Central Coastal Plain Research Articles

Geographic variation in skull shape of the water rat Scapteromys tumidus (Cricetidae, Sigmodontinae): isolation-by-distance plus environmental and geographic barrier effects?

The geographic variation in skull size and shape of the swamp rat Scapteromys tumidus was examined in samples from eight geographic clusters in almost of its distribution in southern Brazil and Uruguay. For analysis we used two-dimensional geometric morphometric methods for dorsal, ventral and lateral views of the skull. The geometric descriptors showed no significant differences in skull size between geographic clusters, while differences in shape were highly significant. We found a significant and moderate correlation between geographic and morphological distances, corroborating the isolation-by-distance model. Samples from the Rio Grande do Sul central coastal plain were the most differentiated, segregating completely from all other samples in canonical variate analysis for the dorsal view. The most visible variable regions in skull were the zygomatic arch (mainly the squamosal root of zygomatic) and the lateral braincase borders. Once correlation between geographic and morphological distances were not strong, it is possible that other factors (environmental heterogeneity and/or geographic barriers) may are acting in S. tumidus skull differentiation.

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

Summary Surface water connectivity can influence the richness and composition of fish assemblages, particularly in harsh environments where colonisation factors and access to seasonal refugia are required for species persistence. Studies regarding influence of connectivity on Arctic fish distributions are limited and are rarely applied to whole assemblage patterns. To increase our understanding of how surface water connectivity and related hydrologic variables influence assemblage patterns, we investigated species richness and composition of Arctic lake fishes over a large region, 8500 km2, of the central Arctic Coastal Plain, Alaska. We collected fish presence/non‐detection data from 102 lakes and used a hierarchical multispecies occupancy framework to derive species richness and inform species composition patterns. Our mean estimate of regional richness was 12.3 (SD 0.5) species. Presence of a permanent channel connection was an overriding factor affecting species richness (mean 3.6, 95% CI 3.1–4.9), presumably driving lake colonisation potential. In lakes without a permanent channel connection, data suggest richness (mean 2.0, 95% CI 1.7–3.3) increased with the availability of in‐lake winter refugia and with the potential of ephemeral connections during spring floods. Fish species functional traits and environmental faunal filters contributed to patterns of richness and assemblage composition. Composition corresponded with richness in a coherent manner, where each successive level of richness contained several discrete assemblages that showed similar responses to the environment. Lakes with permanent channel connections contained both widespread and restricted species, while the species‐poor lakes that lacked a connection contained mainly widespread species. This work provides useful baseline information on the processes that drive the relations between patch connectivity and fish species richness and assemblage composition. The environmental processes that organise fish assemblages in Arctic lakes are likely to change in a warming climate.

A late Quaternary multiple paleovalley system from the Adriatic coastal plain (Biferno River, Southern Italy)

A buried paleovalley system, up to 2km wide and exceeding 50m in relief, made up of multiple cross-cutting depressions incised into the Lower Pleistocene bedrock, is reported from the central Adriatic coastal plain at the mouth of Biferno River. Through a multi-proxy approach that included geomorphological, stratigraphic, sedimentological and paleontological (benthic foraminifers, ostracods and molluscs) investigations, the facies architecture of distinct, superposed valley fills is reconstructed and their relative chronology established along a transverse profile with extremely high data density (average borehole spacing 75m). Regional tectonic uplift appears as the major controlling factor of initial (Middle Pleistocene) river down-cutting and paleovalley formation. In contrast, glacio-eustatic fluctuations drove fluvial-system response over the last 120ky, when valley incision was primarily induced by the last glacial base-level lowering and climatic forcing. A fragmented record of coastal and shallow-marine deposits is available for the lower paleovalley fill, which is penetrated by a limited borehole dataset. Multiple erosion phases probably related to the post-MIS 5e sea-level fall are reconstructed from the upper paleovalley fill, where a buried fluvial terrace succession is identified a few tens of meters below the ground surface. The flat surfaces of two buried fluvial terraces suggest longer-term, stepped relative sea-level fall, and are correlated with fluvial incisions that took place possibly at the MIS 5/4 transition and at the MIS 3/2 transition, respectively. A laterally extensive gravel body developed on the valley floor during the Last Glacial Maximum. During the ensuing latest Pleistocene–early Holocene sea-level rise the Biferno paleovalley was transformed into an estuary. Upstream from the maximum shoreline ingression, the vertical succession of well-drained floodplain, poorly-drained floodplain, and swamp deposits evidences increasing marine influence in the estuary, in response to continuing sea-level rise. The interfluves were drowned around 8cal.ky BP, when brackish conditions developed in the study area. Decreasing marine influence in the uppermost 15m of the paleovalley fill suggests the onset of the modern delta: when the rate of sea-level rise was overwhelmed by sediment supply, delta progradation took place.

Permafrost Carbon: What soil science has to say about its distribution and fate

Permafrost Carbon: What soil science has to say about its distribution and fate

A Late Iron IIA Destruction Layer at Tel Aphek in the Sharon Plain

The article deals with a late Iron IIA destruction layer at Tel Aphek in the Sharon Plain. The remains, which were uncovered during Moshe Kochavi and Pirhiya Beck's excavations, have important implications for the history of the central Coastal Plain. The study of the finds suggests that during the late Iron IIA, Aphek increased in size, and that the ceramic tradition of the town exhibited similarities to that of the Northern Kingdom. This may be explained against the background of Israelite expansion to the coast during the 9th century BCE. Detailed analysis of the pottery repertoire indicates that Aphek was destroyed during the final phase of the Iron IIA, presumably in the course of an Aramean military campaign to the south.

Fish faunal provinces of the conterminous United States of America reflect historical geography and familial composition

Although the conterminous USA has a long history of ichthyological exploration, the description of biogeographical provinces has been ad hoc. In this study we quantitatively determined fish faunal provinces and interpreted them in the context of the geological history of North America. We also evaluated influences of major river basin occupancy and contemporary environmental factors on provincial patterns. Our data set comprised 794 native fishes, which we used to generate a presence and absence matrix for U.S. Geological Survey (USGS) four-digit hydrologic units. Three nested data sets were analysed separately: primary freshwater families, continental freshwater families (including primary and secondary families) and all freshwater families (including primary, secondary and peripheral families). We used clustering analysis to delimit faunal breaks and one-way analysis of similarity (ANOSIM) to determine significance among clusters (i.e. provinces). We used an indicator-species analysis to identify species that contributed most to province delineations and a similarity-percentage (SIMPER) analysis to describe the relative influence of representatives from each category (i.e. primary, secondary, peripheral) on provincial boundaries. Lastly, we used a parsimony redundancy analysis to determine the roles of historical (i.e. major river basin) and contemporary environmental factors in shaping provinces. Analysis of the nested data sets revealed lessening provincial structure with inclusion of more families. There were 10 primary freshwater provinces, 9 continental freshwater provinces and 7 all freshwater provinces. Major basin occupancy, but not contemporary environmental factors, explained substantial variance in faunal similarities among provinces. However, provincial boundaries did not conform strictly to modern river basins, but reflected river-drainage connections of the Quaternary. Provinces represent broad-scale patterns of endemism and provide a starting point for future studies. Relative malleability of province boundaries in the continental interior highlights this region as biogeographically diverse and dynamic. Interior-core provinces of this region (Central Gulf Coastal Plains, Northern Interior) have not been recognized previously and warrant further study.

Archeometallurgical characterization of Late Roman- and Byzantine-period Samaritan magical objects and jewelry made of copper alloys

Characterization of eleven copper alloy artifacts, dated between the 4th and 6th (or early 7th) centuries AD, retrieved from archeological excavations of remains associated with Samaritan sites along the central Coastal Plain of Israel, was performed. The assemblage includes three inscribed polygonal finger rings, four finger rings with decorated bezel (of which one bears a legend in the Samaritan script), two inscribed amulet pendants, and two thin cylindrical foils (containers of phylacteries, designated for the safekeeping of a magical or religious text written on papyri or parchment). The aim of this research is to use archeometallurgical non-destructive and destructive methods in order to determine manufacturing processes of the objects, and if possible their production place, their origin of ore and their use.The results indicate that the three polygonal rings were prestige objects made of gunmetal and manufactured by lost-wax casting followed by heat-treatment probably at the same workshop. Among the four finger rings with decorated bezel, the two with incised motifs were made of gunmetal alloy, while the one with eye-shaped bezel was made of relatively pure leaded-copper, and the other ring, with the inscribed bezel, was made of brass. These rings were manufactured by using dissimilar techniques; the two with decorated bezel by casting and then shaped by hammering and annealing cycles; the eye-shaped bezel ring by casting with no further treatment; and the inscribed bezel ring made of brass by manufacturing two different parts, hoop and bezel, that were brazed together, and then hammered and annealed.Both amulet pendants were manufactured by lost-wax casting and given their shape and composition they were probably manufactured at two different workshops.Both cylindrical foils were made of leaded-copper that was first cast into an open mold, then hammered into a thin foil and folded at a later stage, probably at the same workshop.All the examined gunmetal and brass artifacts contained 4–20wt.% Zn, indicating that their alloys were originally manufactured by cementation, produced of recycled metal, probably due to economic considerations. The present study indicates the existence of a limited number of local metal workshops which specialized in the manufacture of copper alloy jewelries and related objects; some were apparently operated by Samaritans.

Statistical modeling to women self-help groups of Odisha based on socio-economic developmental parameters in aquaculture

Multiple linear regression analysis was performed to estimate the relative effect of nine independent variables, i.e., age of the women self-help groups (WSHGs), number of group members, monthly savings of the group, pond area, fish production, number of literate members, number of technical trained members, bank loan and profit on average financial contribution of a WSHG (the dependent variable), a primary factor for socioeconomic development of women. Socioeconomic data on 90 WSHGs were collected from 27 blocks of eight districts from four physiographic zones, namely Northern Plateau, Central River Basin, Eastern Hills and Coastal Plains of Odisha during 2008–2009. It is revealed from the study that in all the four physiographic zones of Odisha, bank loan and profit have significant positive effect on average financial contribution of a WSHG (p < 0.05). On the other hand, number of group members is a negative contributing factor (p < 0.05) which explains that with increase in members, amount of bank loan and profit is proportionately reduced per member. Three factors such as monthly group savings, pond area and number of literate members are significantly contributing to average financial contribution of a group in Coastal Plains (p < 0.05). As the WSHGs in Coastal Plains were more developed than the WSHGs in other three physiographic zones, the multiple linear regression model of Coastal Plains may be considered as a best fit model. The regression equation is expressed as $$\hat{Y}$$ = 1,746.876 − 125.763members + 1.295mogrsav + 313.730area + 449.373literate + 0.023loan (p < 0.05).

Rescuing degrading aquifers in the Central Coastal Plain of North Carolina (USA): Just process, effective groundwater management policy, and sustainable aquifers

AbstractStrategic management of degrading coastal aquifers in eastern North Carolina (USA) became imperative after a severe imbalance occurred between withdrawal and recharge rates. To ameliorate this growing problem, an aggressive water policy was developed through public input by creating the Central Coastal Plain Capacity Use Area (CCPCUA) to maintain beneficial use of groundwater resources. Insights from social psychology, and socio‐legal studies are used to evaluate how procedural justice and public participation played major roles to resolving groundwater resource management problems. A mixed methods approach uses archival data and interviews with various rule‐making participants to assess the process of stakeholder involvement that led to creation of the policy. In addition, data analysis techniques are utilized to evaluate the effects of the policy on aquifer health (through water levels) over a ∼10 year period. Results suggest that not only did a stakeholder group participate in a process that was deemed fair, understandable, and relatively easy to administer for users and regulators, but public participation resulted in an effective plan that ensures the long‐term sustainable use of groundwater. Declining groundwater withdrawals and recovering water levels suggest that the rule is achieving its intended goal of protecting the aquifers from depletion and degradation. This paper touches on global themes that are essential to water demand and consumption, water management techniques, and water resources protection.

Sedimentary architecture and depositional evolution of the Quaternary coastal plain of Maricá, Rio de Janeiro, Brazil

The coastal geomorphology of Marica (Rio de Janeiro state) is characterized by a large lagoon and by two sandy barriers that confine a series of small isolated chain-like lagoons. Data collected from ground-penetrating radar and boreholes from the central coastal plain of Marica provided information on the sedimentary architecture and evolution of this area in the Quaternary. Six lithological units were identified comprising three depositional sequences limited by erosional surfaces, related to barrier-lagoon systems that migrated onshore, offshore, and longshore, giving rise to a sedimentary deposit 25 m thick or more. The data reveal a retrograding barrier overlying a basal mud unit which rests in unconformity upon Precambrian basement, thus characterizing an important Pleistocene transgression. A second Pleistocene barrier of 45,000 cal years BP migrated over a lagoonal mud unit (48,000-45,000 cal years BP) reaching over the previous barrier. A progradational phase followed due to a fall of sea level. A long interval of erosion of the barrier created an unconformity that represents the Pleistocene-Holocene boundary. A beachrock in nearby Itaipuacu, 100 m offshore from the present-day beach, dated as 8,500 cal years BP marks the onset of Holocene sedimentation due to gradually rising sea level, which continued until at about 5,000 years ago. This promoted the retrogradation of the barrier-lagoon system. A brief episode of progradation is observed as a series of paleobeach scarps. Today's rising sea level is causing the retrogradation of the barrier.

Climatological onset date of summer monsoon in Vietnam

ABSTRACTIn this study, the climatological summer monsoon onset in Vietnam was investigated by using the 25‐year in situ observations and reanalysis gridded dataset recorded from 1979 to 2003. Results suggested that the onset date varies considerably among the sub‐regions. Rainfall criteria indicate that the earliest onset generally occurs in the northwestern mountainous area around April 25. That in the northern and southern plains is in mid‐May, along with the full establishment of monsoon circulation over the Indochina Peninsula. In the central coastal plain, however, the Foehn wind, an effect of the Asian summer monsoon, causes a dry summer rather than a rainy season. This peculiar characteristic differs substantially from the rainy season in the adjacent regions. Therefore, a new specific criterion for this region is proposed: The summer dry season onset date, which is subjectively indicated in late May, is defined as the appearance time of the dry, downslope Foehn wind.Monsoon onset in Vietnam and surrounding areas is preceded by the development of convective activity and circulation features over the equatorial Indian Ocean and the southern Bay of Bengal. It also coincides with the northward retreat of mid‐latitude westerlies and the eastward retreat of the easterly trade wind associated with the western Pacific sub‐tropical high. A relationship between the occurrence of the Meiyu front and the summer monsoon onset over the South China Sea (SCS) is identified. Particularly, cyclonic development concurrent with monsoon onset appears over the SCS and Taiwan area, and a large amount of moisture is observed to converge along the southern side of the front. Simultaneously, the northward extension of the tropical easterly jet (TEJ), which is driven by the reversed poleward temperature and pressure gradient as a consequence of warming over inland India relative to the surrounding ocean, also plays an important role in summer monsoon circulation.

Paleoambiente e Palinologia de um Nível de Sedimento de Cerca 40.000 Anos A.P. Retirado da Lagoa de Itaipu, Estado do Rio de Janeiro

The lake of Itaipu is located in the central coastal plain, northern to the city of Rio de Janeiro. It started during the late Pleistocene upon an elder swampy underground. During its aging into the Holocene period, the vegetation changed between the domains of forests, savannas and hydrophytes. A 160 cm long sediment core was obtained and a sample was selected at the basis of the core for pollen analysis, dated of 38,490 À 940 non-calibrated years B.P.. Pollen analysis identified 32 pollen types leading to characterize four types of vegetation: the rain forest vegetation, the forest pioneer vegetation, the herbaceous swamp vegetation and the field vegetation. Pollen grain frequency and concentration showed that at this time the area was covered with a mosaic of plant communities, that the lake was not yet installed, and that a humid environment provided the maintenance of high plant diversity.

Contrasting phylogeographic histories between broadly sympatric topminnows in the Fundulus notatus species complex

Sympatrically distributed closely related species provide opportunities for studying evolutionary patterns of diversification. Such studies must account for historical contingencies in interpreting contemporary patterns of variation. Topminnows in the Fundulus notatus species complex are distributed sympatrically across much of the southern and Midwestern United States. Throughout most of their ranges F. olivaceus is often found in headwater stream habitats, and F. notatus is more typically distributed along the margins of larger river habitats. However, in some drainages, ecological associations of the respective species are reversed, with F. notatus populations isolated in headwater streams and F. olivaceus in downstream river habitats. Phylogeographic analyses of AFLP marker and multi-locus sequence data detected historical isolation in F. notatus consistent with pre-Pleistocene drainage patterns. Four F. notatus clades corresponded to (i) the Western Gulf Slope, (ii) the southwestern Ouachita Highlands, (iii) the Mobile Basin, and (iv) central Coastal Plain and Mississippi River Basin. In contrast, a relative lack of range-wide geographic structure in F. olivaceus is consistent with recent range expansion over much of the same geographic area. The southwestern Ouachita Highlands and Mobile Basin F. notatus clades corresponded to regions where ecological associations between the two species are reversed, providing evidence of the independent evolution of variation in contemporary habitat associations. Fundulus olivaceus from several drainages demonstrated introgression of mitochondrial DNA from F. notatus, but none of the sites in this study included individuals with hybrid ancestry in their nuclear genome. Phylogenetic analyses that included only nuclear loci supported the reciprocal monophyly of F. notatus, F. olivaceus and a third narrowly endemic species, Fundulus euryzonus, and supported a sister relationship between F. olivaceus and F. euryzonus.

CONTRIBUTION TO THE KNOWLEDGE OF THE BIOLOGY OF THE BANDED NEWT (TRITURUS VITTATUS VITTATUS) IN RAINPOOLS IN ISRAEL

ABSTRACT The period of activity, population parameters and food habits of adult Triturus v. vittatus were studied in a small rainpool system, in the central coastal plain of Israel. During November-December adults occurred on land. Thereafter, until the end of February, they occurred mostly in water. Breeding took place in February. The newts disappeared from the area of the pools by the end of February. The period of activity in and around the pools was shorter by 2–4 months than that reported for a northern population. On land as well as in water the highest proportion of newts were found when the ambient midday temperature ranged from 17° to 21°C. The observed population comprised more males than females. Males were significantly longer than females. Adult T. v. vittatus feed on a wide range of terrestrial and aquatic invertebrates but may exhibit some degree of food selection.

Toposequence of sandy soils in the northern coastal plain of Israel: Polygenesis and complexity of pedogeomorphic development

Catenary relationships of surface soils in the vicinity of kibbutz Shomrat in the Galilee coastal plain of Israel were studied including optically stimulated luminescence (OSL). The research provides new insights into the local pedogeomorphic history and confirms that the study area is of different age than the central coastal plain of Israel. The soil toposequence is composed of polygenic red Hamra (Rhodoxeralf) on the hilltop, a calcareous Rhodoxeralf (Husmas) on the middle slope, both older than 250ka, and a complex pedosedimentary sequence in a lower position spanning Middle Pleistocene–Holocene OSL ages. The hilltop red Hamra is strongly reworked by soil burrowing animals, magnetically enhanced, and contains aged clay coatings and a few petrocalcic nodules. Micromorphology revealed a relict nature of cemented carbonate nodules and allowed us to establish a sequence of pedogenic episodes, e.g. rubification and clay illuviation that intermittently affected nodule growth and re-crystallization. All soils are dominated by interstratified illite–smectite, whose amount and expandability increase downhill. In the lowest topographic positions, soil development was compounded by additional fine-grained accumulation via eolian and slope processes which may have intensified during periods of geomorphic instability. Our data and interpretations suggest that to the north of Haifa Bay, coastal geomorphic surfaces are formed by late Mid-Pleistocene exhumed paleosol toposequences, which are sporadically overprinted by younger paleosols, and continue to function as presently active soils.

The roles of water vapour, rainfall and solar radiation in determining air temperature change measured at Bet Dagan, Israel between 1964 and 2010

Monthly mean values of climate at Bet Dagan in the central coastal plain of Israel, downwind of Tel Aviv, were analysed to yield seasonal and annual values of long- and short-wave irradiance which were then related to changes in air temperature measured between 1964 and 2010. Over half the large interannual variation and significant increase in atmospheric long-wave radiation, which averaged 0.7 W m−2 per decade, was associated with concurrent changes measured in specific humidity. The remaining changes were attributed to increases in concentrations of carbon dioxide and other anthropogenic radiatively active gases. Large decadal variations and a significant overall reduction in short-wave solar radiation were measured averaging 3.6 W m−2 per decade which were, in part, attributed to urban pollution. Changes in downwelling long- and short-wave irradiances together accounted for 58% of interannual variation in the mean annual temperature. Climate sensitivity to short-wave radiation forcing was very low compared with that of long-wave forcing resolving the paradox of the sharp rise in temperature accompanying negative all-wave radiative forcing (RF). Possible physical mechanisms explaining the decoupling between annual values of solar irradiance and air temperature are discussed. A significant, inverse correlation between temperature and the annual number of rain days was found, accounting for 21% of the interannual variation in air temperature unexplained by surface RF. During the last 45 years, changes in annual temperature at Bet Dagan, a near-coastal site with a strong urban influence situated in the semi-arid Mediterranean climate, were associated, in the following order of importance, with changes in water vapour, rainfall and solar radiation. Copyright © 2012 Royal Meteorological Society

Groundwater chemistry patterns in the phreatic aquifer of the central Belgian coastal plain

The Holocene geological evolution of the Belgian coastal plain is dominated by a transgression of the North Sea, silting up of the coastal plain and human intervention (impoldering). This has led to a typical pattern in groundwater quality which is discussed here for the central part of the coastal plain. Therefore, a database with available groundwater samples is composed. Water type according to the Stuyfzand classification is determined and different hydrosomes and their hydrochemical facies are identified. Based on this, the origin and evolution of the water types is explained using Piper plots and geochemical calculations with PHREEQC. Before the impoldering, salinising and freshening conditions alternated with a general salinisation of the aquifer after about 3400 BP. This results in a dominance of brackish and salt NaCl subtypes which are still found in the deeper part of the aquifer. The subsequent impoldering resulted in an major freshening of the aquifer leading to NaHCO3, MgHCO3 and CaHCO3 subtypes. Overall, mixing, cation exchange, carbonate mineral dissolution and oxidation of organic matter are identified as the major processes determining the general water quality. The close link between geological evolution, water quality and what is still observable today is illustrated with this example of the Belgian coastal plain.

Tell Qudadi and Tel Gerisah: Two Early Bronze III Sites on the Yarkon River

Tell Qudadi and Tel Gerisah are two multi-period sites located on the Yarkon River. Recent research has revealed that they were the only settlements along the central Coastal Plain that were inhabited during the Early Bronze Age III. Tell Qudadi and Tel Gerisah could have played important roles as an outpost and as a main inner anchorage site, respectively, in maritime activities between Old Kingdom Egypt and the North Levantine coast.

Predation of amphibians by carabid beetles of the genus Epomis found in the central coastal plain of Israel

The genus Epomis is represented in Israel by two species: Epomis dejeani and Epomis circumscriptus. In the central coastal plain these species are sympatric but do not occur in the same sites. The objective of this study was to record and describe trophic interactions between the adult beetles and amphibian species occurring in the central coastal plain of Israel. Day and night surveys at three sites, as well as controlled laboratory experiments were conducted for studying beetle-amphibian trophic interaction. In the field we recorded three cases of Epomis dejeani preying upon amphibian metamorphs and also found that Epomis adults share shelters with amphibians. Laboratory experiments supported the observations that both Epomis species can prey on amphibians. Predation of the three anuran species (Bufo viridis, Hyla savignyi and Rana bedriagae) and two urodele species (Triturus vittatus and Salamandra salamandra infraimmaculata) is described. Only Epomis dejeani consumed Triturus vittatus. Therefore, we conclude that the two species display a partial overlap in food habit.

Onset of a pandemic: characterizing the initial phase of the swine flu (H1N1) epidemic in Israel

BackgroundThe swine influenza H1N1 first identified in Mexico, spread rapidly across the globe and is considered the fastest moving pandemic in history. The early phase of an outbreak, in which data is relatively scarce, presents scientific challenges on key issues such as: scale, severity and immunity which are fundamental for establishing sound and rapid policy schemes. Our analysis of an Israeli dataset aims at understanding the spatio-temporal dynamics of H1N1 in its initial phase.MethodsWe constructed and analyzed a unique dataset from Israel on all confirmed cases (between April 26 to July 7, 2009), representing most swine flu cases in this period. We estimated and characterized fundamental epidemiological features of the pandemic in Israel (e.g. effective reproductive number, age-class distribution, at-risk social groups, infections between sexes, and spatial dynamics). Contact data collected during this stage was used to estimate the generation time distribution of the pandemic.ResultsWe found a low effective reproductive number (Re = 1.06), an age-class distribution of infected individuals (skewed towards ages 18-25), at-risk social groups (soldiers and ultra Orthodox Jews), and significant differences in infections between sexes (skewed towards males). In terms of spatial dynamics, the pandemic spread from the central coastal plain of Israel to other regions, with higher infection rates in more densely populated sub-districts with higher income households.ConclusionsAnalysis of high quality data holds much promise in reducing uncertainty regarding fundamental aspects of the initial phase of an outbreak (e.g. the effective reproductive number Re, age-class distribution, at-risk social groups). The formulation for determining the effective reproductive number Re used here has many advantages for studying the initial phase of the outbreak since it neither assumes exponential growth of infectives and is independent of the reporting rate. The finding of a low Re (close to unity threshold), combined with identification of social groups with high transmission rates would have enabled the containment of swine flu during the summer in Israel. Our unique use of contact data provided new insights into the differential dynamics of influenza in different ages and sexes, and should be promoted in future epidemiological studies. Thus our work highlights the importance of conducting a comprehensive study of the initial stage of a pandemic in real time.