This thesis assesses the impacts of climate change on the CEH River Lambourn Observatory, Boxford, UK. This comprises a 10 ha chalk valley, riparian wetland and 600 m of the River Lambourn, designated for its conservation value and scientific interest. A field campaign targeted knowledge gaps in previous research to enable development of a conceptual model of hydrological functioning. The physically based, distributed model MIKE SHE was chosen to simulate hydrology due to flexibility in process representation and proven applicability to wetland hydrology. Model results were consistent with field observations and confirmed the conceptual model. Findings showed that groundwater/surface-water interaction dominates hydrological processes. Channel head boundaries broadly control water levels across the wetland. Areas of groundwater upwelling control discrete head elevations and contain high concentrations of nitrate. These support confined growth of Carex paniculata surrounded by poor fen communities in reducing higher-phosphate waters. In-channel macrophyte growth and its management through cutting acutely affect water levels. Impacts of climate change were assessed by driving the MIKE SHE model with projected changes in hydrometeorological inputs for the 2080s, derived from UKCP09. Areas of groundwater upwelling caused amplified response of water levels at distinct locations. Simulated water levels were linked to requirements of the MG8 plant community and Desmoulin’s whorl snail (Vertigo moulinsiana). Impacts on each differed spatially, in line with hydrological impacts. The PHABSIM habitat modelling methodology was modified to assess river habitat response for brown trout (Salmo trutta), using outputs from the 1D hydraulic component of MIKE SHE, MIKE 11. Reductions in habitat availability were pronounced through periods of low flows, more so for adult than juvenile trout. Different hydrological requirements for species in distinct areas of the site support separate management strategies. Multiple objective management may be achieved through adaptive modification of the current management regime
