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Aybar, M., Perez-Calleja, P., Li, M., Pavissich, J. P., & Nerenberg, R. (2019). Predation creates unique void layer in membrane-aerated biofilms. Water Res., 149, 232–242.
Abstract: The membrane-aerated biofilm reactor (MABR) is a novel wastewater treatment technology based on oxygen-supplying membranes. The counter diffusion of oxygen and electron donors in MABRs leads to unique behavior, and we hypothesized it also could impact predation. We used optical coherence tomography (OCT), microsensor analyses, and mathematical modeling to investigate predation in membrane-aerated biofilms (MABs). When protozoa were excluded from the inoculum, the MAB's OCT-observable void fraction was around 5%. When protozoa were included, the void fraction grew to nearly 50%, with large, continuous voids at the base of the biofilm. Real-time OCT imaging showed highly motile protozoa in the voids. MABs with protozoa and a high bulk COD (270 mg/L) only had 4% void fraction. DNA sequencing revealed a high relative abundance of amoeba in both high and low-COD MABs. Flagellates were only abundant in the low-COD MAB. Modeling also suggested a relationship between substrate concentrations, diffusion mode (co- or counter-diffusion), and bioflim void fraction. Results suggest that amoeba proliferate in the bioflim interior, especially in the aerobic zones. Voids form once COD limitation at the base of MABs allows predation rates to exceed microbial growth rates. Once formed, the voids provide a niche for motile protozoa, which expand the voids into a large, continuous gap. This increases the potential for biofilm sloughing, and may have detrimental effects on slow-growing, aerobic microorganisms such as nitrifying bacteria. (C)2018 Elsevier Ltd. All rights reserved.
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Billi, M., Mascareno, A., Henriquez, P. A., Rodriguez, I., Padilla, F., & Ruz, G. A. (2022). Learning from crises? The long and winding road of the salmon industry in Chiloe Island, Chile. Mar. Pol., 140, 105069.
Abstract: The rapid development of salmon aquaculture worldwide and the growing criticism of the activity in recent decades have raised doubts about the capacity of the sector to learn from its own crises. In this article, we assess the discursive, behavioral and outcome performance dimensions of the industry to identify actual learning and lessons to be learned. We focus on the case of Chiloe Island, Chile, a global center of salmon production since 1990 that has gone through two severe crises in the last 15 years (2007-2009 ISAV crisis and 2016 red tide crisis). On the basis of a multi-method approach combining qualitative analysis of interviews and statistical data analysis, we observe that the industry has discursively learned the relevance of both self-regulation and the wellbeing of communities. However, at the behavioral and outcome performance levels, the data show a highly heterogeneous conduct that questions the ability of the sector as a whole to learn from crises. We conclude that detrimental effects for ecosystems and society will increase if learning remains at the level of discourses. Without significant changes in operational practices and market performance there are no real perspectives for the sustainability of the industry. This intensifies when considering the uneven responses to governance mechanisms. The sector needs to adapt its factual performance to sustainable goals and reflexively monitor this process. The first step for achieving this is to produce reliable data to make evidence-based decisions that align the operational dynamics of the entire sector with a more sustainable trajectory in the near future, as well as advancing towards hybrid and more reflexive governance arrangements.
Keywords: Crisis; Learning; Discourse; Behavior; Outcome performance; Aquaculture; Salmon industry; Governance; Regulation
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Mascareno, A., Cordero, R., Azocar, G., Billi, M., Henriquez, P. A., & Ruz, G. A. (2018). Controversies in social-ecological systems: lessons from a major red tide crisis on Chiloe Island, Chile. Ecol. Soc., 23(4), 25 pp.
Abstract: Connecting the discussions on resilience and governance of social-ecological systems (SESs) with the sociological analysis of social controversies, we explore a major red tide crisis on Chiloe Island, southern Chile, in 2016. Theoretically, we argue that controversies not only are methodological devices for the observation of the complex relations between nature and society in moments of crisis, but also are materially embedded in the SES dynamics and can work for or against systemic resilience. Empirically, we show that Chiloe's SES is an unstable regime prone to sudden shifts and identify the configuration of different lock-in mechanisms expressed in the reproduction of structural fragilities over the last three decades. From the examination of the social controversies on the 2016 red tide crisis, we draw several lessons. First, there is a complex interplay of visible and hidden fragilities of Chiloe's SES that, while being ignored or their resolution postponed to the future, materialize in the daily experience of inhabitants as a series of historical disappointments. Second, the unfolding of Chiloe's social-ecological crises involves epistemic disputes not only over concrete events but also on the very construction of the SES as a social-natural reality. In turn, this creates conditions for the emergence of strategic alignments between local, national, and transnational actors and shows the extent to which the socio-political articulation of knowledge may contribute to either improve or block the governance of the SES. Third, the social resources that came to light with the controversies reveal pathways for improving the governance regime of Chiloe Island's SES. This dimension highlights the normative relevance of commitments to recognize multiple scales of knowledge and articulate a plurality of actors in a nonhierarchical logic of cooperation.
Keywords: Chiloe Island; controversy; governance; regime shift; resilience; salmon aquaculture
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Mascareno, A., Henriquez, P. A., Billi, M., & Ruz, G. A. (2020). A Twitter-Lived Red Tide Crisis on Chiloe Island, Chile: What Can Be Obtained for Social-Ecological Research through Social Media Analysis? Sustainability, 12(20), 38 pp.
Abstract: Considering traditional research on social-ecological crises, new social media analysis, particularly Twitter data, contributes with supplementary exploration techniques. In this article, we argue that a social media approach to social-ecological crises can offer an actor-centered meaningful perspective on social facts, a depiction of the general dynamics of meaning making that takes place among actors, and a systemic view of actors' communication before, during and after the crisis. On the basis of a multi-technique approach to Twitter data (TF-IDF, hierarchical clustering, egocentric networks and principal component analysis) applied to a red tide crisis on Chiloe Island, Chile, in 2016, the most significant red tide in South America ever, we offer a view on the boundaries and dynamics of meaning making in a social-ecological crisis. We conclude that this dynamics shows a permanent reflexive work on elucidating the causes and effects of the crisis that develops according to actors' commitments, the sequence of events, and political conveniences. In this vein, social media analysis does not replace good qualitative research, it rather opens up supplementary possibilities for capturing meanings from the past that cannot be retrieved otherwise. This is particularly relevant for studying social-ecological crises and supporting collective learning processes that point towards increased resilience capacities and more sustainable trajectories in affected communities.
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Pavissich, J. P., Li, M., & Nerenberg, R. (2021). Spatial distribution of mechanical properties in Pseudomonas aeruginosa biofilms, and their potential impacts on biofilm deformation. Biotechnol. Bioeng., 118(4), 1564–1575.
Abstract: The mechanical properties of biofilms can be used to predict biofilm deformation under external forces, for example under fluid flow. We used magnetic tweezers to spatially map the compliance of Pseudomonas aeruginosa biofilms at the microscale, then applied modeling to assess its effects on biofilm deformation. Biofilms were grown in capillary flow cells with Reynolds numbers (Re) ranging from 0.28 to 13.9, bulk dissolved oxygen (DO) concentrations from 1 mg/L to 8 mg/L, and bulk calcium ion (Ca2+) concentrations of 0 and 100 mg CaCl2/L. Higher Re numbers resulted in more uniform biofilm morphologies. The biofilm was stiffer at the center of the flow cell than near the walls. Lower bulk DO led to more stratified biofilms. Higher Ca2+ concentrations led to increased stiffness and more uniform mechanical properties. Using the experimental mechanical properties, fluid‐structure interaction models predicted up to 64% greater deformation for heterogeneous biofilms, compared to a homogeneous biofilms with the same average properties. However, the deviation depended on the biofilm morphology and flow regime. Our results show significant spatial mechanical variability exists at the microscale, and that this variability can potentially affect biofilm deformation. The average biofilm mechanical properties, provided in many studies, should be used with caution when predicting biofilm deformation.
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