Summer Blooms Of Cyanobacteria Research Articles

Long-term primary production trends in the Laurentian Great Lakes: a comparison of geochemical methods

Sediment cores from 12 locations throughout the Laurentian Great Lakes basin were analyzed for geochemical indicators of primary production. Sediment analytes included organic and inorganic contents, carbonates, sediment accumulation rates, total organic carbon and nitrogen concentrations, carbon and nitrogen isotope composition, and trends in spectroscopically inferred chlorophyll a (and its main diagenetic products). When multiple indicators were considered, production records related to recent cultural eutrophication and catchment activities were clear in the paleorecords. Indicators derived from loss-on-ignition (organic and inorganic content) were strongly associated with periods of human settlement in the catchments that increased overall sediment loads to the lakes. The ratio of carbon to nitrogen tracked catchment inputs of carbon, especially during periods of watershed development in western Lake Superior. Sediment records such as chlorophyll a and δ13Corg appear to be reliable indicators of trends in past algal abundance, particularly in Lake Erie, which has a well-known history of higher production and cultural eutrophication. These analytes also correlated well with past measured water quality surrogates for lake primary productivity and stressor data such as human populations in adjacent watersheds. A comparison among indicators revealed that several show redundancy as good proxies of production or productivity, though context was important. For instance, heavier isotopes of carbon and nitrogen are often prescribed as sedimentary indicators of lake productivity, but these two analytes were negatively correlated in Lake Superior, possibly due to long-term increases in cyanobacteria or changes in the nitrogen source. An increase in sediment carbonates can indicate summer blooms of cyanobacteria (a phenomenon that was clearly apparent in Lake Ontario) or catchment erosion. To make convincing geochemical inferences of primary production in the Great Lakes, it is recommended that a weight of evidence be built through the use of multiple indicators.

Drivers of phytoplankton dynamics in old Tampa Bay, FL (USA), a subestuary lagging in ecosystem recovery

In the past four decades, consistent and coordinated management actions led to the recovery of Tampa Bay, FL (USA) – an estuary that was declared dead in the 1970s. An exception to this success story is Old Tampa Bay, the northernmost subestuary of the system. Compared to the other bay segments, Old Tampa Bay is characterized by poorer water quality and spring and summer blooms of cyanobacteria, picoplankton, diatoms, and the saxitoxin-producing dinoflagellate Pyrodinium bahamense. Together, these blooms contribute to light attenuation and lagging recovery of seagrass beds. Yet, studies of phytoplankton dynamics within Old Tampa Bay have been limited – both in number and in their spatiotemporal resolution. In this study, we used field sampling and continuous monitoring to (1) characterize temporal and spatial variability in phytoplankton biomass and community composition and (2) identify key drivers of the different phytoplankton blooms in Old Tampa Bay. Overall, temporal variability in phytoplankton biomass (using chlorophyll a as a proxy) and community composition surpassed spatial variability of these parameters. We found a base community of small diatoms and flagellates, as well as certain dinoflagellates, that persisted year round in the system. Seasonally, freshwater runoff stimulated phytoplankton growth, specifically that of chlorophytes, cyanobacteria and other dinoflagellates -- consistent with predictions based on ecological theory. On shorter time scales, salinity, visibility, and freshwater inflows were important predictors of phytoplankton biomass. With respect to P. bahamense, environmental drivers including salinity, temperature and dissolved nutrient concentrations explained ∼24% of the variability in cell abundance, indicating missing explanatory parameters in our study for this taxon, such as cyst density and location of cyst beds. Spatially, we found differences in community trajectories across north–south and west–east gradients, with the northernmost sampling station being the most unique in the region. This work contributes to the knowledge of phytoplankton biomass and community composition in Tampa Bay by generating spatially and temporally rich phytoplankton community and environmental data for the Old Tampa Bay subestuary. Moreover, it enhances our understanding of bloom drivers and provides recommendations for ecosystem management. Specifically, our findings support continued nutrient reduction measures as a way to mitigate seasonal blooms of diatoms, cyanobacteria and chlorophytes, but not necessarily blooms of P. bahamense. Prediction and mitigation of P. bahamnese blooms should incorporate first order drivers such as cyst location and abundance.

Cyanobacterial blooms in the Gulf of Gdańsk (southern Baltic): the main effect of eutrophication

Abstract The most striking aspect of eutrophication in the Baltic are the summer blooms of cyanobacteria. Some of the blooms are toxic to marine organisms and poisonous to people. Our studies, conducted over the last three decades, report on mass occurrences of Aphanizomenon flos-aquae (L.) Ralphs and Nodularia spumigena Mertens. It is generally assumed that cyanobacterial blooms in the Baltic Sea are stimulated by the low ratio of N:P and initiated by high water temperatures. The mean annual value of this ratio in the Gulf of Gdańsk, since 1981, is 7:1-8:1, with the lowest values, of about 4, being seen in July when the cyanobacterial blooms begin. During three years of observations (1992-1994) the smallest number of recorded taxa was reported in 1993, concurrent with the lowest water temperature (16°C in summer). In August 1994, when the temperature increased to 22°C, a huge bloom was seen. Nodularia spumigena was very abundant in that bloom, and nodularin concentration of 2.59 mg toxin per g dry weight of bloom sample was recorded. A similar situation has also been observed in the years 2003-2006.