Catchment Soils Research Articles

A Bayesian approach to understanding the key factors influencing temporal variability in stream water quality – a case study in the Great Barrier Reef catchments

Abstract. Stream water quality is highly variable both across space and time. Water quality monitoring programmes have collected a large amount of data that provide a good basis for investigating the key drivers of spatial and temporal variability. Event-based water quality monitoring data in the Great Barrier Reef catchments in northern Australia provide an opportunity to further our understanding of water quality dynamics in subtropical and tropical regions. This study investigated nine water quality constituents, including sediments, nutrients and salinity, with the aim of (1) identifying the influential environmental drivers of temporal variation in flow event concentrations and (2) developing a modelling framework to predict the temporal variation in water quality at multiple sites simultaneously. This study used a hierarchical Bayesian model averaging framework to explore the relationship between event concentration and catchment-scale environmental variables (e.g. runoff, rainfall and groundcover conditions). Key factors affecting the temporal changes in water quality varied among constituent concentrations and between catchments. Catchment rainfall and runoff affected in-stream particulate constituents, while catchment wetness and vegetation cover had more impact on dissolved nutrient concentration and salinity. In addition, in large dry catchments, antecedent catchment soil moisture and vegetation had a large influence on dissolved nutrients, which highlights the important effect of catchment hydrological connectivity on pollutant mobilisation and delivery.

Anoxic in situ production of bacterial GMGTs in the water column and surficial bottom sediments of a meromictic tropical crater lake: Implications for lake paleothermometry

Branched glycerol monoalkyl glycerol tetraethers (brGMGTs) are membrane-spanning lipids which were initially identified in marine settings and have more recently been found in peats and lake sediments. In the latter settings, their abundance relative to that of the branched glycerol dialkyl glycerol tetraethers (brGDGTs) appears to increase under warmer climate conditions. Furthermore, their relative distribution in bottom sediments from an altitudinal transect of East African lakes has been linked to local mean annual air temperature (MAAT). To shed light on their sources and identify potential environmental factors driving their production in lakes, we investigated their occurrence and distribution in the water column, surficial lake-bottom sediments, and catchment soils of Lake Chala, a permanently stratified (meromictic) tropical crater lake in East Africa. Data from the water column comprise both suspended particulate matter (SPM) collected monthly at eight depth intervals between 0 and 80 m for 17 consecutive months, and settling particles collected monthly at a depth of 35 m over a period of 53 months. In catchment soils, brGMGTs are either relatively scarce or absent. In the water column, their occurrence is dominated by four of the seven known brGMGTs and mostly limited to the anoxic zone. Whereas the spatial distribution and concentration of brGMGTs in SPM were strongly influenced by the seasonal cycle of strong water-column stratification alternating with deep mixing, this trend is not consistent on the multi-year timescale of the settling-particles record. Moreover, their relative distribution in both SPM and settling particles did not respond to temperature variation during the studied interval. In contrast to the water column, surficial lake-bottom sediments contain the full suite of known brGMGTs in a distinct and spatially uniform fractional abundance, strongly suggesting that the majority of brGMGT production takes place there. BrGMGT-inferred MAAT for the Chala area reasonably estimates measured MAAT and conforms to the East African lake brGMGT calibration. Our results have important implications for the use of brGMGTs as proxy for MAAT, in that outside of the equatorial zone the presumably greater offset between bottom-water temperature and MAAT may create a bias towards cold-season air temperature. Regardless, the more singular source of brGMGTs in lake sediments is an advantage for paleotemperature reconstruction compared to brGDGTs, which several studies now indicate to have a mixed aquatic and terrestrial source of which the relative contribution cannot easily be disentangled or assumed to have been constant through time.

The Multiscale TROPIcal CatchmentS critical zone observatory M‐TROPICS dataset II: Land use, hydrology and sediment production monitoring in Houay Pano, northern Lao PDR

AbstractMountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land‐use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long‐term impact of the conversion of traditional slash‐and‐burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro‐meteorological and soil loss parameters at both microplot (1 m2) and small catchment (0.6 km2) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M‐TROPICS). The data shared by M‐TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land‐use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment‐scale models focused on hydrology and water quality issues. The dataset may be further used to, for example, assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g., contaminants other than faecal bacteria), and assess the relative impacts of both climate and land‐use change on the catchment.

Late-Holocene diatom community response to climate driven chemical changes in a small, subarctic lake, Northwest Territories, Canada

The paleolimnological record of diatoms and climate, spanning the last 2800 years, was investigated in a small subarctic lake (Pocket Lake) that from AD 1948 to 2004 was contaminated by gold smelting waste. An age-depth model was constructed using a combination of 210Pb, 14C, and tephra to determine a 2800 year history of lake ontogeny (natural aging), biological diversity, and regional climate variability. Diatoms form six strong paleoecological assemblages over time in response to changes in local hydrological and sedimentological conditions (including metals). Selected environmental variables explained 28.8% of the variance in the diatom assemblages, with Fe, Ca, and sediment end member distribution being important indicators. The diatom assemblages correlated to the Iron Age Cold Epoch (2800–2300 cal BP), Roman Warm Period (2250–1610 cal BP), Dark Age Cold Period (1500–1050 cal BP), Medieval Climate Anomaly (ca. 1100–800 cal BP), and the Little Ice Age (800–200 cal BP). The disappearance of Staurosira venter highlights the change from the Iron Age Cold Epoch to the Roman Warm Period. After deposition of the White River Ash (833–850 CE; 1117–1100 cal BP), transition to circumneutral conditions was followed in tandem by a transition to planktic influenced communities. Ten discrete peaks of Cu, Pb, and Zn were observed and attributed to soluble mobility from catchment soils through enhanced seepage and spring snowmelt. The prominent metal spikes were aligned with increases in Brachysira neoexilis. Downward mobilization of arsenic and antimony from contaminated surficial sediments highlight the problem of post depositional industrial contamination of paleosediments. Results demonstrate that paleoclimatic changes in the region, modulated by solar radiation, impacted temperature and precipitation in the lake catchment, influencing temporal shifts in diatom ecology. Changes in diatom taxa richness provided valuable information on the relative influence of water quality (planktic taxa) and sediment input (benthic taxa). The diatom assemblage succession also provides evidence that natural aging over time has played a role in the ecological evolution of the lake.

Anthropocene climate warming enhances autochthonous carbon cycling in an upland Arctic lake, Disko Island, West Greenland

Abstract. The Arctic is rapidly changing, disrupting biogeochemical cycles and the processing, delivery and sedimentation of carbon (C), in linked terrestrial–aquatic systems. In this investigation, we coupled a hydrogeomorphic assessment of catchment soils, sediments and plants with a recent lake sediment sequence to understand the source and quality of organic carbon present in three Arctic upland lake catchments on Disko Island, located just south of the low–high Arctic transition zone. This varied permafrost landscape has exposed soils with less vegetation cover at higher altitudes, and lakes received varying amounts of glacial meltwater inputs. We provide improved isotope and biomarker source identifications for palaeolimnological studies in high-latitude regions, where terrestrial vegetation is at or close to its northerly and altitudinal range limit. The poorly developed catchment soils lead to lake waters with low dissolved organic carbon (DOC) concentrations (≤1.5 mg L−1). Sedimentary carbon/nitrogen (C/N) ratios, the C isotope composition of organic matter (δ13Corg) and biomarker ratios (n-alkanes, n-alkanols, n-alkanoic acids and sterols) showed that sedimentary organic matter (OM) in these lakes is mostly derived from aquatic sources (algae and macrophytes). We used a 210Pb-dated sediment core to determine how carbon cycling in a lake–catchment system (Disko 2) had changed over recent centuries. Recent warming since the end of the Little Ice Age (LIA∼1860 CE), which accelerated after ca. 1950, led to melt of glacier ice and permafrost, releasing nutrients and DOC to the lake and stimulating pronounced aquatic algal production, as shown by a >10-fold increase in β-carotene, indicative of a major regime shift. We also demonstrate that recent increases in catchment terrestrial vegetation cover contributed to the autochthonous response. Our findings highlight that in Arctic lakes with sparsely developed catchment vegetation and soils, recent Anthropocene warming results in pronounced changes to in-lake C processing and the deposition of more reactive, predominately autochthonous C, when compared with extensively vegetated low-Arctic systems.

Climate-driven fluxes of organic-bound uranium to an alpine lake over the Holocene

Uranium (U) isotopic signatures and concentration in sediments are widely used as paleo-redox proxies, as the behavior of U is often controlled by bottom water oxygenation. Here, we investigated the processes controlling U accumulation in the sediments of Lake Nègre (Mediterranean Alps, South-East France) over the past 9200 years. Exceptionally high natural U concentrations (350–1250 μg·g−1) allowed the measurement of U along with other elements by high-resolution X-Ray Fluorescence core-scanning. Weathering and erosion proxies (Ti content, Zr/Al and K/Ti ratios) indicate that sedimentary inputs were controlled by Holocene climatic variations. After a period of low erosion during the Holocene Climatic Optimum, a major regime shift was recorded at 4.2 kyr BP when terrigenous fluxes consistently increased until present with high sensitivity to centennial-scale climatic events. Sedimentary organic matter (OM) inputs were dominated by terrigenous OM from the catchment soils until 2.4 kyr BP, as attested by carbon to nitrogen (C/N) and bromine to organic carbon (Br/TOC) ratios. From 2.4 kyr BP to present, lake primary production and soils equally contributed to sedimentary OM. Uranium fluxes to the sediments were well correlated to terrigenous OM fluxes from 7 kyr BP to present, showing that U supply to the lake was controlled by U scavenging in the soils of the watershed followed by transport of U bound to detrital organic particles. Higher U/OM ratios before 7 kyr BP likely reflect the development of the upstream wetland. The fluctuations of U sedimentary inputs appear to be independent of bottom water oxygenation, as estimated from constant Fe/Mn ratios and δ238U isotopic signatures, and rather controlled by the production, erosion and sedimentation of terrigenous OM. This finding confirms that the use of U (and potentially other metals with high affinity to OM) concentrations alone should be used with caution for paleo-redox reconstructions.

SHETRAN and HEC HMS Model Evaluation for Runoff and Soil Moisture Simulation in the Jičinka River Catchment (Czech Republic)

Due to the improvement of computation power, in recent decades considerable progress has been made in the development of complex hydrological models. On the other hand, simple conceptual models have also been advanced. Previous studies on rainfall–runoff models have shown that model performance depends very much on the model structure. The purpose of this study is to determine whether the use of a complex hydrological model leads to more accurate results or not and to analyze whether some model structures are more efficient than others. Different configurations of the two models of different complexity, the Système Hydrologique Européen TRANsport (SHETRAN) and Hydrologic Modeling System (HEC-HMS), were compared and evaluated in simulating flash flood runoff for the small (75.9 km2) Jičinka River catchment in the Czech Republic. The two models were compared with respect to runoff simulations at the catchment outlet and soil moisture simulations within the catchment. The results indicate that the more complex SHETRAN model outperforms the simpler HEC HMS model in case of runoff, but not for soil moisture. It can be concluded that the models with higher complexity do not necessarily provide better model performance, and that the reliability of hydrological model simulations can vary depending on the hydrological variable under consideration.

Correlation of natural radionuclides (Ra-226, Ra-228 and K-40) in catchment soil and river sediment from Middle Langat River Basin

Natural radionuclides Ra-226, Ra-228 and K-40 along three (3) stations in Middle Langat River Basin were collected over a 9-year period at 3 months interval. Variations of activity concentration in the catchment soil and river sediment samples were analysed using HPGe detector to identify temporal and spatial trend. Activity concentrations show indication of long-term fluctuation especially for K-40, but will require long data for further validations. Increased activity concentrations in the down-river direction suggests a couple catchment loss and river sediment relative gain based on analysis of the ratios between element pair. Correlation of Ra-226 and Ra-228 is very strong, but their correlation with K-40 varies considerably possibly due to the high potassium solubility.

Centennial-scale age offsets of plant wax n-alkanes in Adirondack lake sediments

Lacustrine sediments have the potential to preserve paleoenvironmental proxies such as terrestrial plant waxes at high temporal resolution. The temporal fidelity of plant wax records, however, can be up to several thousand years older than the corresponding sediment, based on compound-specific radiocarbon (14C) analysis. Unfortunately, the factors controlling 14C age offsets between plant waxes and sediments are not well understood. The aims of this study are to quantify and compare plant wax n-alkane 14C age offsets among lakes within the same region, and to determine if drainage and lake basin differences (e.g., size, relief, drainage basin morphology, fluvial inputs) influence these offsets. We collected sediments from five lakes in the Adirondack Mountains, NY, USA that lack petrogenic sources of n-alkanes, and range in drainage basin characteristics. Sediment age models were constructed for each lake using a combination of sediment 210Pb, 137Cs, and macrofossil 14C ages, and compared to 14C ages of long-chain (n-C27, n-C29, n-C31) alkanes sampled from Holocene and Late Glacial aged sediments. The n-alkane 14C ageinitial is a measure of the age offset in n-alkanes relative to the sediment they are deposited in. Across all lakes, the n-alkane 14C ageinitial ranged from penecontemporaneous to 2440 14C yr. This oldest n-alkane 14C ageinitial is significantly outside the distribution of all other samples; when excluded, the overall mean n-alkane 14C ageinitial was 400 ± 255 14C yr (n = 23). The largest n-alkane 14C ageinitial values were observed in the last 1 cal kyr BP (565 ± 180 14C yr (1σ), n = 12)) compared to sediments deposited between 1 and 13 cal kyr BP (220 ± 195 14C yr (1σ), n = 11)). These age offsets develop early after initial lake basin sedimentation and follow a similar pattern in all of the lakes despite differences in lake basin and catchment size, relief, and geomorphology. We speculate that 14C age offsets occur due to reworking of older n-alkanes stored in drainage basin sediments and soils and this mechanism is most effective in the last ∼1 kyr. Regardless, lakes in temperate forested metamorphic bedrock terrains have relatively small and stable n-alkane age offsets compared with lakes with extensive catchment soils or anthropogenic disturbance. By targeting lakes with minimal catchment soils, age offsets may be reduced, thereby minimizing attenuation or age distortion of climate signals in plant wax isotopic records.

Estimating catchment scale soil moisture at a high spatial resolution: Integrating remote sensing and machine learning

Soil moisture information is important for a wide range of applications including hydrologic modelling, climatic modelling and agriculture. L-band passive microwave satellite remote sensing is the most feasible option to estimate near-surface soil moisture (~0–5 cm soil depth) over large extents, but its coarse resolution (~10s of km) means that it is unable to capture the variability of soil moisture in detail. Therefore, different downscaling methods have been tested as a solution to meet the demand for high spatial resolution soil moisture. Downscaling algorithms based on the soil thermal inertia relationship between diurnal soil temperature difference (ΔT) and daily mean soil moisture content (μSM) have shown promising results over arid and semi-arid landscapes. However, the linearity of these algorithms is affected by factors such as vegetation, soil texture and meteorology in a complex manner. This study tested a (i) Regression Tree (RT), an Artificial Neural Network (ANN), and a Gaussian Process Regression (GPR) model based on the soil thermal inertia theory over a semi-arid agricultural landscape in Australia, given the ability of machine learning algorithms to capture complex, non-linear relationships between predictors and responses. Downscaled soil moisture from the RT, ANN and GPR models showed root mean square errors (RMSEs) of 0.03, 0.09 and 0.07 cm3/cm3 compared to airborne retrievals and unbiased RMSEs (ubRMSEs) of 0.07, 0.08 and 0.05 cm3/cm3 compared to in-situ observations, respectively. The study showed encouraging results to integrate machine learning techniques in estimating near-surface soil moisture at a high spatial resolution.

Identifying marine and freshwater overprints on soil-derived branched GDGT temperature signals in Pliocene Mississippi and Amazon River fan sediments

The fractional abundance of branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids in coastal marine sediments has been posited as a proxy for the reconstruction of terrestrial temperatures on the nearby land, based on the assumption that they are produced in soils and delivered to the marine realm by rivers following erosion. Here, we test the suitability of brGDGTs as a continental paleothermometer in Pliocene age sediments from the northern Gulf of Mexico (GoM; speculated Mississippi River input) and the Ceará Rise (speculated Amazon River input). Low branched to isoprenoid tetraether (BIT) index values of 0.00–0.13 and the near absence of pollen and long-chain plant waxes in the GoM sediments suggest that the Mississippi River did not have a strong influence on the delivery of terrestrial organic matter to the site during the Pliocene and soil input was limited. Indeed, the high weighted average of cyclopentane-containing tetramethylated brGDGTs (#ringstetra) in the GoM sediments (0.50 ± 0.09) relative to that of modern soils from the Mississippi catchment (0.25 ± 0.16) indicates that the brGDGTs in the GoM sediments were mostly produced in situ in the marine realm, hampering reliable land temperature reconstruction using the global soil transfer function. In contrast, high BIT index values (0.46 ± 0.21) and low #ringstetra (0.25 ± 0.15) in sediments from the Ceará Rise suggest that these brGDGTs are primarily derived from soils. However, reconstructed temperatures were 11–18 °C lower than modern Amazon catchment temperatures. The relative abundance of 6-methylated brGDGTs (Isomerisation Ratio; IR) in the sediments is 0.82 ± 0.10, which resembles that of suspended particulate matter (SPM) in the modern Amazon River more than that of catchment soils (IR = 0.18 ± 0.18). This reveals that brGDGTs in the Ceará Rise sediments likely have a freshwater, riverine origin. Thus, the majority of the brGDGTs in both the GoM and Ceará Rise sediments are produced in situ, in the marine or river realms, which precludes application of the brGDGT paleothermometer. Our study shows that the sources of brGDGTs in coastal marine sediment archives must be critically evaluated prior to using the proxy for paleoclimate reconstruction.

A 17,000-year multi-proxy study of the Indian Summer Monsoon from Lake Dian, Yunnan, China

Continuous lacustrine records of the Indian Summer Monsoon (ISM) that span the Pleistocene-Holocene transition to the present are relatively rare, yet crucial to providing context to future changes in hydroclimate. We summarize here a 17,000 year continuous multi-proxy record of hydroclimate and primary productivity from Lake Dian in the central Yunnan Province of China. Analysis of sediment composition, opal, carbon to nitrogen ratios, carbon and nitrogen stable isotope ratios, and magnetic susceptibility (MS) are used to identify four distinct units in the sediment record. Unit I sediments from 17,000 to 11,500 years BP are characterized by high MS and uniformly low organic and opal content interrupted by a decrease in MS during the Bølling-Allerød indicating the influence of the North Atlantic on the ISM. We interpret this to reflect cold, dry, and windy conditions during the transition out of the Last Glacial Maximum. Unit II from 11,500 to 5000 years BP is marked by a pronounced decrease in MS, increase in opal, and decrease in δ13Corg of organic carbon driven by peak warmth and wet conditions increasing productivity. Unit III from 5000 to 1800 years BP shows further increases in primary productivity, marked by lower carbon to nitrogen ratios and carbonate precipitation, possibly driven by a drop in lake level. A period of aridity is in wide agreement with a number of other records from the region. Unit IV from 1800 years BP to present is dominated by anthropogenic impacts and hallmark signs of catchment soil erosion and cultural eutrophication. Our interpretations of the Dian sediment record agree well with previous palynological work and add a new dimension to our understanding of lake hydrology and productivity over the past 17,000 years.

Mineral magnetism potentially indicating degrees of soil gleization and their implications for tracing sediment sources: Inferences for a small catchment on Guizhou Plateau, SW China

Ten soil profiles were sampled from a small catchment and two sediment cores were retrieved from a reservoir built in it on the Guizhou Plateau, SW China. Mineral magnetism measurements, particle size, TOC and TN analysis were performed on the soils and sediments. 137Cs activity analysis was made for one of the cores. Precipitation data were collected for 1957–2017. Vegetation cover and land-use data were acquired for 11 or 12 years included in this period by interpreting remote-sensing images. Magnetic characteristics of topsoil suggest that soils closely around the reservoir were generally strongly gleyed due to lower-lying positions and more frequent waterlog and those distant to it were less or not gleyed owing to better drainage. Particle-size, TOC and C/N data support this inference. The average of χlf, χARM and IRM300mT/SIRM is only 41 10-8 m3 kg−1, 144 10-8 m3 kg-1and 0.84 for the topsoil of the strongly gleyed profiles, while the average is high (95 10-8 m3 kg−1, 380 10-8 m3 kg−1 and 0.92, respectively) for the topsoil of the less- or non-gleyed profiles. With the aid of the other data, the sediment magnetism in comparison of the topsoil’s suggests varying contributions of the less- or non-gleyed soils versus strongly gleyed soils to the sediments with changes in precipitation and land use. When rainfall was low and vegetation was sparse, contributions to the sediments from the weakly gleyed and non-gleyed soils farther away from the reservoir were bigger. When rainfall decreased and vegetation was better developed particularly in the fields distant to the reservoir, contributions from the strongly gleyed soils distributed closely around the reservoir would relatively increase while those from the remote and weakly gleyed and non-gleyed soils decrease. These results suggest that gleization may strengthen spatial magnetic variability of catchment soils and help to infer sediment sources.

Exploring the Benefits of Small Catchments on Rural Spatial Governance in Wuling Mountain Area, China

China is facing an important period of rural governance innovation and restructuring of territorial spatial patterns. This paper selects catchments as the most closely related spatial units for rural industrial development and rural settlement activities, profoundly revealing the characteristics of transformational development and spatial governance in mountainous areas. To date, extensive literature in this area has produced a broad multidisciplinary consensus on catchment water and soil conservation and rural industry development; however, the interactive mechanism of ecological, social, and economic networks, and the characteristics behind small catchments which benefit from spatial governance, have never been analyzed and are relatively new to the sphere of rural governance. Our research argues the relative importance of multi-scale catchment units compared with traditional administrative village units in enhancing the organizational benefits of rural revitalization in terms of workforce, resources, and capital, using the case study of a catchment in the Wuling mountainous area. Our study presents a framework to explore the multi-dimensional governance experience of a small catchment in the Wuling mountainous area and proposes to integrate the resource endowment advantages of small catchments into rural industries development and transform the economic and social benefits contained in the ecological environment into multi-scale spatial benefits among farmers, villages, and the regional rural area. However, not all cases provide positive evidence. The overall development of a catchment is confronted with complex constraints, which are mainly related to the development stage and local historical and geographical factors. Furthermore, affected by the top-down “project-system” in the “poverty era”, the logic of “betting on the strong” and the single-centered logic of resource allocation at the grassroots level exacerbated the fragmentation of the mountainous area. Generally speaking, the catchment perspective promotes regional linkage development and multi-center governance modes and triggers multidisciplinary theoretical thinking to some extent. The catchment’s overall development helps play to the comparative advantage of mountainous areas and promotes endogenous sustainable development to a certain degree. However, the promotion of catchment governance in poverty-stricken mountainous areas is faced with a lack of financial foundation and needs support in order to break through the national system and local social constraints.

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.

Interpretations of Hg anomalous sources in drainage sediments and soils in China

China Geochemical Baselines project provides mercury dataset of drainage catchment sediments and soils during 2008–2012 in China. Fifty-seven mercury anomalous regions exceeding the risk limits of the China National Environmental Standards for Heavy Metals in Soil (GB 15618-1995) are delineated in China. The sources of Hg risk anomalies of the top and deep samples are variously interpreted with respect to geology/mineralisation and human activities. Nearly 72% anomalies (41 among the totaling 57 anomalous locations) are due to natural geological mineralisation belts and mining of Hg, As, Sb, Au, Ag, Pb, Zn, coal etc. The mining activities cause superimposed contents of Hg on the natural mineralisation belts. The influence of large-scale mining of Hg, non-ferrous metals and gold are significantly reflected in the geochemical maps. The anthropogenic sources of urbanisation emission, agriculture, coal combustion, and smelting industry cause the much more degree of mercury pollution in the eastern China where is highly populated and industrial density areas. Agriculture is an important Hg-emission source in the eastern China and Chengdu Plains where agricultural base for more than 2500 years in China. It is critical to carry out the follow-up detailed source investigation and monitor the temporal changes of Mercury in soils.

Development of an in situ branched GDGT calibration in Lake 578, southern Greenland

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are abundant in lake sediments and can potentially be used as proxies for evaluating past environmental conditions. The degree of methylation of brGDGTs has a strong relationship with the ambient temperature, and numerous brGDGT temperature reconstructions have been generated ranging from the tropics to high latitudes and over a variety of timescales. However, this proxy still requires calibration and validation in Arctic settings, which are among the most climatically sensitive regions on Earth. Here, we investigate Lake 578, a dimictic lake located in southern Greenland, and examine brGDGTs in a sediment core, surface sediments, catchment soils, and settling particulate matter (SPM). Our results suggest that sedimentary brGDGTs are mainly produced in the water column, and the SPM MBT′5ME (Methylation of Branched Tetraethers) values are significantly correlated with depth-integrated summer water temperature. Here, we provide the first lake water temperature-brGDGT calibration based on the MBT′5ME index, with an improved root mean square error (RMSE) of 0.52 °C. Like previous studies, we find that watershed soils differ in brGDGT distributions from those of the SPM or lake sediments, and we conclude that most brGDGT production in Lake 578 is occurring in situ. In the sediment core, we observe a significant cooling trend in the uppermost 7 cm, but this result is unrealistic because it conflicts with the instrumental temperature record from this region. This “core-top cooling” is associated with increasing relative abundances of brGDGT-IIa and IIIa, and with decreasing brGDGT-Ia, and we speculate that it may be driven by diagenetic effects or changing microbial communities in the sediment subsurface. The anomalous “core-top cooling” phenomenon, which is noted in numerous other published lacustrine brGDGT records, highlights the need for further studies of brGDGTs in modern and recent lake sediments. Constraining the source organisms of brGDGTs and better understanding the relationship between brGDGTs and environmental factors are essential, prior to their use in paleoclimate reconstructions.

Reconstruction of temperature and precipitation spanning the past 28 kyr based on branched tetraether lipids from Qionghai Lake, southwestern China

The Indian summer monsoon (ISM) significantly influences the climate of southwestern China; however, continuous quantitative temperature reconstructions since the Last Glacial Maximum are rare, which limits our understanding of ISM evolution. In this study, we analyzed the branched glycerol dialkyl glycerol tetraethers (brGDGTs) from a lacustrine sediment core from Qionghai Lake to reconstruct the paleoclimatology of southwestern subtropical China over the past 27.7 kyr. Our results suggest that the brGDGTs in Qionghai Lake sediments were probably sourced from catchment soils, with some contributions from in situ lacustrine production. We found that the temperature of the Last Glacial Maximum and Holocene Climatic Optimum was ~3 °C cooler and ~ 2.5 °C warmer than present-day conditions, respectively, based on brGDGTs-reconstructed mean annual air temperatures (MATs). Generally, temperature and precipitation showed synchronous paleovariability in ISM regions. Moreover, Northern Hemisphere summer insolation was the dominant control on climate variability in ISM regions on the precessional scale, while Atlantic Meridional Overturning Circulation activity, Intertropical Convergence Zone positioning, and glacial boundary conditions (ice sheet extent and sea surface temperature) contributed to climate shifts on millennial timescales.

The flood cooking book: ingredients and regional flavors of floods across Germany

River flooding is a major natural hazard worldwide, whose prediction is impaired by limited understanding of the interplay of processes triggering floods within large regions. In this study we use machine learning techniques such as decision trees and random forests to pinpoint spatio-temporal features of precipitation and catchment wetness states which led to floods among 177 267 rainfall-runoff events observed in 373 German river basins. In mountainous catchments with high annual precipitation rates and shallow soils, event rainfall characteristics primarily control flood occurrence, while wetness conditions and the spatial interplay between rainfall and catchment soil moisture drive flood occurrence even more than event rainfall volume in drier basins. The existence of a snow cover also enhances flood occurrence. The identified ingredients and regional flavors shed new light on the spatial dynamics of hydro-meteorological processes leading to floods and foster regional adaptation of flood management strategies and early warning systems.

Native woodland establishment improves soil hydrological functioning in UK upland pastoral catchments

AbstractExtreme rainfall and flood events are predicted to increase in frequency and severity as a consequence of anthropogenic climate change. In UK upland areas, historical over‐grazing and associated soil compaction have further exacerbated peak flood levels and flash‐flood risk along many river catchments. As a result, the reinstatement of upland woodland is increasingly seen as a key component of an integrated suite of options forming part of natural flood management (NFM) associated with a 'public money for public goods' approach to European agriculture. Nevertheless, understanding the impact of native woodland establishment on upland soil hydrology remains relatively poor. We compare physical and hydrological properties from the surface soils of establishing woodland and grazed pasture across four flood vulnerable upland headwater catchments in Dartmoor National Park, SW England. We show upland native woodland establishment is a viable soil recovery option, with a doubling of soil saturated hydraulic conductivity, increased 'wetness threshold' and reduced surface soil compaction and bulk density within 15 years of establishment. Our study supports the establishment of native woodland as an effective tool to improve the hydrological functioning of soils in upland pastoral catchments and the provision of flash‐flood mitigation 'ecosystem services'. We caution, however, that land managers and policymakers must consider past and present management, soil type and catchment location when planning new NFM schemes if environmental benefits are to be maximised and 'public money for public goods, are to be commensurate with outcomes.