Lake Level Fluctuations Research Articles

Solar activity dominated the multidecadal- to centennial-scale humidity oscillations during the Little Ice Age in arid central Asia

Climatic instability has major impacts on water resources and catastrophic effects on fragile ecosystems in arid Central Asia (ACA). Short-term (decadal to centennial) climate fluctuations over the last millennium can help predict whether future climate instability and the frequency of extreme climate events will increase. Research has revealed higher moisture variability during the Little Ice Age (LIA) than during the Medieval Warm Period (MWP). However, the age control quality and temporal resolution of the proxy records that are used make it difficult to characterize the specific unstable climate fluctuations on decadal to centennial scales. Here, we present a well‐dated high‐resolution ostracod record from a remote alpine lake (Dalongchi Lake) in the central Tianshan Mountains, northwestern China, ACA, which has an average ∼ 3–4-year resolution and provides a record of inferred lake level fluctuations over the past millennium. The abundance of deep-water adapted Fabaeformiscandona gyirongensis was generally higher in the LIA and lower in the MWP and Current Warm Period (CWP), which confirmed the associations of warm–dry and cold–wet conditions in ACA. Notably, our ostracod records captured several distinct and dramatic secondary lake level fluctuations during the LIA. The abundance of F. gyirongensis peaked in four intervals at 1380–1460, 1540–1580, 1640–1720 and 1800–1940 CE, indicating sharp lake level increases, while the abundance decreased sharply in the three intervals of 1460–1540, 1580–1640 and 1720–1800 CE, indicating significant lake level decreases. There was a strong, inverse relationship between the lake level and the total solar irradiance (TSI) on the multidecadal to centennial scale, and the spectral analysis and wavelet coherence results suggest the presence of Gleissberg cycles. We propose that the century Gleissberg solar cycle directly affected regional humidity changes through temperature and evaporation forcing. Our findings suggest that solar activity probably plays an important role in determining future hydroclimatic changes in ACA.

Variations of organic matter content and type within the sequence stratigraphic framework of the lacustrine deep-water Dongyuemiao formation, Sichuan Basin, Western China

The organic matter (OM) enrichment patterns and mechanisms in lacustrine deep-water shale successions were controlled by complex geological and biological processes, rather than any single factor. The integration of sedimentology, petrography, geochemistry, and sequence stratigraphy in the study of shale successions is vital to the development of robust paleoenvironmental interpretations and OM enrichment model. Based on a systematic sedimentological, petrographic, and geochemical analysis of three continuous cored wells of the Lower Jurassic Dongyuemiao Formation, Sichuan Basin, within a sequence stratigraphic framework, this study reports the complex geological responses in detrital input, sedimentation rate, benthic redox conditions, primary water column productivity, and OM enrichment pattern that caused by lake-level fluctuation. The results indicate that none of the proxies for detrital input, redox conditions, or productivity exhibit a significant correlation with total organic carbon (TOC) content in sediments. The OM enrichment was regulated by a complex interplay of these three factors, which is a function of relative lake-level fluctuation. In general, detrital input was decreased during lake-level transgression; whereas increased during lake-level regression. Reducing conditions and primary productivity were generally enhanced during lake-level transgression; whereas diminished during lake-level regression. Coupled relationships between lake-level fluctuation, bulk TOC content, and OM types were observed. The bulk TOC content and liptinite proportion in sediments increased gradually during the lake-level transgression. In contrast, the bulk TOC content and liptinite proportion in sediments gradually decreased during the lake-level regression. This general principle applies to both second-order and third-order lake-level fluctuation. Our study demonstrates that the development of a reliable OM enrichment model in lacustrine shale successions requires a comprehensive sequence stratigraphic framework.

2000 years of lake-level fluctuations and human adaptation around China's largest freshwater lake

The human society is facing growing flood risks due to the rapidly-changing global climate. Understanding how early human coped with flooding will shed light on the increase of contemporary social resilience to projected intensified extreme climate change. However, assessment of such ancient human response to hydrological changes remains difficult due to the paucity of records for flood risk coupled with ancient human activities. Here, we present a two-millennium continuous reconstruction of water level changes for Poyang Lake, China's largest freshwater body, using microbial tetraethers extracted from a well-dated sedimentary core. The rising trend of lake water level over the past 2000 years indicates an increase in flood risks for this fertile region that has long been populated by ancient human settlements. A comparison with spatial-temporal distribution of ancient cities and towns in the lake basin reveals that, during the first millennium, human settlements passively retreated outwards and upwards away from the lake to minimize flood risk due to the rising lake water. However, a reversal pattern occurred at ∼1000 CE, witnessing human settlements to moving closer to lakeshore during the second millennium despite of the high water table. The strategic shift, accompanied by a booming economy in southern China during the Song Dynasty, was possibly facilitated by technology innovations, such as intensified water conservancy construction and enhanced shipbuilding, in and around the lake basin. Such an enhanced social resilience in responding to flood risks as early as 1000 years ago remains as a common practice today although the unprecedented scale of anthropogenic climate change in the near future may post additional and unexpected challenges.

Responses of sedimentary proxy indicators to lake-level fluctuations on the central Tibetan Plateau since the last deglaciation

Lake sediments are valuable archives to investigate past changes in climate and environment on various timescales. Closed-basin lakes can be regarded as precipitation gauges, which are ideal for studying past climate changes. However, the climatic implications of various sedimentary proxy indicators from closed-basin lakes are often confounded by lake-level fluctuations, which are affected by lake watershed processes, besides climate change. Here, we present records of multi-proxy indicators since the last deglaciation at Lake Cuoe, on the central Tibetan Plateau, which was once connected with Selin Co and became separated during the middle Holocene, as evidenced by a series of paleo-shorelines. The sedimentary proxies are categorized into three groups based on their origins, with differences in their environmental significance. The proxy indicators derived from within-lake processes effectively revealed past lake-level fluctuations, including the Ca/(Al, Ti, Fe) ratio, Fe/Mn ratio, carbonate minerals, stable carbon and oxygen isotopes of authigenic carbonate, and the percentage of aquatic inputs (Paq) derived from n-alkanoic acids. These proxy indicators showed obvious changes at ∼7–6 ka, when Lake Cuoe became hydrologically separated from Selin Co. The stable oxygen isotope record of Lake Cuoe, apparently modulated by lake-level changes, differs significantly from that from Selin Co. The proxy indicators reflecting watershed processes, including terrigenous elements, Rb/Sr ratio, grain size, and the chain length proxy based on n-alkanoic acids, directly reflected changes in the regional climate and environment. The proxy indicators derived from both allochthonous and authigenic sources, including total organic carbon (TOC) and total nitrogen (TN), reflected the effects of climate change as well as lake-level fluctuations. Overall, our results suggest that great caution should be applied in interpreting proxy records of climatic and environmental changes from closed-basin lakes on the Tibetan Plateau. They also highlight the potential of using sedimentary proxies to reconstruct continuous records of lake-level fluctuations.

Assessment of lake-level fluctuation as an indicator of fire activity in boreal Canada

Fuel moisture content is a highly variable property that dictates the ignition and combustion potentials of wildfire fuels. The Canadian Fire Weather Index (FWI) System—a subset of the established Canadian Forest Fire Danger Rating System—relies solely on weather observations to track fuel moisture and compute indices of fire potential. Ancillary environmental measures, such as lake levels in non-regulated lake systems, may integrate climatic and landscape factors that better reflect environmental moisture deficits and thereby complement the FWI System. Accordingly, we investigated whether inter-annual variation in lake levels has potential to serve as an indicator of regional fire activity using a quasi-binomial regression approach. This study combines annual measurements of fire activity, lake level, and other climatic variables from the Boreal Shield and Boreal Plain ecozones of Canada from 1980 to 2019 to determine whether variation in regional area burned can be explained by lake-level fluctuation, and whether this explanatory power differs by ecozone. Results indicated that lake-level fluctuation is a significant predictor of regional area burned for many lakes (28–48%). It often performs as well as or better than traditional fire-weather metrics (such as temperature and precipitation), and this relationship is stronger on the Boreal Shield compared to the Boreal Plain. Lake-level fluctuation provides information on fuel availability unaccounted for by traditional fire-weather metrics, suggesting that this variable could be added to the suite of environmental indicators of regional fire activity in Canada.

Unconventional Petroleum Sedimentology: A Key to Understanding Unconventional Hydrocarbon Accumulation

The commercial exploitation of unconventional petroleum resources (e.g., shale oil/gas and tight oil/gas) has drastically changed the global energy structure within the past two decades. Sweet-spot intervals (areas), the most prolific unconventional hydrocarbon resources, generally consist of extraordinarily high organic matter (EHOM) deposits or closely associated sandstones/carbonate rocks. The formation of sweet-spot intervals (areas) is fundamentally controlled by their depositional and subsequent diagenetic settings, which result from the coupled sedimentation of global or regional geological events, such as tectonic activity, sea level (lake level) fluctuations, climate change, bottom water anoxia, volcanic activity, biotic mass extinction or radiation, and gravity flows during a certain geological period. Black shales with EHOM content and their associated high-quality reservoir rocks deposited by the coupling of major geological events provide not only a prerequisite for massive hydrocarbon generation but also abundant hydrocarbon storage space. The Ordovician–Silurian Wufeng–Longmaxi shale of the Sichuan Basin, Devonian Marcellus shale of the Appalachian Basin, Devonian–Carboniferous Bakken Formation of the Williston Basin, and Triassic Yanchang Formation of the Ordos Basin are four typical unconventional hydrocarbon systems selected as case studies herein. In each case, the formation of sweet-spot intervals for unconventional hydrocarbon resources was controlled by the coupled sedimentation of different global or regional geological events, collectively resulting in a favorable environment for the production, preservation, and accumulation of organic matter, as well as for the generation, migration, accumulation, and exploitation of hydrocarbons. Unconventional petroleum sedimentology, which focuses on coupled sedimentation during dramatic environmental changes driven by major geological events, is key to improve the understanding of the formation and distribution of sweet-spot intervals (areas) in unconventional petroleum systems.

Holocene millennial lake-level fluctuations of Lake Nam Co in Tibet using OSL dating of shorelines

In the past decades, most Tibetan lakes experienced large-scale rises in response to current global warming, conflicting with the limited amplitudes and gradual fluctuation in shoreline-based lake-levels that occurred over the Holocene. The discrepancy is a critical issue in understanding the regional response to global climate. In this study, we reconstructed the Holocene lake-level variations based on high-resolution luminescence ages of thirty-seven samples from fourteen shorelines of Nam Co in interior Tibet. The findings of this work concluded that Nam Co witnessed millennial large-scale lake-level fluctuations with periodical outflows during 11.9–8.3 ka and a broad decrease thereafter. Seven highstand events with ages of ca. 11.9–11.0, 8.3, 6.7, 5.1, 4.2–3.4, 2.4 and 1.1 ka were identified, consistent with the North Atlantic warmer intervals indicating a quick response to global climatic events. In particular, the dramatic lake-level decline during the transition from the Medieval Warm Period to Little Ice Age demonstrated its potential rapid and sensitive response to millennial climatic changes. Our high-resolution OSL dates enabled detection of millennial-scale highstand events. Based on comparison with other global and regional paleoclimatic records, we suggested that Holocene highstands were mainly attributed to the strengthened monsoonal precipitation and increased glacier meltwater that amplifies lake-level fluctuations of glacier-fed lakes, and that paleoclimate and paleo-lake-level reconstruction by core proxies during lake overflow stages could be problematic.

Holocene hydrological history of a Tibetan glacier-fed lake Taro Co in response to climate change

Lake hydrological fluctuations on the Tibetan Plateau (TP) are highly sensitive to global climate change, which can be reconstructed directly by dating paleoshorelines representing past lake-levels. In this study, we reconstructed the Holocene lake-level history of Taro Co lake system (Taro Co, Zabuye Salt lake and Lagkor Co) on the southwestern TP, based on seventeen optically stimulated luminescence ages of paleoshorelines. The results showed that lake-levels were at the broad highstands of ∼40 m above modern lake-level (amll) from 11.6 to 7.0 ka, during which the three lakes were integrated and formed a mega paleolake. After 7.0 ka, the mega paleolake fluctuantly contracted, and Lagkor Co and Zabuye Salt Lake probably became separated at ∼6.9 and ∼3.4 ka, respectively. Seven rapid millennial low lake stands were identified at 11.3–11.2 ka (14 m amll), 9.9–8.7 ka (< 28 m amll), 8.2–7.9 ka (6 m amll), ∼6.9 ka (5 m amll), ∼3.0 ka (8 m amll), 2.1–1.1 ka (< 6 m amll) and ∼0.4 ka (6 m amll). The large magnitude lake-level declines indicated that they reflected effective moisture in response to global millennial-scale climate events, e.g., the 11.1, 10.3, 9.4, 8.2 and 7.2 ka events in the early and middle Holocene, and the 4.2 ka and Little Ice Age events in the late Holocene. Holocene lake-level fluctuations were simultaneous with that of other lakes on the south-central TP. Comparisons with other paleoclimatic records suggested that the Holocene hydrological history of Taro Co was mainly dominated by both monsoonal precipitation and glacial meltwater supply, as well as evaporation and basin topography. Differences in meltwater supply probably led to different lake-level change histories for endorheic lakes in the lake system. In the future warming and wetting, Tibetan endorheic lakes would keep expanding, hence Taro Co lake system would be formed again through hydrological connections.

Sequence stratigraphic control on the variations of organic matter in Eocene lacustrine shales within the Dongying Depression, Eastern China

• A third-order sequence is identified in Eocene shales in the Dongying Depression. • The abundance, type and preservation of organic matter (OM) are intimately related to the sequence development. • Sequence development affects OM accumulation, resulting in differential OM distribution within the Eocene sequence stratigraphic framework. Eocene organic-rich shales in the Dongying Depression, Eastern China, are well preserved and ideal for examining stratigraphic controls on the variations of organic matter (OM). This study concerns the Eocene sedimentary succession in the Dongying Depression and recognizes a third-order sequence based on the stacking patterns of lithofacies, mineralogical changes, and geochemical proxies. The total organic carbon content, Rock-Eval parameters S1 and S2 values, and the chloroform bitumen “A” content are low in the lowstand systems tracts, reaching their maxima within the transgressive systems tracts and gradually decreasing within the highstand systems tracts. The paleoclimate index and ratios of quartz/feldspar, Sr/Ca, TiO 2 /Al 2 O 3 , Cr/Al, Ni/V, Th/U, Zn/Al, and Ni/Al indicate that OM accumulation was influenced by primary productivity, sedimentation rate (SR), and redox conditions, which are intimately related to the sequence development under the influence of tectonics, climate, sediment supply, and relative lake-level fluctuations. The OM distribution is related to the sequence stratigraphy in three ways: (1) climate and relative lake-level fluctuations affected the primary productivity and OM production via algae blooms and terrestrial OM input; (2) relative lake-level fluctuations and sediment supply were influenced by tectonics and climate, causing a change in SR and OM deposition; and (3) relative lake-level fluctuations under different climatic conditions affected the development of anoxic bottom-water favoring OM preservation.

Interaction Model of Rainfall, Lake, and Ground Waters

This research intends to build an interaction model between rainfall, lake water, and ground water. The location of research is in the Sentani Lake where is placed in the Jayapura Regency-Papua-Indonesia. Sentani Lake is a lake in the Sentani Watershed. Sentani Lake is located between Jayapura City and Jayapura Regency-Papua Province. The area of Sentani Lake is 9,630 ha with the depth is 75 m over the sea. In the northern of this lake are the Cyclops Mountains (Dafonsero) that separate the Sentani Lake and the Pacific Sea. The Sentani Lake functions as the track of transportation, food source, drinking water source, and tourism. Based on the bathymetry analysis result which is obtained from the River Region Institution of Papua, the Sentani Lake has the smallest elevation from 13.05 mdpl until 71.5 mdpl with a maximum storage capacity of 4.8 milliard m3. The methodology of this research consists of 1) To set and to simulate of Hydrology Model; 2) Analysis of water balance; 3) To set up the hydro-geology model; 4) To simulate the integration of rainfall-lake water- ground water. The interaction model between rainfall and lake waters is built based on the relation between the outlet discharge and the rainfall at 10 points and then is validated at the 5 points of observation data. This model produces the formulation as follows: inflow to the lake from rainfall = 0.067 x rainfall – 5. The interaction model between the lake water level and the ground water level is built based on the value of ground water-level fluctuation and the lake water level at the 10 points, and it is validated at the 6 points of observation data. This model produces the following formulation: fluctuation of ground water level = 0.1529 x fluctuation of lake water level. By combining the ground water and run-off in the Sentani Watershed, it is known as follows: inflow total of lake = base-flow + 0.067 x rainfall – 5.

Paleosalinity and lake level fluctuations of the 3rd Member of Paleogene Shahejie Formation, Chezhen Sag, Bohai Bay Basin

Paleosalinity and lake level fluctuations of the 3rd Member of Paleogene Shahejie Formation, Chezhen Sag, Bohai Bay Basin

Relative lake level reconstructions for glacial Lake Agassiz spanning the Herman to Campbell levels

Lake Agassiz was the largest North American pro-glacial lake during the last deglacial period, and the routing of the overflow is hypothesized to have affected thermohaline circulation and in turn, global climate. Here an existing glacial isostatic adjustment model is applied to Campbell beach strandline data to synthesize and correlate published radiocarbon- and OSL-dated lake level indicators in an effort to produce relative lake-level curves and a drainage history. The curves highlight where the water level history of Lake Agassiz is well understood, and where additional work is necessary. Many OSL-dated strandlines between 14.5 and 13.2 ka record meltwater routing through a southern outlet to the Gulf of Mexico during this time, and that lake levels fell due to sill incision and glacial isostatic adjustment (GIA). Oxygen isotope records from marine sediments tracking continental runoff, plus deglacial isochrones, suggest eastern outlets to the Atlantic Ocean opened at around 13.2 ka, near the onset of the Younger Dryas (YD) stadial, but the evidence within the basin is scant. At some point during the YD, Lake Agassiz overflow shifted to a northwestern outlet into the Arctic Ocean, and the reconstructed lake levels track lake-level rise driven by uplift of the northwestern outlet, which eventually transferred water to the southern outlet to create the Campbell level of Lake Agassiz. The apparent shallow water depth (∼4 m) of overflow at the southern outlet relative to earlier phases suggests multiple active outlets at this time (northwestern, southern, and perhaps eastern). Oxygen isotope records from the Gulf of Mexico indicate overflow via the southern outlet occurred in two brief phases, likely explained by an oscillating ice margin that regulated overflow. Considerable work remains to assess the timing of deglaciation to understand when Lake Agassiz first drained east and north. Lacking are details of eastern drainage and any dated stratigraphic record of likely lake level fluctuations during the Younger Dryas.

Characteristics and Sources of DOM in Lake Sediments Under Different Inundation Environments

The characteristics and sources of DOM in sediments are significantly affected by fluctuations in lake water levels. However, the impact of spatial differences on water levels remain unclear. Here, 36 sediment samples were collected from the flood passage and coastal beach of East Dongting Lake. The differences in the composition and source of DOM in sediments under perennial inundation and seasonal inundation were studied using UV-visible absorbance (UV-Vis) and fluorescent excitation-emission matrix (EEM)-parallel factor analysis (PARAFAC). Three fluorescent components of DOM in the sediment were identified. The relative abundance of protein-like components was as high as (72.95±8.94)%, including tryptophan (C2) and tyrosine (C3). However, the humic-like component (C1) abundance was (27.05±8.94)%. Compared with that in perennial inundation, DOM in seasonal inundation had a higher and lower relative abundance of protein-like components and humic-like components, respectively. Further, the aromatic and hydrophobic components were higher in perennial inundation, showing a spatial pattern of the middle>entrance>outlet of the lake, which was more conducive to the migration of pollutants. The high FI (1.93) and BIX (0.91) and low HIX (1.57) indicated that the DOM in sediments had the mixed characteristics of being mainly endogenic and relatively weakly terrigenous. This was mainly influenced by human input and sediment characteristics. The direct effect of sewage discharge was intensified by sediment exposure in the seasonal inundation zone. Additionally, the contents of clay and total nitrogen (TN) were significantly positively correlated with FI, indicating that high nutrients and clay in sediments enhanced the endogenous input of DOM (FI>1.9). The perennial inundation zone was influenced by external runoff input. At the same time, the pH and C/N were significantly positively correlated with HIX and C1, indicating that DOM in the sediments had higher terrigenic characteristics (HIX=1.38±0.57) than those in the seasonal inundation zone owing to the alkaline environment (pH>7.5) and runoff input. The results above revealed the relevant theories of the response of DOM in sediment to water quality and pollution in the process of hydrology and human activities and provide a scientific basis for the prevention and control of sediment pollution in lakes.

Microbially induced sedimentary structures and the preservation of vertebrate tracks on the Colorado River delta in Lake Powell, Hite, Utah

Microbially induced sedimentary structures (MISS) increase the preservation potential of vertebrate and invertebrate ichnofossils. The Colorado River forms a delta in Lake Powell at Hite, Utah, and the deltaic shoreline provides a natural laboratory to examine the development of MISS and their influence on vertebrate track preservation. Two types of MISS were identified: pustular and blister. Pustular MISS occur in proximity to the June 2020 high water line. The pustular morphology is characterized by mm-scale small mounds, or pimple-like shapes. Field emission scanning electron microscopy (FESEM) examination identified preserved filamentous cyanobacteria intertwined with fine silt- and clay-sized sediment and well-preserved freshwater diatoms. Branta canadensis (Canada goose) tracks are well developed and they vary from single tridactyl tracks to trampled horizons. Blister MISS, in contrast to pustular MISS, are present in lower elevations, forming in deeper water, greater than 0.5 m. Blisters are mm- to cm-scale irregular mounds that consist of arching mats that are detached from the underlying sediment creating a pore space. Through time the blister mat mounds are destroyed by fragmentation due to desiccation combined with wind processes. FESEM and energy-dispersive spectroscopy system (EDS) analyses indicate the presence of filamentous cyanobacteria on the exterior and palisade Bacillus-type bacteria are in the interior of the blister arch, and gypsum crystals within the mat arch. Freshwater diatoms are present in both mat types. A single human track and multiple trackways of Canis latrans (coyote) were identified on the blister mats. Weakly impressed Canada goose tracks are present. Tracks cross cutting or modifying the pustular MISS have preserved MISS surface textures except in the heavily trampled areas, whereas tracks linked to the blister mat typically do not have reserved mat texture, and usually contain fragmented mat within the impression. Because of fluctuating lake levels and desiccation, these track types had a limited temporal window where they may be produced when moisture conditions permitted MISS development, about two months. Any vertebrates through the area out of the “track window” were not recorded in sediment and mat modification. Tracks imprinted on pustular MISS in lacustrine environments will have a high preservation potential if there are annual fluctuations in lake levels.

Paleoenvironmental reconstructions along the southern margin of Eocene Lake Uinta during a period of climatic variability

The stratigraphy preserved in the lacustrine Eocene Green River Formation suggests a variety of depositional environments that were subject to pulses of sediment and lake level fluctuations in the Uinta Basin. This paper defines 13 facies within six facies associations observed in outcrop and core from the middle to upper Green River Formation in Gate Canyon, south-central Uinta Basin, and Willow Creek/Indian Canyon, western Uinta Basin, along the margin of the ancient lake system. The facies associations are defined by dominant lithology, relative siliciclastic sediment supply, relative slope, and lake zonation, and encompass a suite of facies revealing distinct environments across a relatively small region (~35 km apart). In the lower interval, a shift from a high energy, steeper ramp setting in the east, to a lower energy, shallower ramp setting to the west suggests a transition off the main depositional axis. Correlatable siliciclastic and carbonate dominated packages reflect the impact of early Eocene hyperthermal events that followed the Paleocene-Eocene Thermal Maxi- mum, and the diverse facies present at the two study areas suggest variable responses to these climatic events. In the overlying stratigraphy, the facies are consistent in both regions and consist of organic rich and poor carbonate mudstones and siltstones. The interval thickens slightly from east to west, and the overlying Horse Bench Sandstone transitions from a wave-dominated shoreface sequence to a river-dominated deltaic sequence, indicating an overall shift in the lake depocenter towards the west. This study offers a unique glimpse at the paleoenvironmental changes along the margin of a continental interior lake system during a time of climatic variability. It also highlights the need to use multiple depositional models to accurately characterize marginal deposits in different regions of large internally-drained lake systems which, unlike typical marine depositional models, are more sensitive to basin geometry, size, and sediment fairways.

Improving coastal resilience planning with respect to long-term water level fluctuations by examining decadal coastal profile behavior at sandy, harbor filet beaches along Lake Michigan in the Great Lakes of North America

Resilient planning for coastal hazards requires an understanding of both short-term and long-term coastal change dynamics. Numerous studies have been conducted throughout the Great Lakes of North America on processes and responses associated with short-term coastal changes, such as storms and seasonal fluctuations in lake level; however, few datasets exist that can capture long-term coastal morphodynamics in this region. Lack of data and knowledge creates a barrier for accurately modeling future coastal change, which underpins proactive coastal management. This is particularly problematic at sites adjacent to coastal infrastructure, such as those near harbors. To address this, we utilize a 32-year record of coastal profile change from several sites along the Lake Michigan shoreline of Michigan to examine profile evolution in response to changing lake levels and human disturbance. These data reveal that coastal sites without shoreline armoring can recover from erosive high lake level phases if lake level remains low for an extended period. However, if sites are armored, or if future climate conditions result in more frequent or more extreme lake level fluctuations, full recovery of the coastal profile is unlikely. Managers and decisionmakers can utilize this information to evaluate their site conditions and proactively plan for future coastal changes.

Luminescence dating of shoreline sediments indicates a late deglacial lake-level rise of Selin Co on the central Tibetan Plateau

The palaeo-shorelines around the lakes on the Tibetan Plateau can be used to reconstruct water level variations, which serve as sensitive indicators of hydroclimate change. Extensive studies have been carried out to constrain the Holocene lake level fluctuations by dating shorelines with a variety of methods (e.g., luminescence, 14C, 10Be and U–Th series). In comparison, the timing of the lake level variations during the last glacial and subsequent deglaciation periods has been rarely studied. The driving factors of such changes, therefore, remain elusive. In this study, we performed a detailed luminescence dating investigation on six samples taken from a nearshore sedimentary outcrop in the south of Selin Co basin. The post-IR IRSL signals measured at 225 °C (pIRIR225) on sand-sized K-feldspar grains demonstrated a generally good behavior and yielded reliable chronologies, while the optically stimulated luminescence (OSL) signals of quartz showed systematical age underestimation, which was attributed to anomalous fading. Six pIRIR225 ages ranging from 15 to 10 ka suggested that the lake level of Selin Co during the last deglaciation reached up to 40–45 m high above the modern lake level. In view of the regional precipitation and temperature proxy records, we consider that the glacier meltwater supply has likely been the primary contributor to the lake highstands during the last deglaciation.

Sub-fossil chironomids as indicators of hydrological changes in the shallow and high-altitude lake Shen Co, Tibetan Plateau, over the past two centuries

Understanding climate and monsoonal dynamics on the Tibetan Plateau is crucial, as recent hydrological changes, evidenced by rising lake levels, will be accelerated by current global warming and may alter aquatic habitats and species inventories. This study combines chironomid assemblages with sedimentological, mineralogical and geochemical data of a short sediment core (37.5 cm) from the high-altitude (&gt; 4,733 m asl), saline (9 g L-1) and shallow (~5 m water depth) Shen Co, located in the southern part of the central Tibetan Plateau. The predominantly littoral, species-poor (10 chironomid morphotypes) chironomid assemblages are dominated by salt-tolerant taxa, that are highly sensitive to lake level fluctuations and macrophyte vegetation dynamics, making them ideally suited for tracking lake level changes over time. Results indicate a period (from ca. 1830 to 1921 CE) of drier conditions with low runoff and high evaporation rates in the Shen Co catchment, as indicated by a dominance of low-Mg calcite and dolomite and increased Ca/Fe and Sr/Rb ratios. This resulted in a decline in lake levels, an increase in salinity and the periodic occurrence of desiccation events at the sampling site. The first chironomid morphotype to appear after the dry period is Acricotopus indet. morphotype incurvatus, which indicate still low (&lt;2 m) but rising lake levels after 1921 CE due to increasing runoff and a lower evaporation/precipitation ratio, as reflected by coarser grain size, higher quartz content and increased TN, TOC and Al/Si ratios. A replacement of A. indet. morphotype incurvatus by Procladius is observed as lake level rise continued after 1950 CE. The highest lake level is proposed for the period since 2006 CE. From 1955 to 1960 CE and from 2011 to 2018 CE, the presence of the phytophilic taxon Psectrocladius sordidellus-type supported abundant macrophyte growth. These changes are consistent with climate reconstructions from the northern and central Tibetan Plateau, indicating warmer and wetter climate conditions since the beginning of the 20th century, which have led to an increase in lake level in a number of Tibetan lakes. Our study specifically highlights 1920 and 1950 as years with enhanced precipitation. This can be attributed to the strong, with overlapping multidecadal cycles of Westerlies and monsoon systems. This study demonstrates the significance of studying small, shallow lakes, as they frequently contain aquatic communities that respond more rapidly to the changes in the lake system. In addition, this study expands our understanding of the ecology of Tibetan chironomid morphotypes, highlighting this group’s potential as paleolimnological proxies for investigating past environmental and climatic changes.

Long-Term Changes in Relationship between Water Level and Precipitation in Lake Yamanaka

Lake water levels fluctuate due to both natural and anthropogenic influences. Climate change can alter precipitation, driving fluctuations in lake water levels. Extreme fluctuations can cause flooding, water shortages, and changes in lake water quality and ecosystems, as well as affecting fisheries and tourism. Despite the need to predict future water-level rises, especially in the context of climate change, long-term hydrological studies are scarce. Here, we analyzed 93 years of data from 1928 to 2020 to identify changes in the relationship between water level and precipitation in Lake Yamanaka, Japan. We found that the six-day maximum rise in water level for the same six-day maximum precipitation was significantly greater in the later period than in the earlier period; the difference increased with increasing precipitation. Particularly large increases in precipitation were sometimes caused by a single event or by multiple events occurring in succession.

OSL Dating of Paleo-Shorelines at Dagze Co, Central Tibetan Plateau

Well-preserved paleo-shoreline systems suggest lake shrinkage occurred in a vast region of the Tibetan Plateau, indicating dramatic paleo-environmental changes that linked closely to variations in Asian monsoon precipitation, glacial meltwater, and evaporation. The elevation and chronology of these shoreline features can be used to reconstruct lake level fluctuation history and regional paleo-climate. Here, we report optically stimulated luminescence (OSL) dating of 14 sediment samples from three of seven paleo-shorelines at south of Dagze Co, central Tibetan Plateau, using coarse-grained quartz and K-feldspar. Two fine grain silt samples were also measured. The results suggest the following: 1) The highest paleo-shoreline for Dagze Co has an elevation around 4,525 m (+55 m above modern lake). Its age is estimated to be 9.1 ± 0.5 to 9.6 ± 0.6 ka, suggesting a relative humid condition in the early Holocene. 2) After that, the lake level dropped ∼20 m and remained relatively stable (+35 m) from ∼8 to 5 ka, implying a dry condition with reduced runoff. Lake level further declined for ∼40 m since about 5 ka. 3) The general trend of shrinkage for Dagze Co broadly matches studies from adjacent lakes, suggesting a common pattern of lake’s evolution on the south/central plateau in the late Quaternary. The long-term decreasing trend of Asian monsoon precipitation should be the main reason.