Effects of Drying and Re-Wetting on Litter Decomposition and Nutrient Recycling: A Manipulative Experiment

Abstract

Climate change and water abstraction may change stream flow from perennial into intermittent lotic systems, modifying their abiotic and biotic benthic environment and impacting ecosystem processes such as nutrient turnover. We conducted a microcosm experiment to investigate the interactive effect of water intermittency, macrofauna and leaf size (Populus nigra leaves) on nutrient mineralization and recycling. Leaf disks (1 or 5 cm diameter) were incubated for 40 days with or without the leaf-consumer, Potamophylax cingulatus larvae (Trichoptera, Limnephilidae) and with or without an intervening, 10-days simulation of stream drying and subsequent rewetting. Nutrient fluxes, residual leaf biomass and leaf elemental composition were measured to evaluate how intermittency, macrofauna and leaf size affect organic matter mineralization rates and stoichiometry. Results suggest that drying slows decomposition rates, impacting both the microbial and setting to zero macrofauna activities. The presence of macrofauna increases mineralization and nutrient (C, N and P) regeneration rates. Our findings also suggest that leaf disks with higher diameter display higher microbial activity and NH 4 + regeneration. During the experiment, the C:N:P ratios of residual litter changed, as the leaf material became enriched with N and P. Our study suggests that increasingly frequent dry events might slow mineralization rates and downstream nutrient transport.

Response of stream fungi on decomposing leaves to experimental drying

“…Most other studies have found a slower breakdown of leaves in streams that are dry, whether intermittent or ephemeral. Invertebrates that consume leaves, shredders, often contribute significantly to leaf breakdown, so if these animals are lost upon drying, rates will be much lower (Datry et al, 2011;Ledger, Harris, Armitage, & Milner, 2012;Palmia et al, 2019). Microbes, the other biological player in The control treatment leaves remained immersed in the stream for the 2 weeks of treatments; the drying treatments were exposed to air for 2 weeks.…”

Regulation of CO2 fluxes along gradients of water saturation in irrigation canal sediments

“…Among them, are the organic matter pool and its macromolecular composition, that may vary among canals and among sites, the sediment permeability and the length of air exposure period. We speculate that increased exposure periods to the atmosphere may affect microbial communities and related activity, organic matter aging and sediment properties, with implication for fluxes (Amalfitano et al 2008;Ylla et al 2010;Palmia et al 2019).…”

“…In general, metabolic rates should decrease along with the time of exposure due to progressive depletion of the more labile organic matter fraction or the increase of C:N ratios in the residual litter (Palmia et al 2019). As during 2019 the 5 canals were dried out at the beginning of October and samplings occurred during the last 2 weeks of October, sediments were exposed for a period comprised between 2 and 4 weeks.…”

“…We calculated theoretical turnover rates of the organic carbon sedimentary pools, from available data of organic matter content and measured CO 2 emission rates. These calculations are based on uncertain assumptions as the constancy over time of CO 2 production, which is unlikely due to varying quality of the organic C pool with time and to decreasing temperatures (Palmia et al, 2019). Moreover, we considered in our calculations only the upper 0-3 cm sediment layer, which underestimates the true C sedimentary pool, and we assumed that during the dry period additional inputs of organic matter to the canal exposed sediments are negligible as they lay within ploughed lands.…”

Mapping Apennines river paths along different hydrological conditions from satellite images: A description of the method and potential applications

“…Indeed, there is an urgent need to understand the effects that climate change, reduced water availability, and hydrological intermittency on river ecology. Studies focus on the dynamics of macrofauna and on the implications for organic matter processing and downstream nutrient transport (Corti et al, 2011; Palmia et al, 2019). They also analyze the possible implications for river groundwater interactions, hatch success of crustaceans, fish, and amphibians using riverbed for eggs deposition and sediment transport (Uys & O'keeffe, 1997; Vander Vorste et al, 2020; Whiles & Goldowitz, 2001).…”