Unexpected post-settlement freshening and increase in charophytes in Bombah Broadwater (Myall Lakes, New South Wales, Australia)
Bombah Broadwater is a shallow coastallake within the Ramsar-listed Myall Lakes system onthe mid-north coast of New South Wales, Australia.Increased nutrient and sediment loads resulting fromcatchment modification are thought to have instigatedthe loss of aquatic plants in the lake, causing it to``switch¿¿ from a clear, macrophyte dominated system(similar to the conditions in present day Myall Lake) toa turbid, phytoplankton dominated system. To assessthis hypothesis, charophytes, foraminifera and aquaticfauna remains from an 800 year sediment record wereexamined. The sediment chronology was establishedusing 14C, 210Pb and 137Cs radiometric dating andsediment composition. Interestingly, a clear increase in charophytes since European arrival conflicted withthe hypothesised aquatic plant loss. Hence, it appearsBombah Broadwater has not undergone a change instable state since European arrival. An additional andunexpected finding in the patterns of the foraminiferaand testate amoeba suggest that Bombah Broadwaterhas freshened substantially since European arrival.This freshening may have resulted from increasedcatchment run off as a result of the clearance ofcatchment vegetation. Since catchment vegetationclearance is widespread in Australia, this findingraises the possibility that post-settlement freshening ofcoastal lakes may be a common occurrence.
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