Real-time model predictive and rule-based control with green infrastructures to reduce combined sewer overflows.

The impact of integrating large-scale distribution of green infrastructures (GIs) with different real-time control strategies on combined sewer overflows (CSOs) is assessed for the southern area of the City of Montreal's combined sewer system (Canada). An iterative process involving a synthetic design rainfall event and model predictive control (MPC) of the sewer system is developed to distribute GIs according to cost-efficiency and spatial analysis criteria. The distributed GIs are alternatively integrated with static, rule-based control (RBC) and MPC, for which model simulations are performed for a two-month period. The performance of the three strategies is compared in terms of CSO volume and frequency reductions, fulfillment of the outfall environmental priorities and transfer of runoff capture to CSO volume reduction. A gradual increase in GI implementation levels and an alternative scenario of GIs distribution are also considered to assess the performance of the two real-time control (RTC) strategies. By comparing the scenarios where GIs are uniformly distributed with those where no GIs are implemented and omitting the most extreme rainfall event, average CSO volume reduction is about 65%, 82% and 92%, respectively, for static control, RBC and MPC. Moreover, the scenario integrating GIs with MPC is the only one permitting to avoid almost all CSO events and the fulfilment of the outfall environmental priorities. GIs efficiency performance (the transferability between global runoff capture and CSO volume reduction) is also the highest under MPC, even when considering varying GI implementation levels and spatial distribution schemes.

Short-term N2 fixation kinetics in a moss-associated cyanobacteria.

N(2) fixation by moss-associated cyanobacteria plays an important role in the nitrogen cycling of terrestrial ecosystems. Recent studies have mainly focused on boreal ecosystems; little is known about such association in other ecosystems. Moss-associated cyanobacteria are subject to rapid changes (hourly or less) in environmental conditions that may affect N(2) fixation kinetics. Using a recently developed method (Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectroscopy, ARACAS) with higher sensitivity and sampling frequency than the conventional method, we characterize short-term kinetics of N(2) fixation by cyanobacteria on moss carpets from warm and cold temperate forests. We report the identification of a heretofore unknown multispecies true-moss-cyanobacteria diazotrophic association. We demonstrate that short-term change in abiotic variables greatly influences N(2) fixation. We also show that difference in relative proportion of two epiphytic diazotrophs is consistent with divergent influences of temperature on their N(2) fixation kinetics. Further research is needed to determine whether this difference is consistent with a latitudinal trend.