Professor Ralf Buckley, Director, International Centre for Ecotourism Research
Griffith University, Parklands Drive, Southport Q 4217
r.buckley@mailbox.gu.edu.au

Abstract
Human waste deposited under natural conditions in shallow catholes in rainforest, eucalyptus forest or coastal sand dunes in sub-tropical eastern Australia is broken down to the point of complete disappearance to the naked eye in periods as short as one to three months. Breakdown is most rapid in rainforests, and slower in coastal sand dunes. Toilet paper also breaks down in less than three months if the paper makes up less than 25% of the total deposit and is mixed in with other material.

Significance for NOLS:
NOLS currently runs semester courses in the wet-dry tropics of Australia. In particular, it runs canoe expeditions down the Drysdale River, through Drysdale River National Park in the Kimberley region of northwest Australia. The principal vegetation types include open eucalyptus woodlands on skeletal sandy soils, gallery forests along sandy river banks, grasslands on deeper sandy soils, and vine thicket with organic soils in protected areas. Mean annual rainfall is higher than in the eastern sub-tropics, but both areas have a long dry season and an intense wet season. Breakdown of human waste in the NOLS operational area is therefore likely to be similar to that at the study site in eastern Australia.

Methods:
Three experimental sites were used, all of them within 100 km of Coolangatta, where the state border between Queensland and New South Wales intersects the coastline. The sites were respectively in: sub-tropical wet-dry rainforest with an organic soil; dry sclerophyll (eucalyptus) woodland with a skeletal sandy loam soil; and coastal heath on deep sand dunes with little or no visible soil prolific development. Each site included a number of sub-sites up to 100 km apart, to average out local variability. All deposits were buried either in shallow catholes 5-15 cm indepth, or directly under rocks. At each site, a different sub-set of deposits were excavated after periods of two weeks, one month, and at monthly intervals up to six months. Toilet paper, less than 25% of total volume and mixed in, was used in 50% of deposits.

Results:
Human waste buried in catholes at the rainforest site decomposes almost completely within a month, and after two months there are no detectable residues. Decomposition is slightly slower in dry eucalyptus woodland, with extensive breakdown after one month and barely detectable residues, for some individual deposits only, after two months. In coastal sand dunes, very little decomposition occurs within the first months and individual deposits are still easily identifiable, though typically traversed by numerous fine shallow plant roots, after two months. After three months slight discoloration of surrounding sand is still evident, and after four months there is no visible residue.

Continuing Research:
Results from experimental work to date will be written up and submitted for publication. There are several options to pursue this project further.

• compare breakdown rates at different burial depths
• conduct tests in the Kimberley, using the breakdown timescale established to date (logistically difficult)
• test for residual nutrients and bacteria in surrounding soils, once visible residues have decomposed
• quantify breakdown rates more accurately during wet and dry seasons, summer and winter
• carry out comparable experiments in a temperate montane ecosystem in southern Australia, for calibration against data from North America and Europe.