Abstract
The structure of macrobenthic assemblages in Rio Grande Harbor was analyzed during and after a sulphuric acid spill in August 1988. Five stations were sampled four times between September 1988 and March 1999. At each station, three samples were taken using a van Veen grab (0.078 m2). A total of 22 taxa were collected including Crustacea (9 spp.), Polychaeta (7 spp.), Mollusca (3 spp.), Phoronida (1 sp.), Nemertinea (1 sp.), and Plathyelminthea (1 sp.). The macrobenthic assemblages suffered different impacts depending on station location and time: 1) immediate impact, i.e., during acid discharge, as at the station nearest (250 m) the acid spill source; 2) impact some time after the discharge, as at the station 500 m downstream from the acid spill source; and 3) absence of direct impact on the remaining sampling points, on the discharge area outer limit. The macrobenthic assemblage recovered six months after the sulphuric acid spill.
Highlights
On August 25, 1998, the Maltese ship NT Bahamas docked at the Rio Grande Harbor to unload approximately 12,000 metric tons of concentrated sulphuric acid (H SO )
Variable salinity characterizes the estuarine region as very unstable chemically (Niencheski & Baumgarten, 1997). These environmental conditions contribute to the low macrobenthic fauna diversity as shown by other works recording a maximum of 40 species in the estuarine region (Capitoli et al, 1978; Rosa-Filho & Bemvenuti, 1998; Bemvenuti & Netto, 1998)
Typical estuarine invertebrates are represented by about 15 species in the Patos Lagoon (Capitoli et al, 1978)
Summary
On August 25, 1998, the Maltese ship NT Bahamas docked at the Rio Grande Harbor to unload approximately 12,000 metric tons of concentrated sulphuric acid (H SO ). Even considering that pH is an important determinant of aquatic species distribution patterns (Abel, 1996), reviews which include many case studies of aquatic environmental pollution contain none on the effects of acid discharge on the structure and dynamics of macrobenthic assemblages in estuarine regions. The area is subject to a microtidal regime (tidal range < 1.0 m), and large fluctuations in water level and salinity are mainly associated with changes in meteorological conditions, such as rainfall and wind direction (Garcia, 1997; Niencheski & Baumgarten, 1997) In this region, winter and spring are usually the rainy seasons, and autumn and summer the dry ones. In the autumn and summer during minimal freshwater discharges and with SW winds, salinity can reach values near 34 in the estuary’s southern portion (Bemvenuti & Netto, 1998)
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