A hydrochemically guided landscape classification system for modelling spatial variation in multiple water quality indices: Process-attribute mapping.

Spatial variation in landscape attributes can account for much of the variability in water quality relative to land use on its own. Such variation results from the coupling between the dominant processes governing water quality, namely hydrological, redox, and weathering and gradients in key landscape attributes, such as topography, geology, and soil drainage. Despite the importance of 'process-attribute' gradients (PAG), few water quality models explicitly account for their influence. Here a processes-based water quality modelling framework is presented that more completely accounts for the role of landscape variability over water quality - Process-Attribute Mapping (PoAM). Critically, hydrochemical measures form the basis for the identification and mapping of effective landscape attributes, producing PAG maps that attempt to replicate the natural landscape gradients governing each dominant process. Application to the province of Southland (31,824 km2), New Zealand, utilised 12 existing geospatial datasets and a total of 28,626 surface water, groundwater, spring, soil water, and precipitation analyses to guide the identification and mapping of 11 individual PAG. The ability of PAGs to replicate regional hydrological, redox, and weathering gradients was assessed on the accuracy with which the hydrochemical indicators of each dominant process (e.g. hydrological tracers, redox indicators) were estimated across 93 long-term surface water monitoring sites (cross-validated R2 values of 0.75-0.95). Given hydrochemical evidence that PAGs replicate actual landscape gradients governing the dominant processes, they were combined with a land use intensity layer and used to estimate steady-state surface water quality. Cross-validated R2 values ranged between 0.81 and 0.92 for median total nitrogen, total oxidised nitrogen, total phosphorus and dissolved reactive phosphorus. Models of particulate species E. coli and total suspended sediment, although reasonable (R2 0.72-0.73), were less accurate, suggesting finer-grained land use, landscape attribute, and/or flow normalised measures are required to improve estimation.

Assessing aluminium toxicity in streams affected by acid mine drainage.

Acid mine drainage (AMD) has degraded water quality and ecology in streams on the Stockton Plateau, the site of New Zealand's largest open-cast coal mining operation. This has previously been attributed largely to the effects of acidity and elevated aluminium (Al) concentrations. However, the toxicity of dissolved Al is dependent on speciation, which is influenced by pH which affects Al hydrolysis, as well as the concentrations of organic carbon and sulphate which complex Al. Methods for the assessment of the toxic fraction of Al, by chemical analysis and geochemical modelling, have been investigated in selected streams on the Stockton Plateau, where dissolved Al concentrations ranged from 0.034 to 27 mg L(-1). Modelling using PHREEQC indicated that between 0.2 and 85% of the dissolved Al was present as the free ion Al(3+), the most toxic Al species, which dominated in waters of pH = 3.8-4.8. Al-sulphate complexation reduced the Al(3+) concentration at lower pH, while Al-organic and -hydroxide complexes dominated at higher pH. Macroinvertebrate richness in the streams identified an Al(3+) 'threshold' of approximately 0.42 mg/L, above which taxa declined rapidly. Colorimetric 'Aluminon' analysis on unpreserved, unfiltered waters provided a better estimation of Al(3+) concentrations than inductively couple plasma-mass spectrometry (ICP-MS) on filtered, acidified waters. The Aluminon method does not react with particulate Al or strong Al complexes, often registering as little as 53% of the dissolved Al concentration determined by ICP-MS.

Metal removal via particulate material in a lowland river system.

Twelve month surveys of acid-soluble and dissolved trace metal concentrations in the lower Waikato River (in 1998/9 and 2005/6) showed abnormally low particulate Fe, Mn, Cu, Pb and Zn concentrations and mass flux in autumn, when the suspended particulate material (SPM) had a relatively high diatom and organic carbon content, and low Fe and Al content. Dissolved Mn, Cu and Zn concentrations also decreased in autumn, while dissolved Fe and Pb concentrations were unaffected. While SPM settlement under the low river flow conditions present in autumn can explain the removal of particulate metals, it does not explain dissolved metal removal. SPM-metal interaction was therefore investigated using seasonal monitoring data, experimental adsorption studies, sequential extraction and geochemical modelling. Pb binding to SPM occurred predominantly via Fe-oxide surfaces, and could be reliably predicted using surface complexation adsorption modelling. Dissolved Mn concentrations were controlled by the solubility of Mn oxide, but enhanced removal during autumn could be attributed to uptake by diatoms. Zn and Cu were also adsorbed on Fe-oxide in the SPM, but removal from the water column in autumn appeared augmented by Zn adsorption onto Mn-oxide, and Cu adsorption onto the organic extracellular surfaces of the diatoms.

Discovery of large conical stromatolites in Lake Untersee, Antarctica.

Lake Untersee is one of the largest (11.4 km(2)) and deepest (>160 m) freshwater lakes in East Antarctica. Located at 71°S the lake has a perennial ice cover, a water column that, with the exception of a small anoxic basin in the southwest of the lake, is well mixed, supersaturated with dissolved oxygen, alkaline (pH 10.4) and exceedingly clear. The floor of the lake is covered with photosynthetic microbial mats to depths of at least 100 m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures, one of which--cm-scale cuspate pinnacles dominated by Leptolyngbya spp.--is common in Antarctica, but the second--laminated, conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp.--has not previously been reported in any modern environment. The laminae that form the conical stromatolites are 0.2-0.8 mm in thickness consisting of fine clays and organic material; carbon dating implies that laminations may occur on near decadal timescales. The uniformly steep sides (59.6 ± 2.5°) and the regular laminar structure of the cones suggest that they may provide a modern analog for growth of some of the oldest well-described Archean stromatolites. Mechanisms underlying the formation of these stromatolites are as yet unclear, but their growth is distinct from that of the cuspate pinnacles. The sympatric occurrence of pinnacles and cones related to microbial communities with distinct cyanobacterial compositions suggest that specific microbial behaviors underpin the morphological differences in the structures.

Potential biogas scrubbing using a high rate pond.

The potential to scrub biogas in a high rate pond (HRP) was evaluated using apparatus designed to maximize gas-liquid contact. Experiments compared the removal of carbon dioxide from synthetic biogas by an "in-pond angled gutter" to that by a simulated "counter-current pit." Results showed that the counter current pit has potential for use in biogas scrubbing, with synthetic biogas carbon dioxide composition consistently reduced from 40% to < 5%. The in-pond angled gutter was less effective due to bubble coalescence which reduced the total bubble surface area available for gas transfer. Measurement of oxygen levels in the scrubbed biogas showed that despite supersaturation of oxygen in the HRP water, there was little transfer to the biogas, so that explosive methane/oxygen mixtures would not be formed. Theoretical calculations indicated that the amount of biogas likely to be formed during anaerobic treatment of municipal wastewater could be scrubbed in the HRP of the same advanced pond system with little influence on HRP pH, algal growth and treatment performance. These encouraging results justify further research on this method of biogas purification.