Increase In Lake Level Research Articles

Paleoenvironmental change in Ao Tien Lake, Ba Be National Park as referred from stable isotopes

Reconstruction of paleoenvironment and paleoclimate aims to clarify the characteristics the environments and climate in the past. The information of paleoenvironment and paleoclimate contributes important data for simulating the environmental and climate change in the future. The purpose of this study aims to reconstruct the paleoenvironmental characteristics in Ao Tien Lake, Ba Be National Park using the geochemical indicators of sediment grain size compositions, organic matter (OM), stable isotopes (δ13C and δ15N) and C/N ratios in one sediment core. The simultaneous variation of the geochemical indicators showed that paleoenvironmental characteristics of the study area since 700 years BP could be divided into the three following periods: The period from 1300 to 1424 AD was characterized by heavy precipitation, relatively high in lake water level and dominance of organic matter originated from C3 plants surrounding lake watershed; The period from 1424 to 1864 AD was characterized by a continuous decrease in the lake water level and reached to the lower water level due to the decrease in the precipitation water entering the lake. The sedimentary organic matter was originated from both C3 plants and lake microalgae with the dominance of chrysophyceae and cyanobacteria; The period from 1864 to the present was reconstructed by a slight increase in lake water level due to the intensifying of moonson activities. The predominance sources of sedimentary organic matter consisted of C3 plants and lake microalgae. The period from the year 1957 to the present was characterized by a decrease in precipitation and a relatively low lake water level. The sedimentary organic matter sources were mainly from cyanobacteria and chrysophyceae microalgae. In which, the chrysophyceae microalgae was predominant in the oligotrophic state. Keywords: Paleoenvironment, Paleoclimate, Stable isotopes, C/N ratios, Lake sediments.

Investigating the role of meltwater versus precipitation seasonality in abrupt lake-level rise in the high-altitude Tso Moriri Lake (India)

We present late Quaternary lake level reconstruction from the high altitude Tso Moriri Lake (NW Indian Himalaya) using a combination of new and published data from shallow and deep water cores, and catchment geomorphology. Our reconstruction indicates two dramatic lake level increases – a late glacial (ca. 16.4–12.6calkyrB.P.) rise of 65m, and a 47m rise during the early Holocene wet phase (ca. 11.2–8.5calkyrB.P.) which are separated by the Younger Dryas (YD) event. We decouple the role of precipitation seasonality and snow melt using a combination of proxies sensitive to the Indian Summer Monsoon (ISM), and a regional spatio-temporal transect that provides information on the eastward penetration of the winter westerlies. A comparison of shallow and deep water cores shows that (i) the first lake level increase (~65m, ca. 16.4–12.6calkyrB.P.) is caused by melt water inflow triggered by the increasing summer insolation; (ii) the second lake level increase (~47m, 11.2–8.5calkyrB.P.) is largely caused by a rise in annual precipitation coupled with reduced summer evaporation; (iii) in contrast to the onset of ISM (Bay of Bengal branch) at ca. 14.7ka in lower elevations in NE India, the hydroclimatic influence of ISM in the high altitude Himalaya is seen only between 12.7 and 12calkyrB.P., though the influence of solar insolation (via increased snowmelt) is visible from 16.4calkyrB.P. onwards; (iv) the eastward penetration of westerlies in Indian Himalayas is strongly influenced by the strength of the Siberian High.

Late Pleistocene to Holocene paleoenvironmental evolution of Lake Hazar, Eastern Anatolia, Turkey

High-resolution seismic reflection profiles and core analyses in Lake Hazar provide a detailed record of the lake level fluctuations and the robust chronology of paleoclimatic events of the Eastern Anatolia during the late Pleistocene to Holocene. The earlier period of Marine Isotope Stage 3 (MIS-3) prior to 48 cal ka BP was accompanied by considerable lake level drop below −95 m, whereas the lake level increase during the later period (ca. 48-29 cal ka BP) gave rise to deposition of a transgressive unit with typical of aggradational architecture in the seismic reflection profiles. High climate variability with the Greenland interstadials and stadials (Dansgard-Oeschger and Heinrich events) in Lake Hazar are sensitively recorded in the core sediments by using multi-proxy analyses. Adjustment of seismic units correlating with the radiocarbon-dated chronostratigraphic units in the studied cores implies that the early Marine Isotope Stage 2 (MIS-2) is marked by an another lowstand lake level existed at ca. −90 m during 29–23 cal ka BP. In comparision to MIS-3 stage, the multi-proxy analyses reveal a general dry evaporative condition during most of the Last Glacial Maximum. In Lake Hazar, the maximum humidity in the late glacial period existed during 14.9–13.5 cal ka BP. The existence of a hiatus in the sedimentary record is documented in the seismic data that coincides with the cold and dry Younger Dryas period, implying a remarkable lake level drop. The multi-proxy records of the Holocene sediments reveal that a maximum precipitation in the early Holocene period prevailed during 10.1–9.3 cal ka BP, leading water level rise in the lake. In Lake Hazar, the middle Holocene until 4.9 cal ka BP is represented by highly climate variations, indicating a series of shorter wet and longer dry climate periods. The late Holocene is accompanied by lake level rises under a general wet climate condition that was interrupted by short dry climate intervals during 3.7–3.3 cal ka BP, 2.8–2.6 cal ka BP and 2.1–1.8 cal ka BP.

Evaporation from a shallow, saline lake in the Nebraska Sandhills: Energy balance drivers of seasonal and interannual variability

Despite potential evaporation rates in excess of the local precipitation, dry climates often support saline lakes through groundwater inputs of water and associated solutes. These groundwater-fed lakes are important indicators of environmental change, in part because their shallow water levels and salinity are very sensitive to weather and climatic variability. Some of this sensitivity arises from high rates of open-water evaporation, which is a dominant but poorly quantified process for saline lakes. This study used the Bowen ratio energy budget method to calculate open-water evaporation rates for Alkali Lake, a saline lake in the Nebraska Sandhills region (central United States), where numerous groundwater-fed lakes occupy the landscape. Evaporation rates were measured during the warm season (May – October) over three consecutive years (2007–2009) to gain insights into the climatic and limnological factors driving evaporation, as well as the partitioning of energy balance components at seasonal and interannual time scales. Results show a seasonal peak in evaporation rate in late June of 7.0mmday−1 (on average), with a maximum daily rate of 10.5mmday−1 and a 3-year mean July-September (JAS) rate of 5.1mmday−1, which greatly exceeds the long-term JAS precipitation rate of 1.3mmday−1. Seasonal variability in lake evaporation closely follows that of net radiation and lake surface temperature, with sensible heat flux and heat storage variations being relatively small, except in response to short-term, synoptic events. Interannual changes in the surface energy balance were weak, by comparison, although a 6-fold increase in mean lake level over the three years (0.05–0.30m) led to greater heat storage within the lake, an enhanced JAS lake-air temperature gradient, and greater sensible heat loss. These large variations in water level were also associated with large changes in absolute salinity (from 28 to 118gkg−1), with periods of high salinity characterized by reductions in mass transfer estimates of evaporation rate by up to 20%, depending on atmospheric conditions and absolute salinity. Energy balance estimates of evaporation, on the other hand, were found to be less sensitive to variations in salinity. These results provide regional insights for lakes in the Nebraska Sandhills region and implications for estimation of the energy and water balance of saline lakes in similar arid and semi-arid landscapes.

High-amplitude lake-level changes in tectonically active Lake Issyk-Kul (Kyrgyzstan) revealed by high-resolution seismic reflection data

Abstract. A total of 84 seismic profiles, mainly from the western and eastern deltas of Lake Issyk-Kul, were used to identify lake-level changes. Seven stratigraphic sequences were reconstructed, each containing a series of delta lobes that were formed during former lake-level stillstands or during slow lake-level increase or decrease. The lake level has experienced at least four cycles of stepwise rise and fall of 400 m or more. These fluctuations were mainly caused by past changes in the atmospheric circulation pattern. During periods of low lake levels, the Siberian High was likely to be strong, bringing dry air masses from the Mongolian steppe blocking the midlatitude Westerlies. During periods of high lake levels, the Siberian High must have been weaker or displaced, and the midlatitude Westerlies could bring moister air masses from the Mediterranean and North Atlantic regions.

Drivers of Change in a 7300-Year Holocene Diatom Record from the Hemi-Boreal Region of Ontario, Canada.

A Holocene lake sediment record spanning the past 7300 years from Wishart Lake in the Turkey Lakes Watershed in the Hemi-Boreal of central Ontario, Canada, was used to evaluate the potential drivers of long-term change in diatom assemblages at this site. An analysis of diatom assemblages found that benthic and epiphytic taxa dominated the mid-Holocene (7300–4000 cal yr BP), indicating shallow, oligotrophic, circum-neutral conditions, with macrophytes present. A significant shift in diatom assemblages towards more planktonic species (mainly Cyclotella sensu lato, but also several species of Aulacoseira, and Tabellaria flocculosa) occurred ~4000 cal yr BP. This change likely reflects an increase in lake level, coincident with the onset of a more strongly positive moisture balance following the drier climates of the middle Holocene, established by numerous regional paleoclimate records. Pollen-inferred regional changes in vegetation around 4000 yrs BP, including an increase in Betula and other mesic taxa, may have also promoted changes in diatom assemblages through watershed processes mediated by the chemistry of runoff. A more recent significant change in limnological conditions is marked by further increases in Cyclotella sensu lato beginning in the late 19th century, synchronous with the Ambrosia pollen rise and increases in sediment bulk density, signaling regional and local land clearance at the time of Euro-Canadian settlement (1880 AD). In contrast to the mid-Holocene increase in planktonic diatoms, the modern increase in Cyclotella sensu lato likely indicates a response to land use and vegetation change, and erosion from the watershed, rather than a further increase in water level. The results from Wishart Lake illustrate the close connection between paleoclimate change, regional vegetation, watershed processes, and diatom assemblages and also provides insight into the controls on abundance of Cyclotella sensu lato, a diatom taxonomic group which has shown significant increases and complex dynamics in the post-industrial era in lakes spanning temperate to Arctic regions.

Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake

The coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia, yet little is known on the impacts of the morphometry of lakes throughout their ontogeny. As Lake Chungará (Central Andean Altiplano, northern Chile) experienced long-term lake-level fluctuations that strongly modified its area:volume ratio, it is an ideal system for exploring the relative roles that long-term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity. In this paper, we review previous data on the percent contents of total organic carbon, total inorganic carbon, total nitrogen, total biogenic silica, isotopic composition of organic matter, carbonates, and diatom frustules, as well as data on the abundance of the chlorophycean Botryococcus braunii in this lake for the period 12,400–1300 cal yr BP. We also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14C and U/Th.Biosiliceous productivity in Lake Chungará was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation. Humid phases dated at approx. 12,400 to 10,000 and 9600 to 7400 cal yr BP coincide with periods of elevated productivity, whereas decreases in productivity were recorded during arid phases dated at approx. 10,000 to 9600 and 7400 to 3550 cal yr BP (Andean mid-Holocene Aridity Period). However, morphometry-related in–lake controls led to a lack of a linear response of productivity to precipitation variability. During the late Glacial to early Holocene, lowstands facilitated complete water column mixing, prompting episodic massive blooms of a large centric diatom, Cyclostephanos cf. andinus. Thus, moderate productivity could be maintained, regardless of aridity, by this phenomenon of morphometric eutrophy during the early history of the lake. The subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion, preventing complete overturn. Surpassing a certain depth threshold at approx. 8300 cal yr BP caused cessation of the morphometric eutrophy conditions associated with Cyclostephanos cf. andinus superblooms. After 7300 cal yr BP, the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability, with a lesser contribution of diatoms to the total primary productivity. Our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogeny.

Reconciling diverse lacustrine and terrestrial system response to penultimate deglacial warming in southern Europe

Unlike the most recent deglaciation, the regional expression of climate changes during the penultimate deglaciation remains understudied, even though it led into a period of excess warmth with estimates of global average temperature 1–2 °C, and sea level ∼6 m, above pre-industrial values. We present the first complete high-resolution southern European diatom record capturing the penultimate glacial-interglacial transition, from Lake Ioannina (northwest Greece). It forms part of a suite of proxies selected to assess the character and phase relationships of terrestrial and aquatic ecosystem response to rapid climate warming, and to resolve apparent conflicts in proxy evidence for regional paleohydrology. The diatom data suggest a complex penultimate deglaciation driven primarily by multiple oscillations in lake level, and provide firm evidence for the regional influence of abrupt changes in North Atlantic conditions. There is diachroneity in lake and terrestrial ecosystem response to warming at the onset of the last interglacial, with an abrupt increase in lake level occurring ∼2.7 k.y. prior to sustained forest expansion with peak precipitation. We identify the potentially important role of direct input of snow melt and glacial meltwater transfer to the subterranean karst system in response to warming, which would cause rising regional groundwater levels. This explanation, and the greater sensitivity of diatoms to subtle changes in temperature, reconciles the divergent lacustrine and terrestrial proxy evidence and highlights the sensitivity of lakes situated in mountainous karstic environments to past climate warming.

The paleohydrology of Sluice Pond, NE Massachusetts, and its regional significance

Seismic, pollen, stable isotope and lithologic stratigraphies of Sluice Pond, northeastern Massachusetts, were investigated to reconstruct local climate conditions from the latest Pleistocene to present. We present a new lake-level curve, constrained largely by acoustic reflectors and well-dated sediment cores from the deep basin and margin of the lake. Bulk δ34S data from the basin core provide valuable information regarding anoxia and water-column stratification. The lake-level history is corroborated with pollen-based, transfer-function-derived reconstructions of temperature and precipitation from the basin core. The lower stratigraphy reveals a time of cold/dry climate from ca. 11.7–8.2 ka BP (1 ka = 1,000 cal yr), with a minor lake-level increase centered at ca. 11.0 ka BP. An increase in regional temperature/moisture is apparent in sediments younger than 8.2 ka BP. A warm/dry climate is reconstructed from ca. 5.1–3.5 ka BP, concomitant with the well-established regional Tsuga (eastern hemlock) minimum. Sediments deposited since 3.5 ka BP reveal a general deepening of the pond and organic-rich conditions, with another minor dry episode from ca. 2.0–1.3 ka BP. Uppermost sediments record anthropogenic disturbance. The hydroclimate variability inferred from the Sluice Pond sediment record is consistent with previous reconstructions of lake level and vegetation in the southern portion of the northeastern US. It is not, however, consistent with reconstructions from locations farther north, many of which possess evidence of a dry period ca. 9.0–5.0 ka BP. The likely explanation for this discrepancy lies in air mass distribution associated with the position and amplitude of the circumpolar vortex throughout the Holocene. This new record of Holocene regional hydroclimate variability adds to the spatial coverage of existing reconstructions, and helps constrain forcings associated with such variability.

The influence of subaquatic springs in lacustrine sedimentation: Origin and paleoenvironmental significance of homogenites in karstic Lake Banyoles (NE Spain)

Banyoles (42°08′N, 2°45′E) is the largest and deepest lake of karstic–tectonic origin in the Iberian Peninsula. The lake comprises two basins and six sub-circularly shaped sub-basins fed by subaquatic springs. Periods of intense groundwater inflow in the deepest sub-basins lead to the fluidization and re-suspension of previously deposited sediments and subsequent settling forming homogenite deposits on the southern basin intermediate platforms. The multiproxy analysis of sediment cores combined with high resolution seismic stratigraphy (3.5kHz pinger and multi-frequency Chirp surveys) allows a precise reconstruction of depositional environments and related hydrological variability and groundwater inflow during the last ca. 7.6cal kyr BP. According to the age model based on 137Cs, 210Pb and AMS 14C dating, homogenite deposition occurred between 7.2 and 5.5cal kyr BP, stopped during the middle Holocene (5.5–2.8cal kyr BP) and greatly increased during the last two millennia with a total of 17 homogenite layers individually up to 75cm-thick. The onset of this unique sedimentation mode at ca. 3cal kyr BP coincides with an increase in lake level, evidenced by the onlapping of fine-grained, distal sediments over coarser massive, carbonate-rich, littoral deposits. A detailed, multidisciplinary study of the homogenites (sedimentology, physical properties, high-resolution elemental geochemistry, mineral composition, grain-size, organic matter content and SEM) combined with seismic stratigraphy demonstrates that the fluidization events triggering the formation of the homogenites were caused by higher and more intense local groundwater inflow, related to increased rainfall during the Late Holocene and likely intensified by land use changes during the last millennium.

Late Holocene hydrology inferred from lacustrine sediments of Laguna Cháltel (southeastern Argentina)

Hydrological changes that occurred during the last 4700years have been reconstructed using multi-proxy analyses of sediment cores from the volcanic crater lake of Laguna Cháltel (50°S, 71°W). The chronology is based on AMS 14C age modeling constrained by paleomagnetic secular variations. Chemical and physical properties of the lake water together with results of lake-water surface-temperature monitoring, as well as sediment characteristics reveal conspicuous features archived as different sedimentary carbonate phases and morphologies which are attributed to lake-level changes.Sedimentological, geochemical and biological proxies together suggest the development from an initial playa lake-phase towards a system with progressively rising lake level. In detail, proxies indicate the existence of an ephemeral lake since 4700cal BP until a glauberite-bearing carbonate crust formed around 4040cal BP which probably is associated to the globally recognized 4.2ka event. This crust is interpreted as a desiccation event terminating the ephemeral lake phase. Following this desiccation a shift towards conditions with a positive hydrological balance of Laguna Cháltel occurs, which leads to the development of a saline lake with ooid formation between 4040 and 3200cal BP. Further lake-level increase with initially high minerogenic input until 2700cal BP resulted in a lake freshening which allowed the preservation of diatoms. Sigmoidal and star shaped carbonate crystals occurred until 1720cal BP indicating a syn- or post-depositional formation of ikaite. Anoxic conditions and increased deposition of clay and sand through fluvial and eolian input are interpreted as a further lake-level rise and/or a prolonged winter ice cover culminating during the Little Ice Age. The highest lake level was probably reached at that time and since then dropped to its present day height.Previous studies have shown that the southern hemisphere westerly winds (SWW) exert an oppositional control on hydrological regimes at the eastern and the western sides of the Patagonian Andes. At Laguna Cháltel SWW forcing is changing evaporation rates by varying wind intensities, air temperatures and lake ice coverages as well as by precipitation rates (easterly vs. westerly sources of moisture). Our data suggests that the lake-level history of Laguna Cháltel reflects changes in the SWW during the last 4.7ka on the eastern side of the Andes. However, the elevated location of Laguna Cháltel on an 800m high plateau at the leeward side of the Andes potentially leads to a local overprint of the SWW influence on the hydrological balance.

Evidence of Low-Magnitude Continued Reservoir-Induced Seismicity Associated with the Pertusillo Artificial Lake (Southern Italy)

The most common observations of reservoir‐induced seismicity (RIS) by filling artificial lakes are generally associated with the initial impoundment of the lake or the lake level increase above a previous maximum. Rarely, RIS persists for many years without a decrease in frequency or magnitude; if this occurs, it is called “protracted” or “continued” seismicity. Pertusillo artificial lake in high Agri Valley (southern Italy) is a small reservoir with a water column that fluctuates yearly by about 10–15 m (on average), corresponding to a pressure perturbation at the bottom of the lake of 0.10–0.15 MPa. Although the reservoir was filled in 1963, the microearthquake activity still occurring around the lake allows the categorization of such RIS as continued seismicity. We collected all microearthquakes ( M L≤2.7) recorded near the reservoir by two different seismic networks from January 2005 to June 2012 and analyzed their frequency–magnitude distribution, which showed a b value ( b =1.40) much higher than that expected for the investigated area. Even though the spatial seismicity pattern shows two distinct clusters to the northeast and southwest of the lake, we found that only the southwest seismicity is significantly correlated with the water level. The findings suggest that the physical driving mechanism is the 1D pore fluid pressure diffusion along the northeast–southwest fault zones, connecting the reservoir to the southern termination of the Monti della Maddalena fault system, with an average hydraulic diffusivity of ∼7.8 m2/s. Online Material: Figures of magnitude comparisons between catalogs, temporal occurrence of events, rainfall versus number of earthquakes, and number of events versus water level, and animated 3D views of seismicity and reservoir.

Late Glacial to Holocene climate change and human impact in the Mediterranean: The last ca. 17 ka diatom record of Lake Prespa (Macedonia/Albania/Greece)

Lake Prespa (Macedonia/Albania/Greece) occupies an important location between Mediterranean and central European climate zones. Although previous multi-proxy research on the Late Glacial to Holocene sequence, core Co1215 (320cm; ca. 17cal ka BP to present), has demonstrated its great value as an archive of Quaternary palaeoclimate data, some uncertainty remains in the interpretation of climate change. With the exception of oxygen stable isotope data, previous palaeolimnological interpretation has relied largely on proxies for productivity. Here, existing interpretation is strengthened by the addition of diatom data. Results demonstrate that shifts in diatom assemblage composition are driven primarily by lake-level changes and thus permit more confident interpretation of shifts in moisture availability over time, while corroborating previous interpretation of catchment- and climate-induced productivity shifts. An inferred cold, arid shallow lake phase between ca. 17.1 and 15.7cal ka BP is not only followed by a high-productivity phase from ca. 15.7cal ka BP with Late Glacial warming, but also is the first evidence for a gradual increase in lake level, in line with other regional records. Clear evidence for a Younger Dryas climate reversal between ca. 13.1 and 12.3cal ka BP is followed by an unusually gradual transition to the Holocene and deeper, oligotrophic–mesotrophic lake conditions are reached by ca. 11.0cal ka BP. In contrast to the arid episode from ca. 10.0 to 8.0ka inferred from positive 18δOcalcite values, rapid diatom-inferred lake-level increase after the start of the Holocene suggests high moisture availability, in line with palynological evidence, but with only very subtle evidence for the impact of an 8.2ka cold event. The maintenance of high lake levels until 1.9cal ka BP, and the peak of inferred humidity from ca. 7.9 to 6.0cal ka BP, matches the oxygen stable isotope profile and confirms that the latter is driven primarily by evaporative concentration rather than reflecting regional shifts in precipitation sources over time. During the Late Holocene progressive eutrophication is inferred between 1.9 and present. Two shallow phases at ca. 1.0cal ka BP and at ca. 100years ago probably represent an aridity response which is added to increase human impact in the catchment. Overall, the study is important in confirming previous tentative inferences that Late Glacial to Holocene moisture availability has strong affinity with other sites in the Eastern Mediterranean. It also tracks the pattern of North Atlantic forcing.

Late Glacial and Early Holocene lake level fluctuations in NE Poland tracked by macro-fossil, pollen and diatom records

Late Glacial and Early Holocene vegetation history and lake level fluctuations in NE Poland were described based on high-resolution plant macrofossils analyses and records of pollen, diatoms, and radiocarbon dates. The development of Lake Kojle-Perty began in the Allerød (GI-1c). Cooling during the Younger Dryas (GS-1) led to the development of communities of heliophyte herbaceous plants. Palaeobotanical and lithostratigraphical records demonstrate that abrupt climate changes at approximately 11,600 and 9450 cal. BP resulted in distinct changes in the vegetation and water level of Lake Kojle-Perty. Climate warming in the Younger Dryas–Holocene transition (11,600 cal. BP) caused the development of the terrestrial vegetation dominated by cold deciduous forest (Betula), and appearance of thermophylious aquatic plants: Typha latifolia, Najas marina, and Ceratophyllum demersum. A gradual decrease in the lake level since 11,200 cal. BP is evident from the appearance of plants from shallow lake environments (Potamogeton natans and Hippuris vulgaris). The low water levels since 10,700 cal. BP resulting from increased temperature and evaporation caused the development of peat on limnic sediments. The dry and warm climatic phase with lowest lake level in the lakes of NE Poland were coeval with the expansion of temperate deciduous forests (Corylus and Ulmus) that commenced at approximately 10,500 cal. BP. A distinctive increase in lake levels at approximately 9450 cal. BP is suggested by the development of rush plants such as Cladium mariscus and aquatic plants such as Najas marina, Chara sp., and Nuphar lutea in the shallow parts of Lake Kojle-Perty. The increased lake levels correspond with the expansion of Alnus glutinosa in North-East (NE) Poland. Our reconstructions of the vegetation development and lake level changes align with results from other studies in the region.

Investigation of the dramatic changes in lake level of the Bosten Lake in northwestern China

Bosten Lake, located in the arid region of northwest China, is the largest inland freshwater lake in China. Water resources in Bosten Lake are of great importance for the regional drinking water supply, agricultural irrigation, and economic development of Xinjiang province. In this study, the dynamics of the lake level in Bosten Lake were investigated from 1956 to 2010. We found that the lake level experienced three different periods of change due to the combined influences of climate variation and human activities. Generally, the lake level has shown a significant downward trend since the first observation started in 1956 and dropped to its lowest level in 1987. Thereafter, the lake level presented a continuous upward trend and rose to its highest value in 2002. Then, the level decreased dramatically from 2002 to 2010. A water balance model and the climate elasticity method were used to estimate the reasons for the lake level changes of Bosten Lake. The results showed that an increase in lake evaporation led to the continuous decrease in lake level from 1958 to 1987. Then, human-controlled lake outflow and increasing lake inflow together led to the increase in lake level from 1988 to 2002. During 2003 to 2010, the emergency project of transferring water to Tarim River led to the increase in lake outflow, while the lake inflow obviously decreased because of a decrease in precipitation. These factors resulted in a sharp decrease in the lake level from 2003 to 2010. The changes in lake level indicate changes in available water resources from Bosten Lake. This reason for the analysis of the change in lake level in this study is to support the water resources management of Bosten Lake.

Water level changes of high altitude lakes in Himalaya–Karakoram from ICESat altimetry

Himalaya–Karakoram (H–K) region hosts large number of high altitude lakes but are poorly gauged by in-situ water level monitoring method due to tough terrain conditions and poor accessibility. After the campaigns of ICESat during 2003–2009, now it is possible to achieve lake levels at decimetre accuracy. Therefore, in present study, high altitude lake levels were observed using ICESat/GLAS altimetry in H–K between 2003 and 2009 to generate baseline information. The study reveals that out of 13 lakes, 10 lakes show increasing trend of water levels at different rate (mean rate 0.173 m/y) whereas three lakes unveiled decreasing trend (mean rate −0.056 m/y). Out of five freshwater lakes, four lakes show an increasing trend of their level (mean rate 0.084 m/y) whereas comparatively six salt lakes (out of seven salt lakes) exhibited ~3 times higher mean rate of lake level increase (0.233 m/y). These observed lake level rise can be attributed to the increased melt runoffs (i.e., seasonal snow and glacier melts) owing to the enhanced mean annual and seasonal air temperature during past decade in north-western (NW) Himalaya. Further, varied behaviours of lake level rises in inter- and intra-basins suggest that the local climatic fluctuations play prominent role along with regional and global climate in complex geographical system of NW Himalaya.

A multivariate model for flood forecasting of lake levels

A new multivariate model for flood forecasting of lake levels has been developed and applied to Lake Wakatipu and Lake Wanaka in the South Island of New Zealand. The model is based on the concept of the projection theorem to derive the optimum projection of the increase in lake levels on the driving factors for this increase. The driving factors that have been considered in this research are observed rainfall at sites in the catchment area or close to it, stream flows from rivers draining this rainfall in the region and outflows from the lakes. About 22 years of observed rainfall, river flows, lake outflows and lake levels have been investigated to select 23 significant events for model calibration and 2 events for model validation. A lag of 10 hours (Lake Wakatipu) and a lag of 7 hours (Lake Wanaka) between cumulative lake rise and cumulative rainfalls have been verified to improve the modelling process and have been utilized in the multivariate model. The analysis of the fitted parameters for the multivariate model has resulted in the removal of some sites from the model due to their insignificant contribution or their being on odd with the realistic physical hydrological process. The projection theorem for orthonormal sets in the Hilbert space has been applied to the statistical characteristics of the data to estimate the optimum parameters of the multivariate model. Two multivariate models have been developed in this research. The first multivariate model is for the long-term forecast of the rise of lake levels based on the forecasted rainfalls at selected rainfall sites in the catchment. The second multivariate model was derived based on the physical process of the hydrologic budget of a catchment and can be used for forecasted lake rise during the flood event based on rainfalls and stream flows gauged in the catchment areas of the lakes, in addition to the lake outflows. Keywords Lake level, flood forecast, flood modelling, Hilburt Space, lagged-correlations, projection theorem, rainfall-runoff, regression analysis Language: en

Monitoring changes of snow cover, lake and vegetation phenology in Nam Co Lake Basin (Tibetan Plateau) using remote SENSING (2000–2009)

The changes of environmental factors such as snow cover, vegetation and hydrologic regime of lakes can reflect ecosystem responses to changing climate. A series of satellite imagery-based environmental data archives including variations in snow cover, vegetation phenology and lake level were mapped in the Nam Co Lake Basin for the period 2000–2009. Results of the synthesis indicate that throughout this period, the average annual snow cover was 19.87% of the total basin, and there is an obvious relation between the elevation and a clear decreasing southeast–northwest trend in snow-cover persistence. Snow mainly happens from October to May. The multi-year mean water storage of Nam Co Lake is 86.40×109m3, with a lake level increase of approximately 2.06m during the study period. Vegetation phenology showed obvious variation with advanced start of season (SOS) and slightly extended duration of season (DOS). The mean DOS for the Nam Co Lake Basin was 154days from 2000 to 2009. Affected by air temperature, the SOS dates coincided with snowmelt. The seasonal-variability of climate factors was also studied. The satellite-derived continuous and multiple datasets offer the advantage of monitoring the temporal and spatial trends of each of these metrics and mapping extensive, remote in mountainous areas with no in-situ data such as represented by the Tibetan Plateau.

Ecosystem responses to climate and disturbances in western central Mexico during the late Pleistocene and Holocene

Central Mexico is a complex area with late Quaternary volcanic activity, climatic diversity and a long history of human occupation. Pollen, microcharcoal and magnetic susceptibility analyses of two sedimentary sequences from Lake Zirahuen in western central Mexico spanning the last 17,000years provide evidence of a highly dynamic environment. During the late glacial Pinus forest developed around the lake, indicating cold and dry conditions. During the last deglaciation climatic amelioration was recorded at 13.5ka, driving a strong and rapid change in vegetation composition and increase in lake levels. From the latest Pleistocene to early Holocene a hiatus, probably related to an erosive event, is recognized in the northern sequence. The central sequence spans the entire Holocene and reveals three periods of important ecological changes during the early Holocene. A first episode between 9.5 and 9.0ka with a decrease in pine forest seems to have been associated with summer insolation increases. A second peak of forest change at 8.2ka and was probably associated with the cold oscillation documented in the North Atlantic. A third abrupt change was evident from 7.5 to 7.1ka with an anomalous plant community related to wetter Holocene climates and possible to a volcanic event. An episode of dry conditions was recorded from 4.5 to 4.2ka, which was related to an increase in ENSO activity. Human influence over the landscape was evident from 3.5ka to the present. The Zirahuen records offer a complex history of a landscape characterized by short and long term vegetation changes associated with factors ranging from global climate to local disturbances.

Vegetation, fire, climate and human disturbance history in the southwestern Mediterranean area during the late Holocene

Detailed pollen, charcoal, isotope and magnetic susceptibility data from an alpine lake sediment core from Sierra Nevada, southern Spain record changes in vegetation, fire history and lake sedimentation since ca. 4100calyr BP. The proxies studied record an arid period from ca. 3800 to 3100calyr BP characterized by more xerophytic vegetation and lower lake levels. A humid period is recorded between ca. 3100 and 1850calyr BP, which occurred in two steps: (1) an increase in evergreen Quercus between 3100 and 2500calyr BP, indicating milder conditions than previously and (2) an increase in deciduous Quercus and higher lake levels, between ca. 2500 and 1850calyr BP, indicating a further increase in humidity and reduction in seasonal contrast. Humid maxima occurred during the Roman Humid Period, previously identified in other studies in the Mediterranean region. Intensified fire activity at this time could be related to an increase in fuel load and/or in human disturbance. An arid period subsequently occurred between 1850 and 650calyr BP, though a decrease in Quercus and an increase in xerophytes. The alternation of persistent North Atlantic Oscillation modes probably played an important role in controlling these humid–arid cycles.