An integrative perspective to predict the performance of the riverine bioreactor

Streams and rivers act as truly bioreactors with an impressive capacity to process with great efficiency diverse organic substrates. The capacity and performance of the riverine bioreactor is determined in turn by the structure of riverine communities, the energy transfer along trophic levels, and the multiple interactions among biotic and environmental factors. Nevertheless, such a complex interplay of variables obscures our mechanistic and predictive knowledge on the riverine bioreactor functioning worldwide.

Ignacio Peralta-Maraver (@peralta_maraver) and Isabel Reche (@isabel_reche_c) from MNAt and the Ecology Department, propose a novel analytical approach to assess (and even predict) the decomposition capacity of the riverine systems, based on established concepts from the metabolic theory of ecology. This study was possible due to the coordination of a truly multidisciplinary team of 21 academics and specialists in aquatic science from 19 universities around the world. These findings have been recently published in Science of the total Environment.

In this perspective, authors first evaluate how biologically driven organic matter decomposition in riverine ecosystems varies in response to latitude across longitudinal dimensions (headwater streams to lowland rivers), vertical dimensions (surface waters to aquifers), lateral dimensions (floodplains and wetlands), and temporal dimensions (temporary systems). They also emphasize the large bias in ecological knowledge of decomposition towards temperate regions, while they identify important knowledge gaps, and suggest fruitful areas for future supra-disciplinary research. Then, authors present a solid conceptual rationale behind the idea of using the size-spectrum of the riverine community as a powerful predictor of organic matter decomposition rates. Subsequently, using metadata from large-scale datasets, authors confirm the validity of their approach. This integrative analytical framework links the energetic constrains of individuals to ecosystem-level processes. Thus, it can be used to assess biotic controls on organic matter decomposition – even between stream habitats and across biomes. Therefore, application of insights gained from such analyses could inform the development of strategies that promote the functioning of the riverine bioreactor across global ecosystems.

FIGURE 1. Conceptual diagram of riverine bioreactor functioning. Organic matter (OM) decomposition processes are hierarchically interconnected through the different compartments of the riverine bioreactor. (a) Litter fall production and temperature are higher and more constant in tropical than in temperate streams and rivers. (b) Anthropogenic release represents a major input source of dissolved organic matter (DOM) and dissolved pollutants in riverine systems. Dissolved compounds penetrate in streambed and reach groundwater systems and aquifers (main sources of drinking water for human consumption). Life activities of streambed macroinvertebrates (c) and groundwater stygobites (subterranean invertebrates that live in groundwater systems) (d) result in bioturbation and bioirrigation phenomena that promote water exchange, water mixing, sediment aeration and boost microbial activity. (e) Protists grazing on biofilms promote its absorption surface and growth. (f) Decomposition of particulate and DOM expands on aquatic-terrestrial ecotones along floodplains, and intermittent streams and rivers as a consequence of the flood-pulse. The metabolic theory of ecology predicts that mean body size of the ectotherms declines as environmental temperature increases at low latitudes to meet the higher energy demands (g). The size spectra can be used as an integrative index to predict and compare decomposition rate at global scales (h).

Reference.

Peralta-Maraver, et al. (2021). The riverine bioreactor: an integrative perspective on biological decomposition of organic matter across riverine habitats. Science of the Total Environment, 145494. https://doi.org/10.1016/j.scitotenv.2021.145494