Dredging impact on an urbanized Florida bayou: effects on benthos and algal-periphyton

Environmental effects of dredging events have been uncommonly reported for shallow, residential estuaries characteristic of the Gulf of Mexico region. The objective of this study was to determine the impact of hydraulic dredg ing on an urbanized estuary. Physicochemical quality, benthic community com position, whole sediment toxicity, periphytic algal community composition a nd trace metal tissue quality were determined prior to and after dredging. The effects on surface water pH, dissolved oxygen, and temperature were neg ligible but photosynthetically active radiation was decreased at several st ations. Dredging significantly reduced benthic diversity and density (P < 0 .05). However, the sediments were not acutely toxic to the epibenthic, Amer icamysis bahia (formerly Mysidopsis bahia); survival averaged 93% (post-dre dging) and to 98% (pre-dredging). There were several post-dredging taxonomi c structural changes in the diatom-dominated, periphyton community but diff erences in mean density and three diversity indices were not significant. T race metal concentrations in periphyton after dredging were reduced from an average of 4-65% and significantly for mercury, zinc and chromium in sever al areas. It was concluded that the environmental impact of small-scale dre dging events in urbanized near-coastal areas, based on the selected paramet ers, are likely to be localized and of short-term environmental consequence . The choice of the target biota, response parameters and chemical analysis are important considerations in the environ-mental impact assessment of th ese periodic episodic events. Published by Elsevier Science Ltd.