Salinity variations in the northern Coorong Lagoon, South Australia: Significant changes in the ecosystem following human alteration to the natural water regime

Abstract

14European settlement and drought have significantly impacted the hydrology of the Coorong a shallow 15 coastal lagoon complex in South Australia, which is part of a terminal wetland at the Mouth of the River 16Murray. An increased salinity associated with lower water levels and progressive isolation from ocean flushes 17 contributed to a severe decline in ecological diversity over the past decades. Here we have conducted a 18 molecular and stable isotopic study of a sedimentary core from the northern Coorong Lagoon spanning more 19 than 5000 years to investigate the recent palaeoenvironmental history of the ecosystem. Major alterations were 20 evident in many biogeochemical parameters in sediments deposited after the 1950s coinciding with the 21 beginning of intensified water regulations. The most prominent shift occurred in δ 13 C profiles of C 21 -C 33 n-22 alkanes from average values of -23.5 ‰ to an average of -28.2 ‰. Further changes included decreases in carbon 23 preference index (CPI) and average chain length (ACL) of the n-alkane series as well as significant increases in 24 algal (e.g. C 20 HBI, long-chain alkenes and C 29 -alkadiene) and bacterial (e.g. 13C depleted short-chain n-alkanes 25 and hopanoids, δ 13 C: -35.9 to -30.1 ‰) derived hydrocarbons. Long-chain n-alkanes with a strong odd-over-26 even predominance as observed here are typically attributed to terrestrial plants. In the Coorong however, 27 terrestrial input to sedimentary OM is only minor. Therefore changes in the before mentioned parameters were 28 2 attributed to a source transition from a major contribution of macrophytes towards predominantly microalgae 29 and bacteria. 30 δD values of C 21 -C 33 n-alkanes showed a general trend towards more enriched values in younger sediments, 31indicating an overall rising salinity. However, the most pronounced positive shift in these profiles again 32 occurred after the 1950s. Altogether this study demonstrates that the recent human induced changes of the 33 Coorong hydrology, compounded by a severe drought led to an increase in salinity and alterations of primary 34 production which have been much more significant than natural variations occurring throughout the Holocene 35 over several thousands of years. 36

Changes of palaeoenvironmental conditions recorded in Late Devonian reef systems from the Canning Basin, Western Australia: A biomarker and stable isotope approach

“…n-Alkanes in sediments with complex marine and terrigenous OMinputs, such as the presently analysed core, typically have mixed sources including phytoplankton as well as terrestrial and aquatic plants (e.g Collister et al, 1994;Lichtfouse et al, 1994;Tulipani et al, 2014). The similar or slightly more positive δ 13 C values of short chain nalkanes in comparison to the predominantly phytoplankton-derived phytane indicate an origin of these hydrocarbons from phytoplankton as well as possibly heterotrophic bacteria (Tulipani et al, in review, and references therein).…”

Sheet Flow Effects on Sediment Transport in a Degraded Ridge‐and‐Slough Wetland: Insights Using Molecular Markers

“…Biomarkers have frequently been used to assess organic matter sources and transport and environmental changes in aquatic environments (e.g., Tulipani et al, ; Zhang et al, ; Zhou et al, ; Zocatelli et al, ). The concept has been successfully applied in a variety of ecosystems in the Florida Everglades, including freshwater marshes (Mead et al, ; Saunders et al, ), mangrove forests (He et al, ), and coastal marine environments (Xu et al, , ) leading to the development of source‐specific molecular markers applicable as proxies for organic matter source, transport, and fate.…”

“…The concept has been successfully applied in a variety of ecosystems in the Florida Everglades, including freshwater marshes (Mead et al, ; Saunders et al, ), mangrove forests (He et al, ), and coastal marine environments (Xu et al, , ) leading to the development of source‐specific molecular markers applicable as proxies for organic matter source, transport, and fate. Lipid biomarkers are abundant in plant waxes (Bush & McInerney, ) and have proved particularly useful to distinguish organic matter sources of different biomass, including terrestrial plants, algae, and bacteria (e.g., Schellekens & Buurman, ; Seki et al, ; Tulipani et al, ). Ratios of n‐alkanes like the average chain length and the aquatic proxy (Paq) have been widely used to trace historical changes in vegetation (Ficken et al, ; Tareq et al, ; Zocatelli et al, ).…”

Short‐ and long‐term evapotranspiration rates at ecological restoration sites along a large river receiving rare flow events

“…As of 2005, over half of the world's large river systems were affected by dams (Nilsson & Berggren, ). There are many stark examples of this globally: In the Murray–Darling system in Australia, the coastal lagoon ecosystem has suffered extensively from lack of freshwater inflows for over half a century (Tulipani, Grice, Krull, Greenwood, & Revill, ), and regular, expensive dredging of the river's mouth is needed to allow the river to flow to the ocean (Kingsford et al, ). Reductions in the Amu Darya River system in Central Asia due to diversions for large‐scale cotton production resulted in the desiccation and salinization of the Aral Sea, leading to the collapse of that unique ecosystem and a vast fishing industry (Micklin, ).…”