We sampled extensively (29 stations) at the Klang estuarine system over a 3-day scientific expedition. We measured physical and chemical variables (temperature, salinity, dissolved oxygen, total suspended solids, dissolved inorganic nutrients) and related them to the spatial distribution of phototrophic picoplankton (Ppico). Multivariate analysis of variance of the physicochemical variables showed the heterogeneity of the Klang estuarine system where the stations at each transect were significantly different (Rao's F₁₈, ₃₆ = 8.401, p < 0.001). Correlation analyses also showed that variables related to Ppico abundance and growth were mutually exclusive. Distribution of Ppico was best explained by the physical mixing between freshwater and seawater whereas Ppico growth was correlated with temperature.

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Temporal variation of Synechococcus, its production (μ) and grazing loss (g) rates were studied for 2 years at nearshore stations, i.e. Port Dickson and Port Klang along the Straits of Malacca. Synechococcus abundance at Port Dickson (0.3-2.3 × 10 cell ml) was always higher than at Port Klang (0.3-7.1 × 10 cell ml) (p < 0.001). μ ranged up to 0.98 day (0.51 ± 0.29 day), while g ranged from 0.02 to 0.31 day (0.15 ± 0.07 day) at Port Klang. At Port Dickson, μ and g averaged 0.47 ± 0.13 day (0.29-0.82 day) and 0.31 ± 0.14 day (0.13-0.63 day), respectively. Synechococcus abundance did not correlate with temperature (p > 0.25), but nutrient and light availability were important factors for their distribution. The relationship was modelled as log Synechococcus = 0.37Secchi - 0.01DIN + 4.52 where light availability (as Secchi disc depth) was a more important determinant. From a two-factorial experiment, nutrients were not significant for Synechococcus growth as in situ nutrient concentrations exceeded the threshold for saturated growth. However, light availability was important and elevated Synechococcus growth rates especially at Port Dickson (F = 5.94, p < 0.05). As for grazing loss rates, they were independent of either nutrients or light intensity (p > 0.30). In nearshore tropical waters, an estimated 69 % of Synechococcus production could be grazed.

With the projected increase in world population to 9 billion by 2050, along with per capita income growth, the demand for land and water resources is going to increase significantly. Conversion of land to intensive agriculture has led to dramatic decreases in plant, animal and insect biodiversity, with approximately 40% of the world's land surface now covered by croplands and pastures. Intensive agricultural practices cause erosion and lead to transport of soil particles and associated sorbed chemical (fertilizers, pesticides and herbicides) contaminants, which are responsible for significant degradation in the quality of both surface and subsurface water bodies. Soil erosion is an outcome of complex interactions between precipitation, physical transport, topography and conservation management strategies; and there have been many physically based mathematical models developed over the past 20 years that attempt to make predictions of erosion rates as a function of these interactions. These have been applied across scales corresponding to the laboratory, plot, hillslope and watershed with varying degrees of success. Two particular characteristic features of erosion data from both the laboratory and field scale that almost all these models have yet to reproduce reliably are hysteresis in the water discharge versus sediment discharge relationship, and the size distributions of transported sediment. We show that the model of Hairsine and Rose is able to produce the known common types of hysteresis curves, these being clockwise, counterclockwise , figure 8 (both flow orientations), and that these forms are in keeping with measured data in the literature. Numerical simulations demonstrate that such curves are a consequence of (i) the soil's sediment size distribution and (ii) the existence and evolution of a deposited layer of non-cohesive sediment on top of original un-eroded cohesive soil. It is shown that the initial state of this layer prior to a rainfall event plays a significant role in determining which type of hysteresis loop evolves. An application to published experimental data for flow-driven erosion down a rill is then considered. Excellent agreement between measured and suspended sediment concentrations was found throughout the hysteretic cycle.

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