Natural and anthropogenic lead in sediments of the Rotorua lakes, New Zealand

Abstract

Global atmospheric sources of lead have increased more than 100-fold over the past century as a result of deforestation, coal combustion, ore smelting and leaded petroleum. Lead compounds generally accumulate in depositional areas across the globe where, due to low solubility and relative freedom from microbial degradation, the history of their inputs is preserved. In lakes there is rapid deposition and often little bioturbation of lead, resulting in an excellent depositional history of changes in both natural and anthropogenic sources. The objective of this study was to use sediments from a regionally bounded set of lakes to provide an indication of the rates of environmental inputs of lead whilst taking into account differences of trophic state and lead exposure between lakes. Intact sediment gravity cores were collected from 13 Rotorua lakes in North Island of New Zealand between March 2006 and January 2007. Cores penetrated sediments to a depth of 16-30 cm and contained volcanic tephra from the 1886 AD Tarawera eruption. The upper depth of the Tarawera tephra enabled prescription of a date for the associated depth in the core (120 years). Each core showed a sub-surface peak in lead concentration above the Tarawera tephra which was contemporaneous with the peak use of lead alkyl as a petroleum additive in New Zealand. An 8 m piston core was taken in the largest of the lakes, Lake Rotorua, in March 2007. The lake is antipodal to the pre-industrial sources of atmospheric lead but still shows increasing lead concentrations from < 2 up to 3.5 µg g -1 between the Whakatane eruption (5530 ± 60 cal. yr BP) and the Tarawera eruption. Peaks in lead concentration in Lake Rotorua are associated with volcanic tephras, but are small compared with those arising from recent anthropogenic-derived lead deposition. Our results show that diagenetic processes associated with iron, manganese and sulfate 2 oxidation-reduction, and sulfide precipitation, act to smooth distributions of lead from anthropogenic sources in the lake sediments. The extent of this smoothing can be related to changes in sulfate availability and reduction in sulfide driven by differences in trophic status amongst the lakes. Greatest lead mobilisation occurs in mesotrophic lakes during seasonal anoxia as iron and manganese are released to the porewater, allowing upward migration of lead towards the sediment-water interface. This lead mobilisation can only occur if sulfides are not present. The sub-surface peak in lead concentrations in lake sediments ascribed to lead alkyl in petroleum persists despite the diagenetic processes acting to disperse lead within the sediments and into the overlying water.

Dynamics of silicon in lakes of the Taupo Volcanic Zone, New Zealand, and implications for diatom growth

“…The concentration of Si in lake bottom sediments was not determined in this study, but scanning electron microscopy (SEM) of Lake Rotorua sediments has shown that Aulacoseira granulata frustules comprise ~97% by volume of the sediment ( Fig. 2a; Pearson 2007, Pearson et al 2010. Rawlence and Reay (1976) also found the sediments of Lake Taupo were dominated by diatom frustules, predominantly Aulacoseira granulata and to a lesser extent Cyclotella stelliger, as were the sediments of Lake Okataina (Mauriohooho and Hendy, University of Waikato, unpubl.…”

“…Ejecta from recent eruptions form distinct tephra layers in the lake sediments and can be used to date the subsequent sediment deposition (Trolle et al 2008, Pearson et al 2010. These tephra also provide a source of Si to the lakes.…”

Local to regional scale industrial heavy metal pollution recorded in sediments of large freshwater lakes in central Europe (lakes Geneva and Lucerne) over the last centuries

“…In Europe, anthropogenic atmospheric heavy metal source has dominated over the geogenic source since industrialization (Schotyk et al, 1998;De Vleeschouwer et al, 2007), but major issues remain about the sources of pollutant metals into aquatic environment. Moreover, some sediment deposits highly contaminated by past human activities (e.g., municipal and industrial waste sediment from wastewater treatment plants (WWTPs)) can present a potential health risk to a population through the possible remobilization of pathogens and inorganic pollutants at the sediment-water interface under the influence of chemical (e.g., changing redox conditions; Pearson et al, 2010) or physical (e.g., mass movement event or dam flushing; Girardclos et al, 2007;Wildi et al, 2004) processes.…”

Parameterisation of sediment geochemistry for simulating water quality responses to long-term catchment and climate changes in polymictic, eutrophic Lake Rotorua, New Zealand

“…The Tarawera tephra has previously been described by Pullar and Kennedy [19] as a dark-coloured coarse material, which is very distinctive and can readily be distinguished visually within a sediment sample. Using tephras from volcanic eruptions has also been used by Trolle et al [11] and Pearson et al [20] to determine sedimentation rates following tephra deposition. Annual N load and 4-year average nitrogen load (t yr -1 ) to Lake Rotorua based on ROTAN R0 (present land use scenario) output.…”