Holocene regional and local vegetation history and lake-level changes in the Torneträsk area, northern Sweden

A combination of pollen and macrofossil analyses from six lakes at altitudes between 370 and 999 m above sea level (a.s.l.) in the Torneträsk area reflect the Holocene vegetation history. The main field study area has been the Abisko valley at altitudes around 400 m a.s.l. The largest lake, Vuolep Njakajaure has annually laminated (varved) sediments. The chronology and sedimentation rates in the pollen-influx calculations are based on varve yrs in this lake and on radiocarbon dated terrestrial plant macrofossils in the other lakes. A strong increase of mountain birch (Betula pubescens ssp. tortuosa) during the early Holocene with a tree-line c. 300 m above the present, indicates that the summer temperature was c. 1.5 °C higher than today, assuming that the land uplift has been 100 m since then. Scattered stands of pine (Pinus sylvestris) may have been growing in the area immediately after the deglaciation but a forest consisting of pine and mountain birch expanded first at low elevations and reached the eastern parts of the Torneträsk area at c. 8300 cal BP and the western parts at c. 7600 cal BP. The highest pine-birch forest limit was not reached until 6300 cal BP (110 m above present pine limit). Warm and dry conditions during the pine forest maximum led to lowering of the water level documented in Lake Badsjön in the Abisko valley about 1-1.5 m lower than today. Pine and mountain birch were growing at the maximum altitude until c. 4500 cal BP. Assuming that land uplift has been in the range of 20-40 m since the mid-Holocene, this implies that the temperature was then c. 1.5-2 °C higher than today. Rising lake-levels and lowering limits of pine and mountain birch since c. 4500 cal BP indicate a more humid and cool climate during the late Holocene.     

Quantification of Holocene lake-level changes in Finnish Lapland using a cladocera – lake depth transfer model

During recent years, numerous studies dealing with Holocene lake level fluctuations have been conducted in Finnish Lapland. However, no quantification of lake level variations exists to date. Here, we applied a recently developed modern cladocera – lake depth transfer model to subfossil cladocerans analysed from three small and shallow (< 6 m) kettle-hole lakes in northwestern Finnish Lapland to provide estimates of the amplitudes of long-term lake-level changes in the region. The quantitative inferences were compared to pollen, charcoal and geochemical records from one of the study sites. The lake levels were inferred to be high during the early Holocene; they faced marked reduction up to 4–6 m in the mid-Holocene (≈7000–4000 cal yr BP), and rose again during the latter part of the Holocene. There is some indication of lowered lake levels around 1500 cal yr BP, but interpretation of such small-scale changes is hazardous due to large prediction errors in the initial cladoceran model. The overall pattern of the Holocene lake level variation generally followed the regional changes in climate humidity as reconstructed in previous studies by means of other sedimentary proxy indicators, such as pollen and oxygen isotopic compositions. We postulate that changes in winter precipitation may have had a greater influence on lake-levels than variations in summer precipitation or evaporation.     

Transmutation of ancient settlements and environmental changes between 6000?2000 aBP in the Chaohu Lake Basin, East China

Based on the temporal-spatial distribution features of ancient settlement sites from the middle and late Neolithic Age to the Han dynasty in the Chaohu Lake Basin of Anhui Province, East China, using the methods of GIS combined with the reconstructed paleoenvironment by the records of lake sediment since Holocene, the transmutation of ancient settlements with response to environmental changes in this area has been discussed. Studies show that the main feature of transmutation of ancient settlements from the middle and late Neolithic Age to the Han Dynasty was that the distribution of settlements in this area changed from high altitudes to low ones and kept approaching the Chaohu Lake with the passage of time. These could be the response to the climate change from warm-moist to a relatively warm-dry condition during the middle Holocene, leading to the lake level fluctuations. The large area of exposed land provided enough space for human activities. These indicate that the above changes in geomorphologic evolution and hydrology influenced by climate conditions affected the transmutation of ancient settlements greatly. The distribution pattern of settlement sites was that the number of sites in the west was more than in the east. This pattern may be related to the geomorphologic conditions such as frequent channel shifting of the Yangtze River as well as flood disasters during the Holocene optimum. Therefore, climate change was the inducement of the transmutation of ancient settlements in the Chaohu Lake Basin, which exerted great influence on the distribution, expansion and development of the ancient settlements.     

Transmutation of ancient settlements and environmental changes between 6000–2000 aBP in the Chaohu Lake Basin,East China

Based on the temporal-spatial distribution features of ancient settlement sites from the middle and late Neolithic Age to the Han dynasty in the Chaohu Lake Basin of Anhui Province, East China, using the methods of GIS combined with the reconstructed paleoenvironment by the records of lake sediment since Holocene, the transmutation of ancient settlements with response to environmental changes in this area has been discussed. Studies show that the main feature of transmutation of ancient settlements from the middle and late Neolithic Age to the Han Dynasty was that the distribution of settlements in this area changed from high altitudes to low ones and kept approaching the Chaohu Lake with the passage of time. These could be the response to the climate change from warm-moist to a relatively warm-dry condition during the middle Holocene, leading to the lake level fluctuations. The large area of exposed land provided enough space for human activities. These indicate that the above changes in geomorphologic evolution and hydrology influenced by climate conditions affected the transmutation of ancient settlements greatly. The distribution pattern of settlement sites was that the number of sites in the west was more than in the east. This pattern may be related to the geomorphologic conditions such as frequent channel shifting of the Yangtze River as well as flood disasters during the Holocene optimum. Therefore, climate change was the inducement of the transmutation of ancient settlements in the Chaohu Lake Basin, which exerted great influence on the distribution, expansion and development of the ancient settlements.     

Environmental changes in the Zirahuén Basin, Michoacán, Mexico, during the last 1000 years

Lago de Zirahuén (19° 26 N, 101° 44 W) lies within a montane basin in highland Michoacán, Mexico at 2075 m a.s.l. The lake basin has high recreational value and is promoted as a tourist attraction. Four short (<1 m), sediment–water interface cores were used to investigate Late Holocene environmental change. The cores span approximately the last 1000 years, based on ²¹⁰Pb dating, AMS ¹⁴C dating and tephrochronology. Cesium-137, Americium-241 and tephra layers from Volcan Paricutín (AD 1943–1952) and Volcan Jorullo (AD 1759–1774) provide independent age markers. Cores were analysed for diatoms, magnetic susceptibility and heavy metals (iron, lead, manganese, copper and zinc). Drier climate around 1000 years BP is tentatively inferred from the diatom assemblage and is concordant with other regional records. Increased soil erosion between ca. AD 1100 and AD 1550 may be associated with Pre-Hispanic settlement in the basin, but there is no archaeological evidence to support this. A period of catchment stability occurred during the early Colonial Period, ca. AD 1550–1750. The dramatic decline in the indigenous population following the Spanish Conquest in 1521 may have promoted vegetation recovery on the basin slopes. After the mid-18th century, a significant change in diatom species composition is observed along with an increase in soil erosion, as inferred from the magnetic susceptibility profile. Concentrations of copper and lead also increased. These changes are associated with the establishment of a copper smelting industry in the basin and increased Colonial agricultural development. Recently, tourist developments and commercial agriculture have impacted on the basin. The diatom flora has changed dramatically in the last 20 years, apparently in response to the onset of cultural eutrophication. The palaeoenvironmental evidence suggests that the lake is responding rapidly to land use intensification in the basin, which may have implications for future developments.     

Vegetation and sedimentation in the Lake Edward Basin, Uganda–Congo during the late Pleistocene and early Holocene

New palynological and sedimentological data obtained from the basal 3 m of core E96-2P from Lake Edward, Uganda–Congo record conditions wetter than present in the Edward basin from 11 000 to 6700 yr BP, in phase with other climate and vegetation records of northern hemispheric East Africa. Dominant pollen taxa include Celtis spp., Alchornea spp., Olea spp., and Moraceae indicating a moist semi-deciduous tropical forest. More xeric indicators such as Amaranthaceae and Asteraceae together with Poaceae comprise less than 5% of the pollen sum throughout this interval as compared with between 44 and 50% during a lake lowstand at 2000 cal yr BP and at the core top (near modern). The differences between these two assemblages suggest a 25 to 60% increase in annual precipitation during the early- to mid-Holocene as compared to modern (1500–2000 vs. 1200 mm/yr today). Early Holocene sediments in E96-2P are composed of laminated diatom oozes with moderately high total sulfur concentrations (2.8–4.7%) and no authigenic calcite, also indicative of conditions wetter than present. Between 9000 and 6700 yr BP, palynological and sedimentary proxies indicate sub-millennial-scale events related to changes in riverine discharge and runoff in the Edward basin. We attribute the variability in runoff, and hence precipitation, to Holocene variability in Indian or Atlantic Ocean SSTs or to shifts in the relative contribution of Indian and Atlantic moisture sources to the western Rift of equatorial Africa.     

Spatial precipitation and evapotranspiration in the typical steppe of Inner Mongolia,China – A model based approach using MODIS data

We present a simple method to derive spatial precipitation (P) and evapotranspiration (ET) for the typical steppe of the Xilin river catchment at 1 km and 8-day resolution during the main vegetation period (23 April to 28 August) of 2006. The hydrological model BROOK90 was parameterised from eddy covariance measurements. The daily model input data, precipitation, minimum (Ta_min) and maximum air temperature (Ta_max), were derived by manipulating MODIS leaf area index (LAI) and surface temperature data. P was estimated based on a linear regression of P measured at several sites against the mean gain of the MODIS LAI of surrounding 3 × 3 pixels areas (R² = 0.76). Ta_min and Ta_max were derived using a relationship between measured Ta_min and Ta_max and MODIS surface temperatures (R² = 0.92 and R² = 0.88, respectively). The mean precipitation was 145 mm; it varied between 52 mm in the north-western region and 239 mm in the eastern region. In spring, the modelled ET was low (<0.8 mm d⁻¹); evaporation dominated over transpiration and spatial differences were small. At the end of June, the mean ET reached its maximum (2 mm d⁻¹) and spatial differences were pronounced. From July on, transpiration dominated over declining evaporation, and spatial differences decreased in August.     

Coping with water scarcity in Kashafroud G-WADI Basin,Iran: climate change or growing demands?

This paper assesses the various factors contributing to climate change in the region of the Kashafroud G-WADI Basin in Iran; quantifies the local impacts of climate change, especially local water scarcity; and simulates and discusses several proposed methods to combat these impacts. Hydrologic and climatic data are statistically analyzed and VENSIM modeling is used for various simulations of water resources in the basin. Results show that the natural climate changes affecting Kashafroud Basin include increased temperature, less rainfall, more frequent droughts, and changes in rainfall patterns, all of which are local symptoms of climate change in recent years. However, the most important challenge in the basin is the overexploitation of surface and groundwater resources to meet the growing water demands, especially domestic needs. Changes in land use, reallocation of water uses, groundwater depletion, and degradation of the quality of surface waters have all contributed to significant changes in the environmental features of this basin, and are the main reason why water demands now exceed the renewal capacity of the basin. Proposed response measures include reallocation of resources among different uses, inter-basin water transfers, drawing water from six small dams on the Kashafroud River, reducing groundwater extraction, and replacing groundwater extraction for agriculture by reuse of urban wastewater. This study concludes that although changes in global climatic parameters have altered environmental features in the basin, local factors, such as water utilization beyond the renewable capacity of the basin, are more significant in worsening the impacts of climate change.     

Population development in rural areas of the United States in the 1980s: turnaround of trends or continuity?

"The article analyses the population growth in rural counties of the U.S.A. for 1970-80 and 1980-86. The growth rates are examined on different levels of aggregation (individual counties, subregions and regions) and in relation to several possible determinants of growth. The main objective of the study is to examine whether the growth patterns in the eighties support the hypothesis of a turnaround in the population development of rural areas.... The results reveal a diversity of growth patterns and significant regional differences. Rural counties within the daily urban system of a metropolitan area have significantly higher growth rates than peripheral rural counties. The results do not support the notion of a turnaround of long established trends. The trends in the eighties bear more resemblance to traditional growth patterns of rural areas." (SUMMARY IN ENG)     

δ~(18)O, δD and d-excess signatures of ground ice in permafrost in the Beiluhe Basin on the Qinghai-Tibet Plateau,China

In this paper, stable isotope(δ~(18)O, δD) investigations were completed in ground ice from a deep borehole in the Beiluhe Basin on northern Qinghai-Tibet Plateau to unravel the isotopic variations of ground ice and their possible source water. The δ~(18)O and δD of ground ice show distinctive characteristics compared with precipitation and surface water. The near-surface ground ice is highly enriched in heavier isotopes(δ~(18)O and δD), which were gradually depleted from top to bottom along the profile. It is suggestive of different origin and ice formation process. According to isotopic variations, the ice profile was divided into three sections: the near-surface ground ice at 2.5 m is frozen by the active-layer water which suffered evaporation. It is possible that ground ice between 3 and 4.2 m is recharged by the infiltration of snowmelt. From 5 to 6 m, the ground ice show complex origin and formation processes. Isotopic variations from 6 to 11.1 m and 20.55 m indicate different replenishment water. The calculated slope of freezing line(S=6.4) is larger than the experimental value(5.76), and is suggestive of complex origin and formation process of ground ice.     

The typology of the American metropolis: monocentricity,polycentricity, or generalized dispersion?

Although the spatial structure of employment in large US metropolitan regions is a well-researched topic, few studies focus on medium-sized and small US metropolitan regions. Consequently, there is no overall typology relating small-to-medium urban form to employment distribution. We address this gap by investigating the spatial structure of employment in 356 metropolitan regions. We conceptualize six typologies based on three categories that have overlapping properties: “monocentricity,” “polycentricity,” and “generalized dispersion.” The study has three main findings. First, the three types of urban form that we identify as “hybrid” outnumber the three “pure” types by almost four to one. Second, job dispersion is a dominant characteristic in almost 70% of all metropolitan statistical areas (MSAs) (including the hybrid types), and polycentricity (56.7% of MSAs) is somewhat more common than monocentricity. Third, there is a strong relationship between population size and density. The population of medium-sized metropolitan areas is generally more dispersed than that of small and large metropolitan areas. Polycentricy emerges mostly in large metropolitan regions, while monocentrity is found in both small and large metropolitan regions.     

Do swarms of migrating barchan dunes record paleoenvironmental changes? — A case study spanning the middle to late Holocene in the Pampa de Jaguay, southern Peru

Swarms of barchan dunes are common in arid environments. Unlike immobile or slowly moving dunes whose stratigraphy can be used to reconstruct paleoenvironmental changes, the high migration rate of barchans seems to prohibit their use as geoarchives. In this paper, a possible use of barchan swarms for paleoenvironmental reconstructions is presented. The approach is based on dune migration. In a case study based on 500 dunes in the Pampa de Jaguay aeolian transport corridor in coastal southern Peru, middle to late Holocene changes in the supply of aeolian material are inferred from calculating the time of dune initiation at the coastline. Limitations posed by the assumptions underlying this approach are discussed.     

Differential changes in precipitation and runoff discharge during 1958–2017 in the headwater region of Yellow River of China

Maintenance of steady streamflow is a critical attribute of the continental river systems for safeguarding downstream ecosystems and agricultural production.Global climate change imposes a potential risk to water supply from the headwater by changing the magnitude and frequency of precipitation and evapotranspiration in the region.To determine if and to what extent the recent climate changes affected streamflow in major river systems,we examined the pattern of temporal variations in precipitation,temperature,evapotranspiration and changes in runoff discharge during 1958–2017 in the headwater region of the Yellow River in northeastern Tibetan Plateau.We identified 1989 as the turning point for a statistically significant 14% reduction in streamflow discharge(P 0.05) for the period 1989–2017 compared with 1958–1988,approximately coinciding with changes in the monthly distribution but not the interannual variations of precipitation,and detected a mismatch between precipitation and runoff after 2000.Both annual precipitation and runoff discharge displayed fourand eight-year cyclic patterns of changes for the period 1958–1988,and a six-year cyclic pattern of changes for the period 1989–2017,with two intensified two-year cyclic patterns in the changes of precipitation and a three-year cyclic pattern in the change of runoff further detected for the later period.Our results indicate that the temporal changes in runoff are not strictly consistent with the temporal variations of precipitation in the headwater region of Yellow River during the period 1958–2017.In particular,a full recovery in annual precipitation was not reflected in a full recovery in runoff toward the end of the study period.While a review of literature yielded no apparent evidence of raised evapotranspiration in the region due to recent warming,we draw attention to increased local retention of rainwater as a possible explanation of differential changes in precipitation and runoff.     

Spatiotemporal variations of maximum seasonal freeze depth in 1950s–2007 over the Heihe River Basin, Northwest China

Investigation on spatiotemporal variations of maximum seasonal freeze depth （MSFD） over the Heihe River Basin is of great importance for systematic understanding of regional climate and environmental change, ecological-hydrological processes, water resources assessment, construction and resource development. Based on soil and air temperatures at the meteorological stations of the China Meteorological Administration （CMA） over the Heihe River Basin, MSFDs time series are structured into a composite time series over the 1960-2007 period. Evaluating the averaged MSFD time series for 1960 2007 reveals a statistically significant trend of 4.0 cm/decade or a net change of-19.2 cm for the 48-year period over the basin. The MSFD had significantly negative correlation with mean annual air temperature （MAAT）, winter air temperature, mean annual ground surface temperature （MAGST）, degree days of thawing for the air （DDTa） as well as for the surface （DDTs）, and degree days of freezing for the surface （DDFs）. While there was significantly positive correlation between DDF,. and MSFD time series, MSFD was deeper and changed greatly in the Heihe River source area. It was shallower in the east-central basin and gradually deepened in other sections of the basin. The MSFD distribution pattern in 2003-2005 is consistent with that of averaged degree days of freezing for air （DDFa） in 1960-2007. However, the maximum of MSFD may not be accurate, because there is no long term observation data in the deep seasonally frozen ground regions near the lower boundary of permafrost. With increasing elevation, averaged DDFa increased at a rate of 51.6 ℃-day/100m, therefore, the MSFG and the date reaching MSFG became deeper and later, respectively.     

Stone runs in the Falkland Islands: Periglacial or tropical?

“Stone runs” is the Falklands vernacular term for openwork boulder accumulations, which include extensive blockstreams like the famous Darwin “stone-river” and associated features such as stone stripes. Since the early 20th century, they have been interpreted as the product of a suite of periglacial processes, including frost-wedging, gelifluction, frost heave, frost-sorting and snowmelt runoff. Following a literature review, the results of recent field investigations of the valley-floor blockstreams of East Falkland are presented. Access to the internal structure of these forms provides evidence for the existence of a three-fold profile, with clear vertical size gradation presenting striking similarities with an inverted weathering profile. Micromorphological analyses, SEM, XRD, thin sections and grain-size analyses lead to the hypothesis of an alternative model of stone run formation. It is suggested that the material forming the stone run profile lato sensu (including the superficial pavement) is not of periglacial origin, but derives directly from the stripping and accumulation downslope of a regolith, possibly Tertiary in age and formed under subtropical or temperate conditions. The valley-floor stone runs should, therefore, be considered as complex polygenetic landforms that may have formed according to a six-stage scenario, including in situ chemical weathering, regolith stripping by mass movements, soil formation, further regolith stripping, downslope accumulation and matrix washing-out (all phases possibly achieved by the Early Quaternary). Periglacial reworking of the stone run material would have operated at a “final” stage, i.e. during Quaternary cold stages, with boulder bioweathering and limonite-staining operating during the temperate intervals including the present one. The suggested antiquity of the Falklands blockstreams is in accordance with Caine's pioneer interpretation of Tasmania blockfields and with recent analyses and cosmogenic datings of blockfields from Scandinavia and North America.     

Scientific documentation of crop land changes in the Sahel: A half empty box of knowledge to support policy?

The Sahel has been subject of considerable environmental research and development efforts, specifically since the droughts of the 1970s and 1980s. This article uses a meta-study approach to summarize knowledge of crop land change, the documented driving forces, and the perceived impacts. The analysis of case studies shows that crop land has increased in the majority of cases mainly due to population increase. However, despite population increase, crop land has been stable in some areas, particularly where land availability is a limiting factor or where farmers are able to intensify their farmers from expanding their plots or because households have diversified their activities. The study shows the huge gap in the scientific literature concerning actual measurements of crop land change in the Sahel, which is in contrast to the attention given to crop land changes in theoretical and policy discourses. On the basis of the poor documentation available on crop land change and the contrasting results observed, we point out the need to exercise caution with regard to simple narratives about crop land change.     

Residents’ Perception of the Recreational Value of Forest Parks: A Case Study in Shanghai,China

Forest parks provide important recreational and tourism bene?ts to residents, so it is essential to know what residents’ perceptions are regarding the recreational value of forest parks for participatory forest planning and management. This study investigated forest park recreational value in the physical, psychological, and social dimensions in Shanghai according to questionnaires completed by 658 respondents, and examined the relationships between recreational value and residents’ social variables by multiple correspondence analysis (MCA). The results show the following: 1) The recreational value of forest parks is perceived as most important in the psychological dimension, while in the social dimension it is appreciated the least. 2) In terms of the differences in forest park recreational value in suburbs and rural areas, the social value in rural areas had significantly higher scores than in the suburbs, and the psychological value in suburbs is much higher than that in the rural areas. 3) Regarding the social variables which characterize residents in suburbs and rural areas, females and younger groups tended to assign higher scores to recreational value than males and older groups. Moreover, citizens with low education or low income also assigned higher scores to recreational value compared to more educated or higher-income residents. The results of this study reveal the recreational value characteristics of Shanghai forest parks in the three dimensions, which can provide a scientific basis for the sustainable development of urban forest resources and contribute to reasonable planning and management.     

Variations in the starting date of the pre-summer rainy season in South China, 1736–2010

The starting dates of the pre-summer rainy season during historical times （1736- 1911） in Fuzhou and Guangzhou of South China, were determined and reconstructed on the basis of historical documents in the Yu-Xue-Fen-Cun archive, together with observed features of precipitation during the pre-summer rainy season. In addition, starting dates of the pre-summer rainy season from 1953 in Fuzhou and from 1952 in Guangzhou were reconstructed for the instrumental period. These data allowed for analyses of inter-annual and inter-decadal changes in the starting dates of the pre-summer rainy season in South China over the past 300 years. Results show that the mean starting date of the pre-summer rainy season in South China was the first pentad of May; in addition, periodicities in the starting dates of 2-3 years, 10 years, and 40 years were detected during the period 1736-1911, and of 2-3 years, 10 years, and 22 years during the instrumental period. From 1736 to 1911, the earliest starting dates at Fuzhou and Guangzhou both occurred at the fourth pentad of April, while the latest starting dates were at the sixth pentad of May in Fuzhou and the first pentad of June in Guangzhou. During the instrumental period, the earliest and latest starting dates were at the fourth pentad of April and the first pentad of June, respectively, in both Fuzhou during 1953-2010 and Guangzhou during 1952-2010. The maximum difference between neighboring decades during 1736-1911 was 2.2 and 1.6 pentads in Fuzhou and Guangzhou, respectively, and during the instrumental period it was 2.5 and 2.4 pentads in Fuzhou and Guangzhou, respectively.