Mass Balance Budget Research Articles

First Ce-Nd isotope measurements of middle and lower continental crust samples support massive lower crust recycling over Earth's history

Long-lived radioactive isotopes provide valuable information on the evolution of Earth's geological reservoirs. Coupled measurements of the 138La-138Ce and 147Sm-143Nd systems have attracted much interest, but some critical reservoirs, such as the deep continental crust, have yet to be investigated. To address this gap, we report Ce-Nd isotope measurements of 35 crustal samples from Canada, western Europe, and Siberia, with Archean to Phanerozoic ages. Most samples from western Europe and Siberia are interpreted to represent the deepest continental crust because of low SiO2 content (< 55 wt%) and generally mafic compositions. In contrast, Precambrian composites from the Canadian shield have highly felsic compositions (61–71 wt% SiO2) and represent the old upper continental crust. Xenoliths from the Massif Central (France) and samples from uplifted massifs in the Ivrea-Verbano zone (Italy) plot on the Ce-Nd mantle array. Precambrian Canadian composites and xenoliths from Udachnaya (Siberian Craton) plot to the left of the mantle array, with the Siberian samples farthest from the array. The La-Ce system yields a ca. 1.8 Ga age for the Siberian xenoliths, distinct from the ca. 2.7 Ga Sm-Nd errorchron age. The La-Ce system was most likely reset during a large-scale episode of delamination and rejuvenation of the Archean lower lithosphere established in Siberia. A change in the La/Ce ratio during this event explains an increasing deviation with time of the Ce-Nd isotopic composition of the Siberian deep crust from the mantle array. We introduce a new parameter (θ) to quantify the likelihood of any rock evolving away from the mantle array. It represents the angle between the evolution vector of a sample and the mantle array, and it is calculated from measured La/Ce and Sm/Nd ratios. Samples that plot to the right of the mantle array have θ > 0, whereas samples that plot to the left of the mantle array have θ < 0. The angle θ was used to compare our samples to a worldwide granulite compilation (1581 samples) because it is independent of the age and the initial isotopic composition of the samples. The majority of lower crust rocks have negative θ, suggesting they are prone to evolve to the left of the mantle array, but to a lesser extent than the Siberian samples that are characterized by the most negative θ values. Thus, the Siberian samples with the most unusual Ce-Nd isotopic compositions are the only group to plot close to the deep crust end-member calculated from classical mass-balance budget of the bulk silicate Earth. These results suggest that the lower crust sampled by Siberian xenoliths is only a minor component in the terrestrial deep crust. We use this database to estimate new parent/daughter ratios for the lower continental crust: 138La/142Ce = 0.00380 ±0.00007 and 147Sm/144Nd = 0.128 ±0.007. Measurements and models are finally reconciled when considering massive recycling of lower continental crust through Earth's history, totaling 3 to 4 present-day, continental crust masses.

Biogeochemical cycling in a periglacial environment – A multi-element mass-balance budget for a catchment in West Greenland

There is an increased awareness that the biogeochemical cycling at high latitudes will be affected by a changing climate. However, because biogeochemical studies most often focus on a limited number of elements (i.e., C, P and N) we lack baseline conditions for many elements. In this work, we present a 42-element mass-balance budget for lake dominated catchment in West Greenland. By combining site specific concentration data from various catchment compartments (precipitation, active layer soils, groundwater, permafrost, lake water, lake sediments and biota) with catchment geometries and hydrological fluxes from a distributed hydrological model we have assessed present-day mobilization, transport and accumulation of a whole suite of elements with different biogeochemical behavior. Our study shows that, under the cold and dry conditions that prevails close to the inland ice-sheet: i) eolian processes are important for the transport of elements associated with mineral particles (e.g., Al, Ti, Si), and that these elements tend to accumulate in the lake sediment, ii) that even if weathering rates are slowed down by the dry and cold climate, weathering in terrestrial soils is an important source for many elements (e.g., lanthanides), iii) that the cold and dry conditions results in an accumulation of elements supplied by wet deposition (e.g., halogens) in both terrestrial soils and the lake-water column, and iv) that lead and sulfur from legacy pollution are currently being released from the terrestrial system. All these processes are affected by the climate, and we can therefore expect that the cycling of the majority of the 42 studied elements will change in the future. However, it is not always possible to predict the direction of this change, which shows that more multi-element biogeochemical studies are needed to increase our understanding of the consequences of a changing climate for the Arctic environment.

Temporal evolution of under-ice meltwater layers and false bottoms and their impact on summer Arctic sea ice mass balance

Low-salinity meltwater from Arctic sea ice and its snow cover accumulates and creates under-ice meltwater layers below sea ice. These meltwater layers can result in the formation of new ice layers, or false bottoms, at the interface of this low-salinity meltwater and colder seawater. As part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), we used a combination of sea ice coring, temperature profiles from thermistor strings and underwater multibeam sonar surveys with a remotely operated vehicle (ROV) to study the areal coverage and temporal evolution of under-ice meltwater layers and false bottoms during the summer melt season from mid-June until late July. ROV surveys indicated that the areal coverage of false bottoms for a part of the MOSAiC Central Observatory (350 by 200 m2) was 21%. Presence of false bottoms reduced bottom ice melt by 7–8% due to the local decrease in the ocean heat flux, which can be described by a thermodynamic model. Under-ice meltwater layer thickness was larger below first-year ice and thinner below thicker second-year ice. We also found that thick ice and ridge keels confined the areas in which under-ice meltwater accumulated, preventing its mixing with underlying seawater. While a thermodynamic model could reproduce false bottom growth and melt, it could not describe the observed bottom melt rates of the ice above false bottoms. We also show that the evolution of under-ice meltwater-layer salinity below first-year ice is linked to brine flushing from the above sea ice and accumulating in the meltwater layer above the false bottom. The results of this study aid in estimating the contribution of under-ice meltwater layers and false bottoms to the mass balance and salt budget for Arctic summer sea ice.

A marine plastic cloud - Global mass balance assessment of oceanic plastic pollution

To improve our understanding and management of marine plastic pollution of the ocean, a total plastic budget is needed which quantifies the sources and sinks, as well as inputs and removal of plastic per unit time. The current state of knowledge indicates that the coastal zone and ocean water column are major locations for plastic pollution, but the fate of much of this must ultimately be the deep ocean floor. We reviewed 23 journal articles that provide 280 observations of deep-sea sediment microplastic concentration across six different off-shelf environments. We calculate the following mean concentrations of microplastic particles (number) per kg of sediment: continental slope 502; submarine canyons 784; submarine fans and continental rise 714; abyssal plains 217; trenches and troughs 2782; and abyssal hills, mountains and other ocean floor 165 particles kg−1. These figures are alarming because several exceed one estimate of ‘safe’ levels of microplastic concentration for benthic marine life (540 particles kg−1). Monitoring of the concentration of plastic particles in sediments of submarine canyons, fans and continental rise environments and in trenches and troughs should be a priority to ensure efficacy of policies and actions taken to curb ocean plastic pollution at both the national and global level. We estimate 3.05 million tonnes of microplastic resides in deep ocean sediments but acknowledge the uncertainties of this figure. If correct, this figure implies that the ocean water column (which may contain as much as 90 million tonnes of microplastic) is a major, transitory sink for MP, forming a suspended, marine plastic cloud. In addition to particle concentrations, further measurements of the size and mass of microplastic in deep-sea sediments and in the water column are needed to advance development of mass balance budgets for marine plastic pollution.

Mosses and lichens enhance atmospheric elemental mercury deposition in a subtropical montane forest†

Environmental context Mosses and lichens are widely distributed in montane forests and their important role in global biogeochemical cycles has been increasingly recognised. This study of mercury accumulation and sources in mosses and lichens, using mercury isotopic data, provides evidence that they promote atmospheric mercury deposition in these forests, which is an important function that should be incorporated into current mercury mass balance budgets for forests. Rationale Mosses and lichens, which are widely distributed in montane forests, are often used to monitor the atmospheric mercury (Hg) depositions. In this study we hypothesised that atmospheric Hg uptake by mosses and lichens could greatly promote Hg depositions in montane forests. Methodology We comprehensively determined the Hg concentration and isotopic signatures of various species of mosses and lichens in a subtropical montane forest, to quantify the Hg accumulation, influencing factors and potential Hg depositions induced by mosses and lichens. Results Our results show that the higher Hg concentrations in mosses than in lichens are mainly due to their species-specific, morphological and physiological differences. Hg isotopic mixing model results display that uptake of atmospheric elemental Hg (Hg0) contributes 89.2 ± 22.8% of Hg in mosses and 88.4 ± 24.4% in lichens. The lichens growing on trees have a lower atmospheric Hg0 source contribution than on the ground (61.3 ± 42.5% versus 93.6 ± 10.0%) because of the elevated rainfall Hg uptake on trees. The Hg storage in live moss and lichen is 28.0 ± 16.5 and 0.9 ± 1.0 μg m−2, respectively. Given the 1–2-year lifespan of moss, the moss induced atmospheric Hg deposition is almost equivalent to litterfall Hg deposition which was previously used as a proxy for atmospheric Hg0 deposition in forests. Discussion Overall, we suggest mosses and lichens play an important role in atmospheric Hg depositions and recommend more research in montane forests.

Efficient carbon and nitrogen transfer from marine diatom aggregates to colonizing bacterial groups

Bacterial degradation of sinking diatom aggregates is key for the availability of organic matter in the deep-ocean. Yet, little is known about the impact of aggregate colonization by different bacterial taxa on organic carbon and nutrient cycling within aggregates. Here, we tracked the carbon (C) and nitrogen (N) transfer from the diatom Leptocylindrus danicus to different environmental bacterial groups using a combination of 13C and 15N isotope incubation (incubated for 72 h), CARD-FISH and nanoSIMS single-cell analysis. Pseudoalteromonas bacterial group was the first colonizing diatom-aggregates, succeeded by the Alteromonas group. Within aggregates, diatom-attached bacteria were considerably more enriched in 13C and 15N than non-attached bacteria. Isotopic mass balance budget indicates that both groups showed comparable levels of diatom C in their biomass, accounting for 19 ± 7% and 15 ± 11%, respectively. In contrast to C, bacteria of the Alteromonas groups showed significantly higher levels of N derived from diatoms (77 ± 28%) than Pseudoalteromonas (47 ± 17%), suggesting a competitive advantage for Alteromonas in the N-limiting environments of the deep-sea. Our results imply that bacterial succession within diatom aggregates may largely impact taxa-specific C and N uptake, which may have important consequences for the quantity and quality of organic matter exported to the deep ocean.

Modeling Litter Stocks in Planted Forests of Northern Mexico

Litter, LS, is the organic material in which locates in the top A soil horizon, playing key ecological roles in forests. Models, in contrast to common allocation factors, must be used in LS assessments as they are currently absent in the scientific literature. Its evaluation assess the mass, input and flux of several bio-geo-chemicals, rainfall interception as one component of the local hydrology, and wildfire regimes, among others, hence its importance in forestry. The aim of this study was to: (i) develop models to assess LS, accumulation, and loss rates; and (ii) assess rainfall interception and fire regimes in 133 northern forest plantations of Mexico. Two developed techniques: the statistical model (SMLS) and the mass balance budget model (MBMLS) tested and validated local and regional LS datasets. Models use basal area, timber, aboveground tree biomass, litter fall, accumulation, and loss sub-models. The best fitting model was used to predict rainfall interception and fire behavior in forest plantations. Results showed the SMLS model predicted and validated LS datasets (p = 0.0001; r2 = 0.82 and p = 0.0001; r2 = 0.79) better than the MBMLS model (p = 0.0001; r2 = 0.32 and p = 0.0001; r2 = 0.66) but the later followed well tendencies of Mexican and World datasets; counts for inputs, stocks, and losses from all processes and revealed decomposition loss may explain ≈40% of the total LS variance. SMLS predicted forest plantations growing in high productivity 40-year-old stands accumulate LS &gt; 30 Mg ha−1 shifting to the new high-severity wildfire regime and intercepting ≈15% of the annual rainfall. SMLS is preliminarily recommended for LS assessments and predicts the need of LS management in forest plantations (&gt;40-year-old) to reduce rainfall interception as well as the risk of high-severity wildfires. The novel, flexible, simple, contrasting and consistent modeling approaches is a piece of scientific information required in forest management.

Assessment of groundwater mass balance and zone budget in the semi-arid region: A case study of Palar sub-basin, Tamil Nadu, India

Assessment of groundwater mass balance and zone budget in the semi-arid region: A case study of Palar sub-basin, Tamil Nadu, India

Treating carbon-limited wastewater by DWTR and woodchip augmented floating constructed wetlands

Floating constructed wetlands (FCWs) have attained tremendous popularity for water purification purposes. However, FCW functions establishment in nutrients removal from carbon-limited wastewater, especially in cold weather, is still a challenge. Here, two drinking water treatment residual (DWTR) based biocarriers (B-I: DWTR cakes, B-II: DWTR cakes combined with woodchips) have been augmented into FCW to enhance the nutrients (N and P) removal performance. Compared to the traditional FCW, the intensified FCWs simultaneously achieved higher N and P removal efficiencies, with average pollutants removal of 52.16 ± 11.51% for TN and 92.72 ± 1.61% for TP in FCW-I and 57.65 ± 9.43% for TN and 92.17 ± 2.55% for TP in FCW-II, respectively, while their removal in FCW-III of 27.74 ± 7.11% for TN and 17.91 ± 9.27% for TP. B-II performed best in overcoming the negative influence of low temperature in nutrients removal. Mass balance budget indicated that most P was enriched in DWTR based biocarriers. Thus it is feasible to recycle and recover P from the surface water. Furthermore, P in the sediment can be changed from active P to stable P, mitigating the internal P release risk. This study can help to expand the understanding of the intensified FCWs and promote the practical application of FCWs.

Sediment and particulate organic carbon budgets of a subarctic estuarine fjard: Lake Melville, Labrador

Sediment and particulate organic carbon (POC) budgets constructed for oceanic regions provide a means to quantify the burial of POC, providing a baseline against which future change can be measured. Here we developed the first mass balance budgets of sediment and POC (terrestrial and marine) for the Lake Melville system (LMS; Goose Bay and Lake Melville) in central Labrador using previously published data (210Pb-based mass accumulation rates, river discharge, and total suspended solids) together with measurements of %OC and δ13C signatures within dated sediment cores collected from the LMS basins and water from main tributaries and Groswater Bay. A two end-member mixing model was used to establish fractions of terrigenous and marine POC. Overall, our mass balance budgets show that the Churchill River is the major supply of sediment (16.7 ± 7.8 × 108 kg y−1) and POCterr (18.4 ± 6.6 × 106 kg y−1) to the LMS, accounting for 47% and 56% of the total input to the system, respectively. Although the Churchill River drains directly into Goose Bay along with the smaller Goose River, the majority of sediment (12.9 ± 7.8 × 108 kg y−1) and POCterr (11.8 ± 7.0 × 106 kg y−1) is transported eastward through the surface water plume into Lake Melville. Inputs of POCmar from autochthonous primary production, estimated by applying an empirical relationship between sediment-surface flux of POCmar and water depth, to Goose Bay (1.8 × 106 kg y−1) and Lake Melville (98.3 ± 4.7 × 106 kg y−1) increase with increasing distance from the Churchill River. To investigate the potential changes to the sediment load of the Churchill River to the LMS following impoundment at Muskrat Falls, we calculated the sediment increase using the median reservoir shoreline erosion potential. This approach showed that the delivery of sediment and POCterr to the LMS by the Churchill River may double during the two years following impoundment of the lower Churchill River.

A carbon mass-balance budget for a periglacial catchment in West Greenland – Linking the terrestrial and aquatic systems

Climate change is predicted to have far reaching consequences for the mobility of carbon in arctic landscapes. On a regional scale, carbon cycling is highly dependent on interactions between terrestrial and aquatic parts of a catchment. Despite this, studies that integrate the terrestrial and aquatic systems and study entire catchments using site-specific data are rare. In this work, we use data partly published by Lindborg et al. (2016a) to calculate a whole-catchment carbon mass-balance budget for a periglacial catchment in West Greenland. Our budget shows that terrestrial net primary production is the main input of carbon (99% of input), and that most carbon leaves the system through soil respiration (90% of total export/storage). The largest carbon pools are active layer soils (53% of total carbon stock or 13 kg C m−2), permafrost soils (30% of total carbon stock or 7.6 kg C m−2) and lake sediments (13% of total carbon stock or 10 kg C m−2). Hydrological transport of carbon from the terrestrial to aquatic system is lower than in wetter climates, but the annual input of 4100 kg C yr−1 (or 3.5 g C m−2 yr−1) that enters the lake via runoff is still three times larger than the eolian input of terrestrial carbon. Due to the dry conditions, the hydrological export of carbon from the catchment is limited (5% of aquatic export/storage or 0.1% of total export/storage). Instead, CO2 evasion from the lake surface and sediment burial accounts for 57% and 38% of aquatic export/storage, respectively (or 0.8% and 0.5% of total export/storage), and Two-Boat Lake acts as a net source of carbon to the atmosphere. The limited export of carbon to downstream water bodies make our study system different from wetter arctic environments, where hydrological transport is an important export pathway for carbon.

Formation of the Ce-Nd mantle array: Crustal extraction vs. recycling by subduction

We present new measurements of 138Ce/142Ce and 143Nd/144Nd isotopic ratios in terrestrial and extra-terrestrial samples. The mean value obtained from nine chondrites defines the 138Ce/142Ce ratio of the chondritic uniform reservoir (CHUR) as 0.02256577±66 (2sd). MORBs and OIBs define the mantle array in the εNd vs. εCe diagram to be εNd=−7.3(±0.5)×εCe+0.4(±0.3). From MORB measurements, we derive the isotopic composition of the depleted MORB mantle (DMM) to be εCe=−1.1±0.6 (2sd). Both CHUR and a modelled early-depleted mantle reservoir plot on the mantle array. Thus, the precise determination of the mantle array does not further constrain the La/Ce and Sm/Nd ratios of the bulk silicate Earth (BSE; i.e., primitive mantle). The composition of 1.8 Ga upper continental crust obtained from aeolian sediments is εCe=1.8±0.3 (2sd; εNd=−11.2), and that of its 2.2 Ga equivalent is εCe=2.3±0.3 (2sd; εNd=−17). Binary mixing models between depleted (DMM) and enriched (upper crust or mafic crust composition) components do not reproduce the linear Ce-Nd mantle array but plots close to the island arc basalt data. When the bulk Ce isotopic composition of the continental crust is calculated from the range of accepted Nd isotope values and a mass-balance budget of the BSE, the mixing curves are closer to the mantle array. However the calculated Ce isotopic composition for the bulk crust is always less radiogenic than measurements. Adjusting the Ce-Nd isotopic composition or the Ce/Nd ratio of the end-members to fully linearise the mixing curve leads to unrealistic values never measured in terrestrial samples. We propose a recycling model to reconstruct the mantle array with the participation of both oceanic crust and sediments in the mantle through time. Cerium is a redox sensitive element, making the La-Ce and Sm-Nd systematics an ideal combination to investigate sediment recycling through time. In this recycling model, the most extreme EM-like signatures require the involvement of oceanic sediments that formed under reduced conditions before the Great Oxygenation Event at 2.4 Ga, and which are devoid of Ce elemental anomalies.

Unraveling the hydrological budget of isolated and seasonally contrasted subtropical lakes

Abstract. Complete understanding of the hydrological functioning of large-scale intertropical watersheds such as the Lake Chad basin is becoming a high priority in the context of climate change in the near future and increasing demographic pressure. This requires integrated studies of all surface water and groundwater bodies and of their quite-complex interconnections. We present here a simple method for estimating the annual mean water balance of sub-Sahelian lakes subject to high seasonal contrast and located in isolated regions with no road access during the rainy season, a situation which precludes continuous monitoring of in situ hydrological data. Our study focuses for the first time on two lakes, Iro and Fitri, located in the eastern basin of Lake Chad. We also test the approach on Lake Ihotry in Madagascar, used as a benchmark site that has previously been extensively studied by our group. We combine the δ18O and δ2H data that we measured during the dry season with altimetry data from the SARAL satellite mission in order to model the seasonal variation of lake volume and isotopic composition. The annual water budget is then estimated from mass balance equations using the Craig–Gordon model for evaporation. We first show that the closed-system behavior of Lake Ihotry (i.e., precipitation equal to evaporation) is well simulated by the model. For lakes Iro and Fitri, we calculate evaporation to influx ratios (E∕I) of 0.6±0.3 and 0.4±0.2, respectively. In the case of the endorheic Lake Fitri, the estimated output flux corresponds to the infiltration of surface water toward the surface aquifer that regulates the chemistry of the lake. These results constitute a first-order assessment of the water budget of these lakes, in regions where direct hydrological and meteorological observations are very scarce or altogether lacking. Finally, we discuss the implications of our data on the hydro-climatic budget at the scale of the catchment basins. We observe that the local evaporation lines (LELs) obtained on both lake and aquifer systems are slightly offset from the average rainfall isotopic composition monitored by IAEA at N'Djamena (Chad), and we show that this difference may reflect the impact of vegetation transpiration on the basin water budget. Based on the discussion of the mass balance budget we conclude that, while being broadly consistent with the idea that transpiration is on the same order of magnitude as evaporation in those basins, we cannot derive a more precise estimate of the partition between these two fluxes, owing to the large uncertainties of the different end-members in the budget equations.

Country-scale greenhouse gas budgets using shipborne measurements: a case study for the UK and Ireland

Abstract. We present a mass balance approach to estimate the seasonal and annual budgets of carbon dioxide (CO2) and methane (CH4) of the United Kingdom (excluding Scotland) and the Republic of Ireland from concentration measurements taken on a ferry along the east coast of the United Kingdom over a 3-year period (2015–2017). We estimate the annual emissions of CH4 to be 2.55±0.48 Tg, which is consistent with the combined 2.29 Tg reported to the United Nations Framework Convention on Climate Change by the individual countries. The net CO2 budget (i.e. including all anthropogenic and biogenic sources and sinks of CO2) is estimated at 881.0±125.8 Tg, with a net biogenic contribution of 458.7 Tg (taken as the difference between the estimated net emissions and the inventory value, which accounts for anthropogenic emissions only). The largest emissions for both gases were observed in a broad latitudinal band (52.5–54∘ N), which coincides with densely populated areas. The emissions of both gases were seasonal (maxima in winter and minima in summer), strongly correlated with natural gas usage and, to a lesser extent, also anti-correlated with mean air temperature. Methane emissions exhibited a statistically significant anti-correlation with air temperature at the seasonal timescale in the central region spanning 52.8–54.2∘ N, which hosts a relatively high density of waste treatment facilities. Methane emissions from landfills have been shown to sometimes increase with decreasing air temperature due to changes in the CH4-oxidising potential of the topsoil, and we speculate that the waste sector contributes significantly to the CH4 budget of this central region. This study brings independent verification of the emission budgets estimated using alternative products (e.g. mass balance budgets by aircraft measurements, inverse modelling, inventorying) and offers an opportunity to investigate the seasonality of these emissions, which is usually not possible.

Carbon storage potential in a recently created brackish marsh in eastern North Carolina, USA

Carbon (C) sequestration through accumulated plant biomass and storage in soils can potentially make wetland ecosystems net C sinks. Here, we collected GHG flux, plant biomass, and litter decomposition data from three distinct vegetation zones (Spartina alterniflora, Juncus roemerianus and Spartina patens) on a 7-year-old created brackish marsh in North Carolina, USA, and integrate these data into an overall C mass balance budget. The marsh fixed an average of 1.85 g C m−2 day−1 through plant photosynthesis. About 41–46% of the fixed C remained in plants, while 18.4% of the C was decomposed and released back to the atmosphere as CO2 and CH4, and 8.6–13.2% of the decomposed C was stored as soil C. In all, this created marsh sequestered 28.7–44.7 Mg CO2 year−1 across the 14 ha marsh. Because the brackish marsh emitted only small amounts of CH4 and N2O, the CO2 equivalent emission of the marsh was −0.87 to −0.56 g CO2-eq m−2 day−1, indicating the marsh has a net effect in reducing GHGs to the atmosphere and contributes to cooling. However, resultant CO2 credit (through the increment of soil C) would be worth only $30.76–$47.90 USD per hectare annually, or $431–$671 per year for the project, which, coupled with other enhanced ecosystem services, could provide landowners with some additional economic incentive for future creation projects. Nevertheless, C mass balance determinations and radiative cooling metrics showed promise in demonstrating the potential of a young created brackish marsh to act as a net carbon sink.

Reflectance–Elevation Relationships and Their Seasonal Patterns over Twelve Glaciers in Western China Based on Landsat 8 Data

Albedo/reflectance is of great importance for glaciers’ mass balance and energy budget. Elevation could be a major factor of influence for glacier reflectance, and therefore when studying glacier reflectance, the altitude ranges should be considered. However, due to the limitations of traditional earth observation systems, conventional analyses usually consider the spatial and temporal patterns of the reflectance average, which is severely restricted. The launch of Landsat-8 gives us the opportunity to study the seasonal glacier reflectance–elevation relationship. We have obtained the monthly near-nadir reflectance per 100 m for twelve glaciers in western China based on 372 scenes of Landsat 8 images acquired from April 2013 to December 2015. Variations of monthly broadband reflectance, reflectance–elevation relationships and reflectance gradients are analyzed and discussed. The results show that the linear trend of the reflectance–elevation relationship (when the altitude is less than 6100 m) is very significant; elevation has greater influence than location on seasonal reflectance variations; and the level of glacier reflectance gradient may relate with its climate. This may be the first work that has used remote-sensing data to analyze seasonal glacier reflectance–elevation patterns.

Long-term sulphate and inorganic nitrogen mass balance budgets in European ICP Integrated Monitoring catchments (1990–2012)

Empirical evidence based on integrated environmental monitoring including physical, chemical and biological variables is essential for evaluating the ecosystem benefits of costly emission reduction policies. The international multidisciplinary ICP IM (International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems) programme studies the integrated effects of air pollution and climate change on ecosystems in unmanaged and calibrated forested catchments. We calculated site-specific annual input-output budgets for sulphate (SO4) and total inorganic nitrogen (TINNO3-N+NH4-N) for 17 European ICP IM sites in 1990–2012. Temporal trends for input (deposition) and output (runoff water) fluxes and the net retention/net release of SO4 and TIN were also analysed. Large differences in the input and output fluxes of SO4 and TIN reflect important gradients of air pollution effects in Europe, with the highest deposition and runoff water fluxes at IM sites located in southern Scandinavia and in parts of Central and Eastern Europe and the lowest fluxes at more remote sites in northern European regions. A significant decrease in the total (wet+dry) deposition of non-marine SO4 and bulk deposition of TIN was found at 90% and 65% of the sites, respectively. Output fluxes of non-marine SO4 in runoff decreased significantly at 65% of the sites, indicating positive effects of the international emission abatement actions in Europe during the last 20 years. Catchments retained SO4 in the early and mid-1990s, but this shifted towards a net release in the late 1990s, which may be due to the mobilization of legacy S pools accumulated during times of high atmospheric SO4 deposition. Despite decreased deposition, TIN output fluxes and retention rates showed a mixed response with both decreasing (9 sites) and increasing (8 sites) trend slopes, and trends were rarely significant. In general, TIN was strongly retained in the catchments not affected by natural disturbances. The long-term annual variation in net releases for SO4 was explained by variations in runoff and SO4 concentrations in deposition, while a variation in TIN concentrations in runoff was mostly associated with a variation of the TIN retention rate in catchments. The net release of SO4 from forest soils may delay the recovery from acidification for surface waters and the continued enrichment of nitrogen in catchment soils poses a threat to terrestrial biodiversity and may ultimately lead to a higher TIN runoff through N-saturation. Continued monitoring and further evaluations of mass balance budgets are thus needed.

Biogeochemical data from terrestrial and aquatic ecosystems in a periglacial catchment, West Greenland

Abstract. Global warming is expected to be most pronounced in the Arctic where permafrost thaw and release of old carbon may provide an important feedback mechanism to the climate system. To better understand and predict climate effects and feedbacks on the cycling of elements within and between ecosystems in northern latitude landscapes, a thorough understanding of the processes related to transport and cycling of elements is required. A fundamental requirement to reach a better process understanding is to have access to high-quality empirical data on chemical concentrations and biotic properties for a wide range of ecosystem domains and functional units (abiotic and biotic pools). The aim of this study is therefore to make one of the most extensive field data sets from a periglacial catchment readily available that can be used both to describe present-day periglacial processes and to improve predictions of the future. Here we present the sampling and analytical methods, field and laboratory equipment and the resulting biogeochemical data from a state-of-the-art whole-ecosystem investigation of the terrestrial and aquatic parts of a lake catchment in the Kangerlussuaq region, West Greenland. This data set allows for the calculation of whole-ecosystem mass balance budgets for a long list of elements, including carbon, nutrients and major and trace metals. The data set is freely available and can be downloaded from PANGAEA: doi:10.1594/PANGAEA.860961.

Long-term soil calcium depletion after conventional and whole-tree harvest

Whole-tree harvest (WTH) may compromise tree productivity and health and lead to soil and surface water acidification. The aim of this study was to assess the long-term change (up to circa 40years) in soil exchangeable calcium (Ca2+) pools following conventional (CH) and WTH at three Swedish coniferous sites. A second aim was to evaluate how well the results could be reproduced by the dynamic model MAGIC (Model of Acidification of Groundwater in Catchments). Soil Ca2+ pools (down to 20cm) decreased at all three sites from stand age 15–16 to 37–38years. The depletion ranged from 2.6 to 8.6kEqha−1 (26.5–52.7%) and 0.2 to 5.0kEqha−1 (2.3–49.1%) in the CH and WTH treatment, respectively. The presence of an interaction effect indicated that the main effect of time was not statistically significant at all three sites. Over the course of time, soil Ca2+ pools have also become more similar between the CH and WTH treatments, but the Ca2+ pools were still significantly lower (p<0.05) after WTH at stand age 37–38years. The measured declines in Ca2+ pools were generally greater than what has been found in other studies and were largely explained by high soil Ca2+ availability and high tree Ca2+ uptake, especially in the CH-plots, as indicated by the MAGIC mass balance budgets. Model simulations by MAGIC partly agreed with the measured data. However, the model exaggerated the soil Ca2+ losses between 1990 and 2013 (CH=3.6–9.9kEqha−1; WTH=3.0–8.3kEqha−1), especially at the spruce sites. Furthermore, MAGIC could not reproduce the rapid diminishing differences between CH and WTH. Uncertainties in model parameters, underestimated soil Ca2+ pools or biological feed-back mechanisms could explain this discrepancy. Until these have been resolved, interpretations of Ca2+ changes related to CH or WTH using dynamic modelling or mass balance budget calculations should be done with caution.

Hydro‐climatic variability and perturbations in Mexico's north‐western temperate forests

AbstractClimate variability and/or change control/s the local hydrologic cycle and consequently forest perturbations such as wildfires and bark beetle outbreaks. This case study addresses the following concerns: (a) the long‐term trends in precipitation, potential and actual evapotranspiration, run‐off, soil moisture content, number of wildfires, burned area, and bark beetle outbreaks and (b) the manner in which the fire occurrence, fire size, and beetle outbreaks are related to these hydrologic variables and multi‐decadal climate indices in Mexico's north‐western temperate forests. Using the daily measurements of precipitation and evaporation as well as the modelled interception loss and evapotranspiration, run‐off and soil moisture content were computed using a mass balance budget model. Mann–Kendall, linear regression, and autoregressive integrated moving averaging techniques were used to evaluate the statistical significance of monotonic trends on the first momentum for the monthly and annual time series of hydro‐climate (1945–2007), forest wildfire (1970–2012), and bark beetle infestation (1999–2012) data. The statistical analysis showed time series to be stationary in the first momentum. Recent wildfires and bark beetle population eruptions are associated with low modelled dry season soil moisture over several years. Drought spells, frosts, and pulses of high area burned, and high number of wildfires preceded acute discrete bark beetle population eruptions. Copyright © 2014 John Wiley &amp; Sons, Ltd.