Water table fluctuations in the riparian zone: comparative results from a pan-European experiment

International audienceSoil saturation is known to be of crucial importance to denitrification and other nitrogen cycling processes within the riparian zone. Since denitrification potential generally increases towards the soil surface, water table elevation can control the degree to which nitrate reduction is optimised. Given their topographic location and sedimentary structure, most floodplains are characterised by high water tables. However, detailed field data on water table levels, hydraulic gradients and flow patterns within the riparian zone are generally lacking. This paper presents data collected as part of a pan-European study of nitrate buffer zones, the Nitrogen Control by Landscape Structures in Agricultural Environments project (NICOLAS). An identical experimental design was employed at each site, allowing riparian zone hydrology and nitrogen cycling processes to be explored across a wide range of temperate climates; only the hydrological data are discussed here. A grid of dipwells at 10-metre spacing was installed at each site and manual measurements made at least once a month for a minimum of one year. In addition, at least one dipwell in each grid was monitored continuously using a data logger. All the riparian zones studied displayed a clear annual cycle of water table elevation, although other factors seemed equally important in influencing the range of variation. Where the riparian zone was flat, the water level in the adjoining river or lake proved more significant in controlling water table levels within the riparian zone than was originally anticipated.

Water table fluctuations in the riparian zone: comparative results from a pan-European experiment

Soil saturation is known to be of crucial importance to denitrification and other nitrogen cycling processes within the riparian zone. Since denitrification potential generally increases towards the soil surface, water table elevation can control the degree to which nitrate reduction is optimised. Given their topographic location and sedimentary structure, most floodplains are characterised by high water tables. However, detailed field data on water table levels, hydraulic gradients and flow patterns within the riparian zone are generally lacking. This paper presents data collected as part of a pan-European study of nitrate buffer zones, the Nitrogen Control by Landscape Structures in Agricultural Environments project (NICOLAS). An identical experimental design was employed at each site, allowing riparian zone hydrology and nitrogen cycling processes to be explored across a wide range of temperate climates; only the hydrological data are discussed here. A grid of dipwells at 10-metre spacing was installed at each site and manual measurements made at least once a month for a minimum of one year. In addition, at least one dipwell in each grid was monitored continuously using a data logger. All the riparian zones studied displayed a clear annual cycle of water table elevation, although other factors seemed equally important in influencing the range of variation. Where the riparian zone was flat, the water level in the adjoining river or lake proved more significant in controlling water table levels within the riparian zone than was originally anticipated

Strategy for the management of complex retinal detachments: the European vitreo-retinal society retinal detachment study report 2

OBJECTIVE: To study the outcome of the treatment of complex rhegmatogenous retinal detachments (RRDs). DESIGN: Nonrandomized, multicenter, retrospective study. PARTICIPANTS: One hundred seventy-six surgeons from 48 countries spanning 5 continents reported primary procedures for 7678 RRDs. METHODS: Reported data included clinical manifestations, the method of repair, and the outcome. MAIN OUTCOME MEASURES: Failure of retinal detachment repair (level 1 failure rate), remaining silicone oil at the study's conclusion (level 2 failure rate), and need for additional procedures to repair the detachments (level 3 failure rate). RESULTS: The main categories of complex retinal detachments evaluated in this investigation were: (1) grade B proliferative vitreoretinopathy (PVR; n = 917), (2) grade C-1 PVR (n = 637), (3) choroidal detachment or significant hypotony (n = 578), (4) large or giant retinal tears (n = 1167), and (5) macular holes (n = 153). In grade B PVR, the level 1 failure rate was higher when treated with a scleral buckle alone versus vitrectomy (P = 0.0017). In grade C-1 PVR, there was no statistically significant difference in the level 1 failure rate between those treated with vitrectomy, with or without scleral buckle, and those treated with scleral buckle alone (P = 0.7). Vitrectomy with a supplemental buckle had an increased failure rate compared with those who did not receive a buckle (P = 0.007). There was no statistically significant difference in level 1 failure rate between tamponade with gas versus silicone oil in patients with grade B or C-1 PVR. Cases with choroidal detachment or hypotony treated with vitrectomy had a significantly lower failure rate versus treatment with scleral buckle alone (P = 0.0015). Large or giant retinal tears treated with vitrectomy also had a significantly lower failure rate versus treatment with scleral buckle (P = 7×10(-8)). CONCLUSIONS: In patients with retinal detachment, when choroidal detachment, hypotony, a large tear, or a giant tear is present, vitrectomy is the procedure of choice. In retinal detachments with PVR, tamponade with either gas or silicone oil can be considered. If a vitrectomy is to be performed, these data suggest that a supplemental buckle may not be helpful. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article