Worldwide retention of nutrient silicon by river damming: From sparse data set to global estimate

© American Geophysical UnionDamming of rivers represents a major anthropogenic perturbation of the hydrological cycle, with the potential to profoundly modify the availability of nutrient silicon (Si) in streams, lakes, and coastal areas. A global assessment of the impact of dams on river Si fluxes, however, is limited by the sparse data set on Si budgets for reservoirs. To alleviate this limitation, we use existing data on dissolved Si (DSi) retention by dams to calibrate a mechanistic model for the biogeochemical cycling of DSi and reactive particulate Si (PSi) in reservoir systems. The model calibration yields a relationship between the annual in-reservoir siliceous primary productivity and the external DSi supply. With this relationship and an estimate of catchment Si loading, the model calculates the total reactive Si (RSi=DSi+PSi) retention for any given reservoir. A Monte Carlo analysis accounts for the effects of variations in reservoir characteristics and generates a global relationship that predicts the average reactive Si retention in reservoirs as a function of the water residence time. This relationship is applied to the Global Reservoirs and Dams database to estimate Si retention by damming worldwide. According to the results, dams retain 163 Gmol yr(-1) (9.8 Tg SiO2 yr(-1)) of DSi and 372 Gmol yr(-1) (22.3 Tg SiO2 yr(-1)) of RSi, or 5.3% of the global RSi loading to rivers.Canada Excellence Research Chair (CERC) program; Ontario Graduate Scholarships (OGS) progra

Clinical benefit and improvement of activity level after reconstruction surgery of Charcot feet using external fixation: 24-months results of 292 feet

Background: Reconstruction of Charcot feet remains a surgical challenge. The goal of this study was to investigate safety and clinical benefit from reconstruction of Charcot feet using an external fixator. There is limited valid data regarding long-term outcomes for Charcot foot procedures. Methods: In a retrospective study, 292 Charcot feet (282 patients) undergoing reconstructive procedures in our clinic from 1996-2010 were included (93 female, 189 male, mean age 57.9 years). Average follow-up was 24.1 months. Exclusion criteria were previous major amputation on the same side. All patients underwent surgery using a Hoffmann II external fixator for six to eight weeks with offloading. The fixator was then removed, and a customized AFO with full weight bearing was applied for another 11 months. After one year, patients received customized orthopedic shoes. Results: Initial amputations were avoided. Patient activity improved significantly by more than 1 level (SD 0.67, p <.001) according to the Hoffer activity score for lower limb amputees. The most common minor complication was persistent or recurrent ulceration in 67 feet (23%). Secondary amputation (after failure of external fixation) was required in only 12 patients (6.2%). Orthopedic shoes were used by approximately 34% of patients 18 months after surgery. Conclusions: Reconstructive surgery of Charcot feet using external fixation is a safe and economically feasible procedure. Activity levels improved significantly by more than 1 level (p < 0.01), severe complications were rare, and secondary amputation was required in only 12 patients (6.2%) of a high-risk patient population. Use of an external fixator offers the advantage that all extraneous material is removed after six weeks; thus, there is no risk of broken screws or plates and the associated potential complications