Toxicity of pH,heavy metals and bisulfite to a freshwater green alga

Low pH markedly reduced the growth and photosynthetic activity of an $\text{Ankistrodesmus}$ sp. The alga could not grow at pH 3 and only slight growth occurred at pH 4. The alga grew well above pH 4 with maximum growth occurring at pH 6. The fixation of ¹⁴CO₂ followed a similar pattern with pH. The algal cells were also sensitive to mercury and bisulfite in acidic conditions. Algal growth and photosynthesis were reduced by mercury and bisulfite more at pH 5 than at pH 7. Lead was relatively non-toxic to the algal cells at both pH levels. Bisulfite inhibited the membrane transport of α-amino-¹⁴C-isobutyric acid at pH 5 but not at pH 7. The results suggest that algal growth and activity may be reduced in acidic lakes by low pH and that the toxicity of mercury and bisulfite is enhanced in acidic conditions.     

Improvements to measuring water flux in the vadose zone

Evaluating the impact of land use practices on ground water quality has been difficult because few techniques are capable of monitoring the quality and quantity of soil water flow below the root zone without disturbing the soil profile and affecting natural flow processes. A recently introduced method, known as equilibrium tension lysimetry, was a major improvement but it was not a true equilibrium since it still required manual intervention to maintain proper lysimeter suction. We addressed this issue by developing an automated equilibrium tension lysimeter (AETL) system that continuously matches lysimeter tension to soil-water matric potential of the surrounding soil. The soil-water matric potential of the bulk soil is measured with a heat-dissipation sensor, and a small DC pump is used to apply suction to a lysimeter. The improved automated approach reported here was tested in the field for a 12-mo period. Powered by a small 12-V rechargeable battery, the AETLs were able to continuously match lysimeter suction to soil-water matric potential for 2-wk periods with minimal human attention, along with the added benefit of collecting continuous soil-water matric potential data. We also demonstrated, in the laboratory, methods for continuous measurement of water depth in the AETL, a capability that quantifies drainage on a 10-min interval, making it a true water-flux meter. Equilibrium tension lysimeters have already been demonstrated to be a reliable method of measuring drainage flux, and the further improvements have created a more effective device for studying water drainage and chemical leaching through the soil matrix.     

Sustainability speak: Discourse and practice paradigms in subdivision design

In the last decade the concept of sustainable development has been widely embraced as the key to environmentally friendly development. However, in many instances the physical sustainability side of the equation stops at a rhetorical level and the ensuing developments fail to respond to ecological imperatives or to protect existing ecological values. Nowhere is this failure more evident than at the urban fringes of Melbourne, Australia, where residential land estate developments relentlessly engulf degraded agricultural lands that often contain the remnants of vegetative and hydrological ecological systems.

This paper postulates that while landscape design practitioners claim the 'authority of nature' (and, by extension, the land) for their design inspiration, in reality narrow practice foci and instrumental approaches have meant that the design of estates and subdivisions often make only token reference to ecological underpinnings. It is argued that instrumental influences on design decision-making are embedded in landscape-architectural professional culture and glossed over with an elusive rhetoric of care and concern for the environment. It is further postulated that individual expressions of interest in the land and its systems can make a substantive contribution to sustainable design practice and practical outcomes.     

Mid-trimester fetal ultrasound: Diagnostic dilemmas

Two cases are reported in which an unusual ultrasound finding preceded diagnostic amniocentesis and led to further work-up. In both cases a decision was made to terminate the pregnancy. One fetus in which a neck mass was detected by ultrasound was shown to be normal on post-mortem examination. The second fetus was aborted because of Rh sensitization and had the abnormality seen by ultrasound. However, this lesion, calcified intrahepatic plaques, had no presumed pathological significance. These cases suggest caution in the interpretation of results obtained with the new technologies used for prenatal diagnosis.     

Power and Sample Size Calculations for Linear Hypotheses Associated with Mixtures of Many Components using Fixed-Ratio Ray Designs

Response surface methodology, often supported by factorial designs, is the classical experimental approach that is widely accepted for detecting and characterizing interactions among chemicals in a mixture. In an effort to reduce the experimental effort as the number of compounds under study is increased, ray designs have been proposed to study combinations of chemicals. When interest is restricted to relevant mixing ratios, we are only interested in making inference along the specific rays of interest, as opposed to methods which use designs that require more experimental effort to support the estimation of a response surface over a broader experimental region. Methods have been developed for the test of additivity along multiple fixed-ratio rays. Of primary importance is the detection of interactions with reasonable power. The objective of this paper is to address power and sample size issues related to the hypothesis of no interaction.     

Behaviour of the institute of oceanographic science's rectangular midwater trawls: Theoretical aspects and experimental observations

The behaviour of two rectangular midwater trawls, the RMT 1+8 and the RMT 1+8M, is described. The RMT 1+8 consists of a pair of rectangular nets contained within the same frame-a small mouth area RMT 1 of mesh size 320 m and a larger RMT 8 of mesh size 4.5 mm. The RMT 1+8M is a multiple version of the RMT 1+8, combining three RMT 1s and three RMT 8s within the same frame. An expression is developed to describe the dependence of mouth angle on speed for the RMT 1+8 when towed horizontally. Theoretical estimates of the changes in mouth angle with speed agree well with experimental observations. Within normal towing speeds the RMT 1+8 is sensitive to changes in speed; this sensitivity is especially marked in the RMT 1. Between speeds of about 2.6 and 8.0 knots the RMT 8 does not alter its mouth angle with changes in speed; this behaviour is not shown by the RMT 1—at least within a practical speed range. The performance of the RMT 1+8M cannot be completely described by the theory developed for the RMT 1+8 and possible explanations for this are discussed. The multiple net is considerably less sensitive to changes in towing speed; all three nets of each type have similar mouth angles at a constant speed. Variations in warp load with speed for both trawls are described.