Changes in the chemistry of sedimentary organic matter within the Coorong over space and time

Abstract

Like many other coastal systems across the world, the Coorong lagoonal ecosystem (South Australia) has degraded over the last 100 years; in this case as a result of extensive regulation and diversions of water across the Murray-Darling Basin following European settlement. To evaluate whether the sources of organic matter (OM) supporting its food-web have changed since the inception of water management and barrage construction, sedimentary OM was characterised in cores spanning the Coorong's salinity gradient at depths representative of the last 100 years over which the management alterations to river and estuarine Xow were most marked. Detailed 210 Pb, 137 Cs and Pu dating in conjunction with palaeolimnological data (Pinus pollen) allowed for the reconstruction of the timing of substantial changes observed in the composition of the OM, most of which occur during the early 1950s, concurrent with management-related variations in water Xow and salinity. Negative shifts in 13 C of up to 8.3‰ in the 2-10 and <2 m fractions after the 1950s suggest a pronounced alteration in biogeochemical cycling or in the origin of OM. Elemental ratios and 13 C values of potential sources are inconclusive as to the cause of these biogeochemical changes. However, 13 C-NMR spectra of the sediments suggest that degraded phytoplankton constitutes a large proportion of today's OM and also reveal that an OM source rich in lignin was present prior to the 1950s. The high 13 C (¡18.3‰) and low C/N (7.5) signatures of the ligninbearing sediments are inconsistent with a C3 terrestrial OM source and instead suggest that the lignin-bearing seagrass Ruppia megacarpa ( 13 C of ¡13‰) contributed to a large degree to the sediment of the North Lagoon. R. megacarpa once was abundant in the North Lagoon but today has all but vanished from the system. Thus, only through a combination of isotopic and spectroscopic techniques was it possible to eVectively decipher the changes in the composition of OM deposited throughout the Coorong over space and time. These results have important implications for research in estuarine OM dynamics in other geographic locations. SpeciWcally, utilising complementary analytical techniques may sometimes be essential in reliably determining OM sources and processes in estuaries and lagoons.

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

“…It is furthermore supported by the 372 range of P aq values reported in these sediments, which are consistent with a major contribution from non-373 emergent aquatic plants to the n-alkanes found in the North Lagoon. This is in accordance with the formerly 374 high abundance of aquatic macrophytes, in particular Ruppia megacarpa, which used to be a significant source 375 14 of OM before its recent extinction due to the rising salinity (Krull et al, 2009). However, particularly with a 376 microalgal contribution to sedimentary n-alkanes, which is likely the case here (see following section), P aq 377 values have to be interpreted with care as the produced odd-chain n-alkanes might be in the same range to those 378 of aquatic plants.…”

“…Shuttleworth et al, 2005;Volkman et al, 2008). Changes in the type of OM -for example 54 caused by different flow regimes -can have a profound impact on the ecosystem since the base of the food-web 55 is affected (Krull et al, 2009). Efficient remediation measures for the Coorong require a profound understanding 56 of the effects of alterations in parameters such as water-level, salinity or quantity of riverine input (all of which 57 have occurred as an immediate result of human water management) on the ecosystem.…”

Sumber Penyumbang Karbon ke dalam Sedimen Dataran Rumput Laut di Muara Sungai Pulai, Johor, Malaysia

“…Bahan organik di perairan air terkepung boleh dibahagikan kepada dua jenis asalan iaitu aloktonus dan autotonus (Krull et al 2009). Bahan organik autotonus boleh dibahagikan kepada beberapa punca primer sebagai tambahan kepada fitoplanton seperti angiosperma akuatik (termasuk rumput laut) dan makroalga.…”

Dynamic Assessment of Oceanic Connectivity in a Coastal Lagoon—the Coorong, Australia

“…Sediment cores were used to look at changes in the origins of organic matter over time in the Coorong. The full spectrum of techniques were applied in one study (Krull et al 2008;Krull et al 2009) to reveal that prior to European settlement, Ruppia species was a much more important source of organic matter in the North Lagoon compared to now. This is a major difference from the present algal-dominated system and points to a substantially different historic food web structure.…”