Non-living Carbon Research Articles

Kelp-carbon uptake by Arctic deep-sea food webs plays a noticeable role in maintaining ecosystem structural and functional traits

The flow of non-living carbon (detritus) is considered an important process because it connects ecosystems and fuels benthic communities. In Norwegian kelp forests, 90% of the kelp production is exported to adjacent ecosystems where it can play a significant role in shaping benthic communities. We quantified the major structural and functional traits of an Arctic deep-sea ecosystem associated with kelp exports and assessed the ecological role of kelp export into the deep-sea system. We first developed a food-web model using the Ecopath with Ecosim (EwE) approach to represent the state of the deep (450 m) ecosystem of the Malangen fjord (Northern Norway) in 2017. Subsequently, we used the temporal dynamic model Ecosim to explore the structure and functioning traits of a theoretical deep-sea ecosystem projecting a decrease of kelp detritus biomass reaching the deep-sea ecosystem. Overall, our findings reveal that kelp detritus from shallow coastal areas has a small but noticeable role structuring the deep-sea ecosystem of Malangen. The temporal simulations show important differences depending on the application of mediating effects, which allow considering the detritus as a mediating group in prey-predator interaction, in addition to its direct role in trophic relationships. When mediating effects are applied, biomass increases for benthopelagic shrimps and suprabenthos groups and decreases for rays and skates, velvet belly, rabbitfish and other commercial demersal fishes under the low kelp detritus scenarios. Biomass-based and trophic-based indicators reveal a noticeable impact on the deep-sea ecosystem structure due to depletion of kelp detritus. To further assess future changes of the Arctic deep-sea ecosystems, dependencies with adjacent ecosystems, such as kelp detritus production, should be included. • Kelp detritus from coastal areas plays a moderate role in the deep-sea ecosystem. • The temporal simulations show differences when mediating effects are applied. • Indicators reveal impacts on the deep-sea ecosystem after kelp detritus depletion. • Further research in mediation effects is needed to obtain more realistic simulations.

Organic matter transfer in Lake Superior's food web: Insights from bulk and molecular stable isotope and radiocarbon analyses

A suite of isotopic methods were combined to provide a comprehensive investigation of organic matter transfer and consumer-resource links in a large lake food web. We applied compound specific isotope analysis (CSIA) of nitrogen within amino acids of organisms, a relatively new method and one not yet widely applied to large lake systems, to determine the trophic positions of several dominant species. Comparison of this CSIA trophic designation to those calculated by traditional bulk stable carbon and nitrogen isotope ratios, as well as gut content analyses, revealed this CSIA method to be the most representative of known trophic links in Lake Superior. Limnocalanus macrurus, an omnivorous copepod, was found to occupy a trophic position higher than would have been predicted based on gut analyses, and one full trophic position above primary consumer Daphnia. Radiocarbon analysis of bulk zooplankton and fish tissue was employed as a modern carbon tracer to elucidate the relative ages of carbon incorporated into, and propagated through, the food web. Comparison of animal tissue, non-living carbon pools (DOC, DIC), and POC radiocarbon content indicate the food web is supported predominately by newly synthesized autochthonous material. The uniquely depleted radiocarbon signature of the benthic amphipod Diporeia, attributed to consumption of aged sedimentary or allochthonous material, was not reflected in its known predators, indicating little overall incorporation of that aged carbon source into the pelagic food web. This multi-method isotopic investigation extends our understanding of food web structure and organic matter flow in this large lake.

Spatial and temporal changes in the partitioning of organic carbon in the plankton community of the Sargasso Sea off Bermuda

The vertical distribution of plankton (bacteria, nanozooplankton, microzooplankton, mesozooplankton, macrozooplankton and salps) biomass in the photic zone near the JGOFS time series station off Bermuda was examined during 2–3 week periods in August 1989 and in March/April 1990. The amount of phytoplankton carbon in the photic zone was lower in August as compared to March/April (398 and 912 mg C m−2, respectively). Total heterotrophic biomass in the photic zone was also lower in August as compared to March/April (1106 and 1795 mg C m−2, respectively). Taken together, bacteria and nanozooplankton constituted approximately 70% of the total heterotrophic carbon in the photic zone on both cruises. Considering their high weightspecific carbon demand relative to micro-, meso-, and macrozooplankton, it is clear that most of the carbon in the surface waters of the Sargasso Sea near Bermuda cycles through bacteria and flagellates—the “microbial loop”. However, both seasonal (August vs. March/April) and withincruise variations in the vertical flux of organic material were related to the biomass of macrozooplankton. Macrozooplankton biomass was lower in August than March/April (93 and 267 Mg C m−2, respectively). There was more non-living carbon (detritus) than living carbon in the photic zone during the August cruise (70% of total organic matter) but about equal amounts of detritus and living carbon in March/April.

Systems model of carbon transformations in soil subsidence

A system model was designed to simulate the interaction of climatologic and biologic factors in the biological oxidation of organic soils in ordert to stimulate research on this diminishing resource and attendant water quality problems in the Florida Everglades area. This is a mass balance model in which carbon and nitrogen are conserved in the transformations. It was designed to test different management alternatives for slowing the rate of soil subsidence and to estimate their potential effect on water quality by simulating subsidence rates and the release rates of nitrates, nitrites, and organic acids to ground and surface waters. The biological submodel is structured about two major compartments — the total non-living carbon compartment and a living carbon compartment that includes the microbial biomass and functioning extracellular enzymes. Simulations of the model show the effects of temperature, organic composition, and water table height on carbon dioxide evolution from the soil.

Feeding of Pseudocalanus minutus on living and non-living particles

A seasonal study of carbon content of living and of carbon and nitrogen content of non-living particulate material in seawater is presented. Grazing by Pseudocalanus minutus on living and non-living particles has been investigated over 1 year. Seasonal variations in the food uptake were associated with seasonal variations of each chemical component of the particles in the water. The amount of non-living carbon constituted the major part of the food ingested, irrespective of season. The ingested living carbon always accounted for a small fraction of the total copepod body carbon. The proportion of living carbon ingested could be equivalent to or even higher than non-living carbon at times during the late spring, summer and fall. The concentration of both living and non-living material within each particle peak of the spectra in the water seemed to affect the balance between non-living and living particle uptake. Non-living particles cannot be considered only as a supplementary food source for small copepods; they are a basic food for P. minutus at all times.