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Non-Point Source Pollution from Abandoned Agricultural Land in the Great Lakes Basin
J. Great Lakes Res., 1979 Internat. Assoc. Great Lakes Res. 5 (2):99-104
NON-POINT SOURCE POLLUTION FROM ABANDONED AGRICULTURAL LAND IN THE GREAT LAKES BASIN
Thomas M. Burton and James E. Hook l Institute of Water Research and Department of Crop and Soil Sciences Michigan State University East Lansing, Michigan 48824
ABSTRACI'. The contribution of abandoned farm fields to non-point source pollution in the Great Lakes Basin was studied on a 7.73 ha old field watershed near East Lansing, Michigan, that had been abandoned 18 years prior to the study. Exports ofnitrogen were low and approached values expected for undisturbed forests in the Great Lakes Basin. Exports of phosphorus were slightly elevated compared to undisturbed forests. Exports and concentra~ions of both Nand P were similar to values listed for cleared, unproductive land for the Great Lakes region by the recent nationwide survey ofEPA. Annual exports of total P, P0 4 -P, N0 3 -N, N0 2 -N, NH4 -N, Organic-N, Cl, Na, Ca, and suspended solids are given. Most exports of all constituents occurred during rainfall or snow-melt generated runoff events during the spring runoff period. Soil and soil-water nutrient concentrations were low, reflecting the low fertility of the study watershed. Nutrient concentrations in runoff reflect this low fertility and would be higher from recently abandoned farm land. The contribution of abandoned fields to nutrient loading of the Great Lakes would decrease from levels typical of agricultural runoff at time of abandonment to levels typical of undisturbed forests within 15 to 20 years following abandonment.
INTRODUCTION Abandoned, formerly cropped open land makes up a small but substantial percentage of land in the United States. In the contiguous 48 states there are 4.7 million hectares of land in this category and another 4.5 million hectares of cropland that is temporarily idle (Stewart and Woolhiser 1976). These 9 .2~illion hectares comprise 5.2% of all cropland in the U.S. The percentage of cleared, formerly cropped farmland in the Great Lakes Basin is unknown, since this category was not included in the land use categories of the recent survey conducted by the Pollution from Land Use Activities Reference Group (PLUARG) of the International Joint Commission OJC). According to estimates of PLUARG, 18.6 million hectares, or 32% of all lands in the Great Lakes Basin, are in agricultural usage with 33% of all agricultural lands occurring in the Lake Michigan Basin [International Joint Commission-Pollution from Land Use Activities Reference Group (IJC-PLUARG) 1977a].
There are estimates of open, formerly cropped farmland for the U.S. portion of the Great Lakes Basin (Drynan and Davis 1978, Appendix A). For the Lake Michigan Basin, 6.7% of all agricultural land or 411,000 hectares were classified as open, formerly cropped farmland while another 132,000 hectares (2.2%) were classified as temporarily idle. Thus, an estimate of the contribution of runoff from such cleared, formerly cropped farmlands to non-point source pollution would be helpful in any assessment of nutrient loadings to the Great Lakes. Runoff from such formerly cropped lands should contain higher nitrogen and phosphorus concentrations than runoff from forested lands, but lower than runoff from intensive agricultural or urban watersheds because of the residual effect of past agricultural practices (Omernik 1977). Converting this formerly cropped land into agricultural production would increase nutrient loadings to the Great Lakes while conversion to forest would decrease loadings. The recent nationwide survey of stream nutrient levels in relation to land use did include such cleared, unproductive lands but the
1 Current
Address: Department of Agronomy, Coastal Plains Experiment Station, Tifton, GA 31794.
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relatively few watersheds in this survey allowed only limited interpretation (Omernik 1977). Nutrient losses in surface runoff from native prairie in west central Minnesota have been intensively studied (Timmons and Holt 1977), but nutrient losses from successional, old field watersheds in the Great Lakes Basin have received little attention. Thus, a study of runoff losses from an abandoned field was included as part of the Felton-Herron Creek Study. Felton-Herron Creek was one of the watersheds selected for intensive study by the pilot watershed group (Task C) of PLUARG. The objective of this study was to quantify losses ofnitrogen, phophorus, and other nutrients from abandoned farm lands in lower Michigan as a means of assessing the impact of abandoned farm fields on nutrient loadings to the Great Lakes. MATERIALS AND METHODS An old field, abandoned approximately 18 years ago, was selected for study. The predominant vegetation on ths field was goldenrod (Solidago canadensis and S. graminifolia) and quackgrass (Agropyron repens), but a very diverse flora existed. Most of this field was included in a 7.73 ha subwatershed with well delineated topographic boundaries on the Michigan State University campus, East Lansing, Michigan. An existing subsurface drainage tile installed while the field was in cultivation was still functional and provided a convenient place to sample runoff from this subwatershed. The drainage tile emptied into an artificial channel at the edge of the field. Discharge from this chalmel was measured with a V-notch weir and a Stevens Type F recorder. Water samples were taken during spring runoff and storm events with an ISCO sequential water sampler. These samples were supplemented by low flow grab samples. Paired soil samples were taken at 24 sites in increments to a depth of 150 cm along a "star" shaped group of criss-crossing transects in 1975. Soil-water samples were taken at weekly intervals at 15 and 150 cm depths with porous cup tubetype vacuum soil-water samplers throughout the 1976 and 1977 ice-free seasons. Precipitation inputs were monitored with three recording rain gauges at nearby localities. Precipitation for the study area averages 77.2 cm/year. Precipitation was below normal during both years of the study and was 73.3 cm during the 1975-76 water year and 61.9 cm during the 1976-77 water year. All runoff samples were analyzed using standard
AutoAnalyzer techniques (U.S. Environmental Protection Agency 1974). These techniques included the automated ferric thiocyanate chloride method, automated colorimetric phenate ammonia nitrogen method, automated diazotization nitrite nitrogen method, automated cadmium reduction nitrate-nitrite nitrogen plethod, automated molybdate reactive phosphorus method, persulfate digestion total phosphorus method, and automated Kjeldahl organic plus ammonia nitrogen method. Sodium and calcium analyses of runoff were done with atomic absorption spectrophotometry and suspended solids analyses followed Standard Methods (American Public Health Association 1971). Nitrate and ammonium in soil-water samples were analyzed by ion-selective electrodes in 1976 (Milham et al. 1970, Orion Research 1971) and by standard_AutoAnalyzer techniques in 1977. All other water-soil analyses were done by standard AutoAnalyzer techniques (U.S. Environmental Protection Agency 1974). Soil samples were analyzed for nitrate extracted from wet samples with IN K2 S04 (approximately a 1:5 soil:solution ratio) (Bremner 1965); for available P extracted with dilute acid-fluoride (1:8 soil:solution ratio) (Jackson 1958) and analyzed by the colorimetric method (Murphy and Riley 1962); for total P by the method of Sommers and Nelson (1972); and for total N by the method of Nelson and Sommers (1972). Runoff loadings from the watershed were calculated using the stratified, random sampling model employing a ratio estimator as suggested in the March 1977 revision of the IJC-PLUARG, Quality Control Handbook for Pilot Watershed Studies. Soils on this site are very heterogeneous and include Miami, Conover, and Kalamazoo loams, Granby loamy sands, Barry and Corunna sandy loams, and Westland silty clay loams. In general, these loamy soils are developed on silt to loam glacial tills and are members of the mixed mesic family of Typic Hapludalfs. There apparently is a fairly continuous clay lens underlying the lower central portion of this watershed, since relatively impermeable reduced clays were encountered at every soil sampling site in the lower central part of the watershed. The existence of this clay lens results in a perched shallow water table. RESULTS AND DISCUSSION Water budgets for this abandoned field watershed were calculated using the technique of Thornthwaite and Mather (1967) and indicated that little, if any, recharge of groundwater occurred
RUNOFF FROM ABANDONED AGRICULTURAL LAND (Table 1). Almost all excess water appears to have been intercepted by the existing tile drainage system and exported from the watershed as runoff. Runoff from this site was excessive compared to nearby unirrigated forest and old field sites monitored as part of other studies. The excessive runoff probably resulted from the clay lens underlying the lower central portion of this watershed and from existence of the tile drain. Since groundwater recharge on this site was minimal as a result of the clay lens and lower than average precipitation, runoff losses should be maximal for such a system. In many other Great Lakes watersheds, runoff losses would be reduced by losses to the groundwater pool. Annual runoff loadings are presented in Table 2. There was runoff in 1977 only during the February to early June period. Exports during the spring runoff period (mid-February through May)
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represent 99.8% of total annual runoff. Thus, the spring runoff data in Table 2 can be used as an approximate estimate of total export during this dry year. Exports were much less than in the wetter 1975-76 water year for all constituents. This variability associated with variable rainfall suggests the need for long-term data from this as well as other watershed studies in the Great Lakes Basin. The annual flow weighted mean concentration of 0.073 mg total P/L is low compared to the 0.152 mg total P/L reported for intense agricultural land for this region (Omernik 1977). It is intermediate between values reported for agricultural and forest land uses as was predicted by Omernik (1977). Orthophosphorus concentrations (0.028 mg P/L) also are intermediate between forest and agricultural land uses as was predicted. Somewhat higher concentrations are expected from watersheds on soils with high clay content (IJC-PLUARG
TABLE 1. Water budgets for the watershed (values in m 3 /ho).
Precipitation
Evapotranspiration
Runoff
Recharge
ANNUAL 1975-76 % of Input
7329.6 100.0
5548.7 75.7
2378.1 32.45
-597.2 -8.15
ANNUAL 1976-77 % of Input
6188.8 100.0
5618.7 90.79
467.6 7.56
102.5 1.66
TABLE 2. Stream exports from the 7.73 ha abandoned farm field watershed.
1975-1976
1976-77
Total Exports (kgjyr ± one std. dev.)
Unit Area Exports (kgjhajyr)
Percent Transported by Runoff* Events
Percent Transported During Spring Runoff**
Exports in Spring Runoff 1977 (kg ± one std. dev.)
Unit Area Exports**· (kgjha)
Molybdate Reactive P Total P Nitrate-N Ammonia-N Nitrite-N Total Inorganic N Organic N Chloride Sodium Calcium Suspended Solids
0.83 ± 0.50 2.34 ± 0.93 1.35 ± 0.29 2.47 ± 2.32 0.39 ± 0.06 4.21 ± 2.34 13.76 ± 4.20 488.35 ± 256.08 440.26 ± 183.18 107396 ± 98.46 307.43 ± 254.85
0.107 0.303 0.175 0.320 0.051 0.545 1.780 63.176 56.955 138.934 39.771
85.6 84.1 76.8 82.8 88.6 81.5 83.0 53.0 69.3 65.3 78.6
71.4 76.6 65.3 91.2 92.9 83.1 82.0 63.3 74.6 76.5 78.9
0.111 ± 0.013 0.363 ± 0.263 0.748 ± 0.103 0.183 ± 0.059 0.040 ± 0.Q11 0.971 ± 0.119 2.166 ± 0.423 170.41 ± 26.44 84.28 ± 16.84 142.80 ± 17.91 28.05 ± 16.72
0.014 0.047 0.097 0.024 0.005 0.126 0.280 22.045 10.903 18.474 3.629
Water (m 3 )
2378.1
307.6
80.0
467.6
60.5
Constituent
*Runoff events were separated on the basis of distinct runoff peaks and include snowmelt and rain peak generated runoff during spring. **Spring runoff includes peak events plus baseflow and interflow conditions from snowmelt until constant runoff ceased. ***Spring only exports, but 99.8% of total runoff in 1976-77 occurred in this season.
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BURTON and HOOK
1978). The concentrations are well above the concentration of 0.010 mg P/L that is generally accepted as the level that can cause eutrophication in lakes (Vollenweider 1968). Annual unit area loads from this old field of 0.1 1 kg/ha/yr (Table 2) are within the 0.10 to 0.25 kg/ ha/yr range predicted for losses from grasslands with medium loam to clay soils and are slightly greater than 0.05 to 0.10 kg/ha/yr losses predicted for forested watersheds by the IJC-PLUARG studies (1978). These losses are essentially identical to the mean losses from forested watersheds with sedimentary substrates and are higher than losses from forests on igneous substrates reported by Dillon and Kirchner (1975) for their study of exports of phosphorus from 34 watersheds in southern Ontario. Thus, losses from this abandoned field watershed are only slightly higher and are already approaching background levels expected from undisturbed forested watersheds in the Great Lakes Basin. Remedial measures on such abandoned farm fields are thus unnecessary and would result in little improvement in water quality in the Great Lakes. Some minor reductions in phosphorus loads to the Great Lakes could be achieved by conversion of these lands to forests. Such a conversion to production of useful biomass is desirable from both an economic and water quality standpoint. Both total and inorganic nitrogen concentrations fall in the range (0.47 N0 3 -N, 0.078 NH 4 -N,0.017 N0 2 -N) reported for forested land (Omernik 1977). It is not surprising that nitrogen concentrations in runoff from this abandoned farm field are so low since nitrogen is normally one of the primary limiting factors to terrestrial plant productivity. Inorganic N is readily immobilized by plant uptake, storage in the organic layer of soils in uncultivated fields, or is rapidly lost by leaching to the groundwater (Harmsen and Van Schreven 1955). In addition, nitrogen application rates on agricultural lands were much lower in the late 1950's when this field was abandoned than they are at present. Thus, any residual inorganic N would have long since been immobilized in the plant biomass, soil organic matter, or soil microbial community or would have been leached to groundwater. Total N exports from this formerly cropped field are 2.33 kg/ha/yr and are in the range of 0.5 to 6.3 kg/ha/yr reported for forested and idle/perennial land uses by IJC-PLUARG (1978). The total N losses from this watershed are almost identical to the 2.37 kg/ha/yr reported from undisturbed forested watersheds in northwestern Ontario (Nicholson 1977). Cropland
losses ranged from 4.3 to 31 kg N/ha/yr according to IJC, so losses from this old field are very low compared to cropland losses in the Great Lakes Basin. It is interesting to note the high percentage of annual exports associated with spring runoff and with runoff events (Table 2). Even during the spring runoff period, runoff events generated by snowmelt on warm days, rainfall, or a combination of the two dominated exports. The runoff of nutrients from old fields depends on the nutrient status of the soils and soil-water. This nutrient status reflects the soil type, fertilizer and cropping practices prior to abandonment, number of years since abandonment, and the successional vegetation present at any particular point. Soils data identify the reservoir of nutrients available for runoff, provide a means to relate runoff to nutrient content of that particular soil, and provide the data necessary for design of management schemes to prevent release of nutrients. Soil-water analyses indicate the very infertile nature of this abandoned farm field. For example, nitrate-N increased to a yearly high of 0.55 ± .52 mg N/L at the 15 cm depth on March 24, 1977, after the soil began to warm, decreased rapidly to less than 0.01 mg N/L by April 28, 1977, then increased slightly by mid-May with the weekly average varying from 0.01 to 0.11 throughout the rest of the summer and fall. Nitrate-N concentrations at the 150 cm depth were similar and varied from a seasonal high of 0.30 ± .16 mg N/L on April 7, 1977, down to a low of 0.06 ± .02 mg N/L in August. Weekly average concentrations varied between 0.06 and 0.13 mg N/L throughout most of the summer and fall. Spring peaks of nitrate-N are the norm in fallow soils (Harmsen and Van Schreven 1955). Ammonia-N levels were also very low in soil-water, with weekly averages varying between 0.02 and 0.25 mg N/L at the IS cm depth and between 0.05 and 0.27 mg N/L at the 150 cm depth. Nitrite-N was always below limits of detection (0.01 mg N/L). Weekly average organic-N concentrations varied from 0.34 to 0.93 mg N/L at the 15 cm depth and from 0.08 to 0.82 mg N/L at the ISO cm depth with no obvious seasonal correlation. Annual flow-weighted mean concentrations of inorganic nitrogen in runoff appear to reflect soil-water concentrations during the spring when' concentrations are highest. Since more than 80% of total runoff of nitrogen occurs during the spring (Table 2), these results are not surprising. Total P concentration in soil-water was also very low, with the weekly average varying from 0.02 to
RUNOFF FROM ABANDONED AGRICULTURAL LAND
0.36 mg P/L at the 15 cm depth and from 0.003 to 0.32 mg P/L at the 150 cm depth. Most weekly averages were less than 0.080 mg P/L at both depths. There were no obvious seasonal trends in soil-water P. The annual flow-weighted mean concentration of total P in runoff (0.073 mg/L) also appears to reflect soil-water concentrations during spring. Soil analyses also indicated the very low fertility of this abandoned farm land (Table 3). Both available (Bray extractable) phosphorus and nitrate were very low in these soils (Table 3). Both elements tended to decrease with depth, with highest concentrations in the top 15 cm of soil where much of the root biomass and soil organic. matter were located. Total Kjeldahl-N also followed the trend of decreases with depth with Kjeldahl-N being more than an order of magnitude greater in the highly organic surface soils (1095 J.1g/g dry soil in the top 5 cmfthan afihe 150 cm depth (68 J.1g/g dry soil). Total P concentrations were also higher in the surface soils (342 ± 204 J.1g/g dry soil in the top 5 cm), decreased rapidly to 254 ± 221 J.1g/g dry soil in the 31-45 cm increment, then leveled off at a concentration of about 250 J.1g/g dry soil and remained at this level down to the 300 cm depth sampled in 1975. TABLE 3. Phosphorus and Nitrogen analyses olsoiis from the abandoned farm field watershed (values in pgjg dry soil ± one standard deviation).
Depth-cm
Bray Extractable P
Total P
0-5 5-10 10-15 15-30 30-45 45-60 60-75 75-90 90-105 105-120 120-135 135-150 AVERAGE
6.48 ±6.94 4.36 ±4.29 3.10 ± 2.31 2.50 ± 2.16 2.93 ±4.33 2.39 ±5.42 2.60 ±4.97 2.34 ± 3.29 2.61 ± 3.43' 2.19 ± 3.02 1.91 ± 2.92 1.30 ± 2.15 2.89 ± 1.35
342 ± 204 341 ±222 324 ±212 283 ± 183 254 ± 221 245 ±202 252 ± 155 282 ± 171 277 ± 162 283 ±232 236 ± 118 231 ±89 279 ± 39
Nitrate-N
Kjeldahl-N
3.84 ±4.24 1095 ± 382 3.94 ±4.85 1008 ± 329 3.65 ± 3.58 762 ± 320 3.00 ± 2.87 599 ±297 2.02 ± 1.39 379 ± 249 1.78 ± 1.14 247 ± 117 1.77 ± 1.04 222 ± 121 1.81 ± 1.25 178 ± 116 1.77 ± 1.08 134 ± 91 1.75 ± 1.14 102 ±75 1.60 ± 1.00 81 ±61 1.61 ± 1.04 68 ±58 2.38 ± .94 406 ± 369
These soil and soil-water data reflect the very infertile nature of this particular abandoned field. Certainly, recently abandoned fields would have losses of nutrients in runoff approaching losses from active agriculture. These data suggest that fields that have been abandoned from 15-20 years will have nutrient losses approaching background
103
levels typical of undisturbed forests. Thus, to precisely calculate nutrient losses from abandoned farm fields to the Great Lakes would require data on time of abandonment, soil nutrients status, etc. CONCLUSIONS
Farm lands that have been abandoned for 15 to 20 years are not major non-point sources of pollution. Phosphorus and nitrogen loadings from such watersheds approach background levels for undisturbed forests. When calculating total loadings to the Great Lakes from such abandoned fields, typical nitrogen loadings for forests as generated by the recent PLUARG studies should be used while phosphorus loadings slightly higher than those typical of forest loadings should be used. Nutrient losses from recently abandoned fields should approach losses typical of agriculture and drop over a 10 to 15 year period to losses typical of forests. No remedial actions to reduce pollution from these abandoned farm lands appear to be practicable or needed. Disruption of still functional drainage tiles could possibly reduce suspended sediment and total P losses from such lands and increase groundwater recharge. Conversion .of these lands to forests would likely result in slight improvements in water quality while producing an economically valuable product. ACKNOWLEDGMENTS
Funds for this project were provided by the U.S. Environmental Protection Agency (Grant Number R005143-Q 1) through the Pollution from Land Use Activities Reference Group of the International Joint Commission established under the CanadaU.S. Great Lakes Water Quality Agreement of 1972. Findings and conclusions are those of the authors and do not necessarily reflect the views or recommendations of the Reference Group, the International Joint Commission, or the Environmental Protection Agency. The authors would like to thank C. S. Annett, W. Baker, P. Bent, J. Ervin, and D. O'Neill for field and technical assistance. REFERENCES American Public Health Association. 1971. Standard methods for the examination of water and wastewater. 13th Edition. Washington D.C. Bremner, J. M. 1965. Inorganic forms of nitrogen. In: Methods of Soil Analysis. C. A. Black, ed. Agronomy Monogr., 9:1179-1237. Amer. Soc. Agron., Madison, Wisconsin.
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Dillon, P. J., and Kirchner, W. B. 1975. The effects of geology and land use on the export of phosphorus from watersheds. Water Research 9:135-148. Drynan, W. R., and Davis, M. J. 1978. Application of the universal soil loss equation to the estimation of nonpoint sources of pollutant loadings to the Great Lakes. Technical Report, International Reference Group on Great Lakes Pollution from Land Use Activities, International Joint Commission, Windsor, Ontario. Harmsen, G. W., and Van Schreven, D. A. 1955. Mineralization of organic nitrogen in soil. In: Advances in Agronomy, Vol. 7, 299-398. A. G. Norman, ed. Academic Press, New York. International Joint Commission-Pollution from Land Use Activities Reference Group. 1977a. Land use and land use practices in the Great Lakes Basin. Joint Summary Report-Task B, United States and Canada, International Joint Commission, Windsor, Ontario. _ . 1977b. Quality control handbook for pilot watershed studies. International Joint Commission, Windsor, Ontario. _ . 1978. Environmental management strategy for the Great Lakes system. Final Report, International Joint Commission, Windsor, Ontario. Jackson, M. L. 1958. Soil chemistry analysis. Prentice-Hall, Inc., Englewood Cliffs, New Jersey. Milham, P. J., Awad, A. S., Paull, R. E., and Bull, J. H. 1970. Analyses of plants, soils and waters for nitrate by using an ion-selective electrode. Analyst 95 :751-753. Murphy, J., and Riley, J. P. 1962. A modification single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta. 27:31-36. Nelson, D. W., and Sommers, L. E. 1972. A simple diges. tion procedure for estimating total N in soils and sediments. J. Env. Qual. 1:423435. Nicholson, J. A.1977 . Forested watershed studies. Summary
Technical Report, PLUARG Task C, Activity 2, International Joint Commission, Windsor, Ontario. Omernik, J. M. 1977. Nonpoint source-stream nutrient level relationships: A nationwide survey. Ecological Research Series Report, EPA-600/3-77-105, U.S. Environmental Protection Agency. Orion Research, Inc. 1971. Instruction manual. Ammonia electrode. Orion Research, Inc., Cambridge, Massachusetts. Sommers, L. E., and Nelson, D. W. 1972. Determination of total phosphorus in soils. A rapid perchloric acid digestion procedure. Soil Sci. Soc. Amer. Proc. 36:902904. Stewart, B. A., and Woolhiser,.D. A. 1976. Introduction, pp. 1-5. In: Control of Water Pollution from Cropland. Vol. II-An overview. B. A. Stewart, D. A. Woolhiser, W. H. Wischmeier, J. H. Caro, and M. H. Frere. Report No. EPA-600/2-75-026b, U.S. Environmental Protection Agency and Report No. ARS-H-5 -2, Agricultural Research Service, U.s. Department of Agriculture. Thornthwaite, D. W., and Mather, J. R. 1967. Instructions and tables for computing potential evapotranspiration and the water balance. Publ. In Climatology, Vol. 10:185-311. Laboratory of Climatology, Drexel Institute of Technology, Centerton, New Jersey. Timmons, D. R., and Holt, R. F. 1977. Nutrient losses in surface runoff from a native prairie. J. Env. Qual. 6(4):369-373. U.S. Environmental Protection Agency. 1974. Methods for chemical analysis of water and wastes. EPA-625/6-74003, U.S. Environmental Protection Agency. Vollenweider, R. A. 1968. Scientific fundamentals of the eutrophication of lakes and flowing waters, with particular reference to nitrogen and phosphorus as factors in eutrophication. Technical Report, Organisation for Economic Co-operation and Development, Paris.
NON-POINT SOURCE POLLUTION FROM ABANDONED AGRICULTURAL LAND IN THE GREAT LAKES BASIN
Thomas M. Burton and James E. Hook l Institute of Water Research and Department of Crop and Soil Sciences Michigan State University East Lansing, Michigan 48824
ABSTRACI'. The contribution of abandoned farm fields to non-point source pollution in the Great Lakes Basin was studied on a 7.73 ha old field watershed near East Lansing, Michigan, that had been abandoned 18 years prior to the study. Exports ofnitrogen were low and approached values expected for undisturbed forests in the Great Lakes Basin. Exports of phosphorus were slightly elevated compared to undisturbed forests. Exports and concentra~ions of both Nand P were similar to values listed for cleared, unproductive land for the Great Lakes region by the recent nationwide survey ofEPA. Annual exports of total P, P0 4 -P, N0 3 -N, N0 2 -N, NH4 -N, Organic-N, Cl, Na, Ca, and suspended solids are given. Most exports of all constituents occurred during rainfall or snow-melt generated runoff events during the spring runoff period. Soil and soil-water nutrient concentrations were low, reflecting the low fertility of the study watershed. Nutrient concentrations in runoff reflect this low fertility and would be higher from recently abandoned farm land. The contribution of abandoned fields to nutrient loading of the Great Lakes would decrease from levels typical of agricultural runoff at time of abandonment to levels typical of undisturbed forests within 15 to 20 years following abandonment.
INTRODUCTION Abandoned, formerly cropped open land makes up a small but substantial percentage of land in the United States. In the contiguous 48 states there are 4.7 million hectares of land in this category and another 4.5 million hectares of cropland that is temporarily idle (Stewart and Woolhiser 1976). These 9 .2~illion hectares comprise 5.2% of all cropland in the U.S. The percentage of cleared, formerly cropped farmland in the Great Lakes Basin is unknown, since this category was not included in the land use categories of the recent survey conducted by the Pollution from Land Use Activities Reference Group (PLUARG) of the International Joint Commission OJC). According to estimates of PLUARG, 18.6 million hectares, or 32% of all lands in the Great Lakes Basin, are in agricultural usage with 33% of all agricultural lands occurring in the Lake Michigan Basin [International Joint Commission-Pollution from Land Use Activities Reference Group (IJC-PLUARG) 1977a].
There are estimates of open, formerly cropped farmland for the U.S. portion of the Great Lakes Basin (Drynan and Davis 1978, Appendix A). For the Lake Michigan Basin, 6.7% of all agricultural land or 411,000 hectares were classified as open, formerly cropped farmland while another 132,000 hectares (2.2%) were classified as temporarily idle. Thus, an estimate of the contribution of runoff from such cleared, formerly cropped farmlands to non-point source pollution would be helpful in any assessment of nutrient loadings to the Great Lakes. Runoff from such formerly cropped lands should contain higher nitrogen and phosphorus concentrations than runoff from forested lands, but lower than runoff from intensive agricultural or urban watersheds because of the residual effect of past agricultural practices (Omernik 1977). Converting this formerly cropped land into agricultural production would increase nutrient loadings to the Great Lakes while conversion to forest would decrease loadings. The recent nationwide survey of stream nutrient levels in relation to land use did include such cleared, unproductive lands but the
1 Current
Address: Department of Agronomy, Coastal Plains Experiment Station, Tifton, GA 31794.
99
100
BURTON and HOOK
relatively few watersheds in this survey allowed only limited interpretation (Omernik 1977). Nutrient losses in surface runoff from native prairie in west central Minnesota have been intensively studied (Timmons and Holt 1977), but nutrient losses from successional, old field watersheds in the Great Lakes Basin have received little attention. Thus, a study of runoff losses from an abandoned field was included as part of the Felton-Herron Creek Study. Felton-Herron Creek was one of the watersheds selected for intensive study by the pilot watershed group (Task C) of PLUARG. The objective of this study was to quantify losses ofnitrogen, phophorus, and other nutrients from abandoned farm lands in lower Michigan as a means of assessing the impact of abandoned farm fields on nutrient loadings to the Great Lakes. MATERIALS AND METHODS An old field, abandoned approximately 18 years ago, was selected for study. The predominant vegetation on ths field was goldenrod (Solidago canadensis and S. graminifolia) and quackgrass (Agropyron repens), but a very diverse flora existed. Most of this field was included in a 7.73 ha subwatershed with well delineated topographic boundaries on the Michigan State University campus, East Lansing, Michigan. An existing subsurface drainage tile installed while the field was in cultivation was still functional and provided a convenient place to sample runoff from this subwatershed. The drainage tile emptied into an artificial channel at the edge of the field. Discharge from this chalmel was measured with a V-notch weir and a Stevens Type F recorder. Water samples were taken during spring runoff and storm events with an ISCO sequential water sampler. These samples were supplemented by low flow grab samples. Paired soil samples were taken at 24 sites in increments to a depth of 150 cm along a "star" shaped group of criss-crossing transects in 1975. Soil-water samples were taken at weekly intervals at 15 and 150 cm depths with porous cup tubetype vacuum soil-water samplers throughout the 1976 and 1977 ice-free seasons. Precipitation inputs were monitored with three recording rain gauges at nearby localities. Precipitation for the study area averages 77.2 cm/year. Precipitation was below normal during both years of the study and was 73.3 cm during the 1975-76 water year and 61.9 cm during the 1976-77 water year. All runoff samples were analyzed using standard
AutoAnalyzer techniques (U.S. Environmental Protection Agency 1974). These techniques included the automated ferric thiocyanate chloride method, automated colorimetric phenate ammonia nitrogen method, automated diazotization nitrite nitrogen method, automated cadmium reduction nitrate-nitrite nitrogen plethod, automated molybdate reactive phosphorus method, persulfate digestion total phosphorus method, and automated Kjeldahl organic plus ammonia nitrogen method. Sodium and calcium analyses of runoff were done with atomic absorption spectrophotometry and suspended solids analyses followed Standard Methods (American Public Health Association 1971). Nitrate and ammonium in soil-water samples were analyzed by ion-selective electrodes in 1976 (Milham et al. 1970, Orion Research 1971) and by standard_AutoAnalyzer techniques in 1977. All other water-soil analyses were done by standard AutoAnalyzer techniques (U.S. Environmental Protection Agency 1974). Soil samples were analyzed for nitrate extracted from wet samples with IN K2 S04 (approximately a 1:5 soil:solution ratio) (Bremner 1965); for available P extracted with dilute acid-fluoride (1:8 soil:solution ratio) (Jackson 1958) and analyzed by the colorimetric method (Murphy and Riley 1962); for total P by the method of Sommers and Nelson (1972); and for total N by the method of Nelson and Sommers (1972). Runoff loadings from the watershed were calculated using the stratified, random sampling model employing a ratio estimator as suggested in the March 1977 revision of the IJC-PLUARG, Quality Control Handbook for Pilot Watershed Studies. Soils on this site are very heterogeneous and include Miami, Conover, and Kalamazoo loams, Granby loamy sands, Barry and Corunna sandy loams, and Westland silty clay loams. In general, these loamy soils are developed on silt to loam glacial tills and are members of the mixed mesic family of Typic Hapludalfs. There apparently is a fairly continuous clay lens underlying the lower central portion of this watershed, since relatively impermeable reduced clays were encountered at every soil sampling site in the lower central part of the watershed. The existence of this clay lens results in a perched shallow water table. RESULTS AND DISCUSSION Water budgets for this abandoned field watershed were calculated using the technique of Thornthwaite and Mather (1967) and indicated that little, if any, recharge of groundwater occurred
RUNOFF FROM ABANDONED AGRICULTURAL LAND (Table 1). Almost all excess water appears to have been intercepted by the existing tile drainage system and exported from the watershed as runoff. Runoff from this site was excessive compared to nearby unirrigated forest and old field sites monitored as part of other studies. The excessive runoff probably resulted from the clay lens underlying the lower central portion of this watershed and from existence of the tile drain. Since groundwater recharge on this site was minimal as a result of the clay lens and lower than average precipitation, runoff losses should be maximal for such a system. In many other Great Lakes watersheds, runoff losses would be reduced by losses to the groundwater pool. Annual runoff loadings are presented in Table 2. There was runoff in 1977 only during the February to early June period. Exports during the spring runoff period (mid-February through May)
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represent 99.8% of total annual runoff. Thus, the spring runoff data in Table 2 can be used as an approximate estimate of total export during this dry year. Exports were much less than in the wetter 1975-76 water year for all constituents. This variability associated with variable rainfall suggests the need for long-term data from this as well as other watershed studies in the Great Lakes Basin. The annual flow weighted mean concentration of 0.073 mg total P/L is low compared to the 0.152 mg total P/L reported for intense agricultural land for this region (Omernik 1977). It is intermediate between values reported for agricultural and forest land uses as was predicted by Omernik (1977). Orthophosphorus concentrations (0.028 mg P/L) also are intermediate between forest and agricultural land uses as was predicted. Somewhat higher concentrations are expected from watersheds on soils with high clay content (IJC-PLUARG
TABLE 1. Water budgets for the watershed (values in m 3 /ho).
Precipitation
Evapotranspiration
Runoff
Recharge
ANNUAL 1975-76 % of Input
7329.6 100.0
5548.7 75.7
2378.1 32.45
-597.2 -8.15
ANNUAL 1976-77 % of Input
6188.8 100.0
5618.7 90.79
467.6 7.56
102.5 1.66
TABLE 2. Stream exports from the 7.73 ha abandoned farm field watershed.
1975-1976
1976-77
Total Exports (kgjyr ± one std. dev.)
Unit Area Exports (kgjhajyr)
Percent Transported by Runoff* Events
Percent Transported During Spring Runoff**
Exports in Spring Runoff 1977 (kg ± one std. dev.)
Unit Area Exports**· (kgjha)
Molybdate Reactive P Total P Nitrate-N Ammonia-N Nitrite-N Total Inorganic N Organic N Chloride Sodium Calcium Suspended Solids
0.83 ± 0.50 2.34 ± 0.93 1.35 ± 0.29 2.47 ± 2.32 0.39 ± 0.06 4.21 ± 2.34 13.76 ± 4.20 488.35 ± 256.08 440.26 ± 183.18 107396 ± 98.46 307.43 ± 254.85
0.107 0.303 0.175 0.320 0.051 0.545 1.780 63.176 56.955 138.934 39.771
85.6 84.1 76.8 82.8 88.6 81.5 83.0 53.0 69.3 65.3 78.6
71.4 76.6 65.3 91.2 92.9 83.1 82.0 63.3 74.6 76.5 78.9
0.111 ± 0.013 0.363 ± 0.263 0.748 ± 0.103 0.183 ± 0.059 0.040 ± 0.Q11 0.971 ± 0.119 2.166 ± 0.423 170.41 ± 26.44 84.28 ± 16.84 142.80 ± 17.91 28.05 ± 16.72
0.014 0.047 0.097 0.024 0.005 0.126 0.280 22.045 10.903 18.474 3.629
Water (m 3 )
2378.1
307.6
80.0
467.6
60.5
Constituent
*Runoff events were separated on the basis of distinct runoff peaks and include snowmelt and rain peak generated runoff during spring. **Spring runoff includes peak events plus baseflow and interflow conditions from snowmelt until constant runoff ceased. ***Spring only exports, but 99.8% of total runoff in 1976-77 occurred in this season.
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BURTON and HOOK
1978). The concentrations are well above the concentration of 0.010 mg P/L that is generally accepted as the level that can cause eutrophication in lakes (Vollenweider 1968). Annual unit area loads from this old field of 0.1 1 kg/ha/yr (Table 2) are within the 0.10 to 0.25 kg/ ha/yr range predicted for losses from grasslands with medium loam to clay soils and are slightly greater than 0.05 to 0.10 kg/ha/yr losses predicted for forested watersheds by the IJC-PLUARG studies (1978). These losses are essentially identical to the mean losses from forested watersheds with sedimentary substrates and are higher than losses from forests on igneous substrates reported by Dillon and Kirchner (1975) for their study of exports of phosphorus from 34 watersheds in southern Ontario. Thus, losses from this abandoned field watershed are only slightly higher and are already approaching background levels expected from undisturbed forested watersheds in the Great Lakes Basin. Remedial measures on such abandoned farm fields are thus unnecessary and would result in little improvement in water quality in the Great Lakes. Some minor reductions in phosphorus loads to the Great Lakes could be achieved by conversion of these lands to forests. Such a conversion to production of useful biomass is desirable from both an economic and water quality standpoint. Both total and inorganic nitrogen concentrations fall in the range (0.47 N0 3 -N, 0.078 NH 4 -N,0.017 N0 2 -N) reported for forested land (Omernik 1977). It is not surprising that nitrogen concentrations in runoff from this abandoned farm field are so low since nitrogen is normally one of the primary limiting factors to terrestrial plant productivity. Inorganic N is readily immobilized by plant uptake, storage in the organic layer of soils in uncultivated fields, or is rapidly lost by leaching to the groundwater (Harmsen and Van Schreven 1955). In addition, nitrogen application rates on agricultural lands were much lower in the late 1950's when this field was abandoned than they are at present. Thus, any residual inorganic N would have long since been immobilized in the plant biomass, soil organic matter, or soil microbial community or would have been leached to groundwater. Total N exports from this formerly cropped field are 2.33 kg/ha/yr and are in the range of 0.5 to 6.3 kg/ha/yr reported for forested and idle/perennial land uses by IJC-PLUARG (1978). The total N losses from this watershed are almost identical to the 2.37 kg/ha/yr reported from undisturbed forested watersheds in northwestern Ontario (Nicholson 1977). Cropland
losses ranged from 4.3 to 31 kg N/ha/yr according to IJC, so losses from this old field are very low compared to cropland losses in the Great Lakes Basin. It is interesting to note the high percentage of annual exports associated with spring runoff and with runoff events (Table 2). Even during the spring runoff period, runoff events generated by snowmelt on warm days, rainfall, or a combination of the two dominated exports. The runoff of nutrients from old fields depends on the nutrient status of the soils and soil-water. This nutrient status reflects the soil type, fertilizer and cropping practices prior to abandonment, number of years since abandonment, and the successional vegetation present at any particular point. Soils data identify the reservoir of nutrients available for runoff, provide a means to relate runoff to nutrient content of that particular soil, and provide the data necessary for design of management schemes to prevent release of nutrients. Soil-water analyses indicate the very infertile nature of this abandoned farm field. For example, nitrate-N increased to a yearly high of 0.55 ± .52 mg N/L at the 15 cm depth on March 24, 1977, after the soil began to warm, decreased rapidly to less than 0.01 mg N/L by April 28, 1977, then increased slightly by mid-May with the weekly average varying from 0.01 to 0.11 throughout the rest of the summer and fall. Nitrate-N concentrations at the 150 cm depth were similar and varied from a seasonal high of 0.30 ± .16 mg N/L on April 7, 1977, down to a low of 0.06 ± .02 mg N/L in August. Weekly average concentrations varied between 0.06 and 0.13 mg N/L throughout most of the summer and fall. Spring peaks of nitrate-N are the norm in fallow soils (Harmsen and Van Schreven 1955). Ammonia-N levels were also very low in soil-water, with weekly averages varying between 0.02 and 0.25 mg N/L at the IS cm depth and between 0.05 and 0.27 mg N/L at the 150 cm depth. Nitrite-N was always below limits of detection (0.01 mg N/L). Weekly average organic-N concentrations varied from 0.34 to 0.93 mg N/L at the 15 cm depth and from 0.08 to 0.82 mg N/L at the ISO cm depth with no obvious seasonal correlation. Annual flow-weighted mean concentrations of inorganic nitrogen in runoff appear to reflect soil-water concentrations during the spring when' concentrations are highest. Since more than 80% of total runoff of nitrogen occurs during the spring (Table 2), these results are not surprising. Total P concentration in soil-water was also very low, with the weekly average varying from 0.02 to
RUNOFF FROM ABANDONED AGRICULTURAL LAND
0.36 mg P/L at the 15 cm depth and from 0.003 to 0.32 mg P/L at the 150 cm depth. Most weekly averages were less than 0.080 mg P/L at both depths. There were no obvious seasonal trends in soil-water P. The annual flow-weighted mean concentration of total P in runoff (0.073 mg/L) also appears to reflect soil-water concentrations during spring. Soil analyses also indicated the very low fertility of this abandoned farm land (Table 3). Both available (Bray extractable) phosphorus and nitrate were very low in these soils (Table 3). Both elements tended to decrease with depth, with highest concentrations in the top 15 cm of soil where much of the root biomass and soil organic. matter were located. Total Kjeldahl-N also followed the trend of decreases with depth with Kjeldahl-N being more than an order of magnitude greater in the highly organic surface soils (1095 J.1g/g dry soil in the top 5 cmfthan afihe 150 cm depth (68 J.1g/g dry soil). Total P concentrations were also higher in the surface soils (342 ± 204 J.1g/g dry soil in the top 5 cm), decreased rapidly to 254 ± 221 J.1g/g dry soil in the 31-45 cm increment, then leveled off at a concentration of about 250 J.1g/g dry soil and remained at this level down to the 300 cm depth sampled in 1975. TABLE 3. Phosphorus and Nitrogen analyses olsoiis from the abandoned farm field watershed (values in pgjg dry soil ± one standard deviation).
Depth-cm
Bray Extractable P
Total P
0-5 5-10 10-15 15-30 30-45 45-60 60-75 75-90 90-105 105-120 120-135 135-150 AVERAGE
6.48 ±6.94 4.36 ±4.29 3.10 ± 2.31 2.50 ± 2.16 2.93 ±4.33 2.39 ±5.42 2.60 ±4.97 2.34 ± 3.29 2.61 ± 3.43' 2.19 ± 3.02 1.91 ± 2.92 1.30 ± 2.15 2.89 ± 1.35
342 ± 204 341 ±222 324 ±212 283 ± 183 254 ± 221 245 ±202 252 ± 155 282 ± 171 277 ± 162 283 ±232 236 ± 118 231 ±89 279 ± 39
Nitrate-N
Kjeldahl-N
3.84 ±4.24 1095 ± 382 3.94 ±4.85 1008 ± 329 3.65 ± 3.58 762 ± 320 3.00 ± 2.87 599 ±297 2.02 ± 1.39 379 ± 249 1.78 ± 1.14 247 ± 117 1.77 ± 1.04 222 ± 121 1.81 ± 1.25 178 ± 116 1.77 ± 1.08 134 ± 91 1.75 ± 1.14 102 ±75 1.60 ± 1.00 81 ±61 1.61 ± 1.04 68 ±58 2.38 ± .94 406 ± 369
These soil and soil-water data reflect the very infertile nature of this particular abandoned field. Certainly, recently abandoned fields would have losses of nutrients in runoff approaching losses from active agriculture. These data suggest that fields that have been abandoned from 15-20 years will have nutrient losses approaching background
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levels typical of undisturbed forests. Thus, to precisely calculate nutrient losses from abandoned farm fields to the Great Lakes would require data on time of abandonment, soil nutrients status, etc. CONCLUSIONS
Farm lands that have been abandoned for 15 to 20 years are not major non-point sources of pollution. Phosphorus and nitrogen loadings from such watersheds approach background levels for undisturbed forests. When calculating total loadings to the Great Lakes from such abandoned fields, typical nitrogen loadings for forests as generated by the recent PLUARG studies should be used while phosphorus loadings slightly higher than those typical of forest loadings should be used. Nutrient losses from recently abandoned fields should approach losses typical of agriculture and drop over a 10 to 15 year period to losses typical of forests. No remedial actions to reduce pollution from these abandoned farm lands appear to be practicable or needed. Disruption of still functional drainage tiles could possibly reduce suspended sediment and total P losses from such lands and increase groundwater recharge. Conversion .of these lands to forests would likely result in slight improvements in water quality while producing an economically valuable product. ACKNOWLEDGMENTS
Funds for this project were provided by the U.S. Environmental Protection Agency (Grant Number R005143-Q 1) through the Pollution from Land Use Activities Reference Group of the International Joint Commission established under the CanadaU.S. Great Lakes Water Quality Agreement of 1972. Findings and conclusions are those of the authors and do not necessarily reflect the views or recommendations of the Reference Group, the International Joint Commission, or the Environmental Protection Agency. The authors would like to thank C. S. Annett, W. Baker, P. Bent, J. Ervin, and D. O'Neill for field and technical assistance. REFERENCES American Public Health Association. 1971. Standard methods for the examination of water and wastewater. 13th Edition. Washington D.C. Bremner, J. M. 1965. Inorganic forms of nitrogen. In: Methods of Soil Analysis. C. A. Black, ed. Agronomy Monogr., 9:1179-1237. Amer. Soc. Agron., Madison, Wisconsin.
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Dillon, P. J., and Kirchner, W. B. 1975. The effects of geology and land use on the export of phosphorus from watersheds. Water Research 9:135-148. Drynan, W. R., and Davis, M. J. 1978. Application of the universal soil loss equation to the estimation of nonpoint sources of pollutant loadings to the Great Lakes. Technical Report, International Reference Group on Great Lakes Pollution from Land Use Activities, International Joint Commission, Windsor, Ontario. Harmsen, G. W., and Van Schreven, D. A. 1955. Mineralization of organic nitrogen in soil. In: Advances in Agronomy, Vol. 7, 299-398. A. G. Norman, ed. Academic Press, New York. International Joint Commission-Pollution from Land Use Activities Reference Group. 1977a. Land use and land use practices in the Great Lakes Basin. Joint Summary Report-Task B, United States and Canada, International Joint Commission, Windsor, Ontario. _ . 1977b. Quality control handbook for pilot watershed studies. International Joint Commission, Windsor, Ontario. _ . 1978. Environmental management strategy for the Great Lakes system. Final Report, International Joint Commission, Windsor, Ontario. Jackson, M. L. 1958. Soil chemistry analysis. Prentice-Hall, Inc., Englewood Cliffs, New Jersey. Milham, P. J., Awad, A. S., Paull, R. E., and Bull, J. H. 1970. Analyses of plants, soils and waters for nitrate by using an ion-selective electrode. Analyst 95 :751-753. Murphy, J., and Riley, J. P. 1962. A modification single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta. 27:31-36. Nelson, D. W., and Sommers, L. E. 1972. A simple diges. tion procedure for estimating total N in soils and sediments. J. Env. Qual. 1:423435. Nicholson, J. A.1977 . Forested watershed studies. Summary
Technical Report, PLUARG Task C, Activity 2, International Joint Commission, Windsor, Ontario. Omernik, J. M. 1977. Nonpoint source-stream nutrient level relationships: A nationwide survey. Ecological Research Series Report, EPA-600/3-77-105, U.S. Environmental Protection Agency. Orion Research, Inc. 1971. Instruction manual. Ammonia electrode. Orion Research, Inc., Cambridge, Massachusetts. Sommers, L. E., and Nelson, D. W. 1972. Determination of total phosphorus in soils. A rapid perchloric acid digestion procedure. Soil Sci. Soc. Amer. Proc. 36:902904. Stewart, B. A., and Woolhiser,.D. A. 1976. Introduction, pp. 1-5. In: Control of Water Pollution from Cropland. Vol. II-An overview. B. A. Stewart, D. A. Woolhiser, W. H. Wischmeier, J. H. Caro, and M. H. Frere. Report No. EPA-600/2-75-026b, U.S. Environmental Protection Agency and Report No. ARS-H-5 -2, Agricultural Research Service, U.s. Department of Agriculture. Thornthwaite, D. W., and Mather, J. R. 1967. Instructions and tables for computing potential evapotranspiration and the water balance. Publ. In Climatology, Vol. 10:185-311. Laboratory of Climatology, Drexel Institute of Technology, Centerton, New Jersey. Timmons, D. R., and Holt, R. F. 1977. Nutrient losses in surface runoff from a native prairie. J. Env. Qual. 6(4):369-373. U.S. Environmental Protection Agency. 1974. Methods for chemical analysis of water and wastes. EPA-625/6-74003, U.S. Environmental Protection Agency. Vollenweider, R. A. 1968. Scientific fundamentals of the eutrophication of lakes and flowing waters, with particular reference to nitrogen and phosphorus as factors in eutrophication. Technical Report, Organisation for Economic Co-operation and Development, Paris.