Flow intermittence alters carbon processing in rivers through chemical diversification of leaf litter

Abstract

The dry phase of intermittent rivers promotes the accumulation of leaf litter on various terrestrial and aquatic habitats. This environmental heterogeneity causes a chemical diversification of leaf litter by a range of physical and biological degradation processes acting across the various habitats. After flow resumption, the chemically diversified leaves are mixed and subject to continued decomposition downstream. We hypothesized that the chemical diversification of leaf litter during the dry phase would affect leaf litter decomposition under re‐established lotic conditions. Our laboratory treatments mimicking dry‐phase habitats caused a strong chemical diversification of leaf litter, which—upon combination in mixed litter bags—accelerated its decomposition in a perennial river reach. We suggest that intermittent rivers may act as hotspots of organic matter diversification, with potential implications for organic matter processing at the river‐network scale.

Drying and fragmentation drive the dynamics of resources, consumers and ecosystem functions across aquatic-terrestrial habitats in a river network.

“…Although the negative effects of flow intermittence on decomposition can be linked to changes in leaf resource nutritional quality (del Campo et al 2021a), most field studies attribute these negative effects to losses of primary consumers such as shredders (Datry et al 2011, Schlief and Mutz 2011, Abril et al 2015, Northington and Webster 2017. We found that increasing flow intermittence had a seasonal positive effect on instream resource quality and quantity, but the negative effects on invertebrate richness and shredder abundances drove the associated decreases in decomposition.…”

“…dictated by the unidirectional flow of water), downstream ecosystem functions may thus depend on the disturbance regime inand connectivity to -upstream habitats. An intermediate amount of upstream intermittence could therefore promote downstream decomposition rates by providing 1) pulses of high quality leaf resources and 2) influx of diverse species best adapted to resource use, from a variety of upstream habitats, following rewetting events (Northington and Webster 2017, del Campo et al 2021a, Catalàn et al 2022.…”

“…Leaf-litter is a key source of organic carbon and nutrients in rivers, exchanged in both lateral (through leaf fall and runoff) and longitudinal (up to downstream flow) dimensions (Catalàn et al 2022, Scherer-lorenzen et al 2022. The decomposition rate of leaf litter in both aquatic and terrestrial habitats depends on several factors including, leaf chemical quality and palatability (Pastor et al 2014, del Campo et al 2021a, environmental factors such as humidity and temperature (Tiegs et al 2019, Annala et al 2022 and decomposer community (i.e. microorganisms and invertebrates) composition and activity (Abelho andDescals 2019, Boyero et al 2021).…”

“…Fungal and bacterial decomposition may however be little affected by drying, if sufficient moisture preserves microbial activity (Riedl et al 2013, Foulquier et al 2015. Drying may also affect leaf-litter quality, altering labile carbon contents and nutrient immobilization by microbial communities, which often reduce palatability for invertebrates (Pastor et al 2014, del Campo et al 2021a. At least 50% of the world's river networks dry, on average, for one day per year due to geological and/or climatic features (Messager et al 2021), and this proportion is likely to increase due to climate change and other anthropogenic alterations (e.g.…”

Anthropogenically driven climate and landscape change effects on inland water carbon dynamics: What have we learned and where are we going?

“…Increases in C emissions from rivers, streams, and lakes are modest when dried areas are included in their global CO 2 emission estimates (Table 4), but represent a source of high variability in seasonal emissions (Liu et al, 2022). Furthermore, dried areas accumulate terrestrial leaf litter that, upon rewetting, can be rapidly mobilized and decomposed, contributing a CO 2 pulse equal to up to 10% from all permanent rivers and streams (Datry et al, 2018;del Campo et al, 2021). These changes in the spatial coverage and duration of dried areas, especially for highly variable small streams and ponds, (Evans et al, 2012).…”