Sabena Blackbird

Efficient burial of carbon in a submarine canyon

Burial of organic carbon (OC) in marine sediments moderates atmospheric CO2 levels on geological time scales, but uncertainties remain about how much OC is buried and about the efficiency of OC burial, particularly in heterogeneous seafloor environments such as ocean margins. Here we describe OC burial in Nazare submarine canyon and the adjacent continental slope off Portugal, an area within which sedimentation rates vary by three orders of magnitude. Using a nested series of observations at different scales, ranging from regional bathymetry to sediment cores, we estimate the annual sediment and OC deposited in the canyon at 620,000 t and 12,500 t, respectively. Nazare Canyon is thus a significant sink of both sediment and OC. Canyon sediments typically contain ~2% OC, both in surface sediments and at depth, and there is a limited correlation between sedimentation rate and OC content. The likely explanation is that the OC has already survived a lengthy period of degradation prior to deposition in the canyon, such that additional exposure to oxygenated water has minimal effect. Burial efficiency is difficult to calculate because of extensive resuspension and reworking of OC in the upper canyon, but probably exceeds 30% in areas of high sedimentation. These areas are shown to be 30 times more effective in burying OC than adjacent areas of the continental slope, indicating that Nazare Canyon is a hitherto overlooked sink of OC on a continental margin where OC burial is otherwise low.

Anthropogenic influence on sediment transport in the Whittard Canyon, NE Atlantic

Unusual peaks in turbidity were detected in two branches of the Whittard Canyon in June 2013. Enhanced nepheloid layers (ENLs) were defined as layers with concentrations of suspended particulate matter exceeding those of nepheloid layers typically observed in a given region. Here, ENLs had peaks in turbidity and elevated suspended particulate matter concentrations exceeding ~1 mg L(-1) with the largest ENLs measuring between ~2-8 mg L(-1). The ENLs measured ~100-260 m in vertical height and were detected in water depths of between 640 and 2880 m. Vessel Monitoring System data showed that high spatial and temporal activity of potential bottom trawling vessels coincided with the occurrence of the ENLs. Molar C/N ratios of the suspended organic material from the ENLs showed a high degree of degradation. Regular occurrences of such events are likely to have implications for increased sediment fluxes, burial of organic carbon and alteration of benthic and canyon ecosystems.

Change to ecosystem properties through changing the dominant species: Impact of Pteridium aquilinum-control and heathland restoration treatments on selected soil properties

It is well known that soils are influenced by the plant species that grow in them. Here we consider the effects of management-induced changes to plant communities and their soils during restoration within a 20-year manipulative experiment where the aim was to change a late-successional community dominated by the weed, Pteridium aquilinum, to an earlier-successional grass-heath one. The ecological restoration treatments altered the above- and below-ground components of the community substantially. Untreated plots maintained a dense Pteridium cover with little understory vegetation, cutting treatments produce significant reductions of Pteridium, whereas herbicide (asulam) produced significant immediate reductions in Pteridium but regressed towards the untreated plots within 10 years. Thereafter, all asulam-treated plots were re-treated in year 11, and then were spot-sprayed annually. Both cutting and asulam treatments reduced frond density to almost zero and resulted in a grass-heath vegetation. There was also a massive change in biomass distribution, untreated plots had a large above-ground biomass/necromass that was much reduced where Pteridium was controlled. Below-ground in treated plots, there was a replacement of the substantive Pteridium rhizome mass with a much greater root mass of other species. The combined effects of Pteridium-control and restoration treatment, reduced soil total C and N as and available P concentrations, but increased soil pH and available N. Soil biological activity was also affected with a reduction in soil N mineralization rate, but an increased soil-root respiration. Multivariate analysis showed a clear trend along a pH/organic matter gradient, with movement along it correlated to management intensity from the untreated plots with low pH/high organic matter and treated plots with to a higher pH/lower organic matter in the sequence asulam treatment, cut once per year to cut twice per year. The role that these changed soil conditions might have in restricting Pteridium recovery are discussed.

Effects of removing sheep grazing on soil chemistry, plant nutrition and forage digestibility: Lessons for rewilding the British uplands

School of Environmental Sciences, University of Liverpool, Liverpool, UK Parque Tecnológico de Boecillo, Valladolid, Spain CEH Lancaster, Centre for Ecology & Hydrology, Lancaster, UK Correspondence Prof. Robert H. Marrs, School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, UK. Email: calluna@liverpool.ac.uk Rewilding is currently being proposed as a means of enhancing the conservation value of marginal land in many parts of the world. This is especially true in the British uplands where rewilding will almost certainly involve either a reduction in livestock grazing, or its complete removal. The aim of reducing stock numbers would be to reverse the degradation of these ecosystems that has been caused by past over-grazing. However, little is known about the likely outcomes, or the time-scales over which such ecosystem recovery might occur. Here, we report preliminary results from a recent study of eight sites at Moor House NNR in the north-Pennines, where permanent plots withand without-sheep grazing were established between 1954 and 1967 on a range of typical upland plant communities. Soils and vegetation were sampled, and their chemical properties analysed; for vegetation an assessment of the herbage quality for animal nutrition was also made. No significant differences in soil properties, above-ground biomass and nutritional status of the vegetation was detected that could be attributed to sheep grazing removal. The only significant effect associated with grazing removal was a reduced digestibility of the vegetation (greater acid detergent fibre concentration) where sheep were removed. These results show that a rewilding strategy that relies only on reducing sheep numbers will have very little impact on ecosystem recovery in terms of soil or herbage chemistry over shortto medium-term time-scales. Rewilding policies, therefore, attempting to restore ecosystems degraded by over-grazing must, therefore, be viewed as long-term (>50 y).