Nonpoint N Runoff from Agricultural Watersheds into the Great Lakes

J. Great Lakes Res. , 1980 Internat. Assoc. Great Lakes Res. 6(3): 195-202

NONPOINT N RUNOFF FROM AGRICULTURAL WATERSHEDS INTO THE GREAT LAKESl

G. H. Neilsen, J. L. Culley2, and D. R. Cameron3 Agriculture Canada, Research Station Summerland, B.C. VOH 1Z0

ABSTRACT. Eleven agricultural watersheds were continuously monitored for discharge and intensively sampled for runoff N, 1975-77, as part of the IJC Pollution from Land Use Activities Reference Group (PLUARG), Task Group C (Canadian). The watersheds, located in southern Ontario, were sampled between 30 to more than 500 times for NH4 -N, N0 3 +N02 -N, and total Kjeldahl N (TKN). The predominant chemical form of runoff N was N0 3 -N with flow weighted concentration means on sampled days ranging from 0.57 to 5.62 mg/L. In contrast, TKN means ranged from 0.64 mg/L to 2.37 mg/L while average soluble NH4 -N concentrations varied from 0.03 mg/L to 0.60 mg/L. High runoff N0 3 -N concentrations occurred from watersheds with extensive areas of tile drainage, row crops (especially com), and high kg/ha fertilizer N application rates. Elevated stream TKN concentrations were associated with watersheds with more impermeable soils. Stream N0 3 -N loadings ranged from 2.1 ± 0.2 to 39.0 ± 7.6 kg N0 3 -N/watershed ha. Significant N fertility losses in excess of 30 kg N0 3 -N ha occurred from some watersheds, while other watersheds with extensive areas of hay and pasture and unimproved land gained more N0 3 -N in precipitation than was lost as runoff. TKN loads averaged 32% and 25% of total N runoff for the 11 watersheds in 1975 and 1976 respectively. Efforts to reduce Ontario watershed N runoff should concentrate first on soluble Nand therefore on improved efficiency of N fertilizer use on the extensive areas of tile drained com in the lower Great Lakes basin. The effectiveness of standard soil erosion control methods, including grassed waterways and contour planting, should be investigated for reduction of TKN runoff.

INTRODUCTION The detrimental effects of excessive N on water quality have been of concern with eutrophication and groundwater contamination receiving considerable attention. (Hore and Maclean 1973, Viets 1975). More recently, realization of the significant energy cost of production of N fertilizer (Pimentel et al. 1976) means that large runoff losses of N will be viewed as increasingly extravagant. Efforts to model nutrient transport from agricultural watersheds (Frere, Onstad, and Holton 1975) and to develop remedial measures to control water pollution resulting from cropland runoff (Stewart et a1. 1975) would benefit from information gained from detailed field studies over a variety of soils and climates. 1 Agriculture

Canada, Research Station, Summerland, B. C. Contribution No. 503. 2 Land Resource Research Institute, Agriculture Canada, Ottawa, Ontario, KiA OC6. 3 Research Station, Agriculture Canada, Swift Current, Saskatchewan, S9H 3X2.

A number of recent studies have been concerned in whole or part with detailed monitoring of N runoff from one (Burwell et al. 1974), two (Taylor, Edwards, and Simpson 1971; Kilmer et al. 1974; Kissell, Richardson and Burnett 1976) or four agricultural watersheds (Schuman et a1. 1973, Burwell et al. 1976). Comparisons between large numbers of watersheds have been restricted to those of small size (Olness et al. 1975) or with limited sampling (Muir, Seim, and Olson 1973). Consequently, it has frequently been difficult to assess N losses from land tracts of a size similar to the area draining into the Great Lakes. From such studies, a number of agricultural practices have been linked to elevated runoff N loadings. These included loss of N from crop and abandoned farmland, (Hill 1978), from winter spreading of manure (Taylor et al. 1971) and from livestock feeding areas (Burwell et al. 1974). Nitrogen residual from general cropping (Kilmer 195

196

NEILSEN, CULLEY, AND CAMERON

et al. 1974) and especially from corn cropping (Webber and Elrick 1967) particularly on impermeable soils (Neilsen and MacKenzie 1977) has also been identified as a potential hazard. Few of these studies assessed the potential for reduction of N runoff. The International Reference Group on Great Lakes Pollution from Land Use Activities (PLUARG) had the responsibility of investigating the extent of pollution in the Great Lakes system from runoff from watersheds with a variety of land use activities including agriculture. The purpose of this paper was to report the chemical form and magnitude of N runoff during 1975-77, and its relationships to agricultural land use and soil characteristics in 11 PLUARG watersheds. Since these watersheds represented a wide range of the rural land use and the kinds of soil occurring in the Lower Great Lakes Basin, the information gathered was used to assess potential reductions in N runoff from agricultural activities. MATERIALS AND METHODS The 11 monitored PLUARG watersheds (Figure 1) drained eventually into Lake Ontario (AG-7, AG-10, AG-II), Lake Erie (AG-2, AG-4, AG-13), Lake St. Clair (AG-I, AG-5), or Lake Huron (AG-3, AG-6, AG-14). Detailed crop (Table 1) and soil and fertilizer use information (Table 2) was available for each watershed from surveys previously carried out by Frank and Ripley (1977). Water samples were collected, 1975-77, for chemical analysis at the continuous flow monitoring stations established at the outlet of each

--,.

c···

I···

FIG. 1. Location of the monitored agricultural watersheds.

watershed and maintained by Environment Canada (AG-2, AG-4, AG-7) or by Ontario Ministry of Environment (O.M.E.), Water Resources Branch. The watersheds were generally manually sampled, weekly or biweekly, during high flow periods, with the exception of watershed AG-Il. Many samples were not taken at this watershed. During 1976, watersheds AG-I, AG-3, AG-4, AG-5, AG-IO, and AG-13 had additional intensive manual and automatic sampling during selected runoff events. Such sampling resulted in the collection of more than 300 samples over the 2-year period for these six watersheds (Table 3). Manual samples were depth integrated while automatic samples were collected from the specific depth of the submersible pump. For both methods, samples were collected into I-pint polystyrene jars for soluble Nand 32-ounce glass bottles for total Kjeldahl N (TKN). Samples were returned immediately to the lab and stored at 4°C awaiting chemical analysis. No preservatives were added. Chemical analyses include TKN on the bulk water samples and dissolved N0 3 +N02-N and N~ -N on water filtered through 0.45 J.l filters. TKN, N0 3 +N02-N, and N~ -N were determined using standard colourimetric methods in use in OME laboratories. N0 3 +N02-N detection involved reduction by Cd and colour development with sulphanilic acid and l-napthylamine. N~ -N was determined colourimetrically by the Berthelot method involving reaction of the NH 4-N with KNaC4 ~ 0 6 and NaOCI. For TKN, the bulk water sample was digested with concentrated H2 S04 and K2 S2 Os prior to detection of the produced NH4-N by the Berthelot method. Suspended solids were determined gravimetrically as the oven dry residue after filtration through a 1-2 J.l glass fibre filter. The N0 3 +N0 2-N value will henceforth be referred to as N0 3 -N since it is likely that runoff N0 2-N concentrations were low (Patni and Hore 1979). The sum of dissolved N0 3 +N~ -N was considered to be dissolved N (DN) while TKN+ N0 3 -N was considered to be total N (TN). Flow weighted means for each parameter were calculated from instantaneous discharge and chemical concentration at the time of sampling. Unit area stream N loadings were calculated at OME using the Beale ratio estimator method (International Joint Commission 1977). This method, as proposed by J. L. Clark, used supplemental information to improve the precision of the estimated loading. Since loading variability is comprised of both flow and concentration vari-

197

N RUNOFF FROM AGRICULTURAL WATERSHEDS TABLE J. Crop use and housing density for PLUARG agricultural watersheds in southern Ontario.

Watershed

Area ha

County

Big Creek (AG.l) Venison Creek (AG-2) Little Ausable River (AG-3) Canagagique Creek (AG-4) Holiday Creek (AG.5) Tributary of Upper Maitland (AG-6) Shelter Valley Creek (AG-7) North Creek (AG-lO) Salt Creek (AG-ll) Hillman Creek (AG-13) Hill Creek (AG-14)

Woodland and Unimproved

Row Crops Corn Cereals %of watershed

Hay and Pasture

Housing Density (houses/kIn 2 )

Essex Norfolk Elgin Huron, Perth

5080

4.

62.

23.

27.

2.

.04

7913

36.

34.

10.

25.

3.

.03

6200

8.

45.

31.

26.

18.

.03

Wellington

1860

7.

19.

19.

35.

37.

.04

Oxford Huron, Wellington

3000

15.

46.

42.

12.

23.

.01

5472

28.

12.

12.

22.

33.

.03

5645

38.

14.

10.

11.

29.

.03

Northumberland Region of Niagara Region of Peel

3025

18.

16.

16.

18.

44.

.05

2383

8.

13.

11.

29.

41.

.08

Essex

1990

7.

66.5

23.

9.

O.

.17

Bruce

4504

9.

10.

10.

12.

67.

.01

TABLE 2. Soil characteristics, fertilizer use, and livestock density in the PLUARG watersheds.

Soil Mean Clay Content Watershed AG- 1 AG- 2 AG- 3 AG- 4 AG- 5 AG- 6 AG· 7 AG-lO AG-l1 AG-13 AG-14

% 35.0 6.6 30.0 25.0 20.0 15.7 9.9 40.0 30.0 10.5 27.5

Estimated Tile Drainage (% of watershed) 80. 2.

SO. 20. 98. 25. 5.

O. 15. 99. 13.

% Fertilizer Fertilizer N (kg/watershed ha)

Applied to Corn

Fertilizer Nand Estimated Manure N (kg/watershed ha)

Livestock Density (animal unit/ha)

58,4 27.9 35.4 12.3 45.6 11.3 15.5 12.6 12.0 67.0 8.1

60.9 39.2 66.6 73.7 90.5 67.1 73.8 57.2 49.0 45.0 72.7

62.1 29.4 70.6 57.8 89.3 53.3 32.6 61.7 35.9 68.1 37.0

.08 .04 .48 .75 .61 .51 .28

ability, the ratio estimator should improve the precision of the loading estimate by removing the portion of the loading variability attributable to flow variability. For these watersheds, data were

.77 .32 .01 .55

generally stratified into two levels. The first stratum consisted of the highest 15% of flows (55 days), the second consisted of the rest. From loading estimates within each stratum, a weighted

198

NEILSEN, CULLEY, AND CAMERON

TABLE 3. Number of N0 3 -N samples measured each year (1974-77) for each PLUARG watershed.

Number of samples/year Watershed

1974

1975

1976

1977*

16

73 41 77 50 74

261 34 321 298 365 59 33 294 10 141 64

45 6 107 19 80 17 5 39 3 86 24

AG- 1 AG- 2 AG-· 3 AG- 4 AG- 5 AG- 6 AG- 7 AG-lO AG-ll AG-13 AG-14

72

44 123 18 79 49

*samples as collected until April 1st, 1977. daily loss rate was calculated for the year. This method allowed for the calculation of the error mean square of the loss estimator. RESULTS

Flow weighted N0 3 -N concentration means, 197577, ranged from 0.57 mgjL for watershed AG-7 to 5.62 mgjL for watershed AG-1 and represented the dominant form of N runoff from all watersheds (Table 4). AG-7 had low intensity agricultural land use with a minimum 25% of total area under cultivation, a maximum 38% wooded and unimproved land, and a minimum 32.6 KgN/watershed hectare added as fertilizer and manure N. In contrast, AG-1

was typical of intensive agricultural activity with a maximum 87% cultivated land, a minimum 4% wooded and unimproved land, and a high 62.1 KgN added as manure and fertilizer Njwatershed ha. Flow weighted TKN averages ranged from a low of 0.64 mgjL at AG-6 and AG-2 to a high of 2.37 mgjL at AG-l, and in general represented the second most common N species lost. Watersheds AG-6 and AG-l had the lowest and highest average channel suspended sediment concentrations respectively. Soluble NH4 -N averages ranged from 0.03 mg/L (AG-6) to 0.60 mg/L (AG-13) comprising the smallest N fraction lost from all watersheds. AG-13 had the maximum rural housing density (Table 1). Simple correlation analyses were performed between monthly flow weighted DN and TKN concentrations and 31 watershed soil and land use characteristics. The most frequent significant correlations during the 24 months of 1975-76 are summarized in Table 5. Watersheds with more corn, tile drainage, and fertilizer N additions frequently had significantly higher monthly DN concentrations. These three watershed characteristics were also correlated with each other since watersheds with extensive corn area tended to be tile drained and to have received high fertilizer N additions. From 39.2% (AG-2) to 90.5% (AG-5) of all watershed fertilizer N additions were made to corn (Table 2). Elevated TKN concentrations frequently occurred from watersheds with relatively imper-

TABLE 4. Flow weighted means, range, and number of samples for total Kjeldahl N, N0 3 -N, soluble NH4 -N, and suspended sediment as measured for the 11 agricultural watersheds, 1975-]977. *watershed A G·] was sampled approximately 20 times in ]974.

N03 -N Watershed

AG- I AG- 3 AG- 5 AG-13 AG- 4 AG-ll AG-10 AG- 6 AG- 2 AG-14 AG- 7

TKN

NH4 -N

Samples

Mean mg/L

Range mg/L

395 506 519 306 367 31 456 148 84 137 82

5.62 5.50 4.33 4.30 3.75 3.34 2.13 2.08 1.05 0.88 0.57

(.01-32.80) (.39-20.40) (.24-11.30) (.05-16.00) (.02-13.00) (.00-4.35) (.00-15.80) (.11-3.60) (.18-6.63) (.00-2.66) (.01-1.19)

Samples

Mean mg/L

Range mg/L

384 510 519 301 368 31 454 150 83 136 82

0.43 0.14 0.24 0.60 0.28 0.41 0.52 0.Q3 0.04 0.11 0.12

(.00-3.50) (.00-1.25) (.00-3.70) (.00-2.95) (.00-2.40) (.00-2.24) (.00-2.90) (.00- .08) (.00- .13) (.00- .24) (.00- .36)

Suspended Solids

Samples

Mean mg/L

Range mg/L

Samples

Mean mg/L

Range mg/L

413 517 521 318 348 32 466 150 87 134 79

2.37 0.96 1.48 2.28 1.51 1.34 2.34 0.64 0.64 0.73 0.74

(.20-8.70) (.24-2.70) (.03-9.20) (.10-5.75) (.40-6.10) (.16-3.90) (.05-5.40) (.24-1.28) (.17-1.70) (.25-1.80) (.07-1.70)

374 467 492 277 314 31 451 142 84 130 78

245 23 56 84 172 33 64 10 47 24 134

(6-4667) (1-391) (1-1794) (0-1225) (2-3588) (2-460) (2-644) (1-192) (1-695) (2-790) (1-395)

199

N RUNOFF FROM AGRICULTURAL WATERSHEDS

meable soils as indicated by the number of monthly positive correlations with average watershed clay content and % of watershed area in pollution group 5 soils (Table 5). Occasionally TABLE 5. Summary of number of months of significant'" correlations for the 4 watershed characteristics most frequently associated with elevated (+) or decreased (-) monthly flow weighted dissolved N (DN) or total Kjeldahl N (TKN) concentration, 1975 - 1976. Number and sign of significant monthly correlations

Watershed characteristic DN 1. % corn 2. % tile drainage 3. fertilizer N (Kg/watershed ha) 4. % woodland and unimproved

14(+) 12(+) 10(+) 4(- )

TKN 1. mean clay content (%) 2. % of soils in pollution group 5 ** 3. livestock density (animal units/ha) 4. % woodland and unimproved;

12(+) 9(+) 4(+) 4(-)

*at p = .05 level. **poorly drained medium and fme textured soil series with a high potential for pollutant transfer to surface and ground water as grouped by C Acton Soil Survey Unit, C.D.A. Guelph in Agricultural Land Uses, Livestock and Soils of the Canadian Great Lakes Basin (1974).

(4/24 months) positive correlations were found between watershed livestock density and stream TKN concentration. A similar number of significant negative correlations were found which suggested increased watershed area of unimproved or woodland was associated with decreased TKN concentration. Stream N0 3 -N loadings ranged from 2.1 ± 0.2 kg N0 3 -N/watershed ha for AG-3 in 1975 (Table 6). TKN stream loadings ranged from 1.1 ± 0.1 kg N/ha (AG-7, 1976) to 10.8 ± 4.0 kg N/ha (AG-l, 1975). Watersheds AG-7 and AG-lO lost more N as TKN than as N0 3 -N. AG-lO had both highest manure N production rate and surface soil clay content. TKN averaged 32% and 25% respectively of 1975 and 1976 stream N loadings from the 11 watersheds. DISCUSSION The supply of N to the Great Lakes has not been strongly associated with accelerated phytoplankton growth with the exception of highly enriched areas with large P supplies (Schelske 1979). Thus, even with high runoff N03 -N, algal growth in receiving Great Lakes is generally not N limited. Although recent literature refrains from setting critical concentrations for N (Viets 1975), runoff from the Ontario watersheds consistently averaged above 0.3 mg available N/L. Accelerated eutrophication has previously been associated with greater than 0.3 mg N/L during spring turnover if no

TABLE 6. 1975 and 1976 unit area N0 3 -N and TKN stream loadings, with 95% confidence limits and % of total N lost as TKN for southern Ontario agricultural watersheds as calculated using the Beale ratio estimator. N0 3 -N kg/ha/yr Watershed AG- 1 AG- 2 AG- 3 AG- 4 AG· 5 AG- 6 AG- 7 AG-lO AG-11 AG-13 AG·14

1975

1976

18.4 ± 8.7 3.2 ± 0.6 39.0 ± 7.6 18.6 ± 12.0 15.7 ± 5.2 9.9 ± 1.0 2.2 ± 1.0 7.0 ± 2.3

10.7 ± 4.0 4.2 ± 0.7 37.4±2.2 14.9±1.4 24.1 ± 6.0 11.4 ± 1.2 2.1 ± 0.2 7.1 ± 0.9 8.3 ± 1.0 21.0 ± 2.7 5.3±2.1

32.1 ± 2.4 3.1 ± 0.6

Kjeldahl-N kg/ha/yr 1976 1975 10.8 ± 4.0 3.0 ± 2.5 4.8 ± 1.1 5.8 ± 3.0 5.0 ± 3.1 3.8 ± 0.3 4.2 ± 6.4 9.4 ± 1.1 3.9 ± 0.7 3.3 ± 0.4

5.3 ± 1.5 2.2 ± 0.2 4.2 ± 0.4 5.4 ± 1.9 7.0 ± 3.7 3.0 ± 0.2 1.1 ± 0.1 8.5 ± 0.6 2.8 ± 0.4 4.2 ± 0.7 4.1 ± 1.1

weighted % (TKN/Total N) *Insufficient sampling during the high flow period in AG-07 required the adoption of a single stratum.

Kjeldahl-N as a % of total N 1975 1976 37. 48. 11. 24. 24. 28. 66. 57. 11. 52.

33. 34. 10. 27. 23. 21. 34. 55. 25. 17. 44.

32.

25.

200

NEILSEN, CULLEY, AND CAMERON

other nutrient limits phytoplankton growth (Biggar and Corey 1969). Thus it would appear that runoff N0 3 -N was not presently of prime importance for eutrophication of the Great Lakes. N0 3 -N may be of serious environmental concern in so far as elevated stream N0 3 -N concentrations reflect elevated groundwater N0 3 -N contamination. The TKN measurement reflected runoff loss of less biologically available N. The apparent association of high TKN with high sediment values implied that TKN may have been associated with sediment as exchangeable N14 -N or organic-N rather than as dissolved soluble organic-N or N14 -N. Soluble NH4 -N concentrations in excess of 3.0 mg N~ -N/L were measured, but only rarely. The highest average soluble NH4 -N concentration occurred in runoff from AG-13, the watershed with maximum rural housing density and minimum rural housing density and minimum livestock density. This suggested that elevated N~ -N concentration can reflect contamination of rural runoff by septic tank seepage. There was a close relationship between extensive watershed corn area, tile drainage, high fertilization rates, and elevated runoff DN concentration. Decreased stream DN concentrations in southern Ontario agricultural watersheds could result from improved matching of N fertilizer applications to com's requirements for N on tile drained land. A rationale for minimizing N water pollution for corn while maintaining optimum yield has been discussed by Stanford (1973). Field studies in Missouri have indicated banding and split applications of N improved the efficiency of fertilizer N uptake by com on claypan soils (Whitaker, Heinemann, and Burwell 1978). However, slow release N fertilizers did not reduce winter N leaching losses in southwestern Ontario (Beauchamp 1977). There was no adequate measure among the 31 watershed characteristics of the contribution of mineralized soil organic N to runoff N. Consequently, the likely possibility that soils with high organic N (and high net N mineralization potential) could have high DN runoff was not tested. The difficulties in developing an adequate watershed soil N index in southern Ontario without extensive soil organic N analysis were also found in Illinois by Klepper (1978). The association of elevated TKN concentration with impermeable soils probably reflected the higher proportion of surface runoff from these watersheds. Such runoff would be relatively

enriched in soluble NH4 -N, organic-N, or sedimentassociated exchangeable N~ -N and organic-N, all detected as TKN. Decreased sediment and surface runoff from unimproved and woodland tracts could indicate why reduced TKN concentrations can be associated with watersheds containing large areas of such land use. The occasional positive correlation between increased TKN concentration and livestock density probably indicated that animal wastes were a source of TKN. The potential high concentration of NH4 -N, soluble organics, and thus TKN in feedlot runoff has been well documented (Loehr 1974). Annual soluble N0 3 -N runoff loadings from watersheds AG-3 and AG-13 in excess of 30 kg N0 3 -N/watershed ha were larger than any cropland N runoff reported by Loehr (1974). Only runoff from 30-ha field sized watersheds, contour planted to com in Iowa (Schuman et aZ. 1973; Burwell et al. 1974), has been of similar magnitude. However, in the Iowa studies, most N was lost in association with sediment. The large soluble N0 3 -N loadings from AG-3 and AG-13 represented a significant fertility loss from these Ontario watersheds when compared to average watershed fertilizer additions (Table 2). In contrast, annual N0 3 -N runoff from watersheds AG-2, AG-7, and AG-14 was less than the 6.6 kg/ha/yr N0 3 -N measured in 1970-71 bulk rural precipitation in the Lake Ontario basin (Shiomi and Kuntz 1973). These watersheds had extensive areas of wooded and unimproved land (Table 1). Reduction of N0 3 -N pollution effects of precipitation can thus occur in some Ontario watersheds where precipitation additions exceeded average unit area runoff N0 3 -N loadings. Similarily low N0 3 -N loadings have been measured in woodland and rangeland runoff. Stream loadings averaged 2.5 kg N0 3 -N/ ha/yr from woodland over a 3-year period in Coshocton, Ohio (Taylor et aZ. 1971) and only 0.4 kg/ha/yr N0 3 -N from nonfertilized rangeland in southwestern Ontario (Campbell and Webber 1969). TKN comprised from 10-66% of 1975-76 stream N loadings from the 11 Ontario watersheds. These percentages were lower than the 7090% sediment N (detected as TKN) lost from five, 150-ha watersheds in southwestern Iowa and central Oklahoma (Burwell et aZ. 1974, 01ness et aZ. 1975). If TKN were primarily associated with sediment, as found .in these U.S. studies, then potentially 32% of 1975 and 25% of 1976 southern Ontario total N runoff could have been

N RUNOFF FROM AGRICULTURAL WATERSHEDS decreased by efficient application of standard erosion control methods such as grassed waterways, strip cropping, and minimum tillage. CONCLUSIONS The predominant chemical form of N runoff from agricultural watersheds in southern Ontario was N0 3 -N, with TKN and Nf4 -N respectively next in concentration. The major environmental concerns differed for each N form. The high average N0 3 -N concentrations which were measured in stream runoff would be of serious concern if they reflected high groundwater N0 3 -N concentrations. N has not been found to be of prime importance for accelerating Great Lakes eutrophication, although N0 3 -N measurements from this study would indicate that runoff would not be N limited. High TKN reflected high sediment and may indicate watersheds undergoing extensive topsoil erosion. High N~ -N can indicate rural watershed runoff contaminated with septic tank seepage rather than enriched runoff from agricultural fields. Intensified agricultural activities in Ontario have influenced stream N concentrations. Elevated stream DN concentrations occurred from watersheds with increased areas of corn, extensive ti1~ drainage, and high unit area fertilizer N additions. Elevated TKN concentrations occurred from watersheds with extensive impermeable soils, high suspended sediment concentrations, and increased surface runoff. Stream N loadings showed considerable watershed variation. Significant fertility losses in excess of 30 kg N0 3 -N/ha occurred from some but not all watersheds with intense agricultural activity as typified by high N fertilizer additions and high row crop areas. In contrast, watersheds with extensive woodlot and hay and pasture posed no N environmental risk since more NO,! -N was gained in precipitation than was lost in runoff. The predominant form of stream N loading was as N0 3 -N indicating that, unlike other areas, control of soluble N rather than sediment N runoff would be most important to N loading reductions in Ontario. The most important consideration for reduction of soluble N0 3 -N runoff from agricultural activities will be efficient management of N fertilizer on the extensive areas of com in the lower Great Lakes basin. Standard erosion control techniques such as grassed waterways and contour planting could reduce surface runoff, sediment loss, and 1/4-1/3 of the total runoffN in Ontario.

201

ACKNOWLEDGMENTS Funding for this study was provided through Task C activities of the Pollution from Land Use Activities Reference Group, International Joint Commission. Findings and conclusions are those of the authors and do not necessarily reflect the view of the Reference Group or its recommendations to the Commission. The authors wish to acknowledge the technical assistance of Ms. Ilona Bain and Don McDill. The co-operation of OME Laboratories and Water Resources, Hydrology and Monitoring section, is also gratefully acknowledged. REFERENCES Beauchamp, E. G. 1977. Slow release N fertilizers applied in fall for corn. Can. J. Soil Sci. 57:487496. Biggar, J. W., and Corey, R B. 1969. Agricultural drainage and eutrophication, pp. 405-445. In Eutrophication, causes, consequences and correctives. Proc. Symp. Nat. Acad. ScL, Washington, D. C. Burwell, R E., Schuman, G. E., Piest, R F., Spomer, R G., and McCalla, T. 1974. Quality of water discharged from two agricultural watersheds in Southwestern Iowa. Water Resour. Res. 10:359-365. ----, , Saxton, K. E., and Heinemann, H. G. 1976. Nitrogen in subsurface discharge from agricultural watersheds. J. Environ. Qual. 5 :325-330. Campbell, F. R., and Webber, L. R 1969. Agriculture's contribution to the fertilization of Canal Lake. J. Soil Water Conserv. 24: 139-141. Frank, R, and Ripley, B. D. 1977. Land use activities in eleven agricultural watersheds in southern Ontario, Canada, 1975-76. Project 5 Task Group C (Canadian section) Activity 1 PLUARG.-IJC. Frere, M. H., Onstad, C. A., and Holtan, H. N. 1975. ACTMO, an agricultural chemical transport model. Agricultural Research Service. U. S. Department of Agriculture. Hill, A. R. 1978. Factors affecting the export of nitratenitrogen from drainage basins in southern Ontario. Water Res. 12:1045-1057. Hare, F. H., and Maclean, A. J. 1973. Agriculture Canada Task Force Report on Implementation of the Great Lakes Water Quality Agreement, Research Branch, Agriculture Canada, Ottawa (unpublished). International Joint Commission. 1977. Quality control handbook for pilot watershed studies. Windsor, Ontario. Kilmer, V. T., Gilliam, J. W., Lutz, J. F., Joyce, R. T., and Eklund, C. D. 1974. Nutrient losses from fertilized watersheds in western North Carolina. 1. Environ. Qual. 3:214-219. Kissel, D. E., Richardson, C. W., and Burnett, E. 1976. Loss of nitrogen in surface runoff in the blackland prairies of Texas. J. Environ. Qual. 5 :288-292. Klepper, R. 1978. Nitrogen fertilizer and nitrate concen-

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