No abstract

No abstract

No abstract

No abstract

Multi-proxy analyses on sediment cores from two closed basin lakes in the Serra Sul de Caraj as were used to reconstruct environmental changes in south-eastern Amazonia during the late Quaternary. The sediment record between 65 000 and 40 000 cal a BP (older dates with high level of uncertainty) is dominated by organic sediments intercalated with detritus (e.g. Al and Ti), indicating fluctuating lake levels related to changes in precipitation. A period of lower precipitation occurred from 40 000 to 35 000 cal a BP. Between $35 000 and 20 000 cal a BP, the dominance of detrital sediments suggests wetter and warmer conditions. However, iron enrichment in a siderite-rich layer associated with the end of this period coincides with the Last Glacial Maximum, suggesting diagenetic changes in the profundal portion of the lakes and indicating a transition from oxidizing to reducing conditions. Subsequently, the period between $20 000 and 15 000 cal a BP was marked by a transition from drier to wetter climate, resulting in higher energy flows (e.g. Zr) and increased erosion of the basins. Another drier period was observed between $7000 and 3000 cal a BP (low detrital input and high Ca/Ti), when the lake levels were very low and eutrophication was high.

High-resolution satellite images, digital elevation models, bathymetric and sedimentological surveys coupled with statistical analysis were used to understand the physical environment and discuss their influence on water quality of the five upland lakes of Serra Sul dos Carajás, southeast Amazonia. The lakes have mid-altitude ranges (elevation), very small (catchment) and shallow to very shallow (central basins). Based on the length, area and volume, Violão and TI (Três Irmãs)-3 lakes may present large vertical movements of the water due to wind action and weakly stratified waters. Trophic conditions based on depth and shore development (Ld) parameters must be used with caution, since Amendoim Lake is relatively deep, but it is oligotrophic to ultra-oligotrophic. Ld values suggest that the lakes are circular to subcircular and are likely formed by solution process, as also suggested by volume development. TI-2 Lake is only presenting convex central basin and has highest dynamic ratio (DR), thus it may have high sedimentation and erosion rates. Based on the relationship between studied parameters, morphometric index and DR likely influence temperature and dissolved oxygen of waters of TI-2 Lake due to its depth profile and wind-induced surface mixing. Nevertheless, water quality parameters are controlled by catchment characteristics of the lakes.

The conversion of mangrove areas into shrimp farming ponds has been indicated as the main activity responsible for the reduction in the area of this ecosystem along the northeastern coast of Brazil. The present study was conducted using remote sensing methods and a geographical information system with the aim of quantifying the participation of this activity in the reduction of the mangrove areas along the northern coast of the State of Pernambuco (northeast, Brazil), where shrimp farming has been implanted in last recent years. From 1973 to 2005, there was reduction of about 2.052 ha of mangrove, 197 ha of which were converted into shrimp ponds. Thus, the real contribution of shrimp farming to this reduction was just 9.6% of the total area. Other anthropogenic activities, such as agriculture, urban expansion and tourism, contributed greatly to the reduction in the mangrove areas along the northern coast of the State of Pernambuco.

No abstract