Table of Contents

Nutrient (nitrogen and phosphorus) loading from expanding urban, agricultural and industrial growth and development in the Neuse River Estuary watershed has in-creased by at least 30% since the 1970's.  During this period, estuarine algal and higher plant production has remained sensitive to nitrogen (N) enrichment (i.e., N limited).  Field and experimental work by a variety of investigators has linked increased N loading to accelerated primary (plant) production, or eutrophication. Both the quantity and quality (chemical forms) of N input, which reflect changing land use in the Neuse basin, are key factors controlling the eutrophication process.  Growing frequencies and magnitudes of nuisance (oxygen depleting, toxic, food web disrupting) algal blooms are the most visible and undesirable products of eutrophication. Blooms generate the organic matter fueling low oxygen (hypoxic) and oxygen depleted (anoxic) conditions that induce widespread finfish and shellfish kills.  Blooms generally follow periods of elevated N loading, except during extremely high runoff periods, as witnessed following hurricane Fran (Sep. 1996), when flushing exceeded the ability of blooms to develop in the estuary.  During these events, hypoxia and anoxia were driven by watershed-derived organic matter loading rather than blooms.  Horizontal and vertical salinity gradients induced by freshwater discharge promote density stratification and the formation of water salt wedges which resist mixing and trap decomposing (oxygen consuming) organic matter, leaving the system susceptible to hypoxia and anoxia.  To some extent, hypoxia and anoxia are naturally occurring events; however, they are exacerbated by increased nutrient loading and eutrophication.

Clearly, nutrient input reduction is the only manageable option for stemming water quality degradation in the Neuse Estuary.  A 30% reduction in total (nonpoint and point sources) N loading, which will also lead to some parallel P input reduction, accom-panied by a nutrient loading cap, has been recommended by scientific and management consensus as an initial target for reducing the unwanted impacts of eutrophication.  The long-term (i.e. decadal) reduction level may need further refinement pending ongoing research, hydrodynamic nutrient-productivity modeling efforts, projected land-based nutrient management, water use, and discharge patterns.  Given current N limited condi-tions and N loading scenarios, such reductions will reduce growth potentials of dominant (bloom-forming) algal genera contributing to eutrophication.  Long-term reduction of growth potentials of these genera will translate into broad-based water quality improve-ment, including a declining trend in the frequency, magnitudes and persistence of nuisance algal blooms, oxygen depletion, and associated fish and shellfish mortality.

 This presentation will underscore an emerging, pressing need to strengthen insights about subtle or overlooked, but potentially significant, impacts of nutrient over-enrichment on our aquatic resources.  Recent efforts to select management strategies in controlling nutrient enrichment to the Neuse have been limited, in part, by lack of sufficient data to characterize present conditions, especially during storm events when high loadings can occur.  Examples will be presented to illustrate how conclusions about the present status of water quality and fish kills are significantly – and more realistically– altered when data are more frequently collected, when storm events are sampled, and when subtle but potentially significant impacts of nutrient over-enrichment to aquatic communities are considered.  The example of fish kills will compare North Carolina and Maryland assessment strategies, and will serve as an introduction to the general topic of the toxic Pfiesteria complex.  Before linkages to nutrient enrichment are discussed, the species identification issues should be addressed; I will summarize an in-depth analysis that documents Pfiesteria piscicida’s major involvement in fish kills/epizootics of the Neuse as well as Maryland estuaries, including data from bioassays with fish and a portfolio from our laboratory confirming P. piscicida’s identification, together with comparative information from a cross-corroborating laboratory.  The remainder of this presentation will summarize what is known about nutrient stimulation of Pfiesteria piscicida and other Pfiesteria-like dinoflagellates.  The recent Cambridge Consensus of aquatic nutrient specialists came to unanimous accord, after reviewing all available information, that under appropriate conditions (quiet, poorly flushed waters with conducive salinity and temperature), Pfiesteria piscicida and other Pfiesteria-like dinoflagellates can be strongly stimulated by N and P over-enrichment.  Illustrations of linkages between P. piscicida and both organic and inorganic forms of N and P will be presented, with concluding recommendations about pressing questions that need to be resolved to make the most rapid and meaningful progress in our understanding about environmental controls on the toxic Pfiesteria complex, and their impacts on our fisheries.

The Albemarle-Pamlico Drainage Basin has been the focus of research over the last 30 years directed at determining causes of water quality degradation, primarily eutrophication.  Several researchers have reported that nitrogen is the limiting nutrient for primary productivity in the estuary. Although a policy to achieve a 30-percent reduction in nitrogen loads in the Neuse River is being considered by North Carolina, there are significant questions about whether simply targeting nitrogen will result in water quality improvements. Based on recent work of the US  Geological Survey's National Water Quality Assessment (NAWQA) Program, streams draining into the Albemarle and
Pamlico Sounds have among the highest median concentrations of total nitrogen and total phosphorus of 20 NAWQA study units in the United States. Additionally, the Neuse River and one of its major tributaries, Contentnea Creek, have the highest concentrations of total nitrogen and total phosphorus of any of the four major basins (Chowan, Roanoke, Tar, and the Neuse) draining into the Albemarle and Pamlico Sounds. In terms of material transport, the Neuse River carries the highest percentage of nitrogen (35 percent) and phosphorus (45 percent) transported by all 4 rivers to the sounds, even though it drains only about 20 percent of the contributing basin.

In order to effectively manage nutrient-related problems in the Neuse and other rivers, it is important to completely identify all important point and nonpoint sources of in-stream loads and identify which tributaries and river sections are major contributors of nutrients.  Work of the Albemarle-Pamlico NAWQA study team shows that predominant
sources of nutrients vary geographically within the Neuse River Basin.  For example, data collected between 1993 and 1995 by the Albemarle-Pamlico NAWQA team were used to examine relations between discharge and nitrogen and phosphorus in the Neuse River at Kinston, NC and Contentnea Creek at Hookerton, NC.  This analysis indicates
that elevated phosphorus concentrations are due primarily to ground-water discharge or point-source discharges to these streams.  Based on NAWQA synoptic studies, ground-water discharge was established as a main contributor of phosphorus in the Neuse Basin. Ground water has not previously been considered as a source in nutrient budgets. Point sources are a major contributor of nitrogen in the Neuse River at Kinston, and both point and nonpoint sources affect nitrogen in Contentnea Creek at Hookerton.  Although preliminary data suggest that ground water is not a major contributor of nitrogen in
the form of nitrate, ground water may contribute significant amounts of nitrogen in other forms, such as ammonium or organic nitrogen.  More detailed studies are needed to assess the importance of these inputs in order to implement effective management procedures.

Identifying all the factors limiting primary production is another necessary step for effective management of the Neuse River. Correlation analysis of chlorophyll-a, nitrate, nitrite, Kjeldahl nitrogen, ammonium, and total phosphorus data collected by the North Carolina Division of Water Quality between 1987 and 1995 indicates algal productivity, which may ultimately cause oxygen depletion and fish kills in the estuary during late summer, is controlled by concentrations of both nitrogen and phosphorus. However, phosphorus exhibits the strongest correlation to chlorophyll-a from Streets Ferry and stations downstream.  These data suggest that phosphorus is at least as important as nitrogen in controlling productivity in the upper Neuse estuary and lower Neuse River where much of the primary productivity occurs.  In order for the Neuse River to comply with literature-based guidelines for both nitrogen and phosphorus, a reduction of 30-50 percent of the 1993-95 phosphorus concentrations and a 30 percent reduction of 1993-95 nitrogen concentrations would be necessary.

 In 1996 a panel of university and state government personnel proposed a 30% minimum decrease in nitrogen loading to control eutrophication in the Neuse River Estuary.  This number was based in part on a 1987 paper which suggested this amount would be sufficient to control the formation of blue-green algal blooms in the freshwater Neuse River.  However, while some panel members expressed concern over phosphorus impacts as well, no additional controls on phosphorus loading were recommended by the panel.  There is strong experimental evidence suggesting that phosphorus control is in fact critical to controlling eutrophication in the Neuse Estuary.  In a series of nutrient addition bioassays conducted from 1990-1992 on oligohaline water from the upper estuary at New Bern, phosphorus additions alone stimulated chlorophyll a production during 53% of the experiments and carbon-14 uptake during 33% of the experiments.  As a comparison, nitrogen additions alone stimulated chlorophyll a production during 60% of the experiments and carbon-14 uptake during 40% of the experiments.  Many of the species found in the phytoplankton near New Bern die upon entering waters of higher salinity downstream.  It is important to note that bottom-water dissolved oxygen sags begin in the fresh to oligohaline areas of the estuary, thus reductions in phosphorus loading upstream should result in less phytoplankton biomass as a source of BOD downstream.  Approaching eutrophication from another critical viewpoint, laboratory experiments and field data have demonstrated that non-toxic forms of the dinoflagellate Pfiesteria piscicida are directly stimulated by organic and inorganic phosphorus loading, thus creating abundant seed populations for later fish kill events.  Additionally, stimulation of other phytoplankton species by phosphorus inputs creates prey populations which can also support increased seed populations of non-toxic Pfiesteria.  Finally, controls on nitrogen without parallel controls on phosphorus could theoretically lead to shifts in the riverine blue-green algal community from non-nitrogen fixers (Microcystis) to nitrogen fixing species (such as Anabaena).  Nitrogen fixing blue-green algae normally die upon reaching salinities of about 1 ppt , and thus become sources of BOD to the estuary.  In sum, decreases in phosphorus loading from both point and nonpoint sources should be an integral part of any Neuse Estuary restoration program.  Removal of phosphorus from point source discharges is commonly accomplished by chemical flocculation and sludge removal.  Nonpoint sources of phosphorus (swine waste spray fields, crop fertilizers, suburban and urban runoff, and other land disturbing activities) can reduce phosphorus inputs to water bodies by practices to reduce sedimentation, installation of vegetated buffer zones, creating of wetlands, and preservation of current wetlands.