Unraveling the spectral and biochemical response of mangroves to oil spills and biotic stressors.

Mangroves are prone to biotic and abiotic stressors of natural and anthropogenic origin, of which oil pollution is one of the most harmful. Yet the response of mangrove species to acute and chronic oil exposure, as well as to other stressors, remains barely documented. In this study, a non-destructive, non-invasive approach based on field spectroscopy is proposed to unravel these responses. The approach relies on tracking alterations in foliar traits (pigments, sugars, phenols, and specific leaf area) from reflectance data in the 400-2400 nm spectral range. Three mangrove species hit by two of the most notorious oil spills in Brazilian history (1983 and 2019) and various biotic stressors, including grazing, parasitism, and fungal disease, were investigated through field spectroscopy and machine learning. This study reveals strong intra- and interspecific variability of mangrove's spectral and biochemical responses to oil pollution. Trees undergoing acute exposure to oil showed stronger alterations of foliar traits than the chronically exposed ones. Alterations induced by biotic stressors such as parasitism, disease, and grazing were successfully discriminated from those of oil for all species based on Linear Discriminant Analysis (Overall Accuracy ≥76.40% and Kappa ≥0.70). Leaf chlorophyll, phenol, and starch contents were identified as the most relevant traits in stressor discrimination. The study highlights that oil spills affect mangroves uniquely, both acutely and chronically, threatening their global conservation.

Remote sensing reveals unprecedented sublethal impacts of a 40-year-old oil spill on mangroves.

Oil spills cause long-lasting mangrove loss, threatening their conservation and ecosystem services worldwide. Oil spills impact mangrove forests at various spatial and temporal scales. Yet, their long-term sublethal effects on trees remain poorly documented. Here, we explore these effects based on one of the largest oil spills ever recorded, the Baixada Santista pipeline leak, which hit the mangroves of the Brazilian southeastern coast in 1983. Historical, Landsat-derived normalized difference vegetation index (NDVI) maps over the spilled mangrove reveal a large dieback of trees within a year following the oil spill, followed by a eight-year recolonization period and a stabilization of the canopy cover, however 20-30% lower than initially observed. We explain this permanent loss by an unexpected persistence of oil pollution in the sediments based on visual and geochemical evidence. Using field spectroscopy and cutting-edge drone hyperspectral imaging, we demonstrate how the continuous exposure of mangrove trees to high levels of pollution affects their health and productivity in the long term, by imposing permanent stressful conditions. Our study also reveals that tree species differ in their sensitivity to oil, giving the most tolerant ones a competitive advantage to recolonize spilled mangroves. By leveraging drone laser scanning, we estimate the loss of forest biomass caused by the oil spill to be 9.8-91.2 t ha-1, corresponding to 4.3-40.1 t C ha-1. Based on our findings, we encourage environmental agencies and lawmakers to consider the sublethal effects of oil spills on mangroves in the environmental cost of these accidents. We also encourage petroleum companies to use drone remote sensing in monitoring routines and oil spill response planning to improve mangrove preservation and impact assessment.

Satellite evidence for pervasive water eutrophication in the Doce River reservoirs following the collapse of the Fundao dam in Brazil☆.

One of the worst socio-environmental disasters to mark the history of Brazil and the world occurred in November 2015 and involved the mining sector. The collapse of the Fundao dam released approximately 43 million m³ of iron ore tailings, which moved downstream to reach the Doce River. This resulted in the contamination of water, soil, and sediments along the entire course of the river, which also affected its mouth in the Atlantic Ocean. Four years after the disaster, several socio-environmental problems continue to persist in the affected areas. In this context, the reservoirs built along the Doce River deserve special attention as they are artificial environments that are highly vulnerable to changes in water parameters. This study aims to determine water quality indicators of these reservoirs using remote sensing data and image processing methods, including semi-analytical algorithms, to comprehend the progress of eutrophication processes. Operational land imager/Landsat-8 data (from 2013 to 2019) were used to map the suspended particulate matter (SPM), euphotic zone (Zeu) and chlorophyll-a (Chl-a) before and after the collapse. The results showed significant changes in SPM and Zeu in the reservoirs after the collapse. Non-conformity of these parameters is observed even now, and they tend to intensify during rainy periods when resuspension processes of sediments occur. Moreover, there has been an increase in the eutrophication of reservoirs as noticed by the significant increase in Chl-a after the disaster, especially in January, July, and August.

Possible contamination of the Abrolhos reefs by Fundao dam tailings, Brazil - New constraints based on satellite data.

The Fundão dam, located in Mariana city, Minas Gerais State, southeastern Brazil, collapsed in November 2015, causing the discharge of over 50 million m3 of iron ore tailings in the Doce river basin. The mud generated by the disaster was composed of fine particulates (silt and clay), which are more sensitive to wind dispersion. Based on laboratory analyses and hydrodynamic modeling, early research postulates the hypothesis that the mud discharged in the ocean traveled 10,000 km up north and may have reached the Abrolhos coral reefs. This research aims to investigate further this hypothesis based on broad-scale remotely sensed data. Satellite images were used to estimate the suspended particulate matter (SPM) in the coastal zone before, during, and after the dam collapse. Results indicate that higher concentrations of SPM appeared during and post-collapse and were restricted to the coastal zone and its shallower regions, including beaches. However, we demonstrate that under exceptional circumstances the wind blew to the north, carrying fine particulate material and potentially-toxic metals derived from the iron ore tailings towards the northeastern Brazilian coastline and possibly the reefs of the Abrolhos Bank.

An assessment of natural and manmade hazard effects on the underwater light field of the Doce River continental shelf.

Natural and manmade disasters have occurred more frequently due mainly to climate change and human pressure for productivity. One of the world's vastest disasters in the mining industry occurred due to the collapse of the Fundao dam, Brazil, which discharged about 43 million m3 of iron tailings at the Doce River basin. Extreme natural events also affect this region and provoke substantial mass movement and substantial floods in the Doce River basin, and flow of anomalous volumes of sediments in its mouth. The extent of tailings and the sediment flow in these events were approached in previous research. However, their effects on the penetration of sunlight into the water column in the coastal region are unknown. Here, we evaluate the effects of an extreme natural event and a manmade disaster on the light regime of the water column at the Doce River mouth, using remote sensing data. In both events, the spatial and temporal distribution of suspended particulate matter (SPM), diffuse light attenuation coefficient (Kd490) and Euphotic Zone (Zeu) were analyzed. During the natural event, light penetration into the water column was strongly attenuated (Kd490: 0.35 m-1; SPM: 8.81 g/m3) but re-established after 1 month due to sediment deposition. In the case of the dam collapse, the attenuation of light penetration was also intense along the event (Kd490: 0.34 m-1; SPM: 13.87 g/m3); however, sediment deposition occurred sooner. Re-suspension of sediments due to wind action was recurrent after 8 months of the dam collapse, in contrast to the natural event, where re-suspension was not perceptible in satellite images. The results indicate that both events have considerable effects on the penetration of light in the water column, but with different intensity and length.

Author Correction: Macro-scale ore-controlling faults revealed by micro-geochemical anomalies.

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Macro-scale ore-controlling faults revealed by micro-geochemical anomalies.

Whereas the mechanism of fluid flow, and thus structural control, linked with mineral deposit formation is quite understood, the specific structures that likely provided controls on mineralization at certain geographic scales are not readily known for a given region unless it is well-explored. This contributes uncertainty in mineral prospectivity analysis in poorly-explored regions (or greenfields). Here, because the spatial distribution of mineral deposits has been postulated to be fractals (i.e., the patterns of these features are self-similar across a range of spatial scales), we show for the first time that micro-geochemical anomalies (as proxies of micro-scale patterns of ore minerals), from few discrete parts of the Sossego iron-oxide copper-gold (IOCG) deposit in the Carajás Mineral Province (CMP) of Brazil, exhibit trends of macro-scale faults that are known to have controlled IOCG mineralization in the CMP. The methodology described here, which led to this novel finding, would help towards detecting mineral exploration targets as well as help towards understanding structural controls on mineralization in greenfields.

Publisher Correction: Geochemical constraints on the Hadean environment from mineral fingerprints of prokaryotes.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.