Soil fertility of fluvial islands increases with proximity to an Amazonian white-water river

The nutrient content of soils is considered a productivity key factor. Sediment input from Amazonian rivers is one of the natural sources of soil fertility for fluvial islands and riverbank flooded forests. Despite the importance of soil factors for ecosystems, few edaphic studies along riverine sediment-gradients have been undertaken in tropical areas. The current study provides a step forward by describing soil nutrients in a mixed water (sediment-poor black water with input of sediment-rich whitewater) fluvial archipelago. To investigate how geographic distance from a whitewater river mouth affects island soil properties, soil chemical and physical attributes were determined at 61 sampling sites on 35 islands. The studied Central Amazon fluvial islands showed high variability in our fluvisols soil properties. In general, the fluvial island soils were acid and with low fertility. Islands from Jaú and other sites closer to the sediment source (the river Rio Branco) had higher soil fertility than islands of the Anavilhanas Archipelago, which are further away from the sediment source. Our results show that sediment inputs from Amazonian rivers can play an important role in soil properties, and this research increases our understanding on the origin and evolution of one of the largest freshwater archipelagos in the world. Given that soil fertility is often correlated with forest productivity, the main results reported here may also help improve management plans and conservation policies for fluvial island environments of Central Amazonia.

Length-weight relationships of ornamental fish from floodplain lakes in the Solimões River basin (Iranduba, Amazonas, Brazil)

This research reports the LWR of ornamental fish from floodplain lakes of the Solimões River basin. The fish were caught in the Paciência island (a fluvial island) in two lakes Sacambú and Cacau using purse seine 7 m × 4 m and mesh size = 3 mm, once during the flood in June 2017 and dry in January 2018. The specimens captured were anesthetized using eugenol 15 mg · L–1, fixed formalin 10% and stored ethanol 70% after 10 days. This study provides the LWR parameters for the species Anablepsoides micropus, Anchoviella jamesi, Cichlasoma amazonarum, Heros efasciatus, Ctenobrycon hauxwellianus, Copella nattereri and Hemigrammus levis. The parameter a ranged from 0.0092 to 0.0229, b ranged from 2.78 to 3.50 and the R2 ranged from 0.985 to 0.998. The results represent new information about ornamental fish from floodplain lakes, with new LWR for five species that are not present in FishBase data set and probably are new for science. This study is preliminary and much work needs to be done especially in the Solimões River floodplain areas and with our research we hope to encourage new studies in the region.

Vegetational changes during the last millennium inferred from a palynological record from the Bananal Island, Tocantins, Brazil

The Bananal Island is regarded the largest fluvial island in the world, bounded by Araguaia and Javaés rivers, being located in southwest of Tocantins. The objectives of this work were to provide information about the vegetational changes that occurred at the Bananal Island, in order to contribute to the understanding the dynamics of past and current savanna and areas of ecotones with forests. Thus, a sedimentary core collected from a small lake at the Bananal Island plain was submitted to pollen and radiocarbon dating analyses. The results showed that the last millennium was dominated by forest reflecting a wet climate. At the beginning of the record (920-770 yr cal BP) the wet climate and high rainfall produced flooding during long rainy seasons that maintained the Javaés River connected to the studied lake, and hence, this environment was marked by the presence of a homogenous forest rich in Moraceae/Urticaceae, due to flooded soils occurrence. During the following period (770-304 yr cal BP) the reduced rainfall and shortening of the rainy seasons isolated the lake from the Javaés River for long periods, which caused a diversification of the forest and gave rise to the appearance of the components of floodplain forest and marsh vegetation adapted to waterlogged soils. Since 304 years cal BP to the present day this environment remained dominated by this diverse forest and the lacustrine conditions were also similar to previous phase, with a slight increase of moisture in the last 84 years that caused the increase of Piranhea.

First record of an immature green turtle Chelonia mydas (Linnaeus, 1758) (Testudines: Cheloniidae) on a fluvial island, Reserva Biológica do Parazinho, Amazonas river, Brazil

On March 8th, 2011 we recorded an immature green turtle Chelonia mydas at the Reserva Biológica do Parazinho, eastern Amazonia, Brazil. This record of C. mydas on a fluvial island, where the aquatic environment is a mixture of fresh and salt water, suggests that this typical marine species potentially tolerates lower levels of water salinity.