A dynamic hydrological Monte Carlo simulation model to inform decision-making at Lake Toolibin,Western Australia

Lake Toolibin, an ephemeral lake in the agricultural zone of Western Australia, is under threat from secondary salinity due to land clearance throughout the catchment. The lake is extensively covered with native vegetation and is a Ramsar listed wetland, being one of the few remaining significant migratory bird habitats in the region. Currently, inflow with salinity greater than 1000 mg/L TDS is diverted from the lake in an effort to protect sensitive lakebed vegetation. However, this conservative threshold compromises the frequency and extent of lake inundation, which is essential for bird breeding. It is speculated that relaxing the threshold to 5000 mg/L may pose negligible additional risk to the condition of lakebed vegetation. To characterise the magnitude of improvement in the provision of bird breeding habitat that might be generated by relaxing the threshold, a dynamic water and salt balance model of the lake was developed and implemented using Monte Carlo simulation. Results from best estimate model inputs indicate that relaxation of the threshold increases the likelihood of satisfying habitat requirements by a factor of 9.7. A second-order Monte Carlo analysis incorporating incertitude generated plausible bounds of [2.6, 37.5] around the best estimate for the relative likelihood of satisfying habitat requirements. Parameter-specific sensitivity analyses suggest the availability of habitat is most sensitive to pan evaporation, lower than expected inflow volume, and higher than expected inflow salt concentration. The characterisation of uncertainty associated with environmental variation and incertitude allows managers to make informed risk-weighted decisions.     

A review of light-scattering techniques for the study of colloids in natural waters

In order to understand the movement of colloidal materials in natural waters, we first need to have a means of quantifying their physical characteristics. This paper reviews three techniques which utilize light-scattering phenomena to measure the translational diffusion coefficient, the rotational diffusion coefficient, and the electrophoretic mobility of colloids suspended in water. Primary emphasis is to provide sufficient theoretical detail so that hydrologists can evaluate the utility of photon correlation spectrometry, electrophoretic light scattering, and electric birefringence analysis.     

Soil-air exchange of organochlorine pesticides in the Southern United States

Soil samples were collected from 30 farms in Alabama, Louisiana and Texas during 1999-2000 to determine residues of organochlorine pesticides (OCPs). One or more of the DDT compounds (p,p'-DDT, o,p'-DDT, p,p'-DDD, p,p'-DDE, o,p'-DDE) was above the quantitation limit (0.1 ng g(-1) dry weight) in every soil, and toxaphene was above the quantitation limit (3 ng g(-1)) in 26 soils. Chlordanes, dieldrin and hexachlorocyclohexane (HCH) isomers occurred less frequently (quantitation limits 0.1 ng g(-1) for dieldrin and 0.05 ng g(-1) for chlordanes and HCHs). OCPs were measured in air at 40 cm above the soil at selected farms to investigate soil-air partitioning. Concentrations of OCPs in air were positively and significantly (P<0.001-0.004) correlated to soil concentrations for toxaphene, p,p'-DDT, o,p'-DDT, p,p'-DDE, dieldrin, and trans-nonachlor. The regression was weaker (P=0.022) for cis-chlordane and not significant for trans-chlordane (P=0.43) nor gamma-HCH (P=0.80). Approach to soil-air equilibrium was assessed by calculating fugacities in the soil and air (f(s) and f(a)) for samples with quantifiable residues in both compartments. The fugacity fraction f(s)=0.5 at equilibrium and is <0.5 or >0.5 for net deposition and net volatilisation, respectively. Fugacity fractions varied greatly for different soil-air pairs, reflecting generally disequilibrium conditions. Mean fugacity fractions indicated near-equilibrium for some OCPs (p,p'-DDE, chlordanes, trans-nonachlor and dieldrin) and net volatilisation for others (p,p'-DDT, o,p'-DDT, toxaphene, gamma-HCH). Chiral analysis showed that enantioselective degradation of (+) or (-) o,p'-DDT in soil was accompanied by enrichment or depletion of the corresponding enantiomers in the overlying air, although there appeared to be some dilution by racemic o,p'-DDT from regional air transport.     

Interactions of metals affect their distribution in tissues of Phragmites australis

Culms of Phragmites australis were grown in vermiculite in a greenhouse. Some plants were exposed to 1000 microg/g Cu or Pb or Zn, or combinations of two or three of those metals. When plants reached senescence, they were harvested and analyzed for metal concentrations in upper leaves, lower leaves, stems and roots. While all metals accumulated in highest concentrations in the roots, Zn accumulated in aboveground tissues far more than the other metals. Furthermore, the concentration of any one metal in the different tissues was affected by the presence of other metals. The amount of copper in upper leaves increased when Zn was also present with the Cu. The amount of Cu in roots was increased in the presence of Pb and/or Zn. The amount of Zn in lower leaves was reduced when Cu was also present along with Zn. Thus, when combinations of metals were present, the distribution of metals was altered. The most important interactions appeared to be of Cu and Zn, which may reflect competition for binding sites on metal-binding proteins.     

Past changes in Arctic terrestrial ecosystems, climate and UV radiation

At the last glacial maximum, vast ice sheets covered many continental areas. The beds of some shallow seas were exposed thereby connecting previously separated landmasses. Although some areas were ice-free and supported a flora and fauna, mean annual temperatures were 10-13 degrees C colder than during the Holocene. Within a few millennia of the glacial maximum, deglaciation started, characterized by a series of climatic fluctuations between about 18,000 and 11,400 years ago. Following the general thermal maximum in the Holocene, there has been a modest overall cooling trend, superimposed upon which have been a series of millennial and centennial fluctuations in climate such as the "Little Ice Age spanning approximately the late 13th to early 19th centuries. Throughout the climatic fluctuations of the last 150,000 years, Arctic ecosystems and biota have been close to their minimum extent within the most recent 10,000 years. They suffered loss of diversity as a result of extinctions during the most recent large-magnitude rapid global warming at the end of the last glacial stage. Consequently, Arctic ecosystems and biota such as large vertebrates are already under pressure and are particularly vulnerable to current and projected future global warming. Evidence from the past indicates that the treeline will very probably advance, perhaps rapidly, into tundra areas, as it did during the early Holocene, reducing the extent of tundra and increasing the risk of species extinction. Species will very probably extend their ranges northwards, displacing Arctic species as in the past. However, unlike the early Holocene, when lower relative sea level allowed a belt of tundra to persist around at least some parts of the Arctic basin when treelines advanced to the present coast, sea level is very likely to rise in future, further restricting the area of tundra and other treeless Arctic ecosystems. The negative response of current Arctic ecosystems to global climatic conditions that are apparently without precedent during the Pleistocene is likely to be considerable, particularly as their exposure to co-occurring environmental changes (such as enhanced levels of UV-B, deposition of nitrogen compounds from the atmosphere, heavy metal and acidic pollution, radioactive contamination, increased habitat fragmentation) is also without precedent.     

Can a water market avert the “double-whammy” of trade reform and lead to a “win–win” outcome?

This paper focuses on the linkages between water and trade policies, using Morocco as a case. This country is typical of many in that policy protects its import competing agricultural and industrial sectors while water in irrigated agriculture is priced below its marginal value product. Changing water policy without correcting for these other distortions leads to a more inefficient allocation of water. On the other hand, reforming trade policy alone can make farmers growing crops protected pre-reform worse off. Using an intertemporal, applied general equilibrium model, we find that trade reform actually creates an opportunity to pursue water policy reform. Creating a water user-rights market post trade reform not only compensates for the decline in farmers’ profits caused by the trade reform, but also raises the efficiency of water allocation and hence benefits the economy as a whole.     

(137)Cs inter-plant concentration ratios provide a predictive tool for coral atolls with distinct benefits over transfer factors

Inter-plant concentration ratios (IPCR) [Bqg(-1)(137)Cs in coral atoll tree food crops/Bqg(-1)(137)Cs in leaves of native plant species whose roots share a common soil volume] can replace transfer factors (TF) to predict (137)Cs concentration in tree food crops in a contaminated area with an aged source term. The IPCR strategy has significant benefits relative to TF strategy for such purposes in the atoll ecosystem. IPCR strategy applied to specific assessments takes advantage of the fact that tree roots naturally integrate (137)Cs over large volumes of soil. Root absorption of (137)Cs replaces large-scale, expensive soil sampling schemes to reduce variability in (137)Cs concentration due to inhomogeneous radionuclide distribution. IPCR [drinking-coconut meat (DCM)/Scaevola (SCA) and Tournefortia (TOU) leaves (native trees growing on all atoll islands)] are log-normally distributed (LND) with geometric standard deviation (GSD)=1.85. TF for DCM from Enewetak, Eneu, Rongelap and Bikini Atolls are LND with GSDs of 3.5, 3.0, 2.7, and 2.1, respectively. TF GSD for Rongelap copra coconut meat is 2.5. IPCR of Pandanus fruit to SCA and TOU leaves are LND with GSD=1.7 while TF GSD is 2.1. Because IPCR variability is much lower than TF variability, relative sampling error of an IPCR field sample mean is up 6- to 10-fold lower than that of a TF sample mean if sample sizes are small (10-20). Other IPCR advantages are that plant leaf samples are collected and processed in far less time with much less effort and cost than soil samples.