A mid–late Holocene flood record from the alluvial reach of the Mahi River, Western India

Flooding of rivers in India is linked with the peak monsoons. Investigating the linkage between monsoonal patterns and flood history of various rivers is therefore of fundamental importance in the Indian context. In the present study, the slackwater deposits in the alluvial reaches of the Mahi river basin, western India have been documented. These occur in the ravines incised during the early Holocene on an alluvial surface comprising sediments of Late Pleistocene age. The slackwater deposits occur at elevations up to 20 m from the present river level and extend to about 500 m inland. The carbonate rich sediments forming the ravine cliffs have provided bank stability and the dissections in the ravines have helped in the accumulation of slackwater deposits due to backflooding of the floodwater from the main channel. Recent gullies have incised the sediments and exposed deposits related to major flood events. The best exposures of slackwater deposits have been observed at Dodka. The sediment succession of the slackwater deposits is dominated by bedsets and laminasets of silt and sand separated by colluvial sediments. Four events of flood deposition occurred during the mid to late Holocene. Two units of slackwater deposits, SWD 2 and 4 have been dated by IRSL at 4.6 ± 1 ka and 1.7 ± 0.5 ka. The stratigraphy of these deposits indicates that the first two slackwater units (SWD1 and SWD2) have resulted due to flooding in a regime of intense monsoon. The other two units, however, represent extreme high magnitude floods in a period of low average precipitation.     

Caesium-137 dating applied to slackwater flood deposits of the Llobregat River, NE Spain

During a palaeoflood study of the Llobregat River (NE Spain), analysis of ¹³⁷Cs was carried out on slackwater flood deposits to obtain an improved flood chronology for the most recent flood sediments. At the Monistrol study reach, ¹³⁷Cs was measured in flood deposits preserved in valley side rock alcoves, with a range of ¹³⁷Cs concentrations of 2.80–10.06 mBq/g measured. The ¹³⁷Cs was associated with sediment mobilised from the upstream catchment by erosion and transported to the alcoves during floods. The onset of measured caesium activity in the sedimentary profiles permitted the deposits to be divided between those from floods that occurred before the mid-1950s and those from events after this period. Combining the information derived from the slackwater flood stratigraphy, the minimum discharge estimates associated with the flood deposits, ¹³⁷Cs analysis and the instrumental peak discharge series, it was possible to identify the particular flood events responsible for the majority of the slackwater flood units. At Vilomara, however, ¹³⁷Cs activity was measured in palaeoflood deposits dated to the Late Bronze Age and located at an elevation not reached by the floodwaters of the largest modern events. The data from this site indicated that the ¹³⁷Cs was not associated with sediments transported by floods but was rainfall-derived, the rainwater reaching the deposits through fissures in the rock. To ensure the successful application of caesium dating to slackwater flood deposits preserved within rock alcoves, or caves, some general guidelines are proposed. The technique is best applied: (1) when there is a sedimentary profile of greater than 1 m depth; (2) when the profile is sampled away from zones affected by direct percolation or springwater entering the alcove; and (3) where there are various levels of contrasting textures within the profile.     

2000-year environmental history of a karstic lake in the Mediterranean Pre-Pyrenees: the Estanya lakes (Spain)

The sediment record of the Estanya lakes (Pre-Pyrenees, Spain) indicates that this region was intensely affected by land use during the Middle and Modern ages, which contrasts with the present-day poor socioeconomic development of the region. The correlation between sediment and biotic data and well-known historical events suggests a reliable history of environmental changes in this area during the last 2000 years. Changes in lake level were mainly controlled by climatic factors, whereas properties such as lithology, organic carbon, ostracods and pollen content are mainly associated with lake management and land use. Major sedimentological changes resulted from the use of the lake for hemp retting at the start of the XIVth century. Subsequent depopulation of the area in the XXth century led to the progressive recovery of the lacustrine ecosystem.     

Human impact in the Holocene fluvial and coastal evolution of the Marche region, Central Italy

Today, the coasts of the Marche region are represented by almost continuous rectilinea sand beaches except in the north, at the border with the Romagna region, and in the central part, around the Conero ridge, where there are active rock cliffs. The sandy coasts are protected almost everywhere by artificial barriers built up as a protection against the general tendency to retreat. Along some tracts, the coastal erosion started at the beginning of this century but became generalized after 1940–1950. This was mainly due, first, to the reduction in sediment supply, following the improvement in agricultural techniques after the Italian Unification, and, later, to the widespread extraction of gravels from the thalwegs related to the rapid increase in urban population in the 1950s. However, in the same period, along the rivers, there was a widespread creation of artificial levees to prevent lateral erosion or flooding and to extend areas suitable for agriculture. Following these practices, the lower-middle tracts of the rivers underwent a strong vertical downcutting which increased as a result of the creation of checkdams downvalley of many bridges which contributed to the store of the sediments in the upper part of the valleys. At present, most of the rivers have an irregular course and are deeply entrenched in the bedrock or inside their own sediments.Up to the beginning of the century, most of the lower tracts of the valleys were characterized by strong aggradation in a braidplain system. This aggradation started as early as the Middle Ages (1100 AD) but increased after the Renaissance as a consequence of a generalized deforestation of the Periadriatic Basin and the following severe soil erosion. In the mean time, the coast underwent a very fast progradation, in some places more than 500 m. Small deltas were created at the mouths of the rivers, and longshore bars and sandy beaches began to occupy the base of the active cliffs which previously extended between one river and another. However, in the mountain parts of the river basins, a meander course existed, and in many cases still exists, expecially where the human interventions were of limited extent.Before 1000–1100 AD, all the rivers had a meander pattern and, at the junction with the sea, entered lagoons and swamps in most cases protected by littoral barrier beaches. These conditions were established earlier than the third century BC and have been attributed to the first systematic land clearance and the following soil erosion during the Bronze and Iron Ages. At that time, the regional coastline became almost rectilinear but with many active cliffs between one river and another.Before being affected by a major human impact (earlier than 4000 years BP) the ‘natural’ coastal environment was represented by active rock cliffs which alternated with pocket beaches corresponding to a river mouth. In some rivers, embayments and beaches were located up to 4–5 km inland from the present-day position. After the Flandrian transgression the evidence presented reveals major changes that can be attributed to human impact.     

The effects of soil moisture variability on the vegetation pattern in Mediterranean abandoned fields (Southern Spain)

The demographic pressure decrease in Southern Spanish Mediterranean mountainous areas in the mid twentieth century led to the abandonment of agriculture and rupture in the geo-ecosystem balance which had existed until then. Since then, different phases of recovery have been put into action to return the landscape to its earlier natural condition according to climate and soil degradation state after the abandon. In Mediterranean climatic conditions (between subhumid and semi-arid regimes), degraded soil recovery has followed different tendencies rendering the landscape in heterogenic and complex one. This heterogeneity has manifested in the vegetation pattern of abandoned fields. In this paper, we analyze the state of three abandoned fields situated under different Mediterranean climatic conditions from the recovery point of view by means of monitoring the effects of spatial and temporal variability of soil moisture in the vegetation pattern over a period of two years sampling (Nov. 2002–Nov. 2004). The results showed that: i) more annual rainfall volume did not guarantee success in the biological recovery of the system due to the influence of other factors such as the degradation state of the soil post-abandonment or the steep slope gradient; ii) soil moisture variability tended to play a more important role in affecting vegetal cover in semi-arid conditions; and iii) in dry climatic conditions the system demonstrated greater signs of recovery (greater biodiversity).     

Effectiveness and geomorphological impacts of check dams for soil erosion control in a semiarid Mediterranean catchment: El Cárcavo (Murcia, Spain)

The construction of transverse structures (check dams) is a widely used method in Spanish Mediterranean areas to stabilise gullies and ephemeral streams, to reduce channel incision and to prevent sediment deposition downstream. The effectiveness of check dams and their effects on the morphology of ephemeral channels (ramblas) were investigated in a semiarid, highly degraded catchment. In the study area, 36 dams were surveyed, of which 29 were filled up with sediments, 2 had been destroyed and only 5 had still not completely filled with sediments. The streams above the dams held sediments, which resulted in a decrease in the longitudinal gradient. Field observations of changes in the cross-sectional shape of the stream channel, the composition of channel bed material, and bankfull stage measurements indicated that the dams cause erosion downstream. The amount of sediments stored by the dams was found to be higher than the amount of eroded material in the downstream reaches of the dam.     

Assessment of shoreline vegetation in relation to use by molting black brant Branta bernicla nigricans on the Alaska coastal plain

To evaluate the importance of large thaw lakes on the Alaska Coastal Plain for molting Pacific black brant Branta bernicla nigricans, distribution and life form of shoreline vegetation were assessed using several scales: satellite imagery, point-intercept transects, cover quadrats, and a parameter for water regime. Brant population and distribution estimates from aerial surveys were used to classify large lakes into high, moderate, and low use. Correlations between brant and abundance of their preferred feeding site — moss flats — were best demostrated by satellite imagery. Intercepts and cover ratings were not correlated, presumably because these techniques were less efficient at assessing area. General observations suggested that the presence of islands, large ice floes, and possibly other physical attributes of the habitat, influenced brant distribution. This area is unique because of low-lying, drained-lake basins that have ideal combinations of moss flats and large water areas where brant seek protection disturbance is vital to the success of this declining species because alternate habitats may not be available elsewhere on the Coastal Plain. in water or on ice floes. Protection of the area from     

Fluxes and storage of fine-grained sediment and associated contaminants in the Na Borges River (Mallorca,Spain)

Samples of suspended and fine channel bed sediment were used to examine the spatial and temporal variability in the amount of fine-grained sediment and associated contaminants temporarily stored in the Na Borges River (319 km²) in Mallorca and the relationship of such channel storage to the fluxes of fine sediment and associated contaminant through the system. This Mediterranean groundwater-dominated river drains a predominantly agricultural catchment, although urbanisation during the twentieth century has changed the catchment hydrology. A re-suspension technique was used to obtain estimates of channel storage at monthly intervals during the 2004–2005 hydrological year at eight locations along the main stem of the stream (i.e. 26 km). The estimates of fine sediment storage ranged between 0 and 13,000 g m^− 2, with a mean value of 2400 g m^− 2. Only Cu exceeded the critical threshold (36 μg g^− 1), established by existing guidelines for the contaminant content of fluvial sediment. The results demonstrated significant spatial and temporal variability, in response to the influence of urban point sources, agricultural practises, seasonal groundwater interactions and the first-flush effect. The amount of fine sediment entering storage during the study period was 515.2 t, representing the net increase in storage over the study period. As a result, the mean specific storage was 21 t km^− 1. Suspended-sediment load and temporary fine sediment storage are the two basic components of the channel sediment budget that interact to determine sediment transport through a channel system, and they can therefore be used to compute the total input of sediment and associated contaminants to the system. Accordingly, storage values were compared with estimates of suspended sediment load and associated contaminant load values at three measuring stations along the river. During the study period, storage in the main channel system represented 87% of the sediment input and 68% of the contaminant input, indicating that deposition was more important than transport. The low gradient of the main channel and the low return period (i.e. 0–2.5 years) of the flood events that occurred during the study period meant that remobilised bed sediment and associated contaminants were redeposited downstream rather than being flushed to the catchment outlet as suspended sediment. Furthermore, the river bed is dry during the summer months, allowing sealing and crusting processes to stabilise the sediment deposited during the wet season and thereby reduce its availability for remobilisation at the beginning of the next wet season. Together, these factors promote sediment deposition and storage, with the result that sediment progressively accumulate over several hydrological years until a major flood event (i.e. return period ≈ 5 years) evacuates the stored sediment.     

Prey depletion caused by overfishing and the decline of marine megafauna in eastern Ionian Sea coastal waters (central Mediterranean)

Surveys primarily aimed at determining dolphin encounter rates were conducted from small inflatable craft in eastern Ionian Sea coastal waters between 1997 and 2004. During 633 surveys totalling 21,276 km of effort, observations of cetaceans and other marine species spotted in a study area of 480 km² were systematically recorded. Common dolphin encounter rates declined 25-fold across the study period, steadily decreasing from 2.18 encounters/100 km in 1997 to 0.09 encounters/100 km in 2004. Encounter rates of tuna also declined significantly. Swordfish encounter rates dropped from 1.03 encounters/100 km in 1997 to 0-0.12 in 1998-2004. Encounter rates of bottlenose dolphins did not show significant trends. The decline of high-order marine predators feeding on epipelagic prey was consistent with the hypothesis of prey depletion, likely resulting from intensive exploitation of local fish stocks, particularly anchovies and sardines. The catholic feeding habits and opportunistic behaviour of bottlenose dolphins may allow them to withstand the effects of overfishing at their present low density.     

吉林西部全新世晚期土壤碳酸盐中碳稳定同位素记录的古气候信息

土壤碳酸盐中碳稳定同位素是记录古气候变化信息的重要载体。本文对吉林省西部大安市姜家甸草场土壤剖面中的δ13C值特征进行了详细分析,并在此基础上推得C3、C4植物生物量;结合野外观察到的剖面特征,作者认为全新世晚期以来,该地区气候曾经历过从干-热～湿-暖～干-热的演变过程。现今吉林西部的干旱化环境正是全新世晚期以来气候持续演化的结果。     

Optimum N concentration in winter wheat grown in the coastal plain region of Virginia

Abstract

Limited information is available on optimum N levels in winter wheat (Triticum aestivum L.), particularly at higher yield levels. Three experiments were conducted in the Coastal Plain region of Virginia where N was applied at rates of 0, 67, 90 and 112 kg/ha to Wheeler, Mc Nair 1003 and Coker 747 soft red winter wheat varieties. Yields ranged from 2.33 to 5.83 Mg/ha in the study. Nitrogen fertilization increased yield up to the 67 kg/ha rate and increased N concentration in the plant tissue up to 67 or 112 kg of N/ha, depending on variety. Optimum N concentration, i.e., N concentration at maximum (100%) yield for Wheeler, Mc Nair 1003 and Coker 747, over the three experiments, was 4.54%, 4.52% and 4.81%, respectively, for entire above‐ground plant samples collected at Feekes growth stage 4 and 4.72%, 4.73% and 4.44% for flag leaf samples collected at Feekes growth stage 10. A N sufficiency range of 4.00–5.00% is suggested for use for the plant parts sampled for both growth stages.     

Impact of mediaeval agriculture on the alluvium in the San River headwaters (Polish Eastern Carpathians)

An abrupt change in sedimentary processes occurs in the alluvium of the San River headwaters in the Bieszczady mountains, Polish Eastern Carpathians. Older gravels are overlain, with a sharp boundary, by an extensive cover of sand and silt, which is enriched in wood debris, partly burned, at the base. The spatial distribution of the fine-grained alluvium, the wood debris composition and radiocarbon ages are best explained by a relatively sudden onset of deforestation and cultivation of the valley bottom and slopes in the middle of the second millennium. This corresponds well with palynological, archaeological and historical data on the agricultural colonisation of the valley.     

Enhancing stocks of the exploited limpet Patella candei d’Orbigny via modifications in coastal engineering

It is widely recognised that microhabitats are important for a variety of marine organisms, yet this knowledge has rarely been applied in the construction of engineered structures as a means of enhancing biodiversity or populations of species at risk. Here we examined the influence of microhabitats on the distribution and survival of the exploited limpet Patella candei on natural shores before determining the effect of introducing such habitats to an artificial seawall. On natural shores individuals were associated with pits (a natural feature of volcanic rocky shores). Animals inhabiting pits showed reduced mortality and were smaller than those on open rock. Microhabitat utilisation was similar over the vertical range of distribution of P. candei. Following observation of natural patterns, we applied this knowledge by experimentally drilling pits at varying densities and sizes in a seawall that had been constructed with simple topographical complexity. Overall, the number of animals increased in areas with experimentally increased microhabitat area. There was evidence that this was the result of immigration (larger animals) but also of increased recruitment. This study demonstrates one cost-effective way of conciliating the need to protect our coastlines while promoting the conservation and stock enhancement of over-exploited species.     

黄河壶口至龙门段全新世古洪水滞流沉积物研究

通过野外考察,在黄河晋陕峡谷发现全新世古洪水滞流沉积物地层。对于采取的沉积物和黄土古土壤样品,进行磁化率、烧失量、碳酸钙和粒度成分的测试分析。综合野外观测和实验分析结果,确定它们是黄河悬移质泥沙在高水位滞流环境当中的沉积物。其主要成分是粉沙,次要成分为细沙,据此确定其质地属于细沙质粉沙。其磁化率略高于黄河河床相沙质沉积物,但是远低于全新世风成黄土和古土壤。其频率曲线为极正偏态,主峰高而且尖锐,表明分析性很好,粒度成分很集中。这是因为其在黄河洪水当中长距离搬运分选的结果。与泾河、洛河和漆水河比较,黄河晋陕峡谷全新世古洪水沉积物粒度成分偏粗。这表明黄河洪水搬运动力较强,且其悬移质泥沙是流域内黄土地区和风沙地区水土流失产物的混合物。这些特大洪水沉积层之间,被坡积角砾石或者石渣土层分隔开来,每一层记录了一个古洪水事件。     

The use of micromorphology in soil pollen analysis: The interpretation of the pollen content of slope deposits in Galicia, Spain

Humic horizons of soil profiles often contain pollen and spores. Comparison of the sequence of pollen associations of soil profiles with pollen zones of reference diagrams offers palyno-ecological information, relevant for reconstruction of landscape ecological development. In palynological studies of semiterrestrial and aquatic deposits, pollen is considered to be part of the sediment and anaerobic conditions in water-saturated deposits promote its conservation. This is not true for pollen in soils. Aerobic conditions in drained soils result in bio-oxidation of unprotected pollen grains. Interpretation of soil pollen associations requires knowledge of the processes of infiltration and conservation of pollen grains in the soil material. Micromorphology is an important technique to investigate these processes. This is demonstrated in a case study of polycyclic slope deposits in Galicia (Spain). The buried cambisols, in pleistocene solifluction deposits, contain post-sedimentary infiltrated pollen. The pollen associations reflect successive phases in soil ecological development. The holocene colluvial deposits contain syn-sedimentary incorporated pollen. The pollen associations reflect environmental conditions during the deposition of colluvial layers.     

Geographic differentiation of morphological traits and isozymes in the Mediterranean island endemic Anchusa crispa: implications for the conservation of a protected species

Understanding population differentiation and genetic diversity within population is critical to the development of conservation programmes for threatened species. The protected species, Anchusa crispa Viv. occurs on coastal sand dunes in three disjunct geographical groups of populations: two populations on the east coast of Corsica, several populations around a single estuary on the west coast of Corsica and at a number of sites in north-west Sardinia, where two different subspecies occur. In this study we quantify differentiation of reproductive traits and isozymes among regions and populations on Corsica and between subspecies on Sardinia. No isozyme variation was detected within any of the studied populations nor among populations from a given geographic region. Two loci showed geographic differentiation between regions on Corsica. On Sardinia, the two subspecies showed no isozyme differentiation, and, depending on the loci examined, are similar to one or other of the two regions on Corsica. Reproductive traits show significant differentiation between geographic regions on Corsica, but little variation among populations within a region. In populations on the west coast of Corsica, flowers are small and have a stigma situated at the same level as the apex of the anthers whereas on the east coast, flowers are larger and have the stigma below the anthers. On Sardinia, A. crispa subsp. crispa has a floral morphology similar to the Corsican plants, whereas subspecies maritima has larger flowers with the stigma positioned above the anthers (approach-herkogamy). Quantitative variation in floral morphology thus agrees with the separation of two taxonomic entities on Sardinia and geographic variation in reproductive traits and isozymes has important ramifications for the sampling of populations for conservation programmes.     

Spatial population structure of the Cabrera vole in Mediterranean farmland: The relative role of patch and matrix effects

There is mounting evidence that both patch networks and the intervening matrix influence species persistence in fragmented landscapes, though the relative importance of each of these factors in determining spatial population structure remains poorly understood. This study examined this issue using a three-year data set on the distribution of Cabrera voles (Microtus cabrerae) in Mediterranean farmland. The spatial pattern appeared consistent with a metapopulation structure, as voles occupied discrete tall herb patches scattered across the agricultural landscape, where local extinctions and colonizations induced temporal changes in occupancy patterns. Patch dynamics determined deviations from classical metapopulation assumptions, with over half the extinctions resulting from agricultural disturbance or vegetation succession, and recolonizations often occurring after the recovery of suitable habitat conditions sometime after disturbance. Occupancy in undisturbed patches was more stable, with vole occurrence in one year strongly reflecting that in the previous year. Overall, occupancy increased with both patch size and connectivity, but the unique contribution of patch variables to explain variation in vole occurrence was far smaller than that of matrix attributes. Voles occurred more often in patches surrounded by natural pastures, while prevalence declined with increasing cover by shrubland, pine plantations, improved pastures and grazed cropland. It is hypothesised that unfavourable land uses may increase the effective isolation of habitat patches through increased predation risk of dispersing voles. Conservation of the Cabrera vole in Mediterranean farmland should thus strive to maintain lightly grazed fields surrounding well-connected networks of suitable habitat patches.     

陕南汉江上游气温变化及其对农业生产的影响

以陕南汉江上游汉中、石泉、安康观测站1960-2010年的逐日、逐月平均气温资料为基础,采用线性趋势法、滑动平均法和Mann-Kendall非参数检验法,分析了该区气温的年际和季节变化趋势、突变特征,以及季节气温变化对农业的影响.结果表明,自1960年以来,陕南汉江上游年平均气温和年平均最低气温呈波动上升的变化趋势,递增速率分别为0.107℃/10a(P ＜0.01)、0.16℃/10a(P ＜0.01),而年平均最高气温呈不显著递增趋势,三者发生突变的时间分别为2001、2000和2001年;各季节的变化特征表现为冬季增温速率最高(P＜0.01),对年平均气温增加的贡献最大;夏季气温变幅较小,变化趋势不显著;春、秋季气温分别呈极显著、显著上升趋势,但日波动性较大;倒春寒天气发生时间推迟,发生频率、强度增大;秋封(冷害)发生频率虽然有所下降,但持续时间较长,强度较大,对该区的水稻、玉米、小麦等农作物生产造成严重影响.深入了解汉江上游气候变化规律及成因,对有效应对气候变化和保障粮食安全具有积极意义.