Applying paleolimnological techniques in estuaries: a cautionary case study from Moreton Bay, Australia

Abstract

Paleoecological techniques are useful tools to identify restoration targets and natural variability for natural resource management programs. However, despite recent advances, caution is required when employing paleoecological techniques in estuaries, due to their dynamic nature relative to lake environments where these techniques were pioneered. This study used a novel combination of chronological, diatom, geochemical and isotopic data to assess the effectiveness of using these techniques in estuaries, and to develop an understanding of environmental changes within Moreton Bay, an open estuarine environment in subtropical east Australia. Results indicated mixed success, with 210Pb results indicating only background unsupported 210Pb levels, 14C results indicating sediment deposition from mixed sources, no diatom preservation and inconsistencies between geochemical and isotope proxies. Evidence did exist that the Moreton Bay sediments have been derived from different sources over the past 10 000 years. However, isotope records were not able to identify the likely sources of these sediments. Problems with diatom preservation were most probably due to the high salinity and temperatures associated with subtropical open embayment estuaries. Future studies attempting to identify environmental histories of estuaries should incorporate river-influenced locations rather than marine-dominated sites to ensure better diatom preservation and more definitive geochemical signals.

Increasing the understanding and use of natural archives of ecosystem services, resilience and thresholds to improve policy, science and practice

“…The residual ecosystem values of the coastal zone remain under threat from urban sprawl and associated land uses (Saunders et al, 1990). Environmental records are of insufficient duration or accuracy to identify natural ecological thresholds or benchmarks, whereas palaeo-ecology is providing management answers through multi-proxy techniques (Logan et al, 2010; Tibby et al, 2008). For example, Logan and Taffs (2011) were able to identify sub-tropical estuarine reference conditions using a combination of geochemical and biological techniques, while studies in the Coorong, South Australia, show the level of temporal detail possible using natural archives (Dick et al, 2011).…”

A Review of Environmental Isotopes: Its Prospective Applications in Disaster-risk Management of Watershed

“…80 In estuaries, the use of paleolimnology always seeks to determine environmental changes occurring over time. 100 In terms of salinity studies, the combined hydrogen isotopic composition of the preserved alkenones and n-alkanes provide information on significant changes in both δD water and δD precipitation of the Black Sea area during the Messinian Salinity Crisis. 93 The study of δ 18 O and δ 13 C in lacustrine authigenic calcites provide a useful indicator of past climatic change through the Holocene period, with a high degree of covariance between these two stable isotopes suggesting that evaporation and exchange have controlled the hydrological balance.…”

Palaeolimnology in eastern and southern Australian estuaries

“…In this volume, the understanding of coastal diatom ecology is extended by Grinham et al (2011) who focus on the relationship between benthic diatoms in a sub-tropical estuarine embayment. Grinham et al (2011) took on this challenge in the highly dynamic Moreton Bay which has posed problems for palaeolimnology (Logan et al 2010). Sediment type was the main driver of diatom composition and short term fluctuations of water chemistry had minimal impacts (Grinham et al 2011).…”