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Climate Versus In-Lake Processes as Controls on the Development of Community Structure in a Low-Arctic Lake (South-West Greenland)
Abstract
The dominant processes determining biological structure in lakes at millennial timescales are complex. In this study, we used
a multi-proxy approach to determine the relative importance of in-lake versus indirect processes on the Holocene development
of an oligotrophic lake in SW Greenland (66.99°N, 50.97°W). A 14C and 210Pb-dated sediment core covering approximately 8500 years BP was analyzed for organic–inorganic carbon content, pigments, diatoms,
chironomids, cladocerans, and stable isotopes (δ13C, δ18O). Relationships among the different proxies and a number of independent controlling variables (Holocene temperature, an
isotope-inferred cooling period, and immigration of Betula nana into the catchment) were explored using redundancy analysis (RDA) independent of time. The main ecological trajectories in
the lake biota were captured by ordination first axis sample scores (18–32% variance explained). The importance of the arrival
of Betula (ca. 6500 years BP) into the catchment was indicated by a series of partial-constrained ordinations, uniquely explaining
12–17% of the variance in chironomids and up to 9% in pigments. Climate influences on lake biota were strongest during a short-lived
cooling period (identified by altered stable isotopes) early in the development of the lake when all proxies changed rapidly,
although only chironomids had a unique component (8% in a partial-RDA) explained by the cooling event. Holocene climate explained
less variance than either catchment changes or biotic relationships. The sediment record at this site indicates the importance
of catchment factors for lake development, the complexity of community trends even in relatively simple systems (invertebrates
are the top predators in the lake) and the challenges of deriving palaeoclimate inferences from sediment records in low-Arctic
freshwater lakes.
Supplementary resource (1)
Data
January 2008
... Lacustrine sediments provide continuous and long-term palaeoenvironmental records, and have been widely acknowledged as important for understanding the regional ecosystem responses to climate change over a range of time-scales (Battarbee, 2000;Cohen, 2003;Anderson et al., 2008). Alpine lakes (usually altitude >3000 m) are sensitive to climate changes as they are usually located in remote places, away from human disturbance and were often regarded as pristine ecosystems (Catalan et al., 2013;Moser et al., 2019;Szabó et al., 2020). ...
... Redundancy analysis (RDA) was used to analyze the relationship between species data and the explanatory variables (i.e., environmental and climatic variables) (Anderson et al., 2008). To separate the impact of climate change and catchment processes on the changes in the cladoceran community, RDA analyses were undertaken using the cladocerans as the response variables and summer insolation (July) at 30 • N (Berger and Loutre, 1991), the stalagmite δ 18 O records from Dongge Cave in SW China (Dykoski et al., 2005), TOC, TN, C/N ratio, δ 13 C org , MS, and Ti concentration of the sequence as the explanatory variables. ...
... To separate the impact of climate change and catchment processes on the changes in the cladoceran community, RDA analyses were undertaken using the cladocerans as the response variables and summer insolation (July) at 30 • N (Berger and Loutre, 1991), the stalagmite δ 18 O records from Dongge Cave in SW China (Dykoski et al., 2005), TOC, TN, C/N ratio, δ 13 C org , MS, and Ti concentration of the sequence as the explanatory variables. A series of partial-RDAs (with sample age as a co-variable) were performed to evaluate the main environmental factors affecting the cladoceran assemblage composition (Anderson et al., 2008) throughout the core and also independently for different time intervals. The significance of the explanatory variables in the RDAs was determined using unrestricted Monte Carlo Permutation tests (499 permutations, p < 0.05). ...
The study of alpine lake ecosystem ontogeny provides an understanding of how climate dynamics and the associated catchment changes impact on lake functioning. Here, a high-resolution subfossil Cladocera sedimentary record, together with geochemistry proxies, from an alpine, treeline lake (Cuoqia Lake) in SW China were analyzed to understand the lake ecosystem response to changes in the regional Indian summer monsoon (ISM) climate and the local mountain environment since the Last Glacial Maximum (LGM, ca. 19.5 cal kyr BP to present). The results show that the cladoceran record from Cuoqia Lake clearly responds to long-term climate change and significant climate events. The lake was depauperate in cladoceran species throughout the late glacial period (ca. 16–11 cal kyr BP) but Daphnia longispina-group and Chydorus sphaericus were the pioneer taxa when the lake was formed. The rapid proliferation of open-water and littoral cladoceran taxa began with increasing water temperature. The Younger Dryas (YD) cold event was recorded by high abundance of the cold-tolerant taxon C. sphaericus during ca. 12–11 cal kyr BP. At the onset of the Holocene (ca. 11 cal kyr BP), Alona spp. and macrophyte-associated taxa became dominant while numbers of C. sphaericus decreased dramatically. In the mid- to late-Holocene, the productivity of Cuoqia Lake seemed to have increased as reflected by higher Cladocera concentration and the appearance of Ceriodaphnia spp. and raptorial P. pediculus which are common in high nutrient waters. Partial Redundancy Analysis (partial-RDA) results highlight the strong effect of indirect climate change (mediated via catchment processes) on cladoceran assemblages during the Holocene. Abrupt shifts in sediment geochemical proxies and regional catchment vegetation at ca. 11 cal kyr BP indicate that substantial nutrient inputs, treeline advancement, and soil development in catchment resulted from the intensified ISM. Therefore, the cladoceran community changes suggest a long-term direct response of the alpine lake ecosystem to climate change since the LGM, but one that was strongly mediated by catchment-vegetation processes, such as the treeline shifts.
... It is often argued that lake ecosystems have experienced dramatic environmental changes together with the increased magnitude of climatic oscillations since the Last Glacial Maximum (LGM) to present time (LGM, ca. 30 000-0 cal year BP) (Bradshaw et al., 2005;Anderson et al., 2008). However, a lake environment is also strongly altered by long-term shifts in local catchment state via a changing nutrient supply indirectly modulated by climate change (Karst-Riddoch et al., 2005;Woodbridge and Roberts, 2011). ...
... However, a lake environment is also strongly altered by long-term shifts in local catchment state via a changing nutrient supply indirectly modulated by climate change (Karst-Riddoch et al., 2005;Woodbridge and Roberts, 2011). For example, a multi-proxy record from a freshwater lake in the low-Arctic of West Greenland revealed the relative forcing effects of direct climate versus indirect catchment processes on biotic interactions during the Holocene (Anderson et al., 2008). Such studies have suggested that climate change has an indirect effect on the lake ecosystem through soil development and terrestrial vegetation succession (as DOC export) and hence in lake chemistry (Pienitz et al., 1999;Anderson et al., 2008). ...
... For example, a multi-proxy record from a freshwater lake in the low-Arctic of West Greenland revealed the relative forcing effects of direct climate versus indirect catchment processes on biotic interactions during the Holocene (Anderson et al., 2008). Such studies have suggested that climate change has an indirect effect on the lake ecosystem through soil development and terrestrial vegetation succession (as DOC export) and hence in lake chemistry (Pienitz et al., 1999;Anderson et al., 2008). ...
Multiple biogeochemical variables in a sediment core from Lake Lugu in southwest China were studied to investigate the effects of regional environmental changes on the ecosystem. Subfossil Cladocera, together with diatom, pollen and geochemical records, were used to examine climate-induced changes in lake ecosystem since the Last Glacial Maximum (30 000–0 cal year BP). Consistency among these biological records indicates that the succession of zooplankton, algae and vegetation changed in response to direct and indirect climatic factors. Alterations in the nutrient supply mediated by climate-induced changes in vegetation and soil processes are likely responsible for the variability of cladocerans. During the Last Glacial Maximum, cladocerans were dominated by littoral taxa (e.g. Alona), indicating an unproductive and oligotrophic lake system. A peak distribution in the pelagic Bosmina highlights the period of increased nutrient availability at 11 500 cal year BP. The ecological changes in Cladocera at 19 000 cal year BP and diatom communities at 18 000 cal year BP reveal independent and indirect responses to nutrient and light conditions induced by solar radiation and increased monsoon intensity across the study region. The palaeoecological archives from Lake Lugu sediments highlight a complex lake ecosystem influenced by both direct and indirect changes corresponding to climate changes and shifts in regional anthropogenic pressure over the last 30 000 years.
... The diatom, cladoceran and carbon accumulation rates in Lugu Lake show broad similarity (Fig. 4A, E, P and Q), reflecting the major effect of lake-catchment interactions, as evidenced by the redundancy analysis and variance partitioning analysis (Fig. 6). The trend in aquatic productivity indicated by diatom and cladoceran AR, as well as abundance of total algae (Fig. 4A, E, H), suggests a lake where primary production was mainly affected by the export of nutrients from the catchment (Anderson et al., 2008). ...
... The recent expansion of C. dubius in Lugu Lake was attributed to a seasonal mixing period, higher nutrient condition and low light availability by Wang et al. (2015). Increased planktonic diatom productivity may represent changes in nutrient transfer and cycling within the lake, perhaps associated with changes in lake thermal structure and/or catchment vegetation (Saros et al., 2012;Anderson et al., 2008;Bradshaw and Anderson, 2012). Variance partitioning shows that catchment processes had a major role in controlling species community development, explaining 13.3e50.1% of the variance in diatom assemblages (Fig. 6). ...
... These changes suggest that a transition in the lake ecosystem occurred in Lugu Lake around 1300 AD. The changes in the cladoceran remains also indicate that the changes in primary producers were transmitted to higher trophic levels in the lake (Anderson et al., 2008) (Table 2). Moreover, the onset of cultural land-use changes at about 1300 AD, were superimposed on climate effects and altered nutrient loadings. ...
... Previous studies have examined lake chemistry, paleolimnological history, and ecology in the Kangerlussuaq region (Aebly and Fritz 2009;Anderson et al. 2008Anderson and Leng 2004;Bocher 1949;Eisner et al. 1995;Fredskild 1977;Fritz and Anderson 2013;Jensen 1889;Leng and Anderson 2003;Leng et al. 2012;McGowan, Ryves, and Anderson 2003;Olsen, Anderson, and Leng 2013;Williams 1991). In the present study, a series of lakes, from the coast to the ice front in the Kangerlussuaq region of southwest Greenland, were sampled ( Figure 1). ...
... Surface-water environments become less hostile to microbial communities with distance from the ice sheet because of warmer temperatures and increased time for the evolution and development of communities. For example, cooler temperatures at about 8,200 years BP caused a definitive decrease in productivity in a lake close to the head of the fjord near Kangerlussuaq, based on isotopic and fossil records from a lake core (Anderson et al. 2008). The cooler, dryer conditions at approximately 8,200 years BP and the reduction in productivity may be related both to the close proximity of the ice sheet to the lake at that time (Anderson et al. 2008) and to thermohaline slow down documented in the North Atlantic (e.g., Alley and Ágústsdóttir 2005). ...
... For example, cooler temperatures at about 8,200 years BP caused a definitive decrease in productivity in a lake close to the head of the fjord near Kangerlussuaq, based on isotopic and fossil records from a lake core (Anderson et al. 2008). The cooler, dryer conditions at approximately 8,200 years BP and the reduction in productivity may be related both to the close proximity of the ice sheet to the lake at that time (Anderson et al. 2008) and to thermohaline slow down documented in the North Atlantic (e.g., Alley and Ágústsdóttir 2005). ...
In west Greenland, an approximate chronosequence of landscape evolution and weathering exists between the coast, which has been ice free for long periods, and more recently deglaciated areas along the present day ice margin. Traditional geochemical and isotopic analyses (δ¹⁸O, δ²H, ³H, δ³⁴S/δ¹⁸O (SO4), and ⁸⁷Sr/⁸⁶Sr) along with novel isotopic tools, such as δ³⁷Cl and δ⁸¹Br, were used to provide new insights into lake geochemical processes along a transect of lakes from the coast to the ice margin in the Kangerlussuaq region. Evaporation was found to be a key process impacting lake chemistry and isotopic signatures in the ice marginal area, with decreasing importance toward the coast. Evaporative processes were apparent in the δ³⁷Cl and δ⁸¹Br isotopic signatures of lake-water chemistry. Consistent with previous work elsewhere (e.g., Blum and Erel, 1995) on increased biotite weathering in glaciated environments, ⁸⁷Sr/⁸⁶Sr isotopic ratios were found to be more radiogenic (>0.73) in lakes found in more recently glaciated terrain. Sulfide oxidation was the main source of sulfur (as sulfate) in lakes in the ice marginal area, while the influence of marine aerosols and bacterial sulfate reduction increased further away from the ice sheet around the fjord Kangerlussuaq. Groundwater discharge significant enough to impact lake chemistry was not observed in any of the lakes studied, suggesting that little groundwater–surface water interaction occurs in the study area or that recharge conditions are present in the majority of the lakes studied.
... Numerous nonclimate factors have been shown to influence diatom assemblages and production including limnological variables, bedrock geology, and other watershed characteristics (e.g., Lim et al. 2001;Bouchard et al. 2004;Fortin and Gajewski 2009;Finkelstein et al. 2014). Changes through time of alkalinity, for example due to vegetation development or climate, alter the lake environment and aquatic communities (Anderson et al. 2008). However, comparative analyses have shown that diatom communities differ greatly between nearby sites due to factors of lake morphometry, dispersal, and watershed characteristics (Smith 2002;Gajewski 2007, 2008; Rühland et al. 2015). ...
... Increases in diatom production, as inferred by increases in BSi, in diatom valve concentrations, or in fluxes of photosynthetic pigments, in Arctic lake sediment records are often interpreted as indicative of warmer temperatures (e.g., Cremer et al. 2001;LeBlanc et al. 2004;Michelutti et al. 2005;Rühland et al. 2015 and references therein). Other studies indicate that in some lakes, diatom production and community composition are more closely related to nutrient availability and light penetration (Baier et al. 2004;Malik and Saros 2016) or lake catchment hydrochemistry and only indirectly controlled by climate (Anderson 2000;Anderson et al. 2008Anderson et al. , 2012Law et al. 2015). Our results suggest that this relationship may be further modified by dissolution in warm periods, and out-of-phase relations would appear between independent temperature proxies and the diatom production proxies (e.g., Michelutti et al. 2007;Wagner et al. 2008). ...
... Natural acidification has been documented for many temperate lakes in forested catchments due to gradual leaching of base cations through weathering processes and export of humic acids with progressive pedogenesis and plant succession. These processes have been invoked as an important mechanism in southern Greenland (Anderson et al. 2008), but they are less applicable to Lake RS29, located in the High Arctic polar desert. The short snow-free season, thin active layer, cold temperatures through the summer, prevailing aridity, and low plant biomass means there is little pedogenesis and slow rates of chemical weathering (Gajewski 2015b). ...
This study presents a diatom-based analysis of the post-glacial Holocene environmental history at Lake RS29 on Somerset Island in the Canadian High Arctic. Earliest post-glacial diatom assemblages (10 200–10 000 cal yr BP) consisted mainly of small, benthic fragilarioid taxa. Poor diatom preservation in the early Holocene (~10 000–6200 cal yr BP) is associated with warm conditions, as determined by pollen data from the same core and other paleoclimate estimates from the region. Analysis of this and other sites from across the Canadian Arctic suggest that zones of poor diatom preservation or diatom absence in lake sediment records may be associated with warm conditions. After 6200 cal yr BP, acidophilic assemblages consisting of Aulacoseira spp. and a suite of periphytic taxa indicate acidification since the mid-Holocene. During this time period, cooling causing changes in lake ice phenology was likely a major driver of the reconstructed mid-Holocene pH decline. Watershed processes, including reduced fluxe...
... Remote Arctic sites offer a rare opportunity where lake ontogeny trajectories can be examined in the absence of significant anthropogenic disturbance. Palaeolimnological evidence from the freshwater, open basin inland lakes of south-western Greenland indicates that production and alkalinity were highest during the early Holocene (prior to 8000 cal a BP) and then declined as the lakes underwent oligotrophication from~6000 cal a BP at the coast and~6500 cal a BP at the inland lakes (Fredskild, 1983;Anderson et al., 2008). The early stages (before 8000 cal a BP) were controlled by climatic amelioration and climate-independent processes set in motion by glacial retreat. ...
... The early stages (before 8000 cal a BP) were controlled by climatic amelioration and climate-independent processes set in motion by glacial retreat. However, the onset of oligotrophication was determined by time-dependent edaphic transitions (e.g., soil and vegetation development) in the catchment (Fredskild, 1983;Anderson et al., 2008;Heggen et al., 2010). Perren et al. (2012) proposed that regardless of lake age and climatic setting, freshwater, open basin lakes in south-western Greenland will demonstrate systematic ecological transitions as a result of time-dependent ontogeny processes. ...
... The chronology was derived through radiocarbon dates, with details of the LOI analyses and the Organic Matter Accumulation Rates (OMAR) given in Anderson et al. (2012). Location of the study region in south western Greenland and the four study lakes (black squares), the location of lakes SS49, SS16 and SS32 from Perren et al. (2012) and SS2 from Anderson et al. (2008) are also shown (white squares). ...
Holocene palaeolimnological records of diatoms and β carotene (a proxy for aquatic production) from four lakes in the low Arctic region of south-western Greenland were used to investigate the role of climate on lake ontogeny. Two of the lakes are located in the maritime, coastal region near Sisimiut and two inland close to the head of Kangerlussuaq fjord, where there is a more continental climate. Diatom records from the four lakes (AT1, AT4, SS1381, SS8) had similar long-term ontogeny trends, independent of climatic setting and the changes are interpreted as responses to first order weathering controls on catchment/lake chemistry. Short-term excursions from these broad trends occurred in one coastal site (AT4) caused by intense erosion of the steep catchment, and at inland sites where temporary hydrological closure and lake level decline occurred during the mid-Holocene (~8000 - 5000 cal a BP). Algal production (as β carotene) was more closely and consistently correlated with climatic changes; it peaked during the mid-Holocene, the warmest period of the Holocene, at all sites and there were transient increases in production in inland lakes during the Medieval Climate Anomaly and Little Ice Age because of fertilization through increased aeolian dust deposition. A synthesis of seven palaeolimnological records from this region identified that only the mid-Holocene was correlated with diatom stratigraphic zones and there was considerable among-site variability in later Holocene lake response to climate forcing in this area. Comparable long-term trends in species assemblage turnover (DCA/CA axis 1 scores) clearly demonstrate that lakes have predictable ontogeny trends in this region, characterised by maximum alkalinity and nutrient availability in the first few millennia followed by progressive oligotrophication and alkalinity loss. However, individual lake and catchment characteristics (lake morphology, catchment geomorphology), when modified by climatic change (vegetation cover, erosion, weathering rates, aeolian dust deposition, lake level) can diverge from this ontogeny template leading to complex ecological transitions in lakes from this region.
... The early stages (before 8000 cal a BP) were controlled by climatic amelioration and climate-independent processes set in motion by glacial retreat. However, the onset of oligotrophication was determined by time-dependent edaphic transitions (e.g., soil and vegetation development) in the catchment (Fredskild, 1983; Anderson et al., 2008; Heggen et al., 2010). Perren et al. (2012) proposed that regardless of lake age and climatic setting, freshwater, open basin lakes in south-western Greenland will demonstrate systematic ecological transitions as a result of time-dependent ontogeny processes. ...
... Fig. 1. Location of the study region in south western Greenland and the four study lakes (black squares), the location of lakes SS49, SS16 and SS32 from Perren et al. (2012) and SS2 from Anderson et al. (2008) are also shown (white squares). ...
... Furthermore, other studies have shown that alkalinity is a strong driver of ecological change in lakes from this region (Ryves et al., 2002; Perren et al., 2009, 2012). Long-term ontogeny trends among our four lakes were compared with equivalent data available from four previously published lakes from the region (lakes SS49, SS16 and SS32; Perren et al. 2012; and SS2; Anderson et al., 2008) using correlation analysis (SPSS) of time series standardized to 100- year time intervals with linear interpolation. For this analysis we used the published axis 1 scores (CA/DCA or CCA) and, where available, proxy data for aquatic production (eg., Chl a or b carotene). ...
... The bicarbonate ions would originate from leaching of catchment soils accompanying the thawing of permafrost. Anderson et al. (2008) postulate that even minimal soil development after deglaciation is sufficient for considerable alkalinity production in the catchment. The low lake water level would promote carbonate supersaturation and precipitation of calcite (Hahn et al., 2013). ...
... The low lake water level would promote carbonate supersaturation and precipitation of calcite (Hahn et al., 2013). Anderson et al. (2008) also show that during the earliest phases of the evolution of lakes in Greenland, carbonate deposition can be performed by charophytes. The presence of Chara oospores in the sediments of Lake Łukie seems to agree with this thesis. ...
... At the end of the Younger Dryas, in the basin of Lake Łukie NAP values declined, while pollen of trees-AP (especially Pinus) became more abundant (Fig. 2). The establishment of a coniferous forest in the vicinity of Lake Łukie led to leaching of soils and consequently intensified delivery of alkalinity and nutrients to the lake (Anderson et al., 2008;Apolinarska et al., 2012). On the other hand, development of dense vegetation cover hampered the efficiency of surface erosion (Lucchini et al., 2003) which is mirrored by the reduced contents of SiO 2ter . ...
In this study we investigate how climate fluctuation in the Late Glacial period influenced the development of a lake and its catchment located in the East European Plain. We analyzed the sediments of the lake for pollen, subfossil Cladocera, macrofossils and chemical composition. We aimed at disentangling: (1) the climate changes and their limno-ecological responses, (2) temperature dynamics with the use of Cladocera-based transfer function (MJT) and macrofossil-based reconstruction of mean minimum July temperature (MMJT), (3) timing of the response of different proxies to environmental changes. The results of multiproxy analyses explicitly suggest that the main driver for changes in aquatic and terrestrial ecosystems as well as geomorphological processes in the catchment was climate. Reconstructed temperatures generally follow the known trends showing the increase at the beginning of the Allerød and decrease at the beginning of the Younger Dryas. However, there are some discrepancies between the two reconstructions as well as between the generally accepted temperature trends in Late Glacial. The timing of the proxy response to climate change differs, the aquatic proxies responding first.
... West Greenland contains hundreds of thousands of Holocene lakes underlain by continuous permafrost and isolated from regional water flow (Anderson et al. 2001;Leng and Anderson 2003;Anderson and Stedmon 2007;Jørgensen and Andreasen 2007). Paleolimnological studies of lake sediments have been particularly important to the current understanding of regional environmental variability in Greenland (Anderson and Leng 2004;Anderson et al. 2008;Olsen, Anderson, and Leng 2013;Olsen et al. 2012). These studies have surveyed multiple lakes in this region, with sampling at the maximum water depth. ...
... The sediment accumulation rate for EVV Upper lake was approximately 0.015 cm yr −1 . Anderson et al. (2008) report sedimentation rates for other small lakes in the region of about 0.02 cm yr −1 for the upper 50 cm, representing approximately 2,500 yr. The δ 13 C org in sediments ranged from −30.3‰ to −29.2‰ (mean ± SD: −29.5 ± 0.5) with the most 13 C depleted isotopic values measured in the shallowest intervals ( Figure 4). ...
Stable isotope compositions of organic carbon (δ13Corg) and nitrogen (δ15N) in macrophytes and sediments are useful in assessing sources of lake productivity and diagenesis of organic matter from formation through sedimentation to decomposition. Despite the increasing importance of high-latitude landscapes to carbon cycling under amplified and accelerating warming in the Arctic, the high density of small closed-basin lakes in this landscape, and the utility of stable isotopes in the study of carbon dynamics, limited data are available on within-lake spatial variability of δ13Corg and δ15N in these systems. The goal of this study was to investigate the spatial variability in stable isotopic composition of three dominant macrophyte species (Hippuris vulgaris, Eriophorum angustifolium, Warnstorfia exannulata) and sediments from littoral and profundal areas of a single closed-basin system among the common small Arctic lakes that populate the ice-free margin of Greenland. The range in δ13Corg of macrophytes (−33.9‰ to −27.1‰) was within the typical range of plants utilizing the C3 pathway for carbon fixation. No notable differences were observed in δ13Corg between segments of the individual macrophytes (emergent, submergent, and root tissues), indicating that the isotopic fractionation of carbon was similar throughout the plant. Between-species variations in δ13Corg were small, but significant (p
... As part of the effort to properly constrain the variables incorporated into a single biomarker dD or d 18 O value, it is important to understand both the applicability of modeled precipitation and the impacts of an arctic environment on leaf water evaporation. The area where this study was conducted, Kangerlussuaq in West Greenland (Fig. 1), is already the site of several paleolimnology studies (Aebly and Fritz, 2009;Anderson et al., 2009 and has provided highly informative lake sediment cores dating back to more than 8000 yr before present (B.P.) (Willemse and Törnqvist, 1999;Anderson et al., 2008;D'Andrea et al., 2011;Olsen et al., 2012). It is also the site of ongoing plant ecology investigations (e.g., Post and Pedersen, 2008) and has a long history of study, making it an ideal location to examine the stable isotope composition of arctic plants given its modern ecological context and applicability to arctic paleohydrology. ...
... The Sandflugtdalen ("Flying Sand Valley"; Fig. 1) spans ~30 km from Kangerlussuaq to the edge of the GrIS and mostly comprises low hills of exposed rock or glacial outwash and floodplain terraces (Storms et al., 2012). Deglaciation of the Søndre Strømfjord began around 10-11 kyr B.P., coupled with the advance of tundra vegetation (Anderson et al., 2008;Leng et al., 2012), and reached the Kangerlussaq area around 8 kyr B.P. (Bennike and Björck, 2002). Today, Kangerlussuaq receives a mean annual precipitation of ~140 mm, and the mean annual temperature is −5.7 °C (data from the Danish Meteorological Institute, DMI). ...
Stable hydrogen and oxygen isotope ratios (δD and δ¹⁸O) of archived plant tissues can be used in paleoenvironmental reconstructions, assuming a well-grounded understanding of the environmental drivers of stable isotope variation in plant waters. Previous plant water calibration studies have focused on lower latitudes, but given the importance of arctic climate reconstructions, it is necessary to understand the drivers of isotope fractionation in plants that are unique to high latitudes. Here, we present δD and δ¹⁸O values of plant waters from the Kangerlussuaq area in West Greenland. We use the evaporation line created by the xylem waters to estimate the hydrogen and oxygen isotope values of local meteoric source water and find values that are lower than modeled estimates. We also apply the modified Craig-Gordon leaf water model, using local climate parameters and xylem water values to model leaf water values. We find that measured plant water values are generally in good agreement with model estimates, and discrepancies are likely explained by plant microclimates that are warmer and drier than average air measurements. This study extends stable isotope calibrations to arctic regions and provides a new estimate of average precipitation water isotopes values, which in turn inform plant proxy-based paleoclimate studies in the Arctic.
... For northern landscapes, such studies often relate distributions of biota to measurements of water chemistry and environmental variables in order to evaluate environmental change (e.g., Pienitz et al. 1995;Bigler and Hall 2002;Fallu et al. 2002;Rühland and Smol 2002;Porinchu et al. 2009). The use of RDAs to analyze spatial environmental gradients has also been applied to temporal gradients for environmental reconstruction (Lotter et al. 1997;Lotter 1998;Anderson et al. 2008). However, a host of internal lake processes and external environmental factors likely simultaneously exert strong influence on aquatic communities (Blenckner 2005). ...
... Fritz and Anderson (2013) alluded to the need to recognize biogeochemical linkages between lakes and their catchments, but these can be difficult to quantify and interpret. The examination of abundance and diversity of aquatic organisms that respond directly and indirectly to environmental variables is often used for the inference of their environment (Walker and MacDonald 1995;Weckström and Korhola 2001;Brodersen and Anderson 2002;Anderson et al. 2008;Medeiros and Quinlan 2011). These types of studies typically focus on direct relationships between singular factors, such as temperature and biotic production (Lotter et al. 1997;Rühland et al. 2015), which are predicated on assumptions that large-scale interactions, such as the effects of alterations in climate or water chemistry, will result in overarching shifts in the distributions of species (Pienitz et al. 1995;Lotter et al. 1999;Battarbee 2000;Fallu et al. 2002;Fritz and Anderson 2013). ...
Biotic communities in shallow northern lakes are frequently used to assess environmental change, however complex interactions among multiple factors remain understudied. Here, we present analysis of a comprehensive data set that evaluates the influence input waters, catchment characteristics, limnology, and sediment properties on diatom and chironomid assemblages in surface sediments of ~49 shallow mainly thermokarst lakes in Old Crow Flats, Yukon. Multivariate analyses and ANOSIM tests identified that composition of diatom (119 taxa) and chironomid (68 taxa) assemblages differ significantly (p<0.05) between lakes with snowmelt- versus rainfall-dominated input water. Redundancy analysis revealed strong correlation of limnological, sediment, and catchment variables with input waters. Variation partitioning analysis showed that unique effects of limnological variables accounts for the largest proportion of variation in diatom and chironomid assemblages (17.2, 12.6 %, respectively). Important independent roles of sediment properties (8.5, 9.5 %) and catchment characteristics (4.9, 5.1 %) were also identified. We suggest that the substantial variation shared among these classes (6.1, 7.9 %) is largely attributable to hydrological processes. Our study demonstrates the utility of multi-factor analysis in northern aquatic research and draws attention to the limitations of one-dimensional comparisons and their interpretations when modelling biotic responses to environmental change.
... The Foy Lake record shows regime shifts that result from an interaction of climate change and lake morphology, with climate causing lake level lowering through altered precipitation-evaporation balance, but morphology determining the diatom response to these (sometimes small) climatic shifts. In forested catchments, or catchments close to the tree line, changes in vegetation affect the supply of DOC and nutrients to lakes, influencing aquatic communities and biological productivity (Anderson et al. 2008; Mackay et al. 2012). Direct influence of treeline dynamics on lake ecosystems is shown by Pienitz et al. (1999;Table 1 , no. 10), who reconstructed an abrupt shift in diatom composition and a rapid decrease in lake-water DOC content following the retreat of spruce (Picea abies (L.) H. Karst.) from the catchment of a subarctic Canadian lake (Queen's Lake). ...
... ation inherent in sediment records. Resolution is also an important factor when discussing terminology and definitions: a shift in ecosystem state is generally considered a regime shift if it is abrupt and persistent (Folke et al. 2004; Lees et al. 2006; Andersen et al. 2009; Williams et al. 2011). But what is persistent on a geological time scale? Anderson et al. (2008) describe a regime shift where the system stays in the new regime for 50 years before shifting back again. In the perspective of modern day monitoring data, this period is long, and the regime persistent, but in some of the other studies presented here, the shift might not be evident in the record due to low time resolution. It is diffic ...
Regime shifts in lake ecosystems can occur in response to both abrupt and continuous climate change, and the imprints they leave in paleolimnological records allow us to investigate and better understand patterns and processes governing ecological changes on geological time scales. This synthesis investigates paleolimnological records that display apparent regime shifts and characterizes the shifts as either smooth, threshold-like or bistable. The main drivers behind the shifts are also explored: direct climate influence on lakes, climate influence mediated through the catchment, lake ontogenetic processes and/or anthropogenic forcing. This framework helps to elucidate the relationship between driver and regime shift dynamics and the type of imprint that the associated regime shifts leaves in sediment records. Our analysis of the limited sites available (22 sites) show that smooth regime shifts are characterized with forcing and response variables acting on similar time scales, whereas regime shifts that demonstrate a threshold like response or a hysteresis response occur on shorter time scales than changes in drivers. The temporal resolution of the record, a common concern in paleo records, limits identification of the timing and rate of the regime shifts. When detected, past regime shifts offer rich opportunities to understand ecosystem responses to climate and other changes and to evaluate the mean state and natural variability of lake ecosystems on time scales of decades to millennia. There are a number of remaining challenges in understanding regime shifts and ecosystem dynamics in a paleolimnological perspective including lack of an appropriate temporal resolution and ecosystem feedback mechanisms. Combining paleoecology with contemporary studies can help clarify the scale of regime shifts and to distinguish patterns in ecosystem changes from natural variability.
... Resolution is also a confounding factor when discussing terminology and definitions: a shift in ecosystem state is generally considered a regime shift if it is abrupt and persistent (e.g. ), but what is persistent on a geological time scale? Anderson et al. (2008), for example, describe a regime shift 8200 years ago where the system stayed in the new regime for 50 years before it shifted back again. In the perspective of modern day monitoring data, this period is long, and the regime persistent, but in some of the other studies presented in Paper III, the shift might not even be evident in the record due to low temporal resolution. ...
... oospores TYPE I -smooth regime shift T YPE II -threshold response TYPE III -hysteresis response Figure 3. Examples of different types of regime shifts from the literature. Type I, smooth regime shift: (a) profiles of key diatom species, ∂ 18 O and ∂ 13 C isotope records redrawn fromAnderson et al. 2008. The increase in ∂ 18 O indicates increased aridity, while the coincidental reduction in ∂ 13 C reflects a reduction in productivity. ...
Regime shifts in lake ecosystems can occur in response to both abrupt and continuous climate change, and the imprints they leave in palaeolimnological records allow us to investigate and better understand patterns and processes governing ecological changes on geological time scales. This thesis aims at investigating palaeolimnological records of regime shifts in lakes during the Holocene to explore how lake ecosystems responded to climate changes and anthropogenic activities and to identify thresholds or tipping points that produced regime shifts. The thesis includes case studies of two Swedish lakes and a synthesis of recently published palaeolimnological records displaying regime shifts. In the first case study a detailed diatom record from Lake Kälksjön, west-central Sweden, was investigated for periods of abrupt ecological change associated with the 8.2 ka cooling event. Using change-point analysis we found two regime shifts in the diatom record: one in response to an abrupt erosion event at c. 8040 cal. yr BP, and another caused by climate warming following the 8.2 ka event. The study demonstrates that not only can regime shifts be detected in sediment records, they can also be quantified and statistically tested for, provided that the sampling resolution is high and the chronological control sufficiently precise. The second case study is focused on recent regime shifts between clear-water and turbid states in Lake Krankesjön in southern Sweden. We combined palaeolimnological records and limnological monitoring data, concentrating on the documented collapse of the clear-water state in 1975 and the subsequent recovery in the late 1980s, in order to increase our understanding of changing ecological patterns and processes in shallow lakes. We found that the shift from clear to turbid conditions was abrupt, while the recovery of the clear-water state was more gradual, and the complex and non-linear reactions of the lake to shifting conditions emphasizes the importance of careful lake and catchment management if a stabilization of the clear-water state is desired. In addition to these studies, the theoretical concept of regime shifts is expanded upon in our synthesis of palaeolimnological records with regime shifts, where we characterize the shifts as either smooth, threshold-like or bistable. The examples are also placed within a conceptual model of potential physical processes that produce regime shifts in lakes and the main drivers behind the shifts are identified: direct climate influence on lakes, climate influence mediated through the catchment, lake ontogenetic processes and/or anthropogenic forcing. This framework helps to elucidate the relationship between driver and regime shift dynamics and the type of imprint that the associated regime shifts leave in sediment records. When detected, past regime shifts and palaeolimnological records offer rich opportunities to increase the understanding of ecosystem responses to climate changes and to evaluate the mean state and natural variability of lake ecosystems on timescales of decades to millennia. Palaeolimnological archives provide a perspective on whether the pre-disturbance "natural" state that may be the target of restoration efforts is actually natural, or if it is an anomaly in lake history, and if this target is at all possible to reach or if it, due to shifting baselines and lake ontogeny, is no longer a realistic restoration endpoint. Furthermore, I argue that linking the timescales of contemporary ecology with palaeoecology/limnology may provide long-term records of lake history and opportunities to further disentangle the role of different forcings on lake ecosystems. An improved understanding of lake ecosystem dynamics and regime shifts in lakes through the cooperation of limnologist/ecologists and palaeolimnologists may better prepare us to face future climate change and to fully understand and perhaps mitigate the effects of global climate change on lake ecosystems.
... Zooplankton plays a major role in the functioning and the productivity of aquatic ecosystems through its impact on the nutrient dynamics and its key position in the water food webs [ 1 ]. Numerous factors potentially influence zooplankton community structure, including in-lake processes like species interactions, or external elements like climate variability, catchment inputs, anthropogenic impact and other indirect factors [ 2 ]. The permanent increase of human activities raises the question of possible long-lasting anthropogenic influence on ecosystems. ...
The zooplankton community composition of Iskar reservoir in Bulgaria was studied in the period 2009-2016 and compared to data from 1961-1962 to assess potential decadal changes. A total of 90 zooplankton taxa of different ranks were recorded during the investigation. Sixteen taxa were registered for 1961-1962 and 86 taxa during the period 2009-2016. Also the 1961-1962 sampling period included the first investigation on diurnal dynamics of freshwater zooplankton in Bulgaria. Rotifera was the most abundant group during both investigated periods. The disappearance of 1/3 of the species found during the first period was registered. Only eight zooplankton species and two zooplank-ton components were common for both periods of investigation. Also, changes in the quantitative parameters of zooplankton were found in Iskar reservoir. The extremely low similarity between the zooplankton of the two studied periods was discussed. The obtained results showed the reservoir ageing and the exploitation effect on zooplankton community of the reservoir. Iskar is a representative reservoir for drinking water source and our zooplankton data can be used to understand the changes in ecosystem structure and function.
... Despite their usefulness, studies on pigments in Arctic regions are limited. They focus on determination of pigments in sea water (Dobrzyn et al., 2009;Pettersen et al., 2011) or lake sediments (Guilizzoni et al., 2006;Anderson et al., 2008;Jiang et al., 2011). However, as proven by the study of Hornsund sediments or Kongsfjorden sediments (Bourgeois et al., 2016), pigments in sediment may also be useful indicators of primary production and phytoplankton taxonomic composition changes in Arctic fjord regions. ...
Arctic climate changes are of global significance. This work investigates the influence of climate change on primary production and phytoplankton taxonomic composition in the western Spitsbergen fjords over the last century, using pigments in sediments. Nine sediment cores were analysed for chloropigment and carotenoid contents, and the five found to be richest in pigments were dated (²¹⁰Pb, ¹³⁷Cs) and analysed for additional parameters (Corg, Ntot δ¹³C, grain size). The three well-dated cores, representing the last 70–130 y, were selected for tracking primary production and phytoplankton taxonomy changes in the past. The sum of chloropigments-a (∑Chlns-a) in the undisturbed sediments is a good marker of primary production in the adjacent Spitsbergen fjord waters. The sum of 19′-hexanoyloxyfucoxanthin and 19′-hexanoyloxy-4-ketofucoxanthin to diatoxanthin ratio (∑Hexcs/Diato) in sediments is proposed as a proxy of changes in haptophytes to diatom and dinoflagellate proportions, connected with climate variability. ∑Chlns-a and ∑Hexcs/Diato ratio sediment profiles have shown that the impact of global warming on primary production and phytoplankton taxonomic composition is observed even in the north of Spitsbergen. In the most northern studied site, Raudfjorden, visible effects of warming started about a decade later than in Kongsfjorden. Recent high primary production in Kongsfjorden and Raudfjorden is related to a high proportion of haptophytes compared to diatoms and dinoflagellates, linked to warm Atlantic Water inflow. In Hornsund, primary production was also observed to have increased, but not as rapidly as at other sites, probably due to a greater influence of cold Arctic Water.
... Subfossil chironomid records in montane lakes are therefore often used for paleo-temperature reconstruction based on regional chironomid-temperature transfer functions (Heiri and Lotter, 2003;Wang et al., 2018;Zhang et al., 2017a, b). Warming climate would promote the growth of warmadapted species (Luoto et al., 2019), and its interaction with nitrogen deposition can increase food availability for chironomids through enhancing primary production (Anderson et al., 2008). ...
Many remote montane ecosystems are experiencing biogeochemical changes driven by warming climate and atmospheric pollution. Compared with circumpolar and temperate lakes, the responses of subtropical montane lakes to these external stressors have been less investigated. Here we present sedimentary multi-proxies records (i.e. chironomids, elements and stable isotope of carbon and nitrogen) in 210Pb-dated cores from two montane ponds (central China). Before the 1900s, low biomass and the dominance of opportunistic species (e.g. Chironomus anthracinus-type) in both ponds might be in response to cold and harsh condition. Thereafter, chironomid communities in both ponds experienced pronounced shifts. Nutrient-tolerant/warm-adapted species (e.g. Chironomus sp., Polypedilum nubeculosum-type and Endochironomus impar-type) proliferated and biomass increased synchronously after the 1900s, suggestive of favorable condition for chironomid growth. Redundancy analyses revealed that changes in chironomid communities in both ponds were significantly correlated with rising temperature and δ15N depletion. Prolonged growing season and nitrogen subsidy would increase primary productivity, and hence enhancing food availability for chironomids. Catchment-mediated indirect effects of warming and nitrogen deposition, such as hydrological changes and terrestrial organic matter inputs, would impose further influences on chironomid communities. Taken together, the combined effects of climate warming and nitrogen deposition have caused significant shifts in primary consumers of these montane ponds, and imposed cascading effects on structure and function of subtropical montane aquatic ecosystems.
... Sedimentary TOC was used as a lake biological productivity indicator (Meyers and Teranes, 2001). The coincidence between climate amelioration and the enhancement of biological productivity reflected by TOC in lakes has been reported (Anderson et al., 2008;Ramrath et al., 1999). TOC content in the sediment was analyzed from the dried and homogenized samples using an elemental CNS analyzer Vario Max CNS (Elementar). ...
... When modeling paleotemperatures from paleoecological proxy data, it is essential to consider secondary environmental gradients that may have driven assemblage changes over time (Brooks et al., 2012;Juggins, 2013;Velle et al., 2010). Changes in lakewater oxygenation, lake substrate and macrophyte cover, and watershed soils and vegetation and resulting changes in nutrient cycling and lakewater pH can all affect chironomid assemblages (Anderson et al., 2008;Heggen et al., 2010;Kaufman et al., 2012). Importantly, the current study site bears evidence of relatively little change in these factors through the Holocene. ...
Arctic temperature shifts drive changes in carbon cycling, sea ice extent and Greenland Ice Sheet mass balance, all of which have global ramifications. Paleoclimate data from past warm periods provide a unique means for assessing the sensitivity of these systems to warming climate, but the magnitude and timing of past temperature changes in many parts of the Arctic are poorly known. Here we assess orbital-scale Holocene temperature change in northwest Greenland near the margin of the ice sheet using subfossil insect assemblages from lake Deltasø. Based upon sedimentation history in this currently proglacial lake, we also place constraints on Holocene extents of the adjacent North Ice Cap, a large independent ice cap. Reconstructed summer temperatures were warmer than present at the onset of lacustrine sedimentation following regional deglaciation by the Greenland Ice Sheet, sometime between 10.8 and 10.1 ka BP. Deltasø experienced the warmest summer temperatures of the Holocene between ∼10 and 6.2 ka BP, followed by progressive cooling that continued through the late Holocene as summer insolation declined, culminating in the lowest temperatures during the pre-industrial last millennium. Deltasø chironomids indicate peak early Holocene summer temperatures at least 2.5–3 °C warmer than modern and at least 3.5–4 °C warmer than the pre-industrial last millennium. We infer based upon lake sediment organic and biogenic content that in response to declining temperatures, North Ice Cap reached its present-day size ∼1850 AD, having been smaller than present through most of the preceding Holocene. Our synthesis of paleoclimate evidence from northwest Greenland, Ellesmere Island and northern Baffin Bay supports the timing of temperature trends inferred at Deltasø, and suggests that quantitative temperature reconstructions from Deltasø may represent a minimum bound on regional early Holocene warming. Collectively, records from the region indicate >4 °C summer cooling through the Holocene. Intense early Holocene warmth around northwest Greenland argues against delayed onset of warmer-than-present conditions due to the influence of the nearby waning Laurentide Ice Sheet, and has implications for understanding the Greenland Ice Sheet's sensitivity to climate change.
... 7.6 cal ka BP, rising temperature affected the primary producer community in Lake Peipsi. Therefore, the rise in trophic status and change in the primary producer community in the middle Holocene can be explained by a combination of climate change and ontogeny of Lake Peipsi, i.e. natural nutrient enrichment (Anderson et al. 2008). ...
We used HPLC to identify and quantify pigments in a Holocene sediment record from large, shallow Lake Peipsi, Estonia. The aim of our study was to track the influence of long-term climate change (i.e. temperature fluctuations) on past dynamics of aquatic primary producers. Sedimentary pigments were separated and quantified in 182 samples that span the last ca. 10,000 years. There was an increasing trend in sedimentary pigment concentrations from basal to upper sediment layers, suggesting a gradual increase in lake trophic status through time. Using additive models, our results suggested that primary
producer dynamics in Lake Peipsi were closely related to temperature fluctuations. We, however, identified two periods (early Holocene and after ca. 2.5 cal ka BP) when the relationship between primary producer composition and temperature was weak, suggesting the influence of additional drivers on the primary producer community. We postulate that: (a) the increase of primary producer biomass in the early Holocene could have been caused by input of allochthonous organic matter and nutrients from the
flooded areas when water level in Lake Peipsi was increasing, and (b) changes in the abundance and structure of primary producer assemblages since ca. 2.5 cal ka BP was related to widespread agricultural activities in the Lake Peipsi catchment. These results
suggest that human activities can disrupt the relationship between the primary producer community and temperature in large, shallow lakes.
... Indeed, rapid warming observed during the first millennia of the Holocene (i.e., Early Holocene, from 10.5 to ca. 8 kyr cal. BP), probably enhanced the effect of natural eutrophication (Anderson et al., 2008) and caused the observed increase in OM contents (Fig. 2). Similar trends in OM accumulation have frequently been found in Holocene sediment records from temperate lakes (e.g., Magny et al., 2012), boreal lakes (e.g., Punning et al., 2005) and Arctic lakes (e.g., Anderson et al., 2009). ...
... Climate (in particular air temperature) is known to have a strong influence on inputs of allochthonous organic matter to lakes (Stallard, 1998), on autochthonous primary productivity (Anderson et al., 2008) and the production of CH 4 -derived biomass during anoxic events (Duc, Crill, & Bastviken, 2010). Therefore, food availability for benthic deposit-feeding invertebrates can be closely related to longterm temperature fluctuations and were expected to be highly variable over time (Belle, Luoto, et al., 2017;van Hardenbroek et al., 2013). ...
1. A paleolimnological study, covering the last c. 12,000 years, was conducted in a small sub-alpine lake located in the Alps to study climate change impacts on carbon flows through food webs in small lakes. We used analysis of sedimentary pigments and carbon stable isotopic composition of chironomid remains (δ13CHC) to reconstruct past dynamics of phytoplankton community and carbon sources sustaining benthic consumers.
2. Chironomid biomass was sustained by a combination of allochthonous, autochthonous, and CH4-derived organic matters, and their relative contributions were correlated to changes in temperature. Relatively high terrestrial contributions to chironomid biomass were observed during period of the Holocene when in-lake production was low. Relatively high incorporation of CH4-derived carbon to chironomid biomass was found during anoxic events co-occurring with the Holocene Thermal Maximum.
3. Results were then compared with those collected in a small boreal lake in Estonia. We tested the hypothesis that responses in carbon flows through benthic food web to past climate change would be similar between these lakes. We found a negative correlation between δ13CHC values of both lakes and inferred air temperature, suggesting that temperature was the major driver to different food sources being incorporated into chironomid biomass.
4. Our study demonstrated that air temperature was the principal driver of the energy flows through benthic food web in the studied small lakes. We conjectured that carbon cycling in food webs of small lakes might be strongly sensitive to climate change.
... The usual approach of microscopically identifying the phytoplankton composition in Arctic regions, also in the Hornsund fjord (Wiktor and Wojciechowska 2005;Piwosz et al. 2009) is time consuming and costly (Paerl et al. 2003). Most of the few papers on pigments in Arctic aquatic environments relate to seawater (Dobrzyn et al. 2009;Pettersen et al. 2011) or lacustrine sediments (Guillizzoni et al. 2006;Anderson et al. 2008;Jiang et al. 2011;Florian et al. 2015); those authors detected chloropigments predominantly by fluorometry, not HPLC. The latter method enables the qualitative and quantitative analysis of pigments and their derivatives (Jeffrey and Wright 1997; Morata and Renaud 2008). ...
Pigments (chloropigments-a and carotenoids) in sediments and macroalgae samples, collected in Hornsund, in July 2015 and July 2016, were analysed (HPLC) in this work. In spite of the aerobic conditions and the periodic intensive solar irradiation in the Arctic environment, neither of which favour pigment preservation in water column and surface sediments, our results indicate that these compounds can provide information about phytoplankton composition, primary production and environmental conditions in this region. The sum of chloropigments-a, a marker of primary production, in the Hornsund sediments varied from 0.40 to 14.97 nmol/g d.w., while the sum of carotenoids ranged from 0.58 to 8.08 nmol/g d.w. Pheophorbides-a and pyropheophorbides-a made up the highest percentage in the sum of chloropigments-a in these sediments, supplying evidence for intensive zooplankton and/or zoobenthos grazing. Among the carotenoids, fucoxanthin and its derivatives (19’-hexanoyloxyfucoxanthin and 19’-hexanoyloxy-4-ketofucoxanthin) contributed the highest percentage, which points to the occurrence mainly of diatoms and/or haptophytes in the water. The pigment markers show that the input of macroalgae to the total biomass could be considerable only in the intertidal zone.
... trophic interactions, can infl uence aquatic community composition and structure. The relative role that these processes play varies spatially and temporally, with the effects of climate and environmental change becoming increasingly important over longer timescales (Anderson et al., 2008). ...
The effects of alpine glaciers on the hydrology, physical features, and biogeochemistry of lakes have been investigated over contemporary time scales. However, the influence of these factors on algal communities over longer time scales remains unclear, yet is critical to paleolimnological interpretation of environmental change in alpine regions. We examined sedimentary algal pigments and fossil diatom assemblages in two proximal lakes with equivalent local climates, one glacier-fed and one snow-fed, in the central Rocky Mountains (USA) to determine how glacier meltwater has altered algal records over the last 3,000 years. Differences between the records of the two lakes intensified during the Medieval Climate Anomaly and the Little Ice Age, with the glacier-fed lake exhibiting an overall increase in fossil algal pigment concentrations and greater diatom assemblage turnover. Starting 1,000 years ago, the glacier-fed lake in this study showed evidence of nitrogen enrichment from glacier meltwater, as indicated by increasing relative abundances of Asterionella formosa and, to a lesser extent, Fragilaria crotonensis. Since the Little Ice Age, diatom species richness declined in the glacier-fed lake, and further decreased following the 1950s, while assemblage turnover increased. These results demonstrate that glaciers can strongly alter the algal sedimentary record and should be considered when interpreting high-elevation lake records.
... Longterm temperature change seemed to have a direct impact on the composition and the quantity of sedimentary organic matter in lake sediments (Fig. 2). Increase in the contribution of aquatic organic matter to lake sediments as well as the rise in organic matter contents in sediments was observed during warming periods (Fig. 2b), and similar patterns in sediment records were already reported (Anderson et al. 2008;Belle et al. 2017a). In addition, an important erosion phenomenon of allochthonous organic matter due to sparse vegetation cover and wet climate was suspected during the Early Holocene (Fig. 2a, b), as previously documented in many lake records (Birks et al. 2000;Fritz and Anderson 2013). ...
In order to forecast the influence of future climate change on lake ecosystems, the paleolimnological approaches are needed to understand the impact of past climate variability. We reconstruct temporal changes in carbon resources sustaining chironomid biomass over the last 14,000 years, by means of carbon stable isotope analysis of subfossil chironomids (δ¹³CHC), with the aim of identifying the response of carbon processing in the benthic food web to climate change. We find a negative linear correlation between reconstructed summer mean air temperature and δ¹³CHC values, revealing that (i) the contribution of allochthonous organic carbon to the chironomid biomass is high during the coldest and low-productive period, (ii) the aquatic organic matter is the main carbon source during intermediate climate conditions, and (iii) a significant part of the chironomid biomass is sustained by methane-derived carbon during the Holocene Thermal Maximum and the Bølling-Allerød. This study confirms that climate change may significantly affect the recycling process of organic carbon in the benthic food web of small lakes. However, deforestation and agricultural practices within the catchment area induced important organic matter inputs into the lake sediments, which seem to disrupt the observed relationship between climate variability and carbon processing in the benthic food web. In this context, complementary studies are needed to better understand the combined effects of the ongoing global warming and human activities on the lake carbon cycling.
... The pronounced gradients in water chemistry identified in this study have been demonstrated in previous surveys around Kangerlussuaq, showing that lakes located inland are more enriched in major ions, nutrients and non-particulate organic carbon (NPOC) (Anderson et al. 2001;Anderson and Stedmon 2007). These patterns are largely driven by local climate where low precipitation: evaporation ratios in the inland and ice sheet marginal areas, together with aerial deposition of dust from the glacial sandur plains have led to the concentration of salts and dissolved organic carbon (DOC), low hydrological flushing rates and strong recycling of nutrients (total N and P) (McGowan et al. 2003;Anderson et al. 2008). This dependence on inlake nutrient recycling leads to the divergence in chemical characteristics across the region and so inland lakes are more chemically diverse than lakes in other areas. ...
Benthic diatoms are commonly used for palaeoenvironmental reconstruction in Arctic regions, but interpretation of their ecology remains challenging. We studied epilithic diatom assemblages from the shallow margins of 19 lakes from three areas (coast-inland-ice sheet margin) along a climate gradient in Kangerlussuaq, West Greenland during two periods; shortly after ice-off (spring) and in the middle of the growth season (summer). We aimed to understand the distribution of Arctic epilithic diatoms in relation to water chemistry gradients during the two seasons, to investigate their incorporation into lake sediments and to assess their applicability as palaeoenvironmental indicators. Diatoms were correlated with nutrients in the spring and alkalinity/major ions in the summer, when nutrients were depleted; approximately half of the variance explained was independent of spatial factors. When categorised by functional attributes, diatom seasonal succession differed among regions with the most obvious changes in inland lakes where summer temperatures are warmer, organic nutrient processing is prevalent and silicate is limiting. These conditions led to small, motile and adnate diatoms being abundant in inland lakes during the summer (Nitzschia spp., Encyonopsis microcephala), as these functional attributes are suited to living within complex mats of non-siliceous microbial biofilms. Seasonal succession in silica-rich lakes at the coast was less pronounced and assemblages included Tabellaria flocculosa (indicating more acidic conditions) and Hannaea arcus (indicating input from inflowing rivers). The nitrogen-fixing diatom Epithemia sorex increased from the coast to the ice sheet, negatively correlating with a gradient of reactive nitrogen. The presence of this diatom in Holocene sediment records alongside cyanobacterial carotenoids during arid periods of low nitrogen delivery, suggests that it is a useful indicator of nitrogen limitation. Nitzschia species appear to be associated with high concentrations of organic carbon and heterotrophy, but their poor representation in West Greenland lake sediments due to taphonomic processes limits their palaeoenvironmental application in this region. Proportions of epilithic taxa in lake sediment records of coastal lakes increased during some wetter periods of the Holocene, suggesting that snowpack-derived nutrient delivery may offer diatom taxa living at lake margins a competitive advantage over planktonic diatoms during the “moating” ice melt period. Thus, further research investigating linkages between epilithic diatoms, snowpack and nutrient delivery in seasonally frozen lakes is recommended as these taxa live on the ‘front-line’ during the spring and may be especially sensitive to changes in snowmelt conditions.
... Organic Lake, Vestfold Hills Bird et al. [40] 13 Lake sediments 26 Highway Lake, Vestfold Hills Bird et al. [40] 14 Lake sediments 24 N island, Amanda Bay Huang et al. [58] 15 Lake sediments 159 Lake Skallen Oike, the Syowa Station Matsumoto et al. [15] 16 Lake sediments 143 Ross Island and Beaufort Island, Ross Rea Liu et al. [23] 17 Lake sediments 140 Marguerite Bay, Antarctic Peninsula Hodgson et al. [59] 18 Lake sediments 25 South Shetland Islands, Antarctic Peninsula Watcham et al. [60] 19 Lake sediments 17 Moutonnée Lake, Alexander Island Smith et al. [34] 20 Lake sediments 8 Ablation Lake, Alexander Island Smith et al. [34] 21 Lake sediments / Long Lake, King George Island Yoon et al. [61] 22 Lake sediments 3 Citadel Bastion Lake, West Antarctica Roberts et al. [62] 23 Lake sediments 43 Fildes Peninsula Liu et al. [63] 24 Lake sediments 115 Xihu Lake, Fildes Peninsula Li et al. [64] 25 Lake sediments / Lake CF3, north-east Baffin Island, Canada Briner et al. [35] 26 Lake sediments 4 Lake SS2, southern West Greenland Anderson et al. [65] ...
The carbon isotopic composition of organic matter (δ 13 Corg) was determined in two sediment cores (IIL1 and IIL9) recovered from Inexpressible Island, Ross Sea, Antarctica, and analyzed to identify the sources of that organic matter. The δ 13 Corg values of sediments of IIL9 were found to vary between −14.6‰ and −11.6‰, with a mean of −13.4‰ (n=48). These values were significantly higher than those of IIL1 sediments which varied between −23.2‰ and −20.4‰, with a mean of −21.8‰ (n=55). The variation in δ 13 Corg values in these two sediment cores indicate different sources of organic matter. The relatively high δ 13 Corg values in IIL9 are in accordance with a source from algae, while the low δ 13 Corg values in IIL1 evince significant influence from penguin guano with algae as the secondary source. Compared with the reference data from other high-latitude lake sediments and plants, the δ 13 Corg values in IIL9 were extremely high, a result likely related to intense competition for CO2 assimilation among algal species during the growing season in this relatively shallow pond. These results indicate that sedimentary δ 13 Corg is a reliable proxy for paleo-primary productivity in ponds at Inexpressible Island.
... In this paper, Holocene mean July air temperature (T jul ) reconstructions based on a 9-m-long lake sequence from the northern boreal zone of NE Fennoscandia, using four biological assemblages (plant macrofossils, pollen, chironomids and diatoms), are compared and evaluated in the light of local-scale and site-specific processes as these factors have been shown to significantly influence fossil assemblages extracted from lake sediments (Anderson et al., 2008;Shala et al., 2014b;Velle et al., 2005). Furthermore, the timing of maximum Holocene summer warming is explored. ...
Four biotic proxies (plant macrofossils, pollen, chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures (Tjul) at Lake Loitsana (northern Finland) during the Holocene. The aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest Tjul in the individual reconstructions. The reconstructed Tjul values are evaluated in relation to local-scale/site-specific processes associated with the Holocene lake development at Loitsana as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. While pollen-based temperatures follow the classical trend of gradually increasing early-Holocene Tjul with a mid-Holocene maximum, the aquatic/wetland assemblages reconstruct higher-than-present Tjul already during the early Holocene, that is, at the peak of summer insolation. The relatively low early-Holocene July temperatures recorded by the pollen are the result of site-specific factors possibly combined with a delayed response of the terrestrial ecosystem compared with the aquatic ecosystem. Our study shows that all reconstructions are influenced at least to some extent by local factors. This finding stresses the need to evaluate quantitatively reconstructed climate values against local lake development and highlights the benefit of using multi-proxy data in Holocene climate reconstructions.
... Interpreting chironomid assemblage shifts Aquatic ecosystems are sensitive to factors other than temperaturefor example, vegetation change and changes in water chemistry that may be associated with watershed ontogeny or eutrophication from external nutrient sources (Anderson et al. 2008;Heggen et al. 2010;Kaufman et al. 2012;Luoto et al. 2015). Such secondary gradients may confound chironomid-based palaeotemperature reconstructions (Velle et al. 2005(Velle et al. , 2010cf. ...
Much of Greenland experienced summers warmer than present in parts of the early to middle Holocene, during a precession-driven positive anomaly in summer insolation. However, the magnitude of that warmth remains poorly known, and its timing and spatial pattern are uncertain. Here we describe the first quantitative Holocene palaeotemperature reconstruction from central East Greenland based upon insect (chironomid) assemblages preserved in lake sediments. We postulate that landscapes like our study site, characterized by minimal soil and vegetation development through the Holocene and thus little influenced by some important secondary gradients, are especially well suited to the use of chironomids to reconstruct Holocene temperatures. The inferred timing of warmth at our study site near Scoresby Sund agrees well with other nearby evidence, including glacial geological reconstructions and temperatures inferred from precipitation isotopes at Renland ice cap, supporting the use of chironomids to reconstruct temperatures at this site. We infer highest temperatures from c. 10 to 5.5 ka, followed by gradual cooling after 5.5 ka and progressively colder and less productive conditions after 3.5 ka. Models based upon two independent training sets yield similar inferred temperature trends, and suggest an average summer temperature anomaly from c. 10 to 5.5 ka of 3 to 4 °C relative to the preindustrial last millennium. The estimated overall rate of Neoglacial cooling averaged over the period from 5.5 to 0.5 ka was 0.6 to 0.8 °C per thousand years, more than twice the rate previously estimated for the Arctic as a whole. Given strong apparent spatial variability in Holocene climate around the Arctic, and the utility of palaeoclimate data for improving climate and ice-sheet models, it should be a priority to further quantify past temperature changes around the margins of the Greenland Ice Sheet, where few quantitative reconstructions exist and future warming will affect global sea level.
... Sedimentary TOC was used as a lake biological productivity indicator (Meyers and Teranes, 2001). The coincidence between climate amelioration and the enhancement of biological productivity reflected by TOC in lakes has been reported (Anderson et al., 2008;Ramrath et al., 1999). TOC content in the sediment was analysed from the dried and ...
This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the mean Millennial temperatures during the 11th, 13th, 15th and 20th centuries and 1–2 °C lower during the 12th, 14th, 17th–18th centuries. A persistent cold period, the Little Ice Age (LIA), occurred between 1550 and 1800 CE, was interrupted by a short warming at 1650 CE. The recognized regional climate fluctuations during the last Millennium affected the lake and its catchment, of which the strongest impact was caused by the LIA cooling. During the LIA the catchment vegetation was impacted by climate deterioration and the lake productivity reached its lowest level during the last Millennium. The current temperature reconstruction is in agreement with a previous continental scale temperature reconstruction for Europe. From obtained results it emerges that during the LIA the climate of western Scandinavia has been dictated by the atmospheric patterns originating from the North Atlantic.
... Based on populations of radiocarbon ages from ice-killed surface tundra moss, Miller et al. (2013a) found several periods of glacier expansion, beginning about 5 ka, and then at various times between 5 and 2 ka, with increasing expansion occurring~1.6 ka, 1.1 ka,~0.7 ka and~0.5 ka (Anderson et al., 2008;Miller et al., 2012Miller et al., , 2013bMargreth et al., 2014). Based on increasing mineral matter input at Donard Lake, glacier expansion is interpreted to have begun~6 ka and intensified at 2.5 ka (following a period nonglacial period from 8 to 6 ka; Miller et al., 2005). ...
In this synthesis paper, we summarize published records showing the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recently published database of highly resolved, quantitative Holocene climate records from the Arctic (Sundqvist et al., 2014). We plot the temperature histories represented by the records in the database and compare them with paleoclimate information based on 54 additional published records (but that don't yield either a quantitative climate reconstruction or are at insufficient resolution for inclusion in Sundqvist et al.’s database). Combined, the records include a variety of climate proxy types that range from ice (ice cores), land (lake and peat sequences) and marine (ocean sediment cores and coastal sediments) environments. The temperature-sensitive records indicate more consistent and earlier Holocene warmth in the north and east, and a more diffuse and later Holocene thermal maximum in the south and west. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0±1.0°C on average (n=11 records). The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 ka, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time. The spatial pattern of temperature change through the Holocene was likely driven by the decrease in northern latitude summer insolation through the Holocene, the varied influence of waning ice sheets in the early Holocene, and the variable influx of Atlantic Water into the study region.
... In order to describe the ongoing effects of climate related impacts on Arctic landscapes and to predict the future, it is essential to have access to data regarding chemical concentrations and biotic properties for a wide range of ecosystem domains and functional units (abiotic and biotic pools). There are several studies investigating different aspects of Arctic ecosystems, in West Greenland (e.g., Anderson et al., 2008;Ryves et al., 2009;Sobek et al., 2014;Jessen et al., 2014;Whiteford et al., 2016) and elsewhere (e.g., Chapin et al., 1995: Rysgaard andGlud, 2007;Smol and Douglas, 2007;Tarnocai et al., 2009;Rydberg et al., 2010;Palmtag et al., 2015;Hindshaw et al., 2016: Lundin et al., 2016. These studies provided crucial insights of high-latitude ecosystems that have increased our understanding of the significance and sensitivity of periglacial landscapes. ...
Global warming is expected to be most pronounced in the Arctic where permafrost thaw and release
of old carbon may provide an important feedback mechanism to the climate system. To better understand and predict climate effects and feedbacks on the cycling of elements within and between ecosystems in northern latitude landscapes, a thorough understanding of the processes related to transport and cycling of elements is required. A fundamental requirement to reach a better process understanding is to have access to high-quality empirical data on chemical concentrations and biotic properties for a wide range of ecosystem domains and functional units (abiotic and biotic pools). The aim of this study is therefore to make one of the most extensive field data sets from a periglacial catchment readily available that can be used both to describe present-day periglacial processes and to improve predictions of the future. Here we present the sampling and analytical methods, field and laboratory equipment and the resulting biogeochemical data from a state-of-the-art whole-ecosystem investigation of the terrestrial and aquatic parts of a lake catchment in the Kangerlussuaq region, West Greenland. This data set allows for the calculation of whole-ecosystem mass balance budgets for a long list of elements, including carbon, nutrients and major and trace metals. The data set is freely available and can be downloaded from PANGAEA: doi:10.1594/PANGAEA.860961.
... In order to describe the ongoing effects of climate related impacts on Arctic landscapes and to predict the future, it is essential to have access to data regarding chemical concentrations and biotic properties for a wide range of ecosystem domains and functional units (abiotic and biotic pools). There are several studies investigating different aspects of Arctic ecosystems, in West Greenland (e.g., Anderson et al., 2008;Ryves et al., 2009;Sobek et al., 2014;Jessen et al., 2014;Whiteford et al., 2016) and elsewhere (e.g., Chapin et al., 1995: Rysgaard andGlud, 2007;Smol and Douglas, 2007;Tarnocai et al., 2009;Rydberg et al., 2010;Palmtag et al., 2015;Hindshaw et al., 2016: Lundin et al., 2016. These studies provided crucial insights of high-latitude ecosystems that have increased our understanding of the significance and sensitivity of periglacial landscapes. ...
... In the sub-Arctic, the boreal forest to tundra transition may be associated with decreases in nutrients, major ions and DOC (Pienitz and Smol 1993;Rühland et al. 2003a). Uncertainty remains as to whether Arctic lakes are more strongly controlled by catchment factors or direct forcing by climate (Michelutti et al. 2007;Anderson et al. 2008;Fritz and Anderson 2013), and in particular how past and future lake responses to climate may be understood in the context of modern biogeochemical gradients. ...
The direction of pan-Arctic ecosystem shifts in response to climate warming is relatively well understood; however, landscape-level linkages among terrestrial, wetland, and lake ecosystems significantly influence the dynamics of each, making it difficult to generalize about lake responses to warming across the Arctic, and at times difficult to interpret paleoclimate records from lake sediments. To investigate differences in lake responses to recent climate change at the boreal-tundra ecotone, we conducted a 2-year survey of diatom assemblages from lakes with varying catchment characteristics in northern Manitoba, Canada. We investigated whether catchment geomorphology and landscape, including slope and vegetative cover, result in characteristic water chemistries and hence diatom assemblage signatures, which could then be used in paleolimnological studies to infer past changes in the catchment. Forty-four lakes were sampled for water chemistry and catchment vegetation was characterized using Landsat Imagery. Lake catchments were generally small (median 702 ha) and dominated by peat (Sphagnum) with or without lowland forest (Picea-Larix), or open tundra, with different amounts of exposed rock/till, upland forest/woodlands, and burn recovery area. Lakes were generally nutrient-poor, with lower nutrient and DOC concentrations in tundra-dominated catchments, and higher nutrients and DOC in catchments with greater forest cover. A diatom-based transfer function for pH (R² = 0.72, \( {\text{R}}_{\text{boot}}^{2} \) = 0.54) was developed and compared with diatom assemblage turnover and sediment geochemistry in cores from eight lakes to reconstruct limnologic conditions over the past ~200 years. Most cores showed similar increases in biogenic silica and carbon burial, beginning around AD 1880 in the tundra lakes and about 1920 in the more forested catchments, likely in response to regional warming. In contrast to lakes in other Arctic regions, our lakes showed only minor pH changes in recent decades. The shift, however, was more pronounced in higher-latitude lakes with less forest cover, suggesting small-scale watershed influence on lake response to climate, even on short time scales. Diatom assemblages did not follow previously published models of climate-linked community change seen in circum-Arctic and sub-Arctic lakes. Translating local changes detected in the paleolimnological record to the regional level requires an understanding of how different catchment properties mediate the response of lakes, and their diatom assemblages, to climate change.
... In addition, climate change may also play a role in ecosystem dynamics ( Anderson et al., 2008). We observed an approximately 1 °C increase in the annual average water temperature and increasing annual pre- cipitation in Lake Chaohu from the 1950s to 2010s, in accordance with the national-scale variations (Piao et al., 2010). ...
... Based on populations of radiocarbon ages from ice-killed surface tundra moss, Miller et al. (2013a) found several periods of glacier expansion, beginning about 5 ka, and then at various times between 5 and 2 ka, with increasing expansion occurring~1.6 ka, 1.1 ka,~0.7 ka and~0.5 ka (Anderson et al., 2008;Miller et al., 2012Miller et al., , 2013bMargreth et al., 2014). Based on increasing mineral matter input at Donard Lake, glacier expansion is interpreted to have begun~6 ka and intensified at 2.5 ka (following a period nonglacial period from 8 to 6 ka; Miller et al., 2005). ...
... 152 DOC is usually scarce because of the absence of terrestrial vegetation and thus the water is very UVR transparent with glacial flour scattering the light and creating an environment suited to cyanobacteria with UVR-screening pigments. 122,150 Marl-secreting charophytes can thrive in these early postglacial base-rich conditions and diatom diversity is usually low. 153 This condition is reliant on the availability of alkaline glacial till material and may not characterize areas of noncarbonate geology or nonerosive glacial regimes. ...
Lakes are active processors and collectors of carbon (C) and thus recognized as quantitatively important within the terrestrial C cycle. Better integration of palaeolimnology (lake sediment core analyses) with limnological C budgeting approaches has the potential to enhance understanding of lacustrine C processing and sequestration. Palaeolimnology simultaneously assimilates materials from across lake habitats, terrestrial watersheds, and airsheds to provide a uniquely broad overview of the terrestrial-atmospheric-aquatic linkages across different spatial scales. The examination of past changes over decadal–millennial timescales via palaeolimnology can inform understanding and prediction of future changes in C cycling. With a particular, but not exclusive, focus on northern latitudes we examine the methodological approaches of palaeolimnology, focusing on how relatively standard and well-tested techniques might be applied to address questions of relevance to the C cycle. We consider how palaeolimnology, limnology, and sedimentation studies might be linked to provide more quantitative and holistic estimates of lake C cycling and budgets. Finally, we use palaeolimnological examples to consider how changes such as terrestrial vegetation shifts, permafrost thaw, the formation of new lakes and reservoirs, hydrological modification of inorganic C processing, land use change, soil erosion and disruption to global nitrogen and phosphorus cycles might influence lake C cycling. For further resources related to this article, please visit the WIREs website.
... This small direct climate influence is similar to that observed in other studies where diatom-climate links have been examined quantitatively -the amount of variance explained by climate is low (cf. Anderson et al., 2008;Lotter and Birks, 2003). However, an equally important route for climate forcing may be indirectly via catchment soil development and the mediating effects of vegetation (Fritz and Anderson, 2013). ...
South-west China is an important area for determining variability of the SW Asian Monsoon; it is, however, also tectonically very active. Palaeolimnological studies in this region generally focus on climate as a direct driver of ecological change, rarely considering the effects of tectonic activity and catchment ontogeny. We present diatom and organic matter data from a Holocene sediment record from Muge Co, an alpine lake located on an active fault zone in the southeast margin of Tibet, and explore the possible drivers of ecological change. A major change occurred at 9000 cal. BP, when the diatom assemblage switched from benthic to predominantly planktonic forms, and organic matter content decreased rapidly. Comparison of the Holocene diatom record with a regional data set of lake surface sediments using detrended canonical correspondence analysis (DCCA) suggests that this change in diatom development was mainly associated with changing water depth, most likely linked to a seismically triggered landslide (which deepened the lake) rather than climate-driven hydrological change. However, diatom changes associated with principal components analysis (PCA) axis 2 agree well with inferred Holocene temperature changes. From the mid-Holocene, shifts in planktonic diatom species were probably related to indirect climate forcing, notably water column mixing depth and catchment vegetation–driven changes in dissolved organic carbon (DOC) and nutrient export. The diatom stratigraphy at Muge Co reflects a complex range of indirect climate- and catchment-controlled processes that were superimposed over a change in lake morphology resulting from tectonic activity.
... Some hundreds of paleolimnological studies have variously associated species in this group with clear or turbid water conditions and with epiphytic, benthic, and/or facultative planktonic habitats (e.g. Karst & Smol, 2000;Bennion, 1995;Sayer, 2001;Gell et al., 2005b;Anderson et al., 2008). Actual studies of living populations, are, however, scant to non-existent and so comparatively little is known regarding the factors that may promote Fragilaria group prevalence or decline. ...
Introduction Historically, limnological and paleolimnological research has focused on large and typically deep lakes but in the last two decades there has been a growing interest in smaller and shallower water bodies. Shallow lakes are justifiably considered as a separate lake type, distinguished physically from deeper waters by the fact that they are permanently mixed (polymictic) with a consequent lack of stratification of temperature or oxygen and with increased potential for nutrient recycling and redistribution of seston by physical water circulation patterns (Carrick et al., 1994). Whilst this is a useful distinction, there is no single definition of a shallow lake (Padisák & Reynolds, 2003). Scheffer (1998), in his classic text book, acknowledged a fundamental difference in the behavior, ecological functioning, and biotic communities of shallow waters and arbitrarily selected a mean depth of less than 3 m to define shallowness. For the purposes of this chapter we have chosen to adopt this definition and thereby to focus on lakes where, under a favorable light climate, benthic algae and/or rooted submerged macrophytes may occupy the majority of the lakebed (see also Jeppesen et al., 1997). Under enriched conditions, however, the mechanisms that stabilize the macrophyte communities of shallow lakes may often break down and a transition to pelagic production with phytoplankton dominance occurs (Scheffer et al., 1993; Vadeboncoeur et al., 2003). Importantly, because of these characteristics, shallow lakes are, for the most part, more vulnerable to a given pollutant load than large lakes.
... Paleolimnological studies also identify the importance of considering the effects of succession in terrestrial vegetation for proglacial lakes. For example, the initial phase after deglaciation in many areas is characterized by lake oligotrophication resulting from nutrient sequestration by the slow establishment of terrestrial vegetation (Anderson et al., 2008). Further, from studies of deglaciation chronosequences, we know that the succession in the terrestrial environment significantly affects the chemistry of lakes and their biota (Engstrom et al., 2000). ...
The current melting of glaciers and ice sheets is a consequence of climatic change and their turbid meltwaters are filling and enlarging many new proglacial and ice-contact lakes around the world, as well as affecting coastal areas. Paradoxically, very little is known on the ecology of turbid glacier-fed aquatic ecosystems even though they are at the origin of the most common type of lakes on Earth. Here, I discuss the consequences of those meltwaters for planktonic organisms. A remarkable characteristic of aquatic ecosystems receiving the discharge of meltwaters is their high content of mineral suspensoids, so-called glacial flour that poses a real challenge for filter-feeding planktonic taxa such as Daphnia and phagotrophic groups such as heterotrophic nanoflagellates. The planktonic food-web structure in highly turbid meltwater lakes seems to be truncated and microbially dominated. Low underwater light levels leads to unfavorable conditions for primary producers, but at the same time, cause less stress by UV radiation. Meltwaters are also a source of inorganic and organic nutrients that could stimulate secondary prokaryotic production and in some cases (e.g. in distal proglacial lakes) also phytoplankton primary production. How changes in turbidity and in other related environmental factors influence diversity, community composition and adaptation have only recently begun to be studied. Knowledge of the consequences of glacier retreat for glacier-fed lakes and coasts will be crucial to predict ecosystem trajectories regarding changes in biodiversity, biogeochemical cycles and function.
Lakes have a disproportionate effect on the global carbon (C) cycle relative to their area, mediating C transfer from land to atmosphere, and burying organic-C in their sediments. The magnitude and temporal variability of C burial is, however, poorly constrained, and the degree to which humans have influenced lake C cycling through landscape alteration has not been systematically assessed. Here, we report global and biome specific trajectories of lake C sequestration based on 516 lakes and show that some lake C burial rates (i.e., those in tropical forest and grassland biomes) have quadrupled over the last 100 years. Global lake C-sequestration (~0.12 Pg year ⁻¹ ) has increased by ~72 Tg year ⁻¹ since 1900, offsetting 20% of annual CO 2 freshwater emissions rising to ~30% if reservoirs are included and contributing to the residual continental C sink. Nutrient availability explains ~70% of the observed increase, while rising temperatures have a minimal effect.
Understanding long-term carbon flows through aquatic food webs is essential to assess impact of climatic and environmental changes on lake ecosystems. We reconstructed temporal changes in carbon sources fuelling chironomid biomass in a small and shallow hemiboreal/boreal lake over the last 11,000 years. Results were compared with temporal dynamics of known potential controlling factors: summer air temperature, human activities, phytoplankton assemblages and organic matter composition. We report an abrupt rise in the contribution of methane-derived carbon to chironomid biomass. However, this sudden increase was not the consequence of drastic changes in the composition of sedimentary organic matter, mean air temperature, lake trophic state or human activities in the catchment area. Our results suggest that shallowing of the lake caused by sedimentary infilling processes was a possible driver of the expansion of anoxic zones, enhancing CH4 cycling in lake sediments. However, complementary studies are needed to better understand the mechanisms by which lake shallowing could affect carbon flows to aquatic consumers, and then better assess the natural dynamics of past carbon processing in the benthic food web of shallow lakes.
Calibration of ancient marine sulfate levels has been done largely using experimental studies of the kinetic isotope effect associated with microbial sulfate reduction and work from modern ocean basins or high-sulfate lakes that are largely restricted and meromictic. The sulfur isotope record of sulfates and sulfides from sedimentary sequences have been used to reconstruct sulfate levels throughout the geologic record and indicate that sulfate concentrations were low relative to modern oceans (28 mM) for most of Earth's history. Despite the higher potential for modern low-sulfate systems to be a better analog for ancient oceans, there are few sulfur isotope studies that have been carried out in these environments. Here, we present δ³⁴S systematics of a modern low-sulfate (~330–600 μM) euxinic lake on the ice-free margin of southwestern Greenland. We find large isotope fractionations (>20‰) between water column sulfate and sulfides, with this fractionation increasing from 23.9‰ during open-water conditions to 42.0‰ under annual ice-cover. While these large kinetic isotope effects associated with microbial sulfate reduction (εSR) are expressed in the water column of this lake, the underlying sedimentary sulfides preserve a notably smaller range of δ³⁴S values (13.0–26.6‰). Geochemical modeling of our data suggests that the δ³⁴S of water column sulfate and sulfides, along with sedimentary sulfides are primarily controlled by εSR and a reservoir effect established under strong thermal stratification during open-water conditions. Under ice-covered conditions εSR appears to be the dominant control on δ³⁴S values, and when combining both seasonal data sets εSR increases as a function of sulfate levels in the lake. Sulfur isotopic data presented here highlight the complexity of seasonal biogeochemical cycling of sulfur in low-sulfate systems, and how system openness affects δ³⁴S fractionations in modern euxinic depositional environments. Specifically, a reservoir effect is only documented in the water column δ³⁴S data under open-water conditions, however a reservoir effect is apparent from sedimentary sulfides under both ice-cover and open-water conditions due to time averaging pyrite δ³⁴S values. Our results add to the growing body of work on modern low-sulfate systems to help further constrain the use of ancient δ³⁴S records for paleoenvironmental reconstructions.
High resolution analysis of subfossil chironomid remains preserved in well-dated lacustrine sediment cores was undertaken to identify whether marked shifts in chironomid assemblages have occurred in recent decades in the Colorado Rocky Mountains. This study will improve our understanding of site-specific aquatic ecosystem variability in the central Colorado Rockies during the 20th and early 21st centuries. An observed increase in chironomid taxa associated with warmer, more productive lakes, e.g. Dicrotendipes, is consistent with the movement of these lakes towards more productive aquatic systems in recent decades. The application of a chironomid-based inference model for mean July air temperature (MJAT) to the midge stratigraphies from these sites provide centennial length reconstructions of MJAT. The chironomid-inferred reconstructions of MJAT closely track gridded MJAT estimates for much of the 20th century; however, the response of the chironomid community is muted relative to the elevated temperatures that characterize this region during the last decade. Complementary analyses of sub-fossil chironomid records, previously developed from additional high elevation lakes located throughout the Intermountain West of the United States, indicate that the rate and magnitude of faunal turnover during the late 20th and early 21st centuries surpass the rate and magnitude of faunal turnover during any preceding interval in the last century. Direct gradient analyses reveal that the chironomid assemblages in the majority of sites became increasingly similar in composition to the assemblages associated with warmer, lower elevation sites between the early 20th and early 21st century.
A high-resolution diatom analysis of a varved sediment sequence from Lac Brûlé, southwestern Québec, was used to study temporal patterns of environmental change in the late Holocene. Key periods of interest in the record included the Medieval Warm Period (~800–1300 CE), the Little Ice Age (~1450–1850 CE), and post-European settlement (~1850–present). Subfossil diatom assemblages were compared to previously published pollen, cladocera, and sediment records from Lac Brûlé, revealing complex dynamics between terrestrial vegetation succession, nutrient fluxes, and trophic interactions. Generalized additive models showed a response to long-term climate variability in the diatom record, although it was not the most influential driver of community changes at Lac Brûlé. Catchment-mediated processes instead played the largest role in governing the structure of diatom assemblages in the lake. For example, nutrient loading following a local fire in the watershed at 1345 CE led to an abrupt and significant increase in Fragilaria spp. Human activity associated with deforestation and the Wallingford-Back Mine (1924–1972 CE) also had strong impacts on the landscape, which triggered further responses in the aquatic communities of Lac Brûlé.
Sedimentary diatom profiles from saline lakes are frequently used to reconstruct lakewater salinity as an indicator of drought. However, diatom-inferred salinity reconstructions (DI-salinity) from geographically-close sites in the Great Plains (USA) have yielded disparate results. Here, I explore how within-lake ecological processes, such as physical changes in lake habitat and zooplankton grazing pressure, may affect the accuracy of diatom-based salinity reconstructions. I examined how relationships differed among drought, lake-level change, and diatom community structure over the last century by developing three-dimensional models of planktic:benthic habitat (P:B) relationships with lake level change. I explored the potential for zooplankton grazing influence by comparing fossil zooplankton records with diatom inedibility for two prominent sites. I also examined ecological characteristics for diatom communities over the past century at six sites in the northern Great Plains, and developed new DI-salinity transfer functions based on ecological subsets of diatoms rather than full communities. I compared these reconstructions and characteristics with instrumental drought records to understand drivers of change in diatom community structure and how drought conditions were recorded in fossil diatom assemblages on a site-by-site basis.
The accuracy of drought reconstructions were affected by site-specific ecological characteristics that interfered with the representation of lakewater salinity signals within diatom records. Three-dimensional basin models showed that P:B habitat changes can strongly influence diatom communities, and in simple basins, P:B of sedimentary diatoms may be a preferable proxy for drought over DI-salinity. Zooplankton community structure varied through time at each site, and the relationship between zooplankton taxa and diatom inedibility also differed between lakes. This suggests that influence of grazing pressure on diatoms is likely unique at each lake, depending on the ecology of dominant zooplankton taxa and other within-lake ecological processes. New DI-salinity reconstructions, based on ecological subsets of diatoms, improved correlations with instrumental drought records at 5 of the 6 sites, though at some lakes ecological features of diatom assemblages were more representative of drought than DI-salinity reconstructions. The integration of additional ecological characteristics into interpretations of paleoclimate records, particularly for biologically-based reconstructions, is important to improve our understanding of site-specific responses to regional environmental changes.
Ecosystem in shallow lakes is generally subjected to the effects of multiple stressors, including nutrient, hydrology and climate.It is important to identify the impacts of multi-stressors for understanding the mechanism of environmental change in the lakes.Based on sedimentary proxies (i.e., ²¹⁰Pb and ¹³⁷Cs dating, diatom, geochemical indicators and particle size) from Chaohu sediment core and documentary data (i.e., hydrology, climate, population and agriculture) in Chaohu basin, this study estimated quantitatively the effects of nutrient, hydrology and climate on diatom succession since 1950 using the redundancy analysis.Before 1978 diatom assemblages were dominated by Aulacoseira granulata, followed by an abrupt increase in eutrophic species (i.e.Cyclostephanos dubius).Since 2000 diatom assemblages were characterized by C.dubius, with increases in eutrophic species (e.g., Cyclostephanos tholiformis and Stephanodiscus parvus).Results showed that sedimentary total phosphorus, total nitrogen, annual mean temperature, annual mean wind speed and annual water level amplitude were five significant variables, explaining solely 6.5%, 4.7%, 4.5%, 4.7% and 3.0% of the variances in diatoms respectively.Therefore, nutrient input was the most impor-tant factor on diatom succession.Meanwhile, changes in climate and hydrological conditions also imposed an effect on diatom suc-cession in Lake Chaohu during the last 50 years.
It is now widely recognized that reliable long-term climatic data are required to evaluate the impact of human activities on climate. Lake-sediment records are an important source of such paleoclimatic information, on timescales from years to millennia. However, unequivocal interpretation of biological climate-proxy data preserved in lake sediments can be very challenging. Here we review the different numerical approaches that are used to evaluate the sensitivity and reliability of species assemblages of aquatic biota (algae and invertebrates) extracted from lake-sediment records as proxies of past climatic conditions. The most common techniques used to assess this relationship between these proxies and climate include calibration functions that model the relationship across modern lake environments between species composition in the indicator group and particular climate-influenced aspects of their aquatic habitat, and assessments of the main directions of variation in species composition in relation to independent climatic data. Other statistical techniques, such as variation partitioning analysis, are used to assess the relative importance of climate versus other factors in influencing limnological changes seen in the sedimentary record. These techniques show that in climate-sensitive lake systems, the sedimentary remains of aquatic biota can be sensitive and trustworthy proxies, permitting quantitative reconstructions of past climatic conditions with high temporal resolution.
This study was based on sedimentary midge (Diptera: Nematocera) assemblages from multilake datasets along environmental transects from Finland (regional), southern Finland (semiregional), and Helsinki district (local) and an intralake dataset from eastern Finland (site-specific). The aim was to examine scale-dependencies in midge distribution. The results imply that distribution and abundance of midge taxa are related to scale: on the regional scale the forcing factors are related to prevailing climate conditions, on semiregional scale they are related to water quality, on more local scales predation pressure is the key variable and on site-specific scales habitat characteristics determine the species assemblages. Although the number of study sites was not equal and not all environmental parameters were possible to measure from all spatial scales, it is apparent that caution is required in midge-based environmental assessments, because changes in faunal composition are driven by factors operating at different spatial scales.
A sediment core from Taibai Lake, a shallow and eutrophic lake (SE China), was analysed for chironomids to track environmental changes in the lake. Nutrient dynamics over the past 1400 years were traced based on subfossil records and a regional chironomid-inferred total phosphorus (CI-TP) transfer function. Between ad 600 and 1370, the coexistence of several macrophyte-related taxa such as Dicrotendipes, Paratanytarsus and Endochironomus reflected a clear-water state with flourishing plants, and total phosphorus (TP) reconstructions ranged from 40 to 60 mu g/L. For the time span from ad 1370 to 1650, the prevalence of Paratanytarsus penicillatus-type indicated a slight decline of TP to lower than 50 mu g/L, but CI-TP increased to previous levels between ad 1650 and 1940. Since the 1950s, Chironomus plumosus-type dominated the chironomid community, which illustrated that the lake suffered from high nutrient loadings and CI-TP increased from 80 to 140 mu g/L. The results suggest that 50-60 mu g/L of TP concentration is the reference condition for Taibai Lake, and similar to 80-110 mu g/L might be considered as the nutrient threshold range between the plant-dominated and algal-dominated status. Variance partitioning analysis (VPA) was used to determine the relative influence of climate and human factors on the lake ecosystem. The analyses revealed that long-term climate change appeared to be the main determinant regulating the chironomid assemblages; however, the impact of human activities on the aquatic ecosystem prevailed over that of climate factors since the 1950s. This study improves our understanding of complex trajectories of aquatic ecosystem development at centennial to millennial timescales, which are influenced by both anthropogenic and climatic factors in a densely populated region. The main finding also provides reference for sustainable management in this lake and other analogous floodplain lakes.
Paleolimnological analyses of two lakes located near the northern treeline in the central part of the Canadian Northwest Territories document a history of abrupt postglacial climatic and limnological changes. A diatom-based transfer function, based on weighted-averaging partial least squares regression (WA-PLS) techniques, was used to give quantitative estimates of past trends in lakewater dissolved organic carbon (DOC), a limnological variable strongly aligned with catchment vegetation and soils. The diatom record from the sediment cores provides evidence for profound limnologic change during the mid-Holocene, corresponding to maximum forest-tundra development between 5000 and 3000 ¹⁴C yr BP in both Queen's and Toronto lakes, with a diatom-inferred relative change in lakewater DOC of up to 5.8 mg L–1 between the mid-Holocene and the present-day. Comparison of the diatom-inferred environmental changes with other proxy data (pollen, stable isotopes) from the same lakes provides strong evidence for an episode of climatic amelioration and lake responses to the associated vegetational changes (from tundra to forest-tundra) at sites near the central Canadian treeline. This study illustrates the usefulness of diatoms as quantitative indicators of past climate-related environmental change in northern treeline regions, and implies that aquatic ecosystems at high latitudes might respond with extreme sensitivity to climate warming.
Paleolimnological analyses of two lakes located near the northern treeline in the central part of the Canadian Northwest Territories document a history of abrupt postglacial climatic and limnological changes. A diatom-based transfer function, based on weighted-averaging partial least squares regression (WA-PLS) techniques, was used to give quantitative estimates of past trends in lakewater dissolved organic carbon (DOC), a Limnological variable strongly aligned with catchment vegetation and soils. The diatom record from the sediment cores provides evidence for profound limnologic change during the mid-Holocene, corresponding to maximum Forest-tundra development between 5000 and 3000 C-14 yr BP in both Queen's and Toronto lakes, with a diatom-inferred relative change in lakewater DOC of up to 5.8 mg L between the mid-Halocene and the present-day. Comparison of the diatom-inferred environmental changes with other proxy data (pollen, stable isotopes) from the same lakes provides strong evidence for an episode of climatic amelioration and lake responses to the associated vegetational changes (from tundra to forest-tundra) at sites near the central Canadian treeline. This study illustrates the usefulness of diatoms as quantitative indicators of past climate-related environmental change in northern treeline regions, and implies that aquatic ecosystems at high latitudes might respond with extreme sensitivity to climate warming.
High-resolution diatom stratigraphies from two lakes on eastern Baffin Island (Nunavut, Canadian Arctic) are used to reconstruct lake-water pH over the past 5 k.y. Despite contrasting geomorphic histories and markedly different diatom floras, the inferred pH of both lakes declined in concert with Neoglacial cooling. This result confirms that climate exerts a first-order influence on the acidity of these poorly buffered oligotrophic lakes, through links between lake ice cover, primary productivity, and dissolved inorganic carbon dynamics. Diatom-based pH inferences from dilute lakes can therefore assist paleoclimatic interpretations from lake sediments.
The Qu'Appelle Valley drainage system provides water to a third of the population of the Canadian Great Plains, yet is plagued by poor water quality, excess plant growth, and periodic fish kills. Fossil algae (diatoms, pigments) and invertebrates (chironomids) in Pasqua Lake were analyzed by variance partitioning analysis (VPA) to determine the relative importance of climate, resource use, and urbanization as controls of aquatic community composition 1920-1994. From fossil analyses, we identified three distinct biological assemblages in Pasqua Lake. Prior to agriculture (ca. 1776-1890), the lake was naturally eutrophic with abundant cyanobacterial carotenoids (myxo- xanthophyll, aphanizophyll), eutrophic diatoms (Stephanodiscus niagarae, Aulacoseira granulata, Fragilaria cap- ucina/bidens), and anoxia-tolerant chironomids (Chironomus). Principal components (PCA) and dissimilarity ana- lyses demonstrated that diatom and chironomid communities did not vary significantly (P. 0.05) before European settlement. Communities changed rapidly during early land settlement (ca. 1890-1930) before forming a distinct assemblage ca. 1930-1960 characterized by elevated algal biomass (inferred as b-carotene), nuisance cyanobacteria, eutrophic Stephanodiscus hantzschii, and low abundance of deep-water zoobenthos. Recent fossil assemblages (1977-1994) were variable and indicated water quality had not improved despite 3-fold reduction in phosphorus from sewage. Comparison of fossil community change and continuous annual records of 83 environmental variables (1890-1994) using VPA captured 71-97% of variance in fossil composition using only 10-14 significant factors. Resource use (cropland area, livestock biomass) and urbanization (nitrogen in sewage) were stronger determinants of algal and chironomid community change than were climatic factors (temperature, evaporation, river discharge). Landscape analysis of inferred changes in past algal abundance (as b-carotene; ca. 1780-1994) indicated that urban impacts declined with distance from point sources and suggested that management strategies will vary with lake position within the catchment.
Limnologistas han venido estudiando patrones de la productividad primaria en los lagos por mas de 60 anos. En lo relativo a la entroficacion a puesto la atencion en el suministro de nutrientes como un regulador de la productividad del lago. Sin embargo la adicion de nutrientes no siempre explica la variacion de la productividad primaria de todos los lagos del mundo. Este articulo se refiere a algunos casos practicos
We measured the ability to regulate oxygen uptake of 16 chironomid taxa from lakes in low-arctic West Greenland by means of oxygen microelectrodes in custom-made respiration chambers. The respiration patterns were modeled using piecewise linear regression with break-point and simple hyperbolic functions. The mathematical constants obtained from the controlled laboratory experiments were good ecophysiological indicators of species-specific "oxy-regulatory capacity." The oxy-regulatory capacity of different chironomid communities was calculated for subfossil assemblages collected from 52 lakes in West Greenland. The overall assemblage structure was expressed using detrended correspondence analysis (DCA). The oxy-regulatory capacity was as strongly correlated to DCA axis 1 (r = 0.72-0.86, p < 0.001), as were surface water temperature (r = 0.82, p < 0.001) and nutrients (r = 0.47-0.86, p < 0.001). Warm-water chironomid assemblages characterized by taxa such as Chironomus, Dicrotendipes, Ablabesmyia, and Procladius had a high oxy-regulatory capacity. Cold-water assemblages were dominated by oxy-conformers such as Heterotrissocladius, Micropsectra, Hydrobaenus, and Diamesa. An expression of the oxy-regulatory capacity of a given chironomid assemblage can be directly inferred from a simple model using weighted averaging of the ecophysiological mathematical constants. The autecological information from controlled experiments provides important additional information for interpretations in chironomid paleolimnology. The results can also be used to identify secondary changes or mismatches in multiproxy down-core paleoclimate studies.
Growth rate data of Oscillatoria redekei van Goor grown under a range of irradiances and light:dark cycles were used to examine the relationship between growth rate and light dose (irradiance × duration), the growth efficiency. When growth efficiency was greatest, growth rate responded directly to light dose and similar values for growth efficiency could be obtained at a range of temperatures. This suggests that under these conditions, respiration losses throughout the light:dark cycle were controlled by the photosynthetic carbon input. The maximum growth efficiency observed was 1·7 E m-2 (400–700 nm) per population doubling. Under continuous light, photosynthesis saturated at higher than incident irradiances so that photosynthesis proceeded at a fraction of the maximum rate; under light:dark cycling, photosynthesis was saturated below the highest growth irradiance and therefore proceeded at the saturation value.
During the transition from the last glacial to the present interglacial climate (late-glacial period), high summer insolation1 combined with the presence of the Laurentide ice sheet is thought to have promoted the development of strong summer thermal gradients in North America south of the ice margin2. Here we use palaeoecological methods to obtain quantitative evidence for the existence of these gradients. Our palaeoclimate reconstructions are based on water temperatures inferred from fossil assemblages of aquatic midge larvae in five lakes along a 240-km transect, extending from central New Brunswick, Canada, to southeastern Maine, USA. We show that the temperature gradient shifted during the Killarney Oscillation (KO) and Younger Dryas (YD) cooling events, and that water temperature differences of 9 and 11°C existed over distances of 55 and 240 km, respectively, during parts of the late-glacial period. These gradients are much stronger than the current north–south trends of lake summer surface water temperatures for these five lakes and for lakes across the northern tree line. The rapid motion of such steep temperature gradients may have affected the progressive development of aquatic and terrestrial ecosystems in the region.
Natural levels of ultraviolet (UV) radiation can harm organisms in shallow aquatic ecosystems in which concentrations of photoprotective dissolved organic carbon are low. These compounds can be removed as a result of acidic precipitation and climate changes, an effect which may have recently been manifested in up to 200,000 boreal lakes. Unfortunately, meteorological and biological monitoring studies are usually too brief to record the magnitudes of past changes in UV radiation fluxes and their effects. Here we demonstrate that certain fossil pigments in lake sediments can be used to document historical changes in the UV radiation environment of lakes. These pigments are produced by benthic algae when exposed to UV radiation and show sedimentary concentrations that are correlated to the depth of penetration of UV radiation within lakes. Analysis of fossil profiles from the sediments of two mountain lakes suggests that past UV radiation penetration has sometimes been-at least in these mid-latitude lakes-greater than dining the period of anthropogenic stratospheric ozone depletion.
In the light of data from the Greenland ice sheet concerning the ice-age climate, and palaeoecological studies of interglacial and Early Holocene deposits, the concept that a large proportion of Greenland's plants and animals may have survived during the ice ages is evaluated. While ice-free areas (refugias) were present, it is concluded that only hardy, cold-adapted species could have survived, which also explains why so few clearly endemic species are present in Greenland. Most members of the present biota are considered to be postglacial immigrants. Some species came to Greenland by walking or flying, but most arrived by passive, long-distance, chance dispersal, carried by wind, sea currents, and, in particular, birds. Transport by birds may explain why so many species arrived from Europe, because vast numbers of geese in particular migrate from northwest Europe to Greenland.
Over 80 lakes were sampled between the ice margin and the coast in West Greenland between 66 and 67°N and analyzed for their pH, alkalinity, conductivity, and major ions. Most of the lakes (67%) are dilute, circumneutral, and have conductivity values <150 μS cm⁻¹. There are, however, also saline lakes (2000–4000 μS cm⁻¹; NaHCO3/CO3, and Mg HCO3/CO3-dominated), mainly around the head of the fjord. The main control on lake chemistry in this area is evaporation as indicated by the fossil shorelines surrounding the saline lakes. The high concentrations of Na indicate extensive inputs from either weathering or from eoliantransported silts (loess) derived from the sand outwash plains at the ice sheet margin. The pattern of cation dominance in the freshwater lakes is Ca > Mg > Na > K. Variability in the water chemistry and the dominant controls on water chemistry were examined using PCA and RDA, respectively. There is a clear gradient in lake chemistry from west to east. This trend reflects the split between the dilute coastal lakes (with higher %C1) and the saline lakes close to the head of the fjord. Altitude is also significant and probably reflects reduced weathering rates at upland sites (~500 m) with limited vegetation cover. A number of lakes had high SO4 concentrations (maximum >10,000 μeq L⁻¹) and were clearly influenced by local geology.
Ultraviolet radiation (UVR) damages most biota, yet little evidence exists for its long-term effects on natural ecosystems. We used paleoecological techniques at three low-elevation lakes to show that algal abundance in lakes was depressed 10-fold by UVR during the first millennium of lake existence. Likewise, analysis of data from a lake near treeline showed that algal biomass declined 10-25-fold both early in the lake history and during the last similar to4000 yr, when inputs of UVR-absorbing dissolved organic matter (DOM) declined despite constant nutrient levels since similar to10,000 C-14 yr before the present. This rapid (-1.25% yr(-1)), sustained (>600 yr) suppression of algal abundance arose from directional climate change that reduced DOM inputs and occurred despite initial reservoirs of photoprotective DOM that are typical of most boreal lakes. Hence, we conclude that many lakes may be vulnerable to order-of-magnitude declines in algal abundance arising from future climate-DOM-UVR interactions.
Hasholt, B. & H. Søgaard 1978: Et forsøg på en klimatisk-hydrologisk regionsinddeling af Holsteinsborg kommune (Sisimut). Geografisk Tidsskrift 77: 72–92. København juni 1,1978.
The Holsteinsborg municipality (Sisimut) has been divided into climatic and hydrological regions. The investigation is of a preliminary character due to the limited possibilities for field work.
The regionalization is based upon selected climatological and hydrological parameters; these were primarily snow cover (precipitation), potential evapotranspiration, run-off, and temperature. Measurements of water quality have been used as indicator of the aridity in the area.
The ecological themes that can be addressed by an analysis of the sediment record include species and assemblage persistence and antiquity, rates and directions of change in lake-basin morphometry. Suggests that contemporary short-term seasonal and inter-annual studies cannot be fully understood without a consideration of the medium-term decadal and longer trajectories provided by palaeoecological analyses. -from Authors
Distribution maps of 31 Greenland limnophytes are presented: one is high-arctic, three circum-Greenlandic, and two mainly and 25 exclusively low-arctic. Ecologically, they are grouped into five types: indifferent, oligotrophic, oligo-mesotrophic, mesotrophic and a type preferring a high content of electrolytes. Flowering and fruiting dependent on the conductivity of the water and temperature: non-flowering specimens predominate near the coast and their northern limit, and upland. A table and map give information on all the lakes and ponds so far cored in Greenland, the period covered, type of analysis carried out (pollen, macrofossil, diatom), and references. For each species the present occurrence is summarized and, if elucidated by pollen or macrofossils, the Holocene history. The first immigrants were generally the circum-Greenlandic species, then came the northernmost of the low-arctic and finally, yet still fairly early, the southernmost ones. Mesotrophic species were abundant in most lakes in the beginning, but as the result of a general oligotrophication during the Hypsithermal became extinct or non-flowering in most lakes. The later decrease in temperature, around 4000 BP, added to the effect of the nutrient-poor water. -Author
Over 80 lakes were sampled between the ice margin and the coast in West Greenland between 66 and 67 degreesN and analyzed for their pH, alkalinity, conductivity, and tivity values < 150 muS cm(-1). There are, however, also saline lakes (2000-4000 muS cm(-1) NaHCO(3)/CO(3), and Mg HCO(3)/CO(3)-doniinated), mainly around the head of the fjord. The main control on lake chemistry in this area is evaporation as indicated by the fossil shorelines surrounding the saline lakes. The high concentrations of Na indicate extensive inputs from either weathering or from eolian transported silts (loess) derived from the sand outwash plains at the ice sheet margin. The pattern of cation dominance in the freshwater lakes is Ca > Mg > Na > K. Variability in the water chemistry and the dominant controls oil water chemistry were examined using PCA and RDA, respectively. There is a clear gradient in lake chemistry front west to east. This trend reflects the split between the dilute coastal lakes (with higher %Cl) and the saline lakes close to the head of the fjord. Altitude is also significant and probably reflects reduced Weathering rates at upland sites (similar to 500 m) with limited vegetation cover. A number of lakes had high SO(4) concentrations (maximum > 10,000 mu eq L(-1)) and were clearly influenced by local geology.
A general model for pH development is presented, based on diatom analysis of sediment cores from about 20 lakes, providing, in part, a new view of acidification history. Four periods are identified: (1) the natural long-term acidification period (12 000 BP- 2300 BP or later), with gradually decreasing pH values from about 7 to 5.5 resulting from soil acidification and declining fluxes of base cations from catchment soils; (2) the anthropogenic alkalization period (2300 BP - 1900 AD) when pH increased to above 6 due to land use; (3) the recent acidification period (about 1900 AD-presnt), when pH decreased to about 4.5 due to acid deposition and possibly altered land use; and (4) the liming period (1970s-present), when pH often increases to values above 7 following liming to counteract acidification. The implications of past pH changes are discussed in the context of contemporary lake acidification and liming policy. -from Authors
1 Diatom analysis of varved sediments from Kassjon (Northern Sweden) were used to determine the productivity response of planktonic and benthic diatoms to the start of agriculture. The development of agriculture was inferred from pollen stratigraphy, which indicated that continuous agriculture in the catchment started in the 13th century. 2 Prior to AD 1200, the diatom assemblages were dominated by benthic Aulacoseira spp., commonly found in boreal lakes, Fragilaria spp. and a variety of small Achnanthes and Navicula spp. From AD 1230 Asterionella formosa percentages increased dramatically, and after 1350 Tabellaria flocculosa cf. var. asterionelloides increased from zero to > 40%. These two planktonic diatoms dominated the diatom assemblages for the next similar to 600 years. Between 1900 and 1980 there were a number of changes consistent with changed nutrient resource ratios, notably an increase in Synedra spp. These changes are assumed to relate to the decline in arable agriculture (and a shift to pasture and reforestation) in the post-1950 period, which resulted in a reduced nutrient load to the lake. 3 Finer resolution pollen analysis between AD 1000 and 1500 suggests that the initial opening of the catchment resulted in the increase in Asterionella. The slightly later establishment of Tabellaria matches with the start of continuous arable fanning and, presumably, higher nutrient concentrations in the lake. There were significant relationships between changes in the diatom assemblages and three pollen types (Salix, Juniperus and Rumex), as determined by constrained ordination (a partial-redundancy analysis) and Monte Carlo permutation tests. 4 Total diatom accumulation rates increased from 2 x 10(6) frustules cm(-2) year(-1) prior to AD 1000 to > 10 x 10(6) frustules cm(-2) year(-1) in the late 19th century. The application of focusing correction factors, to account for the nonuniform pattern of microfossil deposition within the lake, altered the inferred-contribution of the littoral and planktonic diatoms to the palaeoproductivity of the lake. Prior to the start of agriculture the diatom productivity was dominated by benthic diatoms (2-3 x 10(6) frustules cm(-2) year(-1) corrected values). Planktonic diatom accumulation rates increased significantly after AD 1300 and then continued to increase steadily until similar to 1860 (similar to 3 x 10(6) frustules cm(-2) year(-1)) after which they declined. Despite these increased planktonic diatom accumulation rates, benthic diatoms continued to dominate the productivity of the lake with similar to 5 x 10(6) frustules cm(-2) year(-1) in the 19th century. 5 Because of differences in cell size between taxa, planktonic diatoms were corrected by estimates of their mean biovolume and both individual and total planktonic biovolume accumulation rates calculated. Prior to AD c. 1350, planktonic biovolume accumulation rates averaged around 250 x 10(6) mu m(3) cm(-2) year(-1). From this date, they increased steadily, peaking at > 4000 x 10(6) mu m(3) cm(-2) year(-1) in the mid- to late-19th century. There was a statistically significant relationship between the increasing biovolume accumulation rates and the increasing area of fields in the catchment for the period AD 1607-1854.
The Age Calibration Program, CALIB, published in 1986 and amended in 1987 is here amended anew. The program is available on a floppy disk in this publication. The new calibration data set covers nearly 22 000 Cal yr (approx 18 400 14C yr) and represents a 6 yr timescale calibration effort by several laboratories. The data are described and the program outlined. -K.Clayton
A modified ignition loss method is described for determining organic and carbonate carbon in calcareous sedimentary materials using equipment found in most laboratories. The method has been found to equal or excel the accuracy and precision of other methods tested and has the advantage of being considerably faster if large numbers of samples are to be analyzed.
