RESUMO
The physical and biological attributes of riverine ecosystems interact in a complex manner which can affect the hydrodynamic behaviour of the system. This can alter the mixing characteristics of a river at the sediment-water interface. Research on hyporheic exchange has increased in recent years driven by a greater appreciation for the importance of this dynamic ecotone in connecting and regulating river systems. An understanding of process-based interactions driving hyporheic exchange is still limited, specifically the feedbacks between the physical and biological controlling factors. The interplay between bed morphology and sediment size on biofilm community development and the impact on hyporheic exchange mechanisms, was experimentally considered. Purpose built recirculating flume systems were constructed and three profiles of bedform investigated: i) flat, ii) undulating λ = 1 m, ii) undulating λ = 0.2 m, across two different sized sediments (0.5 mm and 5 mm). The influence of biofilm growth and bedform interaction on hyporheic exchange was explored, over time, using discrete repeat injections of fluorescent dye into the flumes. Hyporheic exchange rates were greatest in systems with larger sediment sizes (5 mm) and with more bedforms (undulating λ = 0.2). Sediment size was a dominant control in governing biofilm growth and hyporheic exchange in systems with limited bedform. In systems where bedform was prevalent, sediment size and biofilm appeared to no longer be a control on exchange due to the physical influence of advective pumping. Here, exchange rates within these environments were more consistent overtime, despite greater microbial growth. As such, bedform has the potential to overcome the rate limiting effects of biotic factors on hyporheic exchange and sediment size on microbial penetration. This has implications for pollutant and nutrient penetration; bedforms increase hydrological connectivity, generating the opportunity to support microbial communities at depth and as such, improve the self-purification ability of river systems.
Assuntos
Microbiota , Rios , Biofilmes , Sedimentos Geológicos , HidrologiaRESUMO
Management of mild dyskaryosis remains controversial. In this study, we compared the cost-effectiveness of active versus conservative colposcopic management of women presenting with mild dyskaryosis in two different hospital settings. All women presenting in 2001 with a mild dyskaryotic smear and requiring colposcopy were studied in two different clinical settings (70 women at Darent Valley Hospital (DVH) and 327 at St George's Hospital (SGH)). At DVH, treatment is offered should there be any evidence of cervical intraepithelial neoplasia (CIN). On the other hand, a more conservative approach of cytological and colposcopical follow-up is offered to patients with evidence of low-grade disease at SGH. The outcome of both groups of patients was determined in terms of the number of colposcopy visits per patient, the risk of missing disease as a consequence of patients lost to follow-up and hospital costs as well as costs to patient over a four-year period. The majority (70%) of DVH patients had 1-2 colposcopy visits whereas the majority (60%) of SGH patients had 3-7 visits. At SGH 44% of untreated patients were lost to follow-up and an unknown number of those might have had high-grade disease. Active management is more cost-effective compared with conservative management ( pound323 and pound589 as cost per patient effectively treated in the two hospitals respectively). In conclusion, active management of low-grade disease is associated with lower hospital and patient costs compared with the conservative strategy.
