Three river conceptual models make differing predictions about the major source of primary production in lowland rivers, acknowledging the importance of primary productivity in the ecology and management of lowland rivers. Patterns of primary production in lowland rivers are still an area of considerable uncertainty. The objective of this study was to examine the major sources and transformations of organic matter in an Australian lowland river and compare them to the predictions of existing models. The broad approach adopted was to quantify the contribution from the major ecosystem components and compare these with estimates of system metabolism determined using open water measures of diel oxygen change. Three 4-km river reaches were selected to represent the extent of variation found along the free-flowing lowland sections of the Murray River, one of Australia's largest and most regulated rivers. Annual open water gross primary production (GPP) estimates for the Murray R. during this study ranged from 221 to 376 gC m À2 y À1 and were similar to other large rivers. Examination of the net contribution of organic matter to the channel indicates that primary productivity in the Murray R. is derived from a combination of phytoplankton, riparian vegetation and macrophytes, but that the major source varies both spatially and temporally. The present study confirms that the River Continuum Concept (RCC), the Flood Pulse Concept (FPC) and Riverine Productivity Model (RPM) all have some application to Australian lowland rivers, but that synthesis of the models will be difficult until we can incorporate the extent, causes and consequences of primary production variability. This study also highlights the importance of the microbial loop and macrophytes in the ecology of the Murray R.

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Summary The importance of microeukaryotes (protists, ciliates, fungi, algae and small invertebrates) in riverine food webs is well recognised, but the difficulty in surveying these taxa has meant that monitoring of biodiversity in rivers has focused on larger organisms. Microeukaryote biodiversity was assessed by pyrosequencing of the conserved 18S rRNA gene during summer and autumn at two river sites and a weir pool site that form a flow gradient in the Murray River, Australia. Concurrent measurements were made of phytoplankton concentrations, irradiance conditions, river metabolism and associated water quality attributes. Based on operational taxonomic units derived from the molecular analyses, significant differences were identified in eukaryotes between the river and the weir pool. Taxonomic assignment was possible for 66% of the operational taxonomic units, reflecting the large amount of unsurveyed diversity present. Visual identification of algae corroborated the orders identified in the molecular data set, and more orders were detected using pyrosequencing. Day length, depth of light penetration and phytoplankton biomass and primary productivity were strongly linked to eukaryote community composition suggesting the importance of algae as an energy source. Our finding that microeukaryote biodiversity is linked with environmental characteristics demonstrates the potential of 18S rRNA pyrosequencing for more comprehensive assessment of the condition of an aquatic ecosystem, but further data are required to confirm this potential.

Sell Fisheries hmti!te Gd}'llia. Pol.!md The paper presents data on primary production and chloro phyll a concentrations at two stations located in the Gulf of Gdaiisk (Baltic Sea). The primary production in 1987 was much higher than the mean values for the region, observed in other years when the production was 125-200 g C/m 2 a. Our observations show the primary production in the Puck Bay to be approximately two times that in offshore waters of the Gdaiisk Deep. The chloro phyll contents decrease along the Vistula estuary-Gdaiisk Deep transect.

The paper presents data on Secchi depth in the Southern Baltic waters. The mean annual Secchi depth is 8.2 m in the Gdansk Deep, 9.6 m in the Bomholm Deep, 9.9 m in the southern part of the Gotland Deep, and 5.7 m in the Gulf of Gdansk. The Secchi depth is subject to seasonal fluctuations, their amplitude being approximately 35% of the mean annual value. A trigono• metric polynomial was applied to describe periodic intra-annual changes of Secchi depth in the Baltic. The largest water trans parency was observed in winter, the transparency being lowest in summer. Effects of chlorophyll a concentrations on water transparency are presented in a graphic form.

Consistent and accurate information on inland water quality over wider areas of the Australian continent are required to assess current condition and trends in response to key environmental and climatic impacts. Optical remote sensing offers a method to objectively assess this over multiple spatial scales provided retrieval algorithms are accurate. Here, we present the results of initial research aimed at exploring the optical variability in Australian inland waters and of linear matrix inversion algorithms applied to both in situ reflectance spectra and high resolution satellite data to retrieve water inland water quality parameters. In situ sampling reveals a high degree of optical variability both within and between lakes across the regions sampled with regional patterns evident; sub-tropical and tropical lakes exhibited greater optical complexity than deep lakes in midlatitude regions. Clustering analysis indicated the presence of 8 different optical water types in the water bodies measured. The ability of the linear matrix inversion algorithm to map water quality, tested on in situ reflectance and WorldView2 image datasets, showed relative accuracy when parameter sets were sufficient to achieve algorithm closure. Improved algorithm parameterization will be required to account for the high degree in spatial and temporal optical variability observed in Australian inland waters.