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The controls on stream dissolved organic carbon (DOC) concentrations were investigated in a 68 km² catchment by applying a landscape-mixing model to test if downstream concentrations could be predicted from contributing landscape elements. The landscape-mixing model reproduced the DOC concentration well throughout the stream network during times of high discharge, but was even more useful for providing a baseline for residual analysis, which highlighted areas for further conceptual model development. The landscape-mixing model approach is conceptually simple and easy to apply, requiring relatively few field measurements and minimal parameterization. The residual analysis highlighted areas of the stream network that were not well represented by simple mixing of headwaters, as well as flow conditions during which simple mixing based on headwater watershed characteristics did not apply. Specifically, we found that during periods of base flow the larger valley streams underlain by fine sorted sediments had much lower DOC concentrations than would be predicted by simple mixing; while peatland streams had higher DOC than predicted. During periods of intermediate and high flow the model made more accurate predictions of downstream DOC. Our interpretation is that the higher degree of hydrological connectivity during high flows, possibly combined with shorter stream residence times, increased the predictive power of this whole-watershed based mixing model. However, there was still a clear pattern during high discharge periods, with peatland streams having lower DOC than would be predicted by simple mixing while forested streams had higher DOC. These observations suggest several potential mechanisms to be further explored using more focused field and process-based modeling studies, especially on the role of changing hydrological pathways. [ABSTRACT FROM AUTHOR]

Four river basins in Southern Sweden, catchment size 0.3 to maximum 127 km² (median 1.9), were sampled in October 2007. The 243 samples were analysed for 26 trace elements (Ag, As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, Ga, Ge, In, La, Li, Mo, Ni, Pb, Sb, Se, Sn, Tl, Ti, U, V and Zn) to identify spatial patterns within drainage networks. The sampling design made it possible to compare the difference between 40 stream reaches, 53 stream junctions with 107 tributaries vs. downstream reaches and 36 lakes with 77 inlets vs. outlets comparisons. The largest concentration differences (at reaches, junctions and lakes) were observed for lakes, with outlets usually having lower concentration compared to the inlets for As, Ba, Be, Bi, Cd, Co, Cr, Ga, Ge, Ni, Pb, Sn, Ti, Tl, U, V and Zn. Significantly lower concentrations were observed for Co and Cd when comparing headwaters with downstream sites in each catchment. We found no evidence for elevated concentration of heavy metals Cd, Cu, Zn or Pb in the two acidified areas of South-west Sweden. Common factor analysis revealed that As, Bi, Cr, Ga, Ge, Tl, V co-vary positively with Al, Fe and total organic carbon (TOC) and negatively with La, Li and pH. A better understanding of the quantitative removal of organic carbon and iron will aid in understanding metal fluxes from landscapes rich in organic matter and iron. [ABSTRACT FROM AUTHOR]

Licence applications to build a repository for the disposal of Swedish spent nuclear fuel have been lodged, underpinned by myriad reports and several broader reviews. This paper sketches out the technical and administrative aspects and highlights a recent review of the biosphere effects of a potential release from the repository. A comprehensive database and an understanding of major fluxes and pools of water and organic matter in the landscape let one envisage the future by looking at older parts of the site. Thus, today's biosphere is used as a natural analogue of possible future landscapes. It is concluded that the planned repository can meet the safety criteria and will have no detectable radiological impact on plants and animals. This paper also briefly describes biosphere work undertaken after the review. The multidisciplinary approach used is relevant in a much wider context and may prove beneficial across many environmental contexts. [ABSTRACT FROM AUTHOR]

This paper presents the paleogeographic reconstructions of flooded areas of the Tar - San Martín lacustrine system during the late Pleistocene - Holocene. The dimensions of lacustrine and glaciolacustrine levels of this basin are higher than the current levels of the lakes. The organic matter of lake levels recorded on stratigraphic profiles was described, sampled and dated using AMS, while other paleobathymetric indicators were also identified (height of the fan-delta apex and paleo-coast levels). Deriving out of the reconstruction of flooded areas it was established that the lake system was formed before 28 ka ago and would have reached its maximum expansion around 12 ka ago. The first hunter-gatherer occupation of the basin (11 ka) corresponds to the period of initial contraction of the lake system and the composition of the current configuration of the coastlines. This scenario would have allowed the exploration of western areas and the gradual incorporation of the forest to the action range of hunter-gatherer populations. Similarly, the levels of lakes Tar and San Martín would not have hindered the movement of human populations through the steppe throughout the Holocene. [ABSTRACT FROM AUTHOR]

This paper defines landscape-scale patterns in the character of natural organic matter (NOM) and tests for relationships to catchment soil, vegetation and topography. The drainage network of a boreal catchment, subcatchment size 0.12-78 km², in Northern Sweden was sampled in August 2002 during a period of stable low water flow. The NOM was characterized with UV/Vis spectroscopy, fluorescence, XAD-8 fractionation (%humic substances), gel permeation chromatography (apparent molecular weight), and elemental composition (C:N). The largest spatial variation was found for C:N, absorbance ratio, and specific visible absorptivity. The lowest variation was in fluorescence index, %humic substances and molecular retention time. The variation in total organic carbon (TOC), iron and aluminium concentration was more than twice that of C:N. Between headwater and downstream sites no significant changes were distinguished in the NOM character. At stream reaches, junctions and lakes little change (<10%) in NOM character was observed. Common factor analysis and partial least squares regression (PLS) revealed that the spatial variation in surface coverage of lakes and mires could explain some of the variation of TOC and NOM character. Our suggestion is that the mosaic of landscape elements (different amounts of water from lakes, forest soil and mires) delivers NOM with varying characteristics to a channel network that mixes conservatively downstream, with possible small changes at some stream reaches, junctions and lakes. [ABSTRACT FROM AUTHOR]

Despite carbon (C) exports from continents being crucial in the connection between terrestrial, atmospheric, and oceanic C, there is still limited understanding of the dynamics of C within river basins. The objective of this work was to assess the changes in particulate (POC) and dissolved organic (DOC) and inorganic C (PIC: particulate inorganic carbon, DIC: dissolved inorganic carbon) content, quality, and fluxes within a river basin from its headwaters to its exit at the ocean. A survey was designed in the Thukela basin (from 2012 to 2013 and at six nested catchments ranging from ~10 to ~30,000 km2) in the east of South Africa to evaluate the content, fluxes, and quality (UV spectral slope, 13C, CO2 effluxes from runoff) of the transported C in conjunction with chemical elements (Si, Na) for discriminating between the water sources and estimating C dynamics during low flows. Total carbon exports decreased continuously from 9.75 km2 in the headwater (31.9 kg C km−2 y−1) to ocean (4.7 kg C km−2 y−1) with the highest decrease occurring between the catchment (7614 km2) and large catchment (14,478 km2). About 80% of C exports from the headwaters were POC, followed by DIC (10%) and DOC (10%), while at the ocean, the proportions were 31% (POC), 45% (DIC), 23% (DOC), and 0.7% (PIC). Moreover, there was a sharp decrease in the dissolved organic matter aromaticity from the headwater to ocean and for both DOC and POC that did not correspond to changes in water sources along the river (as indicated by a relatively constant Si/Na ratio). This pointed to the decomposition in the river of the dissolved organic matter originating from soils and to the within-stream organic production. Further in situ investigations need to be performed to quantify the within-stream inputs. [ABSTRACT FROM AUTHOR]

The paradigm for understanding the accumulation of organic carbon in vegetated coastal "blue carbon" habitats holds that burial of organic carbon (Corg) slows decomposition and leads to stability of carbon stocks. Further, it is generally assumed that the presence of the plant communities contributes to the buried organic matter and the stability of the carbon stocks. In this study, these assumptions were tested and the lability of soil organic carbon was examined as a function of environmental and plant community drivers. Samples of surficial sediment and seagrass community characteristics were collected at 93 locations across the ca. 15,000 km2 of seagrass beds in south Florida. Ramped pyrolysis was used to describe the relative lability of soil organic carbon across the landscape. Organic matter (OM) was lost at all temperatures from 180 to 600 °C, suggesting that even the relatively high combustion temperature of 550 °C underestimates OM content by ≈ 10% on average. Additionally, deployments of model substrates (canvas strips) were used to examine decomposition rates of buried and surficial organic material at a subset of these sites. On average, finer, muddier soils contained slightly higher Corg stocks than coarser sediment sites, but the relationships between sediment grain size and seagrass community structure was weak. The lability of soil organic carbon varied with sediment grain size; as much as 80% of the Corg was refractory in coarse-grained soils compared with less than 30% in muddy soils. In muddy soils, burial decreased cellulose decomposition rate by an average of 22–39% compared with surficial breakdown, but in coarse-grained soils, burial enhanced cellulose decomposition rate by at least 55%. Taken as a whole, this study suggests that burial does not enhance Corg storage in all blue carbon environments, and that soil C stores are only weakly correlated with seagrass biomass at the landscape scale. [ABSTRACT FROM AUTHOR]

In agroforestry landscapes, land use, and the associated management practices exert strong impacts upon soil organic carbon stocks. Data on the soil organic carbon were collected for different land-use types within a small watershed, El Salado, located in Lanjarón (SE Spain). Eight land-use types namely: farmland planted in olive, almond, and cereals; forest with Pinus halepensis Mill. and Pinus sylvestris L. stands; shrubland; grassland; as well as abandoned farmland were taken into consideration. Of the land-use types investigated, forest, shrubland, as well as grassland exhibited the highest average soil organic C stocks (100-63 Mg ha-1) in contrast with the abandoned farmland (28 Mg ha-1), with farmland representing a go-between situation (51-49 Mg ha-1). The environmental factors precipitation, temperature, and elevation significantly influenced (P< 0.01) the soil organic C stock, with the contents tending to be higher in mountain soils with respective intermediate values of 600-800 mm, 10-15°C, and 1,000-1,500 m asl. Thus, the present approach offers a comparison of C-sequestration patterns as related to the land-use types in a Mediterranean agroforestry landscape, where the main challenge is to integrate the forest trees and the crops within their harmonious interacting combinations. [ABSTRACT FROM AUTHOR]

Livestock grazing is known to influence carbon (C) storage in vegetation and soil. Yet, for grazing management to be used to optimize C storage, large scale investigations that take into account the typically heterogeneous distribution of grazers and C across the landscape are required. In a landscape-scale grazing experiment in the Scottish uplands, we quantified C stored in swards dominated by the widespread tussock-forming grass species Molinia caerulea. The impact of three sheep stocking treatments ('commercial' 2.7 ewes ha y, 'low' 0.9 ewes ha y and no livestock) on plant C stocks was determined at three spatial scales; tussock, sward and landscape, and these data were used to predict long-term changes in soil organic carbon (SOC). We found that tussocks were particularly dense C stores (that is, high C mass per unit area) and that grazing reduced their abundance and thus influenced C stocks held in M. caerulea swards across the landscape; C stocks were 3.83, 5.01 and 6.85 Mg C ha under commercial sheep grazing, low sheep grazing and no grazing, respectively. Measured vegetation C in the three grazing treatments provided annual C inputs to RothC, an organic matter turnover model, to predict changes in SOC over 100 years. RothC predicted SOC to decline under commercial sheep stocking and increase under low sheep grazing and no grazing. Our findings suggest that no sheep and low-intensity sheep grazing are better upland management practices for enhancing plant and soil C sequestration than commercial sheep grazing. This is evaluated in the context of other upland management objectives. [ABSTRACT FROM AUTHOR]

The deposition of Late Pleistocene and Holocene sediments in the high-altitude lake Meidsee (located at an altitude of 2661 m a.s.l. in the Southwestern Alps) strikingly coincided with global ice-sheet and mountain-glacier decay in the Alpine forelands and the formation of perialpine lakes. Radiocarbon ages of bottom-core sediments point out (pre-) Holocene ice retreat below 2700 m a.s.l., at about 16, 13, 10, and 9 cal. kyr BP. The Meidsee sedimentary record therefore provides information about the high-altitude Alpine landscape evolution since the Late Pleistocene/Holocene deglaciation in the Swiss Southwestern Alps. Prior to 5 cal. kyr BP, the C/N ratio and the isotopic composition of sedimentary organic matter (δ15Norg, δ13Corg) indicate the deposition of algal-derived organic matter with limited input of terrestrial organic matter. The early Holocene and the Holocene climatic optimum (between 7.0 and 5.5 cal. kyr BP) were characterized by low erosion (decreasing magnetic susceptibility, χ) and high content of organic matter (Corg > 13 wt.%), enriched in 13Corg (> −18‰) with a low C/N (~10) ratio, typical of modern algal matter derived from in situ production. During the late Holocene, there was a long-term increasing contribution of terrestrial organic matter into the lake (C/N > 11), with maxima between 2.4 and 0.9 cal. kyr BP. A major environmental change took place 800 years ago, with an abrupt decrease in the relative contribution of terrestrial organic material into the lake compared with aquatic organic material which subsequently largely dominated (C/N drop from 16 to 10). Nonetheless, this event was marked by a rise in soil erosion (χ), in nutrients input (N and P contents) and in anthropogenic lead deposition, suggesting a human disturbance of Alpine ecosystems 800 years ago. Indeed, this time period coincided with the migration of the Walser Alemannic people in the region, who settled at relatively high altitude in the Southwestern Alps for farming and maintaining Alpine passes. [ABSTRACT FROM PUBLISHER]

Lakes have a central role in the carbon cycle of the boreal landscape. These systems typically stratify in summer and their hypolimnetic microbial communities influence burial of biogenic organic matter in sediments. The composition of bacterial communities in these suboxic habitats was studied by pyrosequencing of 16S rRNA amplicons from five lakes with variable dissolved organic carbon (DOC) concentrations. Bacterioplankton communities in the hypolimnetic waters were clearly different from the surface layer with candidate division OD1, Chlorobi and Bacteroidetes as dominant community members. Several operational taxonomic units (OTUs) affiliated with candidate division OD1 were abundant and consistently present in the suboxic hypolimnion in these boreal lakes. The overall representation of this group was positively correlated with DOC and methane concentrations. Network analysis of time-series data revealed contrasting temporal patterns but suggested similar ecological roles among the abundant OTUs affiliated with candidate division OD1. Together, stable isotope data and taxonomic classification point to methane oxidation and autotrophic denitrification as important processes in the suboxic zone of boreal lakes. Our data revealed that while hypolimnetic bacterial communities are less dynamic, they appear to be more diverse than communities from the oxic surface layer. An appreciable proportion of the hypolimnetic bacteria belong to poorly described phyla. [ABSTRACT FROM AUTHOR]

Land cover changes affect ecological landscape spatial pattern, and evolving landscape patterns inevitably cause an evolution in ecosystem functionality. Various ecological landscape variables, such as biological productivity (plant biomass and stock capacity), soil nutrients (organic matter and N content) and water source conservation capacity are identified as landscape function characteristics. A quantitative method and digital model for analyzing evolving landscape functionality in the headwaters areas of the Yangtze River, China were devised. In the period 1986–2000, patch transitions of the region's evolving landscapes have been predominantly characterized by alpine cold swamp meadow, with the highest coverage tending to be steppified meadow or steppe, and desertification landscape such as sand and bare rock land expansion. As the result of such changes, alpine swamp areas decreased by 3.08 × 103 km2 and the alpine cold sparse steppe and bare rock and soil land increased by 6.48 × 103 km2 and 5.82 × 103 km2, respectively. Consequently, the grass biomass production decreased by 2627.15 Gg, of which alpine cold swamp meadows accounted for 55.9% of this loss. The overall stock capacity of the headwaters area of the Yangtze River decreased by 920.64 thousand sheep units, of which 502.02 thousand sheep units decreased in ACS (Alpine cold swamp) meadow transition. Soil organic matter and N contents decreased significantly in most alpine cold meadow and swamp meadow landscape patches. From 1986 to 2000 the total losses of soil organic matter and total N in the entire headwaters region amounted to 150.2 Gkg and 7.67 Gkg. Meanwhile, the landscape soil water capacity declined by 935.9 Mm3, of which 83.9% occurred in the ACS meadow transition. In the headwater area of the Yangtze River, the complex transition of landscape resulted in sharp eco-environmental deterioration. The main indication for these changes involved the intensity of the climate in this region is becoming drier and warmer, resulting in a gradual degradation of the permafrost. [ABSTRACT FROM AUTHOR]

[1] We used a simple hydrological-biogeochemical mixing model to test the hypothesis that export of total organic carbon occurring mainly during spring in taiga and tundra watersheds might be compensated by production and export of bicarbonate (HCO3-) from groundwater during the rest of the year. The investigated watersheds are located in northern Sweden close to the Arctic Circle. An elevated spring flow peak due to snowmelt characterizes the hydrology of boreal and arctic river systems. During this snowmelt, total organic carbon (TOC), previously stored as soil carbon, is flushed and exported from the watersheds, and can be released to the atmosphere via heterotrophic remineralization during riverine transport to the sea, thereby contributing to atmospheric CO2. The TOC yields of the watersheds investigated increased with vegetation and peat cover and ranged across watersheds from 0.5 to 2.8 tons km-2 yr-1. During frozen periods, streamflow is dominated by ‘old’ groundwater. This water has percolated through the soils and is rich in DSi and bicarbonate; that is, atmospheric carbon that has been ‘consumed’ in chemical weathering processes is partly exported as bicarbonate to the sea, where carbon is stored as CaCO3 for geological time. The bicarbonate export of the watersheds investigated was between 0.4 and 1.2 tons C km-2 yr-1 corresponding to 15–73% of the TOC export. Very likely, global warming will affect water flow through the soils in taiga and tundra ecosystems and thus will have an effect on watershed carbon budgets. This bicarbonate export may compensate for significant amounts of the exported TOC, thereby reducing the positive feedback to atmospheric CO2. [ABSTRACT FROM AUTHOR]