Catherine Grimaldi

Mercury distribution in tropical soil profiles related to origin of mercury and soil processes

The aim of the study is to improve our understanding of the vertical and lateral variations in the mercury content [Hg] of tropical soils. In addition to the distance to anthropogenic sources of Hg, the most frequently evoked determining factor is the abundance of Hg-bearing phases. Soil processes (weathering, mass or water transfer) determine the abundance of carrier phases. We assume that soil processes also have a direct impact on the distribution of Hg and that the impact is different according to the lithogenic or atmospheric origin of this element. We compare two types of soil (oxisol and ultisol) in the French Guiana forest, at localities a few tens of metres apart and exhibiting very different Hg contents. We show that vertical profiles of [Hg] are strongly related to the variations of [Hg(atmospheric)], whereas [Hg(lithogenic)] varies little. The penetration of Hg(atmospheric) from the surface deposits is favoured down to a depth of 3 m in the oxisol and limited to the upper horizons of the ultisol because of contrasted hydraulic conductivity between the two soils. Hg is primarily of lithogenic origin in the alteritic horizons of the ultisol. The relative accumulation of Hg(lithogenic) during the progressive weathering of parental material is limited near the soil surface by the disequilibrium of secondary minerals. Remobilization of Hg(atmospheric) or Hg(lithogenic) stored in the soil is a function of the chemical or particulate erosion of Hg-bearing phases, particularly active in the upper horizons of the ultisol, where lateral flow occurs during rain events. The correlations observed between the iron or clay contents and [Hg] can be caused by the affinity of Hg for these carrier phases, but may also reflect the weathering and the transfer processes which affect together the fate of Hg and the mineralogical and chemical composition of the soil.

Identifying seasonal patterns of phosphorus storm dynamics with dynamic time warping

Phosphorus (P) transfer during storm events represents a significant part of annual P loads in streams and contributes to eutrophication in downstream water bodies. To improve understanding of P storm dynamics, automated or semiautomated methods are needed to extract meaningful information from ever-growing water quality measurement data sets. In this paper, seasonal patterns of P storm dynamics are identified in two contrasting watersheds (arable and grassland) through Dynamic Time Warping (DTW) combined with k-means clustering. DTW was used to align discharge time series of different lengths and with differences in phase, which allowed robust application of a k-means clustering algorithm on rescaled P time series. In the arable watershed, the main storm pattern identified from autumn to winter displayed distinct export dynamics for particulate and dissolved P, which suggests independent transport mechanisms for both P forms. Conversely, the main storm pattern identified in spring displayed synchronized export of particulate and dissolved P. In the grassland watershed, the occurrence of synchronized export of dissolved and particulate P forms was not related to the season, but rather to the amplitude of storm events. Differences between the seasonal distributions of the patterns identified for the two watersheds were interpreted in terms of P sources and transport pathways. The DTW-based clustering algorithm used in this study proved useful for identifying common patterns in water quality time series and for isolating unusual events. It will open new possibilities for interpreting the high-frequency and multiparameter water quality time series that are currently acquired worldwide.

Amazonian former gold mined soils as a source of methylmercury: Evidence from a small scale watershed in French Guiana

Total mercury (HgT) and monomethylmercury (MMHg) were investigated in a tropical head watershed (1 km(2)) of French Guiana. The watershed includes a pristine area on the hill slopes and a former gold mined flat in the bottomland. Concentrations of dissolved and particulate HgT and MMHg were measured in rain, throughfall, soil water and at three points along the stream. Samples were taken in-between and during 14 storm events at the beginning and middle of the 2005 and 2006 rainy seasons. Dissolved and particulate HgT concentrations in the stream slightly increased downstream, while dissolved and particulate MMHg concentrations were low at the pristine sub-watershed outlet (median = 0.006 ng L(-1) and 1.84 ng g(-1), respectively) and sharply increased at the gold mined flat outlet (median = 0.056 ng L(-1) and 6.80 ng g(-1), respectively). Oxisols, which are dominant in the pristine area act as a sink of HgT and MMHg from rain and throughfall inputs. Hydromorphic soils in the flat are strongly contaminated with Hg (including Hg(0) droplets) and their structure has been disturbed by former gold-mining processes, leading to multiple stagnant water areas where biogeochemical conditions are favorable for methylation. In the former gold mined flat high dissolved MMHg concentrations (up to 0.8 ng L(-1)) were measured in puddles or suboxic soil pore waters, whereas high dissolved HgT concentrations were found in lower Eh conditions. Iron-reducing bacteria were suggested as the main methylators since highest concentrations for dissolved MMHg were associated with high dissolved ferrous iron concentrations. The connection between saturated areas and stagnant waters with the hydrographic network during rain events leads to the export of dissolved MMHg and HgT in stream waters, especially at the beginning of the rainy season. As both legal and illegal gold-mining continues to expand in French Guiana, an increase in dissolved and particulate MMHg emissions in the hydrographic network is expected. This will enhance MMHg bio-amplification and present a threat to local populations, whose diet relies mainly on fish.

Contrasted dynamics of nitrate and chloride in groundwater submitted to the influence of a hedge

The groundwater close to a bottomland hedge presented strong vertical and lateral gradients of nitrate and chloride concentrations. The strong transpiration by trees in summer and the dissymmetry of the root development induced persistent high chloride level in depth upslope from the hedge. Nitrate concentration, on the other hand, decreased sharply in the same area, taken up by the vegetation or denitrified by the microorganisms, whose activity was enhanced at the bottom of the hedge.

Características químicas de um Gleissolo sob diferentes sistemas de uso, nas margens do rio Guamá, Belém, Pará

Foram estudados os efeitos do uso do solo sobre a fertilidade, em Gleissolo sob tres diferentes sistemas de manejo. As coletas foram feitas antes do periodo chuvoso nos seguintes sistemas de manejo: area cultivada com arroz (Oriza sativa L.) ha aproximadamente 40 anos, com algumas interrupcoes ao longo deste periodo, com o cultivo algumas vezes mecanizado e uso de aracao e gradagem; area sob pastagem de canarana erecta lisa (Echinochloa pyramidalis Hitch.), formada ha cerca de 20 anos sem uso de adubacoes ou calagens; e area sob vegetacao natural de floresta tipica das areas de varzea alta. As amostras de solo foram coletadas em dez pontos a partir de um transecto nas areas, em quatro profundidades 0-10, 10-20, 20-30 e 30-40 cm. Os resultados demonstraram que o solo em condicoes naturais, de modo geral, apresentou atributos quimicos que variaram de bons a muito bons, o que demonstra um grande potencial para o uso agricola. O cultivo agricola dos solos das varzeas do rio Guama provocou uma reducao da concentracao de P e de K. O sistema de uso com pastagem apresentou maior sustentabilidade da fertilidade do que o sistema sob cultivo com arroz, visto que, alem da melhoria das caracteristicas quimicas, a materia orgânica elevou-se, tambem, em relacao ao sistema natural.

Impact of gold mining on mercury contamination and soil degradation in Amazonian ecosystems of French Guiana

As early as the 16th century, major expeditions were searching for gold and other precious metals and ores in the ‘New World’ (Nriagu, 1994; Tandeter, 2006). Later, in the middle of the 19th century, gold rushes that started in California spread to South America, as well as Australia and South Africa (Nriagu, 1994; Ali, 2006). Their main goal was to extract alluvial gold, occurring as fine particles in sediments derived from soils and weathered rocks. Another more current strategy of artisanal mining groups is to extract eluvial gold concentrated in the soil as fine particles and nuggets, originating from the in situ weathering of rocks. The extent of such artisanal small-scale gold mining (ASGM) activities varies with the price of gold (Malm, 1998). According to the United Nations Industrial Development Organization, 10–15 million people worked on ASGM sites throughout the world in 2004 (Veiga and Baker, 2004) in more than 160 mainly developing countries (Telmer and Veiga, 2009). Unfortunately, there is little information about the size and type of ASGM operations (Telmer and Veiga, 2009) or the surface area of soil and sediment worked; thus, the exact spatial extent and magnitude of impacts are difficult to determine. Gold mining changes land use drastically, with a considerable impact on the entire ecosystem, including soil. First, extracting eluvial deposits requires removing vegetation and then using powerful water jets to strip off surface soil horizons and reach the gold-bearing layer (Fig. 9.1). Besides the large loss of topsoil, these practices affect the turbidity of watercourses (Fig. 9.1) and sometimes their drainage patterns (Telmer et al., 2006; Hammond et al., 2007) and thus have impacts far beyond the local site of operation. Second, fine gold particles in sediments and soils are recovered by amalgamating them with mercury (Hg) (Nriagu, 1994; Malm, 1998), which is subsequently burnt to evaporate the Hg. The amalgamation process releases 650–1350 t Hg into the global environment annually (mean annual release of 1000 t, of which 350 t are emitted to the atmosphere through burning of amalgam and 650 t are discharged into the hydrosphere as elemental and particulate Hg (Telmer and Veiga, 2009). Mercury contamination of aquatic trophic chains is the most alarming health risk for local populations, whose protein diet is largely provided by carnivorous fish and 9 Impact of Gold Mining on Mercury Contamination and Soil Degradation in Amazonian Ecosystems of French Guiana

The effect of the chemical composition of a ferrallitic soil on neutron probe calibration

In a ferrallitic soil in French Guiana, the neutron probe calibration appeared to be problematic: considerable variations in the neutron count rate were observed at very short range and with an almost constant volumetric water content. This local variability of the count rate was explained by the mineralogical heterogeneity of the schist weathering horizon where subverticaly oriented layers are especially rich in boron, element with large thermal neutron absorption cross section. Various calibration methods were carried out and their limits were pointed out. The field gravimetric calibration without taking into account the soil physical and chemical spatial variations appeared to be risky, even if different pedological horizons are considered separately. A calibration based on the neutron absorption Ca and diffusion Cd cross sections calculated from chemical analysis led to overestimates of the volumetric water content. This could be explained by the concentration of boron atoms in sandsize tourmaline crystals which reduces their neutron absorption properties. The direct measurement of thermal neutron absorption and diffusion cross sections on soil samples in a graphite pile seems to be the best calibration procedure, but it has to be repeated as often as the spatial variability required.

Using “agroforestry” in the title: serving potential readers better by increasing the chances of being found by search engines

Chances are that you are reading this article on a screen rather than in your library’s bound copy of the journal (the good old days). If so, you most likely found this article with an internet-based search engine such as the Web of Knowledge (ISI), Springer Link or Google Scholar. The way one searches for scientific and academic references has changed with the development of technology. Fewer people visit the library to browse individual journals. Even you wanted to do so, your library may have stopped subscribing to paper copies of your favorite journals. In other cases, some journals (e.g., Plant and Soil) now offer only an electronic version. Increasingly, libraries purchase electronic access to journal packages. Consequently, the journal of Agroforestry Systems should adapt to this practice to serve potential readers better. We used the Web of Knowledge to search for and analyse all papers published in Agroforestry Systems from 2003 to 2012 (Table 1). We discovered that many papers published in Agroforestry Systems cannot be found by searching for the word ‘‘agroforestry’’ in the title or topic in the Web of Knowledge. Of the 798 papers published by the journal during this period, surprisingly only 188 (24 %) included agroforestry in their titles. This is a pity, because readers who are interested in agroforestry and search only for agroforestry in the title may not see the remaining 76 % of the papers. In 2007, only 6 out of 61 papers published (10 %) used agroforestry in the title. From 2007 to 2012, the percentage increased from 10 to 30 %, which is a good sign that should be encouraged. Even when we search by topic (include title, abstract, keywords, keyword plus in Web of Knowledge), still 344 papers (43 % of published in Agroforestry Systems from 2003 to 2012) are invisible. Because all papers in Agroforestry Systems deal with agroforestry in some way, we have verified them during the reference research on this subject and have checked each issue for papers that interest us. But for those rely only on search engines to find papers dealing with agroforestry, future authors could make efforts to increase the chances of finding papers. Although the number of times a paper is cited is not always the best indicator of its quality and influence, it might partly indicate that the number of people who have read it. When searching by title, the average number of citations is 6.0 for papers without agroforestry in title, and 8.2 for those with it, a 35 % increase. When searching by topic, the average number of citations is 5.4 for papers without agroforestry as a topic, and 7.5 for papers with it, a 38 % increase. It is unlikely that this increase is just a coincidence. Adding agroforestry in the title or topic does increase H. Hao (&) C. Grimaldi INRA, UMR1069, Soil Agro and hydroSystem, 35000 Rennes, France e-mail: hongtao.hao@rennes.inra.fr