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Yields and Trends of Nutrients and Total Suspended Solids in Nontidal Areas of the Chesapeake Bay Basin, 1985-96

INTRODUCTION

Excessive concentrations of nutrients and suspended solids in water adversely affect water quality in the Chesapeake Bay. High levels of nutrients in the Bay result in algal blooms and suspended solids reduce water clarity, both of which decrease the amount of light reaching submerged aquatic vegetation (SAV). The die off and decomposition of algae and SAV deplete oxygen supplies in the water. Low dissolved oxygen (DO) levels (less than 5.0 milligrams per liter for aquatic life, U.S. Environmental Protection Agency, 1986) can lead to fish kills and stress other living resources in the Bay. In 1987, the Chesapeake Bay Agreement called for a 40-percent reduction in the amount of controllable nutrients reaching the Chesapeake Bay by the year 2000. This goal was based on results of computer simulations that predicted that periods of low DO would be reduced or eliminated if nutrient inputs to the Bay were reduced by that amount. In an effort to achieve that goal, nutrient-reduction strategies, including banning phosphate detergents, upgrading sewage-treatment plants, controlling runoff from agricultural and urban areas, and preserving forest and wetland areas (Zynjuk, 1995), were implemented in many areas of the basin to help reduce nutrient inputs to the Bay.

In 1997, a basinwide reevaluation of the 40-percent reduction goal was initiated to determine if that goal is achievable and to identify and document any changes in water quality and living resources in response to nutrient-reduction strategies. In support of this reevaluation, the U.S. Geological Survey (USGS) designed a database and retrieved water-quality data from approximately 1,300 nontidal stream sites in the Chesapeake Bay Basin (Langland and others, 1995). At 84 of the 1,300 sites, where sufficient data were available, trends, yields, and annual loads of nutrients and suspended solids were estimated for 1985 through 1996. This report presents: (1) spatial distribution of available nutrient and suspended-solids data for the 84 sites, (2) yields of nutrients and total suspended solids, and (3) trends in concentrations of nutrients and total suspended solids. Results presented here are limited to analyses for total nitrogen (TN), nitrate nitrogen (NO 3 ), total phosphorus (TP), and total suspended solids (TSS).

SPATIAL DISTRIBUTION

The 84 sites selected for analysis, which drain areas ranging from 3.3 to 27,100 square miles, are distributed throughout 10 major river basins in the 64,000-square-mile Chesapeake Bay Basin (fig. 1). Most of the 84 sites are in the basins of the three largest rivers draining into the Bay: the Susquehanna (36 sites), the Potomac (24 sites), and the James (9 sites). These three rivers drain slightly more than 80 percent of the Chesapeake Bay Basin and contribute about 85 percent of the Bay’s mean annual inflow of 69,900 cubic feet per second.

 
Figure 1 -- Click to Enlarge
Figure 1. Locations of the 84 sites in the Chesapeake Bay Basin used for analysis in this study.
 

Data from some areas in the Chesapeake Bay Basin are not discussed in this report because little or no long-term water-quality information is available. One example of this is the eastern shore of Maryland, an area previously identified as having elevated concentrations of nutrients (Zynjuk, L.D., and Feit, B.L., U.S. Geological Survey, written commun., 1996).

YIELDS

In order to calculate an annual yield of a constituent from a stream basin, an annual load (concentration multiplied by streamflow) must first be estimated. Annual loads of TN, NO 3 , TP, and TSS at the 84 sites were estimated by use of the USGS seven-parameter log-linear-regression model (ESTIMATOR) developed and validated by Cohn and others (1992). This model incorporates the minimum variance unbiased estimator (MVUE) model developed by Bradu and Mundlak (1970). The USGS model uses multiple regression to estimate a daily load by multiplying a predicted daily concentration by the daily mean streamflow. The estimated daily loads are summed to estimate the annual load. Annual yields are then calculated as the annual load divided by the drainage basin area. To be consistent with reporting of data in the 1997 reevaluation of the Chesapeake Bay Program (Langland and others, 1998), a mean yield based on annual yields for calendar years 1994-96 is reported here. If 1994-96 annual yields are not available, then the mean annual yield from 1993 to 1995 is reported. The mean annual yields discussed in this report will hereafter be referred to as status yields.

Sampling several high-flow events at different times of the year is extremely important in making accurate estimates of loads and yields. If a concentration-streamflow relation is not accurately defined, annual loads (and therefore annual yields) potentially can be over- or underestimated. Previous studies (Langland and others, 1995; Johnson and Belval, 1998) compared results of analysis of water-quality samples collected at the same site by different agencies over a 5-10 year period. Results indicated large differences in annual loads of TN, TP, and TSS at many of these co-located sampling sites, especially in basins where concentrations vary considerably between stormflow and non-stormflow conditions. These differences are directly related to the presence or absence of samples that represented the entire range of streamflow, especially the high-flow events. Therefore, sampling schemes should be designed to include sampling of the entire range of stream-flow conditions to ensure the best possible estimate of annual loads.

Status yields for TN were computed for 54 of the 84 sites (table 1). TN yields could be calculated for only 8 of the 36 sites in the Susquehanna River Basin because one or more nitrogen species needed to calculate TN (ammonia, organic nitrogen, nitrite, and nitrate) were not analyzed, or at least two of the species were reported at less than the analytical detection limit.

The three sites having the highest status yields for TN (site numbers 35, 51, and 50, fig. 1 and table 1) were located in highly intensive agricultural areas of the lower Susquehanna and the northcentral Potomac River Basins. More than 50 percent of the land that drains to the three sites is classified as agricultural. The Conestoga River (site 35) had a TN status yield of about 42 lb/acre (pounds per acre), more than five times the mean yield (8.4 lb/acre) of all the sites. Conversely, the lowest TN status yields (site numbers 62, 77, and 78, fig. 1 and table 1) were from basins that have a high (greater than 65) percentage of forest cover and a low (less than 20) percentage of agricultural land (Langland and others, 1995). Generally, these sites are in the central and western parts of the Chesapeake Bay Basin, where forests predominate and agricultural activity is less intense because of poor soil conditions and terrain unsuitable for farming.

Status yields of NO 3 (some sites have nitrite plus nitrate results, NO 2 + NO 3 , and are noted in table 1) were calculated for 80 of the 84 sites (table 1). These 80 sites provide good areal coverage of the Chesapeake Bay Basin. Status yields represent both the total (56 sites) and dissolved (24 sites) forms of NO 3 (table 1). Because NO 3 is a major component of TN, generally the sites with the highest status yields of TN also have the highest yields of NO 3 .

The highly intensive agricultural areas in the lower Susquehanna and central Potomac River Basins contain 9 of the 10 sites with the highest NO 3 yields. The highest yields for TN and NO 3 were reported at the same location—Conestoga River at Conestoga (site 35, fig. 1). Elevated yields of nutrients in agricultural areas are associated with nitrogen inputs, primarily from applications of manure and commercial fertilizers in excess of crop uptake. Lindsey and others (1997) estimated that on an annual basis, about 30 lb/acre of excess nitrogen were applied in the Conestoga River Basin in 1993-95. This excess nitrogen is potentially available to run off in surface water or to leach into the soil and enter the ground-water system. Conversely, status yields for NO 3 were lowest (averaging 1.21 lb/acre, sites 75-81, fig. 1 and table 1) in the highly forested upper James River Basin.

Status yields of TP were calculated at 75 of the 84 sites (table 1). Many of the sites that have high TP status yields are in the same highly intensive agricultural areas in the Chesapeake Bay Basin in which the highest status yields of TN and NO 3 were measured. Applications of manure and commercial fertilizer in excess of crop uptake requirements are the most likely cause of these high TP yields. Excess phosphorus adheres to soil particles and is readily transported in surface runoff when soils are disturbed by farming activities. The highest status yield of TP (3.53 lb/acre) was estimated at Conestoga River at Conestoga (site 35, fig. 1), an area of intensive agricultural activities. The lowest TP yield (0.11 lb/acre) was estimated for site 15, a small watershed within the Susquehanna River Basin where forest cover exceeds 90 percent of the drainage area. Additional factors contributing to elevated TP yields include the natural concentrations of phosphorus in the soils and the effects of urban growth in the basin.

Calculated TP yields decreased significantly between site 34 (0.61 lb/acre) and site 36 (0.30 lb/acre) in the Lower Susquehanna River Basin, even though the basin having the highest TP yield (site 35) discharged to the Susquehanna River between the two sites. The reason for this decrease is the presence of large reservoirs behind each of three hydroelectric dams on the Susquehanna River between sites 34 and 36. As water enters these reservoirs, it slows, and suspended particulate matter is deposited. Because phosphorus adheres to particulate matter, phosphorus also is deposited. These three reservoirs annually trap an average of 40 percent of the total phosphorus load entering this river system (Ott and others, 1991).

 
 

Estimated and ranked yields for four constituents at 84 nontidal sites located within 10 river basins in the Chesapeake Bay Basin

[N, nitrogen; P, phosphorus; yield, 1994-96 calendar year mean, in pounds per acre; rank (54), ranking of all yields from largest to smallest; number in parenthesis represents total number of sites with estimated yields; --, data not available; green, samples collected by the Susquehanna River Basin Commission; yellow, samples collected by the U.S. Geological Survey; purple, samples collected by the Metropolitan Washington D.C. Council of Governments; white, samples collected by State Regulatory Agencies, including the Maryland Department of Natural Resources, the Pennsylvania Department of Environmental Protection, and the Virginia Department of Environmental Quality]
 

U.S. Geological
Survey
streamflow
site number

Water-quality
site ID
number

Map site
number

Drainage
area
(square
miles)

Total nitrogen as N

 

Nitrate nitrogen as N

 

Total phosphorus as P

 

Total suspended solids

Yield

Rank
(54)

Yield

Rank
(80)

Yield

Rank
(75)

Yield

Rank
(56)

SUSQUEHANNA RIVER BASIN
01503000 WQN0306
1
2,232
-- --  
3.26
55
 
0.35
1 51
  -- --
01518700 WQN0319
2
446
-- --  
2 2.54
62
 
2 .34
53
 
2120
36
01520000 WQN0320
3
298
-- --  
3.12
57
 
.48
39
 
380
12
01531000 WQN0332
4
2,530
-- --  
3.59
49
 
.36
1 49
 
212
24
01531500 01531500
5
7,797
6.4 0
31
 
3.71
47
 
.58
28
 
461
8
01532000 WQN0318
6
215
-- --   -- --  
.89
15
  -- --
01534000 WQN0317
7
383
-- --  
3.27
54
 
.28
1 61
  -- --
01536000 WQN0313
8
332
-- --  
4.43
38
 
.91
14
 
110
39
01536500 WQN0302
9
9,960
-- --  
3.19
56
 
.40
47
  -- --
01540500 01540500
10
11,220
7.13
26
 
4.14
41
 
.62
1 24
 
396
11
01541000 WQN0406
11
315
-- --  
4.89
34
 
.49
1 37
 
291
15
01541500 WQN0422
12
371
-- --  
3.42
52
 
.24
66
 
180
27
01543000 WQN0420
13
272
-- --  
3.45
51
 
.16
69
 
82.9
42
01544000 WQN0419
14
245
-- --  
4.04
43
 
.13
1 71
 
35.4
51
01545000 WQN0434
15
233
-- --  
3.31
53
 
.11
75
 
13.8
56
01546500 WQN0415
16
87.2
-- --  
14.9
10
 
.31
1 57
 
71.7
43
01547200 WQN0413
17
265
-- --  
11.0
13
 
.28
1 60
  -- --
01547950 WQN0423
18
152
-- --  
2.29
63
  -- --  
33.8
53
01550000 WQN0409
19
173
-- --  
6.69
26
 
.33
1 54
 
35.3
52
01551500 WQN0402
20
5,682
-- --  
3.63
48
 
.43
42
 
245
22
01552000 WQN0408
21
443
-- --  
4.86
35
 
.13
1 71
 
31.9
54
01553500 01553500
22
6,850
7.12
27
 
4.21
40
 
.42
1 43
 
168
29
01554000 WQN0203
23
18,300
-- --  
4.33
39
 
.46
1 40
  -- --
01555000 WQN0229
24
310
-- --  
9.70
18
 
.28
1 60
 
90.6
41
01556000 WQN0224
25
291
-- --  
9.89
17
 
.78
21
  -- --
01558000 WQN0217
26
220
-- --  
6.31
28
 
.35
1 51
  -- --
01562000 WQN0223
27
756
-- --  
9.92
15
 
.31
1 57
  -- --
01567000 01567000
28
3,354
9.51
17
 
7.00
23
 
.41
46
 
70.0
44
01570000 WQN0213
29
470
19.1
6
 
18.6
5
 
.50
1 35
 
283
17
01570500 01570500
30
24,100
-- --  
4.73
36
 
.46
1 40
  -- --
01573560 WQN0211
31
483
-- --  
22.5
3
 
.62
1 24
  -- --
01574000 WQNO210
32
510
-- --  
13.5
11
 
1.3
7
  -- --
01575500 WQN0207
33
222
-- --  
18.0
6
 
1.1
18
  -- --
01576000 0157600
34
25,990
9.60
16
 
6.54
27
 
.61
26
 
564
4
01576754 01576754
35
470
42.0
1
 
39.8
1
 
3.5
1
 
348
13
01578310 01578310
36
27,100
9.74
15
 
7.56
21
 
.33
59
 
193
26
CHOPTANK RIVER BASIN
01491000 01491000
37
113
7.91
23
 
5.12
33
 
.42
1 43
 
109
40
WESTERN SHORE RIVER BASIN
01586000 NPA0165
38
56.6
19.7
5
 
16.3
8
  -- --   -- --
PATUXENT RIVER BASIN
01591000 01591000
39
34.8
13.7
9
 
10.2
14
 
.65
23
  -- --
01592500 PXT0809
40
132
5.15
35
 
2.81
60
 
.12
74
 
29.0
55
01594000 01594000
41
98.4
10.0
14
 
5.48
30
  -- --   -- --
01594440 01594440
42
348
7.93
22
 
5.15
32
 
.53
31
 
229
23
01594526 01594526
43
89.7
-- --  
1 1.64
65
  -- --   -- --
01594670 01594670
44
9.4
1.95
50
 
.530
78
  -- --   -- --
01594710 01594710
45
3.3
8.07
21
 
3.89
44
 
1.1
18
  -- --
POTOMAC RIVER BASIN
01597500 SAV0037
46
106
7.13
25
  -- --  
.15
70
 
138
34
01599000 GEO0009
47
73
6.85
30
  -- --  
.37
48
 
249
21
01610000 POT2766
48
3,109
6.55
29
  -- --  
.51
1 33
 
558
5
01613000 POT2386
49
4,073
5.29
34
 
3.75
46
 
.42
1 43
 
281
18
01614500 CON0180
50
501
24.3
3
 
20.0
4
 
0.77
22
 
408
10
01619500 ANT0044
51
281
26.2
2
 
23.8
2
 
.95
11
 
271
19
01624800 1BCST012.32
52
70.1
10.9
12
 
7.89
20
 
.86
16
  -- --
01625000 1BMDL001.83
53
375
5.04
36
 
3.50
50
 
.28
1 60
 
2 209
25
01626000 1BSTH027.85
54
127
3.47
39
 
2.70
61
 
.83
18
 
118
37
01627500 1BSTH007.80
55
212
4.08
37
 
3.88
45
 
.42
1 43
 
162
30
01629500 1BSSF054.20
56
1,377
10.4
13
 
6.89
24
 
2.9
2
 
538
7
01631000 1BSSF003.56
57
1,642
5.62
33
 
4.65
37
 
.50
1 35
 
173
28
01632000 1BNFS093.53
58
210
3.08
41
 
4.13
42
 
.26
64
  -- --
01632900 1BSMT004.60
59
93.2
9.11
19
 
7.39
22
 
1.7
5
 
265
20
01634000 1BNFS010.34
60
768
2 6.86
28
 
6.27
29
 
.36
1 49
 
158
31
01634500 1BCDR013.29
61
103
2 2.25
48
 
1.46
66
  -- --  
53.6
47
01635500 1BPSG001.36
62
87.8
1.94
52
 
.620
76
 
.20
1 67
 
112
38
01637500 CAC0148
63
66.9
12.7
10
 
12.4
12
 
.49
1 37
 
289
16
01638500 POT1595
64
9,651
9.49
18
 
6.81
25
 
.96
10
 
417
9
01639000 01639000
65
173
17.6
8
 
9.9
16
 
.92
13
  -- --
01639500 BPC0035
66
102
21.6
4
 
16.5
7
 
.93
12
 
547
6
01643000 MON0155
67
817
18.7
7
 
15.2
9
 
1.8
4
 
1,170
2
01646000 1ADIF000.86
68
57.9
8.63
20
 
5.17
31
 
.59
27
  -- --
01646580 PR01
69
11,570
12.0
11
 
3 8.93
19
 
.84
17
 
4 750
--
RAPPAHANNOCK RIVER BASIN
01666500 3-ROB001.90
70
179
7.19
24
 
3.05
58
 
.81
19
  -- --
01668000 01668000
71
1,596
6.16
32
 
3 2.92
59
 
1.5
6
 
1,220
1
01669000 3-PIS009.24
72
28
2.50
47
 
1.15
69
  -- --  
53.9
46
MATTAPONI RIVER BASIN
01674500 01674500
75
601
1.95
51
 
3 .420
80
 
.20
1 67
 
40.0
50
PAMUNKEY RIVER BASIN
01671020 8-NAR005.42
73
463
-- --  
.52
79
 
.13
1 71
 
47.9
49
01673000 01673000
74
1,081
2.87
44
 
3 .970
73
 
.33
1 54
 
151
132
JAMES RIVER BASIN
02013100 2-JKS023.61
76
614
3.34
40
 
1.13
71
 
1.8
3
 
69.1
45
02020500 2-CFP004.67
77
144
1.82
53
 
.950
74
  -- --   -- --
02021500 2-MRY038.10
78
329
1.50
54
 
.650
75
 
.33
1 54
  -- --
02026000 2-JMS229.14
79
3,683
2 2.91
43
 
2 1.33
68
 
2 .55
1 30
 
2 129
35
02027500 2-PNY005.29
80
47.6
2.94
42
 
1.89
64
  -- --   -- --
02029000 2-JMS189.31
81
4,584
2.53
45
 
1.34
67
 
2 .52
32
 
151
132
02035000 02035000
82
6,257
3.64
38
 
3 1.14
70
 
.80
20
 
292
15
02037500 2-JMS117.35
83
6,758
2.52
46
 
1.02
72
 
.51
1 33
 
678
3
APPOMATTOX RIVER BASIN
02041650 02041650
84
1,344
2.10
49
 
3 .570
77
 
.23
66
 
53.6
147

 

 
Status yields for TSS were calculated at 56 of the 84 sites (table 1). TSS yields ranged from a maximum of 1,220 lb/acre (site 71) to a minimum of 13.8 lb/acre (site 15). Similar to phosphorus, the TSS status yield declines in the Lower Susquehanna River Basin, from 564 lb/acre (site 34) to 193 lb/acre (site 36). This is caused primarily by the estimated 70-percent sediment trapping efficiency in the reservoir system on the Lower Susquehanna River (Ott and others, 1991). Once the reservoirs fill, they will no longer trap sediments and nutrients, and loads to the Bay can be expected to increase by 70 percent for phosphorus and 250 percent for suspended sediment (Langland and Hainly, 1997). Although yields of total suspended solids and suspended sediments are not directly comparable because of analytical differences, the transport mechanism (stream-flow) and depositional processes are similar. Suspended sediment status yields were calculated for nine USGS water-quality sites. If TSS data were available at any of the nine sites, then TSS yields were reported in table 1.  

TRENDS

One way to measure the effects of nutrient-reduction strategies in the Chesapeake Bay Basin, and progress toward the nutrient-reduction goal, is to determine if any consistent changes through time, or trends, are evident in the concentrations of nutrients in the waters that enter the Bay. Across the basin, trends in the concentrations of both TN and TP were generally downward, indicating that nutrient- reduction strategies have had a positive effect on the water quality.

Trends in concentration were determined by use of a time coefficient in the ESTIMATOR model (Cohn and others, 1989). The trend results are corrected to account for both flow and seasonality. Where the trend is significant (95-percent significance level), the direction of the trend is indicated by upward or downward pointing arrows (figs. 2a-2d).

 
Figures 2a-2b -- Click to Enlarge
Figure 2. Trends in flow-adjusted concentrations of (A) total nitrogen, and (B) nitrate at stream sites in the Chesapeake Bay Basin.
Figures 2c-2d -- Click to Enlarge
Figure 2. Trends in flow-adjusted concentrations of (C) total phosphorus, and (D) total suspended solids at stream sites in the Chesapeake Bay BasinóContinued.
 

Trends in concentrations of TN were calculated for 54 sites. The trends were downward at 20 of the 54 sites (fig. 2a and table 2) and upward at six sites, four of which are in the Potomac River Basin (fig. 2a). Trends in concentrations of NO 3 were calculated for 81 sites (fig. 2b and table 2). NO 3 trends were upward at 19 sites and downward at 19 sites, but no significant change was detected at 47 sites. The upward trends may be related to (1) a “lag” between applications of fertilizers to the land surface and the delivery of NO 3 in the ground-water portion of streamflow, (2) climatic factors, such as variability in precipitation, that can vary the amount of NO 3 infiltrating the soils and reaching the ground water, (3) upgrades to sewage-treatment facilities that may change ammonia and organic forms of nitrogen to NO 3 , and (4) possible higher concentrations of in-stream NO 3 as nitrogen-consuming plants (such as algae, a source of organic nitrogen) are limited due to in-stream decreases in phosphorus concentrations.

 
 

Estimated flow-adjusted trends in concentrations of four constituents at 84 nontidal sites in the Chesapeake Bay Drainage basin for
calendar years 1985-96

[N, nitrogen; P, phosphorus; min and max define range in the change in concentration (at 95-percent confidence level); --, no results available;
n/s, not significant at 95-percent confidence level; yellow, significant decrease in trend; red, significant increase in trend]
 

U.S. Geological
Survey
streamflow
site number

Water-quality
site ID
number

Map site
number

Drainage
area
(square
miles)

Trends in concentration, in percent

Total nitrogen as N

 

Nitrate nitrogen as N

 

Total phosphorus as P

 

Total suspended solids

min

max

min

max

min

max

min

max

SUSQUEHANNA RIVER BASIN
01503000
WQN0306
1
2,232
-- --   n/s n/s  
-46
-15
 
--
--
01518700
WQN0319
2
446
-- --   n/s n/s  
-56
-21
  n/s n/s
01520000
WQN0320
3
298
-- --   n/s n/s   n/s n/s   n/s n/s
1 01531000
WQN0332
4
2,530
-- --   n/s n/s   n/s n/s   n/s n/s
01531500
01531500
5
7,797
-47
-29
 
2 -38
2 -6
  n/s n/s   n/s n/s
01532000
WQN0318
6
215
-- --  
--
--
 
-64
-21
  n/s n/s
01534000
WQN0317
7
383
-- --   n/s n/s  
-52
-20
  n/s n/s
01536000
WQN0313
8
332
-- --   n/s n/s  
-53
-27
 
-86
-39
01536500
WQN0302
9
9,960
-- --  
-52
-9
 
-69
-46
 
--
--
01540500
01540500
10
11,220
-37
-23
  2 n/s 2 n/s  
-41
-10
  n/s n/s
01541000
WQN0406
11
315
-- --  
-42
-20
 
-86
-65
  n/s n/s
1 01541500
WQN0422
12
371
-- --  
-40
-12
 
-42
-7
  n/s n/s
1 01543000
WQN0420
13
272
-- --   n/s n/s  
-55
-29
 
-87
-19
1 01544000
WQN0419
14
245
-- --   n/s n/s  
-69
-38
  n/s n/s
1 01545000
WQN0434
15
233
-- --   n/s n/s  
-57
-26
  n/s n/s
01546500
WQN0415
16
87.2
-- --  
2
26
 
-62
-32
  n/s n/s
01547200
WQN0413
17
265
-- --  
2
36
 
-73
-57
 
-93
-8
01547950
WQN0423
18
152
-- --   n/s n/s  
--
--
  n/s n/s
01550000
WQN0409
19
173
-- --  
34
67
 
-66
-19
  n/s n/s
01551500
WQN0402
20
5,682
-- --   n/s n/s   n/s n/s   n/s n/s
01552000
WQN0408
21
443
-- --  
37
84
 
-69
-32
  n/s n/s
01553500
01553500
22
6,850
-24
-4
 
2 8
2 29
 
-33
14
  n/s n/s
01554000
WQN0203
23
18,300
-- --   n/s n/s  
-62
-38
 
--
--
1 01555000
WQN0229
24
310
-- --  
-35
-3
 
-49
-4
  n/s n/s
01556000
WQN0224
25
291
-- --  
-34
-9
 
-78
-64
 
--
--
01558000
WQN0217
26
220
-- --   n/s n/s  
-82
-69
 
--
--
01562000
WQN0223
27
756
-- --   n/s n/s  
-78
-61
 
--
--
01567000
01567000
28
3,354
-31
-21
  2 n/s 2 n/s  
-59
-41
  n/s n/s
1 01570000
WQN0213
29
470
-- --   n/s n/s  
-53
-1
  n/s n/s
1 01570500
01570500
30
24,100
-- --  
2 -38
2 -4
 
--
--
 
--
--
01573560
WQN0211
31
483
-- --   n/s n/s  
-64
-41
 
--
--
01574000
WQNO210
32
510
-- --   n/s n/s  
-67
-49
 
--
--
1 01575500
WQN0207
33
222
-- --  
30
100
 
-76
-43
 
-84
-39
01576000
0157600
34
25,990
-37
-22
  2 n/s 2 n/s  
-47
-20
 
-77
-12
01576754
01576754
35
470
-23
-14
  n/s n/s  
-23
-6
 
-70
-5
01578310
01578310
36
27,100
-25
-10
 
2 1
2 24
 
-62
-52
  n/s n/s
CHOPTANK RIVER BASIN
01491000
01491000
37
113
-18
-1
 
2 22
2 55
 
-41
-5
 
3
250
WESTERN SHORE RIVER BASIN
01586000
NPA0165
38
56.6
19
46
 
29
66
 
-81
-48
  n/s n/s
PATUXENT RIVER BASIN
01591000
PXT0972
39
34.8
n/s n/s  
8
40
 
-72
-30
  n/s n/s
01592500
PXT0809
40
132
1
30
  n/s n/s   n/s n/s  
14
213
01594000
01594000
41
98.4
n/s n/s   n/s n/s  
--
--
 
--
--
01594440
01594440
42
348
-60
-53
 
2 -55
2 -44
 
-80
-71
 
-53
-25
01594526
01594526
43
89.7
-- --   n/s n/s  
--
--
 
--
--
1 01594670
01594670
44
9.4
-47
-15
  n/s n/s  
--
--
 
--
--
01594710
01594710
45
3.3
n/s n/s   2 n/s 2 n/s  
-74
-21
 
--
--
POTOMAC RIVER BASIN
01597500
SAV0037
46
106
-48
-29
 
--
--
 
-65
-4
  n/s n/s
01599000
GEO0009
47
73
-46
-19
 
--
--
 
-64
-11
  n/s n/s
01610000
POT2766
48
3,109
n/s n/s   2 n/s 2 n/s  
-72
-36
  n/s n/s
01613000
POT2386
49
4,073
-45
-19
  n/s n/s  
-65
-9
  n/s n/s
01614500
CON0180
50
501
n/s n/s   n/s n/s  
-54
-15
  n/s n/s
01619500
ANT0044
51
281
n/s n/s  
13
48
 
-46
-17
  n/s n/s
01624800
1BCST012.32
52
70.1
n/s n/s   n/s n/s  
-54
-19
  n/s n/s
01625000
1BMDL001.83
53
375
n/s n/s   n/s n/s  
-72
-47
 
-73
-24
01626000
1BSTH027.85
54
127
n/s n/s   n/s n/s  
-52
-10
  n/s n/s
01627500
1BSTH007.80
55
212
-81
-69
 
-71
-54
 
-73
-54
  n/s n/s
01629500
1BSSF054.20
56
1,377
n/s n/s  
1
39
 
-53
-24
  n/s n/s
01631000
1BSSF003.56
57
1,642
n/s n/s  
0
77
 
-68
-28
 
-72
-72
01632000
1BNFS093.53
58
210
n/s n/s  
-50
-1
  n/s n/s   n/s n/s
01632900
1BSMT004.60
59
93.2
2
48
  n/s n/s   n/s n/s   n/s n/s
01634000
1BNFS010.34
60
768
22
88
 
54
215
  n/s n/s   n/s n/s
01634500
1BCDR013.29
61
103
n/s n/s   n/s n/s  
--
--
  n/s n/s
01635500
1BPSG001.36
62
87.8
-46
-5
  n/s n/s   n/s n/s  
-84
-22
01637500
CAC0148
63
66.9
n/s n/s   n/s n/s  
-55
-8
 
61
484
01638500
POT1595
64
9,651
n/s n/s  
9
57
 
-60
-20
  n/s n/s
01639000
01639000
65
173
-76
-27
  n/s n/s  
2
53
 
--
--
01639500
BPC0035
66
102
n/s n/s  
11
34
 
-63
-18
  n/s n/s
01643000
MON0155
67
817
n/s n/s  
76
198
  n/s n/s   n/s n/s
01646000
1ADIF000.86
68
57.9
22
95
 
41
132
  n/s n/s  
-76
-7
01646580
PR01
69
11,570
n/s n/s  
2 52
2 91
 
-58
-42
 
--
--
RAPPAHANNOCK RIVER BASIN
01666500
3-ROB001.90
70
179
n/s n/s   n/s n/s   n/s n/s   n/s n/s
1 01668000
01668000
71
1,596
-36
-15
  n/s n/s  
-53
-22
 
-72
-39
1 01669000
3-PIS009.24
72
28
n/s n/s   n/s n/s   n/s n/s   n/s n/s
MATTAPONI RIVER BASIN
1 01674500
01674500
75
601
-23
-7
 
-49
-21
 
-30
-5
  n/s n/s
PAMUNKEY RIVER BASIN
01671020
8-NAR005.42
73
463
n/s n/s   n/s n/s   n/s n/s   n/s n/s
1 01673000
01673000
74
1,081
n/s n/s   n/s n/s   n/s n/s   n/s n/s
JAMES RIVER BASIN
02013100
2-JKS023.61
76
614
15
58
  n/s n/s  
-86
-66
  n/s n/s
02020500
2-CFP004.67
77
144
n/s n/s   n/s n/s  
--
--
 
-87
-24
02021500
2-MRY038.10
78
329
-37
-4
 
-64
-21
  n/s n/s   n/s n/s
02026000
2-JMS229.14
79
3,683
n/s n/s  
-51
-8
 
-52
-11
 
8
208
02027500
2-PNY005.29
80
47.6
-83
-5
  n/s n/s  
--
--
  n/s n/s
02029000
2-JMS189.31
81
4,584
n/s n/s  
-65
-20
 
-57
-17
  n/s n/s
1 02035000
02035000
82
6,257
n/s n/s   n/s n/s  
-49
-23
  n/s n/s
02037500
2-JMS117.35
83
6,758
n/s n/s  
-77
-24
 
-75
-52
  n/s n/s
1 02041650
02041650
84
1,344
n/s n/s   n/s n/s   n/s n/s   n/s n/s
 

The positive effects of nutrient-reduction strategies are reflected by the downward trends in TP. Significant downward trends in TP were reported at 58 sites (fig. 2c and table 2), no change was reported at 17 sites, and TP was increasing at only 1 site. Reductions in concentrations from point-source discharges, especially sewage-treatment plants (U.S. Environmental Protection Agency, 1997), and the phosphate detergent ban (implemented throughout the basin in different years in the 1980’s) were major factors affecting the widespread downward TP trends in all 10 subbasins.

Significant downward trends for TSS were reported at 13 of the 56 sites. Upward TSS trends were reported at 4 sites— one each in the Patuxent, Choptank, Potomac, and James River Basins (fig. 2d and table 2). No significant trends in concentrations of TSS could be determined at 52 sites. At 10 of the 13 sites where TSS trends were downward, TP trends also were downward. Because a large portion of TP is attached to particulate matter (TSS), and the main transport mechanism for both constituents is surface-water runoff, nutrient-reduction strategies designed to control surface runoff would favorably affect both TSS and TP.

SUMMARY

In support of the 1997 Reevaluation of the Chesapeake Bay Program, water-quality yield and trend data from 1985-96 were analyzed at 84 nontidal sites within 10 major subbasins of the Chesapeake Bay Basin. A mean yield was calculated for total nitrogen, total nitrate, total phosphorus, and total suspended solids at 54, 80, 75, and 56 sites, respectively, for the last 3 years of record. The highest yields were reported at sites in subbasins having a large percentage of agricultural land use, and lowest yields were reported in subbasins with large amounts of forested land. Generally, basinwide trends from 1985 to 1996 for both total nitrogen and total phosphorus were downward, indicating the positive effects of nutrient-reduction strategies. Trends for
nitrate nitrogen, however, were either upward or not statistically significant at about 75 percent of the sites, suggesting that nutrient-reduction strategies for nitrate nitrogen are less effective or that more time is needed to detect significant changes in water quality.

 

REFERENCES CITED

Bradu, Dan, and Mundlak, Yair, 1970, Estimation in lognormal linear models: Journal of the American Statistical Association, v. 65, no. 329, p. 198-211.

Cohn, T.A., DeLong, L.L., Gilroy, E.J., Hirsh, R.M., and Wells, D.K., 1989, Estimating constituent loads: Water Resources Research, v. 25, no. 5, p. 937-942.

Cohn, T.A., Caulder, D.L., Gilroy, E.J., Zynjuk, L.D., and Summers, R.M., 1992, The validity of a simple statistical model for estimating fluvial constituent loads: An empirical study involving nutrient loads entering Chesapeake Bay: Water Resources Research, v. 28, no. 4, p. 2,353-2,363.

Johnson, H.M., and Belval, D.L., 1998, Nutrient and suspended solids loads, yields, and trends in the non-tidal part of five major river basins in Virginia, 1985-96: U.S. Geological Survey Water-Resources Report 98-4025, 36 p.

Langland, M.J., Lietman, P.L., and Hoffman, S.A., 1995, A synthesis of nutrient and sediment data from watersheds within the Chesapeake Bay drainage basin: U.S. Geological Survey Water-Resources Investigation Report 95-4233, 127 p.

Langland, M.J., Edwards, R.E., and Darrell, L.C., 1998, Status yields and trends of nutrients and sediment and methods of analysis for the nontidal data-collection programs, Chesapeake Bay Basin, 1985-96: U.S. Geological Survey Open-File Report 98-17, 60 p.

Lindsey, B.D., Loper, C.A., and Hainly, R.A., 1997, Nitrate in ground water and stream base flow in the Lower Susquehanna River Basin, Pennsylvania and Maryland: U.S. Geological Survey Water Resources Investigations Report 97-4146, 66 p.

Ott, A.N., Takita, C.S., Edwards, R.E., and Bollinger, S.W., 1991, Loads and yields of nutrients and suspended sediment transported in the Susquehanna River basin, 1985-89: Susquehanna River Basin Commission Report, Publication no. 136, 253 p.

U.S. Environmental Protection Agency, 1986, Quality Criteria for Water, 1986: EPA 44015-86-001 (no numbered pages).

_____1997, Chesapeake Bay Nutrient Reduction Progress and Future Directions: Nutrient Reduction Reevaluation Summary Report, October 1997.

Zynjuk, L.D., 1995, Chesapeake Bay: Measuring pollution reduction: U.S. Geological Survey Fact Sheet FS-055-95.

—Michael J. Langland

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