Low Water Level Period Research Articles

Fluctuating water levels control water chemistry and metabolism of a charophyte‐dominated pond

Summary To investigate seasonal variability and importance of environmental drivers of ecosystem metabolism in a shallow pond characterised by low and fluctuating water depth, clear water and shortage of nutrients, we measured primary production and respiration during May–September and examined their relationships to environmental parameters (light, temperature and pH). Using a combination of free water measurements of O2, pH, temperature and conductivity, in situ mesocosm and laboratory bottle experiments, we documented extreme daily variations in environmental variables (e.g. 0–700 mmol O2 m−3, pH 7.5–9.5, 18–32 °C) and high and variable areal rates of gross primary production (GPP, 30–316 mmol O2 m−2 day−1) and community respiration (R, 26–318 mmol O2 m−2 day−1). These rates of benthic charophytes under oligotrophic conditions are comparable to those obtained by pelagic phytoplankton communities under highly eutrophic conditions. By using sediment resources, benthic charophytes can achieve high biomasses and high metabolic rates. Pond metabolism reflected the physiology of the dominant charophyte, with light‐saturated photosynthesis occurring during 55% of the light hours. Experiments and photosynthetic models showed inorganic carbon limitation of GPP at pHs above 9.5 during mid‐summer periods of low water levels, while R was strongly influenced by temperature. According to open water measurements of O2, the pond was net autotrophic (mean NEP = 12 ± 13 (SD) mmol O2 m−2 day−1) but net heterotrophic when based on dissolved inorganic carbon (DIC) dynamics (10 ± 29 mmol CO2 m−2 day−1), suggesting that the significant input of DIC in inflowing water from the surrounding limestone soils mimics elevated respiration.

Research on Port Construction Technique after Water Storage of the Three Gorges Project

With the Three Gorges reservoir built up, the water level rises sharply and the low construction water level in dry season does not exist. The relatively low water level is in draw-off period and building port faces long time of deep water level and precipitous fluctuation of water level in flood period. There are huge quantities under water. The construction period of low water level is short and the height of water level is up to 30 meters. Port construction is more difficult and complex at the Three Gorge reservoir region. This paper aims at these situations and puts forward the port constructing technique in deep water areas. It will provide guidance and reference in wharf construction.

Stone Age settlement and Holocene shore displacement in the Narva‐Luga Klint Bay area, eastern Gulf of Finland

Based on geological and archaeological proxies from NW Russia and NE Estonia and on GIS‐based modelling, shore displacement during the Stone Age in the Narva‐Luga Klint Bay area in the eastern Gulf of Finland was reconstructed. The reconstructed shore displacement curve displays three regressive phases in the Baltic Sea history, interrupted by the rapid Ancylus Lake and Litorina Sea transgressions c. 10.9–10.2 cal. ka BP and c. 8.5–7.3 cal. ka BP, respectively. During the Ancylus transgression the lake level rose 9 m at an average rate of about 13 mm per year, while during the Litorina transgression the sea level rose 8 m at an average rate of about 7 mm per year. The results show that the highest shoreline of Ancylus Lake at an altitude of 8–17 m a.s.l. was formed c. 10.2 cal. ka BP and that of the Litorina Sea at an altitude of 6–14 m a.s.l., c. 7.3 cal. ka BP. The oldest traces of human activity dated to 8.5–7.9 cal. ka BP are associated with the palaeo‐Narva River in the period of low water level in the Baltic basin at the beginning of the Litorina Sea transgression. The coastal settlement associated with the Litorina Sea lagoon, presently represented by 33 Stone Age sites, developed in the area c. 7.1 cal. ka BP and existed there for more than 2000 years. Transformation from the coastal settlement back to the river settlement indicates a change from a fishing‐and‐hunting economy to farming and animal husbandry c. 4.4 cal. ka BP, coinciding with the time of the overgrowing of the lagoon in the Narva‐Luga Klint Bay area.

Prospects for Minimizing the Potential Environmental Impacts of the Hydro-Agricultural Dam of M’Bahiakro (Côte d’Ivoire)

This study aims at characterizing the physical environment and suggesting solutions for a better management of the hydro-agricultural dam of M’Bahiakro which is being constructed over the N’Zi River and is the first inflatable dam in Cote d’Ivoire. In this survey, data related to hydrology, characteristics of the dam and the irrigated rice production area were obtained with the Water Resources Agency and the National Office of Rice Development of Cote d’Ivoire. Physicochemical parameters of the N’Zi River were collected seasonally at three monitoring stations. Results showed that the N’Zi River is characterized by a high water level period from April to November and a low water level period from November to April. The gap between the low flows and the high flows is important (about 206 m3/s on average). The annual average flow is 40 m3/s with a standard deviation of 32.52 m3/s and a variation coefficient of 0.88. The SAR average value (1.63) and the average conductivity (78.44 μS/cm) showed that waters of the N’Zi River are of high quality to be used for irrigation. Suspended sediment concentrations do not present significant difference along the river. But the seasonal variations are important; they are higher during the rainy seasons (45.8 mg/L on average) than in the dry seasons (17.7 mg/L on average). The annual solid flux of the N’Zi River is 41897 tons, i.e. 15810 m3 of sediments. The annual sediment flux is important and can lead to high depositions in the line-shaped reservoir of the dam and that calls for attention to control the silting up of the reservoir. Great efforts concerning interdisciplinary approaches, as well as extensive and intensive field work are needed in order to better manage the hydro-agricultural dam of M’Bahiakro.

The Riverbed Evolution and its Influence on Channel in Tunaozi Reach after Three Gorges Water Storage

Tunaozi reach is one of the three famous sediment depositing reach on the Sichuan section of Yangtze River. It’s on the fluctuation backwater area when the Three Gorges Project is operated at the level of 135 m. According to the measured data before and after impoundment, this paper analyzes and calculates the sediment of the reach, and discusses the variation of silting and scouring of the reach after impoundment. Thus, this paper will have a study on the reason that silting and scouring lead to channel condition change. The result as follow: after impoundment, the bank-up water level of the reach has been head up 2 m during the flood season, sediment deposition becomes heavier than before impoundment; in post-flood season, the water level is 139m in November, it has been head up 7 m, compared with low water level in natural, current slowly flow further, the silt lack of enough scour in flood season, it leads to cumulative deposition. Until December 2005, thalweg plane position move left 200 m after impoundment. The maximum silting height of the thalweg longitudinal section is 30 m. The prime channel has been basically silted flat, year. Since the Three Gorges reservoir began to store water for three years, in low water level periods, ship tank is out of shallow, some timely dredging measure should be taken and make sure the smooth channel.

Effects of water levels on distribution patterns of the Yangtze finless porpoises in Poyang and Dongting Lakes, China

Two large freshwater lakes in China (Poyang and Dongting Lakes) are crucial habitats of the Yangtze finless porpoises. The lakes are confronted with threatens from low water levels. For evaluating possible impacts of low water levels on the porpoises in the lakes, the distribution patterns of the animals in the lakes were monitored in different seasons by using a boat-towing A-tag array from 2009 through 2011. The survey routes were almost same among different seasons. The acoustical detection number (i.e. encounter number) of porpoise in every 3-km section was calculated by counting the bearing angle traces of the sonar sources recorded by the array. The numbers in the same section were compared between high and low water level periods. Results indicated that porpoises appeared to congregate in deep water areas in low water level periods, while they tended to disperse toward the near shore waters in high water level periods. The results suggest concentration of individuals during low water level period. The variations of distribution patterns in different water level periods remind us that protection efforts should be focused on different areas according to the changes of water levels in different seasons.

Reduction in the Water Level of Lake Victoria and Its Implications on Livelihoods in Rwanjaba Lakeshore Community, Uganda

Abstract This paper examines the livelihood challenges experienced in Rwanjaba Lakeshore Community during the period of low water level in Lake Victoria between 2004 and 2007 and identifies the livelihood coping strategies that were adopted to address them. A total of 55 households were randomly sampled and the data collection methods included household questionnaires and participant observations. The data were analyzed using the Statistical Package for Social Science (SPSS) and the results presented with the help of descriptive statistics. The livelihood challenges experienced during the low lake water level included fish shortage (34.5%), household food scarcity (23.6%), sex for fish (18.2%), family breakdown (12.7%), increased theft (7.2%) and accidents due to the exposed rocks in the lake (3.6%). The livelihood coping strategies adopted to redress the challenges included cainternatl labour (32.7%), maize roasting (23.6%), sand mining (18.2%), selling of snacks (12.7%), selling household property (9.1%) and resorting shop and market credits (3.6%). The paper proposes a number of recommendations for improving the livelihood of the community ranging from policy reforms to the diversification of activities.

Responses of phytoplankton diversity to physical disturbance under manual operation in a large reservoir, China

In aquatic ecosystems, physical disturbances have been suggested to be one of the main factors influencing phytoplankton structure and diversity. To elucidate whether large-scale artificial operation of a hydroelectric reservoir has potential impacts on phytoplankton diversity, the impact on phytoplankton biodiversity of physical disturbances under artificial operation from May 2007 to April 2008 in tributaries of the Three Gorges Reservoir (TGR), China, was analysed. Two disturbance parameters, i.e. the absolute incremental rates of discharge (Rd,i) and precipitation (Rp,i), were created in this study for evaluating physical disturbance intensities during low and high water level periods of the TGR. Results showed that river discharge seemed to be the main factor controlling the phytoplankton diversity in low water level periods (≤151 m), and that precipitation was a potential promoter of the physical disturbance. During the 156-m impoundment process, the species diversity clearly decreased due to the high dilution effect on the phytoplankton communities. At high water level periods (>151 m), the low levels of disturbance eventually allowed the phytoplankton community to approach competitive exclusion in late February 2008. Sharply declining diversity values appeared when the Dinophyta blooms occurred in late March and late April 2008 (Peridinium and Ceratium, respectively).

The Effect of Climate Change on Inland Waterway Transport

Generally, inland waterway transport (IWT) is characterised by a high degree of reliability and safety compared to other transport modes. Against the background of the climate change debate however, new concerns are starting to raise attention. IWT is expected to be more sensitive to climate change aspects than other transport modes, e.g. in terms of water level fluctuations and resulting effects on costs and reliability.The present paper specifically addresses the topic of adaptation to climate change, taking IWT as a case-study. The results figuring in the paper are based on the results of the EC funded ECCONET project, which is an interdisciplinary project combining the expertise gained from climatology, hydrology, transport-economics, ship building and inland waterway management. A quantitative approach is applied, using the results of existing climate ensembles, hydrological results from KLIWAS and the transport network models TRANSTOOLS and NODUS.The paper starts first with an overview of expected effects of climate change on the Rhine and Danube. Adaptation measures are evaluated in function of their cost-effectiveness, given the expected impact of climate change on the navigation conditions.The main concern for adaptation is coping with periods of low water levels, as these were empirically established as the most influential for the sector. We consider four focal points for adaptation: fleet- and transport related strategies, operational concepts, improvement of forecasting tools and adaptation of production procedures and storekeeping.

Geochemical appraisal of palaeovegetation and climate oscillation in the Late Miocene of Western Bulgaria

Palaeobotanical methods and geochemical techniques were used to assess plant contribution and palaeoenvironment for the Staniantsi Basin, Bulgaria. The aim was to connect palaeovegetation change and climate oscillation based on pollen and statistical analysis with organic geochemical proxies for a Late Miocene lacustrine to paludial sedimentary succession. Three samples from lignite/marl cycles were studied. The biomarker assemblage and bulk chemical data indicated that gymnosperms were not important in the palaeomire. The presence of des-A-triterpenoids, 17,21- seco-triterpenoids, hopanes, a high content of a D-ring monoaromatic hopane, and aromatized triterpenoids suggested that photochemical and microbial processes significantly contributed to the alteration of the organic matter (OM). A prolonged period of high water table and severe mechanical destruction promoted microbial activity prior to burial and enhanced decay. A geochemical appraisal of short term climate oscillation (ca. 21.7 kyr) was attempted within the limitations of the small number of samples studied. The cycles are expressed as lignite/marl–clay layers combined with cyclic changes in swamp vegetation related to cyclic changes in groundwater level and inundation of the basin. In periods of low water level (swamp phase) lignite accumulation took place. Preliminary results for selected samples suggest that the oscillation may be reflected in the content of friedelin vs. possible degradation products. The ratio of a chromatographic peak tentatively assigned as A-norfriedel-8-en-10-one to friedelin is proposed as a means of detecting short term environmental cycles, where values <1 represent the swamp phase and those >1 reflect periods of inundation. However, time-series analysis using densely sampled lignite–clay layer oscillations are needed to confirm the value of this biomarker ratio for environmental reconstruction.

Drivers of aquatic macrophyte community structure in a Neotropical riverine lake

We explored the hypothesis that flood events and connectivity interact with local factors (biotic and abiotic) to drive changes in aquatic vegetation in a typical backwater lake connected to the River Paraná, Brazil. Over three years, we conducted quarterly surveys to analyse macrophyte composition and abundance, and environmental variables. In total 34 macrophyte species were recorded, with strong dominance of Eichhornia azurea. During periods of low water level, the lake vegetation was primarily structured by distance from the river. Total community abundance and emergent species diversity increased from the outer to the inner lake, while the opposite occurred for submersed and floating species. These changes were strongly associated with gradients of depth, slope, water transparency, oxygen and phosphorus. Two summer flood periods had different effects upon plants depending on flood features (e.g. intensity, duration) and location. Flood-pulses tended to reset the community, both in terms of species abundance and richness, and disrupt competitive processes. Flood disturbances likely governed interactions among facilitation and competition processes. While recovering from the major flood disturbance, E. azurea invested strongly in stem horizontal growth, but less so in leaf production. In this situation the physical structure of E. azurea facilitated colonization by several other macrophyte species, resulting in substantial and rapid increase in species richness. Under a more stable hydrology E. azurea displaced less competitive species by forming dense stands. Connectivity and flood-pulses were the main factors responsible for sustaining high diversity of aquatic macrophytes in the lake, but these drivers interact, in both time and space, with local environmental and biotic drivers to structure the temporally and spatially shifting mosaic of lake vegetation. Our results show the fundamental importance of natural variability of hydrological connectivity and flood disturbances for biodiversity conservation in tropical riverine floodplains.

Contamination Sources of Bomuruella Reservoir at Nuwara Eliya

Bomuruella Reservoir in Nuwara Eliya is an important water source in the area which indirectly contributes to the drinking water supply of the downstream people. Many agricultural lands obtain water from this reservoir and consume its water for washing and cleaning purposes. This research was focused on identifying the contamination sources of Bomuruella reservoir and to investigate the suitability of the reservoir as a drinking water source.According to the water quality analysis, BOD5 and CODMn values of most sample points did not satisfy the specified standards of Central Environmental Authority, Sri Lanka. Municipal wastewater stream and the stream from the cultivated area recorded high BOD5 levels of 7.65 mg/l and 6.55 mg/l respectively in the period of low water level of the reservoir. The stream from the cultivated area reported a high CODMn value of 595.74 mg/l during March and the stream from Kandapola plantation recorded a CODMn value of 74.44 mg/l during May. This concludes that the reservoir was contaminated with significant loads of organic wastes. Furthermore, the effluent from the leachate treatment plant recorded higher conductivity, nitrate and CODMn values which indicated that the leachate treatment plant was malfunctioning.The main cause of pollution of the reservoir is the discharge of agricultural runoff, raw sewage and wastes which include domestic, industrial and hospital waste directly into the feeder streams. It can be concluded that if the reservoir is to be used as a source of drinking water stringent measures have to be taken to control effluents.

Spatial and Temporal Variability of Water Quality of an Urbanized River in Algeria: The Case of Soummam Wadi

Spatial and temporal variations of water quality were investigated at four sites of an urbanized river in Algeria during a period of low water level in the years 2002, 2003, and 2004. Physical-chemical parameters (temperature, pH, conductivity, dissolved oxygen, suspended matter, chemical oxygen demand [COD], and 5-day biochemical oxygen demand [BOD5]) were measured. The Soummam River showed a strong pollutant load, which was organic in origin and expressed by mean concentrations in suspended matter, COD and BOD5 exceeding 150, 100, and 50 mg/L, respectively. The spatial variation highlighted two areas--(1) the first one gathers the upstream and central sites of the river, and (2) the second one is found downstream. In the downstream area, the pollutant load is almost twice as high as in the first area and, the percent saturation of dissolved oxygen is relatively weak (< 55%). This load is the result of the significant volume of urban and industrial emissions in the river, the high temperature during low-water-level periods, and flood events, which occurred just before the period of low water level. The Soummam River was classified according to the criteria of appreciation of surface water and was found to be extremely polluted. This work is one of the first studies on the quality of rivers in Algeria. This research will be useful as a first step for future works in North Africa and will add to knowledge on the water quality in the Mediterranean Basin.

Estimation of nitrate removal by riparian wetlands and streams in agricultural catchments: effect of discharge and stream order

Summary1. Assessment of the role of landscape structures such as buffers is a necessary prerequisite for the sustainable management of water resources in an agricultural setting.2. We monitored nitrate concentrations during interstorm periods at the outlet of 16 subcatchments of different orders within a catchment of 378 km2. We characterised stream network, wetlands, agricultural practices and land cover and identified their relationships with nitrate fluxes and concentrations.3. Two main factors controlled annual nitrate fluxes: the agricultural nitrogen surplus and the nature of the system comprising the wetland zone and adjoining watercourses. In the latter case, nitrate fluxes were reduced in proportion to the surface area of the riparian wetland and the flowpath distance of fluxes in the stream network. At the scale of the order‐6 stream, 53% of annual nitrate flux during interstorm periods was removed during transfer via the wetland and the river, corresponding to 21.1 kg N ha−1 per year.4. The influence of the riparian wetland zone/watercourse system increased during periods of low water level, explaining up to 64% of nitrate concentration variation among locations within the river network, but only 9% during periods of high water level.5. The buffering role was stronger at higher stream orders, and the dependence on stream order was more apparent at low water level, when we observed mean nitrate concentrations in the order‐6 stream that were 47% lower than observed in order‐2 or order‐3 streams.

Effect of drying, salinity and temperature on seed germination of the submersed wetland monocot, Vallisneria australis

Periods of low water level ('drawdown') may kill mature submersed aquatic plants and their vegetative propagules. Re-establishment from a sediment-based seed bank may be limited by desiccation, high temperatures and increased salinity, environmental changes that may often accompany drawdown. Vallisneria australis (Hydrocharitaceae) is a common, submersed clonal wetland plant in southeastern Australia, which reportedly reproduces mainly by vegetative spread. Although vegetative growth in this species is inhibited by drying and salinity, it is not known how such conditions influence the germination of sediment-stored seed, and so whether re-colonisation from seeds can occur after drawdown. Hence, this study examined whether drying, high temperature or high salinity reduced the germination of V. australis seeds. Germination was slowed by drying, with significant germination still occurring 20-30 weeks after re-wetting. The final percentage germination of seeds that had been dried for 8, 16 or 32 weeks and then rewetted was approximately twice that of seeds that remained wet. Moreover, sediment-stored seeds germinated only after drying, suggesting that drawdown would promote germination of V. australis in the field. Final germination of wet-stored seeds was 44 % at 25 °C but only 7 % at 35 °C, indicating that germination may be inhibited over summer in southeastern Australian wetlands. Although percentage germination declined with increasing salinity, some seeds still germinated (∼10 %) at the highest salinity tested, 23 dS m-1. Variability in the time V. australis seeds take to germinate may represent a mechanism that increases the opportunities for regeneration in an unpredictable environment. The demonstrated tolerance of seeds to drying and salinity suggests that, even in salinised wetlands, V. australis may be able to recolonise from the sediment-based seed bank following the loss of mature plants after a drawdown, provided viable seeds are present.

Impact of Water Level Fluctuation on Water Quality and Trophic State of Lake Nasser and its Khors, Egypt.

he morophometric configuration of lakes or reservoirs plays an important role in their water quality variations. The morophometry of Lake Nasser is characterized by the presence of many dendritic side extensions known as side channels or Khors. The surface area, depth and shape of these Khors depend upon the water level upstream the Aswan High Dam (AHD). In the last decade, the water level upstream the Dam fluctuated from about 181m ASL during year 2001 to about 174 m ASL during year 2005.This Fluctuation of water level from year to year affects water quality status of the Lake and its Khors due to the change of their morophometric configuration. To study the effect of water level fluctuation, four main important Khors characterized by gentle slope and sandy bottom with different size were selected. These Khors are Kalabsha, El-Alaki, Toushka, and Sara at Km, 41, 91, 247, and 325 from AHD respectively. The main goal for the present study is to assess the quality of water in the main Khors of Lake Nasser and its main channel during periods of low and high water levels (years 2001 and 2005 respectively). This assessment explores the potential pollution hazards coming from these Khors to the whole Lake. To achieve this goal water quality data generated from the analysis of water samples collected from the Khors and main channel during high and low water levels were used to calculate the water quality and trophic state indices as well as determination of the limiting nutrient factor of the lake. The abundances of Phytoplankton were also considered. The results of the water quality index (WQI) calculations during this study showed that the drop in Lake water levels led to a decline in the water quality of the Lake and Khors from the order of good to medium. Also, the trophic state index (TSI) values revealed that the productivity of the Lake changed from mesotrophic during high water level to eutrophic during low water level. These results are consistent with high phytoplankton counts recorded during low water level period. The values of N/P ratios indicated that phosphorus controls the phytoplankton growth during high water level, while during low water level either phosphorus (P) or nitrogen (N) could be limiting phytoplankton growth. Based on the obtained results of the present study, it could be concluded that the drop in water level upstream the dam may have negative impact on the water Quality of the Khors. This impact may in turn influence the whole Lake due to water rebounce from the Khors to the main channel. Therefore, it is further concluded that khors could be considered as potential pollution sources during low water levels of the lake.

Impacts of environmental changes on the hydrology and sedimentary processes at the confluence of St. Lawrence tributaries: potential effects on fluvial ecosystems

This study examines the effects of changes in St. Lawrence water levels and in hydrological regimes of two tributaries of the St. Lawrence, the Richelieu and Saint-Francois Rivers, on the sedimentary dynamics of their confluence in an historical context and in response to projected climate changes. Analysis of historical data indicates that alteration to St. Lawrence mean water levels and spring flood characteristics (duration, timing, and magnitude) have already impacted flow and sediment dynamics at tributary confluences. The major progradation of more than 1.5 km of the sedimentary front of the Saint-Francois delta into the shallow water of the fluvial Lake Saint-Pierre between 1859 and 2001 is associated with the combined effect of water level reduction in the lake, as a consequence of dredging of the navigation channel, and discharge regulation. High tributary discharges during periods of low water levels in the St. Lawrence have also contributed to accelerated delta front progression. Increases in temperature and changes in the precipitation regime projected for the current century were used into the HSAMI model to obtain hydrological simulations for the tributaries. Results indicate that the greatest hydrological changes will be observed during the winter and spring seasons, a time that is critical for many ecosystems. The mean spring discharge is projected to decrease by 17% for the Richelieu and 40% for the Saint-Francois by the end of the century. During this season, the frequency of discharge higher than the sediment transport threshold will decrease by 63% for the Saint-Francois and by 17% for Richelieu when compared to the reference period. However, during winter, the frequency of these high discharges will be four times higher for both rivers. These changes are expected to occur simultaneously with a decrease of the St. Lawrence water levels, a situation that will have significant impacts on sedimentary processes. A hydro-sedimentological modeling approach based on SEDROUT was used to investigate the morphological response of the river beds to the projected changes on the hydrology of St. Lawrence tributaries and to three base level scenarios. Results show that the combined hydrology and base level effects will lead to an increase in sediment supply compared to the current state, and to the extension of accumulation zones. While the effects will vary among the tributaries according to their particular characteristics, the projected increase in sediment supply will modify the extent of freshwater wetlands at the mouth of the St. Lawrence tributaries with feedback effects on local flow and sediment distributions.

Modal-split effects of climate change: The effect of low water levels on the competitive position of inland waterway transport in the river Rhine area

Future climate change is expected to affect inland waterway transport in most main natural waterways in Europe. For the river Rhine it is expected that, in summer, more and longer periods with low water levels will occur. In periods of low water levels inland waterway vessels have to reduce their load factors and, as a result, transport prices per tonne will increase. One possible consequence of these higher transport prices is a deterioration of the competitive position of inland waterway transport compared with rail and road transport, and thus a change in modal split. We study this issue using a GIS-based software model called NODUS which provides a tool for the detailed analysis of freight transportation over extensive multimodal networks. We assess the effect of low water levels on the costs of transport operations for inland waterway transport in North West Europe under several climate scenarios. It turns out, that the effect on the modal split is limited. Under the most extreme climate scenario, inland waterway transport would lose about 5.4% of the quantity that is currently being transported annually in the part of the European inland waterway transport market considered. The very dry year of 2003 can be seen as an analogue for this scenario.

Adipocere withstands 1600 years of fluctuating groundwater levels in soil

An extraordinarily well-preserved skeleton of a child, interred in a stone sarcophagus in the Late-Roman era, was discovered in the city of Mainz (Germany) in 1998, covered with a puff pastry-like substance assumed to be adipocere. It is the first time that this substance, which is derived from fat under oxygen-deficient conditions and prevents corpses from decaying, has been discovered on corpses buried under conditions described in the present paper. The body was buried at groundwater level (2.9 m below surface) in a moist zone close to the Rhine that was affected by seasonally fluctuating groundwater levels. The fluctuating groundwater levels would appear to have had an effect on the degradation of the interred body. The discovery of the skeleton gave us an excellent opportunity to examine fatty acid material which had been subjected to prolonged fluctuating aerobic and anaerobic conditions in a moderate environment. The body's fatty acid composition and 13C abundance were determined and compared with modern adipocere values. Element analysis of the stone sarcophagus in which the child was buried provided information on the burial environment. Our findings indicate that fatty material must have been converted into adipocere under anaerobic conditions in periods of high water levels, leaving the material open to decay during periods of low water levels. The fact that the excavated body was still covered with adipocere 1600 years after the burial clearly shows the robustness of the material against decay.

Les enjeux agricoles et sociétaux de l'eau sur les monts Bamboutos (Cameroun)

For more than two decades, water on the mountains of western Cameroon has become an increasingly high stakes agricultural and societal resource. This situation is due to the development of speculative crops with high economic value by rural and neo-rural populations along with diversification aimed at responding to the reinforcement of inter- and intraseasonal climatic variation. In spite of the efforts of market gardeners and livestock grazers to adapt their production systems to water shortage, neighbourhood conflicts have multiplied between these consumers. It is especially in the dry season (from December to February), a period of low water level in rivers and worsened by specific dryness that the conflicts for the access and the use of water intensify. This situation appears paradoxical since this zone not only has enormous hydrological and hydric potential but equally has the most drained and watered slopes of the region with more than 2 000 mm of rainfall per year on the Bamboutos mountain slopes. These conflicts lead to the destruction by Fulani grazers of goods belonging to market gardeners. As a solution to these recurrent conflicts, the local authorities have developed ruling strategies according to the nature of the conflicts and the rights claimed.