THE RELATIONSHIP BETWEEN RIVER FLOW AND MICROCYSTIS AERUGINOSA BLOOMS IN THE NEUSE RIVER, NORTH CAROLINA

Abstract

Extensi ve bl ooms o f bl ue-green a1 gae domi nated by M i crocysti s aeruginosa have occurred during some, b u t n o t a l l , recent summers along the Neuse Ri ver, North Carol i na.Nutrients are present in excess of a1 gal needs year-round in the Neuse, b u t blooms seem to develop only d u r i n g those summers with periods of sustained low flow.W e postulated t h a t t h i s 1 inkage between bloom formation and river flow results from faster growth and 1 onger residence time of a1 gae i n the river a t 1 ow f l ows.To eval uate t h i s hypothesis, we devel oped a mathematical simul ation model f o r predicting t h e concentrations of a1 gae in the 1 ower Neuse under various f 1 ow conditions, taking i n t o account the e f f e c t s t h a t f l ow has on r i ver vel oci t y (and hence time-of-travel ) and other variables affecting a1 gal growth such as l i g h t intensity and water depth.Information on the timeo f -t r a v e l of water and a l g a e within the r i v e r came from a s e r i e s of dye tracer studies.In the laboratory we evaluated the regulation of growth of M. aeruginosa by l i g h t and temperature.-Model predictions were in good agreement with observations of bloom occurrence or non-occurrence from 1979 t o 1985.For the months from May through September we evaluated the maximum flow rates, as gaged a t Kinston, N.C., t h a t would a1 low f o r bloom formation.The r e s u l t s were t h a t the combination of water temperature and daylength in July was most conducive t o bloom occurrence, while May and September were the 1 east conducive.Our results may be useful in the management of: (1) low flow augmentation a t the Fa1 1 s Reservoir, ( 2 ) n u t r i e n t 1 oading reduction, and ( 3 ) water use within the Neuse River basin as we1 1 as interbasin transfers invol v i n g the Neuse.