Contributions to the development of theoretical biology and of interdisciplinary directions at the interface between life sciences and earth system science

The goal of this thesis is to present the foundation, implementation, and future developments of a research program at the interface between biogeochemistry and ecotoxicology of heavy metals.

The method used to structure the thesis is that of the logic of the scientific discovery. I have extracted and grouped the contributions or the relevant parts of them into:

·       theoretical (provides the general background of empirical investigations, the framework to formulate hypotheses),

·       methodological (provides structured approaches for exploratory research and to formulate and test hypotheses),

·       field, and experimental research (takes place in the theoretical framework and implements the methodological approach)

·       mathematical modeling (allows the investigation of simplified formulations of the natural processes to detect the influence and relative importance of key variables), and

·       management and institutional development (whose success depends on all research aspects, from theoretical and methodological background to the soundness of empirical research, and the realism and awareness about the limitations of mathematical modeling).

The presented contributions span from 2005 to 2024. The originality of this thesis comes from the method of organization and presentation, underlining the coherence of the research program.

The main theoretical contributions are a reconstruction of the Darwinian law of growth with reproduction, a reconstruction of the potential socio-ecological complexity from the elementary productive processes, a conceptualization of the relationship between multi-scale productive processes at organismal, population and community scale, and the standard nested hierarchy of ecological systems, and a general concept of resilience.

The methodological contributions are an integrated technique for knowledge mapping and conceptual analysis, a framework for integrated modeling of metals biogeochemistry based on the standard nested hierarchy of ecological systems, a highly complex methodology for upscaling ecological processes from a relatively smaller community scale to larger target scale, a simpler complementary framework for integrated modeling based on coupled biological and abiotic processes occurring at different scales, and a methodological framework to study the resilience of biogeochemical services to heavy metals stress.

The empirical contributions published by now are in two directions, one related to scale-dependent patterns of the distribution of organisms in contaminated areas, and one consisting of experimental investigations of biogeochemical processes in soil-plant systems. In the first direction, we found that the decrease of richness in contaminated sites compared to reference sites seemed to be larger as the scale of the organism was smaller, in each site, and a positive correlation between the coefficient of variation of mites’ species richness (log-transformed) and the coefficient of variation of the scores extracted by PCA from in situ measurements of geochemical variables on the tailing surface in each station with a plot of 2 m². In the second direction, we investigated the leaching of elements from soil-plant systems, and the control of toxic elements, and P on plant oxidative stress. While these contributions focused on the effects of heavy metals and nutrients in the soil as independent variables, a complementary approach in the field was to look for the effect of morphometric plant traits on the properties of the vegetation cover controlling the water flow on a hillslope. We produced and published a TRL2 custom-oriented integrated tool-box of procedures/workflows and software modules for extraction of LIDAR metrics describing functional plant cover traits, deterministic models of processes describing the role of plants in the production of target ecosystem services, and coupled experimental and field scale investigations for validations and simulations.

The mathematical modeling started from the problem of including spatially explicit the role of vegetation in erosion models (and associated transport of heavy metals). This led to two complementary problems, one of porting data between scales (different discretization of the model), and one of the deterministic hydrological model with plant variables controlling the flow. We produced a data porting tool and demonstrated it on a model catchment using cellular automata of water flow without vegetation components and a 1D model accounting for the role of plants on the water flowing over hill-slopes, using vegetation porosity as a plant variable.

The environmental management contributions are in a classic nested hierarchy approach (approaches for the integrated monitoring of emergent ecosystem services and restoration of a large alluvial island), and in a multi-scale process approach (triggering an accelerated succession in contaminated areas by inoculation with microorganisms -kind of an eco-remediation technique coupling site scale and landscape scale measures, and a complex approach for catalyzing the development of ecosystems of innovation for environmental services – using bottom-up and top-down measures).

I used the conceptual and methodological results in a simplified form also to organize the teaching, especially by classifying the epistemic strategies reducing the complexity of productive processes in the complementary natural and social domains. At stake was to stimulate interdisciplinarity for solving complex missions instead of competition between experts specializing in various fields and sub-fields.

The future research lines of the research program are also on theoretical, methodological, empirical, mathematical modeling, environmental management, and institutional development directions. In the theoretical direction, we are interested in the comparative ontology of biological and environmental sciences (needed for integration in information systems) and the problem of how different is conceptualized time in different fields and sub-fields of research (with consequences on the up-scaling of complex processes). The methodological direction is coupled with the institutional development of a Critical zone Observatory for catchments with important industrial activity in their structure (including mining). Here we have an already funded Fulbright project and a large-scale project draft for an innovation ecosystem oriented towards the development of a cumulative-impact assessment method in catchments with multiple types of impacts. In this framework, we will implement exploratory projects (for instance one dedicated to the resilience of biogeochemical services to climate change stress, using a stoichiometric approach of elements retention in transversal and longitudinal buffer zones) and projects for technology development (for instance developing to TRL3 the already mentioned LIDAR-based technology).