Urbanization is a major cause of loss of coastal wetlands. Urbanization also exerts significant influences on the structure and function of coastal wetlands, mainly through modifying the hydrological and sedimentation regimes, and the dynamics of nutrients and chemical pollutants. Natural coastal wetlands are characterized by a hydrological regime comprising concentrated flow to estuarine and coastal areas during flood events, and diffused discharge into groundwater and waterways during the non-flood periods. Urbanization, through increasing the amount of impervious areas in the catchment, results in a replacement of this regime by concentrating rain runoff. Quality of run-off is also modified in urban areas, as loadings of sediment, nutrients and pollutants are increased in urban areas. While the effects of such modifications on the biota and the physical environment have been relatively well studied, there is to date little information on their impact at the ecosystem level. Methodological issues, such as a lack of sufficient replication at the whole-habitat level, the lack of suitable indices of urbanization and tools for assessing hydrological connectivity, have to be overcome to allow the effects of urbanization to be assessed at the ecosystem level. A functional model is presented to demonstrate the impact of urbanization on coastal wetland structure and function.

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Monitoring trace metal concentrations in dynamic estuarine waters is not straightforward. This study demonstrated that important information could be obtained from intensive sampling of physicochemical parameters and trace metal concentrations, in the Gold Coast Broadwater, Australia. A regular pattern of variation in Cu and Ni concentrations was related to the movement of water passed point sources with tidal flows, rather than due to conventional estuarine mixing of end-member waters. However, this approach was logistically demanding and expensive. The diffusive gradients in a thin film (DGT) technique was used as an alternative method due to its continual time-integrated response to changes in trace metal concentrations. Significant correlations were found between 24 h DGT-labile measurements and 0.45-microm filterable measurements, on time-averaged composite samples (grab samples combined every 4 h for 24 h), for Cu (n = 24, r = 0.965, p < 0.001), Pb (n = 24, r = 0.799, p < 0.001), Zn (n = 17, r = 0.909, p < 0.001), and Ni (n = 23, r = 0.916, p < 0.001). DGT-labile measurements as a fraction of 0.45 microm-filterable concentrations were 21 +/- 2% for Cu, 29 +/- 11% for Pb, 28 +/- 5% for Zn, and 27 +/- 12% for Ni, demonstrating the speciation capabilities of DGT. Although DGT measurements were confirmed as being highly operationally defined, DGT was still found to be very promising as a monitoring approach, particularly for dynamic estuarine waters.

Various natural and anthropogenic processes influence heavy metal concentrations within estuaries. In situ, time-integrated DGT measurements made over concurrent tidal phases found significantly higher concentrations of Cu (probability p=0.017), Zn (p=0.003) and Ni (p=0.003) during the flood phase, because the incoming tide passes several point sources. DGT-reactive Cu concentrations significantly decreased with increased tidal-flushing and vice versa within a marina (correlation r=-0.788, p=0.02). DGT measurements also recorded significant increases in Cu (4 out of 4 sites, p<0.001) and Zn (3 out of 4 sites, p< or =0.015) after a 24 mm rainfall event. Finally, DGT-reactive Cu increased significantly (p<0.001) during peak boating times, due to increased numbers of Cu-antifouled boats. This study demonstrates that, with judicious selection of deployment times, DGT measurements enable changes in heavy metal concentrations to be related to various cycles and events within estuaries.

The oxygen and nutrient dynamics of the zooxanthellate, upside down jellyfish (Cassiopea sp.), were determined both in situ and during laboratory incubations under controlled light conditions. In the laboratory, Cassiopea exhibited a typical Photosynthesis-Irradiance (P-I) curve with photosynthesis increasing linearly with irradiance, until saturation was reached at an irradiance of *400 lE m -2 s -1 , with photosynthetic compensation (photosynthesis = respiration) being achieved at an irradiance of *50 lE m -2 s -1 . Under saturating irradiation, gross photosynthesis attained a rate of almost 3.5 mmol O 2 kg WW -1 h -1 , whereas the dark respiration rate averaged 0.6 mmol O 2 kg WW -1 h -1 . Based upon a period of saturating irradiance of 9 h, the ratio of daily gross photosynthesis to daily respiration was 2.04. Thus, photosynthetic carbon fixation was not only sufficient to meet the carbon demand of respiration, but also to potentially support a growth rate of *3% per day. During dark incubations Cassiopea was a relatively minor source of inorganic N and P, with the high proportion of NO X (nitrate ? nitrite) produced indicating that the jellyfish were colonised by nitrifying bacteria. Whereas, under saturating irradiance the jellyfish assimilated ammonium, NO X and phosphate from the bathing water. However, the quantities of inorganic nitrogen assimilated were small by comparison to carbon fixation rates and the jellyfish would need to exploit other sources of nitrogen, such as ingested zooplankton, in order to maintain balanced growth. During in situ incubations the presence of Cassiopea had major effects on benthic oxygen and nutrient dynamics, with jellyfish occupied patches of sediment having 3.6-fold higher oxygen consumption and 4.5-fold higher ammonium regeneration rates than adjacent patches of bare sediment under dark conditions. In contrast at saturating irradiance, jellyfish enhanced benthic photosynthetic oxygen production almost 100-fold compared to the sediment alone and created a small sink for inorganic nutrients, whereas unoccupied sediment patches were sources of inorganic nutrients to the water column. Overall, Cassiopea greatly enhanced the spatial and temporal heterogeneity of benthic fluxes and processes by creating ''hotspots'' of high activities which switched between being sources or sinks for oxygen and nutrients over diurnal irradiance cycles, as the metabolism of the jellyfish swapped between heterotrophy and net autotrophy.

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