An approach for the identification of exemplar sites for scaling up targeted field observations of benthic biogeochemistry in heterogeneous environments

Continental shelf sediments are globally important for biogeochemical activity. Quantification of shelf-scale stocks and fluxes of carbon and nutrients requires the extrapolation of observations made at limited points in space and time. The procedure for selecting exemplar sites to form the basis of this up-scaling is discussed in relation to a UK-funded research programme investigating biogeochemistry in shelf seas. A three-step selection process is proposed in which (1) a target area representative of UK shelf sediment heterogeneity is selected, (2) the target area is assessed for spatial heterogeneity in sediment and habitat type, bed and water column structure and hydrodynamic forcing, and (3) study sites are selected within this target area encompassing the range of spatial heterogeneity required to address key scientific questions regarding shelf scale biogeochemistry, and minimise confounding variables. This led to the selection of four sites within the Celtic Sea that are significantly different in terms of their sediment, bed structure, and macrofaunal, meiofaunal and microbial community structures and diversity, but have minimal variations in water depth, tidal and wave magnitudes and directions, temperature and salinity. They form the basis of a research cruise programme of observation, sampling and experimentation encompassing the spring bloom cycle. Typical variation in key biogeochemical, sediment, biological and hydrodynamic parameters over a pre to post bloom period are presented, with a discussion of anthropogenic influences in the region. This methodology ensures the best likelihood of site-specific work being useful for up-scaling activities, increasing our understanding of benthic biogeochemistry at the UK-shelf scale

Comparative Analysis by Magnetic Resonance Imaging of Extracellular Space Diffusion and Interstitial Fluid Flow in the Rat Striatum and Thalamus

Drug delivery to the brain remains a challenge due to the blood-brain barrier. Localized injection of drug therapies represents a promising alternative once the diffusion characteristics of different brain regions have been evaluated. Extracellular space diffusion and interstitial fluid flow of the striatum and thalamus in the rat brain were simultaneously compared using magnetic resonance imaging and the tracer gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). The diffusion parameters, volume distribution, and half-life time were quantified. While there was extensive diffusion of Gd-DTPA in the striatum, Gd-DTPA was rapidly cleared and had a shorter half-life time in the thalamus. The increased clearance rate and shorter half-life of the tracer in the thalamus were associated with increased expression of Aquaporin-4. The tortuosity of the extracellular space did not show a statistically significant difference between the two regions examined. Our research provides a new reference for brain interstitial drug delivery to treat central nervous system diseases and a better understanding of the brain microenvironment.National Natural Science Foundation of China [81171080, 61450004]; National key developmental program for scientific instrument and equipment [2011YQ030114]; National Science and Technology Pillar Program during the Twelve Five-year Plan Period of China [2012BAI15B009]SCI(E)[email protected]