System (POLARIS). Designed for assessing operational capabilities for ships operating in ice, POLARIS is useful for various stakeholders such as the International Association of Classification Society (IACS) organizations and underwriters. Other important beneficiaries are shipowners and their crew. Even though POLARIS deals with topical issues, so far, this system has not been subjected to extensive studies of its capabilities and limitations. The aim of this analysis in hand is to assess the stakes, benefits and limits of POLARIS for Arctic navigation with a managerial approach and through the lens of risk assessment. Results show that POLARIS integrates various parameters to assess risk of navigation in ice, and that POLARIS can provide relevant managerial solutions to shipowners. Nevertheless, certain limitations remain; in particular, human factors such as the lack of crew experience or the issue of non-compliance are not taken into consideration. Finally, it is important to highlight the fact that POLARIS is not a mandatory requiremen