20 Aug 2025

Bioturbation Increases Time Averaging Despite Promoting Shell Disintegration: A Test Using Anthropogenic Gradients in Sediment Accumulation and Burrowing on the Southern California Shelf

Abstract: Bioturbation increases time averaging of young and old shells within the entire mixed layer and accelerating the burial of shells into a sequestration zone. Bioirrigation by oxygenated pore-water promotes carbonate dissolution in the TAZ, and biomixing itself can mill shells weakened by dissolution or microbial maceration, and/or expose them to damage at the sediment–water interface. We fit transition rate matrices to bivalve age–frequency distributions from four sediment cores to assess the competing effects of bioturbation on disintegration and time averaging. Disintegration covaries positively with mixing at all four sites. Mixing and disintegration rates decline abruptly at the base of the 20- to 40-cm-thick, age-homogenized surface mixed layer at the three well-bioturbated sites. In contrast, they are very low in the upper 25 cm at an effluent site with legacy sediment toxicity. Assemblages formed during maximum wastewater emissions vary strongly in time averaging. Thus, even though disintegration rates covary positively with mixing rates, reducing postmortem shell survival, bioturbation has the net effect of increasing the time averaging of skeletal remains on this warm-temperate siliciclastic shelf.

24 Aug 2021

Aligning research and monitoring priorities for benthic cyanobacteria and cyanotoxins : a workshop summary

Abstract: In 2018, the US Army Engineer Research and Development Center partnered with the US Army Corps of Engineers–Buffalo District, the US Environmental Protection Agency, Bowling Green State University, and the Cawthron Institute to host a workshop focused on benthic and sediment-associated cyanobacteria and cyanotoxins, particularly in the context of harmful algal blooms (HAB). Technical sessions on the ecology of benthic cyanobacteria in lakes and rivers; monitoring of cyanobacteria and cyanotoxins; detection of benthic and sediment-bound cyanotoxins; and the fate, transport, and health risks of cyanobacteria and their associated toxins were presented. Research summaries included the buoyancy and dispersal of benthic freshwater cyanobacteria mats, the fate and quantification of cyanotoxins in lake sediments, and spatial and temporal variation of toxins in streams. In addition, summaries of remote sensing methods, omic techniques, and field sampling techniques were presented. Critical research gaps identified from this workshop include (1) ecology of benthic cyanobacteria, (2) identity, fate, transport, and risk of cyanotoxins produced by benthic cyanobacteria, (3) standardized sampling and analysis protocols, and (4) increased technical cooperation between government, academia, industry, nonprofit organizations, and other stakeholders. Conclusions from this workshop can inform monitoring and management efforts for benthic cyanobacteria and their associated toxins.