title: Assessing long-term pH change in an Australian river catchment using monitoring and palaeolimnological data.
abstract: Reviews of stream monitoring data suggest that there has been significant acidification (>1.0 pH unit at some sites) of Victorian streamwaters over the past 3 decades. To assess whether these declines are within the range of natural variability, we developed a diatom model for inferring past pH and applied it to a ca. 3500-yr diatom record from a flood plain lake, Callemondah 1 Billabong, on the Goulburn River, which has among the most substantial observed pH declines. The model has a jackkniffed r2 between diatom inferred and measured pH of 0.77 and a root mean square error of prediction of 0.35 pH units. In the pre-European period, pH was stable (range 6.5-6.7) for approximately 3000 yr. Since European settlement around 160 yr ago, diatom-inferred billabong pH has increased significantly by >0.5 units. We hypothesize that this increase in pH is related to processes associated with land clearance (e.g., increased base cation load and decreased organic acid load). There is no evidence of the recent monitored declines in the Callemondah record, which may indicate that that flood plain lakes and the main stream are experiencing divergent pH trends or that the temporal resolution in the billabong sediment record is insufficient to register recent declines.
authors.affiliation: Centre for Palynology and Palaeoecology, School of Geography and Environmental Science, Monash University, Victoria, Australia 3800. John.Tibby@adelaide.edu.au
authors.forename: John
authors.initials: J
authors.lastname: Tibby
authors.forename: Michael A
authors.initials: MA
authors.lastname: Reid
authors.forename: Jennie
authors.initials: J
authors.lastname: Fluin
authors.forename: Barry T
authors.initials: BT
authors.lastname: Hart
authors.forename: A Peter
authors.initials: AP
authors.lastname: Kershaw
mesh_terms: D015258:Acid Rain; D000383:Agriculture; D017377:Diatoms; D004784:Environmental Monitoring / Q000379:methods*; D019015:Geologic Sediments / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D011157:Population Dynamics; D012016:Reference Values; D045483:Rivers
chemical_list: D015258:Acid Rain