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

Abstract

The clear, shallow, oligotrophic waters of Florida Bay are characterized by low phytoplankton biomass, yet periodic cyanobacteria and diatom blooms do occur. We hypothesized that allochthonous dissolved organic matter (DOM) was providing a subsidy to the system in the form of bound nutrients. Water from four bay sites was incubated under natural light and dark conditions with enrichments of either DOM (>1 kD, 2ÂDOM) or inorganic nutrients (N+P). Samples were analyzed for bacterial numbers, bacterial production, phytoplankton biomass, phytoplankton community structure, and production, nutrients, and alkaline phosphatase (AP) activity. The influence of 2ÂDOM enrichment on phytoplankton biomass developed slowly during the incubations and was relatively small compared to nutrient additions. Inorganic nutrient additions resulted in an ephemeral bloom characterized initially as cyanobacterial and brown algae but which changed to dinoflagellate and/or brown algae by day six. The DIN:TP ratio decreased 10-fold in the N+P treatments as the system progressed towards N limitation. This ratio did not change significantly for 2ÂDOM treatments. In addition, these experiments indicated that both autotrophic and heterotrophic microbial populations in Florida Bay may fluctuate in their limitation by organic and inorganic nutrient availability. Both N+P and 2ÂDOM enrichments revealed significant and positive response in bioavailability of dissolved organic carbon (BDOC). Potential BDOC ranged from 1.1 to 35.5%, with the most labile forms occurring in Whipray Basin. BDOC at all sites was stimulated by the 2ÂDOM addition. Except for Duck Key, BDOC at all sites was also stimulated by the addition of N+P. BDOC was lower in the dry season than in the wet season (5.56% vs. 16.86%). This may be explained by the distinct chemical characteristics of the DOM produced at different times of year. Thus, both the heterotrophic and autotrophic microbial communities in Florida Bay are modulated by bioavailability of DOM. This has ramifications for the fate of DOM from the Everglades inputs, implicating DOM bioavailability as a contributing factor in regulating the onset, persistence, and composition of phytoplankton blooms.

Evidence for Coupling of the Carbon and Phosphorus Biogeochemical Cycles in Freshwater Microbial Communities

“…This is one of the first experimental microcosm studies to provide a quantitative estimate of the C-supplementation effect on APA in microbial communities. It is consistent with prior published research in the natural environment showing that dissolved organic C has significant contributory effects on activity of bacterial alkaline phosphatase and primary productivity in freshwater and marine ecosystems (e.g., Stewart and Wetzel, 1982;Chróst et al, 1989;Boyer et al, 2006). Moreover, similar results of C-enrichment effects on APA were recently reported for laboratory microcosm studies using organic-rich arctic soil microbial communities (Anderson et al, 2018).…”

Presence and patterns of alkaline phosphatase activity and phosphorus cycling in natural riparian zones under changing nutrient conditions

“…Despite decades of research focusing on dissolved reactive P (DRP, mainly as inorganic phosphates), growing evidence indicates that dissolved organic P (DOP) is an important driver of limnological production (Labry et al, 2002;Boyer et al, 2006). As a most-studied enzyme, capable of hydrolyzing a broad spectrum of DOP, alkaline phosphatase (APase) and its activity (APA) have also received increasing attention and are considered to be indicative of P status in both algal cultures and natural phytoplankton populations (Cembella et al, 1984;Dyhrman et al, 2002;Novotna, 2010).…”

Changing Bacterial Growth Efficiencies across a Natural Nutrient Gradient in an Oligotrophic Estuary

“…Bacterial production was also examined in the Boyer et al (2006) Evidence of terrestrial runoff impacting microbial results is present in the current data set and is supported by previous studies. Previous work has shown that freshwater runoff into estuaries lowers both salinity and δ…”

“…As reviewed previously, a large portion of the BR results were negative because of calculated decreases in DIC rather than increases expected during the respiration process (these are represented as <0.001 in Table 3). Additionally, conversion of raw respiration data to μg C L Boyer et al (2006) ), suggesting that temporal variation rather than spatial variation was an influence on BA in the current study.…”

“…The DO samples were analyzed using an automated Winkler titration system (modified from Friederich et al 1991 Both bacterial abundance (BA) and bacterial production (BP) were determined using methods described by Boyer et al (2006). Bacterial abundance assays were performed using the DAPI staining technique (Coleman 1980, Porter andFeig 1980).…”