Diatom taphonomy and silica cycling in two freshwater lakes and their implications for inferring past lake productivity

摘要: Diatom preservation can be a major taphonomic issue in many lakes but is often unrecognised and its impacts on qualitative quantitative inferences (such as productivity biodiversity estimates) from sedimentary archives are seldom explored. Here two palaeolimnological case studies of 20th-century anthropogenic eutrophication freshwater Northern Ireland (Lough Neagh Lough Augher) re-visited new data presented diatom preservation. Assessing problems taphonomy challenges previous interpretations silica dynamics at these sites. was assessed both sediment trap material cores Neagh, Augher. Preservation data, combined with geochemical analysis (Si, Fe), provide an insight into cycling accumulation over range temporal scales lakes. generally good for the material, although differential (better) smaller Aulacoseira subarctica compared to larger Stephanodiscus neoastraea sensu lato valves clear, especially sediments. Porewater showed complex seasonal pattern upper sediment, against expectations steady-state. The Augher poorly preserved, (dissolution) significantly (and positively) correlated bulk sedimentation rate, found control (net) rate across basin. Past severe anoxia did not improve preservation, contrary some studies, which may due extreme changes redox conditions. Finally, using published experimental relationships between dissolution valve loss, correction factors were applied previously profiles last ~150 years (biovolume frustule Augher), suggest that estimates records underestimated by factor 2–4 effects alone. results clearly have implications reliability accuracy diatom-based made records, quantitative, those employ diatoms direct measures or biodiversity.