Biogenic processes or terrigenous inputs? Permanent water bodies of the Northern Ponds in the Lake MacLeod basin of Western Australia

Abstract

The saline wetlands of the Northern Ponds, Lake MacLeod, contravene general classifications for salt lakes because, despite enduring high levels of evaporation, they contain permanently inundated ponds that are continually supplied with seawater by a seepage face from the Indian Ocean. The present study investigated the physical, sediment and chemical characteristics of these ponds, using sonar, flow-rate measurements, microscopy and inductively coupled plasma–mass spectrometry to understand the role of biogenic and terrigenous inputs on the benthic habitats. The chemical composition of the water bodies did not differ significantly from the seawater feedstock, which facilitates biogenic sediment accumulation. The largest permanent water body differs from the other ponds in physical and chemical structure, in that, possibly because of its size, it is dominated by terrigenous inputs, which result in higher nutrient concentrations and non-biogenic sediments. The Northern Ponds represent a system where the hydrology permits the establishment of permanent wetlands in an arid environment. Because of the constant supply of seawater, the ponds have a blend of habitat characteristics from marine and other inland salt-lake environments. The present study showed that a ‘marine-like’ state can override more typical characteristics of inland water bodies where discharge rates are high and water-residence times are low.