Ecological Effects of Sewage Pollution in Biscayne Bay, Florida: Sediments and the Distribution of Benthic and Fouling Macro-Organisms

Evidence is presented on both harmful and fertilizing effects of sewage in northern Biscayne Bay, Florida, as determined by the quantitative distribution of benthic and fouling macro-organisms. Harmful effects, as indicated by absence of benthic life, were limited to 3 of 65 stations within 200 yards of sewage sources in greater than average depths. Absence of spermatophytes at many stations may have been due to pollution. Fertilizing effects, as measured by abundance of benthic life, were most pronounced in a narrow band roughly 200 to 600 yards from sewage sources in shallow water with good tidal circulation where the bottom consisted of firm sandy mud (Md. 0.125 - 0.500 mm.). Indicator organisms of both effects were present. Using in part the principles for describing bottom communities developed by Thorson, two plant-animal associations were found to occupy distinct benthic zones, one primarily in highly polluted areas and the other in less polluted areas. The initially settling fouling organisms in highly polluted waters (greater than 10,000 MPN) were mainly tubiculous amphipods. Sediments have been analyzed for median grain diameter, sorting coefficient, and oxygen uptake measured in the Warburg respirometer. Unusually high oxidizable organic content in sediments was limited to 7 of 65 stations, five of which had median diameters of less than 0.100 mm.