The trophic history of Myall Lakes, New South Wales, Australia: interpretations using δ13C and δ15N of the sedimentary record

Abstract

In an attempt to determine the trophic history of the Myall Lakes complex (New South Wales, Australia) d 13 C org , d 15 N and C org :N profiles were determined for bulk organic matter of two short sediment cores from Bombah Broadwater and Myall Lake. 210 Pb profiles and sediment types indicate significantly different trophic trajectories during the time periods examined. d 13 C org and C org :N indicate Bombah Broadwater has been dominated by increasing inputs of terrestrial organic material over the last century, thought to be related to watershed disturbance including agricultural activity. Primary production appears to be dominated by phytoplankton. d 15 N remained relatively stable at around 1% until the mid-1970s when there was a sharp increase to 4.7%, interpreted as an influx of sewage-derived material. These observations offer an insight into the recent trophic changes at the site. Sedimentation rates are noticeably lower in Myall Lake and the most recent sediment is a flocculent organic rich deposit overlying mineral clay. d 13 C org and C org :N values indicate a transition from plankton to macrophyte dominated primary production around 1800AD. d 15 N values become increasingly negative from approximately 1900AD. This is interpreted as being due to increasing reliance by macrophytes on nitrogen recycled from decomposing sediments driven by natural infilling and eutrophication in this basin. The contrasting sedimentation rates, sediment types and geochemical profiles suggest the different basins of this water body are subject to substantially different internal and external influences which should be considered in management decisions.

Effect of magnesium on charophytes calcification: implications for phosphorus speciation stored in biomass and sediment in Myall Lake (Australia)

“…Therefore, without major external nutrients input from the surrounding, the internal nutrient recycle within the Myall Lake is considered an important process that controls the lake productivity. Furthermore, Drew et al (2008), who collected sediment cores from Myall Lake, showed that the d 15 N values become increasingly negative from approximately 1900 AD, that is, due to the increasing reliance by macrophytes on N recycled from decomposing sediments organic matters. Carignan & Kalff (1980) showed that sediment was the main source of P for the rooted macrophytes growing in oligotrophic and mildly eutrophic lakes.…”

“…The charophytes grow on a thick layer of non-calcareous organic sediment (gyttja) that was typically more than 1 m deep (Asaeda et al, 2007). The layer of gyttja in Myall Lake was produced autochthonously by the decomposition of macrophytes tissues (Drew et al, 2008). Siong & Asaeda (2006) found that charophytes growing in Myall Lake were much less calcified, i.e., less than 10% CaCO 3 of the biomass dry weight.…”

The essentiality of Essential Biodiversity Variables: implementation in nature conservation policies

“…While all are shallow, their geomorphic settings and hydrological properties give rise to differences in geochemical properties. Even though conditions likely have changed towards higher nutrient inputs following European settlement (Drew et al, 2008), the lakes are considered to have relatively pristine and oligotroph waters. Myall Lake and Bombah Broadwater are both freshwater to brackish barrier lakes (Roy et al, 2001) Despite being well-known tourist destinations, the lakes have not been greatly impacted by human activities (OEH, 2012).…”

“…Water quality is impacted by urban runoff, which is more prevalent closer to the ocean. Bombah Broadwater is somewhat more brackish than Myall Lake, due to its closer proximity to the ocean (Drew et al, 2008;OEH, 2012). Bombah Broadwater's primary production is dominated by phytoplankton with significant inputs of terrestrial organic matter (Drew et al, 2008).…”

“…Bombah Broadwater is somewhat more brackish than Myall Lake, due to its closer proximity to the ocean (Drew et al, 2008;OEH, 2012). Bombah Broadwater's primary production is dominated by phytoplankton with significant inputs of terrestrial organic matter (Drew et al, 2008). The water quality in Bombah Broadwater is especially responsive to inputs from the upper Myall River.…”