Developing an empirical model of canopy water flux describing the common response of transpiration to solar radiation and VPD across five contrasting woodlands and forests

A modified Jarvis–Stewart model of canopy transpiration (E_c) was tested over five ecosystems differing in climate, soil type and species composition. The aims of this study were to investigate the model's applicability over multiple ecosystems; to determine whether the number of model parameters could be reduced by assuming that site‐specific responses of E_c to solar radiation, vapour pressure deficit and soil moisture content vary little between sites; and to examine convergence of behaviour of canopy water‐use across multiple sites. This was accomplished by the following: (i) calibrating the model for each site to determine a set of site‐specific (SS) parameters, and (ii) calibrating the model for all sites simultaneously to determine a set of combined sites (CS) parameters. The performance of both models was compared with measured E_c data and a statistical benchmark using an artificial neural network (ANN). Both the CS and SS models performed well, explaining hourly and daily variation in E_c. The SS model produced slightly better model statistics [R² = 0.75–0.91; model efficiency (ME) = 0.53–0.81; root mean square error (RMSE) = 0.0015–0.0280 mm h^‐1] than the CS model (R² = 0.68–0.87; ME = 0.45–0.72; RMSE = 0.0023–0.0164 mm h^‐1). Both were highly comparable with the ANN (R² = 0.77–0.90; ME = 0.58–0.80; RMSE = 0.0007–0.0122 mm h^‐1). These results indicate that the response of canopy water‐use to abiotic drivers displayed significant convergence across sites, but the absolute magnitude of E_c was site specific. Period totals estimated with the modified Jarvis–Stewart model provided close approximations of observed totals, demonstrating the effectiveness of this model as a tool aiding water resource management. Analysis of the measured diel patterns of water use revealed significant nocturnal transpiration (9–18% of total water use by the canopy), but no Jarvis–Stewart formulations are able to capture this because of the dependence of water‐use on solar radiation, which is zero at night. Copyright © 2012 John Wiley & Sons, Ltd.     

Remnant riparian vegetation,sediment and nutrient loads,and river rehabilitation in subtropical Australia

A decline in the ecosystem health of Australia's Moreton Bay, a Ramsar wetland of international significance, has been attributed to sediments and nutrients derived from catchment sources. To address this decline the regional management plan has set the target of reducing the loads by 50%. Reforestation of the channel network has been proposed as the means to achieve this reduction, but the extent of revegetation required is uncertain. Here we test the hypothesis that sediment and nutrient loads from catchments decrease proportionally with the increasing proportion of the stream length draining remnant vegetation. As part of a routine regional water quality monitoring program sediment and nutrient loads were measured in 186 flow events across 22 sub‐catchments with different proportions of remnant woodland. Using multiple linear regression analysis we develop a predictive model for pollutant loads. Of the attributes examined a combination of runoff and the proportion of the stream length draining remnant vegetation was the best predictor. The sediment yield per unit area from a catchment containing no remnant vegetation is predicted to be between 50 and 200 times that of a fully vegetated channel network; total phosphorus between 25 and 60 times; total nitrogen between 1.6 and 4.1 times. There are ~48 000 km of streams in the region of which 32% drain areas of remnant vegetation. Of these 17 095 km are above the region's water storage dams. We estimate that decreasing the sediment and phosphorus loads to Moreton Bay by 50% would involve rehabilitating ~6350 km of the channel network below the dams; halving the total nitrogen load would require almost complete restoration of the channel network. Copyright © 2014 John Wiley & Sons, Ltd.     

The performance of rainwater tanks for stormwater retention and water supply at the household scale: an empirical study

Urban stormwater run‐off degrades the ecological condition of streams. The use of rainwater tanks to supplement water supply can reduce the frequency and volume of urban stormwater run‐off that is otherwise conveyed directly to streams via conventional stormwater drainage systems. Few studies, however, have examined the use of tanks in the context of managing flow regimes for stream protection, with most focussed uniquely on their water conservation benefits. We used measured tank water level data to assess the performance of 12 domestic rainwater tanks against the dual criteria of their ability to (i) reduce potable mains water usage and (ii) retain run‐off from rainfall events and thus reduce the volume and frequency of stormwater run‐off. We found that five households relied almost entirely on tank water. Three of the tanks achieved stormwater retention performance approaching that of the same area of pre‐developed land, although nine did not – a consequence of limited demand and small tank capacity. Our results suggest that tank water usage can result in substantial reductions in mains water use, if regular and sufficiently large domestic demands are connected to tanks. In many cases, such demands will also result in the best stormwater retention performance. Our results highlight an opportunity to design tank systems to achieve multiple objectives. Application of similar analyses in different locations will help to optimize tanks for simultaneous water supply and stormwater retention purposes. Copyright © 2014 John Wiley & Sons, Ltd.     

Refinement of Phosphorus Determination in Quartz by LA‐ICP‐MS through Defining New Reference Material Values

The aim of this study was to improve the quality of laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) determination of phosphorus in crystalline quartz. Over the last decade, the Geological Survey of Norway has routinely performed trace element determinations on quartz from both operating and potential quartz deposits by LA‐ICP‐MS. The determined phosphorus concentrations were, with but few exceptions, consistently within the range of 10 to 30 μg g^?1, results that seemed to be both too high and too consistent. The multi‐material calibration curve obtained from a suite of reference materials (NIST SRM 610, 612, 614, 1830, BAM No. 1 amorphous SiO₂ glass) did not define a precise regression line. Published phosphorus concentrations for the reference materials are poorly constrained and the observed dispersions along the multi‐material calibration curve suggest that some of the reference values may be inaccurate. Furthermore, the calibration curve did not pass through the origin of the [(cps ³¹P/cps ³⁰Si) · cone. Si] vs. P concentration diagram; thus, in addition to the uncertainties of the literature values of phosphorus, it is difficult to define the calibration curve. Three reference materials (NIST SRM 614, 1830, synthetic quartz KORTH) were sent for phosphorus accelerator implantation, providing an independent and accurate (± 3%) approach for determining phosphorus concentrations in crystalline quartz. The intrinsic phosphorus concentrations of the three implanted samples plus those for NIST SRM 610 and 612 were determined by secondary ion mass spectrometry (SIMS), yielding new phosphorus values for NIST SRM 610, 612, 614 and 1830. Using these new values resulted in a better defined LA‐ICP‐MS calibration curve. However, the source of the ICP‐MS related background could not be defined, such that it must still be empirically corrected for.     

Platinum-Group Elements in Sulphide Minerals, Platinum-Group Minerals, and Whole-Rocks of the Merensky Reef (Bushveld Complex, South Africa): Implications for the Formation of the Reef

The concentrations of platinum-group elements (PGE), Co, Re,Au and Ag have been determined in the base-metal sulphide (BMS)of a section of the Merensky Reef. In addition we performeddetailed image analysis of the platinum-group minerals (PGM).The aims of the study were to establish: (1) whether the BMSare the principal host of these elements; (2) whether individualelements preferentially partition into a specific BMS; (3) whetherthe concentration of the elements varies with stratigraphy orlithology; (4) what is the proportion of PGE hosted by PGM;(5) whether the PGM and the PGE found in BMS could account forthe complete PGE budget of the whole-rocks. In all lithologies,most of the PGE (65 up to 85%) are hosted by PGM (essentiallyPt–Fe alloy, Pt–Pd sulphide, Pt–Pd bismuthotelluride).Lesser amounts of PGE occur in solid solution within the BMS.In most cases, the PGM occur at the contact between the BMSand silicates or oxides, or are included within the BMS. Pentlanditeis the principal BMS host of all of the PGE, except Pt, andcontains up to 600 ppm combined PGE. It is preferentially enrichedin Pd, Rh and Co. Pyrrhotite contains, Rh, Os, Ir and Ru, butexcludes both Pt and Pd. Chalcopyrite contains very little ofthe PGE, but does concentrate Ag and Cd. Platinum and Au donot partition into any of the BMS. Instead, they occur in theform of PGM and electrum. In the chromitite layers the whole-rockconcentrations of all the PGE except Pd are enriched by a factorof five relative to S, Ni, Cu and Au. This enrichment couldbe attributed to BMS in these layers being richer in PGE thanthe BMS in the silicate layers. However, the PGE content inthe BMS varies only slightly as a function of the stratigraphy.The BMS in the chromitites contain twice as much PGE as theBMS in the silicate rocks, but this is not sufficient to explainthe strong enrichment of PGE in the chromitites. In the lightof our results, we propose that the collection of the PGE occurredin two steps in the chromitites: some PGM formed before sulphidesaturation during chromitite layer formation. The remainingPGE were collected by an immiscible sulphide liquid that percolateddownward until it encountered the chromitite layers. In thesilicate rocks, PGE were collected by only the sulphide liquid. KEY WORDS: Merensky Reef; Rustenburg Platinum Mine; sulphide; platinum-group elements; image analysis; laser ablation ICP-MS     

城市空间形态的最低成本-周期扩张规律——以昆明为例

城市形态演化反演城市土地利用模式的转变,是内部最低成本土地利用模式驱动力的外部表达。这一城市空间格局演变遵循本文提出的"外部扩张,内部填充"相互交替总体规律。它既是集聚与扩散驱动因子作用的结果,也是植入与再植入的"扬弃"选择过程的交互作用产物。基于最低成本—周期扩张模型的假设,本文选取昆明建成区近现代的影像资料,运用形态学的视角分析城市空间结构的变迁,探寻城市形态演化规律。结果表明:(1)从城市形态演变的一般理性微观、宏观过程来看,城市形态变迁在统计学上遵循最低成本—周期扩张规律假设;(2)在最低成本—周期扩张模型内,公共投资与基层设施建设变动及其要素替代效应对形态的周期性扰动响应是其核心作用机制。     

Between the devil and the deep blue sea: Functional conflicts in Cape Town''s Victoria and Alfred Waterfront

The global phenomenon of waterfront revitalization is a planning strategy commonly employed by city and port authorities eager to overcome the redundancy and associated urban decay of their docklands. The spatial transformation that generally accompanies such initiatives often results in functional conflict. Focusing on the redevelopment of the traditional dockland precinct of the South African portcity of Cape Town, this paper shows how attempts to rationalize pre-existing harbour activities resulted in conflict between the developer, the Victoria and Alfred Waterfront Company, and its largest industrial tenant, the fishing industry. The utilization of existing harbour space and, more specifically, questions of tenure and affordable rentals are identified as the principal elements of the contentious negotiations between these parties.