The presence of reduced sulfur, as both AVS and CRS, is an indicator of the potential for acidity to be generated should such sulfidic material be oxidised. The two sulfide fractions behave and react differently during formation and oxidation. The metastable monosulfide, measured as AVS, is the immediate product of the reaction of reduced sulfur with reactive iron. Hence, the AVS is being used in this study as an indicator of recent sulfate reduction. The bulk of the reduced sulfur present at the Loveday Disposal Basin and in Mussel Lagoon was as pyrite.
Reduced sulfur in the Loveday Disposal Basin and Mussel Lagoon was confined to the recent sediments. The distribution of sulfide minerals, both pyrite and monosulfide, varied across all wetlands. For the Loveday Disposal Basin, the majority of the reduced sulfur was in the upper 30 cm of the sediments, while in Mussel Lagoon, when sampled in both 2008 and 2010, the bulk of the reduced sulfur was more tightly confined to a thin 0-5 cm horizon at the surface.
The distribution of acid-volatile sulfur at the Loveday Disposal Basin and Mussel Lagoon depended on the extent to which the sediments had been exposed to the atmosphere. There were significant quantities of AVS at the surface of Loveday North and at the Museum Site, with lesser quantities at Mussel Lagoon, Berri Evaporation Basin and Loveday South. The Loveday North site had only recently been exposed, whilst the Museum site was inundated at the time of sampling, and under current management programs remains so. Hence, the AVS remains in reducing conditions, and was most abundant at these sites.
For Loveday South, the acid volatile sulfur content of the sediments was low: < 200 mg/kg, with the highest concentration found at ~20-30 cm. Since the Loveday South site had been exposed for a longer period than Loveday North, acid-volatile sulfur was preserved only at depth.
The concentration of acid volatile sulfur at Mussel Lagoon was minimal in 2008, with no more than 30 mg/kg of acid volatile sulfur detected at this site. The low AVS content was presumably due to the long period of exposure of the sediments at Mussel Lagoon at that time. The site was also very acidic in 2008 (pH = 3.25), consistent with the oxidation of previously reduced sulfur content.
When Mussel Lagoon was sampled in 2010, there was a layer of monosulfide overlying the wetland sediments. The AVS content of this layer was ~1100 mg/kg, which is comparable to the inundated sites at Loveday; the CRS content was ~2200 mg/kg.
The presence of sulfides in the freshwater environment of Mussel Lagoon was unexpected, as it has been hypothesised in previous studies that salinity resulted in sulfide precipitation in floodplain wetlands through the inhibition of competition between sulfate reducing and methanogenic bacteria (Hall et al., 2006a; Hall et al., 2006b; Lamontagne et al., 2004).
The concentration of total reduced inorganic sulfur (CRS) in the sediments collected from Mussel Lagoon and the Loveday Disposal Basin were spatially heterogeneous. Similar to the AVS concentrations, the concentrations of CRS were dependent on the length of time to which the sediments had been exposed to the atmosphere. For the Loveday North sites, both the Museum site and 205, there was a significant quantity of pyrite in the sediments between 5 and 40 cm depth, preserved by the water cover at these sites: the Museum site is permanently inundated, while the 205 site, when sampled in 2008 and 2010, had only recently been exposed to the atmosphere. The distribution of CRS at the 400 sites shows the effect of drying and oxidation of these sediments. The concentrations of CRS are considerably lower at these sites, with ~900 mg/kgof reduced sulfur, about a quarter of the amount found in the North Basin. The 400 sites were more acidic as well, consistent with continued oxidation of the sulfidic material in the South Basin leading to the formation of acid sulfate materials.
Nutrient Stores
The bulk nutrient concentrations in Mussel Lagoon and the Loveday Disposal Basin are no higher than that found in most soils (Rayment and Lyons, 2010). There is an exception for the Loveday North site (400), where the values were double those found elsewhere in Loveday or Mussel Lagoon. The experimental studies on Mussel Lagoon and the Loveday Disposal Basin, which are discussed below, suggest that the sediments are not enriched in phosphorus and nitrogen, little of these are fixed, and that more of the phosphorus at Mussel Lagoon is soluble under reducing conditions and readily available. For the Loveday Disposal Basin, the nitrogen is more soluble than the phosphorus due to the salinity, which results in phosphorus forming complexes with calcium and becoming less soluble.
Berri Evaporation Basin
A detailed characterisation of this site was not undertaken, but the data is presented and discussed for comparison with the Loveday Disposal Basin.
6.4.1.
Salinity
The EC in the Berri Evaporation Basin was 30 mS/cmat the surface, due to the concentration of evaporite minerals, but decreased with depth to 2.78 mS/cmat 30 cm.
The Berri Evaporation Basin is hypersaline, and contains aragonite, gypsum and halite (Lamontagne et al., 2004) . The surface waters were not as saline as those found at Loveday.