DNA-Based Arthropod Diversity Assessment in Amazonian Iron Mine Lands Show Ecological Succession Towards Undisturbed Reference Sites

Christina Lynggaard,Douglas W Yu,Cecilio F Caldeira,Markus Gastauer,Martin R Ellegaard,Guilherme Oliveira,M Thomas P Gilbert,Kristine Bohmann,Silvio J Ramos

doi:10.3389/fevo.2020.590976

Abstract

Human activities change natural landscapes, and in doing so endanger biodiversity and associated ecosystem services. To reduce the net impacts of these activities, such as mining, disturbed areas are rehabilitated and restored. During this process, monitoring is important to ensure that desired trajectories are maintained. In the Carajás region of the Brazilian Amazon, exploration for iron ores has transformed the original ecosystem; natural forest and a savanna formation with lateritic iron duricrust outcrops named canga. Here, native vegetation is logged and topsoil removed and deposited in waste piles along with mine waste. During rehabilitation, these waste piles are hydroseeded with non-native plant species to achieve rapid revegetation. Further, seeds of native canga and forest plant species are planted to point ecological succession towards natural ecosystems. In this study, we investigate diversity and composition of the arthropod community along a post-mining rehabilitation and restoration gradient, taking seasonality and primer bias into account. We use DNA metabarcoding of bulk arthropod samples collected in both the dry and rainy seasons from waste-pile benches at various stages of revegetation: non-revegetated exposed soils, initial stage with one-to-three-year-old stands, intermediate stage with four-to-five-year-old stands, and advanced stage with six-to-seven-year-old stands. We use samples from undisturbed cangas and forests as reference sites. In addition, we vegetation diversity and structure were measured to investigate relations between arthropod community and vegetation structure. Our results show that, over time, the arthropod community composition of the waste piles becomes more similar to the reference forests, but not to the reference cangas. Nevertheless, even the communities in the advanced-stage waste piles are different from the reference forests, and full restoration in these highly diverse ecosystems is not achieved, even after 6 to 7 years. Finally, our results show seasonal variation in arthropod communities and primer bias.

Highlights

To minimise the negative impact of mining, and similar forms of disturbance, on biodiversity and ecosystem functioning, the mitigation hierarchy sets guidelines to prioritise the actions that should be taken (Rio Tinto, 2004; Bergès et al, 2020)
The number of operational taxonomic units (OTUs) detected per season and per primer set were as follows: for samples collected during the dry season, 327 OTUs for the Leray primer set and 205 OTUs with Zeale, and for samples collected during the rainy season, 234 OTUs using the Leray primer and 252 OTUs with the Zeale primer
As more OTUs and arthropod taxa were detected with the Leray primer and some of the community composition analyses show similar results, we report here the Leray primer results only

Summary

Introduction

To minimise the negative impact of mining, and similar forms of disturbance, on biodiversity and ecosystem functioning, the mitigation hierarchy (avoidance, minimisation, rehabilitation or restoration, and offsets) sets guidelines to prioritise the actions that should be taken (Rio Tinto, 2004; Bergès et al, 2020). Many countries have a statutory requirement to restore disturbed areas to their original states (SER, 2004) or to rehabilitate them [i.e., restitution of ecosystem structure and functioning, but with a different set of species than the initial ones (SER, 2004; Aronson et al, 2011)]. In order to measure whether biodiversity and/or ecosystem functioning are converging on designated reference (original-state) sites or are moving towards novel assemblages and/or sets of functions (Hobbs et al, 2009), areas under restoration and rehabilitation require monitoring (Derhé et al, 2016; McDonald et al, 2016). Despite the need for monitoring of these areas, no consensus has been reached about which environmental variables are the best indicators for measuring ecosystem state and change (Gastauer et al, 2018, 2020a). Arthropods can be used, as they directly make up a large proportion of terrestrial biodiversity and because arthropod species diversity and composition closely follow the diversity and composition of plant species (Basset et al, 2012; Zhang et al, 2016), providing a convenient way to measure both sets of taxa

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