Katerina Michaelides

Impact of coarse sediment supply from hillslopes to the channel in runoff‐dominated, dryland fluvial systems

Sediment supply from hillslopes to channels is an important control on basin functioning and evolution. However, current theoretical frameworks do not adequately consider processes of runoff-driven hillslope sediment supply, which affect river channels spatially and temporally. Mountainous dryland basins exhibit an important manifestation of these processes because their debris-mantled hillslopes produce coarse sediment and because rainfall is delivered as infrequent, high-intensity, short-duration rainstorms. This paper combines field measurements and modeling to explore runoff-driven coarse sediment supply from hillslopes to the channel and assesses a range of plausible storms on the longitudinal patterns of sediment load and its caliber over a dryland basin reach. Our results show that modeled sediment load and its grain size distribution are determined by the nonlinear interaction between rainfall characteristics and hillslope attributes, resulting in longitudinal fluctuations in sediment supply, the relative magnitude and location of which varies between storms. Results suggest that long hillslopes are most sensitive to rainfall and they exhibit large variations in supplied sediment load and grain size for different runoff characteristics. Short and steep hillslopes are less sensitive to rainfall variations as gradient effects dominate over the role of length in modulating runoff accumulation. Furthermore, the signal of the median fraction (D50) of modeled sediment supplied by the hillslope is preserved in the coarse fraction of the measured in-channel grain sizes (D90). Finally, we propose a simple index, which provides new insights into the effectiveness of different rainstorms in terms of the impact of hillslope sediment supply on the channel.

Linking Short- and Long-Term Soil—Erosion Modelling

Soil erosion by overland flow is a significant process over large areas of the Earth. It leads to specific forms of landform development over both short and long time scales. In some cases, the landscape can be dramatically modified in a matter of hours, as a result of an extreme storm event. Understanding soil erosion is therefore fundamental in being able to explain the geomorphology of these areas. The soil is also a fundamental resource for human food supplies, and its loss means direct and indirect impacts on sustainability. Off-site effects of erosion can be significant both for pollution, particularly when chemical fertilisers and pesticides have been used, and for siltation of reservoirs and other structures. In extreme cases, persistent erosion can lead to a total loss of productivity, leading to desertification. The understanding of soil erosion therefore also has important practical implications.

Paleofluvial landscape inheritance for Jakobshavn Isbræ catchment, Greenland

Subglacial topography exerts strong controls on glacier dynamics, influencing the orientation and velocity of ice flow, as well as modulating the distribution of basal waters and sediment. Bed geometry can also provide a long-term record of geomorphic processes, allowing insight into landscape evolution, the origin of which may predate ice sheet inception. Here we present evidence from ice-penetrating radar data for a large dendritic drainage network, radiating inland from Jakobshavn Isbrae, Greenlands largest outlet glacier. The size of the drainage basin is ∼450,000 km2 and accounts for about 20% of the total land area of Greenland. Topographic and basin morphometric analyses of an isostatically uplifted (ice-free) bedrock topography suggests that this catchment predates ice sheet initiation and has likely been instrumental in controlling the location and form of the Jakobshavn ice stream, and ice flow from the deep interior to the margin, now and over several glacial cycles.

A method for the simultaneous extraction of seven pesticides from soil and sediment

Organic pesticides are difficult compounds to extract from soils and sediments due to their strong affinity for soil particulates. Different pesticide compounds migrate to varying extents in the environment depending on their chemical structures, with effects ranging from strong adsorption to soil particles to rapid dissolution in water. Published methodologies report procedures for extracting and analysing discrete compounds or chemical classes but there is a lack of previous work concerned with methodologies for the simultaneous extraction and analysis of organic pesticides from different chemical classes. The soil environment is a complex matrix and farmers use a variety of compounds for pest control; with regular crop rotation a diverse mixture of chemicals is likely to be present in arable fields. Mindful of a legacy of pesticide contamination in water and the requirement for management of water resources at catchment scales there is a need to quantitatively assess the storage and transport of a variety of organic pesticides in different phases; soil, sediment and water. This paper describes a methodology for analysing seven different organic pesticides representative of five different classes of pesticide using a single methodology. Prior to use all glassware was deactivated using dimethyldichlorosilane to prevent adsorption effects. Soils then underwent a triple ultrasonication in acetone before being methylated with trimethylsilyldiazomethane. Final extracts were dissolved in hexane and analysed by GC/MS. Recoveries from the soil were determined to range between 70% and 114%.

Compound-specific amino acid 15 N stable isotope probing of nitrogen assimilation by the soil microbial biomass using gas chromatography/combustion/isotope ratio mass spectrometry

As already introduced in Chap. 1 (Sect. 1.4.2), the complexity and heterogeneity of soil organic N is partly responsible for limiting understanding of soil N cycling.