The Greenland Ice Sheet is currently not accounted for in Arctic mercury budgets, despite large and increasing annual runoff to the ocean and the socio-economic concerns of high mercury levels in Arctic organisms. Here we present concentrations of mercury in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet and evaluate the export of mercury to downstream fjords based on samples collected during summer ablation seasons. We show that concentrations of dissolved mercury are among the highest recorded in natural waters and mercury yields from these glacial catchments (521–3,300 mmol km−2 year−1) are two orders of magnitude higher than from Arctic rivers (4–20 mmol km−2 year−1). Fluxes of dissolved mercury from the southwestern region of Greenland are estimated to be globally significant (15.4–212 kmol year−1), accounting for about 10% of the estimated global riverine flux, and include export of bioaccumulating methylmercury (0.31–1.97 kmol year−1). High dissolved mercury concentrations (~20 pM inorganic mercury and ~2 pM methylmercury) were found to persist across salinity gradients of fjords. Mean particulate mercury concentrations were among the highest recorded in the literature (~51,000 pM), and dissolved mercury concentrations in runoff exceed reported surface snow and ice values. These results suggest a geological source of mercury at the ice sheet bed. The high concentrations of mercury and its large export to the downstream fjords have important implications for Arctic ecosystems, highlighting an urgent need to better understand mercury dynamics in ice sheet runoff under global warming.

Bacteria are able to colonize and thrive in a variety of different environments as a biofilm, but only within the last half century new insights have been gained in this complex biosystem. Bacterial biofilms play a major role in human health by forming a defensive barrier against antibacterial chemical therapeutics and other potential pathogens, and in infectious disease when the bacteria invade normally sterile compartments. Quorum sensing is the signaling network for cell-to-cell communication and utilized by bacteria to regulate biofilms and other cellular processes. This review will describe recent advances in quorum sensing and biofilms. Initially, it will focus on Streptococcus pneumoniae biofilm regulation and the involvement of the ComABCDE pathway. As part of this review an original analysis of the genotypic and phenotypic variation of the signaling molecule, ComC and its cognate receptor ComD, firstly within the pneumococcal species and then within the genus Streptococcus will be presented. Additionally, a pathway similar to ComABCDE, the BlpABCSRH that regulates bacteriocin and immunity protein production that inhibit the growth of competing bacteria will be described. This review will then examine a third quorum sensing mechanism in the pneumococcus, the LuxS/AI-2, and present a novel gene and protein sequence comparative analysis that indicates its occurrence is more universal across bacterial genera compared with the Com pathway, with more sequence similarities between bacterial genera that are known to colonize the mucosal epithelium.

<p>The current climate trajectory in conjunction with agricultural intensification and the reliance on synthetic fertilisers, present further threat to the resilience of future food production through their contributions to soil degradation and consequent climatic feedback. Innovative sustainable agricultural technologies are needed to produce nutritious and equitable food products in line with the UN’s goal for Zero Hunger and sustainable development. Glacial Rock Flour (GRF) is a fine mineral rock dust, made available through the glacial abrasion of bedrock, and is often enriched in nutrients (e.g. Potassium, Phosphorous, Silicon, trace elements) but low in Nitrogen. It would therefore be a suitable soil fertility amendment for legume crops grown in acidic, nutrient poor soils often found in many mountainous regions (e.g. Hindu Kush Himalaya), where GRF is considered an alluvial ‘waste’ silting up dams and reservoirs. We have investigated the effect of GRF soil amendments in soil-plant mesocosms using a typical UK silt loam arable soil (pH~7) for cultivating red clover (<em>Trifolium pratense</em>) inoculated with <em>Rhizobium</em>. GRF from the Chhota Shigri (India) and Sólheimajökull (Iceland) glaciers were applied at 2 and 20 T/ha, while no GRF treatments included synthetic fertilizer applications of phosphorus (P), potassium (K) and P+K, and they were all compared against control red clover plants grown with no soil amendments. The nitrogen fixation capacity of red clover was estimated via <sup>15</sup>N natural abundance against a rye grass control (<em>Lolium perenne</em>) in two harvests on weeks 14 and 19. Both 20 T/ha GRF treatments appeared to stimulate fixed nitrogen yield compared to synthetic fertilizer treatments and control red clover plants, while the stimulation was more pronounced in the 2<sup>nd</sup> harvest as the soil nutrients were progressively depleted. Soil greenhouse gas fluxes over the growth period (weeks 4-14) were monitored by enclosing pots in sealed chambers. While no difference was observed in carbon dioxide fluxes between treatments, nitrous oxide (N<sub>2</sub>O) flux was negative for all red clover mesocosms with the N<sub>2</sub>O reduction being more prominent in both 20 T/ha GRF treatments towards the end of the first growth period (week 14). Gross N mineralization and nitrification were estimated in post-harvest soils from all the mesocosms using the isotope dilution method, while <sup>15</sup>N-N<sub>2</sub>O and <sup>15</sup>N-N<sub>2</sub> production were also measured after amending the soils with 98 at% <sup>15</sup>N-NH<sub>4</sub><sup>+</sup> and <sup>15</sup>N-NO<sub>3</sub><sup>-</sup><sub>. </sub> Gross N mineralization was not different between treatments, while nitrification was non-detectable, indicating a very tightly coupled N cycle between <em>Rhizobium </em>and red clover. However, when excess nitrate was applied, bacterial denitrification was active but the amendment of the soils with GRF appeared to reduce the production of N<sub>2</sub>O and promote complete denitrification to N<sub>2</sub>. Our novel study on the properties and application of GRF as a sustainable soil fertility amendment under a low nitrogen cropping system, holds promise that it can promote leguminous nitrogen fixation and a tightly-coupled N cycle that maximises N-use efficiency while mitigating N<sub>2</sub>O emissions by promoting complete denitrification.</p>

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