CAN URBANIZATION LIMIT IRON AVAILABILITY TO ESTUARINE ALGAE

Bioavailable forms of iron are highly unstable in oxygenated saline wa ter, but one way in which iron bioavailability to algae can be enhance d is by chelation to dissolved organic matter (DOM). We hypothesized t hat urbanization-associated deforestation in Murrells Inlet, South Car olina caused a reduction of iron bioavailability to estuarine phytopla nkton by decreasing the supply of forest-derived DOM (i.e., the iron c helation source). Bioassay experiments were conducted comparing the po tential for iron depletion by phytoplankton in natural populations and Cylindrotheca closterium (Ehr.) Reimann et Lewin cultures, transferre d to Murrells Inlet and North Inlet (an undeveloped estuary) water. Ch elated iron addition to incubated natural populations transferred to M urrells Inlet water resulted in increased abundances of phototrophic m icroplankton (accounted for by Cylindrotheca), nanoplankton, and picop lankton (dominated by Synechococcus spp.). In North Inlet water, iron enrichment to natural populations only enhanced by Synechococcus growt h, but this stimulation was much less than that in Murrells Inlet wate r. The effect of iron on pro Synechococcus growth in Murrells Inlet wa s striking (up to 34-fold greater abundance in iron-enriched treatment ), suggesting that estuarine Synechococcus may be sensitive to iron st ress. The results indicate that iron could be depleted much more readi ly in Murrells Inlet water, and suggest that iron availability to estu arine phytoplankton may be reduced by urbanization-related practices s uch as coastal forest clear-cutting. Copyright (C) 1997 Elsevier Scien ce B.V.