Lake Sediment Accumulation Research Articles

Sedimentary organic matter load influences the ecological effects of submerged macrophyte restoration through rhizosphere metabolites and microbial communities

Organic matter (OM) accumulation in lake sediments has doubled owing to human activities over the past 100 years, which has negatively affected the restoration of submerged vegetation and ecological security. Changes in the pollution structure of sediments caused by plant recovery and rhizosphere chemical processes under different sediment OM levels are the theoretical basis for the rational application of plant rehabilitation technology in lake management. This study explored how Vallisneria natans mediates changes in sediment N and P through rhizospheric metabolites and microbial community and function under low (4.94 %) and high (17.35 %) sediment OM levels. V. natans promoted the accumulation of NH4-N in the high-OM sediment and the transformation of Fe/Al-P to Ca-P in the low-OM sediment. By analyzing 63 rhizospheric metabolites and the sediment microbial metagenome, the metabolites lactic acid and 3-hydroxybutyric acid and the genus Anammoximicrobium were found to mediate NH4-N accumulation in the high-OM sediment. Additionally, 3-hydroxy-decanoic acid, adipic acid, and the genus Bdellovibrionaceae mediated the transformation of Fe/Al-P to Ca-P in the low-OM sediment. The growth of V. natans enriched the abundance of functional genes mediating each step from nitrate to ammonia and the genes encoding urease in the high-OM sediment, and it up-regulated three genes related to microbial phosphorus uptake in the low-OM sediment. This study revealed the necessity of controlling endogenous pollution by recovering submerged macrophytes under high- and low-OM conditions from the perspective of the transformation of inorganic nitrogen and phosphorus.

Catchment land use effect on mercury concentrations in lake sediments: A high-resolution study of Qinghai Lake

Mercury (Hg) contamination in aquatic environments presents a significant ecological and human health concern. This study explored the relationship between catchment land use and Hg concentrations within Qinghai Lake sediment, the largest lake in China, situated on the Qinghai-Tibet plateau. The study entailed detailed mapping of Hg sediment concentrations and a subsequent environmental risk assessment. Considering the complex nature of the plateau landform and surface vegetation, the study area was delineated at a 100 km radius centered on Qinghai Lake, which was divided into 30 sectors to quantify relationships between land use and the sediment Hg concentration. The results revealed a mean sediment Hg concentration of 29.91 μg/kg, which was elevated above the background level. Kendall's correlation analysis revealed significant but weak associations between sediment Hg concentrations and three land use types: grassland (rangeland and trees) (rs = 0.27, p < 0.05), crops (rs = −0.37, p < 0.05), and bare ground (rs = −0.25, p < 0.1), suggesting that growing areas of grassland correlated with higher Hg levels in the lake sediment, in contrast to bare ground or crops area, which correlated with lower Hg concentrations. Multiple linear regression models also observed weak negative relationships between bare ground and crops with sediment Hg concentration. This research methodology enhances our understanding of the impact of land use on Hg accumulation in lake sediments and underscores the need for integrated watershed management strategies to mitigate Hg pollution in Qinghai Lake.

Heavy Metal Accumulation in Lake Sediments in the Impact Zone of Trout Cage Farm

Heavy Metal Accumulation in Lake Sediments in the Impact Zone of Trout Cage Farm

Origin of the Badar Sand Field and the late pleistocene tectonic movements in the Tunka depression, the Baikal Rift Zone, Eastern Siberia

The Badar Sand Field is a geomorphological phenomenon representing a dome structure that dominates the topography of the subsiding Tunka Depression in the SW Baikal Rift. Many interpretations of its origin, including tectonic uplift, have been proposed, but the question remains open. We propose a new model to explain its genesis, based on a thorough analysis of both new and previously published geomorphological and sedimentological data. We suggest that the accumulation of the Badar Sand Field occurred in two stages: aquatic and aeolian. The lower part of the sandy deposits accumulated during the long-term existence of a landslide-dammed paleolake within the Tunka Depression. The upper part was formed after the drainage of the paleolake due to aeolian redeposition of sands. New results of OSL-dating from the vertical 40-m geological cross-section “Badar” showed that the accumulation of lake sediments occurred in the period 24–15 thousand years ago (MIS2). Based on the analysis of satellite images, we modeled the paleolake and determined that it arose as a result of landslides that dammed the antecedent section of the Irkut river valley in the Elovsky Spur. The analysis of the Irkut river terraces showed the absence of tectonic uplift within the Tunka Depression in the Holocene. The incision of the Irkut River at 40–90 m into the Badar dome occurred as a result of the restoration of equilibrium in the longitudinal profile of the river due to changes in sedimentation conditions in the post-glacial period.

Evidence for postglacial seismicity in lacustrine records in the western Kola Peninsula (north-western Russia)

In this article we describe and interpret disturbances in the sedimentary records of four lakes on the western flank of Lake Imandra (NE Fennoscandia, Kola Peninsula). The research framework comprises sedimentological and textural criteria for a visual description of sedimentary structures sediment core data, chronological (radiocarbon dating) data, and ground-penetrating radar (GPR) data. Disturbances preserved in lake sequences contain a mixture of chaotic fragments of sand, silt, polychromatic gyttja, peat, and wood fragments embedded in the organogenic matrix. The synchronicity of disturbances, fast sediment accumulation in lakes, relationship with Quaternary faults, the observed mass movements in lake sediments are interpreted as potential consequences of the earthquake shaking. A seismic event with a magnitude Mw no less than 4.5–5 and intensity of shaking I0 = IV–VI took place in the Middle Holocene, 6400–6100 cal. yr BP. Our studies show that although this area is not seismically active today, some of the main fault zones experienced short periods of reactivation also in the postglacial time, when glacioisostatic rebound after the ice retreat was already very low.

Configuration of urban water eutrophication abatement systems using a novel regression-based optimization scheme.

A novel regression-based target-oriented robust optimization (R-TORO) framework is introduced to obtain robust designs of surface water eutrophication abatement systems during the early stages of urban water planning. The proposed framework can process a manifold of data for estimating the relationships of system elements and the uncertainty distribution of imprecise parameters, a novel extension of the canonical TORO framework. A demonstrative case study about an early-stage urban water infrastructure planning for abating Phosphorous (P) accumulation in urban waters is employed to demonstrate the R-TORO framework. The following system targets are considered: target cost and target water cycle sustainability index (WCSI). The findings show that the abatement of P accumulation in soil contributes the largest to WCSI. Consequently, the R-TORO-generated system design suggests the implementation of impervious local roads connected to sewers with improved P removal. The simulated/estimated performance of the eutrophication abatement system design obtained using the R-TORO are as follows: import of water=2.88 × 106m3/y; export of P=4.96 × 106gP/y; P concentration in recreational lake=0.04mgP/l; P concentration in canal system=0.30mgP/l; P accumulation in lake sediments=0.08gP/m2,y; P accumulation in canal sediments=1.18gP/m2,y; P accumulation in soil=0.01gP/m2,y.

Rare earth elements in surface lake sediments of Russian arctic: Natural and potential anthropogenic impact to their accumulation

Investigations of the rare earth elements (REEs) concentrations in surface sediments of small lakes in the Arctic zone of the Russian Federation are presented. The territories of Murmansk Region and the Republic of Karelia were used as key study areas. The sampling of 9 lake sediments was carried out. Inductively coupled plasma mass spectrometry (ICP-MS) method was used as a main approach to estimate total concentrations of REEs and heavy metals and content of their elements in different fractions, using sequential extraction method. The role of the natural landscapes factor (tundra, forest-tundra, taiga) in the process of REEs accumulation in lake sediments was evaluated in the course of the work. It was revealed that the highest median accumulation of REEs occurred in the sediments of lakes in the tundra zone, and the lowest median accumulation of REEs occurred in the lakes in the forest zone (taiga). The dynamics of the REEs accumulation in the lakes of the background (pristine) regions of the Arctic, as well as in the lakes of urbanized territories, is shown on the example of the cities of Murmansk Region. The analysis of the vertical distribution of REEs and heavy metals in the cores of sediments of the studied lakes showed that the anthropogenic factor plays an important role in the accumulation of REEs in urban water bodies. First of all, this is due to dust from construction, wear and tear of houses and road structures, and weathering of soils and quaternary deposits in urban areas. All urban lakes showed similarity between distribution of REEs and heavy metals in the sediments. The main fractions of REEs in the sediments of the lakes of the Arctic zone of Russia were determined. It was revealed that the residual phase of sediments and organic matter plays a significant role in the accumulation of REEs in surface sediments of the North of Russia. At the same time, mobile forms and phases of REEs associated with Fe and Mn oxides also did not play a large role in the accumulation of REEs in the sediments of lakes in Northwest Russia.

Precipitation and Lake Water Evaporation Recorded by Terrestrial and Aquatic n‐Alkane δ2H Isotopes in Lake Khar Nuur, Mongolia

AbstractThe compound‐specific hydrogen isotopic composition (δ2H) of n‐alkanes is a valuable proxy to investigate hydrological conditions in lake sediments. While terrestrial n‐alkanes reflect the isotopic signal of the local precipitation, aquatic n‐alkanes incorporate the isotopic signal of the lake's water, which can be strongly modulated by evaporative enrichment. So far, the spatial distribution of the terrestrial and aquatic δ2H signal within lakes have not systematically been investigated. Here, we present compound‐specific δ2H results of terrestrial (δ2HC31) and aquatic (δ2HC23) n‐alkanes of surface sediment samples from Lake Khar Nuur, a semi‐arid and high‐altitude lake in the Mongolian Altai, and additionally investigate the δ2H signal of topsoils from the catchment. Our results show that the majority of the n‐alkane δ2H values from the catchment topsoils correspond well with modeled local growing season precipitation (JJAS). However, few samples in the northern catchment show more positive δ2H values possibly due to increased evapo(transpi)ration by southward exposition and shallower soils there. The only small variability of δ2HC31 in the surface sediments is in the range of most topsoils δ2H from the catchment, and thus, well reflects local growing season precipitation. δ2HC23 in surface sediment samples from the central and deepest parts of the lake, that is, the lake's sediment accumulation zones, shows distinctly more positive δ2HC23 values due to evaporative lake water enrichment. Consequently, Δaq‐terr, which is the isotopic offset between δ2HC23 and δ2HC31, indicates distinct lake water enrichment in the lake's accumulation zones and is a valuable proxy to investigate past hydrological changes.

Sedimentological records of atastrophic mass movements in the lake bottom-sediments of north-western Kola Peninsula and possible scenarios to explain the seismogenic trigger

Abstract. In this present article, we describe disturbances in the sedimentary records of lakes on the western flank of Lake Imandra (NE Fennoscandia, Kola Peninsula). The research framework comprises sedimentological and textural criteria for a visual description of sedimentary structures, borehole drilling data, chronological (radiocarbon dating) data, and ground-penetrating radar (GPR) data. Synchronicity specific features and fast spontaneous sediment accumulation in lakes, as well as traces of strong prehistoric and historical earthquakes and geomorphic setting in the studied area suggest that the observed mass movements in lake sediments are potentially generated by earthquake shaking.

Global acceleration of lake sediment accumulation rates associated with recent human population growth and land-use changes

Global acceleration of lake sediment accumulation rates associated with recent human population growth and land-use changes

HIGH RESOLUTION MINERALOGICAL CHARACTERIZATION OF SEDIMENTS - LAKE BOLĂTĂU-FEREDEU (ROMANIA)

The catchment (bedrock and soil) and sediments of lake Bolătău, Romania were studied by high resolution multi-methodological investigations to characterize paleoenvironmental and formation conditions. Particle size analyses, optical and cathodoluminescence microscopy, FTIR-ATR and Raman spectroscopy, X-ray powder diffraction, and XRF were applied for microtextural, chemical, micro-mineralogical and embedded organic material characterization and distribution of the sediments, especially concerning geochemical conditions, like pH and redox potential change. Our results support physical and chemical weathering in the process of soil formation with appearance of the new minerals appear (10Å sized phyllosilicates and clay minerals). Comparison of these studies offer possible differentiation of syn- and diagenetic mineralization, the clarification of debris contribution, microbial mediation and complex mineralization via decomposition of cell and extracellular polymeric substance. Based on the analyses on the abrasives, a suboxic environment prevailed in the depositional area and considerable microbial contribution is proposed via accumulation of lake sediments.

Why productive lakes are larger mercury sedimentary sinks than oligotrophic brown water lakes

AbstractMercury accumulation in lake sediments is a widespread environmental problem due to the biomagnification of Hg in the aquatic food chain. Soil Hg concentrations, catchment vegetation, erosion, and lake productivity are major factors controlling the accumulation of Hg in lakes. However, their influence on the Hg mass balance in lakes with different catchment characteristics and trophic state is poorly understood. In this multilake study, we decipher the effects of catchment vegetation (coniferous vs. deciduous forest), soil Hg content, and trophic state on Hg sedimentation at six lakes in Germany. We investigated Hg concentrations in leaves, soils, and the lake's water phase. Soils under coniferous stands show slightly higher Hg concentrations than under deciduous forest. Hg concentrations in the water phase were higher in the oligotrophic brown water lakes (8.1 ± 5.6 ng L−1 vs. 3.0 ± 1.9 ng L−1). Lower Hg concentrations in sediment trap material indicate dilution by algae organic matter in the mesotrophic lakes (0.12–0.17 μg g−1 vs. 0.57–0.89 μg g−1). However, Hg accumulation rates in sediment traps were up to 14‐fold higher in the mesotrophic lakes (113–443 μg m−2 yr−1) than in the brown water lakes (32–144 μg m−2 yr−1), which could not be explained by higher Hg fluxes to the productive lakes. Hg mass balance calculation reveals that water phase Hg scavenging by algae is the major reason for the intense Hg export to the sediments of productive lakes which makes them significantly larger sedimentary sinks than oligotrophic brown water lakes.

Human impact on C/N/P accumulation in lake sediments from northeast China during the last 150 years.

Lakes and lake sediments are significant components of the global carbon (C) cycle, and may store very large amounts of organic matter. Carbon sequestration in lakes is subject to substantial temporal and spatial variation and may be strongly affected by human activities. Here, we report accumulation rates (AR) of organic C (OC), total nitrogen (TN) and total phosphorous (TP), and investigate their responses to anthropogenic impact over the past 150 years by analyzing 62 sediment cores from 11 shallow lakes in the Songnen Plain, northeast China. From the center of each of the lakes, we selected one master core for age determination by 210Pb and 137Cs radioisotopes. The contents of OC, TN, TP, dry bulk density and mass specific magnetic susceptibility were then determined for all cores. The regional OCAR, TNAR and TPAR up-scaling from the multiple cores yielded mean values of 51.63±15.13, 2.50±0.98, and 0.90±0.21gm-2 yr-1, respectively. Nutrient AR in the studied lakes increased by a factor of approximately 2×from the middle 19th century to the 1950s, and approximately 5×after the 1950s. Elemental ratios show that the increase in OCAR is mainly the result of C autogenesis from the growth of aquatic plants stimulated by agricultural intensification, including increased chemical fertilizer application and farmland expansion. Significantly enhanced nutrient burial by these lakes after the 1950s resulted from increased anthropogenic impacts in northeast China. More sustainable agricultural practises, including a decrease in P fertilizer use, would result in a lowering of OCAR, TNAR and TPAR in the future.

Fish growth rates and lake sulphate explain variation in mercury levels in ninespine stickleback (Pungitius pungitius) on the Arctic Coastal Plain of Alaska

Mercury concentrations in freshwater food webs are governed by complex biogeochemical and ecological interactions that spatially vary and are often mediated by climate. The Arctic Coastal Plain of Alaska (ACP) is a heterogeneous, lake-rich landscape where variability in mercury accumulation is poorly understood. Earlier research indicated that the level of catchment influence on lakes varied spatially on the ACP, and affected mercury accumulation in lake sediments. This work sought to determine drivers of spatial variation in mercury accumulation in lake food webs on the ACP. Three lakes that were a priori identified as “high catchment influence” (Reindeer Camp region) and three lakes that were a priori identified as “low catchment influence” (Atqasuk region) were sampled, and variability in water chemistry, food web ecology, and mercury accumulation was investigated. Among-lake differences in ninespine stickleback (Pungitius pungitius) length-adjusted methylmercury concentrations were significantly explained by sulphate concentration in lake water, a tracer of catchment runoff input. This effect was mediated by fish growth, which had no pattern between regions. Together, lake water sulphate concentration and fish age-at-size (proxy for growth) accounted for nearly all of the among-lake variability in length-adjusted methylmercury concentrations in stickleback (R2adj = 0.94, p < 0.01). The percentage of total mercury as methylmercury (a proxy for net Hg methylation) was higher in sediments of more autochthonous, “low catchment influence” lakes (p < 0.05), and in the periphyton of more allochthonous, “high catchment influence” lakes (p < 0.05). The results indicate that dominant sources of primary production (littoral macrophyte/biofilm vs. pelagic phytoplankton) and food web structure (detrital vs. grazing) are regulated by catchment characteristics on the ACP, and that this ultimately influences the amount of methylmercury in the aquatic food web. These results have important implications for predicting future mercury concentrations in fish in lakes where fish growth rates and catchment inputs may change in response to a changing climate.

Holocene carbon accumulation in lakes of the current east Asian monsoonal margin: Implications under a changing climate

Carbon (C) present in lake sediments is an important global sink for CO2; however, an in-depth understanding of the impact of climate variability and the associated changes in vegetation on sediment C dynamics is still lacking. A total of 13 lakes were studied to quantify the influence of climate and vegetation on the reconstructed Holocene C accumulation rate (CAR) in lake sediments of the modern East Asian monsoonal margin. The corresponding paleoclimate information was assessed, including the temperature (30–90°N in the Northern Hemisphere) and precipitation (indicated by the δ18O of the Sanbao, Dongge, and Hulu caves). The Holocene vegetation conditions were inferred by pollen records, including arboreal pollen/non-arboreal pollen and pollen percentages. The results showed that the peak CAR occurred during the mid-Holocene, coinciding with the strongest period of the East Asian summer monsoon and expansion of forests. Lakes in the temperate steppe (TS) regions had a mean CAR of 13.41 ± 0.88 g C m−2 yr−1, which was significantly greater than the CARs of temperate desert (TD) and highland meadow/steppe (HMS; 6.76 ± 0.29 and 7.39 ± 0.73 g C m−2 yr−1, respectively). The major influencing factor for the TS sub-region was vegetation dynamics, especially the proportion of arboreal vegetation, while temperature and vegetation coverage were more important for the HMS. These findings indicate that C accumulation in lake sediments is linked with climate and vegetation changes over long timescales; however, there was notable spatial heterogeneity in the CARs, such as opposing temporal changes and different major influencing factors among the three sub-regions during the mid-Holocene. Aridification and forest loss would decrease C storage. However, prediction of C accumulation remains difficult because of the spatial heterogeneity in CARs and the interaction between the CAR and various factors under future climate change conditions.

Sedimentary charcoal proxy records of fire in Alaskan tundra ecosystems

Extensive burning of Arctic tundra landscapes in recent years has contradicted the conventional view that fire is a rare, spatially limited disturbance in tundra. These fires have been identified as harbingers of climate change, despite our limited understanding of Arctic fire frequency and climatic controls. Much of this understanding relies upon sedimentary charcoal-based fire reconstructions, yet the controls on sedimentary charcoal abundance need to be rigorously tested in tundra ecoregions. We compile published charcoal-based tundra fire reconstructions in Alaska and compare them with historical, limnological, and spatial data to: (1) evaluate the spatial and temporal characteristics of tundra fires, (2) identify the primary controls of charcoal accumulation in lake sediments, (3) assess the accuracy of peak analysis in identifying local (<1 km) fire events, and (4) constrain charcoal source area. We find that tundra fires are spatially and/or temporally dichotomous in the historical (observational) period (1940–2015 CE), a characteristic which is mimicked by charcoal accumulation rates. We show that, despite methodological differences in published studies, analyses of charcoal peaks accurately identified local (<1 km) fire events in the historical period. Further, we find that lake properties (e.g. depth and surface area) have weak influences on charcoal accumulation in the tundra and that charcoal source areas in the Alaskan tundra are much broader than in forest and grassland ecosystems. We conclude that the unique nature of tundra fire regimes allows for the reliable use of total charcoal accumulation as a fire proxy.

Eruptive history of the Late Quaternary Ciomadul (Csom\xe1d) volcano, East Carpathians, part II: magma output rates

This study, which builds on high-precision unspiked Cassignol-Gillot K-Ar age determinations, presents an advanced DEM-based volumetrical analysis to infer long-term magma output rates for the Late Quaternary Ciomadul (Csomád) dacitic lava dome complex (East Carpathians, Romania). The volcanic field of Ciomadul developed on the erosional surface of Lower Cretaceous flysch and ~ 2 Ma old andesites and experienced an extended eruptive history from ~ 850 to < 30 ka. Predominantly effusive activity took place during the first stage (~ 850 to ~ 440 ka), producing volumetrically minor, isolated, peripheral domes. Subsequently, after a ~ 250 ky repose interval, a voluminous central dome cluster developed in the second stage (~ 200 to < 30 ka). During the youngest phase of evolution (~ 60 to < 30 ka), highly explosive eruptions also occurred, resulting in the formation of two craters (Mohos and St. Ana). The calculated ~ 8.00 ± 0.55 km3 total volume of the lava domes, which includes the related volcaniclastic (1.57 km3) as well as erosionally removed (0.18 km3) material, is in line with dimensions of other medium-sized dacitic lava domes worldwide. This volume was extruded at an average long-term magma output rate of 9.76 km3/My (0.0098 km3/ky). However, most of the domes (7.53 ± 0.51 km3) were formed in the 200 to < 30 ka period, implying a significantly increased magma output rate of 37.40 km3/My (0.0374 km3/ky), more than 30 times higher than in the first stage. Within these long-term trends, individual lava domes of Ciomadul (e.g. those with volumes between 0.02 and 0.40 km3) would have been emplaced at much higher rates over a period of years to tens of years. The active periods, lasting up to hundreds of years, would have been followed by repose periods ~ 30 times longer. The most recent eruption of Ciomadul has been dated here at 27.7 ± 1.4 ka. This age, which is in agreement with radiocarbon dates for the onset of lake sediment accumulation in St. Ana crater, dates fragmented lava blocks which are possibly related to a disrupted dome. This suggests that during the last, typically explosive, phase of Ciomadul, lava dome extrusion was still ongoing. In a global context, the analysis of the volumetric dynamism of Ciomadul’s activity gives insights into the temporal variations in magma output; at lava domes, short-term (day- or week-scale) eruption rates smooth out in long-term (millenia-scale) output rates which are tens of times lower.

Patterns and controls of mercury accumulation in sediments from three thermokarst lakes on the Arctic Coastal Plain of Alaska

The biogeochemical cycle of mercury will be influenced by climate change, particularly at higher latitudes. Investigations of historical mercury accumulation in lake sediments inform future predictions as to how climate change might affect mercury biogeochemistry; however, in regions with a paucity of data, such as the thermokarst-rich Arctic Coastal Plain of Alaska (ACP), the trajectory of mercury accumulation in lake sediments is particularly uncertain. Sediment cores from three thermokarst lakes on the ACP were analyzed to understand changes in, and drivers of, Hg accumulation over the past ~ 100 years. Mercury accumulation in two of the three lakes was variable and high over the past century (91.96 and 78.6 µg/m2/year), and largely controlled by sedimentation rate. Mercury accumulation in the third lake was lower (14.2 µg/m2/year), more temporally uniform, and was more strongly related to sediment Hg concentration than sedimentation rate. Sediment mercury concentrations were quantitatively related to measures of sediment composition and VRS-inferred chlorophyll a, and sedimentation rates were related to various catchment characteristics. These results were compared to data from 37 previously studied Arctic and Alaskan lakes. Results from the meta-analysis indicate that thermokarst lakes have significantly higher and more variable Hg accumulation rates than non-thermokarst lakes, suggesting that certain properties (e.g., thermal erosion, thaw slumping, low hydraulic conductivity) likely make lakes prone to high and variable Hg accumulation rates. Differences and high variability in Hg accumulation among high latitude lakes highlight the complexity of predicting future climate-related change impacts on mercury cycling in these environments.

Comparative histories of polycyclic aromatic compound accumulation in lake sediments near petroleum operations in western Canada

We examined the historical deposition of polycyclic aromatic compounds (PACs) recorded in radiometrically-dated lake sediment cores from a small, conventional oil and gas operation in the southern Northwest Territories (Cameron Hills), and placed these results in the context of previously published work from three other important regions of western Canada: (1) the Athabasca oil sands region in Alberta; (2) Cold Lake, Alberta; and (3) the Mackenzie Delta, NT. Sediment PAC records from the Cameron Hills showed no clear changes in either source or concentrations coincident with the timing of development in these regions. Changes were small in comparison to the clear increases in both parent and alkyl-substituted PACs in response to industrial development from the Athabasca region surface mining of oil sands, where parent PAC diagnostic ratios indicated a shift from pyrogenic sources (primarily wood and coal burning) in pre-development sediments to more petrogenically-sourced PACs in modern sediments. Cores near in-situ oil sand extraction operations showed only modest increases in PAC deposition. This work directly compares the history and trajectory of contamination in lake ecosystems in areas of western Canada impacted by the most common types of hydrocarbon extraction activities, and provides a context for assessing the environmental impacts of oil and gas development in the future.

Spatiotemporal patterns of mercury accumulation in lake sediments of western North America

For the Western North America Mercury Synthesis, we compiled mercury records from 165 dated sediment cores from 138 natural lakes across western North America. Lake sediments are accepted as faithful recorders of historical mercury accumulation rates, and regional and sub-regional temporal and spatial trends were analyzed with descriptive and inferential statistics. Mercury accumulation rates in sediments have increased, on average, four times (4×) from 1850 to 2000 and continue to increase by approximately 0.2μg/m2 per year. Lakes with the greatest increases were influenced by the Flin Flon smelter, followed by lakes directly affected by mining and wastewater discharges. Of lakes not directly affected by point sources, there is a clear separation in mercury accumulation rates between lakes with no/little watershed development and lakes with extensive watershed development for agricultural and/or residential purposes. Lakes in the latter group exhibited a sharp increase in mercury accumulation rates with human settlement, stabilizing after 1950 at five times (5×) 1850 rates. Mercury accumulation rates in lakes with no/little watershed development were controlled primarily by relative watershed size prior to 1850, and since have exhibited modest increases (in absolute terms and compared to that described above) associated with (regional and global) industrialization. A sub-regional analysis highlighted that in the ecoregion Northwestern Forest Mountains, <1% of mercury deposited to watersheds is delivered to lakes. Research is warranted to understand whether mountainous watersheds act as permanent sinks for mercury or if export of “legacy” mercury (deposited in years past) will delay recovery when/if emissions reductions are achieved.