Performance assessment of a soil and water bioengineering work on the basis of the flora development and its associated ecosystem processes

Abstract

The Atlantic Forest of Brazil is one of the world's 25 biodiversity hotspots, but floodplains in this region are continuously converted into agricultural or urban areas, and riverine ecosystems are affected by anthropogenic interventions. Soil and water bioengineering techniques are a component of ecological engineering that can provide nature-based solutions as an alternative or as complementary measures to conventional hydraulic or civil engineering approaches. However, there is a lack of post-evaluation of interventions and there are still great difficulties in identifying valid evaluation criteria and measurement variables, especially in countries like Brazil where soil and water bioengineering measures have only been implemented in the last decade. Another limitation to the widespread application of the techniques is the lack of knowledge about their technical performance, their impact on ecological processes and the evolution of the species used. This study aims to investigate the development of species, evaluate the technical performance of the intervention and assess the ecological benefits and processes of one of the first soil and water bioengineering riparian restoration interventions in Brazil, which was carried out in 2010 on the Pardinho river. Parameters on bank stability, development of species used in different construction techniques and its ecological benefits and ecological processes (plant species and soil fauna richness and diversity, ecological group and recruitment species, invasive species, soil organic matter and soil temperature) were collected over a period of ten years. The study proved that soil and water bioengineering works can both stabilise and control erosion, and at the same time initiate ecological processes on degraded riverbanks. The active introduction of native species has promoted vegetation succession, increased the biodiversity of both plants and soil fauna on the site and improved the site conditions. The establishment of native vegetation led to sediment and organic material deposition, which changed the local ecological conditions (e.g., soil properties, light, flow conditions) and thus facilitated rapid establishment of other plants and re-established interactions between plants and soil fauna groups. This study provides a monitoring approach which examines the technical performance of the measures and species used, as well as their impact on the ecological process over time, which is essential for establishing soil and water bioengineering techniques as the standard in the field of river engineering in Brazil. Furthermore, the results obtained will help in planning and designing future works in the field of soil and water bioengineering in Brazil, adding to the knowledge of the techniques and species to be selected, as well as supporting the evaluation of the success of interventions.