Southeastern Tunisia Research Articles

Heavy metal transport and fate in soil-plant system: study case of industrial cement vicinity, Tunisia

During the last decades, Southeastern Tunisia has suffered from an industrial expansion leading to a serious pollution problem. In this work, heavy metal contamination near Gabes cement plant (Southeastern Tunisia) was assessed in the soils and statistically compared with a control site located 12 km away. Soil samples were collected from 5 to 15 cm below the surface layer. Concentrations of Cr, Mn, Co, Ni, Cu, Zn, Cd, Pb, and Fe and chemical parameters (conductivity, pH, CaCO3, OM) were measured. The variance analysis exhibited a significant difference (p < 0.05) in metal content between the two sites reflecting the cement plant contamination effect on the surrounding area. Eleven plant species widely distributed in the study area were collected together with the soil in which they were rooted, to assess their phytoextraction potential. Principal component analysis (PCA) was applied to understand the complex connection between soil, plants, and heavy metal contents. Lygeum spartum with respective total bioaccumulation factor (MBF = 1.48 ˃ 1 and Echiochilon fruticosum with a total translocation factor (MTF = 7.06) ˃ 1 were revealed as pertinent candidates for phytoremediation applications.

‘The Wrestlers’: A Roman mosaic from North Africa

In 2018 the Nicholson Museum, The University of Sydney, acquired a small Roman mosaic known as ‘The Wrestlers’ (NM 2018.135). The mosaic is of North African origin and is almost certainly the product of a local Tunisian workshop during the 3rd century, a period of intense urbanisation and wealthy local patronage in the Roman provinces. The mosaic depicts two athletes in the final stages of a pankratic competition and is framed by a distinctive red and black border, parallels for which are found in mosaics from Gightis near modern Boughrara in southeastern Tunisia. This paper analyses the mosaic within the context of decorative mosaic art and places it chronologically and stylistically within the broader scope of the mosaic industry in Africa Proconsularis.

Drivers of nest survival rate in a southern Tunisian population of Laughing Doves (Spilopelia senegalensis)

BackgroundInvestigating the ecological factors and processes shaping nest survival is of great importance for assessing the breeding success of bird populations and understanding their spatio-temporal dynamics. Here, this question is addressed for the Laughing Dove (Spilopelia senegalensis), an expanding Afro-tropical bird in the Tunisian oasis habitat.MethodsThis study took place in Kettana oasis, in south-eastern Tunisia. Natural Laughing Dove nests were searched for and monitored by means of regular visits, from the discovery date until the end of the breeding attempt (i.e. fledging or failure). Data were then used to investigate the relevance of laying date, nest age (days after clutch initiation), nest height and vegetation structure in the close nest tree environment as predictors of daily nest survival rate, using logistic-exposure models that accounted for heterogeneity in monitoring period among the studied nests. Models including different combinations of covariates were ranked according to their AICc scores, and the model-averaging technique was used for the assessment of the effects of covariates on daily nest survival rate.ResultsVegetation structure in the close nest tree environment and nest age provided important predictors of daily nest survival rate, whereas neither nest height nor laying date showed significant effects. Daily nest survival rate was negatively associated with the presence of date palm trees in the close nest tree environment, but it was positively related to nest age. Daily nest survival rate was higher during the post-hatching stage than during the pre-hatching stage.ConclusionsNests placed on fruit trees close to clumps of palm trees suffered higher predation risks compared to those placed on fruit trees situated far from palm trees. This is probably because palm tree clumps provided refuges for nest predators, notably the Black Rat (Rattus rattus) which has been reported to be the main nest predator in the oasis habitat. The predatory activity of this rodent seemed more directed against eggs than nestlings, which may explain the observed increase in daily survival rate with nest age.

Nesting Parameters of the Little Egret (Egretta garzetta) in Boughrara Lagoon, Southeastern Tunisia

Investigating the breeding ecology of waterbirds in the Mediterranean is essential for understanding their population dynamics and for conservation purposes. Here, the reproductive parameters of the Little Egret (Egretta garzetta) were investigated in Boughrara Lagoon, a poorly known breeding area in southeastern Tunisia. In total, 152 nests were monitored April-July 2014 from egg-laying to hatching. The nesting period extended from late April to late June, showing three distinct peaks. All nests were constructed < 2 m from the ground in nitre shrubs (Nitraria retusa). Clutch size ranged from 2 to 5 eggs, with a modal clutch of 4 eggs. Average egg volume (± SE) was 25.11 ± 0.08 cm3, which is within the range of known values for the species studied. Using the Mayfield method, hatching rate was estimated at 71%. Our results showed that clutch size and hatching success decreased as the breeding season progressed. This seasonal decrease in breeding performance is in agreement with the general trend in waterbirds and could be explained by the poorer quality of late breeders compared to early ones, or alternatively to the deterioration of environmental conditions late in the breeding season.

Use of the magnetic, geochemical, and sedimentary records in establishing paleoclimate change in the environment of Sebkha: Case of the Sebkha Mhabeul in southeastern Tunisia

In this study, we explored the evidence of late Holocene climate changes in southern Tunisia, examining extreme events of flood and sandstorm sedimentary succession records, in Sebkha Mhabeul. A sediment-derived climatic proxy was inferred from a 93.5-cm-deep core (Mh1), whose dating by tephrochronology has already been achieved in previous works. Multiple geochemical, sedimentological, magnetic susceptibility, and quartz grain microtexture proxies were used to determine the shifts in regional climatic conditions. The Sebkha core captured sensitive changes in the precipitation/evaporation (P/E) balance by adjustments in salinity, and is especially valuable for reconstructing variability over centennial timescales. The Sebkha Mhabeul area showed higher salinity during the Roman Warm Period (RWP: 2100–1400 cal yr BP), the Medieval Warm Period (MWP: 1000–600 cal yr BP) and the present era, and generally lower salinity during the Dark Ages (DA: 1400-1000 cal yr BP) and the Little Ice Age (LIA: 600-200 cal yr BP).In southeastern Tunisia, the hydrological behavior was sometimes consistent with the flood activities in the eastern Mediterranean, and sometimes contemporaneous with the flood pulsations of the western Mediterranean.

Allometry, condition factor and growth of the swimming blue crab Portunus segnis in the Gulf of Gabes, Southeastern Tunisia (Central Mediterranean)

The blue swimming crab Portunus segnis (Forskål, 1775) is one of the earliest Lessepsian invaders of the Mediterranean Sea, and is recorded since decades in various areas of the Mediterranean. Its presence in the southeastern Tunisian coasts (Gulf of Gabes) is, however, very recent. Allometry, condition factor and growth of P. segnis were studied along the Gulf of Gabes coasts. Sampling was performed by artisanal fishing gears as well as trawl net during a one-year period (October 2015 to September 2016) as processed 4971 crabs were collected. The crab carapace width (CW) ranged from 45 to 168 mm for males and 50 to 159 mm for females. The crab carapace length (CL) was 22.02-89.20 mm and 38.70-85.28 mm, respectively for males and females. The carapace width-carapace length, carapace width- front, carapace width-carapace height and carapace width-weight relationships were studied in separate sexes of crab. The covariance analysis indicates a significant difference between the two sexes with respect to the carapace width-carapace length and the carapace width-weight relationships. The condition factor ranged between 0.0042 and 0.0118 with a mean of 0.0078. The condition factor decreased with increasing crab size. The Von Bertalanffy growth parameters CW∞, K and t0 were estimated on the basis of Length-frequency modal progression analysis methods. The mean values of L∞ (mm), K (year-1) and t0 would be, respectively, 206.48 mm, 1.34 and -0.130 for males; 183.89 mm, 1.42 and -0.127 for females and, 190.60 mm, 1.02 and -0.177 for combined sexes.

On a longirostrine crocodylomorph (Thalattosuchia) from the Middle Jurassic of Tunisia

The geographic origins and distributional patterns of Gondwanan teleosauroids during the Jurassic have been fiercely debated over many years. Unlike the rich thalattosuchian fossil record from Laurasia, teleosauroids described from Gondwanan ecosystems are relatively scarce. Most of the known occurrences consist of isolated and fragmentary bones collected in Madagascar, Morocco, Tunisia, India, and Ethiopia. Nevertheless, these specimens, although fragmentary, have provided substantial information for assessing the evolutionary scenarios of multiple teleosauroid lineages and have shown that certain teleosauroid taxa were widespread rather than endemic to Western Europe. Here, a partial skeleton of a teleosauroid crocodylomorph is described. It was found in the late Middle Jurassic (Callovian) deposits of southeastern Tunisia by a team of French and Tunisian paleontologists; however, it has not been thoroughly studied at both macro- and microscopic scale until now. The new specimen is composed of an incomplete symphyseal portion of a lower jaw in addition to isolated teeth, osteoderms (both dorsal and ventral), thoracic and caudal vertebrae, and several thoracic ribs. The specimen has several morphological characters that are reminiscent of longirostrine teleosauroids. Due to the total absence of other cranial bones, as well as the pectoral and pelvic girdles, the specimen is not diagnostic to the generic level. However, these new remains represent the youngest ascertained occurrence of a definitive non-machimosaurin teleosauroid in Africa, provide additional insights into the geographic distribution of Thalattosuchia, and raise once again the question whether the origins of this clade were Gondwanan or Laurasian.

Monitoring of heavy metal contamination in soils and terrestrial isopods sampled from the industrialized areas of Sfax (southeastern Tunisia)

To evaluate the influence of soil contamination on the distribution of terrestrial isopods, species richness, relative abundance, and diversity, various indices were studied in 20 sampling sites from five industrial areas located in Sfax (SE Tunisia). The following hypotheses were tested: (1) is isopod diversity affected by soil properties? (2) What are the environmental factors that influence the isopod distribution? A total of 445 individuals were sampled and eight species of terrestrial isopods were identified. Porcellionides pruinosus was the most abundant species (38%); however, the highest specific richness per area was equal to four species. To evaluate the impact of metal contamination on isopod distribution, cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), and iron (Fe) concentrations were measured in soils and terrestrial isopods. Moreover, multivariate analyses revealed a negative correlation between heavy metal concentrations and ecological parameters suggesting an impact of the contamination degree on biodiversity. In addition, to characterize the heavy metal accumulation in isopods, the bioaccumulation factor (BAF) was determined and revealed that Cu and Zn were the most accumulated elements. Results showed that for all species, the order of the BAF values is as follows: Cu ≫ Zn ≫ Cd > Pb > Fe. On the contrary, all species seemed to be deconcentrators of Fe and Cd, with some exceptions.

Natural radioactivity and radiation hazard assessment of industrial wastes from the coastal phosphate treatment plants of Gabes (Tunisia, Southern Mediterranean Sea)

This work is a first contribution to the knowledge of natural radionuclides (226Ra, 238U, 40K, and 232Th) activities in phosphate rock (NORM), phosphogypsum, and phosphogypsum foam (TENORM) from the coastal fertilizer plants of Gabes (Southeastern Tunisia) and the assessment of their radiation hazards on human health and the surrounding environment. In the three studied materials, activities were found to be in the range of 35.4 (40K)–375.1 (226Ra), 10.0 (40K)–220.2 (226Ra), and 79.2 (232Th)–1168.6 Bq kg−1 (226Ra), respectively. Considering the studied radionuclides and materials, the corresponding decreasing activity orders were found to be 226Ra > 238U > 40K > 232Th and PGF > PR > PG, respectively. All human health hazard indices exceeded the worldwide recommended safety limits, which show that the workers in Gabes phosphate fertilizer plants as well as the neighboring human community may potentially be exposed to significant radiation, which may cause several diseases and malformations. It is therefore recommended to avoid and/or reduce the potential fertilizer industry radioactive impact in the area.

Effect of traditional check dams (jessour) on soil and olive trees water status in Tunisia

In the arid regions of south eastern Tunisia, the land use is predominated by olive trees cropping, where two main cultivation strategies can be found: using of water harvesting techniques to overcome the scarcity and variability of rainfall (in the Matmata mountains) and dryland farming (in the Jeffara plain). In these arid areas, soil moisture is the main limiting factor for crop growth and it should be monitored to benchmark different management options. Different conventional methods are available for point soil moisture monitoring, but the increased availability of remotely sensed data offers major opportunities for spatial analyses. The aim of this paper is to perform a comparative study on the soil water status for rainfed olive tree growing in three major landscape areas: in the mountains with traditional water harvesting check dams (called jessour), in the piedmont on floodwater harvesting (called tabias), and in the plain with full dryland farming conditions. Time series of Normalized Difference Infrared Index (NDII), derived from Landsat 7 satellite, were retrieved from the novel Google Earth Engine platform. NDII values were related to measured soil water content, which was taken at non-regular time intervals between 2009 and 2017. The analysis of NDII data, indicating the water content of the vegetation, shows that jessour can adequately ensure water supply for olive trees. Increased soil moisture conditions in the jessour areas are visible both in the dry and the humid seasons, indicating the effectiveness of this traditional water harvesting system. Moreover, our results show that Landsat 7 NDII values are correlated with the root-zone soil moisture in the monitoring sites (r2 ranging from 0.62 to 0.67), allowing the use of NDII to estimate soil water contents in our study area.

GIS-based MCDM – AHP modeling for flood susceptibility mapping of arid areas, southeastern Tunisia

Floods are considered as a major natural disaster due to their devastating effects that lead to socio-economic losses. The present study is an attempt to prepare a flood hazard susceptibility map of the Gabes region using ‘multi-criteria decision making – analytical hierarchy process’ model in geographic information system environment. Eight factors have been used in the flood modeling: elevation, land use/land cover, lithology, rainfall intensity, drainage density, distance from the drainage network, slope, and groundwater depth. The impact of each factor contributing in the flood risk was examined by weights using analytical hierarchy process method. The results obtained shows that the most prominent flood occurrence factor is the elevation (22.5%), around 15% of the total area is flooded and the flood hazard index is equal 6.30. The validation of results by a susceptibility zones histogram showed that 74.51% of the observed flood areas are mainly concentrated in a moderate to very high susceptibility zone.

Assessing the impact of climate change on rainwater harvesting in the Oum Zessar watershed in Southeastern Tunisia

Climate change is believed to have a large impact on water resources system both globally and regionally. It has become a major global issue, especially in developing countries because these are most affected by its impacts. Rainwater harvesting techniques offer an alternative source of water and represent specific adaptive strategies to cope with water scarcity within future climate change. Studying the impact of climate change on rainwater harvesting techniques, however, is difficult, because the general circulation models (GCMs) which are widely used to simulate scenarios of future climate change operate on a coarse scale. We estimated the impact of climate change on water availability at the watershed level by downscaling precipitation and temperature from the GCMs using a statistical downscaling model. A water harvesting model then assessed the performance of the rainwater harvesting techniques for the Oum Zessar watershed in southeastern Tunisia under current climatic conditions and scenarios of future climate change. Annual temperature tended to increase and precipitation tended to decrease. These changes of climatic variables were used in the water harvesting model to simulate future water availability. Changing the directions of water flow between sub-catchments in combination with changing the spillway heights strongly affected the performance of rainwater harvesting under the scenarios of future climate, resulting in a sufficient water supply for 92% of all sub-catchments, compared to 72% without these changes.

Groundwater depth monitoring and short-term prediction: applied to El Hamma aquifer system, southeastern Tunisia

In arid and semi-arid areas, such as Tunisia, groundwater depth assessment and monitoring is an important task for groundwater resources sustainable management. The objective of this work is to assess and forecast groundwater depth (GWDs) at short-term, under different impact factors, using stochastic time series (STS) and artificial neural network (ANN). Each model was conceptualized and implemented. Groundwater depth, rainfall, pumping rate and temperature over the period 30 years extending from 1986 to 2016 were used. Root mean squared error, bias, R2, AIC, and BIC were used as sensitivity model performance criteria. Models were implemented, trained, and tested over an observation period and forecasting groundwater depth at short-term over a period 2017–2030. Results show that groundwater abstraction rates increase around 0.46 Mm3/year, whereas a groundwater depth is in continuously drawdown with a rate of 0.3 m/year which requires a monitoring network for sustainable management of water resources. The results are promising and indicate an outstanding suitability of stochastic time series and ANN models for groundwater depth assessment and predictions at short time. The predicted results at short-term will help to draw attention of local authority for clear groundwater sustainable management policy for studied area.

Variability of the grain-sized fractions during the last three millennia within the sedimentary fillings of the saline system of Mhabeul: the Holocene cyclostratigraphy

Cyclostratigraphy is the study of cyclicity potentially recorded in sedimentary series. It is a specific method of stratigraphy studying the succession of different geological layers, based on results of climatology, astronomy, and mathematical techniques. Cyclostratigraphic signal, showing distinct orders of sedimentary cyclicities, is the result of variations in a climatic variable. Indeed, the Milankovitch theory, corresponding to the ancient cyclostratigraphy, is related to geographical locations and orbital factors, though the Holocene cyclostratigraphy is related to the solar activity and other oceanographic and astronomical factors. This study aims to infer the climatic signal within the sedimentary filling of sebkha Mhabeul, relying on the study of the grain-sized distribution, specifically the variability of the silty and sandy fractions. Previous granulometric study of the clay pan of Mhabeul (Essefi et al., J Basic Appl Res Int 15(2–4):140–152, 2015a) showed the importance of coarse fractions to highlight changes related to the sedimentary dynamics. Indeed, the percentages of different sandy and silty fractions contribute to the understanding of climatic conditions and the depositional environment. This work is meant to study the climatic cyclicity along a 100.5-cm core (Mh 1) from the saline system of Mhabeul, located in southeastern Tunisia through the grain-sized fractions. Based on the age model of Marquer et al. (Quat Res 70:240–250, 2008), the core covers the last three millennia (≈ 2600 yr. BP). A high-resolution sampling of 3 mm was carried out (335 samples). In terms of analyses, different fractions were recuperated based on five sieves (50, 63, 100, 250, and 500 μm). Based on the spectral analysis, we found out cycles of ≈ 2000, 1700, 1500, 1300, 700–800, 630, 533, 433–383, and 122 years. The 1700 yr. cycle is related to the oceanic activity. Also, the 1500-year and 700–800 yr. cycles are possibly related to the oceanic thermohaline circulation. About 1500 years can have a link with a NAO-like circulation. The 2000-yr. cycle is related to the solar activity and the monsoonal regime. About 1300 years and 630 yr. cycles have a link with the North Atlantic fluctuations. About 500 yr. cycles are may be related to the solar activity. About 433–383 years and 122 yr. cycles are possibly linked to other atmospheric and oceanographic forcings.

Investigation of paleoclimate signatures in Sfax deep groundwater (Southeastern Tunisia) using environmental isotopes and noble gases

To investigate paleoclimate conditions and mean annual ground temperatures at the time of infiltration, concentrations of dissolved atmospheric noble gases, 18O, 2H and 14C were studied in Sfax deep groundwater in southeastern of Tunisia. Carbon-14 corrected ages are up to 40 Ka BP suggesting that most of this water infiltrated during Late Pleistocene. Noble gas temperatures (NGTs) clearly show the presence of water that infiltrated under much cooler conditions than at present. According to the NGT's, the mean annual temperature in this mid latitude coastal site during the last glacial maximum (LGM) was 5.5 ± 1.0 °C colder than during the Holocene. This transition of Holocene –Pleistocene is well marked by a depletion of oxygen-18 isotope composition by 1.5‰ when compared to the modern rain water signature. Furthermore, the amount of excess air, which is closely linked to the magnitude of groundwater table fluctuations, provides further information on drought and wet period alternations during Late Pleistocene in Northern Africa.

Geochemical and statistical studies of Mio-Pliocene aquifer's mineralization in Jerba Island, South-eastern Tunisia

Management of water resources is a major concern for arid and semi-arid regions mainly because of the high groundwater salinization which impacts water quality. Here, Hydrochemical data of major and minor ions such as (sodium (Na+), Calcium (Ca2+), Magnesium (Mg2+), potassium (K+), chloride (Cl−), bicarbonate (HCO3−) and sulfate (SO42−) were used to study the Mio-Pliocene (MP) aquifer of Jerba Island, southeastern Tunisia, whose groundwater resources are characterized by a high mineralization. Bromide (Br−), iron (Fe) and Hydrogen sulfide (H2S) measurements as well as statistical data were used to identify the main processes involved in the mineralization of this aquifer. The major hydrochemical facies in Jerba confined aquifer is NaClSO4. Multivariate statistics analysis was used to visualize similarities between variables, investigate the origin of anomaly in groundwater mineralization and determine the hypotheses that would be developed in the geochemical study. Rock-water interaction and dissolution/precipitation of halite, feldspar, gypsum and carbonate are responsible for the chemical constituents of groundwater. The iron concentrations were between 0 and 1.6 mg/l. These concentration values may be due to the leaching of a sand-salty sandstones unit, rich in red clay, where the deep aquifer is housed. The H2S map shows that the highest concentration of this gas is in the central part of the Island which may be due to the presence of faults systems and a petroleum well (Robbana).

EAU ET CHANGEMENT CLIMATIQUE : QUELLES STRATÉGIES D’ADAPTATION POUR LA GESTION DE L’EAU D’IRRIGATION DANS LE SUD-EST TUNISIEN

The objective of this study was to identify the different irrigators’ strategies and to analyze the economic profitability of irrigated production systems in relation to adaptations to the scarcity of groundwater resources in a context of climate change in the South east of Tunisian. Based on surveys of 190 irrigated farms, this research shows that eighty-five percent (85%) of respondents clearly perceive climate change in southeastern Tunisia. These changes result in a decrease and an increasing irregularity of the rains, a disruption of the winter season, a greater frequency of pockets of drought and the decrease of the piezometric level of the water tables. In response to these changes, irrigators have adopted adaptation strategies, the most common of which are: offensive strategy or “chasing”, defensive strategy and contractive strategy. These strategies include various adaptation measures such as annual cleaning and deepening of wells, the use of water saving, the change of the cropping system and the reduction of irrigated area. These readjustments for most of the measures adopted by the irrigators have an impact on the elements of their operating account. In addition, offensive and defensive strategies appear to be the most economically profitable types of adaptation at the 1% level. Knowledge of different adaptation strategies and their economic returns enables adaptation options to be identified that are both realistic in terms of implementation and ambitious in terms of their objectives, and help develop priorities for adaptation of water resources for irrigation.

Assessment of groundwater quality of El Ouara aquifer (southeastern Tunisia), geochemical and isotopic approaches

Water scarcity is a major problem all over the world due to changes in precipitation patterns and intensity. Water quality is also so far affected. Despite the fact that water covers about 70% of the Earth’s surface, safe and clean drinking water is not available only to 1 in 9 people worldwide. And more than one third of Africa’s population lacks access to safe drinking water. Therefore, experts must target this concern and analyze the different complications related to the precious natural resource in order to save it from wastage. As a matter of fact, Tunisia is not an exception. It is struggling from the same water shortages. From here emerges the goal of this present study which is to determine the main factors and the geochemical processes that control water chemistry of the Mio-Plio-Quaternary (MPQ) aquifer for El Ouara plain, located in southeastern of Tunisia. And in order to monitor the water quality and assess the main physicochemical processes in this aquifer, a total of 30 samples were collected in Mio-Plio-Quaternary aquifer from wells located in Tataouine and Medenine regions and analyzed for various physical and chemical parameters, such as electrical conductivity, pH, dissolved solids (TDS), Na+, Mg2+, K+, Ca2+, Cl−, HCO3−, SO42−, NO3−, and Br−. The major and minor elements were analyzed by the liquid chromatography at the Laboratory of Water Geochemical Analysis at the Higher Institute of Water Sciences and Techniques of Gabes. Stable isotopes of δ18O and δ2H were measured by isotopic water liquid using laser absorption spectrometry and were expressed in δ‰ with respect to the Vienna Standard Mean Ocean Water (VSMOW). The hydrochemical data from a total of 30 groundwater samples indicate that the groundwater is characterized by the dominance of Na-Cl and Ca-Mg-SO4 water types. The plotting of all samples in Gibbs diagram illustrated that the groundwater chemistry is controlled by rock-water interaction and evaporation processes. Nitrate concentrations are significantly higher than WHO guideline drinking water values and are probably linked to the overfertilization, septic system, uncontrolled sewage, and animal waste. Isotope data reveal enriched groundwater in δ2H and δ18O suggesting an evaporation effect during recharge processes and depleted groundwater recharged during paleoclimate periods. This difference attests to the heterogeneity of recharge modes and probably longer residence time in the MPQ aquifer.

Drought distribution using the standardized precipitation index: case of Gabes Basin, South Tunisia

The current research examines the temporal and spatial distribution of drought in Gabes Basin (South-Eastern Tunisia), observed over the last four decades. Monthly data of precipitation, registered in nine synoptic stations spread over the watershed for the period extending from 1977 to 2015, were used to determine the standardized precipitation index to characterize drought. The SPIs displayed results, as computed at 3, 6, 12, 24, 48, and 72 months, helped define the periods of rainfall excess and deficit, corresponding to wet and dry periods, respectively. The relevant results proved to highlight a significant variability in the SPI-associated values. On the short-term scale, the reached results proved to display a frequent fluctuation exceeding the standards, while the long-term scale relating results appeared to indicate that the dry and wet periods turned out to be rather pronounced. Furthermore, by the increasing of time scales, the extension of drought conditions will increase. On the medium and long terms, however, dry spells characterized with long periods become less frequent. Thus, the most remarkable periods in drought intensities, durations, and extensions were detected during the end of 1980 and the beginning of 2000 for different rainfall stations studied. The major drought sequence was detected to take place over the period extending from 2001 to 2005 relevant to the SPI-72 months, affecting the whole watershed. It was also found that drought occurrence in the region was mainly influenced by medium- and long-term climatic factors. Furthermore, the spatial map distribution of extreme drought events for the long term was developed displaying the variation of drought severity across the study basin.

Effects of temporal factors, nesting microhabitat and nest position on the survival of passerine nests in a Tunisian oasis habitat

Identifying the ecological factors shaping bird nest survival is essential for understanding bird population dynamics, as well as for conservation purposes. Using data obtained by monitoring natural bird nests in one oasis in south-eastern Tunisia, we fitted logistic exposure models to investigate the effects of nesting microhabitat, nest position and temporal parameters on nest survival rates. Nest age was the most important predictor of daily nest survival rate for the five focal species. However, contrary to many previous studies, daily nest survival rate was positively related to nest age. This finding could be explained by the fact that the main nest predators in Tunisian oases are rodents that are more likely to consume eggs rather than chicks and therefore their impact on bird nests is assumed to be higher during incubation than after hatching. Nesting microhabitat variables and nest position as well as date of nest initiation and year did not significantly affect bird nest survival in the studied oasis. Further studies on the ecology and behaviour of nest predators are needed to more accurately identify the determinants of bird nest survival in the oasis habitat.