Inland waters emit significant quantities of greenhouse gases (GHGs) such as methane (CH4) and carbon dioxide (CO2) to the atmosphere. On a global scale, these emissions are large enough that their contribution to climate change is now recognized by the Intergovernmental Panel on Climate Change. Much of the past focus on GHG emissions from inland waters has focused on lakes, reservoirs, and rivers, and the role of small, artificial waterbodies such as ponds has been overlooked. To investigate the spatial variation in GHG fluxes from artificial ponds, we conducted a synoptic survey of forty urban ponds in a Swedish city. We measured dissolved concentrations of CH4 and CO2, and made complementary measurements of water chemistry. We found that CH4 concentrations were greatest in high‐nutrient ponds (measured as total phosphorus and total organic carbon). For CO2, higher concentrations were associated with silicon and calcium, suggesting that groundwater inputs lead to elevated CO2. When converted to diffusive GHG fluxes, mean emissions were 30.3 mg CH4·m−2·d−1 and 752 mg CO2·m−2·d−1. Although these fluxes are moderately high on an areal basis, upscaling them to all Swedish urban ponds gives an emission of 8336 t CO2eq/yr (±1689) equivalent to 0.1% of Swedish agricultural GHG emissions. Artificial ponds could be important GHG sources in countries with larger proportions of urban land.

Mercury (Hg) in peatlands remains a problem of global interest. To mitigate the risks of this neurotoxin, accurate assessments of Hg in peat are needed. Treatment of peat that will be analysed for Hg is, however, not straightforward due to the volatile nature of Hg. The drying process is of particular concern since Hg evasion increases with the temperature. Samples are, therefore, often freeze-dried to limit Hg loss during the drying processes. A problem with freeze-drying is that cost and equipment resources can limit the number of samples analysed in large projects. To avoid this bottleneck, we tested if drying in a 60 °C-degree oven could be an acceptable alternative to freeze-drying. We both freeze-dried and oven-dried (60 °C) 203 replicate pairs of peat samples, and then examined the differences in total Hg concentration. The Hg concentration differed significantly between the two drying methods with a median Hg deficit in oven-dried samples of 4.2%. Whether a 4.2% deficit of Hg depends on one’s purpose. The lower median Hg concentration in oven-dried samples has to be weighed against the upside efficiently drying large sets of peat samples. By freeze-drying a subset of the samples, we fitted a function to correct for Hg loss during oven-drying ($$y=0.96x+0.08)$$ y = 0.96 x + 0.08 ) . By applying this correction, the freeze-drying bottleneck could oven-dry large-scale inventories of total Hg in peatlands with results equivalent to freeze-drying, but only have to freeze-dry a subset.

<p>Dependence of Total Mercury in Superficial Peat With Nutrient Status: Implications for Stability of Peat as an Archive of Hg Deposition</p><p> </p><p>Jacob Smeds<sup>1</sup>, Mats B. Nilsson<sup>2</sup>, Wei Zhu<sup>2</sup>, Kevin Bishop<sup>3</sup></p><p>[1]Department of Earth Sciences, Uppsala University, Uppsala, Sweden</p><p>[2]Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå, Sweden</p><p>[3]Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden</p><p> </p><p>Although Mercury (Hg) has decreased considerably in the atmosphere during recent decades, this potent neurotoxin still constitutes a threat to ecosystems globally through the Hg stored in soils. The mitigation of the risks related to this legacy Hg was a reason to implement the Minamata Convention. Subsequent work under the convention is dependent on assessments of the Hg stored in the environment. A way of doing this is to study environmental archives of atmospheric deposition such as ice cores, lake sediments, and peatlands. A previous study along a chronosequence of mires along the northern coast of Sweden showed Hg content differing by a factor of 2 and correlating strongly with mire age. This was hypothesized to indicate that differences in minerogenic water supply along the chronosequence influenced the stability of Hg after deposition from the atmosphere to the mire surface. Declining access of minerogenic elements with increasing peatland age results in a less nutrient demanding plant species composition as well as decreasing access to microbial electron acceptors. But that study looked at just one 10 cm layer at a depth with peat ca 50 years old. Here we present a more rigorous test of that hypothesis by presenting the total amount and vertical pattern of Hg accumulation during the last 200 years in the superficial peat along that peatland chronosequence.</p><p>Eleven peatlands along the northern coast of Sweden near Umeå were sampled. This is an area where isostatic rebound continues to raise the land above the sea level. Triplicate peat cores were collected from both lawns and hummocks, when present. A total of 54 peat cores, each 50 cm deep, were collected and frozen immediately. The cores were then sliced into 2 cm layers, and each slice was analysed for total Hg. Due to the land rising out of the sea, the different peatlands have ages ranging from 100-2000 years since establishment, despite being located within a distance of <10 km. The peatland age correlates with availability of mineral elements and pH. This is due to the fact that the underlying postglacial mineral soil is a source of elements. The distance to the mineral soil increases as peat accumulates with peatland age. Certain elements also leach from the peatlands over time. This documentation of the vertical distribution of Hg in all the peat laid down during the past 200 years in each mire tests the hypothesis that the propensity of Hg to evade back to the atmosphere in this area is related to the amount and composition of inorganic elements.</p>

<p>The major objective behind peatland restoration is to improve ecosystem services, such as increased biodiversity, increased carbon sequestration, increased groundwater storage, and improved surface water quality. However, a century or more of drained conditions has drastically changed the soil properties in relation to natural wetlands and this is likely to profoundly influence the potential for various biogeochemical peat processes. Thus, peatland restoration may result in undesired impacts and potential environmental threats. Two such undesired effects are increased methane production and increased mercury methylation.</p> <p>In this study, we investigated how nine boreal peatlands across a latitudinal gradient in Sweden have been affected by rewetting after up to a century of drained conditions. Each peatland was sampled for three 50 cm deep peat cores that were analyzed for carbon, nitrogen, δ<sup>13</sup>C, δ<sup>15</sup>N, bulk density, and organic matter proportion. Adjacent to each restored peatland, we sampled a corresponding pristine (natural) peatland to facilitate a comparison of how the peat properties have been affected by drainage and subsequent rewetting of the peatlands. Groundwater depth was monitored at all peatland locations to confirm restored conditions at the rewetted peatlands.</p> <p>The results indicate that a long period of drained conditions and subsequent rewetting have changed the peat properties, with differences shown in C/N ratio, dry bulk density, and organic matter content. Rewetting will thus not regenerate a pristine environment. Instead, it creates new conditions to which various biogeochemical processes will respond and these do not necessarily represent conditions prior to disturbance. Our study will provide background information to understand the biogeochemical dynamics in peatlands after restoration, especially since the study covers a large span of nutrient conditions and catchment settings. This understanding will be fundamental for the development of strategies to minimize undesired biogeochemical responses following peatland restoration.</p> <p> </p> <p>Presentation preference: Oral, virtually</p> <p>Billing address:</p> <p>SLU Fakturamottagning</p> <p>Box 7090</p> <p>750 07 Uppsala</p> <p>Referens: 241MOT </p> <p> </p>