Abstract
Freshwater lagoons comprise important coastal ecosystems and natural buffers between urbanized land areas and open ocean in the Rio de Janeiro State, Brazil. Studies of sediment and water chemistry, zooplankton and bacterial communities to assess the extent of anthropogenic disturbance are available. Here we contribute with an organic-geochemical approach supplemented by some microbiological aspects to complete the characterization of these lagoonal ecosystems. Bulk organic matter and extractable lipids (aliphatic hydrocarbons, alcohols and fatty acids, sterols) were investigated from two locations per lagoon: at the seaward site and landward ends - and at two depth intervals (0-3 and 3-6 cm) per site. Urbanized Imboacica Lagoon received increased anthropogenic input over the most recent years represented by the topmost 3 cm of sediment, whereas deeper sediment layers are less affected by human influence. Eutrophication or nutrient availability favored enhanced algal/cyanobacterial growth. In remote Cabiúnas and Comprida Lagoons pristine conditions are preserved. Organic matter from vascular plants dominates (chain length of free lipids up to C36), which is exceptionally well preserved by acidic lagoonal waters. Differentiation between landward and seaward sites in these two lagoons is less well established due to much smaller surface/volume to catchment ratios. No anthropogenic influences are yet detectable in sediments of Cabiúnas and Comprida Lagoons.
Highlights
In the densely populated Rio de Janeiro State (Brazil), freshwater lagoons comprise important coastal ecosystems, often forming natural buffer regions between urbanized land areas and the openKLAUS-GERHARD ZINK ET AL.et al 1998) and bacterial communities (Furtado and Esteves 1997, Biesboer et al 1998)
It supports bacterial activity that results in decomposition and nutrient recycling
The lagoons are situated in the coastal area of the Macaé region, Brazil (22 ̊30’S and 44 ̊42’W) (Fig. 1) and were formed during the last Holocene transgression period (Perrin 1984)
Summary
In the densely populated Rio de Janeiro State (Brazil), freshwater lagoons comprise important coastal ecosystems, often forming natural buffer regions between urbanized land areas and the open. Et al 1998) and bacterial communities (Furtado and Esteves 1997, Biesboer et al 1998). In addition studies in the Patos Lagoon (Brazil), the largest in South America, have demonstrated chemical processes concerning nutrients and trace metals on a larger scale but in a comparable environmental setting (Windom et al 1999). Organic material from autochthonous and allochthonous origin accumulates in the sediment of aquatic ecosystems. It supports bacterial activity that results in decomposition and nutrient recycling. For a complete characterization of lagoonal ecosystems, an approach using organic-geochemical techniques combined with microbiological data and general limnological studies is especially informative
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