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Peatlands are important ecosystems for biodiversity conservation, global carbon cycling and water storage. Hydrological changes due to climate variability have accelerated the degradation of global and regional ecosystem services of peatlands. Diatoms are important producers and bioindicators in wetlands, but comprehensive diatom-based inference models for palaeoenvironmental reconstruction in peatlands are scarce. To explore the use of diatoms for investigating peatland hydrological change, this study established a training set consisting of diatom composition and twelve environmental factors from 105 surface samples collected from five Sphagnum peatlands in northeastern China. Diatom communities were dominated by Eunotia species. Ordination analyses showed that depth to the water table (DWT) was the most important factor influencing diatom distribution, independently accounting for 4.99% of total variance in diatom data. Accordingly, a diatom-based DWT transfer function was developed and thoroughly tested. The results revealed that the best-performing model was based on weighted averaging with inverse deshrinking (R2 = 0.66, RMSEP = 8.8 cm with leave-one-out cross validation). Quantitative reconstruction of DWT on a short peat core collected from the Aershan Peatland (Inner Mongolia) recorded climate-mediated hydrological changes over the last two centuries. This study presents the first diatom-water table transfer function in Sphagnum peatlands, and highlights the potential of diatoms as a powerful tool to assess the magnitude of past hydrological changes in peatlands of northeastern China, as well as similar peaty environments worldwide.

Accurate chronologies for recent sediments of shallow lakes in the Yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century. This study presents the results of detailed 210Pb analysis from eight lake sediment cores collected from the middle Yangtze reaches, southeast China. Unsupported 210Pb activities generally declined exponentially with mass depth in the eight cores. The chronologies and sedimentation rates for the sediment cores were calculated using different 210Pb-based mathematical models. The 137Cs chronomarker (i.e. the 1963 fallout peak) and the spheroidal carbonaceous particle (SCP) chronomarker (i.e. the start of the rapid increase in 1970 AD) were selected to validate the 210Pb dating. Sedimentation rates derived from different models were validated using historical data including lake area, arable land area, sediment discharge and reservoir volume in the Yangtze basin. The SCP-corrected CRS (constant rate of supply) model performs better than other models, based on validation using historical documents in the Yangtze basin. The 137Cs chronomarker might be erroneous due to catchment-driven 137Cs inputs from soil erosion and post-depositional diffusion. Both SCPs and 137Cs are susceptible to inputs from catchment soil erosion, but SCPs show no apparent degradation and post-depositional changes in lake sediments. The SCP profile provides a relatively reliable chronomarker, which can be used for validating 210Pb chronologies in these floodplain lakes. Generally, sedimentation rates in the eight lakes were less than 0.2 g cm-2 yr-1 before the 1930s, and then increased to a peak in the 1960s. Afterwards, sedimentation rates decreased and remained low after the 1980s.

Multi-proxy analyses of an 8 m sediment core from Lake Hayk, a closed, freshwater lake in the north-central highlands of Ethiopia, provide a record of changing lake level and inferred regional climatic change for the last 15.6 cal ka years. Between ca. 15.6–15.2 cal ka BP, a lowstand was synchronous with Heinrich Event 1 and an intense drought across Eastern Africa. At ca. 15.2 cal ka BP a lake began to develop at the core site in response to wetter conditions, at the onset of the African Humid Period (AHP). However, in contrast to other lakes in eastern Africa, Hayk lake level fell around ca. 14.8 cal ka BP, indicating a climate shift towards aridity. The lake began filling again at ca. 12.3 cal ka BP and reached maximum water depth between ca. 12.0–10.0 cal ka BP. Lake level declined slowly during the Holocene, culminating in the termination of the AHP at Hayk between ca. 5.2–4.6 cal ka BP. In the late Holocene, ca. 2.2–1.3 cal ka BP, Lake Hayk was again deep and fresh with some evidence of short-term lake level variability.The palaeo-record from Lake Hayk indicates that while it experienced, to a broad degree, the same glacial-interglacial dynamics and sub-millennial shifts in climate found in other palaeolimnological records from eastern Africa, there are offsets in timing and rate of response. These differences reflect chronological discrepancies between records, as well as the varying climate sensitivities and site-specific factors of individual lake basins. This record highlights the different responses by lakes in a climatically vulnerable area of Ethiopia.

Human activities are threatening Borneo's unique biodiversity, but little is known on the status of freshwater invertebrates. We assessed changes in diversity and distribution of freshwater mussels (Bivalvia: Unionida) in northern Borneo, and identified drivers of present distribution and threats. Past distribution data were collected from literature and museum resources. Present distribution data were collected from 21 river basins, and 47 water quality, climatic, landscape and human variables explored as potential predictors of species presence/absence. Species delimitations were identified by morphology and COI barcoding, and haplotype networks generated. Our data indicate that over the past 50?years, four of originally five native species have become very rare or possibly locally extirpated. Since these four species are endemic to Borneo, other Bornean river basins should urgently be surveyed to identify any remaining populations. In the same time span, the non-native Sinanodonta woodiana has become the most widespread freshwater mussel in northern Borneo. The fifth native species was identified as Rectidens sumatrensis and found in four Sarawakian river basins, thus contradicting previous assumptions of an endemic Bornean Rectidens species. Although a number of stable R. sumatrensis populations are retained across Sarawak, the species' strong spatial contraction in mainland Sundaland and apparent low tolerance to eutrophication suggest that it is vulnerable to further habitat alteration. Our results indicate that Borneo's (endemic) freshwater invertebrate biodiversity is declining rapidly. Comprehensive surveys targeting an array of invertebrate and vertebrate taxa are needed to identify Borneo's freshwater biodiversity hotspots, where conservation efforts should be concentrated.

With the substantial number of lake sediment ?18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water ?18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments.

With the substantial number of lake sediment δ18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water δ18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments.

With the substantial number of lake sediment δ18O records published in recent decades, a quantitative, process-based understanding of these systems can increase our understanding of past climate change. We test mass balance models of lake water δ18O variability against five years of monthly monitoring data from lakes with different hydrological characteristics, in the East-Midlands region of the UK, and the local isotope composition of precipitation. These mass balance models can explain up to 74% of the measured lake water isotope variability. We investigate the sensitivity of the model to differing calculations of evaporation amount, the amount of groundwater, and to different climatic variables. We show there is only a small range of values for groundwater exchange flux that can produce suitable lake water isotope compositions and that variations in evaporation and precipitation are both required to produce recorded isotope variability in lakes with substantial evaporative water losses. We then discuss the potential for this model to be used in a long-term, palaeo-scenario. This study demonstrates how long term monitoring of a lake system can lead to the development of robust models of lake water isotope compositions. Such systematics-based explanations allow us to move from conceptual, to more quantified reconstructions of past climates and environments.

The Limfjord region of northern Jutland, Denmark, supports a rich archaeological record dating back to the Mesolithic, which documents long-term change in human practices and utilisation of marine resources since approximately 7500 BP. The presence and availability of marine resources in the Limfjord is sensitively regulated by environmental parameters such as salinity, sedimentary regime, nutrient status and primary productivity, but long-term changes in these parameters are currently poorly understood. In this study a multiproxy approach (including sedimentary parameters, diatoms, molluscs, foraminifera, sedimentary pigments, C and O stable isotopes and plant macrofossils) has been adopted to assess environmental change over the period ca 7500–1500 cal yrs BP at Kilen, a coastal fjord (before AD 1856) situated in the Western Limfjord. A diatom-based salinity transfer function based on a pan-Baltic training set has been applied to the fossil diatom dataset for quantitative assessment of salinity change over the study period. This study demonstrates that large-scale shifts in salinity are a common feature of the Limfjord's long-term history and are driven by the level of connection with the North Sea and the Skagerrak respectively, which in turn is likely driven by the complex interplay between climate, sea-level change, current velocity and rates of erosion/sedimentary accretion. Three shifts in state at Kilen are identified over the study period: a deep, periodically stratified fjord with medium–high salinity (and high productivity) between ca 7500–5000 BP, followed by a gradual transition to a shallow benthic system with more oceanic conditions (i.e. higher salinity, lower productivity, slower sedimentary accumulation rate and poorer fossil preservation) after ca 5000 BP and no stratification after ca 4400 BP, and lastly, within this shallow phase, an abrupt shift to brackish conditions around 2000 BP. Environmental–societal interactions are discussed on the basis of the data presented in this study and current environmental hypotheses for cultural change are challenged

Freshwater ecosystems are under new and increasing threats from anthropogenic change. Ability to detect and predict consequences of environmental perturbations on ecosystem function and water quality is limited by the lack of empirical data over relevant time scales. Paleoecological records present a unique opportunity to broaden understanding of ecological transitions over decadal to millennial timescales. This study tested the occurrence of regime shifts to track changes throughout the lake food web beyond the typical instrumental era, using both “traditional” paleoecological proxies (e.g., cladoceran zooplankton, zoobenthos, and pigments) and more recently developed molecular genetic methods based on sedimentary DNA. We used sediment cores from the perialpine Lake Joux (Swiss Jura), where the history of human settlement and land-use practices in the catchment has been well documented since the Medieval period. Paleoecological evidence revealed an abrupt and unprecedented biological reorganization in the second half of the 20th century, following several centuries of relatively stable communities despite growing human pressure. Time-varying autoregression computed using dynamic linear modelling identified this transition, triggered by the onset of rapid cultural eutrophication in the 1950s, as a true regime shift. Since this time, despite decades of re-oligotrophication, biotic communities of Lake Joux have not returned to pre-disturbance composition, most likely due to other confounding factors, including climate warming, that may prevent the lake from returning to an earlier equilibrium state. Paleoecological reconstruction further suggested that cladocerans responded earlier to disturbance, which is highly relevant for lake monitoring and management strategies.