High Lake Levels Research Articles

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.

Perspectives on Great Lakes coastal management: A case study of the Point Pelee foreland, Canada

Coastal systems on the Laurentian Great Lakes are highly affected by meter scale variability in water levels that occur across a range of temporal scales, from hourly wind set-up and seiches to inter-annual highs and lows driven by longer-term patterns of precipitation and evaporation. High lake level periods are often associated with increased coastal erosion and flooding, stress on sensitive wetland ecosystems, and damage to infrastructure. During the late 2010s, water levels on the Great Lakes neared or exceeded record highs, initiating a renewed interest in coastal management across the region. The objective of this study was to inform and engage regional experts and local interest groups and to examine their perspectives on the important processes, coastal management solutions, and applied research needed for the conservation of the Point Pelee (PP) foreland in Lake Erie. A virtual conference, the Point Pelee ‘Hackathon,’ used a crowd-sourced approach to problem solving where participants were presented ‘the sum of the discourse,’ or the current state of knowledge on coastal processes and management affecting the region. The conference covered a range of topics through invited speaker presentations, followed by individual surveys and moderated group discussions. Q-methodology surveys incorporated concepts informed by the sum of the discourse and identified statistically significant sources of agreement and disagreement on management challenges and solutions among ‘like-minded’ individuals. Common viewpoints identified harbours & jetties and sediment nourishment projects as an important cause of erosion and mitigation strategy, whereas highly opposed viewpoints were held on the importance of sediment supply and adopting a ‘do-nothing’ approach for coastal management. Emergent and more nuanced viewpoints were also found within group discussions, highlighting important considerations that can be used to advance the discourse on proposed management solutions. The results of this study can be used to guide the development of a regional coastal management strategy, and a similar methodology can be used to inform and engage stakeholders and examine perspectives on a range of issues affecting the world's marine and lacustrine coasts.

Lessons from a lakebed: unpicking hydrological change and early human landscape use in the Makgadikgadi basin, Botswana

The intersection of archaeological material with the landscape is investigated using OSL dating of landforms associated with Middle Stone Age (MSA) archaeology in the Makgadikgadi basin, Botswana. In this study, MSA archaeological sites on the Makgadikgadi pan floor date to two dry periods in the basin during the late Quaternary. Site formation at one site occurred during dry, or seasonally dry conditions that followed a period of high lake levels between 128 ± 18 ka and 81 ± 6 ka. The site was buried by sediments from a subsequent period of high lake levels dating to between 72 ± 5 ka and 57 ± 8 ka. At other investigated sites, the archaeological material was most likely deposited during a second dry period sometime after this. Overlying dunes are much younger (late Holocene) than the late Pleistocene lakebed sediments associated with the archaeological sites. Rapid burial of the archaeological sites by clayey sands has resulted in limited disturbance and weathering of archaeological material which appears to have only been exposed very recently, perhaps in the last 350 years when conditions have been particularly dry and susceptible to deflation. The spatial patterning of both sediment accumulation and deflation strongly influences archaeological visibility both within and around the Makgadikgadi basin.

Stable isotopes reveal the lake shrinkage and groundwater recharge to lakes in the Badain Jaran Desert, NW China

The evolutionary stages of the different lakes in the Badain Jaran Desert (BJD) are unknown, and there is a need to elucidate the hydrological implications of the hydrodynamic environmental differences among these lakes. In this study, a stable isotope mass balance model incorporating the effect of evaporation from the lake basins was developed, and the model was used to calculate the remaining water fraction f of 94 lakes relative to the high lake levels in the Middle Holocene, as well as the groundwater recharge rate χG to the lakes. The results show that only 10–20 % (average of 15 %) of the original lake water remains. One-third of the lakes have become terminal lakes, and half are still gradually drying. If the climatic conditions remain unchanged, the water levels of these lakes will drop by an average of 11 mm per year. χG has a certain degree of correlation with elevation, suggesting the likely presence of more water recharge sources for the north lakes, which may include the Beida Mountains and the Zongnai Mountains. The total annual groundwater recharge to all of the lakes in the BJD is 1.63 × 107 m3/yr. The δ18O evolution model of a typical lake (Cherigele Lake) reveals that humidity h and atmospheric vapor δa18O play the leading role in the evolution of the lake δ18O, suggesting that this model may serve as a tool for estimating lake evaporation and for reconstructing the paleoclimate. The findings of this study provide support for analyzing the evolution and future trends of lakes in arid desert areas, as well as deeper insights into the water cycle in the BJD.

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 (> 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 (<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.

Late Holocene paleoenvironmental changes inferred from multi-proxy studies of the Kholasht-Kouh Lake sediments in the Gilan mountains, northern Iran

Past vegetation and environmental changes and the role of climate as well as human activities are of major interest. The Hyrcanian region with a high number of endemic species has a poorly known paleoenvironmental history, especially the western region of northern Iran. This study aims to investigate a radiocarbon-dated sediment core of the Kholasht-Kouh Lake (KHL) for the recorded between ca. 510 and 1180 cal yr BP. KHL is located at 2000 m elevation and surrounded with steppe vegetation above the present-day forest line. Multi-proxy analyses including pollen, non-pollen palynomorphs, charcoal, loss on ignition, and X-ray fluorescence were applied to reconstruct past environmental dynamics. The results indicate the dominance of herbaceous vegetation (mainly Poaceae, Artemisia, and Amaranthaceae) around the lake during the whole record, except for the period between 1010 and 740 cal yr BP. During this period of the Medieval Climatic Anomaly (1000–700 cal yr BP) mixed forest increased, consisting mainly of Quercus, Fagus, Carpinus, and Juniperus. The K, Ti and Si elements (as indicators for increased in detrital inputs) suggest relatively humid condition between 1180 and 1010 cal yr BP. Furthermore, higher lake levels may indicate from low values of the Mn/Ti, Ca/Ti and Sr/Ti ratios. After 1010 until 740 cal yr BP the highest value of the Si/Fe ratio, suggested warmest period of the record. While the lowest value of the Si/Fe ratio, in line with the reduction of other elements and ratios, between 740 till 510 cal yr BP represented cold and dry period. Humans were present around the study area at least since beginning of the record, but did not played an important role impacting the vegetation.

Remote Sensing Application for Landslide Detection, Monitoring along Eastern Lake Michigan (Miami Park, MI)

We assessed the nature and spatial and temporal patterns of deformation over the Miami Park bluffs on the eastern margin of Lake Michigan and investigated the factors controlling its observed deformation. Our approach involved the following steps: (1) extracting bluff deformation rates (velocities along the line of sight of the satellite) using a stack of Sentinel-1A radar imagery in ascending acquisition geometry acquired between 2017 and 2021 and applying the Intermittent Small Baseline Subset (ISBAS) InSAR time series analysis method; (2) generating high-resolution (5 cm) elevation models and orthophotos from temporal unmanned aerial vehicle (UAV) surveys acquired in 2017, 2019, and 2021; and (3) comparing the temporal variations in mass wasting events to other relevant datasets including the ISBAS-based bluff deformation time series, lake level (LL) variations, and local glacial stratigraphy. We identified areas witnessing high line-of-sight (LOS) deformation rates (up to −21 mm/year) along the bluff from the ISBAS analysis and seasonal deformation patterns associated with freeze-thaw cycles, suggesting a causal effect. The acceleration of slope failures detected from field and UAV acquisitions correlated with high LLs and intensified onshore wave energy in 2020. The adopted methodology successfully predicts landslides caused by freezes and thaws of the slope face by identifying prolonged slow deformation preceding slope failures, but it does not predict the catastrophic landslides preceded by short-lived LOS deformation related to LL rise.

Hydrochemical characteristics and paleoclimate changes recorded from Sugan Lake on the northern boundary of Tibetan Plateau since mid-Holocene

The Qaidam Basin, located in the northern Tibetan Plateau, is one of the three largest interior basins in China. It is surrounded by Kunlun, Altun and Qilian mountains with arid climate, sparsely vegetated landscape and a fragile ecological environment. Investigations on Holocene climate variations in this northern part of the Tibetan Plateau are essential for a better understanding of regional climate dynamics. A mid-Holocene sediment record from Sugan Lake in the Qaidam Basin was investigated using the grain size, mineral, total organic matter content (TOC), C:N ratio (C/N) and element analyses. A depth-age model since ∼ 7750 cal a BP had been made based on 8 AMS 14C data after taking out 2200 years carbon reservoir effect. SO42--type water and sparse terrestrial vegetation with considerable evaporation caused by high temperature during the Holocene Megathermal Maximum were recorded from ca. 7750 to 5800 cal a BP. From 5800 cal a BP, hydrochemical characteristics shifted dramatically to the Cl-type, while aeolian activities intensified concurrently. A higher lake level with low evaporation/precipitation ratio as the result of cool and wet conditions were inferred between 5800 and 3580 cal a BP when the EASM weakened and westerly jet intensified. Colder and drier conditions were recorded probably due to the strengthening of the mid-latitude westerly circulation after 3580 cal a BP. However, the EASM probably prevailed shortly at 3580 ∼ 3000 cal a BP and 1800 ∼ 810 cal a BP, respectively. Cold/dry, cold/wet and cold/dry Little Ice Age fluctuation climate conditions and aeolian activities with risen lake level and diluted water were inferred from 580 to 280 cal a BP.

Imprints of the Little Ice Age and the severe earthquake of AD 2001 on the aquatic ecosystem of a tropical maar lake in El Salvador

Using a 530-year sediment record from the maar Lake Apastepeque, El Salvador, and based on diverse geochemical and biological (cladocerans, chironomids, diatoms, ostracods, testate amoebae) indicators, we estimated climatic and environmental alterations during the Little Ice Age (LIA) and reconstructed the recent history of the lake. Results demonstrate relatively humid conditions in the mid-elevations (500 m a.s.l.) of El Salvador during most parts of the LIA, resulting in high lake levels. Contrarily, the first part of the LIA was characterized by drier climates comparable to studies from Mexico and Belize, which correlated this phase with the Spörer minimum. Regional comparison with palaeorecords from the northern Neotropics reveals a high heterogeneity in local expressions of the LIA in Central America, likely connected to the high topographic heterogeneity of the region. Since the beginning of the 20th century, Lake Apastepeque has experienced enhanced human impact expressed as increased nutrient supply. The most recent period was characterized by significant environmental disturbance, which we relate to an upper-crustal earthquake, one of the strongest over the last 500 years, that affected the region on 13th February 2001 (Mw = 6.6, epicentre at 10 km depth, 30 km from the lake). The release of toxic bottom components such as hydrogen sulphide and high turbidity and turbulence of water caused major species turnover in the lake ecosystem, resulting in a massive fish kill and colonization by large cladocerans. Modern sediments still show slightly altered biota communities compared to pre-earthquake assemblages, indicating that the ecosystem has still not fully recovered.

Holocene climate background for lake evolution in the Badain Jaran Desert of northwestern China revealed by proxies from calcareous root tubes

AbstractIt has been unclear whether Holocene lake evolution in the Badain Jaran Desert of northwestern China, an area in which lakes are mainly recharged by groundwater, responded to climate change. In this study, we analyzed the Mg/Ca ratio and phytolith assemblages from 10 Holocene calcareous root tube samples from the desert to reconstruct changes in effective moisture and mean annual precipitation (MAP) at the millennial scale during the Holocene and to explore the factors affecting lake evolution. Our results revealed that the effective moisture at 7000–5000 cal yr BP was higher than that of 5000–2000 cal yr BP. Similarly, the MAP was higher at 7000–5000 cal yr BP (175 ± 37 to 205 ± 37 mm) than at 5000–2000 cal yr BP (145 ± 37 to 165 ± 39 mm). The expansion of the lakes during the Early Holocene would have resulted from the input of groundwater from the meltwater in the recharge area. High lake levels in the Middle Holocene corresponded to increased monsoonal precipitation and groundwater recharge. The gradual decline of lake levels in the Late Holocene indicated a relatively arid climate with decreased monsoonal precipitation and groundwater recharge.

Paleoenvironmental Changes Since the Late Pleistocene Revealed by Ostracodes Record in Changmu Co., Western Tibet

A 4.9-m profile (BG-1) in Changmu Co., western Tibet, provides a continuous climate record from the Late Pleistocene to mid-Holocene on the basis of ostracode assemblages and shell trace elements. The results show six distinct climate change zones from 23.4 to 4.9 ka BP based on U-Th dating. The climate remained extremely cold until 13 ka BP because of the influence of the Last Glacial Maximum, which was indicated by the rare ostracodes occurring in this period. After that, the temperature rose gradually and the paleolake (Changmu Co.) enlarged. The ostracode assemblage during this period had high abundance and diversity, although the dominance of cold-water species and low Mg/Ca ratios indicate that the climate was still cold. More runoff water from a relatively warm climate entering into the lake, suggested by the increased U/Ca and Mn/Ca, led to a high lake level of 13–10.5 ka BP; this trend was also verified by the decreasing Sr/Ca values. The climate changed from humid to drought between 10.5 and 7.9 ka BP, which was inferred from the decreased abundance of ostracodes; however, there was a short humid period from 9.5 to 9.2 ka BP suggested by increased U/Ca and Mn/Ca ratios. A gradual transition to a humid environment began at 7.9 ka BP and ended at 5.3 ka BP. After this period, an extremely arid climate occurred after rising temperature and increasing evaporation, indicated by sharply increased Mg/Ca and Sr/Ca ratios. Eventually, the Changmu Co. paleolake shrank and dried up at some time after 4.9 ka BP. The changes in paleoclimate in Changmu Co. since the Late Pleistocene corresponded well to changes that occurred in the Westerlies-dominated Central Asia, suggesting that the climate in this region was mainly controlled by Westerlies circulation.

Turbidity and Estimated Phosphorus Retention in a Reconnected Lake Erie Coastal Wetland

Nearly all of the wetlands in the coastal zone of Lake Erie have been degraded or destroyed since the 1860s, and most of those that remain are separated from their watersheds by earthen dikes. Hydrologic isolation of these wetlands disrupts ecosystem benefits typical to Great Lakes coastal wetlands, particularly the ability to trap sediments and retain nutrients when inundated by runoff and lake water. High-frequency measurements of turbidity and discharge were taken in 2013 and 2014 to observe turbidity and water flow dynamics to estimate total phosphorus flux of a hydrologically reconnected diked wetland pool in the Crane Creek-Lake Erie wetland complex. Modeled estimates suggest the reconnected pool retained 8% of the total phosphorus loading in 2013 and 10% in 2014, which included short periods of phosphorus export to Lake Erie. Water flowing out of the wetland generally had lower turbidity than inflowing water, but flux in and out of the pool varied seasonally and was linked to changes in lake-levels, seiche dynamics, and weather conditions. More frequent storms, higher winds, and stronger seiches in the spring and fall created turbidity patterns that suggest more phosphorus retention than in summer or winter. Estimates suggest that phosphorus was released during the summer when higher lake levels and the absence of frequent storms, larger short-term seiche oscillations, and potentially soil oxygen availability were driving flux dynamics. This study demonstrated that reestablishing lake hydrology through reconnection of wetland pools can reduce loading and alter timing of delivery of total phosphorus to Lake Erie.

Remotely sensed time series of rapid terrace formation: Laguna del Viedma valley (Patagonia)

The Patagonian Andes were affected by a range of geophysical drivers of landscape incision during the Last Glacial Interglacial Transition and Early Holocene. Deciphering drivers of river system response during this period is complex, and magnitudes and timescales of landscape change are poorly constrained. Herein, a remotely sensed time series of modern terrace formation is investigated from the Laguna del Viedma valley as a modern analogue of Late Quaternary landscape evolution in Patagonia. The aim of the research was to constrain the timing of terrace formation following lake level fall of the Laguna del Viedma over a 35 year period from 1985-2019. The objectives were to: 1) use satellite imagery from 1985-2019 to document glacier and lake changes in the study area; 2) map landforms of the Laguna del Viedma valley; and 3) analyse terrace elevations. In total seven terrace surfaces were distinguished, with the oldest four pre-dating the ALOS PALSAR DEM (February 2000) used. Landform evidence shows the highest, and vegetated, T1 terrace surface (+40-75 m) grades to the highest lake level and was likely the elevation of the valley floor during Holocene neoglacials. Viedma glacier recession then led to a phase of lake regressions/transgressions with an overall trend of lake level fall. The DEM shows ~20 m incision from the 1985 floodplain level (T3) to the T4 level floodplain by 2000. This constrains a minimum rate of incision of 1.33 m/yr, however, the satellite time series demonstrates rapid T3 terrace formation, with evidence for mass movements contributing to lateral terrace erosion by 1986. The implications of the data are discussed within the context of the Late Quaternary palaeohydrology of Patagonia where lake level falls of 10s to 100s of metres occurred within many large river systems of the Patagonian Andes from 42-52⁰ S. The data herein demonstrate that base level falls from sudden lake drainage events were likely a major driver of rapid landscape change in Patagonia during deglaciation.

Lake level changes of Nam Co since 25 ka as revealed by OSL dating of paleo-shorelines

Many lakes in the Tibetan Plateau (TP) experienced dramatic lake level changes in the late Quaternary, as suggested by well-preserved paleo-shorelines up to ∼200 m above present lake levels. These relic shorelines provide direct geomorphic record to reconstruct past lake level fluctuation history and water volume changes, linked closely to variations in paleo-climatic controls including Asian monsoon, westerlies and glacial meltwater. In this study, 27 near-shore sediment samples from three of eight paleo-shorelines at north of Nam Co were dated by Optically Stimulated Luminescence (OSL) technique, using coarse grains of quartz and potassium feldspar. Our results indicate that: 1) S1 is the highest/most developed shoreline (+26 m). Sediment from upper part of S1 has a consistent age of ∼25 ka (nine samples from 3 gullies), suggesting a high lake level of Nam Co occurred around 25 ka. An overflow point west of Nam Co has a close elevation to that of S1 and thus limits the presence of higher lake levels; 2) sediment profile from the slightly lower S2 (+22 m) contains two parts, silty sand (6.9–8.9 ka) at the bottom and shoreline deposits atop (∼2.3 ka), suggesting Nam Co maintained a relative high lake level in the early Holocene and such lake level occurred again at about 3.0–2.0 ka; 3) In contrast to the swift variations of monsoon precipitation and glacial meltwater in the late Quaternary, water level of Nam Co remained relatively stable during the period from ∼25 ka to about early Holocene (from +26 m to +22 m), implying a continuous outflowing stage and lake infill constantly exceeds evaporation; 4) S5 (+11 m) has an age of 0.7–1.4 ka. Nam Co showed a much accelerated pace of shrinkage since about 2.0 ka in the late Holocene in roughly two steps: it dropped from +22 m to +11 m from ∼2.0 ka to 1.4 ka, and subsequently dropped another 11 m after 0.7 ka.

Geotechnical Issues in Decommissioning Surface Lignite Mines—The Case of Amyntaion Mine in Greece

Recent changes in the fossil-fuel energy sector require coal mining industries to plan for the future, including developing procedures for decommissioning and closure associated with mines. In surface coal mining, the geotechnical issues of decommissioning include the long-term stability of the pit slopes, particularly as the pit is gradually filled with water. This paper investigates such slope stability issues, with emphasis on the conditions prevailing in the Amyntaion surface lignite mine, in Western Macedonia, Greece. Analytical and numerical methods have been developed and used to estimate the temporal evolution of the overall safety factor, as the water level in the pit rises, creating a lake. It is shown that until the water level in the lake reaches a critical depth of approximately 15–35% of the final equilibrium condition, the safety factor against the overall slope instability decreases slightly (by about 3% in the case study, and up to 5–10% in other conditions) compared to its value at the end of exploitation. At higher lake levels, the safety factor increases significantly, as the beneficial effect of the lake water pressure acting on the slope overcomes the adverse effect of pore water pressure rise inside the slope. In typical mines, the critical water depth is achieved within a few years, since the surface area of the pit is smaller at deeper levels; thus, more favorable slope stability conditions are usually reinstated a few years after mine closure, while the small reduction in safety during the initial stages after closure is inconsequential. The paper investigates the parameters influencing the magnitude of the small reduction in the short-term safety factor and produces normalized graphs of the evolution of the safety factor as the lake water level rises. The results of the analyses can be used in preliminary closure studies of surface coal mines.

Monitoring the environmental evolution and its relationship with anthropogenic activities using magnetic and geochemical proxies on Lake Melincué sediments

Two sediment cores, collected from the center of the Lake Melincué (Santa Fe, Argentina), were analyzed using rock magnetic results, element composition, Total Organic and Inorganic Carbon (TOC and TIC) and Total Nitrogen (TN) to reconstruct the environmental variations in the last three centuries, associated with climatic changes and/or human activities. 210Pb dating, chronostratigraphic markers, and paleomagnetic results were used to create the age model of the cores. Rock magnetic analyses suggest that (titano)magnetite and a low proportion of hematite are the main magnetic phases. In addition, geochemical results compared with rock magnetic analysis indicate the possible presence of diagenetic dissolution. Four well-differentiated environmental phases were found with variations from cold to more humid and warmer environmental conditions. Unit 0 from 1750 CE to 1783 CE with a cold environment and high lake level, Unit 1 from 1783 CE to 1878 CE with continuing cold environmental conditions but a low lake level, showing the end of the Little Ice Age (LIA) toward the top, Unit 2 from 1878 CE to 1874 CE with a wetter environment and Unit 3 from 1974 CE to 2016 CE with wet and warm conditions and a high lake level.

Extent of Sedge-Grass Meadow in a Lake Michigan Drowned River Mouth Wetland Dictated by Topography and Lake Level

Water-level fluctuations are critical in maintaining diversity of plant communities in Great Lakes wetlands. Sedge-grass meadows are especially sensitive to such fluctuations. We conducted vegetation sampling in a sedge-grass dominated Lake Michigan drowned river mouth wetland in 1995, 2002, and 2010 following high lake levels in 1986 and 1997. We also conducted photointerpretation studies in 16 years dating back to 1965 to include responses to high lake levels in 1952 and 1974. Topographic data were collected to assess their influence on areal extent of sedge-grass meadow. Dominant species in short emergent and submersed/floating plant communities changed with water availability from 1995 to extreme low lake levels in 2002 and 2010. Sedge-grass meadow was dominated by Calamagrostis canadensis and Carex stricta in all years sampled, but Importance Values differed among years partly due to sampling in newly exposed areas. Photointerpretation studies showed a significant relation between percent of wetland in sedge-grass meadow and summer lake level, as well as the number of years since an extreme high lake level. From the topographic map created, we calculated the cumulative area above each 0.2-m contour to determine the percent of wetland dewatered in select years following extreme high lake levels. When compared with percent sedge-grass meadow in those years, relative changes in both predicted land surface and sedge-grass meadow demonstrated that accuracy of lake level as a predictor of area of sedge-grass meadow is dependent on topography. Our results regarding relations of plant-community response to hydrology are applicable to other Great Lakes wetlands.

Environmental changes since 14 ka BP in the southernmost Kuril islands (North-Western Pacific) and regional correlation of events

• New data on climatic changes at the late Pleistocene-Holocene boundary for Kurils. • Climate fluctuations and volcanic ash-falls were mail drivers in lake-mire evolution. • The lake level was highest during warmer and humid climate of the Allerød. • Younger Dryas cooling in the Kuril Islands was less distinct than on the continent. • Pollen record vegetation changes on the land bridge at Late Glacial–early Holocene. Despite considerable progress in understanding Late Pleistocene and Holocene palaeoenvironmental changes worldwide, there are still very few such data for the Far East, and Kuril islands, in particular. Here, the sea level rise during the Late Glacial–Holocene transition was accompanied by a loss of the land connectivity culminating into the development of isolated islands. The ecosystems evolution and importance of isolation for vegetation dynamics on islands are still insufficiently understood. We investigated a unique natural record of environmental change since 14 ka has been recently discovered in lake–mire complex on Kunashir Island. The sediments include 12 tephra layers from Kunashir and Hokkaido volcanoes. The lake level was highest during warmer and humid climate of the Allerød. Diatom assemblages indicated the higher lake level between 12 730–12 160 cal yr BP. The first half of Younger Dryas was characterized by heavy snowfalls. Cooling attributed to the Younger Dryas in the Southern Kurils was less distinct than on the continent. The pollen assemblages recorded changes in vegetation on the land bridge. At the end of the Pleistocene large areas were occupied by birch forests and shrub pine. The broadleaf species first appeared at the end of Allerød. Starting from the Pleistocene-Holocene transition and during the early Holocene , the role of conifers sharply increased. In the middle Holocene the proportion of broadleaf trees in forests increased. Coniferous forests became abundant during the Little Ice Age. Short-tern climatic fluctuations correlate well with regional pattern, particularly with fluctuations of the moisture supply.

Foredune and Beach Dynamics on the Southern Shores of Lake Michigan during Recent High Water Levels

From 18 January 2013 (175.16 m a.s.l.) to 8 September 2020 (177.82 m a.s.l.), Lake Michigan experienced its fastest and highest rise (2.67 m) since 1860, when instrumental measurements began. Extensive foredunes developed since the last high lake levels began eroding in 1997 at fast rates. This study focuses on coastal morphodynamics along the 800 m coast within the central Indiana Dunes State Park on Lake Michigan’s southern shores during this time. Severe foredune erosion, in terms of total horizontal dune loss and total volume of eroded sand, occurred unevenly over the three-year period, both temporally, during a single storm, a season, a year, or three years, and spatially, in the eastern, central, and western study areas. Late autumn storms accounted for most foredune erosion in 2018 and 2019, when foredune scarps retreated up to 4 and 9 m, respectively. Erosion was highest in the updrift eastern study area, where about 8 m3/m of sand was removed in 2018 and about 19 m3/m of sand was removed in 2019. The lack of shelf ice along the shore, rising lake levels, and convective storms that triggered meteotsunamis changed the foredune erosion pattern in 2020. Erosion became most vigorous in the downdrift central (13 m scarp retreat) and western (11 m scarp retreat) study areas. The average volume of eroded sand (21.5 m3/m) was more than double that of 2019 (8 m3/m), and almost quadruple the 2018 volume (5.5 m3/m). After foredune erosion events, the beach rapidly recovered and maintained its width as the shoreline migrated landward. On many occasions following these severe erosion events the dry portion of the beach aggraded and absorbed significant sand amounts removed from the foredunes. The remaining sand was transferred to the surf zone, where it changed the sand bar morphology and led to their coalescence and flattening.

Past terrestrial hydroclimate sensitivity controlled by Earth system feedbacks

Despite tectonic conditions and atmospheric CO2 levels (pCO2) similar to those of present-day, geological reconstructions from the mid-Pliocene (3.3-3.0 Ma) document high lake levels in the Sahel and mesic conditions in subtropical Eurasia, suggesting drastic reorganizations of subtropical terrestrial hydroclimate during this interval. Here, using a compilation of proxy data and multi-model paleoclimate simulations, we show that the mid-Pliocene hydroclimate state is not driven by direct CO2 radiative forcing but by a loss of northern high-latitude ice sheets and continental greening. These ice sheet and vegetation changes are long-term Earth system feedbacks to elevated pCO2. Further, the moist conditions in the Sahel and subtropical Eurasia during the mid-Pliocene are a product of enhanced tropospheric humidity and a stationary wave response to the surface warming pattern, which varies strongly with land cover changes. These findings highlight the potential for amplified terrestrial hydroclimate responses over long timescales to a sustained CO2 forcing.