Aim To produce an inventory of south-west Atlantic saltmarshes (from latitude 31°48¢ S to 43°20¢ S) using remotely sensed images and field sampling; to quantify their total area; to describe the biogeographical variation of the main habitats characterized by dominant vascular plants, in relation to major environmental factors; to test the hypothesis of predominance of the reversal pattern in plant distribution (sedges and grasses dominate the lower, regularly inundated zones, while the upper zones are occupied by more halophytic species) previously described; and to compare these south-west Atlantic saltmarshes with others world-wide. Location South-western Atlantic saltmarshesMethods Field samples of dominant emergent plant species positioned by the global positioning system (GPS) were obtained from most coastal saltmarshes (14) between southern Brazil and northern Patagonia, Argentina. Landsat satellite images were obtained and coastal saltmarsh habitats were quantified by supervised classification, utilizing points gathered in the field.Results Three main plant species dominated the low and middle intertidal saltmarsh, Spartina alterniflora Loesel., Spartina densiflora Brong. and Sarcocornia perennis (P. Mill.) A.J. Scott. The total area of the studied coastal saltmarshes was 2133 km 2 , comprising 380 km 2 of Sp. alterniflora marsh, 366 km 2 of Sp. densiflora marsh, 746 km 2 of Sar. perennis marsh and 641 km 2 of brackish marsh (dominated by Juncus acutus L., Juncus kraussii Hochst., Scirpus maritimus L., Scirpus americanus Pers. and Phragmites australis (Cav.) Trin.). Cluster analysis showed three habitat types: saltmarshes dominated by (1) Sp. densiflora and brackish species,(2) Sp. alterniflora and Sar. perennis and (3) Sp. densiflora only. The analysis of abiotic variables showed significant differences between groups of habitats and coordinated gradients of the abiotic variables. The southwest Atlantic coast showed decreasing mean annual rainfall (1200 to 196 mm) and increasing mean tidal amplitude (< 0.5 to > 2.5 m) from latitude 31°to 43°.Main conclusions South-west Atlantic saltmarshes are globally important by virtue of their total extent. Remote sensing showed that the reversal pattern in plant distribution is not widespread. Indeed, south-west Atlantic saltmarshes are better characterized by the presence of the halophytic genera Spartina and Sarcocornia. Our results support the interpretation that south-west Atlantic saltmarshes constitute a class of temperate type (sensu Adam, 1990) with transitional characteristics between Australasian-South African saltmarshes and west Atlantic saltmarshes.

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An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon processing at the global scale.

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1. Shallow lakes and ponds contribute disproportionally to species richness relative to other aquatic ecosystems. In-lake conditions (e.g. presence of submerged plants) seem to play a key role in determining diversity, as has been demonstrated for temperate lakes. When water quality deteriorates and turbidity increases, conditions in such lakes are affected drastically resulting in a loss of diversity. However, it is not clear whether subtropical lakes show the same pattern and whether the richness of all groups reacts similarly to environmental changes. 2. Our aim was to analyse the main factors explaining patterns of species richness in plankton, fish and submerged macrophyte assemblages in both turbid and clear subtropical shallow lakes. We analysed abiotic and biotic features of 18 subtropical, small-to mediumsized, shallow lakes along the Uruguayan coast. We compared both turbid and clear ecosystem states and evaluated the relative variance explained by the factors measured. 3. Variables describing lake and catchment morphology, as well as the percentage of the water column occupied by submerged macrophytes (%PVI) and water turbidity, had strong effects on taxon richness. Interestingly, individual biotic groups had dissimilar richness patterns. Macrophyte %PVI decreased with increasing lake area, while fish species richness showed the opposite pattern. Phytoplankton species richness increased with macrophyte %PVI, while the zooplankton richness pattern varied depending on the taxonomic group considered. 4. Overall, our results indicate that, as found for temperate lakes, a greater submerged plant cover promotes higher species richness in several groups, and that this may overwhelm the otherwise expected positive effect of lake size on species richness. On the other hand, small-bodied zooplankton predominated in lakes with high plant abundance. Our findings concur with recent studies, indicating that refuge capacity of aquatic plants might be weaker in (sub)tropical than in temperate shallow lakes.

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Lake Rodó (Montevideo, Uruguay) is a small, urban, hypertrophic lake undergoing restoration. In this study, we evaluated the nutrient removal efficiency and water quality improvement attributable to a water recirculation system, consisting of the lake and three connected pools converted to artificial wetlands dominated by free-floating hydrophytes. Eichhornia crassipes and Spirodela intermedia dominated the hydrophyte community during summer and winter, respectively, with the biomass production being maintained throughout the year. The maximum production values of E. crassipes were 11.3 and 5.6 g DW m -2 d -1 in the summers of 1998 and 2000, respectively, while those of S. intermedia were 2.7 and 0.8 g DW m -2 d -1 in the summers of 1999 and 2000, respectively. The aquatic plant community reduced the concentration of nutrients in the water column but did not significantly affect the sediment concentrations. Harvesting the hydrophytes removed the equivalent of 58-88% and 39-78% of the nitrogen (N) and phosphorus (P) load associated with the water column, respectively. In contrast, the harvests accounted for only 1-2% of the N and P load associated with the sediments. In the pools, the combination of water recirculation and hydrophytes generally diminished the algal biomass and the associated N and P, compared to that observed for the lake. The combined use of adequate aquatic plant harvests and hydraulic management increased the efficiency of the system and, therefore, seems to be a useful tool for restoring small, shallow lakes in tropical and subtropical regions.