Patterns of phytoplankton primary productivity in the Neuse River estuary, North Carolina, USA

The recently described toxic dinoflagellate Pfiestena piscicida and morphologically similar Pfiesteria-like dinoflageiiates have become a major water quality issue with possible fish mortality and reported human health implications. The linkages between accelerated nutrient loading, eutrophication, and the proliferation of this group of dinoflagellates, however, are not well established for natural Systems. Phytoplankton pnmary production may provide a key link between nutrient inputs and potential outbreaks of Pfiesteria-like biflagellated zoospores in the Neuse River Estuary, North Carolina. The impacts of nutrient (NO3--nitrogen and ~0,~--phosphorus) supply rates, sediment-water column exchange, water column m~xing, and phytoplankton prey on the abundance of Pfiesteria-like non-toxic biflagellated zoospores were examined seasonally over 18 mo in a region of the Neuse River Estuary where fish-kiils attnbuted to P piscicida have been reported. Phytoplankton community responses to the manipulated vanables indicated that biomass and productivity were consistently N limited. Dominant phytoplankton taxa, including chlorophytes, diatoms, and cyanobacteria, exhibited significant biomass increases in response to N (as NO3-) additions. Phosphate (as ennchments did not additionally influence the relative growth and abundance of individual algal groups. Pfiesterialike zoospores did not exhibit significant increases in abundance in response to mixing, sediment, or nutnent-addition treatments. Seasonally, the number of Pfiesteria-like zoospores was positively correlated with phytoplankton biomass and productivity. The abundance of Pfiesteria-like zoospores followed general trends in phytoplankton biomass and production in the estuary, suggesting that the source of organic nutrition supporting growth is likely phytoplankton based. Lowering of phytoplankton growth and bloom potentials through proposed nutrient-input reduction strategies should translate into broad-based water quality improvement, including declines in the frequency and magnitudes of nuisance algal blooms, 0, depletion, and associated fish and shellfish mortality in the Neuse &ver Estuary

Section: Discussionsupporting

confidence: 78%

Responses of phytoplankton and Pfiesteria-like dinoflagellate zoospores to nutrient enrichment in the Neuse River Estuary, North Carolina, USA

Pinckney¹,

Paerl²,

Haugen³

et al. 2000

“…It has been indicated that variations in river flow, governed primarily by watershed rainfall, regulate the magnitude of estuarine primary production and periodicity of algal blooms, influence a seasonal shift in limiting nutrients and affect the extent of seasonal oxygen depletion in summer (Malone et al 1988, Dortch & Whitledge 1992, Fisher et al 1992, Boyer et al 1993, Mallin et al 1993. The impact of freshwater input on phytoplankton dynamics is likely to vary among systems, although functional similarities may be expected.…”

Section: Discussionmentioning

confidence: 99%

Phytoplankton responses to freshwater inputs in a small semi-enclosed gulf (Gulf of Trieste, Adriatic Sea)

Malej¹,

Mozetič²,

Malačič³

et al. 1995

Phytoplankton variations in response to freshwater inputs and water column structure in a shallow (c25 m) semi-enclosed Mediterranean gulf (Gulf of Trieste, Adriatic Sea) are described. Hydrographic profiles and In situ fluorescence were recorded at high resolution, while nutrients and phytoplankton were analysed at 5 pre-set depths. Analyses of the phytoplankton community structure were completed by determinations of the pigment pool using reverse-phase high-performance liquid chromatography and size-fractionated primary production. The phytoplankton standing crop, community structure and primary production were profoundly influenced by freshwater inputs and water column stratification. The water column was well mixed and supported modest phytoplankton concentrations during winter. A spring diatom bloom (Skeletonema costatum, Nitzschia spp., Chaetoceros spp.) developed in response to major freshwater input to the surface layer; a similar increase in diatoms (Rhizosolenia delicatula, R. fragilissima) followed October-November freshets. A shift from diatomdominated winter-spring phytoplankton to a flora wlth increased numbers of flagellates in the stratified water column during late spring-summer was reflected in the composition of accessory pigments [lower fucoxanthin : 19'-hexanoyloxyfucoxanthin ratio, an increase of chlorophyll b (chl b) and peridinin concentration]. Primary productivity was correlated with chl a biomass and showed surface peaks in April and June. The 2 to 10 pm phytoplankton contributed significantly to the total productivity in January and June, while on an annual basis the most important producers were > l 0 pm. The smallest fraction (<2 pm) seemed to contribute little, except in July. Our data indicate that the new production resulting from land-born nutrient inputs was the main cause of major phytoplankton blooms, while the nutrient supply from the bottom became comparatively more important during dry summer months.

“…l . Because of highly colored and turbid waters, primary productivity in this estuary is dominated (>g0 %) by planktonic (as opposed to benthic) phototrophs (Boyer et al 1993, Paerl et al 1995. The OM loading attributable to planktonic productivity was calculated by multiplying primary productivity and water volume (m3) for 6 representative segments of the estuary and integrating the value over the length of the study area.…”

Section: Methodsmentioning

confidence: 99%

Ecosystem responses to internal and watershed organic matter loading:consequences for hypoxia in the eutrophying Neuse River Estuary, North Carolina, USA

Paerl¹,

Pinckney²,

Fear³

et al. 1998

475

328

ABSTRACT. The contrasting impacts of externally supplied (runoff) and internally generated (nutrientstimulated phytoplankton blooms) organic matter on oxygen (02) depletion were examined and evaluated in the eutrophic, salinity-stratified Neuse River Estuary, North Carolina, USA. This nitrogen (N)-limited estuary is experiencing increasing anthropogenic N loading from expanding urban, agricultural and industrial development in its watershed. Resultant algal blooms, which provided organic matter loads capable of causing extensive low O2 (hypoxic) and depleted O2 (anoxic) conditions, have induced widespread mortality of resident fin-and shellfish. Phytoplankton blooms followed periods of elevated N loading, except during extremely high runoff periods (e.g. hurricanes), when high rates of flushing and reduced water residence times did not allow sufficient time for bloom development. During these periods, hypoxia and anoxia were dominated by watershed-derived organic matter loading. Externally vs internally generated organic matter loading scenarios were examined in sequential years (1994 to 1996) to compare the differential impacts of an average discharge year ( l 0 yr mean hydrological conditions) (1994), N-stimulated summer algal blooms [1995), and a major hurricane (Fran; September 1996). The responses of primary production, hypoxia, and anoxia to these hydrologically contrasting years and resultant organic matter loadings help distinguish watershed from internal forcing of 0, dynamics and fish kills.