Periods Of Wetter Climate Research Articles

Effects of climate variability and/or land use dynamics on the hydrological balance of the Cavally river catchment at Toulepleu, West Africa

Abstract The study focuses on assessing the individual and combined impacts of climate variability and land use change on hydrological responses. The results indicate that the basin, urban area, cropland, degraded forest, and open forest shows an increasing trend, while gallery forest show a decreasing trend over the period 1992–2015. Climatic variability is marked by two climatic periods (a wet one from 1980 to 1996 and a dry one from 1997 to 2016) with a 35% decrease in rainfall. Regardless of the state of the landcover used, the simulated mean annual runoff decreases by 67.92% between the wet and dry climate periods. Changes in land use between 1992 and 2015 reduce mean annual runoff by 4.71%. Analysis of the joint effect of climatic and LU variation shows a 68.96% reduction in runoff. In this catchment, the joint impact has a clearly greater effect on runoff than the climatic impact, which is greater than that of human activities. There is a need for policymakers to prioritise sustainable land use practices and integrated water resource management strategies in the area to mitigate the combined effects of climate variability and anthropogenic activities, ensuring the long-term resilience of the ecosystem and water availability for local communities.

Travertine records climate-induced transformations of the Yellowstone hydrothermal system from the late Pleistocene to the present

Chemical changes in hot springs, as recorded by thermal waters and their deposits, provide a window into the evolution of the postglacial hydrothermal system of the Yellowstone Plateau Volcanic Field. Today, most hydrothermal travertine forms to the north and south of the ca. 631 ka Yellowstone caldera where groundwater flow through subsurface sedimentary rocks leads to calcite saturation at hot springs. In contrast, low-Ca rhyolites dominate the subsurface within the Yellowstone caldera, resulting in thermal waters that rarely deposit travertine. We investigated the timing and origin of five small travertine deposits in the Upper and Lower Geyser Basins to understand the conditions that allowed for travertine deposition. New 230Th-U dating, oxygen (δ18O), carbon (δ13C), and strontium (87Sr/86Sr) isotopic ratios, and elemental concentrations indicate that travertine deposits within the Yellowstone caldera formed during three main episodes that correspond broadly with known periods of wet climate: 13.9−13.6 ka, 12.2−9.5 ka, and 5.2−2.9 ka. Travertine deposition occurred in response to the influx of large volumes of cold meteoric water, which increased the rate of chemical weathering of surficial sediments and recharge into the hydrothermal system. The small volume of intracaldera travertine does not support a massive postglacial surge of CO2 within the Yellowstone caldera, nor was magmatic CO2 the catalyst for postglacial travertine deposition.

Sedimentary Characteristics and Depositional Model of the Paleogene Dawenkou Formation in Eastern China: Insights from the Huanggang Depression

The Huanggang depression in eastern China is a significant Cenozoic salt-bearing basin that formed during the alternating dry and wet climate periods from the Eocene to the Oligocene. Despite the economic importance of the Huanggang depression, its saliferous model remains controversial. To address this issue, we conducted comprehensive analyses of the sedimentology and elemental geochemistry on the YZR1 borehole core, which hosts a relatively complete sedimentary record of the Huanggang depression, consisting of five lithofacies’ assemblages. The combined lithofacies and geochemical ratios, including B/Ga, Sr/Ba, and V/(V + Ni), provide insights into the paleolake’s evolution in the Huanggang depression. Our analyses indicated that the paleolake underwent a transition from a freshwater lake to a brackish water/saline lake, subsequently transforming into a salt lake, reverting back to a brackish water/saline lake, and ultimately returning to its original state as a freshwater lake. These changes are reflected in the sedimentary record and inform the six stages of evolution of the paleolake of the Dawenkou Formation. We propose two metallogenic models to explain the accumulation of the thick halite (LA1) and thin halite layers (LA2), respectively. LA1 is primarily dominated by halite deposition, forming in an extremely shallow water environment under arid climate conditions. In contrast, LA2 records the alternating deposition of halite, anhydrite, and mudstone, and formed in a shallow water environment under arid to semi-arid climatic conditions. LA1 has a much drier climate and higher salinity than LA2. Our results suggest that the salt-forming period in the Huanggang depression occurred from the late Eocene to the early Oligocene. The halite in the Huanggang depression formed in a shallow water environment, providing the basis for the halite deposition model of the depression. This study sheds light on the formation mechanism of halite in the Paleogene in eastern China.

Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition

Paleoclimate records across the Intermountain West region of North America show significant regional variation in timing and magnitude of wet conditions that accompanied the last glacial-interglacial transition. To understand the climate controls on paleohydrologic change, well-dated records are needed across the region. The Plains of San Agustin (New Mexico, USA) is a closed-basin watershed of the American Southwest influenced by both winter westerly and summer North American Monsoon precipitation. The flat valley floors of the Plains contain lake and groundwater discharge deposits that record multiple periods of past wet climate. We present a record of hydroclimate for the past 26,000 years based on radiocarbon, U–Th series, and OSL dating of these deposits and stratigraphic correlation across the three sub-basins of the lake system. We find that two major lake oscillations occurred, coincident with the global Last Glacial Maximum (∼23–18 ka) and with Heinrich Stadial 1 (∼17–14 ka). The LGM lake cycle created a deep lake in the lowermost sub-basin, fed by marsh/lake overflow in the upper sub-basins. The Heinrich Stadial 1 wet interval attained the highest recorded lake level between ∼17.0 and 15.3 ka, merging the lower two sub-basins into one lake. Both lake cycles agree well in timing and magnitude with other lake-based records from the southwestern U.S., supporting previous interpretations that a south-shifted cool season storm track brought a dipole-like pattern of enhanced moisture to the southwest at the expense of drier conditions in the northwest during the LGM and deglaciation. A transition from lake to groundwater discharge conditions followed during the Bølling-Allerød (14.7–12.9 ka) across the study area. Wet meadows prevailed in the lower sub-basin during the Younger Dryas (12.9–11.7 ka), with marsh and open lake conditions in the upper and middle sub-basins, respectively. During the early Holocene, discrete wet intervals are recorded by ages for wet meadow deposits in all sub-basins with centennial-millennial frequency at 9.9, 8.8, 8.2 ka. These events agree well with other Intermountain West records showing wetter-than-present conditions prior to 8 ka. Two additional wet periods, centered at 6.8 and 5.4 ka, occurred during the driest known interval of the middle Holocene, and likely were partly supported in the Plains of San Agustin by summer moisture associated with the peak strength of the North American Monsoon. Our record highlights that both winter and summer moisture support water resources in New Mexico watersheds.

Relict soil features in cave sediments record periods of wet climate and dense vegetation over the last 100 kyr in a present-day semiarid region of northeast Brazil

The present-day semiarid region of NE Brazil experienced multiple periods of increased precipitation during the Quaternary. They were likely linked to global-scale events (e.g., Heinrich Events) and drove changes in vegetation dynamics, leading to the expansion of rainforest vegetation. Here, we hypothesize that soil features preserved in cave sediments records paleoenvironmental changes induced by global-scale events that affected NE Brazil during the Late Pleistocene - Early Holocene. To test this hypothesis, we analyzed the elemental and isotopic geochemistry composition, bulk sediment mineralogy, soil micromorphological features, and fauna fossil type and content of a well-preserved 6 m cave sediment profile spanning 103 kyr – 8 kyr in Toca de Cima do Pilão at the Serra da Capivara National Park. Our approach provides new information on the history of soil formation, vegetation, and climate of NE Brazil during the Late Pleistocene - Early Holocene. The results demonstrated that severe weathering and dense vegetation was the dominant paleoenvironmental conditions during wet periods, when latosolization was the main soil forming process. The evidence for wet and intense weathering periods was the co-existence of speleothems layers with Ferralsol features, such as runiquartz, granular microstructure, Fe nodules and gibbsite formation. Some of these features were found in layers deposited in synchrony with Heinrich Stadial and Younger Dryas periods, suggesting that past soil processes in NE Brazil were affected by those global-scale events. We propose five phases of latosolization in our study area during the last 100 kyr. The first was identified around 80 kyr, the second occurred around 29 kyr. The third coincided with Heinrich Stadial 1 (16 kyr) and the fourth likely occur during the Younger Dryas, and the fifth phase occurred during the middle Holocene.

Topographic development of a compressional mountain range, the western Transverse Ranges of California, USA, resulted from localized uplift along individual structures and regional uplift from deeper shortening

Abstract The western Transverse Ranges are a tectonically active mountain belt in southern California (USA) characterized by fast rates of shortening and rock uplift. Large drainages at the western end of this mountain belt, including the Santa Ynez River and its tributaries, transect regional west–northwest-striking reverse faults and folds. We used fluvial strath terraces within the Santa Ynez River watershed as geomorphic markers for measuring Quaternary rock uplift and deformation across these structures. Mapping, surveying, and numerical dating of these strath terraces in both hanging-wall and footwall blocks of the major reverse faults allow us to separate regional uplift from localized uplift along individual structures. Luminescence dates from 18 sites within the Santa Ynez River watershed show that the three prominent terrace levels present throughout the area formed between ca. 85 ka and 95 ka, 55 ka and 75 ka, and 30 ka and 45 ka. All three fluvial terrace straths grade into marine paleo-shore platforms along the coast that formed during sea-level highstands. The fluvial straths were formed as a result of lateral erosion during warm, dry climate intervals when vertical incision was temporarily arrested. Incision of the terraces followed during intervening periods of wet climate. Mapping and valley-long profiles of the terraces document deformation by faults and folds, and we infer minimum rock-uplift rates from the amount of incision below the terrace strath surfaces. Rock-uplift rates range from 0.3 mm/yr to 4.9 mm/yr, with faster rates in the hanging-wall blocks of the major reverse faults and slower rates in the footwall blocks. Rock-uplift rates calculated from strath terraces in the footwall blocks range from 0.3 mm/yr to 1.6 mm/yr, which indicates a regional component of uplift that results from deeper deformation. Higher rates of rock uplift in the hanging-wall blocks (0.5–4.9 mm/yr) are superposed on this regional component. Incremental rock-uplift rates calculated over three time intervals and differences in terrace deformation with age suggest that deformation rates across some structures have decreased over the past 85 k.y. We conclude that topographic growth of the western Transverse Ranges results from a combination of localized uplift along individual structures that varies both spatially and temporally and a more constant regional uplift that likely results from deeper ductile deformation or slip along detachment faults that have been inferred to underlie the area.

Identification of shallow groundwater in arid lands using multi-sensor remote sensing data and machine learning algorithms

The focus of this study is to locate shallow groundwater (SGW) occurrences in arid lands using the Western Desert (WD; area: ∼680,000 km2) of Egypt as a test site. The SGW in the study area originated from paleo-precipitation during previous wet climatic periods. In wet periods, fossil groundwater was at higher levels, ascended along high-angle faults, and discharged at the surface. In contrast, at present, the water levels are lower, and the discharge occurs at near-surface elevations. Spring locations were identified as the dependent variable, while the independent variables included remote sensing–based variables and geomorphological features indicative of current or paleo discharge locations, including elevation, slope, curvature, distance to sapping features, soil moisture, NDVI, radar backscatter coefficient, and brightness temperature. Relationships between SGW occurrences (target) and their controlling factors (independent variables) were established using extreme gradient boosting (XGB), support vector machine (SVM), and logistic regression (LR) methods. The trained models were used to map SGW locations across the entire WD. Findings include the following: (1) the XGB yielded the most favorable result in identifying SGW locations (overall accuracy: 0.93) compared to SVM (overall accuracy: 0.88) and LR (overall accuracy: 0.87); (2) areas with a very high probability of SGW occurrences were found in lowlands and proximal to sapping features; (3) the overwhelming majority of the cultivated lands within the southern and central sections of the WD lie within areas identified as high and very high probability SGW locations; (4) our models identify-two previously unrecognized major SGW occurrences, an eastern zone (EZ; length: 800 km; width: 9 to 80 km; area: 43,000 km2) and an east–west trending northern zone (NZ) centered over the Qattara depression (length: 500 km; width: 200 km; area: 62,150 km2); (5) additional criteria were used to refine the modeled (XGB) SGW distribution (southern and central WD: 43,200 km2 to 23,400 km2; EZ: from 21,300 km2 to 17,400, and NZ: from 62,150 to 30,700 km2) including presence of shallow aquifers to accommodate rising Nubian waters, Nubian water salinity (fresh to brackish), and low to moderate thickness (<1 km) of post-Nubian successions that rising waters interact with. The techniques are cost-effective and efficient and could be readily applied to large sectors of Saharan Africa and Arabia, whose landscape and fossil aquifers bear many resemblances in their geologic, climatic, and geomorphic characteristics to the Nubian Sandstone Aquifer System.

The Groundwater Flow Behavior and the Recharge in the Nubian Sandstone Aquifer System during the Wet and Arid Periods

The Nubian Sandstone Aquifer System (NSAS) is made up of three major sub-basins: Kufra, Dakhla, and the N. Sudan Platform. It is one of the world’s largest groundwater systems. The aquifer’s hydrologic setting, connectivity of its sub-basins, and groundwater flow across these sub-basins are currently unclear. To address these issues, we used a combined approach that included: (1) a regionally calibrated groundwater flow model that mimics early (&gt;10,000 years) steady-state conditions under wet climatic periods and later (&lt;10,000 years BP–1960; 1960–2010) transient conditions under arid climatic periods; and (2) groundwater ages (36Cl, 81Kr) and isotopic (18O, 2H) data. The NSAS was recharged on a regional scale in previous wet climatic periods; however, in dry periods, its outcrops are still receiving local modest recharge. A progressive increase in 36Cl groundwater ages was found along groundwater flow directions and along structures that are sub-parallel to the flow direction. The NE–SW Pelusium mega shear zone is a preferential groundwater flow conduit from the Kufra to the Dakhla sub-basin. The south-to-north groundwater flow is hampered by the Uweinat–Aswan basement uplift. The findings provide useful information about the best ways to use the NSAS.

A New Look at Landslides of the Vermilion and Echo Cliffs, Northern Arizona

ABSTRACT The Vermilion and Echo Cliffs form a nearly continuous escarpment more than 160 km long within the Colorado Plateau physiographic province of North America. The cliffs overlie the Marble Platform in northern Arizona and are located along the Colorado River, just upstream of the Grand Canyon. Large rotational block landslides mantle the erosional escarpment along most of its extent. Although these landslides have been noted for over 100 years, their likely origin has never been explained. Landslide failure surfaces appear to be influenced by the Petrified Forest Member of the Triassic Chinle Formation, a shale layer containing smectite clay weathered from volcanic ash. Although landslides are common along the majority of escarpments comprising the Colorado Plateau where the Petrified Forest Member and other shales outcrop, most appear to have been inactive since the early Holocene. Multiple generations of landslides and remnants of previous slides exist up to 3 km from the present cliff face. Multiple working hypotheses explaining these landslides are explored in this article, including past landslides and/or lava dams along the Colorado River within the Grand Canyon, periods of wetter climate with higher groundwater levels, and earthquakes related to nearby faulting and volcanism. Various sliding modes along these cliffs are described along with potential triggering mechanisms. Back-analysis of these landslides has been conducted using mechanical properties of the formations involved as well as varying groundwater levels. Calculated factors of safety for existing slides under present conditions are greater than unity, consistent with their apparent stability.

Response of Drainage Pattern and Basin Evolution to Tectonic and Climatic Changes Along the Dinarides-Hellenides Orogen

The junction of the Dinaric and Hellenic mountain belts hosts a trans-orogenic normal fault system (Shkoder-Peja Normal Fault, SPNF) that has accommodated oroclinal bending, as well as focused basin formation and drainage of the Drin River catchment. Analysis of fluvial morphology of this catchment reveals higher values of river slope indices (ksn) and χ (Chi) between the normal faults of the SPNF and the Drin drainage divide. The drainage divide is predicted to be migrating away from the SPNF, except at the NE end of the SPNF system. Two basins analysed in the hangingwall of the SPNF, the Western Kosovo Basin (WKB) and Tropoja Basin (TB), contain late Pliocene-to-Holocene sedimentary rocks deposited well after the main fault activity and immediately after the Last Glacial Maximum (LGM). These layers document an early Pleistocene transition from lacustrine to fluvial conditions that reflects a sudden change from internal to external drainage of paleo-lakes. In the TB, these layers were incised to form three generations of river terraces, interpreted to reflect episodic downstream incision during re-organisation of the paleo-Drin River drainage system. 36Cl-cosmogenic-nuclide depth-profile ages of the two youngest terraces (∼12, ∼8 ka) correlate with periods of wetter climate and increased sediment transport in post-LGM time. The incision rate (∼12 mm/yr) is significantly greater than reported in central and southern Albania. Thus, glacial/interglacial climatic variability, hinterland erosion and base-level changes appear to have regulated basin filling and excavation cycles when the rivers draining the WKB and TB became part of the river network emptying into the Adriatic Sea. These dramatic morphological changes occurred long after normal faulting and clockwise rotation on the SPNF initiated in late Oligocene-Miocene time. Faulting provided a structural and erosional template upon which climate-induced erosion in Holocene time effected reorganisation of the regional drainage pattern, including the formation and partial demise of lakes and basins. The arc of the main drainage divide around the SPNF deviates from the general coincidence of this divide with the NW-SE trend of the Dinaric-Hellenic mountain chain. This arc encompasses the morphological imprint left by roll-back subduction of the Adriatic slab beneath the northwestern Hellenides.

Relict Soil Features in Cave Sediments Record Periods of Wet Climate and Dense Vegetation Over the Last 100 Kyr in a Present-Day Semiarid Region of Northeast Brazil

Relict Soil Features in Cave Sediments Record Periods of Wet Climate and Dense Vegetation Over the Last 100 Kyr in a Present-Day Semiarid Region of Northeast Brazil

Dry and Wet Climate Periods over Eastern South America: Identification and Characterization through the SPEI Index

A large part of the population and the economic activities of South America are located in eastern regions of the continent, where extreme climate events are a recurrent phenomenon. This study identifies and characterizes the dry and wet climate periods at domain-scale occurring over the eastern South America (ESA) during 1980–2018 through the multi-scalar Standardized Precipitation–Evapotranspiration Index (SPEI). For this study, the spatial extent of ESA was defined according to a Lagrangian approach for moisture analysis. It consists of the major continental sink of the moisture transported from the South Atlantic Ocean throughout the year, comprising the Amazonia, central Brazil, and the southeastern continental areas. The SPEI for 1, 3, 6, and 12 months of accumulation was calculated using monthly precipitation and potential evapotranspiration time series averaged on ESA. The analysis of the climate periods followed two different approaches: classification of the monthly SPEI values as mild, moderate, severe, and extreme; the computation of the events and their respective parameters (duration, severity, intensity, and peak). The results indicate that wet periods prevailed in the 1990s and 2000s, while dry conditions predominated in the 2010s, when the longest and more severe dry events have been identified at the four scales.

Vegetation evolution in response to climate change and rapid sea-level rise during 8.2–7.0 cal ka BP: Pollen evidence from the northwest coast of Bohai Bay, north China

To understand vegetation dynamics and their response to climate changes and sea-level rise (SLR) on the northern coast of the Bohai Sea during a marine transgression period (8.2–7.0 cal ka BP), we obtained two sedimentary cores (HG01 and HG02) with high-resolution accelerator mass spectrometry carbon-14 (14C) data from the coastal plain of Bohai Bay in northeastern China. A general warming and wetting trend from 8190 to 7920 cal a BP was indicated by the greater abundance of deciduous broadleaved forest, which showed that the Asian summer monsoon was stronger over this period. The abundance of deciduous broadleaved trees was relatively high, which revealed that the climate was relatively warm and wet and that the Asian summer monsoon was strong, during the periods of 7920–7690 cal a BP and 7230–7020 cal a BP. Broadleaved tree abundance decreased over the intervening period—from 7610 to 7230 cal a BP—suggesting a declining monsoon, and relatively cool, dry climate. The abrupt cooling event from 7460 to 7230 cal a BP may have been a global event, closely related to the decrease in solar activity and rapid SLR before 7460 cal a BP. The results also showed that the large number of halophytes mainly Chenopodiaceae, sharply increased at times, mirroring four SLR fluctuation periods: 7940–7860 cal BP, 7760–7700 cal BP, 7560–7460 cal BP, and 7230–7130 cal BP. SLR in Bohai Bay occurred during warm and wet climate periods, and the phased SLR observed during ~7.9–~7.1 cal ka BP may have been the local manifestation of a global event.

Long-range, high-resolution stratigraphic correlation of Rotliegend fluvial-fan deposits in the central Dutch offshore

The Rotliegend feather-edge area in the central part of the endorheic Southern Permian Basin in the Dutch offshore is characterized by a predominance of mud-prone, evaporite-bearing playa and lake deposits with a subordinate amount of interbedded, thin, fluvial sheet sandstones. The distribution and lateral facies changes of the sandstone bodies have been analyzed by generating a long-range, high-resolution chronostratigraphic correlation framework. The correlation technique of pattern matching of GR logs was applied, supported by calculating spectral trend curves. Flooding events are the primary near-synchronous correlation surfaces, which can be traced up to and over 100 km. The basin setting of the Southern Permian Basin, the studied sandstone depositional architecture (logs) and sedimentary characteristics (core) are analogous to the depositional setting of laterally-amalgamated terminal lobes of dryland-river systems in an endorheic basin, such as the Holocene Altiplano Basin in Bolivia, present-day Lake Eyre (Australia) and the Miocene Ebro Basin (Spain). The integrated approach has yielded a stratigraphic reservoir-architecture framework in which the reservoir sandstones, with net sand up to 10 m, have been identified as amalgamated terminal-splay sandstone sheets formed at the end of dryland-river pathways, alternating with lacustrine mudstone layers deposited during short-duration, high-magnitude flooding in intermittent wet climate periods.

Sequence stratigraphic analysis of thick coal seams in paralic environments – A case study from the Early Permian Shanxi Formation in the Anhe coalfield, Henan Province, North China

To study the possible role of base-level oscillations in the formation of thick coal seams in coastal plain (paralic) environments, the Early Permian Shanxi Formation No.21 thick coal seam was investigated in 3 cores spanning a distance of 29 km in the Anhe (Anyang-Hebi) coalfield, Henan Province using sedimentology, sequence stratigraphy, and coal petrology. The accommodation condition and origin of the peatland can be interpreted from maceral and mineral composition in the No.21 coal seam. Coals that accumulated in a low accommodation peat of ombrotrophic origin are characterized by relatively high inertinite content and relatively low mineral matter abundance. Coals accumulated in a balanced accommodation peat of rheotrophic origin are characterized by high vitrinite content and low abundances of inertinite and mineral matter. Coals with relatively high vitrinite content and relatively low inertinite content are interpreted to have accumulated in a high accommodation peat of rheotrophic origin. The No.21 coal seam was developed as part of a transgressive systems tract (TST) and displays maximum thickness in the central Anhe coalfield due to the local rapid subsidence of the formative delta plain. Six types of key stratigraphic surfaces are recognized in the coal seam, including terrestrialization (TeS), paludification (PaS), give-up transgressive (GUTS), accommodation-reversal (ARS), exposure (ES), and flooding (FS) surfaces. The No.21 coal seam consists of at least three drying-up and wetting-up cycles defined by these surfaces, with each cycle spanning from 20 ka to 30 ka. The variation of peatland type from rheotrophic through ombrotrophic and back to rheotrophic peat in the landward area implies the role of high-frequency climatic fluctuations, and the water level changes in the central and seaward areas may reflect sea-level fluctuations due to the hydrological connection to the sea and the change in rainfall to evaporation rates. These cycles arrived at a period close to that of climatic precession for Milankovitch cycles during the early Permian. The oscillating high and low summer insolation would have caused the alternating wet and dry climate periods that were then recorded as the wet-dry cycles in the coal seams. The results of this study can provide insights for research addressing hydrological conditions in ancient peatlands, and paleoclimate and sea-level fluctuations recorded in thick paralic coal seams.

6600 years of human and climate impacts on lake-catchment and vegetation in the Julian Alps (Lake Bohinj, Slovenia)

Mountain grazing and ore processing had a significant impact on the Alpine environment in the last 5000 years, but few studies have so far focused on environmental changes of the south eastern Alps. This study investigates the vegetation history and sedimentary processes in the catchment of Lake Bohinj (Julian Alps, Slovenia), where a 12-m-long core was collected in the central part of the lake. Sediment in the early Holocene section of the core was partially reworked due to a major seismic event dated to 6711–6523 yr cal BP (Rapuc et al. 2018), therefore a detailed palaeoenvironmental reconstruction was performed only for the top 4.4 m of the core. Here the results of mineralogical, sedimentological, geochemical, stable isotope (δ13C and δ15N), and pollen analysis are presented in order to better understand the impact of people (agriculture, grazing, mining) on the environment, and climate-human interactions over the last 6600 years.The results of palynological research suggest that at ca. 6000 yr cal BP Lake Bohinj was surrounded by mixed forest composed of Picea, Abies, deciduous Quercus, with Fagus becoming dominant after ca. 3300 yr cal BP. In the Bronze and especially the Iron Age (3500–2500 yr cal BP), when the region was, according to archaeological data, densely populated, clearing of forests due to agriculture, livestock production and metallurgical activities was detected through Cerealia type pollen, Plantago lanceolata, and the decline of Abies. These activities probably triggered soil erosion recorded as increased sedimentation rates. In the subsequent centuries human impact on the environment continued (increased), but it seems that the watershed was not destabilised again. Several periods of high terrigenous input were recorded at 6100–6000, 5700–5550, 5000–4600, 3900, 3700–3550, 2300–2200 yr cal BP and could be associated with a mobilisation of river inflow from the eastern flysch bearing catchment, due to river migration during periods of wetter climate. These flood patterns match with periods of enhanced flood activity in the wider Alpine region.

Prehispanic and colonial landscape change and fluvial dynamics in the Chalco Region, Mexico

The late Quaternary deposits of the lakeshore plain and western edge of Lake Chalco in the southeastern Basin of Mexico were explored in order to understand the influence of alluvial sedimentation on archeological visibility and preservation, as well as to seek out records that would permit direct comparison of erosion and sedimentation with the demographic record derived from the archeological survey. The Chalco lakeshore plain is traversed by two of the largest rivers in the region, and the pattern of human settlement recorded here by archeological survey is partly an artifact of alluvial sedimentation, where the most prominent settlements were observed in areas with little or very slow sedimentation. Detailed radiocarbon dating of the alluvial deposits indicates that prior to the establishment of a sedentary lifestyle, alluvial sedimentation was slow. Catastrophic soil erosion is inferred from a period of widespread rapid alluviation and mass movements during late Preceramic, Early and Middle Formative periods, which were periods of rapid population growth. Mass movements appear to coincide also with periods of wetter climate. No evidence of sedimentation was noted during the population collapse that occurred at the end of the Formative. The next phase of alluvial sedimentation occurred during the Early Classic to Late Toltec periods, which were also periods of population expansion during a gradually drying climate. The Postclassic period, which was the largest Pre-Columbian demographic expansion, was paradoxically accompanied by minor evidence of alluvial activity. The last and most widespread period of alluvial activity occurs in the post-Conquest period and is difficult to date with precision but appears to occur primarily during the seventeenth and eighteenth centuries.

Rapid alluvial sedimentation aided expansion of Moissac during the High Middle Ages along the Tarn River in southern France

We examine medieval urban expansion of Moissac, a town located at the outlet of the Tarn River basin draining 15,400 km2 in southern France, in order to understand the association of Moissac's expansion to river position and sedimentation patterns in the river valley. A chronostratigraphic framework was derived from three auger holes and an archaeological excavation using radiocarbon dating and standard field and laboratory characterization of sediments. Five radiocarbon dates were obtained from one auger hole, along with particle size, magnetic susceptibility, organic matter, and quantitative soil color analyses to augment field descriptions. Results indicate Moissac spawned from the Abbey of Saint-Pierre on the apex of a small alluvial fan surrounded by backswamps ca. 850 CE, and urban growth radiated down the fan toward the river bottomlands throughout the following several centuries. At ca. 1000–1200 CE, human-induced soil erosion in the watershed caused very rapid aggradation of surrounding alluvial backswamps (at long-term average sedimentation rates of 20–30 mm/y). Such rapid bottomland accretion probably was driven by rampant agricultural soil erosion linked with wet climatic periods and enhanced flooding. This bottomland accretion enabled urban expansion and agricultural activities to cover the former backswamp and wetlands by the late Middle Ages (ca. 1300–1500 CE). Although we normally associate human-induced soil erosion with negative consequences of ecosystem services, the rapid bottomland accretion and resulting habitable and arable land can be viewed as a positive ecosystem service outcome resulting from human-induced soil erosion.

Palaeohydrology and its impact on groundwater in arid environments: Gebel Duwi and its vicinities, Eastern Desert, Egypt

From ancient times, access to water in arid and hyper-arid regions has been crucial for life. Increased knowledge about groundwater conditions is therefore extremely important for the future development of desert areas. Gebel Duwi, a limestone ridge, sited in the today hyper-arid Eastern Desert of Egypt, was chosen for testing current hypotheses concerning the interdependence of palaeohydrologic features and geologic settings for groundwater investigations. Two sub-basins are identified in affecting Gebel Duwi: Wadi Nakheil and Wadi Sodmein. Both have extraordinary high stream order, indicating the reality of a very old drainage system. Several additional palaeohydrologic features such as wadi terraces, alluvial fans, and playa deposits are also recorded in these sub-basins. These features, as well as finds from an important archaeological site (Sodmein Cave), provide information about palaeoenvironmental changes and wetter climatic periods in the younger geologic past, mainly in the Late Pleistocene and Holocene, which have affected the occurrence of present day groundwater. This study combines new results of geological and geomorphological field studies, examinations of digital elevation models, as well as of rock and water analyses in an integrated approach. Resulting maps comprise landforms, lithology, elevation, drainage lines slope, structural lineaments and flow directions. The hydrogeologic condition indicates suitable locations for groundwater recharge and accumulation. The research presented is interdisciplinary in approach and is recommended for future studies with regard to groundwater exploration, sustainable groundwater use, and the protection of archaeological sites in arid lands.

Subsurface water-use strategies and physiological responses of subtropical eucalypt woodland vegetation under changing water-availability conditions

This study investigated subsurface water-use strategies and physiological responses of subtropical remnant eucalypt woodlands in south-eastern Queensland, Australia. A land surface temperature (LST) model-data approach was used to detect daily use of subsurface water (i.e. soil moisture obtained from depths >30cm and aquifer groundwater) by woody vegetation to a confidence level of 95%. Vegetation subsurface water use was quantified over a 13-year period (2000–2012) coinciding with a series of wet and dry climatic periods. Land surface temperature and subsurface water use time-series data were compared to local meteorological (vapour pressure deficit, rainfall, and soil water availability) and vegetation (leaf area index, stomatal resistance and latent heat loss) data to determine vegetation strategies to declining shallow (<30cm depth) soil water availability. Different vegetation subsurface water-use strategies and physiological response to changes in water availability were identified at inter- and intra-annual time-scales. At the intra-annual scale, frequency of subsurface water use by vegetation was strongly influenced by availability of shallow soil water. From January–September in this landscape, frequency of subsurface water use by vegetation remained relatively constant, supplementing decreasing shallow soil water availability and/or increasing evaporative demand. From October–December, the vegetation opportunistically utilised more abundant shallow soil water arising from more frequent, intense rainfall events, rather than relying on subsurface water. At the inter-annual scale, vegetation increased frequency of subsurface water use and decreased leaf area to reduce latent heat loss in response to dry conditions. Then, during wet years, subsurface water use by vegetation decreased in frequency as water was increasingly sourced from shallow soil layers. However, despite preceding dry periods of different severity, and exhibiting different average annual rainfall, air temperatures and reduction in the frequency of subsurface water use by vegetation, leaf area increased by approximately the same amount for both ‘recovery’ years. This suggests that investment in canopy leaf growth by this vegetation was more sensitive to the onset of increased water availability after drought rather than the overall volume of water made available by rainfall.