In the early nineteenth century, Iceland entered the global market, which caused a large expansion and modernisation of agricultural practices, including rising livestock numbers, higher crop density and the introduction of artificial fertilizers and pesticides. However, the impact of these pressures on Icelandic ecosystems over the past two centuries are largely unknown. This study applies paleolimnological analyses to a sediment core taken from Vestra Gíslholtsvatn, a small lake in southern Iceland surrounded by three farms that broadly reflect national agricultural trends, to assess how changes in agricultural practices have influenced lake-ecosystem dynamics over the past 250 years. Geochemical proxies such as total organic carbon and total nitrogen show increasing trends alongside decreasing δ13C values, suggesting increased terrestrial and/or algal organic matter influx, which coincide with the introduction of artificial fertilizers. Additionally, Chironomidae head capsules were analysed to investigate changes in the lake ecosystem. The chironomid community shows no sustained change in the assemblage, with a continuous dominance of Heterotrissocladius grimshawi-type, which favours cold and oligotrophic waters, and Psectrocladius sordidellus-type, which prefers macrophyte-rich littoral habitats. Only Chironomus spp. shows some short term increases possibly in response to artificial fertilizer usage. Despite the relative stability in the chironomid assemblage, statistical analyses of the chironomid record reveal increasing skewness, kurtosis and amplitude of the rate of change towards the top of the core. These results possibly represent early warning signals of ecosystem instability. In spite of these signals, no ecological tipping point was reached within the studied period, indicating that impacts from the agricultural intensification were insufficient to drive regime shifts in the lake ecosystems. Our results highlight the resistance of Icelandic lake ecosystems to the agricultural pressures of the past two centuries, despite growing instability.
Subfossil cladoceran assemblages from a dated sediment core collected from a small, shallow forest lake in northwestern Poland were used to reconstruct changes in water availability and habitat structure over the past ca. 2000 years. To assess the reliability of cladoceran-based paleohydrological record in a dynamic shallow-lake system, we applied both a qualitative planktonic-to-littoral (P/L) ratio and a quantitative modern analog technique (MAT) approach. Both approaches indicate substantial Late Holocene variability in inferred water availability and habitat structure, with relatively high inferred water availability from ca. 70 BC to AD 200, followed by greater variability and an overall tendency toward lower water availability. Some reconstructed phases broadly overlap with commonly recognized regional climatic intervals, including the Roman Warm Period, Dark Ages Cold Period, Medieval Climate Anomaly, and Little Ice Age, although these relationships should not be interpreted as evidence of precise chronological synchrony or direct climatic causation. Water availability is interpreted as the principal external driver of lake development, whereas trophic state, macrophyte structure, oxygen conditions, and possible fish predation acted as interconnected modifiers of the cladoceran signal. These local ecological processes complicate the interpretation of the hydrological signal and should therefore be considered in paleohydrological reconstructions of shallow lakes. The P/L ratio primarily reflects changes in littoral–open-water habitat structure, whereas the MAT model provides semi-quantitative depth estimates that may be sensitive to other changes in species–environment relationships. Agreement between the two approaches supports broad relative trends but does not constitute independent validation because both are derived from the same cladoceran assemblages. Cladoceran-based reconstructions therefore provide a useful record of relative hydrological variability, although absolute water-depth estimates remain uncertain.
Calcite varves are commonly deposited and preserved in the sedimentary record of stratified hardwater lakes. Year-to-year variation in the characteristics of individual calcite varves emphasizes their sensitivity to various environmental controls, mainly lake water temperature and pH. However, knowledge on the relation between environmental variability and calcite-varve characteristics is still limited, and prevents utilizing this year-to-year variation for accurate paleoenvironmental reconstruction. This study uses monthly sediment trap sampling, physical and geochemical characterization of lake water, and environmental monitoring in Tiefer See (NE Germany) to trace the transfer of environmental signals into the sediments. Calcite formation in the lake occurs in the epilimnion during the spring–summer and is experiencing substantial year-to-year variations. Between 2013 and 2019, the annual endogenic calcite accumulation during the spring–summer varies by a factor of 3 between 85 and 277 g m−2 within a period of 64–182 days, which comprises 72–97
The “top–bottom” approach in paleolimnology provides a rapid means of assessing environmental change by comparing selected proxies of change in modern surface sediments with those in deeper intervals, assumed to pre-date major human disturbances (ca. pre-1880). However, spatial differences in sediment accumulation rates can undermine the assumption that data from a single sediment-core depth represent background conditions in each study lake. The largest “top–bottom” study ever undertaken was the Canadian LakePulse Network, for which 664 sediment cores were collected from 12 ecozones as part of a comprehensive program aimed at assessing the health of lakes across Canada. To estimate minimum depths that correspond to pre-industrial conditions for the LakePulse study sites, we compiled age-depth data from 357 published 210Pb-dated sediment cores from lakes across Canada and the northern United States. Those data were used to generate a spatially-interpolated sedimentation map, providing a national framework for Canadian lakes that can be used to inform future “top–bottom” studies. A representative subset of 212 LakePulse lakes was evaluated using excess 210Pb measurements to test whether estimated bottom-interval depths reached pre-industrial age. Target bottom depths differed among ecozones, ranging from 22 cm in the northern regions of the Taiga Plains, Taiga Cordillera and Boreal Cordillera, to 47 cm in the Boreal Plains, Semi-Arid Plateaux and Prairies. Basal target depths by ecozone were related to the average human impact index of the corresponding ecozone, indicating that watershed land use is a key driver of recent sediment accumulation rates. Validation analyses, using excess 210Pb uncertainty, showed that failure to reach pre-industrial conditions at or below the target depths occurred in < 9
Impoundment of rivers is a common strategy used by communities to mitigate flood risk and ensure a reliable supply of municipal water. However, damming disrupts natural sediment transport causing significant deposition and retention within the impounded system which reduces reservoir volume and functionality over time. Variable inputs of watershed (allochthonous) inorganic particles and organic matter (OM) and internal primary production (autochthonous OM), coupled with sediment mineralization, influence overall sediment-accumulation rates (SARs). To protect the longevity and functionality of reservoir systems, it is essential to track reservoir SARs through time and the primary source(s) of OM inputs for effective management-solution development and implementation. In Central Texas, USA, a region known as “Flash-Flood Alley”, the created reservoir systems are essential to the continued growth of the region but are periodically subjected to significant watershed inputs of materials. Despite this, SAR and sediment-source dynamics have been infrequently monitored. In this study, we estimated SARs and OM sources by collecting a deep core from the accumulating portion of the last two reservoirs on the Texas Colorado River, Lake Austin and Lady Bird Lake, each important to the region for municipal, recreational, and flood-control purposes. Radioisotopic (cesium-137 and lead-210) signatures indicated SARs were more rapid (up to 11 cm yr−1) in Lake Austin than Lady Bird Lake (< 2 cm yr−1), despite significant urban inputs to the latter system. From the Lake Austin core, observed large shifts in sand content (tenfold), and carbon and nitrogen contents (> 2x), molar ratios (> 1.5
Traditional lake-percussion-coring systems conducted from a stable ice-pack surface involve repeatedly lifting and dropping a weighted driver below the ice surface in relatively deep (≥ 4 m) lakes. Modifications are presented for relatively shallow (< 4 m-depth) ice-covered lakes whereby driving the core barrel(s) is conducted above the ice. The equipment utilizes off-the-shelf materials and is sufficiently lightweight for transport by plastic snow sled(s) into remote wilderness. A polycarbonate core liner strengthens the core barrel and compensates for the thickness of the core-catcher/cutting-edge assembly. Three options for core barrel driving are pulling down on two straps connected to the top of the core barrel assembly, ratcheting the two straps coupled to ice screws in the ice, and pounding the top of the core barrel with a mallet. Each method can exert 900 N, > > 5000 N, and 1200 N of force, respectively, which exceeds the 80 N of the traditional gravity-driven subsurface weighted driver.
In the context of ongoing climate change, understanding the global carbon cycle, especially the role of aquatic systems, is a major scientific challenge. Inland water bodies can act as sources or sinks of greenhouse gases, depending on their internal characteristics and the influence of external factors. Current global estimates of organic carbon accumulation rate (OCAR) in inland water bodies are mostly based on the reuse of available paleolimnological data. These estimates are mainly derived from total organic carbon (TOC) values converted from loss-on-ignition at 550 °C (LOI), using the LOI:TOC conversion factor established by Dean (1974). Our study focuses on the LOI:TOC relationship, based on 1,324 observations of lacustrine sediment samples derived from a broad typological gradient of sites (n = 465). Linear regression analysis revealed a strong relationship between LOI and TOC (TOC = LOI/2.27; R2 = 0.79; p < 0.05). However, the predictive model provides estimates that differ distinctly from measured elemental TOC, especially at low LOI values. Change point analysis, based on the mean and variance of the LOI:TOC, suggests that the relationship is strong for LOI values greater than 15
Over the past decades, there has been growing interest in understanding how trace metal contamination has evolved over time and the impact of pre-industrial activities on this trend. Although Italy has a long history of human settlement and major metal mining, studies on historical contamination remain limited. To address this gap, three sediment cores spanning up to the last 10,000 years were analyzed: Lake Ledro (Trento, Norhern Italy, 10,000 calibrated years before present (cal. yr. BP)), Lake Lungo (Rieti, Central Italy, 2700 cal. yr. BP) and the Pantano Grande saltmarsh (Messina, Southern Italy, 3700 cal. yr. BP). This study investigates the temporal variability of major and trace elements, with a focus on potentially toxic elements such as lead (Pb) and mercury (Hg), through statistical and compositional multivariate analysis. The main objectives were to evaluate potential pollution legacies from human impact, and to estimate site-specific natural background values for the selected areas. Results indicate that each sediment core recorded anthropogenic impacts at different points in time, according to the local history of each site. In general, Pb downcore distributions showed notable shifts at specific depths linked to local environmental changes mainly driven by human activity. Therefore, no similar Pb and Hg patterns emerged across the sites, except for a general increasing trend towards the upper (and more recent) portions of the cores, reflecting the well-documented impact of population growth and intensified human activities on trace metal dispersion. This study enriches the Mediterranean dataset for pollution reconstruction, providing a robust reference for future assessments and contributing to improved environmental management in the context of intensifying anthropogenic and natural pressures.
When considering the environmental conservation of brackish lakes, it is essential to assess the influence of tidal inflow from the sea and the associated changes in the lake bottom sediments. In conducting such assessments, methods focusing on the characteristics of sediment grain size, which reflect their sources and sedimentary processes as employed in paleolimnology, prove effective. However, grain-size distributions in lake bottom sediments with multiple sources and processes coexisting are often complex. We investigated sediment supply and transport into Lake Hinuma, a brackish lake in central Japan, through detailed analysis of bottom-sediment grain-size distributions. Surface sediments were collected from 21 offshore sites, and three gravity cores down to 34 cm depth were obtained. The cores were divided into 1-cm intervals for grain-size analysis. The grain-size distributions were decomposed into lognormal components using the expectation–maximisation algorithm, and additive logratio analysis was applied to the mixing proportions. The distributions were separated into five or six lognormal components with consistent characteristics. The proportion of the finest component (mean grain size: 9.6 phi) varied little among the samples. Logratio analysis using this component as a reference showed that finer components exhibited little variation, whereas coarser components varied both spatially and vertically. The spatial pattern of coarser components indicates sediment supply and transport by flood tidal currents, and their upward increase suggests enhanced transport by these currents over time. This study demonstrates that component separation combined with logratio analysis can effectively extract grain-size components with distinct sources and reveal past changes in sediment transport, which is beneficial for the environmental conservation of brackish lakes.
This study investigated the impacts of eutrophication on a marl lake (Sunbiggin Tarn, United Kingdom) using the geochemical and molecular composition of a 33.5 cm radiometrically dated sediment core. The core revealed that there was a period of rapid increase in sedimentation rates with associated enrichment in δ15N, δ13Corg, carbon/nitrogen (C/N) and the flux of photosynthetic pigments. This represented a period of enhanced eutrophication which shifted the ecological composition of algal taxa towards greater abundances of chlorophytes and cryptophytes indicating higher nutrient availability. The higher sedimentation rates and nutrient availability was likely to be driven by the increase in Black-headed Gull (BHGU) population around the lake during the 1980s which resulted in extensive loss of fenland surrounding the lake and increase in open water area. From 1996 to 2005 the gull population declined and the lake showed signs of recovery with overall abundance of photosynthetic pigments declining and water clarity increasing, indicative of reduced nutrient loading. However, it is likely the lake was still in a period of recovery decades after the peak of the gull populations as indicators of nutrient loading continued to decline. This study highlights that even typically resilient marl lakes can be sensitive to eutrophication.
Lacustrine systems of the tropical Andes are recognized as important carbon sinks, although the sensitivity of their carbon cycle remains poorly understood. This study assessed organic matter sources and controls on carbon accumulation in the high-altitude Conococha lacustrine system of the central Peruvian Andes using elemental and isotopic proxies. Two 30-cm sediment cores were analyzed for total organic carbon (TOC), total nitrogen (TN), and stable isotopes of carbon (δ13C) and nitrogen (δ15N). Sediment chronology was established using excess 210Pb activity and the Constant Flux-Constant Sedimentation (CFCS) model to calculate sediment accumulation rates (SAR) and carbon burial rates. The mean SAR was 0.36 cm yr−1, covering approximately 1940–2020 AD. Average TOC accumulation rates ranged from 128.3 to 146.6 g m−2 yr−1, with the highest values recorded in the nearshore core. A marked increase in carbon accumulation began around 2000 AD, coinciding with the construction of a water-retention dam in 2001. Relative to pre-dam conditions, TOC fluxes increased by 1.34 times offshore and 1.52 times nearshore, indicating that hydrological regulation enhanced carbon burial efficiency through reduced flow velocity, longer water residence time, and greater retention of sediments and organic matter. Stable isotopes and TOC:TN ratios revealed spatial differences in organic matter sources: nearshore sediments recorded a mixed organic matter source, whereas offshore sediments reflected mainly algae-derived material linked to eutrophic conditions. This study illustrates how this lacustrine system acts as a hydrologically sensitive site of carbon accumulation, highlighting the influence of human-driven hydrological modifications on long-term biogeochemical dynamics in this high-Andean lacustrine system.
Subfossil Cladocera zooplankton preserved in lake sediments provide valuable insights into long-term ecological and environmental change and offer a robust basis for defining reference conditions for lake restoration. We analyzed a 42-cm long sediment core collected from Baiyangdian Lake, northern China, and established an age–depth model using 210Pb and 137Cs dating. Subfossil Cladocera were examined from the upper 34 cm of the core, spanning approximately 1917–2020. A total of 26 Cladocera taxa were identified, with Chydorus sphaericus dominating the assemblage, followed by Bosmina longirostris and Alona spp. Stratigraphic analysis revealed a major reorganization of the Cladocera community around the early 1960s, characterized by a shift from a predominantly littoral, macrophyte-associated assemblage to a community, increasingly dominated by planktonic taxa. The environment attributed as the improved habitat, shifted back to a macrophyte-dominated littoral zone since 1995. Multivariate analyses indicated that total organic carbon and total nitrogen were strongly associated with changes in Cladocera composition, while climatic variables such as precipitation played a secondary role. Prior to the 1960s, community dynamics were largely consistent with natural hydrological variability under low nutrient conditions, whereas subsequent changes were closely associated with increased nutrient enrichment and organic matter accumulation. These findings demonstrate the value of paleolimnological records for distinguishing natural variability from anthropogenically associated change and for establishing realistic reference conditions for the management and restoration of shallow lake ecosystems.
Accelerated soil erosion due to land use is a far-reaching problem for today’s society. Soil degradation leads to outwash and redistribution of soil organic matter, which not only impacts soils but also adjacent ecosystems by downstream eutrophication of freshwater bodies. Despite the severity of the problem and the ever-growing footprint of agriculture, little is known about the long-term effects of past soil degradation periods on catchment soils and lake systems. This study addresses this question by analyzing a sediment sequence retrieved from Lake Lavijärvi, located near the city of Sortavala, north of Lake Ladoga in the Republic of Karelia, Russia, which has witnessed a period of intensive farming at the beginning of the twentieth century, followed by abandonment of the land post-World War II. We applied a multi-proxy approach using geophysical properties, the geochemical and isotopic composition of the bulk sediment, as well as the distribution of sedimentary leaf waxes and their relative ages (compound-specific radiocarbon dating). With the beginning of industrialization (ca. 1900 CE), we observed severe soil erosion, evident as maxima in magnetic susceptibility and Ti concentrations, as well as high sediment mass accumulation rates. Intensive farming led to a reduction of soil-carbon-residence times (mean transfer time, MTT), indicated by the washout and deposition of pre-aged soil organic carbon. During the same time, the lake became eutrophic and varves were deposited, due to a surplus of soil-derived nutrients. Decreasing MTT after World War II reflected depopulation and land abandonment that resulted in stabilization of catchment soils. Even though soil erosion declined and the trophic status of Lake Lavijärvi returned to more oligotrophic conditions during the post-war period, the lake still suffers from anoxia today. We show that land-use legacies exert a major influence on freshwater ecosystems decades after land-use relaxation.
Understanding paleolimnological dynamics in the Rio Negro floodplain provides a window into broader paleoclimatic variability and long-term environmental change across western Amazonia. Here, we analyzed diatom assemblages (relative abundance and valve density; valves g−1), grain size, bulk organic geochemistry (TOC and C/N), chlorophyll derivatives (SPDU), δ13C and δ15N in a 146 cm sediment core from Lago Airo, recovering the last 15,050 years, based on seven radiocarbon dates. A total of 73 diatom taxa were identified, dominated by acidophilic species, revealing four successive stratigraphic Units that document a long-term transition from a river-influenced and low-productive environment to a more internally driven lacustrine system. Unit IV (15,050–10,100 cal yr BP) is sand-dominated (> 99
Sedimentary DNA (sedDNA) offers potential advantages for paleolimnological reconstructions by enabling better characterization of short- and long-term trends in aquatic communities. However, the temporal range and influence of different environmental variables on species-specific sedDNA distribution patterns are poorly understood, particularly for migratory species like diadromous fishes. Given their transient nature, it is unclear if and where diadromous fish sedDNA will accumulate in lake sediments, as well as to what extent sedDNA can capture historic diadromous fish signals. Using 12S rRNA metabarcoding, quantitative PCR, and occupancy modeling, we investigate the spatiotemporal distribution of fish assemblages and diadromous alewife (Alosa pseudoharengus) in sedDNA and eDNA samples from a coastal, oligotrophic lake in Maine, USA. Through paired water and sediment samples collected across various depths, habitats, and seasons, we found a heterogeneous distribution in fish sedDNA, with higher alewife detection probabilities associated with greater lake depth. While historic alewife sedDNA was detected in several samples, we highlight the potential rapid degradation and/or dilution rate of fish surface sedDNA in natural systems, contrasting previous studies. Collectively, our findings demonstrate that despite their seasonal presence, sediment focusing mechanisms play a critical role in the distribution and detection of diadromous alewife sedDNA, emphasizing lake depocenters as optimal locations for contemporary monitoring and historic reconstructions of these migratory species.
To assess the anthropogenic impact on carbon and nitrogen accumulation rates in wetlands associated with Lake Titicaca, sediment cores recording the past century in contrasting environmental conditions were analyzed using elemental and isotopic proxies. Duplicate 50-cm sediment cores were collected from wetlands within the National Reserve environment of Lake Titicaca, and from a wetland area under the direct influence of a sewage plant. Subsamples were analyzed for total organic carbon (TOC), total nitrogen (TN), δ13C, and δ15N. Sediment accumulation rates (SAR) and Mass accumulation rates (MAR) were calculated from 210Pb-excess activity using the Constant Flux Constant Sedimentation method (CFCS). The SAR in the impacted area averaged 0.38 cm yr−1, up to twofold higher than in the “National Reserve”, likely due to increased organic matter influx from anthropogenic activities. Although δ13C values showed no significant differences between the study areas, abrupt shifts in organic matter sources and significantly heavier δ15N values were observed in the impacted area after the 1970s, indicating that carbon and nitrogen sources derive from a mix of terrestrial vegetation, algae, and cyanobacteria, fertilized by nutrient enrichment from anthropogenic activities. Despite no significant differences in carbon and nitrogen fluxes between both studied areas, the lower stocks in the impacted area indicate a lower accumulation capacity due to a higher contribution of labile organic matter. This study underscores the crucial role of wetlands associated with Lake Titicaca in the deposition and accumulation of organic carbon driven by both natural and anthropogenic factors and highlights the importance of wetland preservation in maintaining the accumulation capacity of these ecosystems in the context of global wetland eutrophication.
Mongolia hosts about three thousand lakes across arid and semi-arid continental interiors, where tectonic, climatic, and ecological diversity makes lacustrine systems sensitive archives of Late Quaternary to modern environmental change. Located at the intersection of the mid-latitude westerlies, the East Asian summer monsoon, and the Siberian High, Mongolian lakes record spatially heterogeneous responses to climate forcing, basin evolution, and cryospheric dynamics. Since the early 1990s, lake-based research in Mongolia has expanded substantially; however, a nationally integrated synthesis linking geological timescales, basin controls, and the evolution of research themes has remained limited. Here we review 214 lake-related studies published between 1990 and 2025, classified by publication year, study region, research focus, author nationality, and journal–publisher structure in order to evaluate how Mongolian lake research has developed and become increasingly integrated into the international scientific literature. This classification also provides insight into the evolution of publication outlets and language transitions within global lake research. The synthesis reveals strong regional contrasts in lake evolution, reflecting interactions among tectonic processes, hydroclimatic variability, and cryospheric change. Over time, research has shifted from climate-driven lake-level reconstructions toward multi-proxy interpretations supported by improved chronological frameworks and remote-sensing observations. Future research will benefit from integrating high-resolution sediment archives, improved chronological frameworks, and long-term hydrological monitoring. Important knowledge gaps remain in desert and steppe lake basins of eastern and southern Mongolia, where sedimentary records and coupled climate–human impacts remain comparatively underexplored. The synthesis also highlights key knowledge gaps and emerging research priorities for future lake-based Quaternary studies in Mongolia.
Elemental and Sr isotopic (87Sr/86Sr) distributions in multiple mineralogical phases of lake sediments are modulated by catchment processes, but their controlling mechanisms and paleoenvironmental indications remain poorly understood. This study employs a 20-step incremental leaching approach to analyze the distribution of elements and 87Sr/86Sr ratios in carbonate-rich lake sediments. Targeted phases include water-soluble salts (water leaching), exchangeable phase (NH4Ac leaching), carbonates (incremental HOAc leaching), Fe–Mn oxides (NH2OH·HCl leaching), chlorite phase (heated HCl leaching), and residual silicates (HF-HNO3 digestion). Our results reveal that most elements peak in residual silicate phase, while other phases exhibit distinct elemental preferences: Na, K, Ca, Rb and Sr in water-soluble salts; Ca, Sr, Mn, and P in exchangeable phase; Ca, Sr, Mg, Mn and P in carbonate phase; Fe, Mn, Mg, Sr and P in Fe–Mn oxide phase; and K, Fe, Mg, Mn, Rb, Sr and P in chlorite phase. The 87Sr/86Sr ratios exhibit consistently low values of 0.7111–0.7114 in water-soluble, exchangeable, and carbonate phases (leached by 0.25 and 1
Diatoms extracted from two lacustrine sediment cores from the Rensselaer Plateau of eastern New York state (USA) reveal patterns of considerable late Pleistocene and Holocene climate variability associated with droughts possibly linked to Laurentide ice sheet meltwater releases that caused changes in the Atlantic Meridional Overturning Circulation or solar forcing of North Atlantic sea surface temperatures. Samples were taken from Dyken and Shaver Ponds, glacial kettle lakes that contain sediment records extending to > 13.3 and > 11.5 cal kyr BP, respectively. The species assemblages in the sediments of both ponds are typical of low alkalinity lakes of the northeastern United States. The most common taxa include several members of the genus Aulacoseira, Asterionella ralfsii var. americana, Tabellaria fenestrata, Discostella stelligera, and Lindavia intermedia, although over 250 different taxa were encountered. Several changes in the diatom flora coincide with changes in forest composition as determined from paired pollen and plant macrofossil studies and suggest climate disruptions at 10.6, 9.2, 8.2, and 6.1 cal kyr BP. The last of these events precedes the classical hemlock (Tsuga) decline in the US Northeast that began at 5.5 cal kyr BP and is notable in the sudden appearance of the diatom Lindavia rossii in Shaver Pond. This species shows repeated oscillations throughout the period of the decline and suggests that climate became much drier during the middle Holocene, shifting the hydrologic balance of the lake toward greater importance of alkaline groundwater inflow. Additional features of the Rensselaer Plateau diatom records reveal evidence of Younger Dryas cooling that created tree canopy gaps and made way for nitrogen-fixing alders (increase in diatom taxa that respond to nutrient enrichment) and response of both lakes to late Holocene neoglacial cooling (increase in acidophilic and dystrophic taxa as boreal conifers regained prominence).
Global biodiversity is decreasing due to anthropogenic activity, especially in freshwater ecosystems and within insect communities. Freshwater insect-diversity loss impacts all trophic levels and ecosystem services within and beyond the freshwater environment. Insect diversity monitoring typically covers short timescales relative to the onset of anthropogenic activity. Therefore, the ability to identify the dominant drivers of biodiversity loss is limited, restricting effective ecosystem management. Palaeoecological studies provide a long-term perspective on changing ecosystems, especially with regard to insect communities. Loe Pool, a lake in the south-west of England, has a known history of varied anthropogenic activity: mining, a water treatment works, agriculture, and flow regulation have impacted the lake and its catchment since the eighteenth century. Two sediment cores were retrieved from Loe Pool and were analysed using chronological, sedimentological, and palaeoecological techniques. This created a centennial-scale record of the diversity dynamics of lower trophic levels. Our results show the impacts of both mining waste and agriculture-associated nutrient pollution on chironomid and diatom assemblages over time. An intensification of mining (1900–1938) was reflected by chironomid and diatom taxa tolerant to disturbance and pollution, especially mining effluent and heavy metals. Some post-mining recovery away from metal pollution-tolerant taxa was interrupted by the canalisation of the River Cober (1947). Following an intensification of agriculture in the catchment from the 1960s, both chironomids and diatoms shifted towards eutrophy-indicating taxa. While some reduction in eutrophic taxa post-1995 is seen in the chironomid record, this was not apparent in the diatom record, suggesting that systemic recovery has not taken place. Combined, we show that the chironomid and diatom assemblage and diversity changes clearly respond to anthropogenic activity and land use in the Loe Pool catchment. Despite some potential biodiversity recovery, the original composition and diversity have not been restored. This lack of success may be due to insufficient management efforts, or the need for more time for restoration efforts to make a positive impact.
