The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

/pdf/planetary-boundaries-guiding-human-development-on-a-changing-5gmf909etg.pdf

Planetary boundaries: Guiding human development on a changing planet

TiO2 photocatalysis and related surface phenomena

Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. We propose a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. We have identified nine planetary boundaries and, drawing upon current scientific understanding, we propose quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere <350 ppm and/or a maximum change of +1 W m-2 in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels); stratospheric ozone (<5% reduction in O3 concentration from pre-industrial level of 290 Dobson Units); biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation of N2 to 35 Tg N yr-1) and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural background weathering of P); global freshwater use (<4000 km3 yr-1 of consumptive use of runoff resources); land system change (<15% of the ice-free land surface under cropland); and the rate at which biological diversity is lost (annual rate of <10 extinctions per million species). The two additional planetary boundaries for which we have not yet been able to determine a boundary level are chemical pollution and atmospheric aerosol loading. We estimate that humanity has already transgressed three planetary boundaries: for climate change, rate of biodiversity loss, and changes to the global nitrogen cycle. Planetary boundaries are interdependent, because transgressing one may both shift the position of other boundaries or cause them to be transgressed. The social impacts of transgressing boundaries will be a function of the social-ecological resilience of the affected societies. Our proposed boundaries are rough, first estimates only, surrounded by large uncertainties and knowledge gaps. Filling these gaps will require major advancements in Earth System and resilience science. The proposed concept of "planetary boundaries" lays the groundwork for shifting our approach to governance and management, away from the essentially sectoral analyses of limits to growth aimed at minimizing negative externalities, toward the estimation of the safe space for human development. Planetary boundaries define, as it were, the boundaries of the "planetary playing field" for humanity if we want to be sure of avoiding major human-induced environmental change on a global scale.

/pdf/planetary-boundaries-exploring-the-safe-operating-space-for-ir5ysgjg96.pdf

Planetary boundaries: Exploring the safe operating space for humanity

Photoinduced reactivity of titanium dioxide

The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/10-1510.1

The value of estuarine and coastal ecosystem services

An assessment was made of biological phosphorus and nitrogen removal and related sludge bulking control in both intermittent cyclic and continuous activated sludge systems. Experimental results from a laboratory-scale investigation using fermented domestic sewage indicated the advantages of achieving high levels of P and N removal and good sludge-settling properties using the intermittent cyclic process, as compared to the continuous process. The modified intermittently fed and decanted system incorporating non-mixing sequences produced an effluent quality of NO3-N 60 mg L-1, TP-9 mg L-1 and RBCOD < 30 mg L-1). In contrast, the modified 4-stage Bardenpho process could not achieve effluent NO3-N and PO4-P concentrations of < 10 and < 1 mg L-1, respectively. The sludge volume index (SVI) values were always higher than 250 mL g-1 and occasionally reached as high as 422 mL g-1. The causative filaments were low F:M growers - Types 0041/0675.

A comparison of biological nutrient removal in intermittent cyclic and continuous activated sludge systems

Performance evaluation of hybrid and conventional sequencing batch reactor and continuous processes.

Phenol biodegradation in a fluidized-bed biofilm reactor was studied. A biofilm model was derived based on reaction-diffusion considerations and was used in conjunction with the fluidized bed reactor flow model to predict the substrate removal in the reactor. A method was developed to evaluate the active biomass in the reactor. The models were verified experimentally and good agreement was found between predicted and observed substrate removal in the reactor. A combination of orthogonal collocation and Rungi-Kutta-Gill techniques was used to solve the fluidized bed reactor models.

Unified Models for Phenol Degradation in a Fluidized Bed Biofilm Reactor

Vermicompost filtration is a new on-site waste treatment system. Consequently, little is known about the filter medium properties. The aim of this preliminary study was to quantify physical and compositional properties of vermicompost filter beds that had been used to treat domestic solid organic waste and wastewater. This paper presents the trials performed on pilot-scale reactors filled with vermicompost from a full-scale vermicompost filtration system. Household solid organic waste and raw wastewater at the rate of 130 L/m2/d was applied to the reactor bed surface over a four-month period. It was found that fresh casts laid on the bed surface had a BOD of 1290 mg/g VS while casts buried to a depth of 10 cm had a BOD of 605 mg/g VS. Below this depth there was little further biodegradation of earthworm casts despite cast ages of up to five years. Solid material in the reactor accounted for only 7-10% of the reactor volume. The total voidage comprised of large free-draining pores, which accounted for 15-2...

Characterizing The Physical And Chemical Properties of a Vermicompost Filter Bed

To optimize the use of knowledge when selecting R&D projects for technology-based innovation, all possible techniques - whether based on mathematical programming, or behavior, organization and information, or strategic consistency and integration - should be considered. We present a readily operationalized and flexible approach to this task, under which different project selection techniques are rendered comparable with reference to the normative methodology in economics and relevance to a core-model description of the real world in any application.

Paul F. Greenfield

Papers

A comparison of biological nutrient removal in intermittent cyclic and continuous activated sludge systems

Performance evaluation of hybrid and conventional sequencing batch reactor and continuous processes.

Unified Models for Phenol Degradation in a Fluidized Bed Biofilm Reactor

Characterizing The Physical And Chemical Properties of a Vermicompost Filter Bed

Selecting R&D projects for technology-based innovation: An application of the core model approach