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  • 1. Akselsson, Cecilia
    et al.
    Olsson, Jonas
    Belyazid, Salim
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Capell, René
    Can increased weathering rates due to future warming compensate for base cation losses following whole-tree harvesting in spruce forests?2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 89-105Article in journal (Refereed)
    Abstract [en]

    Whole-tree harvesting, i.e. harvesting of stems, branches and tops, has become increasingly common during recent decades due to the increased demand for renewable energy. Whole-tree harvesting leads to an increase in base cation losses from the ecosystem, which can counteract recovery from acidification. An increase in weathering rates due to higher temperatures is sometimes suggested as a process that may counteract the acidifying effect of whole-tree harvesting. In this study the potential effect of increasing temperature on weathering rates was compared with the increase in base cation losses following whole-tree harvesting in spruce forests, along a temperature gradient in Sweden. The mechanistic model PROFILE was used to estimate weathering rates at National Forest Inventory sites at today's temperature and the temperature in 2050, as estimated by two different climate projections. The same dataset was used to calculate base cation losses following stem-only and whole-tree harvesting. The calculations showed that the increase in temperature until 2050 would result in an increase in the base cation weathering rate of 20-33 %, and that whole-tree harvesting would lead to an increase in base cation losses of 66 % on average, compared to stem-only harvesting. A sensitivity analysis showed that moisture changes are important for future weathering rates, but the effect of the temperature change was dominating even when the most extreme moisture changes were applied. It was concluded that an increase in weathering rates resulting from higher temperatures would not compensate for the increase in base cation losses following whole-tree harvesting, except in the northernmost part of Sweden.

  • 2. Alfredsson, Hanna
    et al.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Clymans, Wim
    Stadmark, Johanna
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Conley, Daniel J.
    Amorphous silica pools in permafrost soils of the Central Canadian Arctic and the potential impact of climate change2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 124, no 1-3, p. 441-459Article in journal (Refereed)
    Abstract [en]

    We investigated the distribution, storage and landscape partitioning of soil amorphous silica (ASi) in a central Canadian region dominated by tundra and peatlands to provide a first estimate of the amount of ASi stored in Arctic permafrost ecosystems. We hypothesize that, similar to soil organic matter, Arctic soils store large amounts of ASi which may be affected by projected climate changes and associated changes in permafrost regimes. Average soil ASi storage (top 1 m) ranged between 9600 and 83,500 kg SiO2 ha(-1) among different land-cover types. Lichen tundra contained the lowest amounts of ASi while no significant differences were found in ASi storage among other land-cover types. Clear differences were observed between ASi storage allocated into the top organic versus the mineral horizon of soils. Bog peatlands, fen peatlands and wet shrub tundra stored between 7090 and 45,400 kg SiO2 ha(-1) in the top organic horizon, while the corresponding storage in lichen tundra, moist shrub- and dry shrub tundra only amounted to 1500-1760 kg SiO2 ha(-1). Diatoms and phytoliths are important components of ASi storage in the top organic horizon of peatlands and shrub tundra systems, while it appears to be a negligible component of ASi storage in the mineral horizon of shrub tundra classes. ASi concentrations decrease with depth in the soil profile for fen peatlands and all shrub tundra classes, suggesting recycling of ASi, whereas bog peatlands appeared to act as sinks retaining stored ASi on millennial time scales. Our results provide a conceptual framework to assess the potential effects of climate change impacts on terrestrial Si cycling in the Arctic. We believe that ASi stored in peatlands are particularly sensitive to climate change, because a larger fraction of the ASi pool is stored in perennially frozen ground compared to shrub tundra systems. A likely outcome of climate warming and permafrost thaw could be mobilization of previously frozen ASi, altered soil storage of biogenically derived ASi and an increased Si flux to the Arctic Ocean.

  • 3.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bartoli, Marco
    Marchant, Hannah K.
    Bruchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Seasonal oxygen, nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns2014In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 119, no 1-3, p. 139-160Article in journal (Refereed)
    Abstract [en]

    The regulatory roles of temperature, eutrophication and oxygen availability on benthic nitrogen (N) cycling and the stoichiometry of regenerated nitrogen and phosphorus (P) were explored along a Baltic Sea estuary affected by treated sewage discharge. Rates of sediment denitrification, anammox, dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, oxygen (O2) uptake and penetration were measured seasonally. Sediments not affected by the nutrient plume released by the sewage treatment plant (STP) showed a strong seasonality in rates of O2 uptake and coupled nitrification-denitrification, with anammox never accounting for more than 20% of the total dinitrogen (N2) production. N cycling in sediments close to the STP was highly dependent on oxygen availability, which masked temperature-related effects. These sediments switched from low N loss and high ammonium (NH4+) efflux under hypoxic conditions in the fall, to a major N loss system in the winter when the sediment surface was oxidized. In the fall DNRA outcompeted denitrification as the main nitrate (NO3-) reduction pathway, resulting in N recycling and potential spreading of eutrophication. A comparison with historical records of nutrient discharge and denitrification indicated that the total N loss in the estuary has been tightly coupled to the total amount of nutrient discharge from the STP. Changes in dissolved inorganic nitrogen (DIN) released from the STP agreed well with variations in sedimentary N2 removal. This indicates that denitrification and anammox efficiently counterbalance N loading in the estuary across the range of historical and present-day anthropogenic nutrient discharge. Overall low N/P ratios of the regenerated nutrient fluxes impose strong N limitation for the pelagic system and generate a high potential for nuisance cyanobacterial blooms.

  • 4.
    Burrows, E.H.
    et al.
    Univ New Hampshire.
    Bubier, J.L.
    Mount Holyoke College.
    Mosedale, A.
    Univ New Hampshire.
    Cobb, G.W.
    Mount Holyoke College.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Net Ecosystem Exchange of Carbon Dioxide in a Temperate Poor Fen: A Comparison of Automated and Manual Chamber Techniques,2005In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 76, no 1, p. 21-45Article in journal (Refereed)
    Abstract [en]

    We used five analytical approaches to compare net ecosystem exchange (NEE) of carbon dioxide (CO2) from automated and manual static chambers in a peatland, and found the methods comparable. Once per week we sampled manually from 10 collars with a closed chamber system using a LiCor 6200 portable photosynthesis system, and simulated four photosynthetically active radiation (PAR) levels using shrouds. Ten automated chambers sampled CO2 flux every 3 h with a LiCor 6252 infrared gas analyzer. Results of the five comparisons showed (1) NEE measurements made from May to August, 2001 by the manual and automated chambers had similar ranges: -10.8 to 12.7 μmol CO 2 m-2 s-1 and -17.2 to 13.1 μmol CO 2 m-2 s-1, respectively. (2) When sorted into four PAR regimes and adjusted for temperature (respiration was measured under different temperature regimes), mean NEE did not differ significantly between the chambers (p < 0.05). (3) Chambers were not significantly different in regression of ln( - respiration) on temperature. (4) But differences were found in the PAR vs. NEE relationship with manual chambers providing higher maximum gross photosynthesis estimates (GPmax), and slower uptake of CO 2 at low PAR (α) even after temperature adjustment. (5) Due to the high variability in chamber characteristics, we developed an equation that includes foliar biomass, water table, temperature, and PAR, to more directly compare automated and manual NEE. Comparing fitted parameters did not identify new differences between the chambers. These complementary chamber techniques offer a unique opportunity to assess the variability and uncertainty in CO 2 flux measurements.

  • 5.
    Chi Fru, Ernest
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Cardiff University, UK.
    Callac, Nolwenn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Posth, Nicole R.
    Argyraki, Ariadne
    Ling, Yu-Chen
    Ivarsson, Magnus
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kilias, Stephanos P.
    Arsenic and high affinity phosphate uptake gene distribution in shallow submarine hydrothermal sediments2018In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 141, no 1, p. 41-62Article in journal (Refereed)
    Abstract [en]

    The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment-seawater interaction, produces nutrient-deficient porewaters containing<2.0ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.

  • 6.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sobek, Anna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Smedberg, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Modeling total particulate organic carbon (POC) flows in the Baltic Sea catchment2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 51-65Article in journal (Refereed)
    Abstract [en]

    The largest input source of carbon to the Baltic Sea catchment is river discharge. A tool for modeling riverine particulate organic carbon (POC) loads on a catchment scale is currently lacking. The present study describes a novel dynamic model for simulating flows of POC in all major rivers draining the Baltic Sea catchment. The processes governing POC input and transport in rivers described in the model are soil erosion, in-stream primary production and litter input. The Baltic Sea drainage basin is divided into 82 sub-basins, each comprising several land classes (e.g. forest, cultivated land, urban areas) and parameterized using GIS data on soil characteristics and topography. Driving forces are temperature, precipitation, and total phosphorous concentrations. The model evaluation shows that the model can predict annual average POC concentrations within a factor of about 2, but generally fails to capture the timing of monthly peak loads. The total annual POC load to the Baltic Sea is estimated to be 0.34 Tg POC, which constitutes circa 7-10 % of the annual total organic carbon (TOC) load. The current lack of field measurements of POC in rivers hampers more accurate predictions of seasonality in POC loads to the Baltic Sea. This study, however, identifies important knowledge gaps and provides a starting point for further explorations of large scale POC mass flows.

  • 7. De Brabandere, Loreto
    et al.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kononets, Mikhail Y.
    Viktorsson, Lena
    Stigebrandt, Anders
    Thamdrup, Bo
    Hall, Per O. J.
    Oxygenation of an anoxic fjord basin strongly stimulates benthic denitrification and DNRA2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 126, no 1-2, p. 131-152Article in journal (Refereed)
    Abstract [en]

    Hypoxia hampers eutrophication reduction efforts by enabling high nutrient fluxes from sediment to bottom waters. Oxygenation of hypoxic water bodies is often proposed to reduce benthic ammonium and phosphate release. This study investigates the functional response of benthic nitrate-reducing processes to a long-term engineered oxygenation effort in a density-stratified fjord with euxinic bottom waters. Oxygenation was achieved by mixing surface water with deep, euxinic water, which increased oxygen and nitrate concentrations in the deep water column. The presence of nitrate instigated benthic nitrate reduction in the newly oxidized sediments by equally stimulating denitrification and dissimilatory nitrate reduction to ammonium (DNRA). DNRA and total nitrate reduction rates, as well as the contribution of DNRA to total nitrate reduction, decreased with increasing exposure time of the sediments to oxygen. The relative importance of DNRA as a nitrate sink was correlated to nitrate concentrations, with more nitrate being reduced to ammonium at higher bottom water nitrate concentrations. Overall, engineered oxygenation decreased the net efflux of dissolved inorganic nitrogen from the sediments by stimulating net nitrate removal through denitrification.

  • 8.
    Duc, Nguyen Thanh
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick, M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Implications of temperature and sediment characteristics on methane formation and oxidation in lake sediments2010In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 100, no 1-3, p. 185-196Article in journal (Refereed)
    Abstract [en]

    Methane emissions from aquatic environments depend on methane formation (MF) and methane oxidation (MO) rates. One important question is to what extent increased temperatures will affect the balance between MF and MO. We measured potential MF and MO rates simultaneously at 4, 10, 20 and 30A degrees C in sediment from eight different lakes representing typical boreal and northern temperate lake types. Potential MF rates ranged between 0.002 and 3.99 mu mol CH4 g(d.w.) (-1) day(-1), potential MO rates ranged from 0.01 to 0.39 CH4 g(d.w.) (-1) day(-1). The potential MF rates were sensitive to temperature and increased 10 to 100 fold over the temperature interval studied. MF also differed between lakes and was correlated to sediment water content, percent of organic material and C:N ratio. Potential MO did not depend on temperature or sediment characteristics but was instead well explained by MF rates at the in situ temperature. It implies that elevated temperatures will enhance MF rates which may cause increased methane release from sediments until MO increases as well, as a response to higher methane levels.

  • 9.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Humborg, Christoph
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Swaney, D. P.
    Mörth, Carl-Magnus
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Riverine nitrogen export in Swedish catchments dominated by atmospheric inputs2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 203-217Article in journal (Refereed)
    Abstract [en]

    We present the first estimates of net anthropogenic nitrogen input (NANI) in European boreal catchments. In Swedish catchments, nitrogen (N) deposition is a major N input (31-94%). Hence, we used two different N deposition inputs to calculate NANI for 36 major Swedish catchments. The relationship between riverine N export and NANI was strongest when using only oxidized deposition (NOy) as atmospheric input (r(2) = 0.70) rather than total deposition (i.e., both oxidized and reduced nitrogen, NOy + NHx deposition, r(2) = 0.62). The y-intercept (NANI = 0) for the NANI calculated with NOy is significantly different from zero (p = 0.0042*) and indicates a background flux from the catchment of some 100 kg N km(-2) year(-1) in addition to anthropogenic inputs. This agrees with similar results from North American boreal catchments. The slope of the linear regressions was 0.25 for both N deposition inputs (NOy and NOy + NHx), suggesting that on average, 25% of the anthropogenic N inputs is exported by rivers to the Baltic Sea. Agricultural catchments in central and southern Sweden have increased their riverine N export up to tenfold compared to the inferred background flux. Although the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition, these catchments do not show significantly elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention may be saturating as loading rates increase. In northern and western Sweden the export of nitrogen is largely controlled by the hydraulic load, i.e., the riverine discharge normalized by water surface area, which has units of distance time(-1). Besides hydraulic load the percent total forest cover also affects the nitrogen export primarily in the northern and western catchments.

  • 10.
    Guelland, Kathi
    et al.
    Institute of biogeochemistry and pollutant dynamics, ETH Zurich.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Göransson, H.
    Bernasconi, S. M.
    Hajdas, I.
    Kretzschmar, R.
    Evolution of carbon fluxes during initial soil formation along the forefield of Damma glacier, Switzerland2013In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 113, no 1-3, p. 545-561Article in journal (Refereed)
    Abstract [en]

    Soil carbon (C) fluxes, soil respiration and dissolved organic carbon (DOC) leaching were explored along the young Damma glacier forefield chronosequence (7-128 years) over a three-year period. To gain insight into the sources of soil CO2 effluxes, radiocarbon signatures of respired CO2 were measured and a vegetation-clipping experiment was performed. Our results showed a clear increase in soil CO2 effluxes with increasing site age from 9 +/- A 1 to 160 +/- A 67 g CO2-C m(-2) year(-1), which was linked to soil C accumulation and development of vegetation cover. Seasonal variations of soil respiration were mainly driven by temperature; between 62 and 70 % of annual CO2 effluxes were respired during the 4-month long summer season. Sources of soil CO2 effluxes changed along the glacier forefield. For most recently deglaciated sites, radiocarbon-based age estimates indicated ancient C to be the dominant source of soil-respired CO2. At intermediate site age (58-78 years), the contribution of new plant-fixed C via rhizosphere respiration amounted up to 90 %, while with further soil formation, heterotrophically respired C probably from accumulated 'older' soil organic carbon (SOC) became increasingly important. In comparison with soil respiration, DOC leaching at 10 cm depth was small, but increased similarly from 0.4 +/- A 0.02 to 7.4 +/- A 1.6 g DOC m(-2) year(-1) over the chronosequence. A strong rise of the ratio of SOC to secondary iron and aluminium oxides strongly suggests that increasing DOC leaching with site age results from a faster increase of the DOC source, SOC, than of the DOC sink, reactive mineral surfaces. Overall, C losses from soil by soil respiration and DOC leaching increased from 9 +/- A 1 to 70 +/- A 17 and further to 168 +/- A 68 g C m(-2) year(-1) at the < 10, 58-78, and 110-128 year old sites. By comparison, total ecosystem C stocks increased from 0.2 to 1.1 and to 3.1 kg C m(-2) from the young to intermediate and old sites. Therefore, the ecosystem evolved from a dominance of C accumulation in the initial phase to a high throughput system. We suggest that the relatively strong increase in soil C stocks compared to C fluxes is a characteristic feature of initial soil formation on freshly exposed rocks.

  • 11.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Savchuck, Oleg P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Müller-Karulis, Bärbel
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 134, no 3, p. 301-317Article in journal (Refereed)
    Abstract [en]

    In this study we examine pools of carbon (C), nitrogen (N), and phosphorus (P) in the Baltic Sea, both simulated and reconstructed from observations. We further quantify key fluxes in the C, N, and P cycling. Our calculations include pelagic reservoirs as well as the storage in the active sediment layer, which allows a complete coverage of the overall C, N, and P cycling on a system-scale. A striking property of C versus N and P cycling is that while the external supplies of total N and P (TN and TP) are largely balanced by internal removal processes, the total carbon (TC) supply is mainly compensated by a net export out of the system. In other words, external inputs of TN and TP are, in contrast to TC, rather efficiently filtered within the Baltic Sea. Further, there is a net export of TN and TP out of the system, but a net import of dissolved inorganic N and P (DIN and DIP). There is on the contrary a net export of both the organic and inorganic fractions of TC. While the pelagic pools of TC and TP are dominated by inorganic compounds, TN largely consists of organic N because allochthonous organic N is poorly degradable. There are however large basin-wise differences in C, N, and P elemental ratios as well as in inorganic versus organic fractions. These differences reflect both the differing ratios in external loads and differing oxygen conditions determining the redox-dependent fluxes of DIN and DIP.

  • 12. Göransson, Hans
    et al.
    Edwards, PeterJ.
    Perreijn, Kristel
    Smittenberg, RienkH.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Olde Venterink, Harry
    Rocks create nitrogen hotspots and N:P heterogeneity by funnelling rain2014In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 121, no 2, p. 329-338Article in journal (Refereed)
  • 13. Hodgkins, Suzanne B.
    et al.
    Chanton, Jeffrey P.
    Langford, Lauren C.
    McCalley, Carmody K.
    Saleska, Scott R.
    Rich, Virginia I.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cooper, William T.
    Soil incubations reproduce field methane dynamics in a subarctic wetland2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 126, no 1-2, p. 241-249Article in journal (Refereed)
    Abstract [en]

    A major challenge in peatland carbon cycle modeling is the estimation of subsurface methane (CH4) and carbon dioxide (CO2) production and consumption rates and pathways. The most common methods for modeling these processes are soil incubations and stable isotope modeling, both of which may involve departures from field conditions. To explore the impacts of these departures, we measured CH4/CO2 concentration ratios and C-13 fractionation factors (alpha(C), indicating CH4 production pathways) in field pore water from a thawing subarctic peatland, and compared these values to those observed in incubations of corresponding peat samples. Incubation CH4/CO2 production ratios were significantly and positively correlated with observed field CH4/CO2 concentration ratios, though observed field ratios were similar to 20 % of those in incubations due to CH4's lower solubility in pore water. After correcting the field ratios for CH4 loss with an isotope mass balance model, the incubation CH4/CO2 ratios and alpha(C) were both significantly positively correlated with field ratios and alpha(C) (respectively), both with slopes indistinguishable from 1. Although CH4/CO2 ratios and alpha(C) were slightly higher in the incubations, these shifts were consistent along the thaw progression, indicating that ex situ incubations can replicate trends in in situ CH4 production.

  • 14. Hodson, Andy
    et al.
    Roberts, Tjarda Jane
    Engvall, Anne-Christin
    Stockholm University, Faculty of Science, Department of Meteorology .
    Holmen, Kim
    Mumford, Paul
    Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic2010In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 98, no 03-jan, p. 171-184Article in journal (Refereed)
    Abstract [en]

    We describe the climatology, hydrology and biogeochemistry of an extreme nitrogen deposition event that occurred in the highly glacierised environment of the European High Arctic during June 1999. Meteorological analysis, three-dimensional air mass trajectories and a 3D transport model show that blocking high pressures over Scandinavia and the rapid advection of western European pollution toward Svalbard were sufficient to cause the most concentrated (1.15 ppm NO3-N and 1.20 ppm NH4-N), high magnitude (total 26 mm and up to 2.4 mm h(-1) at 30 m above sea level) nitrogen deposition event on record in this sensitive, high Arctic environment (78.91A degrees A N, 11.93A degrees A E). Since the event occurred when much of the catchment remained frozen or under snow cover, microbial utilisation of nitrogen within snowpacks and perennially unfrozen subglacial sediments, rather than soils, were mostly responsible for reducing N export. The rainfall event occurred long before the annual subglacial outburst flood and so prolonged (ca. 10 day) water storage at the glacier bed further enhanced the microbial assimilation. When the subglacial outburst eventually occurred, high runoff and concentrations of NO3 (-) (but not NH4 (+)) returned in the downstream rivers. Assimilation accounted for between 53 and 72% of the total inorganic nitrogen deposited during the event, but the annual NO3 (-) and NH4 (+) runoff yields were still enhanced by up to 5 and 40 times respectively. Episodic atmospheric inputs of reactive nitrogen can therefore directly influence the biogeochemical functioning of High Arctic catchments, even when microbial activity takes place beneath a glacier at a time when terrestrial soil ecosystems remain frozen and unresponsive.

  • 15. Hong, Bongghi
    et al.
    Swaney, Dennis P.
    McCrackin, Michelle
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Svanbäck, Annika
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Gustafsson, Bo
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Yershova, Alexandra
    Pakhomau, Aliaksandr
    Advances in NANI and NAPI accounting for the Baltic drainage basin: spatial and temporal trends and relationships to watershed TN and TP fluxes2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 133, no 3, p. 245-261Article in journal (Refereed)
    Abstract [en]

    In order to assess the progress toward eutrophication management goals, it is important to understand trends in land-based nutrient use. Here we present net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) for 2000 and 2010 for the Baltic Sea watershed. Overall, across the entire Baltic, between the 5-year periods centered on 2000 and 2010, NANI and NAPI decreased modestly by -6 and -4%, respectively, but with substantial regional variation, including major increases in the Gulf of Riga drainage basin (+19 and +58%, respectively) and decreases in the Danish Straits drainage basin (-25 and -40% respectively). The changes were due primarily to changes in mineral fertilizer use. Mineral fertilizers dominated inputs, at 57% of both NANI and NAPI in 2000, increasing to 68 and 70%, respectively, by 2010. Net food and feed imports declined over that period, corresponding to increased crop production; either fewer imports of food and feedstocks were required to feed humans and livestock, or more of these commodities were exported. A strong linear relationship exists between regional net nutrient inputs and riverine nutrient fluxes for both periods. About 17% of NANI and 4.7% of NAPI were exported to the sea in 2000; these relationships did not significantly differ from those for 2010. Changes in NANI from 2000 to 2010 across basins were directly proportional rather than linearly related to changes in total N (TN) fluxes to the sea (i.e., no change in NANI suggests no change in TN flux). Similarly, for all basins except those draining to the Baltic Proper, changes in NAPI were proportional to changes in total P (TP) fluxes. The Danish Straits decreased most between 2000 and 2010, where NANI and NAPI declined by 25 and 40%, respectively, and corresponding fluxes of TN and TP declined 31 and 18%, respectively. For the Baltic Proper, NAPI was relatively unchanged between 2000 and 2010, while riverine TP fluxes decreased 25%, due possibly to lagged effects of fertilizer reduction resulting from socio-political changes in the early 1990s or improvements in sewage treatment capabilities. For most regions, further reductions in NANI and NAPI could be achieved by more efficient production and greater substitution of manure for imported mineral fertilizers.

  • 16. Korth, Frederike
    et al.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Liskow, Iris
    Voss, Maren
    Uptake of dissolved organic nitrogen by size-fractionated plankton along a salinity gradient from the North Sea to the Baltic Sea2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 111, no 1-3, p. 347-360Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is known for its ecological problems due to eutrophication caused by high nutrient input via nitrogen fixation and rivers, which deliver up to 70% of nitrogen in the form of dissolved organic nitrogen (DON) compounds. We therefore measured organic nitrogen uptake rates using self produced N-15 labeled allochthonous (derived from Brassica napus and Phragmites sp.) and autochthonous (derived from Skeletonema costatum) DON at twelve stations along a salinity gradient (34 to 2) from the North Sea to the Baltic Sea in August/September 2009. Both labeled DON sources were exploited by the size fractions 0.2-1.6 mu m (bacteria size fraction) and > 1.6 mu m (phytoplankton size fraction). Higher DON uptake rates were measured in the Baltic Sea compared to the North Sea, with rates of up to 1213 nmol N l(-1) h(-1). The autochthonous DON was the dominant nitrogen form used by the phytoplankton size fraction, whereas the heterotrophic bacteria size fraction preferred the allochthonous DON. We detected a moderate shift from > 1.6 mu m plankton dominated DON uptake in the North Sea and central Baltic Sea towards a 0.2-1.6 mu m dominated DON uptake in the Bothnian Bay and a weak positive relationship between DON concentrations and uptake. These findings indicate that DON is an important component of plankton nutrition and can fuel primary production. It may therefore also contribute substantially to eutrophication in the Baltic Sea especially when inorganic nitrogen sources are depleted.

  • 17.
    McCrackin, Michelle L.
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Cooter, Ellen J.
    Dennis, Robin L.
    Harrison, John A.
    Compton, Jana E.
    Alternative futures of dissolved inorganic nitrogen export from the Mississippi River Basin: influence of crop management, atmospheric deposition, and population growth2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 133, no 3, p. 263-277Article in journal (Refereed)
    Abstract [en]

    Nitrogen (N) export from the Mississippi River Basin contributes to seasonal hypoxia in the Gulf of Mexico (GOM). We explored monthly dissolved inorganic N (DIN) export to the GOM for a historical year (2002) and two future scenarios (year 2022) by linking macroeonomic energy, agriculture market, air quality, and agriculture land management models to a DIN export model. Future scenarios considered policies aimed at encouraging bioenergy crop production and reducing atmospheric N-emissions, as well as the effect of population growth and the states' infrastructure plans on sewage fluxes. Model-derived DIN export decreased by about 9% (from 279 to 254 kg N km(-2) year(-1)) between 2002 and 2022 due to a 28% increase in area planted with corn, 24% improvement in crop N-recovery efficiency (NRE, to 0.52), 22% reduction in atmospheric N deposition, and 23% increase in sewage inputs. Changes in atmospheric and sewage inputs had a relatively small effect on DIN export and the effect of bioenergy crop production depended on nutrient management practices. Without improved NRE, increased production of corn would have increased DIN export by about 14% (to 289 kg N km(-2) year(-1)) between 2002 and 2022. Model results suggest that meeting future crop demand while reducing the areal extent of hypoxia could require aggressive actions, such improving basin-level crop NRE to 0.62 or upgrading N-removal capabilities in waste water treatment plants beyond current plans. Tile-drained cropland could contribute up to half of DIN export; thus, practices that reduce N losses from tile drains could also have substantial benefit.

  • 18.
    Schurig, Christian
    et al.
    UFZ Helmholtz Ctr Environm Res, Dept Environm Biotechnol, D-04318 Leipzig, Germany.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Berger, Juergen
    Max Planck Inst Dev Biol, Electron Microscopy Unit, Tubingen, Germany .
    Kraft, Fabio
    UFZ Helmholtz Ctr Environm Res, Dept Environm Biotechnol, D-04318 Leipzig, Germany.
    Woche, Susanne
    Goebel, Marc-O.
    Leibniz Univ Hannover, Inst Soil Sci, D-30167 Hannover, Germany .
    Heipieper, Hermann
    UFZ Helmholtz Ctr Environm Res, Dept Environm Biotechnol, D-04318 Leipzig, Germany.
    Miltner, Anja
    UFZ Helmholtz Ctr Environm Res, Dept Environm Biotechnol, D-04318 Leipzig, Germany.
    Kaestner, Matthias
    UFZ Helmholtz Ctr Environm Res, Dept Environm Biotechnol, D-04318 Leipzig, Germany.
    Microbial cell-envelope fragments and the formation of soil organic matter: a case study from a glacier forefield2013In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 113, no 1-3, p. 595-612Article in journal (Refereed)
    Abstract [en]

    Genesis of soil organic matter (SOM) during pedogenesis is still a matter of controversy in soil science. Recently, it was hypothesized that microbial cell-envelope fragments contribute significantly to SOM formation. We tested the relevance of this process during pedogenesis by evaluating the development of SOM along a chronosequence of a glacier forefield (Damma glacier). Samples of increasing soil age collected along the forefield were analyzed for C and N contents, phospholipid and total fatty acids (PLFA and tFA), water contact angle, micro-hydrophobicity and surface coverage by microbial cell-envelope residues. The surface coverage was visualized and quantified by analysis of representative, equally-scaled scanning electron micrographs (SEM). Increasing SOM contents were accompanied by increasing coverage and overall abundance of microbial cell-envelope fragments as evaluated on the basis of scanning electron microscopy; this is also reflected in the amounts of tFA and PLFA, the trend of C/N ratios, and the increasing hydrophobicity and water contact angles of the soil samples. Using SEM and the image analysis approach, we can provide a process-based description of the development of SOM in the newly developing ecosystem of the glacier forefield. The majority of small-sized SOM visible with scanning electron microscopy appears to consist of bacterial cell envelope fragments that remain stable after cell death, such that their shape does not change with soil age. Our results show the importance of microbial processing of SOM, and highlight the existence of microbial necromass as a significant part of the fine-particulate SOM even in later stages of soil development.

  • 19.
    Smith, S.V.
    et al.
    Centro de Investigacio´n Cientı´fica y de Educacio´n Superior de Ensenada (CICESE), Departamento de Ecologı´a, Ensenada, Baja California, Mexico.
    Swaney, D.P.
    Boyce Thompson Institute, Cornell University, Ithaca, NY 14850, USA.
    Buddemeier, R.W.
    Kansas Geological Survey, University of Kansas, Lawrence, KS 66047, USA.
    Scarsbrook, M.R.
    National Institute of Water and Atmospheric Research (NIWA), P.O. Box 11-115, Hamilton, New Zealand.
    Weatherhead, M.A.
    National Institute of Water and Atmospheric Research (NIWA), P.O. Box 8602, Riccarton, Christchurch, New Zealand.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Eriksson Hägg, Hanna
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hannerz, Fredrik
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    River nutrient loads and catchment size2005In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 75, p. 83-107Article in journal (Refereed)
    Abstract [en]

    We have used a total of 496 sample sites to calibrate a simple regression model for calculating dissolved inorganic nutrient fluxes via runoff to the ocean. The regression uses the logarithms of runoff and human population as the independent variables and estimates the logarithms of dissolved inorganic nitrogen and phosphorus loading with R2 values near 0.8. This predictive capability is about the same as has been derived for total nutrient loading with process-based models requiring more detailed information on independent variables. We conclude that population and runoff are robust proxies for the more detailed application, landscape modification, and in-stream processing estimated by more process-based models. The regression model has then been applied to a demonstration data set of 1353 river catchments draining to the sea from the North American continent south of the Canadian border. The geographic extents of these basins were extracted from a 1-km digital elevation model for North America, and both runoff and population were estimated for each basin. Most of the basins (72% of the total) are smaller than 103 km2, and both runoff and population density are higher and more variable among small basins than among larger ones.While total load to the ocean can probably be adequately estimated from large systems only, analysis of the geographic distribution of nutrient loading requires consideration of the small basins, which can exhibit significant hydrologic and demographic heterogeneity between systems over their range even within the same geographic region. High-resolution regional and local analysis is necessary for environmental assessment and management.

  • 20. Soana, Elisa
    et al.
    Naldi, Mariachiara
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Racchetti, Erica
    Castaldelli, Giuseppe
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Viaroli, Pierluigi
    Bartoli, Marco
    Benthic nitrogen metabolism in a macrophyte meadow (Vallisneria spiralis L.) under increasing sedimentary organic matter loads2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 124, no 1-3, p. 387-404Article in journal (Refereed)
    Abstract [en]

    Organic enrichment may deeply affect benthic nitrogen (N) cycling in macrophyte meadows, either promoting N loss or its recycling. This depends upon the plasticity of plants and of the associated microbial communities, as those surrounding the rhizosphere. Rates of denitrification, dissolved inorganic N fluxes and N uptake were measured in sediments vegetated by the submerged macrophyte Vallisneria spiralis L. under increasing organic matter loads. The aim was to investigate how the combined N assimilation and denitrification, which subtract N via temporary retention and permanent removal, respectively, do vary along the gradient. Results showed that V. spiralis meadows act as regulators of benthic N cycling even in organic enriched sediments, with negative feedbacks for eutrophication. A moderate organic load stimulates N uptake and denitrification coupled to nitrification in the rhizosphere. This is due to a combination of weakened competition between macrophytes and N cycling bacteria and enhanced radial oxygen loss by roots. An elevated organic enrichment affects N uptake due to hostile conditions in pore water and plant stress and impairs N mineralisation and its removal via denitrification coupled to nitrification. However, the loss of plant performance is almost completely compensated by increased denitrification of water column nitrate, resulting in a shift between the relative relevance of temporary and permanent N removal processes.

  • 21.
    Wild, Birgit
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Gothenburg, Sweden.
    Alaei, Saeed
    Bengtson, Per
    Bodé, Samuel
    Boeckx, Pascal
    Schnecker, Jörg
    Mayerhofer, Werner
    Rütting, Tobias
    Short-term carbon input increases microbial nitrogen demand, but not microbial nitrogen mining, in a set of boreal forest soils2017In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 136, no 3, p. 261-278Article in journal (Refereed)
    Abstract [en]

    Rising carbon dioxide (CO2) concentrations and temperatures are expected to stimulate plant productivity and ecosystem C sequestration, but these effects require a concurrent increase in N availability for plants. Plants might indirectly promote N availability as they release organic C into the soil (e.g., by root exudation) that can increase microbial soil organic matter (SOM) decomposition (priming effect), and possibly the enzymatic breakdown of N-rich polymers, such as proteins, into bio-available units (N mining). We tested the adjustment of protein depolymerization to changing soil C and N availability in a laboratory experiment. We added easily available C or N sources to six boreal forest soils, and determined soil organic C mineralization, gross protein depolymerization and gross ammonification rates (using N-15 pool dilution assays), and potential extracellular enzyme activities after 1 week of incubation. Added C sources were C-13-labelled to distinguish substrate from soil derived C mineralization. Observed effects reflect short-term adaptations of non-symbiotic soil microorganisms to increased C or N availability. Although C input promoted microbial growth and N demand, we did not find indicators of increased N mobilization from SOM polymers, given that none of the soils showed a significant increase in protein depolymerization, and only one soil showed a significant increase in N-targeting enzymes. Instead, our findings suggest that microorganisms immobilized the already available N more efficiently, as indicated by decreased ammonification and inorganic N concentrations. Likewise, although N input stimulated ammonification, we found no significant effect on protein depolymerization. Although our findings do not rule out in general that higher plant-soil C allocation can promote microbial N mining, they suggest that such an effect can be counteracted, at least in the short term, by increased microbial N immobilization, further aggravating plant N limitation.

  • 22.
    Wild, Birgit
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Vienna, Austria; University of Gothenburg, Sweden.
    Ambus, Per
    Reinsch, Sabine
    Richter, Andreas
    Resistance of soil protein depolymerization rates to eight years of elevated CO2, warming, and summer drought in a temperate heathland2018In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 140, no 3, p. 255-267Article in journal (Refereed)
    Abstract [en]

    Soil N availability for plants and microorganisms depends on the breakdown of soil polymers such as proteins into smaller, assimilable units by microbial extracellular enzymes. Changing climatic conditions are expected to alter protein depolymerization rates over the next decades, and thereby affect the potential for plant productivity. We here tested the effect of increased CO2 concentration, temperature, and drought frequency on gross rates of protein depolymerization, N mineralization, microbial amino acid and ammonium uptake using N-15 pool dilution assays. Soils were sampled in fall 2013 from the multifactorial climate change experiment CLIMAITE that simulates increased CO2 concentration, temperature, and drought frequency in a fully factorial design in a temperate heathland. Eight years after treatment initiation, we found no significant effect of any climate manipulation treatment, alone or in combination, on protein depolymerization rates. Nitrogen mineralization, amino acid and ammonium uptake showed no significant individual treatment effects, but significant interactive effects of warming and drought. Combined effects of all three treatments were not significant for any of the measured parameters. Our findings therefore do not suggest an accelerated release of amino acids from soil proteins in a future climate at this site that could sustain higher plant productivity.

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