Evidence for dissolved organic nitrogen and phosphorus uptake during a cyanobacterial bloom in Florida Bay

Abstract

Florida Bay, a shallow, seagrass-dominated bay in southern Florida, USA, receives significant nutrient inputs and has experienced seagrass losses and microalgal blooms within the last several decades. Inorganic nutrient inputs have been well characterized, but the role of organic nutrients, specifically of dissolved organic nitrogen (DON) and organic phosphorus (DOP), in supporting microbial processes in the bay is unknown. In this study various techniques were used to assess the importance of these nutrients along a transect in Florida Bay when a cyanobacterial bloom occurred in the central region in November 2002. These techniques included measurements of ambient particulate and dissolved nutrients, enzyme (urease and alkaline phosphatase) activities, and experiments to determine rates of 15 N uptake (nitrate, ammonium, urea, and amino acids over a period of 0.5 h) and long-term (48 h) changes in microbial biomass and 15 N natural abundance in enrichment bioassays. The cyanobacterial bloom in central Florida Bay was associated with the highest concentrations of DON and DOP, whereas the microflagellate-and diatom-dominated eastern bay region was associated with the highest concentrations of inorganic nutrients. The zeaxanthin:chlorophyll a ratio (an indicator of the relative contribution of cyanobacteria to phytoplankton biomass) was positively correlated with the rate of uptake of urea, and negatively correlated with the rate of uptake of inorganic nitrogen. The opposite pattern was observed for the fucoxanthin:chlorophyll a ratio (indicative of relative diatom biomass) and the peridinin:chlorophyll a ratio (indicative of relative photosynthetic dinoflagellate biomass), suggesting that different algal groups were using different N substrates. Biomass responses in the bioassay experiments showed that phytoplankton (as chlorophyll a) responded to DON additions in the western region and to DOP additions in the eastern region, but heterotrophic bacteria, in contrast, responded to DOP additions in the west and DON additions in the east. These findings thus demonstrate the potential for different sources of N, including DON, to stimulate different components of the algal community, and for the phytoplankton and bacteria to respond differently to N and P.KEY WORDS: Florida Bay · Cyanobacteria · Organic N · Organic P · Nutrient limitation · Urease · Alkaline phosphatase · Bioassay · Nutrient uptake rates Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 280: [73][74][75][76][77][78][79][80][81][82][83] 2004 changes. Since the onset of industrialization in the 1880s, the health of the Florida Bay ecosystem has been negatively impacted on both decadal (e.g. increasing eutrophication) and centurial (e.g. changes in land use and water management practices within southern Florida) time-scales (Fourqurean & Robblee 1999). These anthropogenic changes have led to a significant alteration in freshwater flow patterns within the Everglades, causing declines in seagrass d...

The role of dissolved organic matter bioavailability in promoting phytoplankton blooms in Florida Bay

“…The question we then ask is how much of the N and P in DOM is accessible to the phytoplankton? Specific components of DOM, such as urea, may be taken up directly by some phytoplankton (Waser et al, 1998;Lewitus et al, 2000;Glibert et al, 2004), but they are typically minor fractions of the pool. Therefore, the majority of the DOM pool must first be remineralized to the inorganic forms by bacteria prior to phytoplankton uptake.…”

Spatial variability in Florida Bay particulate organic matter composition: combining flow cytometry with stable isotope analyses

“…These differences are not unexpected, as noted in previous studies of the Florida Bay planktonic community (Phlips & Badylack, 1996;Lavrentyev et al, 1998;Phlips et al, 1999;Glibert et al, 2004;Frankovich et al, 2006). Indeed, the physical and chemical variability of the system and the isolated nature of the various basins of Florida Bay certainly lead to the high level heterogeneity in planktonic communities.…”

“…is a superior competitor for phosphorus, coupling high SRP affinity with rapid uptake velocities and the facility for luxury uptake. In addition, this genus is very well adapted to changing environmental conditions, exhibiting a broad range of salinity tolerance, the ability to saturate photosynthesis and growth at very low irradiance, and potential to assimilate dissolved organic nutrients (Stockner, 1988;Phlips et al, 1989;Luo & Mitsui, 1994;Lavrentyev et al, 1998;Glibert et al, 2004). In contrast, Cyanobacteria 4, with higher chlorophyll, and slightly larger-sized cells, were absent from Trout Creek and present in lower abundance in the northeastern bay as compared to the western stations.…”

“…2; Cyanobacteria 2), with 801.9±56.3Â10 3 and 532.9±25.0Â10 3 cells ml )1 present only at the western Florida Bay sites (Ninemile Bank and Sprigger Bank, respectively). S. elongatus is known to form blooms in central and western Florida Bay (Lavrentyev et al, 1998;Phlips et al, 1999;Glibert et al, 2004). A second population of Synechococcus sp, distinguished by higher phycoerythrin and a smaller size ( Fig.…”

“…Isotopicenrichment tracer techniques assessing utilization of organic nitrogen (N) substrates during a cyanobacteria bloom event have shown in one instance that cyanobacterial blooms in Central Florida Bay are associated with high dissolved organic nutrient availability, whereas areas dominated by microflagellate and diatom communities are dependent upon inorganic nutrient resources (Glibert et al, 2004). The utility of natural isotopic abundance measurements to assess biogeochemical coupling between nutrient resources and planktonic communities has not been well explored.…”