High Cyanobacterial Abundance in Three Northeastern Gulf of Mexico Estuaries

Aquatic phytoplankton comprise a wide variety of taxa spanning more than 2 orders of magnitude in size, yet studies of estuarine phytoplankton often overlook the picoplankton, particularly chroococcoid cyanobacteria (cf. Synechococcus). Three Gulf of Mexico estuaries (Apalachicola Bay, FL; Pensacola Bay, FL; Weeks Bay, AL) were sampled during summer and fall 2001 to quantify cyanobacterial abundance, to examine how cyanobacterial abundance varied with hydrographic and nutrient distributions, and to estimate the contribution of cyanobacteria to the bulk phytoplankton community. Cyanobacterial abundances in all 3 estuaries were high, averaging 0.59 ± 0.76 X 109 L–1 in Apalachicola Bay, 1.7 ± 1.2 X 109 L–1 in Pensacola Bay and 2.4 ± 1.9 X 109 L–1 in Weeks Bay (mean ± standard deviation). Peak abundances typically occurred in the oligohaline zone (low salinity estuarine zone) during the summer. Freshwater sites had nearly undetectable abundances, and marine sites had abundances several-fold lower than the oligohaline zone. When converted to equivalent chlorophyll a concentrations, cyanobacteria comprised a large fraction of the total phytoplankton biomass, at times approaching 100% in all 3 systems. These observations clearly indicate a cyanobacterial community of estuarine origin that can make up a large proportion of phytoplankton biomass

Benthic Nutrient Flux in a Small Estuary in Northwestern Florida (USA)

Benthic nutrient fluxes of ammonium (NH4+), nitrite/nitrate (NO2- + NO3-), phosphate (PO4-3), and dissolved silica (DSi) were measured in Escambia Bay, an estuary within the larger Pensacola Bay system of northwestern Florida (USA). Our study occurred during a severe drought which reduced riverine inputs to Escambia Bay. Laboratory incubations of field-collected cores were conducted on 8 dates between June and October 2000 to estimate nutrient flux, and cores were collected from locations exhibiting a range of sediment organic matter content. NH4+ flux ranged from – 48.1 to 110.4 μmol m-2 h-1, but the mean flux was 14.6 μmol m-2 h-1. Dissolved silica (DSi) fluxes were also variable (-109. 3 to 145.3 μmol m-2 h-1), but the mean net flux (9.3 μmol m-2 h-1) was from the sediment to the water column. Bay sediment fluxes for NO2-+ NO3- and PO4-3 were less variable during this period (– 7.93 to 28.73 and – 1.74 to 3.29 μmol m-2 h-1 for NO2-+ NO3- and PO4-3, respectively). Low NH4+ fluxes were similar to published estimates from lagoonal Gulf of Mexico (GOM) estuaries, possibly due to the reduced freshwater input. Diminished regeneration of phosphate relative to inorganic nitrogen observed during the study period was consistent with previous research in Pensacola Bay suggesting phytoplankton phosphorus limitation. Finally, the estimated residence time of Escambia Bay and the mean turnover times for NH4+ and NO2-+ NO3- suggested that benthic flux significantly influenced nitrogen concentrations in overlying water

Biomass and Productivity of Thalassia testudinum in Estuaries of the Florida Panhandle

Thalassia testudinum often dominates seagrass meadows of the Florida panhandle but few measurements of productivity, biomass, density, turnover or leaf area index in this region have been made. We targeted 5 estuaries located at similar latitudes, 30⁰ ± 0.3⁰N: Big Lagoon, Santa Rosa Sound, St. Andrew Bay, St. Joseph Bay, and St. George Sound. This study was one component of a collaborative partnership of state and local researchers examining factors preventing recovery in panhandle estuarine areas that had historically contained seagrass in the 1940s and 1950s. Measurements were made twice in 2016, once in June and then again in summer or fall, except in Santa Rosa Sound where measurements were made 3 times. In the estuaries sampled for the second time in July or August, aboveground productivity was greater than in June. St. Joseph Bay had the highest aboveground productivity (4.3 g/m2/d) and 1—sided leaf area index (4.2) while St. George Sound had the lowest values (0.41 g/m2/d and 1.0). Principal component analysis suggested that St. Andrew Bay, Big Lagoon and Santa Rosa Sound were the most similar, with higher values for shoot densities and leaf turnover and lower salinities and watershed:water ratios. St. Joseph Bay had high aboveground productivity and salinity, and low turbidity. St. George Sound had low aboveground productivity, high total suspended solids and the highest watershed:water ratio. These baseline productivity estimates will be useful to assess the success of restoration efforts targeting seagrasses in the Florida panhandle and evaluate impacts of climate change on seagrasses

Implications of changing trends in hydroclimatic and water quality parameters on estuarine habitats in the Gulf Coastal Plain

Florida’s low elevation and geographic location make it particularly vulnerable to climate change effects such as sea level rise, increased intensity and frequency of storm events, and altered precipitation. Climate change is expected to exacerbate hydrological cycling with potential widespread implications for estuarine habitats that thrive under specific salinity regimes. We used historical data from sites in the eastern Gulf Coastal Plain, USA to examine trends and trend variability of several climatic, hydrologic, and estuarine water quality variables which have implications on seagrass and oyster habitat extent in downstream estuarine environments. We analyzed temperature, precipitation, low-flow and high-flow metrics (including the highest or lowest daily, 7-day average, and 30-day average) for each season annually over the period 1985–2020. We also analyzed estuarine water clarity metrics and salinity within waterbody segments of four estuary systems within the study area. Hydroclimate results showed that temperature increased at most sites. While there was variation in streamflow, the overall trend was declining streamflow. Declining trends were observed in most water clarity metrics, indicating improved clarity, especially in winter. Salinity generally declined across the study area. While overall streamflow decreased, main river stems to the estuaries had increasing trends in maximum streamflow characteristics, likely contributing to the decrease in estuarine salinity across the region. These results indicate that trends in streamflow (both magnitude and timing) in the watershed affect downstream estuarine water quality. These results have important implications on seagrass and oyster restoration and management efforts in the region, indicating that it is important to understand changing climatic and hydrologic conditions and how they may impact the estuarine resources

Spatial and seasonal patterns in sediment nitrogen remineralization and ammonium concentrations in San Francisco Bay, California

Nitrogen remineralization and extractable ammonium concentrations were measured in sediments from several locations in North and South San Francisco bays. In South Bay. remineralization rates decreased with depth in sediment and were highest in the spring following the seasonal phytoplankton bloom. At the channel stations, peak remineralization lagged peak water-column phytoplankton biomass (as measured by chlorophyll a) by a month. Remineralization rates were generally higher in South Bay than North Bay. The lower remineralization rates in North Bay may be a result of anomalously low phytoplankton production and thus reduced deposition to the sediments, as well as low riverine organic inputs to the upper estuary in recent years. Remineralization rates were positively correlated to carbon and nitrogen content of the sediments. In general, ammonium profiles in South Bay sediments showed no increase in deeper (4-8 cm) sediments. In North Bay, ammonium concentrations were greatest at stations with highest remineralization rates, and, in contrast to South Bay, extractable ammonium increased in deeper sediment. Differences in ammonium pools between North Bay and South Bay may be a result of increased irrigation by deep-dwelling macrofauna, which are more abundant in South Bay.Journal Articl

Production, respiration and net ecosystem metabolism in U.S. estuaries

Primary production, respiration, and net ecosystem metabolism (NEM) are useful indicators of ecosystem level trophic conditions within estuaries. In this study, dissolved oxygen data collected every half hour between January 1996 to December 1998 by the National Estuarine Research Reserve System Wide Monitoring Program were used to calculate primary production, respiration, and net ecosystem metabolism. Data from two sites at each of 14 Reserves were analyzed. On average, three quarters of the data available could be used to calculate metabolic rates. Data from two of the Reserves were used to evaluate the assumption of homogeneity of water masses moving past the oxygen sensor. Temperature was the single most important factor controlling metabolic rates at individual sites, although salinity was also important at about half the sites. On an annual basis, respiration exceeded gross primary production demonstrating that all but 4 of the 28 sites were heterotrophic.Journal ArticleFinal article publishe

Factors controlling net ecosystem metabolism in U.S. estuaries

High frequency dissolved oxygen data were analyzed to calculate primary production, respiration and net ecosystem metabolism (NEM) from 42 sites within 22 National Estuarine Research Reserves (NERR), 1995–2000. NERR sites are characterized by a variety of dominant plant communities including phytoplankton, salt marsh, seagrass, macroalgae, freshwater macrophyte, and mangrove, and are representative of the coastal bioregions of the United States. As expected from the wide diversity of sites, metabolic rates were temporally and spatially variable with the highest production and respiration occurring during the summer in Southeastern estuaries. Sites within different regions exhibited consistent seasonal trends in production, respiration, and NEM. Temperature was the most important environmental factor explaining within-site variation in metabolic rates; nutrient concentrations were the second most important factor. All but three of the 42 sites were heterotrophic (respiration was greater than production) on an annual basis. Habitat adjacent to the monitoring site, estuarine area, and salinity explained 58% of the variation in NEM. Open water sites or sites adjacent to mangroves or in marsh creeks were heterotrophic, while sites in or adjacent to submerged aquatic vegetation (eelgrass or macroalgal beds) were either autotrophic or near balance. Estuarine area was also a significant factor explaining variability in NEM; larger systems were closer to balance than smaller systems that trended toward heterotrophy. Freshwater sites were more heterotrophic than saline sites. Nutrient loading explained 68% of the variation in NEM among some of the sites. When these estimates were compared to the literature, metabolic rates from the NERR sites were much larger, often two to five times greater than rates from other estuarine and coastal systems. One explanation is that these small, generally shallow sites located near shore may have greater allochthonous organic inputs as well as significant benthic primary production than the large, deeper systems represented by the literature.Journal ArticleFinal article publishe

Nitrogen fixation in subtropical seagrass sediments:: Seasonal patterns in activity in Santa Rosa Sound, Florida, USA

Seagrass beds are important coastal habitats that are diminishing globally. Nitrogen, a key nutrient, often limits seagrass growth. Nitrogen fixation provides new, bioavailable nitrogen to the plants. This study explores its importance and factors controlling rates in sediments colonized by two dominant taxa in Northwest Florida, Thalassia testudinum and Halodule wrightii, compared to unvegetated sediments. We hypothesized that nitrogen fixation rates would be greater in seagrass colonized sediments, particularly during high growth periods. We expected to observe a positive relationship between rates and porewater sulfide concentrations because sulfate reducers were the dominant diazotrophs in similar studies. Rates were higher in vegetated areas. In H. wrightii beds, nitrogen fixation was driven by the decreased availability of porewater ammonium relative to phosphorus. In T. testudinum beds, rates were highest during winter. Organic matter may be a controlling factor in all substrate types albeit the exact mechanism driving nitrogen fixation differs slightly. During the summer and fall, nitrogen fixation provided between 1–15% of T. testudinum nitrogen demand. Annually, nitrogen fixation provided 4% and 1% of T. testudinum and H. wrightii nitrogen demand, respectively. Nitrogen fixation was an important source of nitrogen during periods of senescence and dormancy when organic matter content was high.Journal ArticleFinal article publishedThis article belongs to the Special Issue Organic Matter and Nutrient Cycling in Coastal Wetlands and Submerged Aquatic Ecosystems in an Age of Rapid Environmental Change – the Anthropocene

Progress report submitted to the U.S. Environmental Protection Agency, Region 4: Atmospheric deposition of mercury and trace metals to the Pensacola Bay watershed

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