|The effects of heatwaves on sediment biogeochemistry, with a focus on nutrients|
Temmerman, Y. (2021). The effects of heatwaves on sediment biogeochemistry, with a focus on nutrients. MSc Thesis. NIOZ Royal Netherlands Institute for Sea Research: Yerseke. 28 pp.
Extreme weather events have occurred more frequently in recent decades with reports of two consecutive heatwaves in Europe during the months of June and July in 2019. Heatwaves have the potential to influence marine ecosystem functions. The aim of this research was to study the effects of heatwaves on functional processes, specifically the nitrogen, phosphorous and silicate cycles in muddy marine sediments. In particular, this research explored the effects of light and increased temperature on benthic porewater nutrient concentrations. The data was collected during a heatwave experiment in June 2020. Sediment cores were collected from the Zandkreek intertidal flat in the Dutch Eastern Scheldt. The experiment was conducted in a climate-controlled chamber where the sediment cores were exposed to a 5-day heatwave of 35°C followed by 2 weeks of recovery at 20°C. During the experiment, there were 3 sampling moments where porewater nutrient samples were collected. The porewater nutrient concentrations (μmol/L) were then used to see if the heatwave affected the benthic nutrient cycles. It was found that the effect of light during a heatwave was not statistically significant. Increased concentrations of ammonium (NH4+) deeper layers suggested that there was an increased rate of anoxic remineralization in the sediment due to the heatwave. The results suggest that heat induced enhancement of organic matter remineralization increased sediment NH4+ concentrations. There were no observed alterations to the phosphorus cycles during the heatwave. Silicates, however, showed significantly higher concentrations caused by the heatwave due to increased dissolution rates. These results suggest that heatwaves influence sediment biogeochemistry by increasing the bioavailable nutrients in the sediment. This knowledge is valuable as it can possibly be linked to larger temperature-induced ecosystem effects, which increases our understanding of climate change impacts.