Spatial and temporal variability in nutrient ...

Freshwater Contamination (Proceedings of Rabat Symposium S4, April-May 1997). IAHSPubl.no. 243, 1997

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Spatial and temporal variability in nutrient concentrations in surface waters of the Chattahoochee River basin near Atlanta, Georgia, USA NORMAN E. PETERS, GARY R. BUELL & ELIZABETH A. FRICK US Geological Survey, 3039 Amwiler Rd., Atlanta, Georgia 30360-2824, USA

Abstract Nutrient concentrations from the early 1970s through 1995 were evaluated at several sites along the Chattahoochee River and its tributaries near Atlanta, to determine general patterns and processes controlling nutrient concentrations in the river. A spatial analysis was conducted on data collected in 1994 and 1995 from an intensive nutrient study of the Chattahoochee River and its tributaries by the Georgia Department of Natural Resources, Environmental Protection Division. The 1994-1995 data show step increases in ammonium (NH4-N), nitrite plus nitrate (N0 2 + N03-N), and total-phosphorus (Tot-P) concentrations m the river. The step increases occur downstream of two wastewater treatment facilities (WWTFs) and Peachtree Creek, a small tributary inflow with degraded water quality draining a predominantly urban and industrial area. Median N0 2 + NO3-N and Tot-P concentrations in 1the mainstem increase downstream of these inputs from 0.5 to 1 mg l" and from 0.04 to 0.13 mg T1, respectively. NH4-N concentrations were typically low with 95% of the 2575 observations less than 0.21 mg l"1 throughout the river system, except some high values ( > 1 mg l" ) in some tributaries, particularly near the central part of Atlanta. High NH4-N concentrations are attributed to sewage discharge as they also are associated with high biological oxygen demand and faecal coliform bacteria concentrations. Nutrient concentrations vary temporally. An assessment of four sites, two mainstem and two tributaries, from 1970 to 1995 indicates a progressive increase and variability in N0 2 + N03-N concentrations during the period. The progressive increase in N0 2 + N03-N concentrations and their variability is similar to that reported for surface waters throughout the world and for which increased fertilizer usage has been attributed. Tot-P concentrations increase at mainstem sites through the middle to late 1980s and decrease markedly thereafter, due to improvements to WWTFs and a 1990 phosphate detergent ban. NH4-N concentrations, although less pronounced than Tot-P, display a similar decrease from the late 1980s to 1995 at the four sites. Tot-P concentration variability has increased at the tributary sites since 1993, although recent concentrations, on average, are the lowest since 1970 at each of the four sites.

INTRODUCTION Human activities have had a profound impact on the environment. Alteration of the land surface for a variety of uses including light and heavy industry, urbanization, and suburban developments has changed water pathways and induced changes to natural processes. Human activities are accompanied by sources of nutrients that are contributed to the landscape and receiving waters through various pathways, including atmospheric deposition, and solid and liquid waste disposal (Puckett, 1995). In addition, mechanisms for waste disposal and quality of waste are not static.

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Improved understandings of the effects of nutrient forms or species on the environment have affected practices for land and water management. The threat of degradation with respect to land-use change and waste disposal from previous and ongoing activities is quite high. Synoptic water-quality sampling provides an overview of water-quality conditions in an area, and when taken periodically and augmented with routine monitoring at selected sites, provide the basis for assessing patterns in a variety of environments, i.e. precipitation, soils, groundwater and surface waters, which in turn, contributes information to effectively manage the environment (Heathwaite et al, 1996). The need remains, therefore, to

EXPLANATION Metropolitan Atlanta Basin Boundary Stream Water-quality Monitoring Site 30 KILOMETERS

Chattahoochee River at Franklin Fig. 1 Location map.

Wastewater-Treatment Facility

Variability in nutrient concentrations in surface waters — Chattahoochee basin, Atlanta

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continually assess the status of stream ecosystems to provide feedback on resource management decisions. To this end, the spatial and temporal patterns in nutrient concentrations for surface waters of the Chattahoochee River basin in the Atlanta region from the early 1970s to 1995 are reported herein. BACKGROUND Chattahoochee River basin The Chattahoochee River and some of its tributaries (Fig. 1) provide public water supplies for the Atlanta region. The study area is in the Atlanta region and extends from the Chattahoochee River at Buford Dam, the base level for Lake Sidney Lanier, to the Chattahoochee River at US Highway 27 at Franklin, upstream of West Point Lake. The climate of the Atlanta region is warm, temperate, and subtropical, and annual air temperature averages 16°C. Average annual precipitation is 1250 mm, primarily as rainfall (Hodler & Schretter, 1986). Annual runoff averages approximately 400 mm (Carter & Stiles, 1983). Flow in this section of the river is regulated by dam releases. Urbanization, forest and agriculture are the dominant land cover and land use in the study area. Urbanization in the Metropolitan Atlanta area increased from 1140 km2 for 1972-1978 to 1660 km2 for 1990, as a result of rapid population growth from about 1.5 million people in 1970 to about 2.6 million in 1990, a 65% increase (Atlanta Regional Commission, written comm., 1996). Water releases from the Buford Dam are regulated primarily for power generation, but also for flood control, water supply for navigation in the lower Apalachicola-Chattahoochee-Flint (ACF) River basin, recreation, fish and wildlife, and pubic water supply (Fanning et al., 1991; Marella et al, 1993). Approximately 1.2 million m3 day"1 of freshwater were withdrawn for public supply from the surface waters of the Chattahoochee River basin near Atlanta in 1990; a similar amount was withdrawn for thermoelectric power generation (Marella et al, 1993). The Atlanta region accounts for 80% of all public water supply withdrawals from surface water in the entire ACF basin (drainage area of 51 300 km2). In contrast, approximately 0.92 million m3 day"1 (77% of water withdrawals) of treated municipal effluent was discharged to surface waters in the study area in 1990 (Marella et al., 1993; Frick et al., 1996). Nutrient water-quality data Nutrient water-quality data have been collected within the Chattahoochee River basin by Federal, State, and local governments, colleges and universities, and other organizations. These water-quality data were obtained to meet diverse objectives over varying temporal and spatial scales. Data for this report were obtained from readily available computerized data bases. Data limitations and handling procedures are detailed in Frick et al. (1996). The data analyses herein focus on concentrations of ammonium as N (NH4-N), nitrite plus nitrate as N (N02 + N03-N), and total phosphorus (Tot-P), due to data availability.

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Table 1 Site ID, river kilometre (RK) upstream from the mouth, station name, drainage area upstream of the station and number of 1994 and 1995 nutrient samples (n) for a spatial assessment of water quality in the Chattahoochee River basin near Atlanta. Long-term monitoring sites used for a temporal assessment are in bold. Site ID CR0015 TR0010 TR0020 CR0060 TR0030 CR0100 TR0040 TR0050 TR0060 CR0130 TR0070 TR0071 TR0080 CR0160 TR0090 TR0091 TR0100 CR0210 TR0110 TR0112 TR0120 CR0320 TR0130 CR0350 TR0140 TR0141 CR0370 TR0150 TR0160 CR0400 TR0170

RK 560.45 559.93 557.52 556.39 555.91 552.84 550.68 549.23 544.04 532.21 529.84 529.84 525.32 523.63 523.17 523.17 515.99 515.85 510.65 510.65 507.01 502.97 500.06 499.48 496.42 496.42 492.98 490.23 489.78 487.48 483.57

TR0171 TR0174 CR0490 TR0180 TR0190 TR0200 CR0530 TR0210 TR0220 TR0221 CR0600 TR0230 TR0240 CR0640

483.57 483.57 480.72 478.68 475.78 475.64 474.20 469.09 464.29 464.29 460.29 456.20 455.38 453.40

TR0250 TR0260 TR0270 TR0280 TR0290 TR0291 TR0300

453.01 452.87 446.18 444.00 441.93 441.93 440.05

Station Chattahoochee River at Buford Dam Tailwater Haw Creek at Parker Road Richland Creek at Suwanee Dam Road Chattahoochee River at Highway 20 James Creek at James Burgess Road Chattahoochee River at McGinnis Ferry Road Level Creek at Settles Bridge Road Dick Creek at Old Atlanta Road Suwanee Creek at US Highway 23 Chattahoochee River at Medlock Bridge Road John's Creek at State Bridge Road John's Creek at Buice Road Unnamed Creek at Rivermont Parkway Chattahoochee River at Holcomb Bridge Road Crooked Creek at Spalding Drive Crooked Creek at Peachtree Corners Circl Ball Mill Creek at Spalding Drive Chattahoochee River at Eves Road Big Creek at Roswell Water Intake Big Creek at Holcomb Bridge Road Willeo Creek at Highway 120 Chattahoochee River at Morgan Falls Dam March Creek at Brandon Mill Road Chattahoochee River at Johnson Ferry Road Sope Creek at Columns Drive Sope Creek at Lower Roswell Road Chattahoochee River at Powers Ferry Road Long Island Creek at Northside Drive Rottenwood Creek at Akers Mill Road Chattahoochee River at Paces Ferry Road Peachtree Creek at Ridgewood Road (long-term site 6 km upstream) Nancy Creek at West Wesley Road Peachtree Creek at Moore's Mill Road Chattahoochee River at Highway 280 Proctor Creek at Highway 280 Nickajack Creek at Highway 278 Sandy Creek at County Road 1288 Chattahoochee River at Highway 139 Utoy Creek at Highway 70 Sweetwater Creek at East Point Intake Sweetwater Creek at Blairs Bridge Road Chattahoochee River at Highway 166 Camp Creek at Cochran Road Deep Creek at Cochran Road Chattahoochee River at Highway 92 near Fairburn Anneewakee Creek at Highway 166 Tuggle Creek at Highway 70 Pea Creek at Highway 70 Bear Creek (Douglas County) at Highway 166 Bear Creek at Woodruff Road Bear Creek (Fulton County) at Highway 70 Dog River at Dog River Dam

Drainage area (km2) 2693.6 4.5 22.8 2745.4 39.3 2843.8 21.3 18.3 119.5 3038.1 30 24.9 6.3 3133.9 13.1 21.9 8.3 3159.8 252.8 266.5 41.7 3548.3 12.6 3626 83.8 91.7 3677.8 16.1 50.5 3755.5 95.8

n 74 5 31 75 30 59 30 1 87 59 4 31 4 56 45 4 2 72 82 4 30 56 30 56 26 4 56 29 72 72 54

95.9 339.2 4118.1 38.3 82 11 4283.9 87.5 633 681.2 5128.2 75.5 75.5 5335.4

27 3 56 48 33 32 56 70 82 5 55 30 28 70

72.8 8.2 35 44 68 66.6 169.6

50 5 16 28 43 4 23


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Table 1 continued. Site ID TR0301 CR0710 TR0310 TR0320 TR0330 TR0340 TR0350 TR0351 TR0352 CR0770

RK 440.05 436.28 434.38 430.15 428.93 421.11 420.35 420.35 420.35 418.10

TR0360 TR0361 TR0370 TR0380 TR0390 TR0400 TR0410 TR0430 TR0450 TR0460 TR0470 CR0940

412.79 412.79 411.23 410.97 407.51 403.28 400.08 392.11 387.95 386.48 380.56 378.86

Station Dog River at Highway 5 Chattahoochee River at Capps Ferry Road Hurricane Creek at Highway 5 Wolf Creek at Wilson Road White Oak Creek at Highway 70 Snake Creek at Black Dirt Road Cedar Creek at Sewell Mill Road Panther Creek at Sewell Mill Road Cedar Creek at Brimer Road Chattahoochee River at US Highway 27A near Whitesburg Wahoo Creek at Wagers Mill Road Wahoo Creek at Welcome-to-Sargent Road Thomas Creek at Payton Road Moore Creek at Sitton Road Acorn Creek at Highway 5 Whooping Creek at Highway 5 Yellowdirt Creek at Old Lowell Mill Road Hilly Mill Creek at Enon Grove Road Nutt Creek at Nutt Road Harris Creek at Highway 34 Centralhatchee Creek at US Highway 27 Chattahoochee River at US Highway 27 near Franklin

Drainage area (km2) 203.1 5879.3 14.5 43.3 41.7 123.6 102 11.4 111.9 6293.7 67 86.1 20.6 8.9 28 70.2 66.6 28.4 13.2 15.9 147.2 6941.2

4 55 4 27 27 28 24 24 4 71 63 4 4 1 28 67 4 27 4 1 28 72

The spatial patterns of nutrient concentrations were evaluated from data collected from May through October in 1994 and 1995 for a Georgia Environmental Protection Division (EPD) nutrient study of the Chattahoochee River (17 sites) and its tributaries (57 sites) from Buford Dam to Franklin, as listed in Table 1 (Roy Burke, EPD, written comm., 1996). Temporal patterns of nutrient concentrations from the early 1970s to 1995 were evaluated at four streamwater sites. Two sites were on the mainstem of the Chattahoochee River; one is at Atlanta and the other is downstream of Atlanta at State Highway 92 near Fairburn. The other two sites were on tributaries to the Chattachoochee River; Peachtree Creek drains a developed highly urbanized basin and Big Creek drains a rapidly developing area in the northern part of the study area.

VARIABILITY IN NUTRIENT CONCENTRATIONS Tot-P concentrations of more than 40% of the 1994-1995 EPD surface-water samples exceed U.S. Environmental Protection Agency (USEPA) recommendation of 0.1 mg T1, a concentration threshold established to control eutrophication in flowing waters, and 75% of samples exceed USEPA's recommendation of 0.05 mg l"1, a concentration threshold recommended to control eutrophication where streams enter a lake or reservoir. However, Tot-P concentrations, although generally high, are much lower than in the 1970s and 1980s. In contrast, N0 2 + N03-N concentrations in surface-water samples from the Chattahoochee River basin in the Atlanta region

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generally are much less than the USEPA concentration limit of 10 mg l"1 in drinking water (USEPA 1986, 1990, 1995) with a median for all 2 575 EPD samples of 0.44 mg T1; N0 2 + N03-N concentrations of the mainstem are slightly higher (0.54 mg l"1) than the tributaries (0.32 mg l"1). A very small percentage (< 1%) of the stream samples exceed the NH4-N concentration threshold of 2.1 mg l"1 (USEPA, 1986), a limit associated with ecosystem degradation due to chronic exposure of aquatic organisms to unionized ammonia. Urban development has affected the nutrient concentrations in the Chattachoochee River basin. Major sources of nutrients in the Chattahoochee River basin include municipal wastewater effluent, animal manure, fertilizer, and atmospheric deposition. Point sources discharging to surface waters in the area include municipal- and industrial-storm drains, wastewater effluent, sanitary and combined sewer overflows (SSOs and CSOs, respectively), and untreated wastes or runoff from illegal outfall pipes. Effluent from municipal wastewater generally contributes a small percentage to loads of N and P to an entire watershed, but is a very important source because it is discharged directly to surface waters. SSOs and CSOs can discharge a mixture of raw sewage and storm runoff directly to streams typically during storms when the storm runoff exceeds the capacity of the sewers. Nonpoint-source inputs have broad source areas, ranging in areal extent from less than 1 km2 to thousands of km2. A small, but often unknown, percentage of nonpoint-source inputs of nutrients enters the hydrologie system by leaching, runoff, or atmospheric deposition on water surfaces. Anthropogenic nonpoint-source inputs of nutrients for the study area are derived primarily from animal manure, fertilizer, and atmospheric deposition. Leaching of fertilizer into groundwater can provide a sustained nutrient-enriched, i.e. as N0 3 , source as groundwater is discharged to streams. The fertilizer in the Atlanta region is primarily applied to grasses and shrubs in residential and commercial areas including golf courses and parks. Spatial patterns Nutrient concentrations for the 74 sites sampled by EPD in 1994 and 1995 vary markedly in the basin (Fig. 2). Nutrient concentrations in the mainstem of the Chattahoochee River for the EPD study increase markedly downstream of river kilometre (RK) 485 (Fig. 2 and Table 1). A tributary, Peachtree Creek, draining a highly urbanized and industrial area, and two major WWTF outfalls, R. L. Sutton and R. M. Clayton, are relatively major contributors of nutrients to the mainstem. Median Tot-P concentration of all mainstem sites from RK 485 to 378 was 0.13 mg l"1 exceeding the USEPA limit of 0.1 mg l"1; whereas, median concentrations of the tributaries downstream of RK 485 were 0.09 mg l"1. Upstream of RK 485, the tributaries have much higher median Tot-P concentrations (0.10 mg l"1) than the mainstem (0.04 mg l"1). For the N parameters, median N0 2 + N03-N concentration of tributaries and mainstem were similar upstream of RK 485 (0.43 and 0.45 mg l"1, respectively); whereas downstream of RK 485, median concentration in the tributaries was much lower than that of the mainstem (0.2 and 1.9 mg l"1, respectively). Median N0 2 + N03-N concentration, like Tot-P concentration, increases markedly


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downstream of RK 485 from 0.45 to 1.9 mg l"1, possibly due to the WWTF discharges (no N0 2 + N03-N concentrations were available for the WWTFs). Median NH4-N concentrations show a similar pattern of increases in the mainstem downstream of RK 485, and are higher in tributaries upstream than downstream (0.03 mg 1"! upstream and

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