Chemical and biological signatures of water and fluxes from clouds to rivers at the watershed level in a natural context.

Abstract:

The connectivity of environmental compartments through chemical and biological exchanges is often difficult to study. However, understanding the functioning of fluxes is essential in the context of climate change and the assessment of anthropogenic impacts. These exchanges can be realized through water cycle fluxes establishing interactions between the atmosphere, surface water and land.

To examine the interactions between the atmosphere, surface water and land via water fluxes, we conducted a large scale field study at the watershed level, involving multiple disciplines from chemistry to meteorology and microbiology. The chemical and biological contents of water from the atmosphere (cloud and rain), to mid-mountain hydrological continuum (streams, wetlands and lake) and soil (agricultural plots) were assessed in the natural and agricultural area from Puy De Dôme (Central France) along an altitudinal gradient from puy de Dôme Mountain summit (1465 m asl) to the plain (~ 600 m asl). We set up experimental procedures for sampling, handling and analysing each environmental matrix, and the environmental context was characterized through meteorological and hydrological measurements and models. The biological and chemical variables included: isotopes of water (¹H/²H and ¹⁶O/¹⁸O; laser spectroscopy), major ions (Na⁺, NH4⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, NO₃^-, SO₄^-, IC), amino acids (LC-MS), bacterial diversity (16S metabarcoding and high-throughput sequencing) and microbial enzymatic activity associated with the nitrogen, carbon and phosphorus cycles (fluorimetric activity assays for whole Beta-Glucosidase, Leucine Aminopeptidase and Phosphatase activities).

The multi-compartment analysis revealed significant differences between the compartments by the chemical variables, highlighting the compartment specificity. We estimated a chemical flux of major ions and amino acids from the atmosphere to the surface (soil and surface water). Bacterial diversity analysis showed a core community in these compartments, confirming their connectivity. Thereafter, we tried to explain bacterial diversity by the chemical variables from the studied compartments. Our analysis on microbial enzymatic activity showed an enzymatic activity associated with the nitrogen, carbon and phosphorus cycles in clouds and rain.

Here, our study contributes to the understanding of atmosphere-surface interaction through field observations and atmospheric models and we attempted to better understand environmental fluxes. Our field study emphasized the importance of considering the interaction of environmental compartments in future investigations for future and gobal assessments of anthropogenic impacts, such as agrosystem effects to natural ecosystems.

 

Key words:

Field observations, Environmental interaction, Chemical flux, Microbial diversity, Atmosphere, Surface water, Soil.