Excessive human-derived nutrient availability has been implicated as a primary driver in the decline of the water quality and biota of coastal ecosystems. In 2003, seven sites along an urbanized section (∼100 km) of the Atlantic littoral coastline in east-central Florida were assessed for the bio-availability of the primary nutrients nitrogen and phosphorus. Ratios of dissolved inorganic nitrogen (DIN = nitrate nitrite ammonium) to soluble reactive phosphorus (SRP) in 74 beach water samples averaged 8:1, indicating strong water column nitrogen-limitation. DIN concentrations ranged from 0.69 to 8.11 µM with a grand mean of 2.10 µM, a value two-fold above the reported threshold value of ∼1 µM that saturates growth of Florida red tide, Karenia brevis and macroalgae species utilized in this study, such as Ulva lactuca. The majority (mean = 56%) of this DIN was in the form of ammonium, even during a peak upwelling event in June and August, suggesting the importance of anthropogenic land-based nitrogen as the primary N source. Macroalgae from subtidal sabellariid worm reefs were assessed for δ15N. At all study sites, macroalgal tissue mean δ15N values ranged from 8.7 to 9.9‰, values similar to those in macroalgae from sewage-polluted coastal areas, such as Boston Harbor. Many of the abundant macroalgae collected on these reefs, including Ulva lactuca, Chaetomorpha linum, Gracilaria tikvihae, and Caulerpa prolifera, are known sewage indicator species in other eutrophic coastal water bodies receiving excessive anthropogenic nutrient loads. These results suggest the need for improved nutrient removal in wastewater treatment facilities that discharge nearly 100 million liters of secondary-treated sewage effluent/day into the highly transmissive silica-sand barrier island of Brevard and Indian River Counties in east-central Florida.
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