ics, nutrient loading and algal 

 response in major coastal river 

 systems. Their research located 

 areas where nutrients were 

 deposited and confirmed that 

 those areas were prone to algal 

 blooms. 



Through more than a 

 decade of work, researchers were 

 able to identify limiting nutrients 

 over seasonal, spatial and climate 

 changes, and they characterized 

 the dominant algal communities 

 during various seasons and 

 nutrient loading patterns. 



Charles Daniel, a researcher 

 from the U.S. Geological Survey, 

 developed a model to describe 

 the water flow in the Chowan 

 River. Water movement patterns 

 affect algal growth and dispersal. 

 The model verified that both lunar and 

 wind tides are present in the Chowan, but 

 that the wind tides are far more significant. 

 During low flows, however, lunar tides can 

 influence the river as far north as the 

 Blackwater River, which is six miles north 

 of Franklin, Va. 



Augustus Witherspoon, a North 

 Carolina State University researcher, 

 showed that the river could be subdivided 

 into two sections. The upper river had 

 nutrient concentrations great enough to 

 support relatively high algal growth, but 

 the water flow there was too fast to allow 

 for excessive phytoplankton growth. 



By contrast, the slow-moving lower 

 river acted more like a lake. This allowed 

 for more interaction between algae and 

 nutrients, resulting in high algal growth. 

 Blue-green algae that formed surface 

 blooms dominated the species composition 

 of the lower river, as is common in nutri- 

 ent-enriched freshwater areas. 



Other work focused solely on nutri- 

 ents and algal growth. John Hobbie, 

 currently of the Marine Biological Labora- 

 tory in Woods Hole, Mass., and Don 

 Stanley, now at East Carolina University, 

 found that high rates of nitrogen loading 

 prompted algal blooms. Nitrogen and 

 phosphorus are the key nutrients that 



In 1 983, researchers used experimental enclosures 

 to examine the effect of nutrient additions in the Chowan. 



support algal growth in aquatic systems. 

 Often there is plenty of one nutrient but not 

 enough of the other. The lacking nutrient is 

 considered the limiting nutrient because it 

 controls the productivity that can take place. 



In freshwater systems, phosphorus is 

 usually the limiting nutrient. In estuarine 

 systems, on the other hand, nitrogen gener- 

 ally controls algal production. In the lower 

 Chowan, however, Hobbie and Stanley 

 found that nitrogen from decomposing 

 organic matter in the sediments functioned 

 as the limiting nutrient for algal growth 

 mainly during the summer instead of year- 

 round. 



Later studies by Ed Kuenzler, a UNC- 

 Chapel Hill researcher, found that both 

 phosphorus and nitrogen simultaneously 

 limited total algal growth in most experi- 

 ments, but that phosphorus was the most 

 critical limiting nutrient to certain species of 

 blue-green algae that dominated blooms in 

 freshwater segments of the lower Chowan 

 River. 



Paerl confirmed these findings and 

 showed that high nitrogen inputs during the 

 spring created a potential for early blooms 

 of species other than blue-green algae. His 

 work also showed that once these blooms 

 died and sank to the bottom of the river, 

 their decomposition depleted oxygen levels. 



Phosphorus was then released in this 

 anaerobic (oxygen-free) environment and 

 stimulated blue-green algae blooms later in 

 the summer. 



From this decade of research, scientists 

 were able to conclude that controls of both 

 nitrogen and phosphorus were necessary to 

 reduce the frequency and magnitude of algal 

 blooms in the river. Reducing the amount of 

 nutrients flowing into the river would also 

 reduce the concentration of chlorophyll-a, a 

 plant pigment used to measure phytoplank- 

 ton growth. Witherspoon and Roger Pearce, 

 his graduate student provided specific 

 guidelines for reducing these nutrients. 



Two Decades of 

 Management 



The fertilizer plant in Tunis stopped 

 discharging nitrogen into the river in 1972, 

 and the next few years saw a marked 

 reduction in algal blooms. In 1976, how- 

 ever, small pulse blooms appeared, and in 

 1978, severe blooms recurred. State regula- 

 tors verified that nutrients continued to seep 

 from storage lagoons at the fertilizer plant. 



In addition, the United Piece 

 Dyeworks plant near Colerain and the 

 Union Camp pulp and paper facility in 

 Franklin, Va., were identified as significant 

 point sources of nutrients in the basin. North 



22 SPRING 1999 



