Harmful Freshwater Algal Blooms, With an Emphasis on Cyanobacteria

Abstract

Suspended algae, or phytoplankton, are the prime source of organic matter supporting food webs in freshwater ecosystems. Phytoplankton productivity is reliant on adequate nutrient supplies; however, increasing rates of nutrient supply, much of it manmade, fuels accelerating primary production or eutrophication. An obvious and problematic symptom of eutrophication is rapid growth and accumulations of phytoplankton, leading to discoloration of affected waters. These events are termed blooms. Blooms are a prime agent of water quality deterioration, including foul odors and tastes, deoxygenation of bottom waters (hypoxia and anoxia), toxicity, fish kills, and food web alterations. Toxins produced by blooms can adversely affect animal (including human) health in waters used for recreational and drinking purposes. Numerous freshwater genera within the diverse phyla comprising the phytoplankton are capable of forming blooms; however, the blue-green algae (or cyanobacteria) are the most notorious bloom formers. This is especially true for harmful toxic, surface-dwelling, scum-forming genera (e.g., Anabaena, Aphanizomenon, Nodularia, Microcystis) and some subsurface bloom-formers (Cylindrospermopsis, Oscillatoria) that are adept at exploiting nutrient-enriched conditions. They thrive in highly productive waters by being able to rapidly migrate between radiance-rich surface waters and nutrient-rich bottom waters. Furthermore, many harmful species are tolerant of extreme environmental conditions, including very high light levels, high temperatures, various degrees of desiccation, and periodic nutrient deprivation. Some of the most noxious cyanobacterial bloom genera (e.g., Anabaena, Aphanizomenon, Cylindrospermopsis, Nodularia) are capable of fixing atmospheric nitrogen (N2), enabling them to periodically dominate under nitrogen-limited conditions. Cyanobacteria produce a range of organic compounds, including those that are toxic to higher-ranked consumers, from zooplankton to further up the food chain. Both N2- and non-N2-fixing genera participate in mutualistic and symbiotic associations with microorganisms, higher plants, and animals. These associations appear to be of great benefit to their survival and periodic dominance. In this review, we address the ecological impacts and environmental controls of harmful blooms, with an emphasis on the ecology, physiology, and management of cyanobacterial bloom taxa. Combinations of physical, chemical, and biotic features of natural waters function in a synergistic fashion to determine the sensitivity of water bodies. In waters susceptible to blooms, human activities in water- and airsheds have been linked to the extent and magnitudes of blooms. Control and management of cyanobacterial and other phytoplankton blooms invariably includes nutrient input constraints, most often focused on nitrogen (N) and/or phosphorus (P). The types and amount of nutrient input constraints depend on hydrologic, climatic, geographic, and geologic factors, which interact with anthropogenic and natural n...

Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea

“…Additionally, its occurrence and dominance was also possibly associate with the enhanced nutrient supply and resultant eutrophication in the lagoon water, in particular enrichment of dissolved nitrogen as described earlier (E. Gladfelter, personal communications; Piehler et al, 2004). For these cyanobacteria that do not contain heterocysts, both high nitrogen and phosphorus are needed to grow and develop (Pearl et al, 2001). Therefore, the high nutrient input in the lagoon water might influence the specific phytoplankton assemblages in there.…”

The low TN:TP ratio, a cause or a result of Microcystis blooms?

“…In our experiment, Microcystis bloomed in the enclosures (where the nutrient concentrations were in excess) either in an initial TN:TP o29 or TN:TP>29, indicating that the TN:TP ratio is not a deterministic factor for Microcystis blooms at least in the highly eutrophic Lake Donghu. Paerl et al [3] suggested that the ''N:P rule'' is less applicable to highly eutrophic systems when both N and P loadings are very large and N and P inputs may exceed the assimilative capacity of the phytoplankton. In the present study, TP in the enclosures with P-rich sediment enclosures increased dramatically with the development of Microcystis blooms, leading to a remarkable decrease of TN:TP ratios to about 10.…”

“…Historically, the most notorious nuisance algae in freshwater are cyanobacteria blooms which cause a variety of water quality problems including toxin production, hypoxia generating, odors, scums and possibly unsafe drinking water [1][2][3]. This has stimulated numerous investigations to seek for the deterministic factors for the anarchical dominance of cyanobacteria in phytoplankton community [4][5][6][7][8][9][10].…”

“…This has stimulated numerous investigations to seek for the deterministic factors for the anarchical dominance of cyanobacteria in phytoplankton community [4][5][6][7][8][9][10]. As noted by Pearl et al [3], many factors (e.g. temperature, light, N, P, C, grazing and microbial interactions) may be involved in the ecological success of cyanobacteria.…”

Critical nutrient thresholds needed to control eutrophication and synergistic interactions between phosphorus and different nitrogen sources

“…This is mainly because the process is controlled by lots of physical-chemical factors except for N/P ratio (Paerl 2009). Furthermore, the dominant species in Miyun Reservoir, Microcystis spp., belong to a non-nitrogen-fixing cyanobacterial genus (Paerl et al 2001), making their proliferation highly dependent on exogenous nitrogen sources.…”