Sediment chemistry and nutrient influx in a hydrologically restored bottomland hardwood forest in Midwestern USA

Exchanges of total N and C between a river and its floodplain forest have been enhanced by sedimentation processes during flood pulses at a 5‐ha bottomland hardwood forest located at the Olentangy River Wetland Research Park in central Ohio. In the spring of 2000, the forest was hydrologically restored by notching an artificial levee that had separated the Olentangy River and its floodplain forest for 100 years. One‐hundred flat sediment traps (30 cm × 30 cm) were used to collect sediment samples during spring/summer flooding events from 2003 to 2005. Results showed that sediment deposition is determined by the landscape variability during flooding events, Net sediment deposit in the wettest area averaged 134 ± 12 g‐dry wt m^?2 in 2003, 127 ± 17 g‐dry wt m^?2 in 2004 and 149 ± 23 g‐dry wt m^?2 in 2005. Total N and C sedimentation ranged from 0.49 to 0.92 g‐N m^?2 and 5.2 to 19.9 g‐C m^?2. Fe dominates the sediment chemistry and results show the elemental abundance in the order of Al > Fe > Ca > K > Mg > S > P > Na > Mn > Zn > B > Cu > Mo. A hydrologic pulsing index (HPI) could be used as an indicator for mass changes of energies with hydrologic pulsing events. Restoration of seasonally flooded bottomland forests could stimulate potentially large nutrient and Fe releases, which would eventually lead to an enhanced forest productivity and biodiversity. Copyright © 2007 John Wiley & Sons, Ltd.     

Correction to: How to model and prove hybrid systems with KeYmaera: a tutorial on safety

International Journal on Software Tools for Technology Transfer -     

Pegasus: sound continuous invariant generation

Formal Methods in System Design - Continuous invariants are an important component in deductive verification of hybrid and continuous systems. Just like discrete invariants are used to reason about...     

Tactical contract composition for hybrid system component verification

We present an approach for hybrid systems that combines the advantages of component-based modeling (e.g., reduced model complexity) with the advantages of formal verification (e.g., guaranteed contract compliance). Component-based modeling can be used to split large models into multiple component models with local responsibilities to reduce modeling complexity. Yet, this only helps the analysis if verification proceeds one component at a time. In order to benefit from the decomposition of a system into components for both modeling and verification purposes, we prove that the safety of compatible components implies safety of the composed system. We implement our composition theorem as a tactic in the KeYmaera X theorem prover, allowing automatic generation of a KeYmaera X proof for the composite system from proofs for the components without soundness-critical changes to KeYmaera X. Our approach supports component contracts (i.e., input assumptions and output guarantees for each component) that characterize the magnitude and rate of change of values exchanged between components. These contracts can take into account what has changed between two components in a given amount of time since the last exchange of information.     

How to model and prove hybrid systems with KeYmaera: a tutorial on safety

This paper is a tutorial on how to model hybrid systems as hybrid programs in differential dynamic logic and how to prove complex properties about these complex hybrid systems in KeYmaera, an automatic and interactive formal verification tool for hybrid systems. Hybrid systems can model highly nontrivial controllers of physical plants, whose behaviors are often safety critical such as trains, cars, airplanes, or medical devices. Formal methods can help design systems that work correctly. This paper illustrates how KeYmaera can be used to systematically model, validate, and verify hybrid systems. We develop tutorial examples that illustrate challenges arising in many real-world systems. In the context of this tutorial, we identify the impact that modeling decisions have on the suitability of the model for verification purposes. We show how the interactive features of KeYmaera can help users understand their system designs better and prove complex properties for which the automatic prover of KeYmaera still takes an impractical amount of time. We hope this paper is a helpful resource for designers of embedded and cyber–physical systems and that it illustrates how to master common practical challenges in hybrid systems verification.     

A formally verified hybrid system for safe advisories in the next-generation airborne collision avoidance system

The Next-Generation Airborne Collision Avoidance System (ACAS X) is intended to be installed on all large aircraft to give advice to pilots and prevent mid-air collisions with other aircraft. It is currently being developed by the Federal Aviation Administration (FAA). In this paper, we determine the geometric configurations under which the advice given by ACAS X is safe under a precise set of assumptions and formally verify these configurations using hybrid systems theorem proving techniques. We consider subsequent advisories and show how to adapt our formal verification to take them into account. We examine the current version of the real ACAS X system and discuss some cases where our safety theorem conflicts with the actual advisory given by that version, demonstrating how formal hybrid systems proving approaches are helping to ensure the safety of ACAS X. Our approach is general and could also be used to identify unsafe advice issued by other collision avoidance systems or confirm their safety.     

Applying science to conservation and restoration of the world's wetlands.

The world has an estimated 7 to 9 million km2 of wetlands which can be defined through their hydrology, physiochemical environment, and biota. Many human cultures have lived in harmony with wetland environments for centuries. Many others have not, resulting in drainage or severe impact of wetlands throughout the world. Conservation of wetlands needs to be a priority for the cultural and ecological values they provide. But a more optimistic note is that large-scale restoration and re-creation of wetlands and riverine systems is beginning to happen throughout the world through ecological engineering. Examples of large-scale wetland restoration projects are presented for Delaware Bay, the Skjern River (Denmark), Florida Everglades, Louisiana Delta, the Mississippi River Basin, and the Mesopotamian Marshlands of Iraq.     

Effects of recycled FGD liner material on water quality and macrophytes of constructed wetlands: a mesocosm experiment

We investigated the use of flue-gas-desulfurization (FGD) by-products from electric power plant wet scrubbers as liners in wetlands constructed to improve water quality. Mesocosm experiments were conducted over two consecutive growing seasons with different phosphorus loadings. Wetland mesocosms using FGD liners retained more total and soluble reactive phosphorus, with lower concentrations in the leachate (first year) and higher concentrations in the surface water (second year). Leachate was higher in conductivity (second year) and pH (both years) in lined mesocosms. Surface outflow did not reveal any significant difference in physicochemical characteristics between lined and unlined mesocosms. There was no significant difference in total biomass production of wetland plants between lined and unlined mesocosms although lower average stem lengths and fewer stems bearing flowers were observed in mesocosms with FGD liners. Potentially phytotoxic boron was significantly higher in the belowground biomass of plants grown in lined mesocosms with low phosphorus loading. A larger-scale, long-term wetland experiment close to full scale is recommended from this two-year mesocosm study to better predict the potentially positive and negative effects of using FGD by-products in constructed wetlands.