Landscape Disturbance and Lake Response: Temporal and Spatial Perspectives

Abstract. Strong similarities in Holocene climate reconstructions derived from multiple proxies (BSi, TOC – total organic carbon, δ13C, C∕N, MS – magnetic susceptibility, δ15N) preserved in sediments from both glacial and non-glacial lakes across Iceland indicate a relatively warm early to mid Holocene from 10 to 6 ka, overprinted with cold excursions presumably related to meltwater impact on North Atlantic circulation until 7.9 ka. Sediment in lakes from glacial catchments indicates their catchments were ice-free during this interval. Statistical treatment of the high-resolution multi-proxy paleoclimate lake records shows that despite great variability in catchment characteristics, the sediment records document more or less synchronous abrupt, cold departures as opposed to the smoothly decreasing trend in Northern Hemisphere summer insolation. Although all lake records document a decline in summer temperature through the Holocene consistent with the regular decline in summer insolation, the onset of significant summer cooling occurs ∼5 ka at high-elevation interior sites but is variably later at sites closer to the coast, suggesting that proximity to the sea may modulate the impact from decreasing summer insolation. The timing of glacier inception during the mid Holocene is determined by the descent of the equilibrium line altitude (ELA), which is dominated by the evolution of summer temperature as summer insolation declined as well as changes in sea surface temperature for coastal glacial systems. The glacial response to the ELA decline is also highly dependent on the local topography. The initial ∼5 ka nucleation of Langjökull in the highlands of Iceland defines the onset of neoglaciation in Iceland. Subsequently, a stepwise expansion of both Langjökull and northeast Vatnajökull occurred between 4.5 and 4.0 ka, with a second abrupt expansion ∼3 ka. Due to its coastal setting and lower topographic threshold, the initial appearance of Drangajökull in the NW of Iceland was delayed until ∼2.3 ka. All lake records reflect abrupt summer temperature and catchment disturbance at ∼4.5 ka, statistically indistinguishable from the global 4.2 ka event, and a second widespread abrupt disturbance at 3.0 ka, similar to the stepwise expansion of Langjökull and northeast Vatnajökull. Both are intervals characterized by large explosive volcanism and tephra distribution in Iceland resulting in intensified local soil erosion. The most widespread increase in glacier advance, landscape instability, and soil erosion occurred shortly after 2 ka, likely due to a complex combination of increased impact from volcanic tephra deposition, cooling climate, and increased sea ice off the coast of Iceland. All lake records indicate a strong decline in temperature ∼1.5 ka, which culminated during the Little Ice Age (1250–1850 CE) when the glaciers reached their maximum Holocene dimensions.

We undertook a comprehensive comparison between the pigment composition of surface sediment samples and contemporary catchment and limnological data deriving from 308 mountain lakes in 11 mountain regions (Lake Districts) covering a wide latitudinal and longitudinal gradient across Europe. This paper examines whether photosynthetic algal and bacterial pigments stored in the lake sediment can be used to identify different lake typologies and population dynamics of primary producers. We focus on a multivariate numerical analysis relating the relative abundance of marker pigments of algae, cyanobacteria and phototrophic sulphur bacteria to a set of physical and chemical factors (both natural and anthropogenic) determining the environmental conditions in mountain lakes. Redundancy Analysis (RDA), including partial RDA, of carotenoid assemblages constrained by environmental variables suggests that the main differences between lake districts are caused by geographic position (e.g. longitude), catchment characteristics (e.g. % carbonate rocks) and chemical variables (e.g. Mg, NO3). Other variables such as temperature and phosphorus play a minor role, probably be cau se of the short length of the gradient covered by these cold and mostly oligotrophic lakes. Pigment composition varies primarily in response to catchment geology and pollution (i.e. acidification from long range transport) gradients. Purple sulphur photosynthetic bacteria (okenone) and cyanobacteria (echinenone, canthaxanthin, scytonemin) are replaced by siliceous algae (fucoxanthin and diatoxanthin), cryptophytes (alloxanthin) and dinoflagellates (diadinoxanthin). With respect to site classification, the pigment ordination shows a clear distinction between the more pristine lakes (in the Pyrenees) and the more polluted sites (in the Tatra Mountains and Central Southern Alps) or those with water higher in solute content (the Julian Alps and Greenland).

A paleolimnological investigation of post-European sediments in a Lake Michigan coastal lake was used to examine the response of Lower Herring Lake to anthropogenic impacts and its role as a processor of watershed inputs. We also compare the timing of this response with that of Lake Michigan to examine the role of marginal lakes as ‘early warning’ indicators of potential changes in the larger connected system and their role in buffering Lake Michigan against anthropogenic changes through biotic interactions and material trapping. Sediment geochemistry, siliceous microfossils and nutrient-related morphological changes in diatoms, identified three major trophic periods in the recent history of the lake. During deforestation and early settlement (pre-1845–1920), lake response to catchment disturbances results in localized increases in diatom abundances with minor changes in existing communities. In this early phase of disturbance, Lower Herring Lake acts as a sediment sink and a biological processor of nutrient inputs. During low-lake levels of the 1930s, the lake goes through a transitional period characterized by increased primary productivity and a major shift in diatom communities. Post-World War II (late 1940s–1989) anthropogenic disturbances push Lower Herring Lake to a new state and a permanent change in diatom community structure dominated by Cyclotella comensis. The dominance of planktonic summer diatom species associated with the deep chlorophyll maximum (DCM) is attributed to epilimnetic nutrient depletion. Declining Si:P ratios are inferred from increased sediment storage of biogenic silica and morphological changes in the silica content of Aulacoseira ambigua and Stephanodiscus niagarae. Beginning in the late 1940s, Lower Herring Lake functions as a biogeochemical processor of catchment inputs and a carbon, nutrient and silica sink. Microfossil response to increased nutrients and increased storage of biogenic silica in Lower Herring Lake and other regional embayments occur approximately 20–25 years earlier than in a nearby Lake Michigan site. Results from this study provide evidence for the role of marginal lakes and bays as nutrient buffering systems, delaying the impact of anthropogenic activities on the larger Lake Michigan system.

Abstract. Microscopic charcoal particles are fire-specific tracers, which are ubiquitous in natural archives such as lake sediments or ice cores. Thus, charcoal records from lake sediments have become the primary source for reconstructing past fire activity. Microscopic charcoal particles are generated during forest and grassland fires and can be transported over large distances before being deposited into natural archives. In this paper, we implement microscopic charcoal particles into a global aerosol–climate model to better understand the transport of charcoal on a large scale. Atmospheric transport and interactions with other aerosol particles, clouds, and radiation are explicitly simulated. To estimate the emissions of the microscopic charcoal particles, we use recent European charcoal observations from lake sediments as a calibration data set. We found that scaling black carbon fire emissions from the Global Fire Assimilation System (a satellite-based emission inventory) by approximately 2 orders of magnitude matches the calibration data set best. The charcoal validation data set, for which we collected charcoal observations from all over the globe, generally supports this scaling factor. In the validation data set, we included charcoal particles from lake sediments, peats, and ice cores. While only the Spearman rank correlation coefficient is significant for the calibration data set (0.67), both the Pearson and the Spearman rank correlation coefficients are positive and significantly different from zero for the validation data set (0.59 and 0.48, respectively). Overall, the model captures a significant portion of the spatial variability, but it fails to reproduce the extreme spatial variability observed in the charcoal data. This can mainly be explained by the coarse spatial resolution of the model and uncertainties concerning fire emissions. Furthermore, charcoal fluxes derived from ice core sites are much lower than the simulated fluxes, which can be explained by the location properties (high altitude and steep topography, which are not well represented in the model) of most of the investigated ice cores. Global modelling of charcoal can improve our understanding of the representativeness of this fire proxy. Furthermore, it might allow past fire emissions provided by fire models to be quantitatively validated. This might deepen our understanding of the processes driving global fire activity.

Spatial heterogeneity of lake sediment hydraulic conductivity, hydrological connectivity and causes analysis under the influence of sand mining activities: In-situ tests in a typical large sand mining lake (Poyang lake).

Pollen and spores with resistant exines are preferentially preserved in soils, and during periods of soil erosion they can become incorporated into lake sediments. As a result, the contemporary vegetation may be poorly represented by the palynomorphs in the lake sediments because of the reworked component of inwashed pollen and spores. We record the proportion of palynomorphs with corroded exines in sediment cores from four lakes in the eastern North Island of New Zealand to document changing sources of palynomorphs over the last 2000 years. During this period, the catchments experienced major vegetation disturbances, both natural (from volcanism and fire) and anthropogenic including deforestation ca. 600 years ago, and the European conversion of fern-scrubland to pasture in the 19th century. Corroded palynomorphs are more abundant in inwashed sediments than authigenic sediments. Catchment soil disturbance was minor during the forested period, and characterised by small, inwashed, sediment pulses after storms, and a relatively low percentage of corroded palynomorphs. Although initial Maori forest clearance by fire led to a temporary increase in erosion in one lake catchment, rapid replacement of forest by a dense bracken fern cover helped to minimise soil erosion and reworking of palynomorphs in this period. European pastoralists replaced the bracken fern with shallow-rooted pasture grasses about 150 years ago. In erosion prone lake catchments, this led to a rapid increase of inwashed eroded soils and littoral sediments, and their component of resistant palynomorphs, reaching the lake sediments. As a result, the palynological records from these catchments during the European period are distorted by reworking. By contrast, over the same period, the palynological record from a lake with no inflowing streams and stable catchment soils more faithfully represented the contemporary vegetation cover. Exine corrosion has been used to help identify periods of reworking in the lake sediments and to allow for a correction of distortion caused by reworking.

Identification and inventory of wetlands are essential components of natural resource management. To be effective in these endeavors, it is critical that the process used to detect and document wetlands be time efficient, accurate, and repeatable as new environmental information becomes available. Approaches dependent on aerial photographic interpretation of land cover by individual human analysts necessitate hours of assessment, introduce human error, and fail to include the best available soils and hydrologic data. The goal of the current study is to apply hierarchical modeling and Bayesian inference to predict the probability of wetland presence as a continuous gradient with the explicit consideration of spatial structure. The presented spatial statistical model can evaluate 100 km 2 at a 50 x 50 meter resolution in approximately 50 minutes while simultaneously incorporating ancillary data and accounting for latent spatial processes. Model results demonstrate an ability to consistently capture wetlands identified through aerial interpretation with greater than 90 % accuracy (scaled Brier Score) and to identify wetland extents, ecotones, and hydrologic connections not identified through use of other modeling and mapping techniques. The provided model is reasonably robust to changes in resolution, areal extents between 100 km 2 and 300 km 2, and region-specific physical conditions.

The amount of organic phosphorus (OP) and its distribution among different pools in lake sediments depend on biotic and abiotic processes driving OP fractionation. The key abiotic factors governing these transformation processes between different OP fractions in sediments were studied on the basis of distribution characteristics of OP pools in sediments from Lake Hulun (HLH). The results showed the order of the size of OP pools in the surface sediments from Lake Hulun to be: Re-OP (residual OP) ≫ FAOP (fulvic acid fraction) ≥ HCl-OP (OP extracted by HCl) > HAOP (humic acid fraction) ≫ LOP (labile OP); lower concentrations of LOP were found in lake surface sediments with high pH (pH > 9) of lake overlying water indicating a governing role of pH in LOP degradation in an aquatic environment. The pattern of total OP (TOP) spatial distribution showed an obvious decreasing trend from the west to the east lake districts in surface sediments from HLH, which was attributed to the inputs of dust and dry grass driven by the prevailing wind and the finer grain size in the west lake districts. However, the spatial distribution pattern of dissolved OP (DOP) in overlying water, which presented different trends with TOP and total organic carbon (TOC) in surface sediments, indicated that the biological factors and terrestrial inputs showed a joint influence on DOP distribution in HLH. The higher levels of Re-OP and lower levels of HCl-OP observed in HLH may reveal that calcium ions and their minerals were the key governing factors of OP fractionation in sediments from HLH. This work revealed the main abiotic process or mechanism driving OP fractionation in the aquatic environment helping to understand the geochemical information archived in OP pools in lake sediments.

Estimates of historical disturbance patterns are essential to guide forest management aimed at ensuring the sustainability of ecosystem functions and biodiversity. However, quantitative estimates of various disturbance characteristics required in management applications are rare in longer-term historical studies. Thus, our objectives were to (1) quantify past disturbance severity, patch size, and stand proportion disturbed and (2) test for temporal and subregional differences in these characteristics. We developed a comprehensive dendrochronological method to evaluate an approximately two-century-long disturbance record in the remaining Central and Eastern European primary mountain spruce forests, where wind and bark beetles are the predominant disturbance agents. We used an unprecedented large-scale nested design data set of 541 plots located within 44 stands and 6 subregions. To quantify individual disturbance events, we used tree-ring proxies, which were aggregated at plot and stand levels by smoothing and detecting peaks in their distributions. The spatial aggregation of disturbance events was used to estimate patch sizes. Data exhibited continuous gradients from low- to high-severity and small- to large-size disturbance events. In addition to the importance of small disturbance events, moderate-scale (25-75% of the stand disturbed, >10ha patch size) and moderate-severity (25-75% of canopy disturbed) events were also common. Moderate disturbances represented more than 50% of the total disturbed area and their rotation periods ranged from one to several hundred years, which is within the lifespan of local tree species. Disturbance severities differed among subregions, whereas the stand proportion disturbed varied significantly over time. This indicates partially independent variations among disturbance characteristics. Our quantitative estimates of disturbance severity, patch size, stand proportion disturbed, and associated rotation periods provide rigorous baseline data for future ecological research, decisions within biodiversity conservation, and silviculture intended to maintain native biodiversity and ecosystem functions. These results highlight a need for sufficiently large and adequately connected networks of strict reserves, more complex silvicultural treatments that emulate the natural disturbance spectrum in harvest rotation times, sizes, and intensities, and higher levels of tree and structural legacy retention.

This paper raises fundamental questions about the sole use of paleolimnological techniques to identify sediment sources and develop catchment management plans. The concept of an integrated lake: catchment framework was established 30 years ago, yet paleolimnologists occasionally fail to appreciate the dynamics of the contributing catchment. This is especially critical when the predominant source of sediment accumulating in a lake is allochthonous. In this paper we argue that a detailed appraisal of catchment sources and investigation of historical documentary evidence is needed to identify and evaluate the relative significance of sediment sources. We used such an approach at Aqualate Mere, Shropshire, UK. Mineral magnetic and radionculide signatures of potential catchment sources and accumulating lake sediments were compared in an attempt to match the sources to sediments deposited in the Mere. Dated lake sediments indicate there has been an increase in sedimentation rate and the relative amount of minerogenic material delivered to the Mere over the last 200 years. In contrast to a previous study at the same site, there is no evidence to attribute this increase to an overspill from a nearby canal. Other catchment disturbances include landscaping in parkland surrounding the Mere in the early nineteenth century and drainage systems installed to improve catchment agriculture over the last ca. 150 years. Both activities may explain the change in sedimentation rates and types, independent of the hypothesized canal origin. Although our results exclude the canal as a major sediment source, identifying the contribution of other potential catchment sources remains problematic. 137Cs inventories for the lake are similar to those recorded at a local reference site, suggesting little influx of 137Cs-bearing topsoil, yet 137Cs activities remain high in the upper 20–30 cm of the lake sediment profile, indicating a topsoil origin. Combined radionuclide and mineral magnetic signatures proved to be relatively poor discriminators of potential sources, and the high atmospheric pollution load from the West Midland conurbation has probably altered recent lake sediment signatures. Although further research is required to identify the origins of recent (last ca. 200 years) minerogenic sediment inputs to the Mere, we suggest that the combined lake: catchment approach offers a more rigorous method for understanding the impact of catchment disturbance than analysis of the paleolimnological record alone.

Lake ecosystems face a variety of pressures arising from catchment-based anthropogenic activities and long-term changes in background environmental conditions, which greatly threaten their structure, function and the sustainable provision of essential ecosystem services. The response of lakes to external perturbations is controlled by a complex interaction of top-down (predation) and bottom-up (resource availability) food web processes. A better understanding of how these processes interact is vital if they are to be effectively manipulated in the remediation of degraded lakes. In this study, Esthwaite Water, a eutrophic lake in the English Lake District, was used as the model ecosystem to investigate the relative importance of these two opposing forces in determining water quality changes in response to anthropogenic pressures, specifically eutrophication and climate change. The research is presented as three studies which address the historical, contemporary and future impact of stressors on the ecological structure and function of Esthwaite Water. Analysis of long-term monitoring data determined that phosphorus availability was the main driver of water quality degradation throughout the study period (1970 to 2014). Despite substantial reductions to the external phosphorus load in later decades, water quality improvements were not observed. Phosphorus release from lake sediments and the effects of climate change on phytoplankton community structure appear to have buffered against the desired impact of reduced external nutrient loads. Analysis of contemporary surface sediments revealed a legacy of phosphorus enrichment from years of high external loading, including from aquaculture cages previously installed on the lake. Much of the sediment phosphorus was determined to be stored in release-sensitive forms. The PROTECH lake model was used to test the response of the phytoplankton community to variations in both nutrient availability and zooplankton grazing rate. The dominant controlling factor on total phytoplankton biomass was nutrient availability. When nutrient loads were high, cyanobacteria dominated the phytoplankton community. Such conditions limited the potential for top-down regulation by herbivory owing to food quality constraints upon zooplankton. The inclusion of climate warming in modelling scenarios resulted in the exacerbation of the symptoms of eutrophication. As such, it is recommended that future attempts at water quality improvement take a bottom-up approach, with a focus on controlling the internal phosphorus load.

Governments provide technical, political, and financial incentives to encourage timber harvesting for the purpose of mitigating natural forest disturbance. To provide guidance concerning these incentives, this paper integrates a natural disturbance regime into a dynamic model of forest management. The model is used to estimate live and salvage timber harvest subsidies needed to incorporate disturbance‐mitigating benefits before and after three types of natural disturbance: insect outbreak, storm, and wildfire. While not specific to a particular country or state, results indicate that the degree of forest mortality may be a poor metric for gauging management response due to various degrees of endogeneity across different types of disturbance events. The live timber harvesting subsidy is substantial but quickly declines after a disturbance event. In contrast, salvage subsidies increase following a disturbance event but remain modest.

To reconstruct Lateglacial and Holocene environmental changes in the British uplands, two c. 5.8 m long sediment cores from Crummock Water (NW England), together with several hundred soil samples from the Crummock Water catchment, were studied using magnetic techniques. Optically stimulated luminescence (OSL) dating using fine silt quartz and14C dating of terrestrial plant macrofossils were used to establish a chronology for the lake sediments. A good agreement between optical and14C ages indicates first, that the OSL dating method can be used to date lake sediments in the British Isles; second that macrofossil-based14C dating can be used to avoid the problem of `old carbon' error associated with bulk sample14C dating of lake sediments and third, that the established chronology is robust. The lake sediment magnetic properties indicate a series of changes in sediment composition during the Holocene, which correlate well with sediment lithology, water content and weight-loss-on-ignition. The first change corresponds to the Lateglacial/Postglacial climatic shift at around 11400 years ago; the subsequent suite of changes corresponds to a probable regional onset of human activity at 2000 BC, and particularly to the intensification of human activity at around AD 900. A comparison of the lake sediment magnetic properties and those of the catchment soils shows a clear linkage for the Lateglacial period, and for the period after AD 900. In contrast, detailed magnetic measurements of the early- through mid-Holocene sediments suggest that their magnetic properties are dominated by bacterial magnetosomes.

Lake sediments can be significantly impacted by industrial activities. These impacts vary among sites and include both local point sources and atmospherically-derived pollution. Here we present results of a lake sediment pollution record from Ullswater, UK, where lead mining activities have taken place within the catchment since 1690, although large-scale mining did not begin until 1840. Metal concentration data from 12 cores taken along a lake bed transect illustrate that lead mining at Greenside Mine had a significant impact on the lake sediments. High Pb concentrations were identified throughout Ullswater, and exhibited a spatial gradient from south to north, with concentrations decreasing with greater distance from the main source of input at Glenridding. Furthermore, inter-element correlations exhibit spatial variation that reflects the processes by which they are incorporated into the lake sediment record. Together, these observations illustrate potential shortcomings in palaeoenvironmental reconstructions and pollution studies based on single cores from large and morphologically variable lakes. Sedimentation rates were estimated by matching this pollution record with the historical record of mining activities. Within Ullswater, sedimentation rates from 1840 to the present varied from 0.67 to 2.33 mm year−1 with a mean of 1.4 mm year−1; highest sedimentation rates were observed in the deepest section of the lake and close to the main inputs, and lowest sedimentation rates were observed in the northern part of the lake, furthest from the main input. Despite the considerable changes in mining techniques and production, there is little evidence to suggest significant changes in sedimentation rates over time.

The first part of an investigation designed to cover most of the tarns of the English Lake District is described. This investigation was planned as an application of the techniques of Quaternary research to a detailed analysis of the late-Quaternary history of a single limited area which forms a clearly defined geographical region. The primary concern of the investigation is the relationship between stratigraphy and pollen content of the lake deposits, in an attempt to reconstruct the history of deposition in each tarn in relation to late- and post-Glacial changes in climate, and consequent changes in soil and vegetation in the drainage basins. In the account of pollen analysis of the sediments of six tarns at various altitudes in the south-western quadrant of the Lake District, comparisons between these various pollen diagrams from a fairly small area serve to emphasize the contrast between those widespread regional changes due to climatic change on which the pollen zonation is based, which are common to all the diagrams, and local changes due to local topography and human history, which differ in a consistent way from one tarn to another. The differences between the late-Glacial deposits of the six tarns are related to topography, and the probable limits of the last corrie glaciation of the Lake District. Evidence from pollen analysis suggests very strongly that in the early post-Glacial period forest extended over the Lake District hillsides up to the altitude of the highest tarn investigated (1800 ft.). The first indication of disturbance of the primary forest occurs at the zone boundary VIIa/b the elm decline (which, as Godwin showed in his Croonian lecture of 1960, has been established to be broadly synchronous in north-west Europe at ca. 3000 B.C.). Evidence is put forward suggesting that destruction of the elm in the Lake District during the early Neolithic period was particularly pronounced round tarns near to the sites of the stone-axe factories. The next phases of forest clearance are shown to be most clearly demonstrated in those tarns around which are abundant remains of upland settlement of Bronze Age type. The relation between the successive phases of forest clearance, post-Glacial soil degradation, peat formation and soil erosion is discussed, in relation to chemical investigations by F. J. H. Mackereth (at the Windermere laboratory of the Freshwater Biological Association) which suggest that the lake deposits are derived mainly from soils in the drainage basins.