Bridging between litterbags and whole-ecosystem experiments: a new approach for studying lake sediments

Abstract

Nearshore sediments have a major influence over the functioning of aquatic ecosystems, but predicting their response to future environmental change has proven difficult. Previous manipulative experiments have faced challenges controlling environmental conditions, replicating sediment mixing dynamics, and extrapolating across spatial scales. Here we describe a new approach to manipulate lake sediments that overcomes previous concerns about reproducibility and environment controls, whilst also bridging the gap between smaller microcosm or litterbag experiments and whole-ecosystem manipulations. Our approach involves submerging moderate-sized (~15 L) artificial substrates that have been standardised to mimic natural sediments within the littoral zones of lakes. We show that this approach can accurately mirror the absolute dissolved organic carbon concentrations and pH of pore water, and to a lesser degree inorganic carbon concentrations, from natural lake sediments with similar organic matter profiles. On a relative basis, all measured variables had similar temporal dynamics between artificial and adjacent natural sediments. Late-summer zooplankton biomass also did not differ between natural and artificial sediments. By offering a more realistic way to manipulate freshwater sediments than previously possible, our approach can improve predictions of lake ecosystems in a changing world.

Feasting on terrestrial organic matter: Dining in a dark lake changes microbial decomposition

“…Mesocosms were arranged in a block design between two sampling bays, submerged in rows at increasing distance from the shoreline, and covered with a 1 × 1 mm nylon mesh screen to standardize shading and resuspension within lakes. Importantly, sediment pore water samples taken from our mesocosms have been found to reflect the biogeochemistry of natural lake sediments (Tanentzap et al, 2017), allowing us to extrapolate our findings to field conditions. The sediment manipulations interacted with lake conditions to produce experimental gradients in pore water OM quality and quantity within each lake, which we directly measured from optical properties and DOC concentrations, respectively (Supporting Information Figure S1).…”

“…We predicted that sediment bacteria would allocate carbon differently, either to enzyme production or CO 2 production, in a clear and dark lake with increasing additions of terrestrially derived OM, and we used metagenomics to reveal the underlying mechanisms for these changes. We tested our prediction in sediment mesocosms that mirror natural ecosystems in their biogeochemical dynamics and provide a controlled way to replicate t‐OM inputs across lakes with contrasting water quality and clarity (Tanentzap et al, ). Microbial community composition and the environment are closely linked, and a major challenge is to decouple these two effects on microbial function (Logue et al, ).…”

Climate-driven shifts in sediment chemistry enhance methane production in northern lakes

“…We mixed the FPOM with a “base inorganic sediment” (0.3% OM, determined by loss-on-ignition at 500 °C for 2 h) to create final OM concentrations (by dry-weight) of 20% across the three amendments (CON, DEC, TYP). We used 20% to approximate typical OM concentrations found in littoral zones of northern lakes 22 (and confirmed in a nearby lake 38 ) but we also measured CH 4 production with 10 and 40% OM to confirm similarity of patterns across conditions. The base sediment was collected from the shoreline of Geneva Lake (near Sudbury, Canada: 46°45'27.2″N, 81°33'19.8″W) away from T. latifolia beds and direct inputs of forest-derived OM and was sieved to exclude particles larger than 2 mm.…”

“…We further confirmed the association between C5 and litter-derived phenol leachates using ultra-high resolution mass spectrometry data collected on a subset of samples in our PARAFAC model from an accompanying field-scale incubation study broadly described in ref. 38 (Supplementary Fig. 6 ).…”

Climate-driven shifts in sediment chemistry enhance methane production in northern lakes

“…We mixed the FPOM with a “base inorganic sediment” (0.3% OM, determined by loss-on-ignition at 500°C for two hours) to create final OM concentrations (by dry-weight) of 20% across the three amendments (CON, DEC, TYP). We used 20% to approximate typical OM concentrations found in littoral zones of northern lakes ( 19 ) (and confirmed in a nearby lake ( 35 )) but we also measured CH 4 production with 10 and 40% OM to confirm similarity of patterns across conditions. The base sediment was collected from the shoreline of Geneva Lake (near Sudbury, Canada: 46°45'27.2"N, 81°33'19.8"W) away from T. latifolia beds and direct inputs of forest-derived OM and was sieved to exclude particles larger than 2 mm.…”