Biological and microbiological assessment of the upper Chattahoochee River basin, Georgia

Geological Survey

By Bruce W. Lium, John K. Stamer, Theodore A. Ehlke, Robert E. Faye, and Rodney N. Cherry

In 1972, the Committee recommended that the U.S. Geological Survey conduct nlultidis-

ciplinary river-quality studies. The firrt study was conducted in the Willamette River basin, Oregon, and began in January 1973. The objectives were to define the types and quantities of data required to assess river-quality problems and to develop methods for assessing t,_e planning alternatives in terms of potential impacts on river quality.

The Chattahoochee River basin was selected as the study area for a second river-quality assessment. The river-quality as.sessment of the upper Chattahoochee River basin (fig. 1) up.. stream of the West Point Dam began April 1, 1975. Its purpose is to provide meanill gful information to resource managers a.nd to suggest alternatives for basin development and for future uses of the Chattahoochee River, in which maintenance and improvement cf water quality are requisites.

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cal and microbiological data to aid in estimating water-quality conditions in selected river reaches and two lakes (West Point and Sidney Lanier), (2) to assess the potential for algal growth in both lakes and selected reaches of the river, and (3) to determine what factors affect biological and microbiological communities and populations. The scope of this report includes a discussion of hydrology, land use and water use, and general biological and microbiological conditions in the study area.

Acknowledgments-We express our sincere appreciation for the interest shown by the Advisory Committee on Water Data for Public Use and the Advisory Committee's Working Group for River-Quality Assessments.

The upper Chattahoochee River (fig. 1) rises on the southern slopes of the Blue Ridge Mountains in northeas.t Georgia and flows generally southwestward through the metropolitan Atlanta area to the Georgia-Alabama State line. The drainage area of the upper Chattahoochee River is 3,440 mi • Land surface altitudes range frrom about 4,000 ft in the headwaters to about 635 ft above West Point, Ga.

Rainfall in the basin averages about 54 in. a year with higher rainfalls occurring in the upland areas and in the southernmost part of the basin. Annual air temperatures in the basin average about 16°C with the coldest temperatures occurring in the mountainous areas.

The flow of the Chattahoochee River is dependent on rainfall and regulation by hydroelectric-generating facilities. The highest flows generally occur during the spring of the year, and the lowest, in late autumn. The average flow at Buford Dam, based on 35 years of record, is 2,168 ft /s. At Atlanta, which is about midway in the study area, the average daily discharge based on 43 years of record, is 2,603 ft /s. A maximum discharge of 59,000 ft /s occurred at the Atlanta gage in 1946, and a minimum daily discharge of 296 ft 3/s occurred in 1957.

Flow in the reaches has been regulated for many years because of hydroelectric-generating facilities at Buford Dam and Morgan Falls. The most pronounced changes in regulated flow have occurred subsequent to the construction of Buford Dam. Figure 2 shows the flow durations of the Chattahoochee River at ltlanta before and after regulation by Buford Dam. The frequency of both the higher and lower flows has decreased.

In 1960, the city of Atlanta and the Georgia Power Co. modified the Morgan Falls Da.m and reservoir to provide· a minimum flow of 750 ft /s from Morgan Falls. In 1974, the Georgia Environmental Protection Division reccgnized the increasing demand for water supply ~.nd the need for high-quality water downstrean1 from Atlanta for waiter-quality maintenance r.nd required a minimum flow of 750 ft js just upstream of Peachtree Creek. This requir<)ment, considering water-supply withdrawals, results in a minimum release from Morgan F:'.lls of approximately 1,100 ft js.

Land in the upper Chattahoochee River basin from its headwaters to the West Point Dam is predominantly forest (table 1). Upstrnam of Buford Dam, about 80 percent of the land is forested and 16 percent used for agriculture. Agricultural activities are concentrated in the stream valleys and on the lower slopes. Crops and pastures occupy a significant part of the agricultural land. Poultry operations, primarily broiler chicken production, are an econmnically dominant agricultural activity. GainesYille is the largest urban area in this part of the basin.

In the river reach from Buford Dam to Atlanta, about 60 percent of the land is forested, 22 percent is urbanized, and 18 percent is agricultural. About 40 percent of the agricultural land consists of cropland and pasture with corn and soybeans as the dominant crops.

The basin from Atlanta to West Point Dam includes most of metropolitan Atlanta, the largest city in the basin. Land in the l tlanta area is predominantly residential, but com- I ties include automobile assembling, food procesmercial and industrial activities are significant. I sing, and light manufacturing. Downstream Some of the more important industrial activi- from Atlanta, forest land is predominant.

Agricultural use of the land is about the same as in the Buford Dam-Atlanta. reach, and the types of agricultural operations are similar.

The waters of the upper Chattahooche River are utilized extensiv·ely for power generation, water supply, water-quality maintenance, and recreation.

Six electric, power-generating facilities are located adjacent to the Chattahoochee River and have a combined generating capacity of about 3.8 million kilowatts. Buford Dam and Morgan Falls Dam are peak-power, hydroelectric-generating facilities and plants. Atkinson, McDonough, Yates, and Wansley are fossil-fuel thermoelectric powerplants. Morgan Falls is a run ... of-the-river facility which utilizes hydropower-released waters from Buford Dam. The estimated average water use and generating capacity for the plants are shown in table 2.

In 1976, water-supply withdrawals in the upper Chattahoochee River basin were about

290 ft /s, of which about 276 ft /s. was with-

drawn directly from the Chattahoochee River in the re31Ch from Buford Dam to Fairburn. Other water supplies were withdrawn from Lake Sidney Lanier and West Point Lake. Table 3 lists the major water users in the basin and shows p~resent (1976) and estimated withdrawals for the year 2000. Large amounts. of wastewater are discharged to the Chattahoochee River, particula.rly in the Atlanta area (table 4).

Several reaches of the river are used extensively for recreation. The mountainous headwater areas are popular for trout fishing, camping, and hunting. Lake Sidney Lr.nier, a popular water resort area, has numero~Js public aceess areas, boat-launching facilities, campgrounds, marinas, yacht clubs, and cottages. Lake Sidney Lanier has a higher number of annual visitor-days than any other U.S. Army Corps of Engineers facility in the N ation (Metropolitan Atlanta Water Resources Study Group, 1976). The reach from Buford Dam to Atlanta is periodically ·stockr·!} with game fish and provides recreation for fishermen, canoeists, and rafters. This reac1' is being considered for an urban national park. The reach between Morgan Falls Dam and Peachtree Creek is one of the most scenic on the river and is the site for an annual raft race that inv;olves thousands of participants. and onlookers. The shoals in the reach from Whitesburg to Franklin are popular for fishing and boating. West Point Lake, a U.S. Army Corps of Engineers impoundment created by the construction of West Point Dam in 197 4, is us.ed for fishing, boating, camping, and swimming.

Future consideration for modifying the flow regime from Buford Dam to meet increasing demands for water supply include construction of a new regulation structure downstream from Buford Dam, modification of Morgan Falls Dam and reservoir, or changes in the hydropower releases from Buford Dam (Metropolitan Atlanta Water Resources Study, 1977).

In the year 2000, during an extended drought period such as occurred in 1954-56, a minimum flow of 1,717 ft: /s could be maintained from Buford Dam. Considering water-supply withdrawals, wastewater returns, and no streamflow accretions between Buford Dam and Atlanta, the estimated net flow at Atlanta in the year 2000 would be 1,310 ft:ls. The flow would

from the Atlanta gage and 750 ffl/s for water-quality maintenance. Average water-supply withdrawals in the reach from Buford Dam to Fairburn (RM 281.88) are estimated to be 669 ft Is (table 3) in the year 2000. During a drought period, net flow at Fairburn, assuming no accretion of tributary inflow and an average wastewater return of 350 ft Is, would

during low flow periods in 1976.

The problems as.sociated with water quality in the upper Chattahoochee River basin are generally related to urbanization. Urbanization has created large demands on the Chattahoochee River as the major water supply for Atlanta and as the major transporter of municipal wastes from Atlanta. In 1976, about 280 ft ls was withdrawn from the river upstream of Peachtree Creek (river-mile (RM) 300.54) for water-supply and about 180 fV Is of secondary treated wastewater was discharged into the river between Peachtree Creek and Fairburn (RM 281.88). In this reach two thermoelectric powerplants withdraw and subsequently discharge heated effluent directly into the river. The net effect of discharges from these powerplants and from other point sources is to reduce the waste-assimilative capacity of the river.

During periods of rainfall, combined sewer overflows and direct runoff from streets and parking lots can contribute large dissolved and suspended constituent loads to the river. During these periods, sediment loads carried by the Chattahoochee River and its tributaries can be high. During periods of low flow, low dissolved oxygen (DO) and high biochemical oxygen demand (BOD) concentrations and high fecal coliform bacteria counts occur in the river downstream from Atlanta.

Several alternatives have been J: ~oposed to modify the flow regime of the river to meet the increasing water-supply demand. Regardless of which alternative is selected, streamflow downstream from Atlanta will not be greatly different from that at present, and wastewater discharges will increase.

Biological, microbiological, chernical, and physical data were collected from October 1975 to September 1976 at strean1 and lake stations shown on figure 1. Monthly water samples were collected at each stat~ 0n for determination of algal growth potential (AGP), phytoplankton, dissolved nitrate as nitrogen (NO:~- N), and dissolved orthophosphate as phosphorus (P04- P) concentrations. Additional wat•er samples were collected for chemical and microbiological determinations during low and high streamflows.

Water samples. for determination of AGP were filtered in the field in a pressure· vessel through a 0.22-micrometer Millipore filter at pressures of less than five pounds per square inch and then chilled to 4 oc. The· algal assay is a widely used procedure, but two basic methods of sample preparation exist. One method (Greene and others, 1975; Miller and others, 1975) autoclaves the sample before filtration, provides a total AGP. The total AGP is usually higher than the dis,solved AGP because autoclaving releases nutrients from the plankton. The other method, def'~ribed by Greeson and others (1977) measur~s the dissolved AGP and was used throughout the study. ' trations occurring in W~est Point LakE. down-Unfiltered samples for phytoplankton determinations were preserved with a solution containing copper sulfate, formaldehyde, and a detergent. Water samples for nitrogen and phosphorus determinations were filtered in the fi·eld through a 0.45-micrometer Millipo,re filter.

Nitrifying bacteria and related chemical constituents were measured during sustained low flow in the Chattahoochee River. The flow was maintained at 1,150 ft /s for 3 days before Bampiing on June 1-2, 1977. Nitrifying bacteria were determined from water and riverbed samples collected at sites shown on figure 1. Water samples were collected in 1-L autoclaved bottles made of polypropylene using depth-integrat,ed techniques. Riverbed samples were collected using a USGS, BM 60 sampler. After retrieving the sample, the top 1 em of sediment was subsampled with a sterilized test tube and placed in a sterile Whirlpakplastic bag. Both water and sediment samples were placed in an ice chest while en route to the laboratory. In-stream. DO and te~mperature measurements were made using a DO meter (Yellow Springs model 57) .Separate water samples were collected for laboratory determinations of BOD, NH4-N (ammonium as nitrogen), N02-N (nitrite as nitrogen) and NO~- N. The laboratory chemical methods used are described by Brown and others (1970) with the exception of BOD, which was determined by the method described by Hines and others (1977).

Nitrifying bacteria in water column and riverbed sediments were determined by a modification of the three tube most probable number (MPN) procedure described by Greeson and others (1977). A 1-mL aliquot of culture material was tested for the presence or absence of nitrite at intervals of 30, 45, and 60 days and the highest value (usually the last one) was recorded as the MPN estimate.

Concentrations of phytoplankton (diatoms, green algae, and blue-green algae) were generally higher downstr·eam from Atlanta than upstream. Concentrations of phytoplankton were higher in Lake Sidney Lanier (a bottomrelease dam) and West Point Lake than in the river and tributaries, with maximum concenstream from Franklin.

Figure 3 shows phytoplankton concentrations from the headwaters of the Chattahoochee River to the West Point Dam during August 1976. The highest concentrations (mostly blue-green algae) occurred in West Point Lake. The lowest concentration occurred at Norcross. Figures 4, 5, and 6 ~show the monthly variation in average concentrations of the variour phytoplankton genera in Lake Sidney Lanier and West Point Lake. Average concentrations. of blue-green and green algae were highest in West Point Lake. In the spring, montl'ly concentrations of diatoms (fig. 4) were highest in Lake Sidney Lanier. The spring diatom increag.e, as shown in figure 4, did not occur in West Point Lake. Blue-green algae were dominant in both lakes,, and concentratiors were highest during the summer months. Diatom c10nc,entrations generally exceeded the greenalgae concentrations. in both lakes.

Figure 7 shows mean annual concentrations of total phytoplankton, dissolved P0-1- P, and N02 + N03- N from the upper reache·~:· of the Chattahoochee River to the West P10irt Dam. Phytoplankton concentrations upstream of Lak~e Sidney Lanier were les1s than 1,0( () cells/ mL, and in the lake they were about 10,000 cells/mL. Concentrations downstrean1 from Lake Sidney Lanier to the upstream end of West Point Lake at Franklin were less than 4,000 eells/mL. Maximum concentrations in West Point Lake were about 90,000 cells/mL.

The dissolved P04- P and N02 + N03 concentrations were highest in the river reaches and the upper parts of the two lake:s, and lowest at the dam pools of both lakes. Tl' ~ high N02 + N03- N concentrations downstrer.m from Atlanta we·re primarily a result of nitrification of treated sewage effluent by the Nitrosomonas and Nit1·obacter bacteria (Ehlke, 1978).

Figure 8 shows the mean annual concentrations of AGP, dissolved P04- P and N02 +NO a-N from the upper to lower reaches of the study area. The AGP and nutrient concentrations were less than 10 and 0.4 rr<r/L respectively upstream of Atlanta.

AGP decreased from about 25 rng/L at Franklin to about 1 mg/L at the Wert Point Lake dam pool. Dissolved P04- P d~reased

100~---L------------~-----~~--~L---~L-----~--~~~~--~

from 0.1 mg/L at Franklin to less than 0.01 mg/L at the West Point dam pool, and dissolved N02 + N03- N decreased from 0.6 mg/ L at Franklin to about 0.1 mg/L at the dam pool.

A multiple-variable regression equation of the general form

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o...:

~ /~ /,l''v' / \

was used to determine the relation of various nutrients to AGP. The regression equation includes a dependent variable designr.ted as Y; several independent variables designated as Xh X 2 ................. Xn; and partial regres<;'ion coefficients designated as bo, b1, b2 ..................bn. The subscript n indicates the number of irdependent variables.

I 14 ,1

en 1o,ooo

.,..,. -·····'t'

--+ -- Lake Sidney Lanier

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FIGURE 5.-Average green algae concentrations by month in Lake Sidney Lanier and West Point L6ke.

0>t----- ~~ ~···· ...........i.................... __ ...

\ \ \ \ \ zw

fI II II II

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II I \

Regression parameters used in this study include the multiple correlation coefficient and the standard error of estimate, which indicate, respectively, the degree of association between the dependent and independent variables and the predictive quality of the regression model. Significance tests used were the F-test and t-test. Values of F indicate the "worth" of the entire regression, and values of t are measure of the significance of the regression parameters.

Several regression equations based on the general form described were developed and used to evaluate the relation of dissolved concentrations of NH4-N, N02-N, N03-N, P04-P, and SiOz (silica) to AGP. The best equation determined from the regression of available data (table 5) from West Point Lake is defined by equation 2, which shows that orthophosphate and nitrate are the principle nutrients aff·ecting AGP (Cherry and others, 1978). AGP (mg/L) =211 (P04-P, mg/L) + 13.4 (N03- N, mg/L) -0.8 (2)

The multiple correlation coefficients and standard error of estimate of equation 2 are 0.96 and 3.7 mg/L. The computed F of the regression is 172.5, which is significant at level of confidenc•e greater than 99 percent. The significance of orthophosphate and nitrate concentrations relative to APG is indicated l~y the results of the t-test as follows:

Thus, concentrations of dissolved orthophosphate are shown to be more significantly related to AG P than corresponding concentrations of dissolved nitrate. Statistically, both parameters are highly significant.

A comparison of calculated (equation 2) and observed AGP, as presented in figure 9, shows that AGP in West Point Lake can be estimated when only concentrations of dissolved orthophosphate and nitrate are known.

OBSERVED ALGAL GROWTH POTENTIAL, IN MILLIGRAMS PER LITER FIGURE 9.-Comparison of calculated and observed algal growth potential in the West Point Lake from Franklin to West Point Dam.

Plots relating phytoplankton con~entrations to water temperature at sites in West Point Lake are shown in figure 10 (Cherry and others, 1978). Phytoplankton COJ]centrations increa-se with increasing temperature at all sites. The concentrations are generally higher at downstream sites than at ups~ream ones at the s·ame temperature, except at the dam pool, where the concentrations are l'lwer at the higher temperatures than at the Abbottsford site.

The observed AG P and phytoplankton concentrations. are plotted against river miles downstream from the Franklin station in Figures 11 and 12. A linear relation between miles downstream of Franklin and AG P and phytoplankton concentrations occurred during all sampling periods when AGP was greater than about 0.5 mg/L.

Figures 11 and 12 and data in table 5 (July-September 1976) indicate that, ,.vhere algal zw

1------r--·

<i 25

growth potential was less than about 0.5 mg/ L, a decrease in the phytoplankton concentration occurred downstream. Therefore, the availability of nutrients, as indicated by AGP, ap-

pears to be limiting phytoplankton growth in the lower reaches of the lake.

The rates of change of AGP and phytoplankton concentrations increased with distance for

c each of the sampling periods and are plotted II against water temperature in figures 13 and · 14 (Cherry and others, 1978). Both rates increased with increasing temperature greate1· than 13°C.

FIGURE 12.-Plots of observed phytoplankton concentrations by river mile downstream from Franklin station.

The relationship between the rate of change of AGP and water temperature with river mile is defined from about 10oC to 30oC by the following equation : A1 =- (0.0673T-0.625), where A1 =rate of change of AGP per river mile in (mg/L) /RM, and T=a.verage water temperature, in oc. The relationship' between the rate of change of phytoplankton concentration and wat,er temperature with river mile is defined from about 10°C to 30°C by the following equation:

offi

ocn

a::

·~. :::l .05

l:

P1 =rate of change of phytoplankton con-

TherefoTe, knowing the AGP and phytoplankton concentrations and the water temperature of the lake, the AGP and phytoplankton concentrati,on can be estimated at down-Btream sit,es in the lake using the following equations (Che·rry and others, 1978) :

where T=average wate·r temperature, in oc.

Cm.= AGP in mgiL at river mile R, down-

A1 =rate of change of AGP, in (mgiL) I

R =river mile downstream of Franklin,

Ca.;= AGP, in mgiL, from Franklin.

Cpr= phytoplankton concentration in

P 1 =rate of increase of phytoplankton con-

centration per river mile, in (log" cellslmL) IRM,

amd

(loge) cellslmL at riv·er mile, R, downstream from Franklin,

Estimated maximum phytoplankton ·concentrations at sites in the West Point L2ke at various temperatures are shown in figure· 17. At 30°C, a maximum phytoplankton conc~ntra tion in the lake would occur at the dan1 pool with a estimated ·minimum of 47 mgiL AGP concentration at Franklin. At 30°C, a maximum phytoplankton concentration would occur at Abbottsford with an estimated minimum of 35 mg/L AGP at Franklin. Maximum phytoplankton concentrations, at 30°C, at other upstream sites would occur with lower AGP at Franklin. Estimated phytoplankton conc"?.ntrations, at 30°C, and with a 47 mg/L AGP at Franklin, would not exceed 7 ,500, 101,000, 750,000, and 3.5 million cells/mL at Franklin, LaGrange, Abbotsford, and the dam pool, respectively.

The analysis of the relation of ·phytoplankton to AGP indicates that at sites where the AG P has decreased to less than about 0.5 mg/L, the phytoplankton concentrations decrease downstream. Where AGP is greater than about 0.5 mg/L, phytoplankton concentr?tions are dependent on water temperature and distance downstream from Franklin. Wl·~ther factors other than AGP would limit phytoplankton growth approaching 3.5 n1illion cells/mL could not be determined fro:n the data.

~ w.-----------------------------------.

oC:::c=~==~===·-4~~~

the river w·ere attributed to a combination of nitrogenous and carbonaceous oxygen demands. Nitrogenous demands (nitrification) caused approximately 50 percent of the DO decrease in the reach (Stamer and others, 1978) . Figure 19 shows the DO decrease re"Sulting from nitrificati,on to the total decrease in DO during the period of June 1-2, 1977.

Nitrification or oxidation of NH4 - N to nitrate proceeds in two steps catalyzed by the chemoautotrophic bacteria, Nitrosomonas and Nitrobacte'r (Alexander, 1964) : N itrosomonas NH4 + + 1-1/2 0:: N02- +2H+ +H20 Nitro bacte1·

The treatment of wastewater reduces the carbonaceous oxygen demand because utilizable carbon substrates are quickly attacked by many heterotrophic bacteria (Strom r.nd others, 1976). The nitrogenous oxygen demands often are not greatly affected during wastewater treatment because initially the reaction kinetics of nitrification proceed slowly. As a result, nitrification may occur downst':'eam from treated wastewater outfalls.

The mean concentrations of Nitrosomonas and Nitrobacter bacteria in the water column and benthic sediments during the period June 1-2, 1977, as determined by Ehlke (1978) are shown in figures 20 and 21. 10- The N itrosomonas concentration was 100 times greater in the benthic sediment than in the water column. This is consistant with studies elsewhere (Tuffey and others, 1974; Curtis and others, 1975). The J.litrosomonas concentration in the water column was the least at RM 302.97 but was almost constant .further

z

DISTANCE DOWNSTREAM FROM FRANKLitl. IN RIVER MILES FlGURE 16.-Comparison of calculated and observed phytoplankton concentrations for each sampling pf.riod.

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downstream. This collection site was upstream of all facilities in metropolitan Atlanta. Nit·roso'monas concentrations generally were greatest near RM 298.77. This site is downstream from the two major Atlanta was1tewater treatment facilities (RM 300.24 and RM 300.52). Nit?·osomonas concentrations at Capps Ferry Bridge (RM 271.19) and Franklin (RM 235.46) were also greater than at most other collection sites.

The concentration of N'itrobacterr in benthic sediment was greatest near RM 271.19 and RM 235.46, approximately 10 per gram. In the reach containing municipal point-source discharges (RM 300.52-RM 283.78), concentrations of Nitttobactet· generally were less in benthic sediments than elsewhere in the study area. The N-itttobactett concentration in the water column was nearly constant from RM 302.97 to RM 235.46. As with other studies (Tuffey and others, 1974; Curtis and others, 1975), the Nit1·obactett ooncentration in benthic sediments was 10-100 times greater than in the water column. The Nitrobacte1· concentration

was generally lower than the Nit1·osmnonas concentration.

The observed mean NH4- N, 1'-T02- N, and N0 3 -N concentrations for June 1-2, 1977, are shown in ·figure 22. During the June 1-2, 1977, sampling period, the concentrationE of NH.1- N and N02-N were lowest near RM 302.97. The concentration of N0:1 - N, which is the end product of nitrification, was about 0.1 mg/L at RM 302.97 and increased to about 1.2 mg/L at RM 235.46. The concentrations of NH4- N and N02 - N increased rapidly downstream from the municipal wastewater outfalls. The NH.1 - N concentration was maxirnum at RM 298.77.

The concentrations of NH4- N decreas.ed at almost a constant rate of 0.02 mg/L/h during June 1-2, 1977, from RM 298.77 to RM 235.46, based on a travel time of 65.07 hand a change in concentration of NH-t- N from 1.8 mg/L to 0.2 mg/L (fig. 22).

Concentrations of NO:{- N increased at almost a constant rate of 0.02 mg/L/h during the x0

FIGURE 19.-Comparison of decreases in dissolved oxygen resulting from nitrification to total decrease in dis- solved oxygen in the Atlanta to Franklin reach during low flow period, June 1-2, 1977.

I '"""' / --....... I ........ , / .....................

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J

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zz0

period of June 1-2, 1977, from RM 302.97 to RM 246.93. The disappearance of NH4- N was approximately equal to the formation of NOa-N during the period of June 1-2, 1977, from RM 298.99 to RM 246.97.

Generally, the higher nitrifying-bacteria concentration in riverbed sediments compared with that in the water column has led many investigators to conclude that most nitrifying-bacteria activity pvobably occurs in benthic ,...e...

sediments, not in the water column (Tuffey and others, 1974; Matulewich and Firstein, 1978).

All·sampling for nitrifying bacteria was done when the flow of the Chattahoochee River was near 1,150 ft/s and the m.ean de:')th from RM 302.97 to RM 258.6-3 was about 1.42 m. Using the data of figures 20 and 21, the relative concentrations of Nitrosomonas and 1 Titrobacter in a 142-cm water column and 1-cm benthic sediment column can be calculated. J.veraging the

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a:1- z

data, 53 percent of the NitTosomonas is calculated to be in the water column and 47 percent, in the top 1 em of benthic sediment. Similarly, 72 percent of the Nitrobacte1· was pres.ent in the water column and 28 percent, in the benthic sediment. This indicates that, during the study period, most nitrifying-bacterial activity occurred in the wa.t~er column, not in the benthic s-ediment.

For more than ten years, the Advisory Committee on Water Data for Public Use has been interested in obtaining information needed for planning river basin development. The upp·er Chattahooche~e River basin study began April 1, 1975, and was the second intensive riv,erquality assessment conducted by the U.S. Geological Survey, with the purpose of providing demonstration products for management decisions, alternatives for basin dev,elopment, and maintenance and improvement of water quality in the upp·er Chattahoochee Rive-r basin.

The biological and associated chemical data were collect•ed from October 1975 through September 1976 at selected stations in Lake Sidney Lanier, West Point Lake, and the Chattahoochee River.

Concentrations of NitTosomonas in the water column and .in the benthic sediment increased in the reach RM 302.97 to RM 298.99, ard decreased from RM 298.99 to RM 235.46 during the low flow period, June 1-2, 1977. Nitrifying bacteria were present in greater concentrf.tions in the benthic sedim·ent than in the water column on a number-p·er-milliliter or per-gram basis. If the entire water column (1.4 m) were considered, the total number of nitrifying bacte-ria was grea.ter in the water columnthaninthe top 1 em of benthic sediment. It is probable that most nitrifying-bacteria activity would occur in the water column rather than in the benthic sediment of the Chattahoochee River. The rate of NH1- N disap,pearance (0.02 mg/L/h) was approximately equal to the formation of NOa- N during the period of June 1-2,1977.

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