Consequences of intensive forest harvesting on the recovery of Swedish lakes from acidification and on critical load exceedances

Across much of the northern hemisphere, lakes are at risk of re-acidification due to incomplete recovery from historical acidification and pressures associated with more intensive forest biomass harvesting. Critical load (CL) calculations aimed at estimating the amount of pollutants an ecosystem can receive without suffering adverse consequences are dependent on these factors. Here, we present a modelling study of the potential effects of intensified forest harvesting on re-acidification of a set of 3239 Swedish lakes based on scenarios with varying intensities of forest biomass harvest and acid deposition. There is some evidence that forestry would have caused a certain level of acidification even if deposition remained at 1860 levels. We show that all plausible harvest scenarios delay recovery due to increased rates of base cation removal. Scenario results were used to estimate critical loads for the entire population of lakes in Sweden. The forestry intensity included in critical load calculations is a political decision. After scaling calculations to the national level, it was apparent that a high but plausible forest harvest intensity would lead to an increase in the area of CL exceedances and that even after significant reductions in forest harvest intensity, there would still be areas with CL exceedances. Our results show that forest harvest intensity and regional environmental change must be carefully considered in future CL calculations

On the circulation, water mass distribution, and nutrient concentrations of the western Chukchi Sea

17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.5194/os-18-29-2022Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through the Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along the Alaskan coast, as Alaskan Coastal Water. A central pathway exhibits intermediate salinity and nutrient concentrations, while the most nutrient-rich water enters the Bering Strait on its western side. Towards the Arctic Ocean, the flow of these water masses is subject to strong topographic steering within the Chukchi Sea with volume trans port modulated by the wind field. In this contribution, we use data from several sections crossing Herald Canyon collected in 2008 and 2014 together with numerical modelling to investigate the circulation and transport in the western part of the Chukchi Sea. We find that a substantial fraction of water from the Chukchi Sea enters the East Siberian Sea south of Wrangel Island and circulates in an anticyclonic direction around the island. This water then contributes to the high nutrient waters of Herald Canyon. The bottom of the canyon has the highest nutrient concentrations, likely as a result of addition from the degradation of organic matter at the sediment surface in the East Siberian Sea. The flux of nutrients (nitrate, phosphate, and silicate) and dissolved inorganic carbon in Bering Summer Water and Winter Water is computed by combining hydrographic and nutrient observations with geostrophic transport referenced to lowered acoustic Doppler current profiler (LADCP) and surface drift data. Even if there are some general similarities between the years, there are differences in both the temperature–salinity and nutrient characteristics. To assess these differences, and also to get a wider temporal and spatial view, numerical modelling results are applied. According to model results, high-frequency variability dominates the flow in Herald Canyon. This leads us to conclude that this region needs to be monitored over a longer time frame to deduce the temporal variability and potential trends.The science was financially supported by: US National Science Foundation (Grant Number: GEO/PLR ARCSS 575 IAA#1417888), the Department of Energy (DOE) Regional and Global Model Analysis (RGMA), the Swedish Research Council Formas (contract no. 2018-01398), and the Swedish Research Council (contract nos. 621-2006-3240, 621-2010-4084, and 2012-1680). This work was carried out with logistic support from the Knut and Alice Wallenberg Foundation and from Swedish Polar Research Secretariat. The Department of Defense (DOD) High Performance Computer Modernization Program (HPCMP) provided computer resources. This study was also supported by the Russian Scientific Foundation (grant no. # 21-77-580 30001).The science was financially supported by: US National Science Foundation (Grant Number: GEO/PLR ARCSS 575 IAA#1417888), the Department of Energy (DOE) Regional and Global Model Analysis (RGMA), the Swedish Re search Council Formas (contract no. 2018-01398), and the Swedish Research Council (contract nos. 621-2006-3240, 621-2010-4084, and 2012-1680). This work was carried out with logistic support from the Knut and Alice Wallenberg Foundation and from Swedish Polar Research Secretariat. The Department of Defense (DOD) High Performance Computer Modernization Program (HPCMP) provided computer resources. This study was also supported by the Russian Scientific Foundation (grant no. # 21-77-580 30001)

Four decades of changing dissolved organic matter quality and stoichiometry in a Swedish forest stream

Dissolved organic matter (DOM) concentrations have risen by a factor of two or more across much of Europe and North America during recent decades. These increases have affected the carbon cycle, light regime, drinking water treatability, and the energy and nutrient budgets of lakes and streams. However, while trends in DOM quantity are well characterised, information on how/whether qualitative properties of DOM have changed are scarce. Here, we describe over 40 years of monitoring data from a forested headwater stream in the Gårdsjön experimental catchment, southwest Sweden, which provides a unique record of biogeochemical change, including optical and stoichiometric DOM quality metrics, spanning the entire period of recovery from acidification. For the period 1980–2020 we find a 71% reduction in decadal mean sulphate concentrations, and a similar reduction in inorganic aluminium concentrations, alongside a 64% increase in dissolved organic carbon (DOC) concentrations. Over the same period, colour (absorbance at 420 nm) increased almost twice as much as DOC, whereas dissolved organic nitrogen (DON) increased by only one third as much. These results demonstrate a shift in stream water composition, with DOM becoming dominated by highly coloured, complex, nitrogen-poor compounds. This material is likely more resistant to biological degradation, but more susceptible to photochemical degradation. Changes in DOM stoichiometry could lead to intensified nitrogen and/or phosphorus limitation in surface waters, while increased colour/DOC ratios could intensify light-limitation of primary production beyond that expected from DOC increases alone. We observed increases in organic matter associated metals (iron 117%, organically complexed aluminium 85%) that exceeded the increase in DOC, consistent with their increased mobilisation by more aromatic organic matter. All observed changes are consistent with recovery from acidification being the primary driver of change, implying that past acidification, and ongoing recovery, have profoundly affected terrestrial and aquatic biogeochemistry, ecology and the carbon cycle

A new global interior ocean mapped climatology: the 1° × 1° GLODAP version 2

We present a mapped climatology (GLODAPv2.2016b) of ocean biogeochemical variables based on the new GLODAP version 2 data product (Olsen et al., 2016; Key et al., 2015), which covers all ocean basins over the years 1972 to 2013. The quality-controlled and internally consistent GLODAPv2 was used to create global 1°  ×  1° mapped climatologies of salinity, temperature, oxygen, nitrate, phosphate, silicate, total dissolved inorganic carbon (TCO2), total alkalinity (TAlk), pH, and CaCO3 saturation states using the Data-Interpolating Variational Analysis (DIVA) mapping method. Improving on maps based on an earlier but similar dataset, GLODAPv1.1, this climatology also covers the Arctic Ocean. Climatologies were created for 33 standard depth surfaces. The conceivably confounding temporal trends in TCO2 and pH due to anthropogenic influence were removed prior to mapping by normalizing these data to the year 2002 using first-order calculations of anthropogenic carbon accumulation rates. We additionally provide maps of accumulated anthropogenic carbon in the year 2002 and of preindustrial TCO2. For all parameters, all data from the full 1972–2013 period were used, including data that did not receive full secondary quality control. The GLODAPv2.2016b global 1°  ×  1° mapped climatologies, including error fields and ancillary information, are available at the GLODAPv2 web page at the Carbon Dioxide Information Analysis Center (CDIAC; doi:10.3334/CDIAC/OTG.NDP093_GLODAPv2)

Ventilation of the Arctic Ocean: Mean ages and inventories of anthropogenic CO2 and CFC-11

The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed because of logistical difficulties, although the importance of the Arctic Ocean for global circulation and climate is widely recognized. For instance, the concentration and inventory of anthropogenic CO2 (C ant) in the Arctic Ocean are not properly known despite its relatively large volume of well-ventilated waters. In this work, we have synthesized available transient tracer measurements (e.g., CFCs and SF6) made during more than two decades by the authors. The tracer data are used to estimate the ventilation of the Arctic Ocean, to infer deep-water pathways, and to estimate the Arctic Ocean inventory of C ant. For these calculations, we used the transit time distribution (TTD) concept that makes tracer measurements collected over several decades comparable with each other. The bottom water in the Arctic Ocean has CFC values close to the detection limit, with somewhat higher values in the Eurasian Basin. The ventilation time for the intermediate water column is shorter in the Eurasian Basin (∼200 years) than in the Canadian Basin (∼300 years). We calculate the Arctic Ocean C ant inventory range to be 2.5 to 3.3 Pg-C, normalized to 2005, i.e., ∼2% of the global ocean C ant inventory despite being composed of only ∼1% of the global ocean volume. In a similar fashion, we use the TTD field to calculate the Arctic Ocean inventory of CFC-11 to be 26.2 ± 2.6 × 106 moles for year 1994, which is ∼5% of the global ocean CFC-11 inventor

Swedish National Nitrogen Budget – Forest and semi-natural vegetation

This report describes the flow of reactive nitrogen for forests and semi-natural vegetation in Sweden according to the methodology developed within the framework of the Task Force on Reactive Nitrogen (TFRN). Forest and semi-natural vegetation (FS) constitute one out of 8 pools for the Swedish National Nitrogen Budget. The FS pool is divided into the three compartments; forest, wetland and other land. Together they amount to 71% of the country area. The data used has been collected from Swedish official statistics and reports and are representative for year 2015 whenever possible. In total, the FS pool has inflows of reactive nitrogen of 175.8 kilotonnes (kt) and outflows of 188.6 kt. The largest inflow is from atmospheric deposition (99.3 kt) and the largest outflow is via leaching/runoff (67.4 kt). Forestry is a major industry in Sweden and the nitrogen flow from the forest due to harvest is the second largest outflow from the FS-pool (58.5 kt). Biological fixation of nitrogen is an important inflow for both forest (39.5 kt) and wetland (32.1 kt). Other land (which mostly consists of mountains) is of smaller quantitative importance and only has two flows: leaching/runoff and deposition (2.9 kt N and 2.9 kt N, respectively).Denna rapport beskriver flödet av reaktivt kväve för skog och seminaturlig vegetation i Sverige för år 2015 enligt en metodik som tagits fram inom ramen för Task Force on Reactive Nitrogen (TFRN). Skog och seminaturlig vegetation utgör en av totalt 8 delar av en nationell kvävebudget för Sverige. De största inflödena av reaktivt kväve var atmosfärisk deposition och kvävefixering. De största utflödena utgjordes av läckage och avrinning från mark samt denitrifikation. Denna rapport finns endast på engelska

Påverkan på luftkvalitet i städer av utsläpp från närliggande jordbruk

IVL Svenska Miljöinstitutet har på uppdrag av Naturvårdsverket undersökt hur stor påverkan utsläpp av ammoniak (NH3) från närliggande jordbruk har på stadsluften i Uppsala, med fokus på halterna av små partiklar (PM2.5) samt potential för utsläpps¬minskningar för att förbättra stadsluften från denna påverkan. Denna fråga är viktig att belysa eftersom utsläppen av NH3 från jordbruket inte förväntas minska i samma takt som utsläpp av andra luftföroreningar. Man har kunnat konstatera, i andra regioner, att det inte bara är viktigt att minska på utsläppen av svavel- och kväveoxider utan att även NH3-utsläppen behöver minskas. En jämförelse av skillnader i halterna av små partiklar och deras komponenter visar en ökad effekt av jordbruksemissioner av NH3 på vintern, då bidraget ökar från årsmedelvärden på 2,3 % och 1,2 % för regional bakgrund och centrala staden till 3,3 % och 1,6 % för vintermedelvärdet. Skillnaderna mellan säsongerna beror på ett flertal faktorer som exempelvis hur mycket NO3- och SO42- som finns tillgängligt för att bilda partiklar. På vintern är ammoniakutsläppen lägre och NOx- och SOx-utsläppen är relativt sett högre samtidigt som omblandningen är lägre jämfört med övriga delar av året. Detta gör i sin tur att kvoten mellan ammoniak och HNO3 och SO42- är lägre och en större del av ammoniakutsläppen kommer därför att bilda partikelformig NH4+. Under sommaren är, förutom den högre kvoten mellan NH3 och nitrat och sulfat, även kondensation av nitrat på partiklarna reducerad p.g.a. högre temperaturer vilket begränsar ammoniakens potential att bidra till partiklar ytterligare. Detta innebär att utsläpps¬minskningar av NH3 kan ha större effekt på vintern/hösten med avseende på bildning av sekundära aerosoler än under vår och sommar och kan vara jämförbar med effekten från ytterligare minskningar av SOx- och NOx-utsläpp, även om NH3-utsläppen är högre på våren och sommaren