The experimental verification of a towed body and cable dynamic response theory

Measurements of towed body motion in a laboratory towing tank have validated the mathematical model used as a basis for predicting body and cable dynamic behaviour under seagoing conditions.     

Estimation of surface chlorophyll on an exposed mudflat using digital colour-infrared (CIR) photography

The usefulness of field-based digital Colour-InfraRed (CIR) photography to quantify concentrations of chlorophyll on the surface of exposed mudflats is investigated. Multiple images, each 626 mm by 467 mm, were acquired during Austral summertime using a Duncantech three-band CIR camera from two areas of mudflat in the upper reaches of Sydney Harbour. Sediment samples were obtained from within the field of view of the camera and their chlorophyll concentration was estimated spectrophotometrically. After the camera images were normalised to compensate for the effects of variations in the intensity of downwelling solar radiation, chlorophyll was estimated for each 0.9 mm square pixel using a suite of five different vegetation indices. Regression analysis was used to determine the strength of the relationship between the index values and the estimates of chlorophyll from the in situ samples. Indices constructed from near-infrared and red bands were found to have the strongest relationships with in situ chlorophyll estimates (R² ranging from 0.28 to 0.79) and indices derived from near-infrared and green bands the weakest (R² ranging from 0.16 to 0.22). The vegetation indices highlighted complex small-scale variability in chlorophyll distribution that was not evident in the original camera images. These findings indicate that field-based CIR photography will provide a useful tool for the non-destructive determination of benthic chlorophyll.     

Content versus concentration: Effects of units on measuring the biogeochemical properties of soft sediments

A variety of scientific disciplines require measurements of the biological, physical and chemical (biogeochemical) properties of soft sediments. These properties vary temporally and spatially in a highly complex fashion, due to interaction and feedback between the processes that control them. This paper presents theoretical and real examples showing how interaction between the properties of sediments and the use of different units of expression (i.e. content and concentration) can change patterns in the data and thereby alter the interpretation of results. Common mistakes leading to incorrect measurements being taken and incorrect inference of data are presented and a new conceptual way of thinking about natural sediments is discussed. We conclude that the presentation and interpretation of data expressed as concentration is preferable to content for biogeochemical measurements in sediments, because content data is confounded by various factors (including core density/mass), leading to mistaken inference.     

Effect of biodeposits from mussel culture on macroinvertebrate assemblages at sites of different hydrodynamic regime

The present study examined for differences in macroinvertebrate assemblage composition inside and outside of mussel farm sites experiencing different hydrodynamic regimes. Multivariate analysis revealed that there were significant differences in macroinvertebrate assemblage composition (averaged across seasons) between samples taken inside and outside of the two relatively low energy sites, whilst no such difference was observed for the relatively high energy site. Taxa that best discriminated between the dissimilarities observed in macroinvertebrate assemblage composition inside and outside farms were principally polychaetes (more abundant inside) and ophiuroids (more abundant outside). Sediment total organic matter and number of mussel shells were the parameters that best explained the difference in macroinvertebrate assemblage observed at the two relatively sheltered farm study sites. No taxa or environmental variables were particularly good at discriminating or explaining differences observed inside and outside the relatively high energy farm site. The present study indicates there is a relationship between the hydrodynamic regime of a farm site, organic enrichment of seabed sediments by mussel biodeposits, and a subsequent modification of the macroinverebrate assemblages. This finding has implications for the site selection of mussel farms in coastal environments.     

Diffraction of multidirectional random waves by multiple rectangular submarine pits

A numerical model is presented to predict the interaction of multidirectional random surface waves with one or more rectangular submarine pits. The water depth is assumed uniform and the method involves the superposition of diffraction solutions based on linearized shallow water wave theory obtained by a two-dimensional boundary integral approach. The incident wave conditions are specified using a discrete form of the Mitsuyasu directional spectrum. The present numerical model has been validated through comparisons with previous theoretical results for regular waves. Good agreement was obtained in all cases. Based on these comparisons it is concluded that the present numerical model is an accurate and efficient tool to predict the wave field around multiple submarine pits and navigation channels in many practical situations.     

Acute ecological risk associated with soot deposition: a Persian Gulf case study

Many studies have been carried out in the past to provide solutions to the threat of chemicals to the ecosystem. However, the basic scientific capability to predict the risk of adverse effects on the ecological system has not kept pace with society's increasing demand for uses of chemicals. As a scientific methodology for quantifying the risk to the environment associated with exposure to chemicals, ecological risk assessment is increasingly important in environmental problem solving. The purpose of this paper is to present a methodology for conducting ecological risk assessment using deterministic and probabilistic approaches. A systematic discussion on elements of ecological risk assessment is presented. A framework of ecological risk assessment is explained with the help of the Persian Gulf environmental problem as a case study. The study was based on the output of a long-range transport model of soot deposition in the Gulf. Results of the assessment using the deterministic and probabilistic approaches are discussed.     

Boundary element modeling of multidirectional random waves in a harbor with partially reflecting boundaries

A numerical model is presented for the prediction of the wave field due to the diffraction of directional random waves in a harbor of arbitrary shape with partially reflecting boundaries. The water depth is assumed uniform and the method is based upon the superposition of diffraction solutions for monochromatic waves obtained by a two-dimensional boundary integral equation approach. The incident wave conditions are specified using a discrete form of the Mitsuyasu directional spectrum. The present numerical model has been validated through comparisons with previous experimental data and theoretical results for both regular and random wave diffraction by offshore breakwaters and in harbors. Good agreement was obtained in all cases. Based on these comparisons it is concluded that the present numerical model is an accurate and efficient tool to predict the wave field inside a harbor or around a breakwater in many practical applications.     

An empirical expression for aerodynamic resistance in the unstable boundary layer

In unstable conditions, the set of equations defining the aerodynamic resistance to sensible heat transfer, r _a , cannot be solved analytically. An iterative technique must be used to obtain r _a exactly, but this is cumbersome and time consuming. In this paper, a new, empirical equation is presented relating the ratio, Q, of the aerodynamic resistances in neutral and unstable conditions, to the bulk Richardson number, Ri _B . The equation takes the form Q = a + b(–Ri) ^c , where a, b and c are empirical functions of (z – d)/z _om . This model is shown to predict r _awith a mean absolute error of 0.06 s m^–1 over the ranges -15 < Ri _B < 0 and 10 < (z – d)/z _om < 2300. Statistical comparison with other equations that have been proposed for r _a in unstable conditions indicates the superior precision of the model presented here.     

Multiproxy record for the last 4500 years from Lake Shkodra (Albania/Montenegro)

A multi‐proxy record is presented for approximately the last 4500 cal a BP from Lake Shkodra, Albania/Montenegro. Lithological analyses, C/N ratio and δ¹³C of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic. The δ¹⁸O record of bulk carbonate indicates the presence of two prominent wet periods: one at ca. 4300 cal a BP and one at ca. 2500–2000 cal a BP. The latter phase is also found in southern Spain and Central Italy, and represents a prominent event in the western and central Mediterranean. In the last 2000 years, four relatively wet intervals occurred between ca. 1800 and 1500 cal a BP (150–450 AD), 1350–1250 (600–700 AD), 1100–800 (850–1150 AD), and at ca. 90 cal a BP (1860 AD). Between ca. 4100 and 2500 cal a BP δ¹⁸O values are relatively high, with three prominent peaks indicating drier conditions at ca. 4100–4000 cal a BP, ca. 3500 and at ca. 3300 cal a BP. Four additional drier events are identified at 1850 (ca. 100 AD), 1400 (ca. 550 AD), 1150 (800 AD) and ca.750 cal a BP (1200 AD). The pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area, which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment. However, since ca. 900 cal a BP a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities. Copyright © 2012 John Wiley & Sons, Ltd.     

Stochastic Modeling of Groundwater Extractions over a Data-Sparse Region of Australia

Setting limit on groundwater extractions is important to ensure sustainable groundwater management. Lack of extraction data can affect interpretations of historical pressure changes, predictions of future impacts, accuracy of groundwater model calibration, and identification of sustainable management options. Yet, many groundwater extractions are unmetered. Therefore, there is a need for models that estimate extraction rates and quantify model outputs uncertainties arising due to a lack of data. This paper develops such a model within the Generalized Linear Modeling (GLM) framework, using a case study of stock and domestic (SD) extractions in the Surat Cumulative Management Area, a predominantly cattle farming region in eastern Australia. Various types of extraction observations were used, ranging from metering to analytically-derived estimates. GLMs were developed and applied to estimate the property-level extraction amounts, where observation types were weighted by perceived relative accuracy, and well usage status. The primary variables found to affect property-level extraction rates were: yearly average temperature and rainfall, pasture, property area, and number of active wells; while variables most affecting well usage were well water electrical conductivity, spatial coordinates, and well age. Results were compared with analytical estimates of property-level extraction, illustrating uncertainties and potential biases across 20 hydrogeological units. Spatial patterns of mean extraction rates (and standard deviations) are presented. It is concluded that GLMs are well suited to the problem of extraction rate estimation and uncertainty analysis, and are ideal when model verification is supported by measurement of a random sample of properties.