Pollutionfrom land runoff -
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What its origins are, how they may affect the Great Lakes, and what remedial measures may be taken were addressed by a study of eight areas William C. Sonzogni Great Lakes Basin Commission Ann Arbor, Mich. 481 06
G . Chesters D. R. Coote D. N. Jeffs J. C. Konrad R. C. Ostry J. B. Robinson One of the most extensive studies of nonpoint sources of pollution was recently completed with the submission of the final report of the International Reference Group on Great Lakes Pollution from Land Use Activities (PLUARG) to the US.-Canadian International Joint Commission (IJC). Feature articles in ES&T hace by-lines. represent the ciews o f t h e authors, and are edited bJ the Washington staff, I f you are interested in contributing an article. contact the managing &editor 148
Environmental Science & Technology
This reference group, composed of representatives of federal, provincial, and state governments in the U S . and Canada, and supported by a host of scientific and technical experts, was charged to determine, with respect to the North American Great Lakes: Are nonpoint sources of pollution affecting the Great Lakes? What are the causes of this pollution? What practical remedial measures may alleviate this pollution?
Background The multimillion dollar PLUARG study was initiated as a result of the 1972 U S - C a n a d a Agreement on Great Lakes Water Quality. The final report was presented in July 1978, and public hearings have since been held in the U S . and Canada on the results. These hearings were preceded by a unique public participation program to inform interested citizens on the find-
ings. Overall, this study represents a milestone in managing a large international water body and its basin. One of the first steps undertaken in this study was an inventory of land use over the entire Great Lakes basin. It showed that more than 50% of the basin consists of forested or wooded land. Agricultural land comprises about one-third, while -urban land, which includes residential areas and most of the basin's large population, makes up only about 3%. Agricultural land is concentrated in the southern Lake Michigan, southern Lake Huron, Lake Erie, and Lake Ontario watersheds. The inventory of land use and other characteristics provides an overview of important features of the basin which should be considered when evaluating the extent, causes, and location of pollution from land drainage. In order to obtain more specific information, eight areas, representing the full range
0013-936X/80/0914-0148$01,00/0 @ 1980 American Chemical Society
of land use activities found in the basin, were selected for detailed study. Pollutant loads One of the main outputs of the pilot watershed studies was information on unit area loads for areas with a single land use. (Unit area loads are defined as the pollution contributions of a land area divided by the size of the land area.) A comparison of these unit area loads showing the relative contributions from different types of rural and urban land, as well as the observed range in values, is given in Table I . Table 1 illustrates the wide range in unit area loads that occurs when land use alone is considered. It also shows that the loads of suspended sediment, phosphorus, and nitrogen from intensive agriculture (cultivated land) and urban areas are 10- 100 times greater than forested and idle lands. Forested and idle land loads are probably similar to natural or background levels. Unit area loads for improved pastures overlap Lhe upper range of forcsted and idle land categories and the lower range of the cropland category. Loads of lead from general urban lands are about I O times greater than the upper range of general agriculture and cropland. Phosphorus u n i t area loads for wastewater spraj irrigation areas approximate the loads from general agriculture, cropland, and urban categories. while nitrogen loads from wastewater spray irrigation areas are up to I O times greater than those from other land uses. While it was obvious even before the
study that certain land uses within the same region generally contributed more pollutants than others per unit area, the reasons for differences among sites of the same land use were unclear. A major conclusion of the study was that land factors such as land form, land, use intensity, and materials usage must he considered along with land use when an area is evalbated as a nonpoint pollution source. Differences in climate must also be considered, especially with regard to year-to-year variations i n unit area loads. A knowledge of these factors and how they affect nonpoint source pollution is fundamental.
Effects of land form Many past studies have mistakenly identified land use as the cause of nonpoint source problems, when, in fact, land form was the dominant factor. Land form characteristics include soil texture, soil type (mineral or organic), surficial geology, physiography (slope, drainage density), and soil chemistry. These characteristics, in many cases interrelated, describe the “form” of the land. While most land sites have certain unique form characteristics, generalizations concerning the importance of basic form characteristics have emerged for the Great Lakes basin. From an overall perspective, the single most important characteristic has generally been found to be soil texture (soil particle size distribution). Overland runoff is more prevalent on fine-grained clay soils than on coarse
sandy soils, since sandy soils tend to allow rapid water infiltration. Claysized particles are easily suspended, but usually settle very slowly, so the probability of transport over the land is high. Sorption of pollutants by clay-sized particles generally results in clay soils hiving more associated pollutants because of the chemical and physical characteristics of such soils. Not surprisingly, those sections of the Great Lakes basin which have sandy soils. such as the upper Lake Michigan basin, have relatively good water quality; those with clayey soils, such as the Lake Erie basin, tend to have poorer water quality even when land use is similar. Some physiographic characteristics are also important and can explain problems associated with specific sites. For example, a heavy clay soil on a steep slope generates more poorquality runoff than it does on relatively flat land. Drainage density (the degree of runoff carrying channel development) affects the transport of material to the mainstream, so that the potential for pollutant movement to receiving water increases w i t h greater drainage density. Surficial geology is important, particularly in explaining the origin of land form characteristics. The surficial geology is also related to the soil chemistry, an important form characteristic. The natural soil fertility affects the nutrient loss from agricultural lands. Calcareous soil, related to the geology of the area, contributes relatively high unit area loads of
TABLE 1
Ranges of unit area loads by land use, kg1ha.y Land uses
Suspended solids
Total phosphorus
Rural General 3-5600 0.1-9.1 agriculture Cropland 20-5100 0.2-4.6 Improved 30-80 0.1-0.5 pasture Forestlwooded 1-820 0.02-0.67 7-820 0.02-0.67 Idle/perennial Sewage sludge 0.2 Wastewater spray 0.2-1.4 irrigation Urban General urban 200-4800 0.3-4.8 Residential 620-2300 0.4-1.3 Commercial 50-830 0.1-0.9 Industrial 450-1 700 0.9-4.1 Developing urban 27 500 23 Dash (-) indicates data not available a
Filtered reactive phosphorus
Total nitrogen
Lead
Comer
Zinc
Chloride
0.01-0.6
0.6-42
0.002-0.08
0.002-0.9
0.005-0.3
10-120
0.05-0.4 0.02-0.2
4.3-31 3.2-14
0.005-0.006 0.004-0.015
0.014-0.064 0.021-0.038
0.026-0.083 0.019-0.172
10-50
1-6.3 O.O1-O.lOa 0.5-6.0 0.01-0.07 11 0.01 0.1-1.3 370
0.01-0.03 0.01-0.03 0.01 -
0.02-0.03 0.02-0.03 0.005 __
0.01-0.03 0.01-0.03 0.2 -
2-20 20-35 10
0.05-0.4 0.2 0.02-0.08 0.3 0.1
0.14-0.5 0.06 0.17-1.10 2.2-7.0 3.0
0.3-1.0 0.02 0.25-0.43 3.5-12.0 -
130-750 1050 10-150 75-160 -
6.2-18 5-7.3 1.9-11 1.9-14 63.0
0.02-0 21 0.03 0.07-0.13 0.29-1.3
-
-
-
Total dissolved phosphorus
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149
phosphorus, suspended solids, and chloride.
Effects of land use intensity The degree to which land is developed has a major effect on water quality. For example, the way in which rural land is farmed or the intensity of industrialization of an urban area are major characteristics which affect land pollution potential. Any land practice that exposes soil to the erosive forces of rainfall and runoff represents an erosion and pollution hazard. I n general, the greater
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the canopy and ground cover protection, the lower the erosion potential. Rural lands with progressively greater erosion potential have been found to be permanent pasture, hay, small grains, corn in rotation, continuous corn, white beans and similar cash crops, some horticultural crops, and plowed land. Of the’cultivated land in the Great Lakes basin, widely-spaced row crops were found to contribute the greatest amounts of sediments and associated pollutants. Similarly, PLUARG’s urban investigations indicated that, in
developing urban areas, construction sites where soil is exposed are perhaps the most hazardous of urban land activities, in terms of generating sediment. Intensive livestock operations, including feedlots, significantly add to the pollution potential of land. In some studies, livestock was found to account for about 20% of the agricultural load of soluble phosphorus. As the density of livestock increases,’ the pollutant potential increases. Of the different livestock operations investigated, intensive beef cattle operations were
Location of pilot watershed studies 1 Genesee
2 Maumee 0
Kenora
Long Lake Diversion
0 8
3 Menomonee 4 Felton-Herron Creek 5 Mill Creek 6 Saugeen 7 Grand 8 Forested watersheds 0 9 Agricultural subwatersheds A
~..
Nipigon
St Lawrence ’River
Lake / Simcoe
Lake Winnebago ------.
3 5
Lake St. C!air
A
-%Grand Rapids
Chicag 80
0
I--
50
0
-
80
180 km
50
100 miles
Source: PLUARG Final ReDon 1978
The study areas, termed pilot watersheds, included: the basin of the Genesee River, a U.S. tributary to Lake Ontario which drains a combination of land uses the basin of the Maumee River, which drains a major U.S. agricultural area and is the largest tributary to Lake Erie the Menomonee River basin, which is located within the Milwaukee metropolitan area and is a source of urban drainage to Lake Michigan Felton-Herron and Mill Creeks, two
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small tributaries of Lake Michigan’s Grand River which drain a wastewater spray irrigation area and orchard, respectively the Saugeen River basin, which drains into Lake Huron and includes a large Canadian agricultural area the basin of the Grand River, ihe largest Canadian tributary to Lake Erie, which drains both agricultural and urban lands
eleven small agricultural subwatersheds representing major agricultural regions in southern Ontario several small forested watersheds, located outside the Great Lakes basin in northern Ontario, but representative of much of the forested area in the northwestern part of the Great Lakes basin. Results of these studies, especially when integrated with other information, such as measured river mouth loadings, formed the basis for many of the technical conclusions of PLUARG.
found to exert the greatest impact in some areas, while dairy operations were most important in other areas. The intensity of cultivation practices also affects pollutant contributions from land. For example, the nature and timing of tillage methods affect the amount of soil exposed to erosion. Since many soils in the Great Lakes basin are often wet and difficult to till during the spring, many farmers routinely plow their land during the fall. This exposes bare soil over the winter, thereby providing greater opportunities for erosion and asociated pollution. Streambank erosion was found to contribute only a small quantity of pollutants relative to sheet and rill erosion. The total annual streambank sediment contribution, estimated at 827 000 metric tons, accounted for about 7% of the estimated total tributary sediment load. The estimated phosphorus load from streambank erosion, 426 metric tons, accounted for only about 2% of the total tributary phosphorus. (Streambank materials tend to be lower in phosphorus than topsoil eroded from fields.) On some intensely farmed clay soils, such as found in parts of the Lake Erie basin, artificial drainage is practiced to increase crop production. Although in the past it has been discounted as a significant soil erosion control practice, tile drainage can reduce soil loss and its associated pollution, especially on poorly drained clay soils which pose a particularly severe pollution hazard. I n forested ecosystems, practices
such as clearcutting and scarification result in increased exposure of soil. While this can lead to increased pollutant loads, the contributions are generally small. Since revegetation is usually rapid (two to five years) following harvesting, the effect is often of short duration. Transportation corridors, particularly in urban areas, are an intense land use which can result in unusually high accumulations of chloride, pesticides, oil and grease, and heavy metals. Also, aerial fallout from automobile exhausts is a source of lead to all land surfaces, but is particularly important around intensive transportation areas.
Urban areas In urban areas, the degree of impervious cover, degree of industrialization, and factors such as tree density and urban animal population can also affect pollutant contributions. For example, phosphorus from leaf litter accumulating in gutters of residential areas is readily leached by rainwater and carried through storm sewers to nearby lakes and streams. In studies of urban drainage, a high correlation was found between the amount of runoff and the quantity of pollutant, so that increased soil impermeability results in more runoff and greater pollutant loads. Contrary to a widely held notion, concentrations of pollutants in urban drainage do not vary much with flow. Significantly higher concentrations of pollutants do not occur in the early stages of runoff.
Small scale, private waste-disposal systems (septic systems) have not been found to be a major source of Great Lakes pollution. In areas where large urban and rural populations use private disposal systems, improperly designed or maintained systems may have some local impact on water quality. High chloride levels were often found along transportation corridors as a result of highway deicing operations. Levels of chloride in groundwaters and surface waters adjacent to highways at sites studied within the basin were also found to be elevated. Although salt use as a deicing agent appears to have greatly increased in recent years, no deleterious effects on the Great Lakes are apparent (even though, for example, salt usage on Ontario highways has doubled between 1970 and 1975).
Effect of fertilizers A number of materials are applied to land in the Great Lakes basin which, in combination with land form and land use intensity factors, can influence the quality of drainage water. The most important materials include commercial fertilizers, agricultural animal manure, agricultural pesticides, and road salts. The application of commercial fertilizers on land, both agricultural and residential, may serve to increase nutrient loads over levels from unfertilized soils, but only to a limited degree. Results of this study indicate that fertilizer is not a major diffuse source Volume 14, Number 2, February 1980
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of pollution in the Great Lakes basin. A large part of the nutrients lost from agricultural land can be accounted for by the relatively high natural nutrient content of most soils used for intensive agriculture. Nevertheless, practices which fail to incorporate fertilizers into the soil, such as the broadcasting of fertilizer without immediate plowdown, permit exposure of the fertilizer to the runoff. This runoff has been found to contain increased soluble nutrients, such as phosphorus and nitrate. Further, application of fertilizers in excess of that needed for optimum plant growth may lead to some increased phosphorus and nitrogen loads over levels in unfertilized soils. Applying animal manure as a fertilizer also can increase the level of pollution contributed. Failure to incorporate manure into the soil, as with commercial fertilizers, can lead to higher soluble phosphorus and nitrogen concentrations in runoff waters. For example, spreading manure on frozen land exposes the material to runoff and leads to increased soluble nutrients in streams. Manure storage or livestock feeding areas may also cause problems. However, like commercial fert i I i zer s , ma nu r e a p p I i ca t i on s ere not found to be the major cause ,of pollution from agricultural land.
Effects of pesticides Pesticides, which include herbicides, insecticides, and fungicides, are applied in varying quantities to almost all types of land found in the Great Lakes basin. Pesticides, if persistent (not rapidly degradable), can be carried off the land and into receiving waters.
Pesticide residues may continue to contaminate drainage water for long periods after the use of the pesticide is discontinued. For instance, DDT and dieldrin residues in water are derived from past uses in the basin of DDT and aldrin (the parent compound of dieldrin). Little can be done to change this slow release to water. Thus, DDT serves as an example of how small amounts of certain pesticides and other toxic agents can create long-term problems. However, agricultural pesticide use is currently well controlled, and it is expected that persistence or carryover associated with pesticides will soon be virtually eliminated. Of the variety of pesticides monitored in the PLUARG study, only a limited number were detected in drainage waters. Levels were generally too low to calculate precise pesticide load estimates. Among the pesticides detected were atrazine, simazine, derivates of DDT, dieldrin, endosulfan, lindane, endrin, and heptachlor. Of the pesticides currently used, only atrazine was frequently identified in stream samples. Despite its widespread use in corn-producing areas, atrazine does not appear to be a hazard since it degrades relatively rapidly in the environment. Orchards often have particularly high pesticide application rates. Currently, guthion, an organophosphate broad-spectrum pesticide, is commonly used in fruit orchards in many parts of the basin. However, guthion. although sometimes found in orchard drainage waters, degrades rapidly and does not 'appear to pose a threat to the Great Lakes' water quality. But residues of organochlorine pesticides, such as DDT, which were used in the past on
orchards, are still found in orchard drainage.
Effects of climate A unit area load from a diffuse source varies from year to year, depending on precipitation. Meteorological factors affecting runoff and associated erosion include rainfall intensity and duration, frequency of storms, snow cover, and antecedent rainfall. Thus, annual changes in unit area loads can occur even though land form, land use intensity, and materials applied to the land are unchanged. Unit area loads generally increase in proportion to increases in stream flow or runoff. The annual load from a unit of land is also not evenly distributed over the year. A large portion of the annual load can occur during runoff events. Runoff events from rural land are most likely to occur in the Great Lakes basin during the snowmelt runoff period and during a critical period between the spring melt and the time when vegetative cover is established. Phosphorus loads In order to demonstrate quantitatively the importance of land characteristics, Table 2 presents unit area loads of total phosphorus for several land uses under different combinations of land form (soil texture) and use intensity. The tables were based on results from the pilot watershed studies, as well as numerous other studies which provided pertinent information. Phosphorus is considered the key nutrient affecting Great Lakes productivity, and is perhaps the most important pollutant in runoff water from most of the basin.
TABLE 2
Total phosphorus unit area loads, kg/ha.y Soil texture Land use and intensity
Sand
Coarse loam
Medlum loam
Fine loam
Clay
0.25
0.65
0.85
1.05
1.25a
0.10
0.20
0.30
0.55
0.85
0.05 0.05
0.05 0.05
0.10 0.10
0.40 0.15
0.60 0.25
Organic
Rural Cultivated fields-row crop (low animal density) Cultivated fields-mixed farming (medium animal density) Pasturehange-dairy (medium animal density) Grassland
Forest General
0.05
0.l o b
Wetlands Natural area "Muck" farm Unit area toads may be higher when soil has an unusually high clay content. Unit area ioads may be higher in certain unique forested areas with clay soils; for exampfe, the Nemadji River basin, whlch flows into Lake Superior, contributes about 1.0 kg/ha-y. a
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Table 2 shows that while unit area loads for a particular land use may vary by an order of magnitude or more, knowledge of certain characteristics of the watershed nermit a more refined estimate of a re‘presentative value. For example, certain combinations of factors, such as row crops grown on a soil of high clay content, produce a high unit area load of phosphorus. Statistical studies done on some of the rural watersheds in the basin actually show that, on a watershed-to-watershed basis, close to 90% of the variability in measured unit area loads of total phosphorus are accounted for by differences in soil texture and the portion of the area in row crops. For urban sites, unit loads of phosphorus tend to vary with the degree of urbanization. That is, a highly industrialized urban area contributes more phosphorus per unit area than a residential area. Also, compared to nonurban land uses, phosphorus unit area loads are high. Urban construction sites, for example, contributed more phosphorus per hectare than other land uses studied. However, in terms of overall loads to the Great Lakes, urban land is not the major contributor, as only about 3% of the basin is urbaniied. The phosphorus unit area loads presented in Table 2 represent the integration and condensation of vast amounts of quantitative and qualitative data. Frorn a management perspective, the relative differences in the numbers are perhaps most important. Unique characteristics of individual land areas may result in significantly different unit area loads. For instance, forested areas in portions of the “red clay” region of the Lake Superior basin have loads several times higher than those of most forested areas in the basin (which tend to be on sandy soils). Similarly, agricultural soils with unusually high clay contents, such as those found in !some parts of the Lake Erie basin, can have typical unit area loads for row crops which exceed those given in Table 2 . Phosphorus availability While results are presented here for total phosphorus, it is important to realize that not all of the phosphorus derived from land drainage is biologically available. Recent evidence indicates that 40-50% or more of the total phosphorus contributed by Great Lakes tributaries is unavailable for plant growth. A large fraction of the unavailable phosphorus is associated with suspended soil particles. Despite the fact that all is not bioavailable, phosphorus
inputs based on measurements of total phosphorus have proven useful in predicting lake trophic response. Priority By considering the previously discussed factors which affect pollution loading from land as well as available data on tributary loads, one can identify those general areas where nonpoint source control programs will likely be most beneficial. For example, in the Great Lakes basin, the intensively farmed clay soils of northwestern Ohio and southwestern Ontario were identified as priority nonpoint pollution contributing areas in need of remedial measures. Other priority rural areas include portions of southeastern Wisconsin, eastern Michigan, the Niagara peninsula of Ontario, and the lowlands of New York at the eastern end of Lake Ontario. Once the most important contributing areas in the region have been identified, individual watersheds or subwatersheds must be examined closely to define specific source or “hydrologically active” areas. Such areas, because of their proximity to channels and streams as well as their specific land characteristics, may contribute most of the nonpoint source pollution to a watershed, even though they may make up only a small portion of the watershed. If remedial measures a r e aimed at the source areas where pollution from runoff is at its highest concentration, these measures may not be required for large areas of land. Consequently, i f site-specific hydrologically active areas can be identified, most appropriately through planning at the local or individual farm level, control measures can be most cost-effectively applied.
Johnson, M. G.; Comeau, J. C.; Heidtke, T. M.; Sonzogni, W. C.; Stahlbaum, B. W., “Management. Information Base and Overview Modelling,” PLUARG Special Report. Windsor, Ontario (1978). PLUARG, “Environmental Management Strategy for the Great Lakes System,” Final Report to the International Joint Commission, Windsor, Ontario (July 1978).
1 1
William Sonzogni serces as staffscierztist t o the US.Grear Lakes Basin C o m m i s sion, Ann Arbor. Mich.
G . Chesters ( I ) is director of the Wisconsin Water Resources Center, professor of soil science, and chairman o f the Water Chemistry Prograni, Unicersitj. of Wis consin- Madison. D. R. Coote ( r ) serves as research scientist, Land Resource Research Institute, Agriculture Canada, Ottawa.
Acknowledgments W e thank the many individualsin both U S . and Canada who, through the PLUARG study, directly and indirectly contributed to this paper. In particular, we thank R. Stiefel, r. Bahr, D. M. Whitt, D. Gregor, H . Shear, W . Rast, R. Drynan. and G. Welsh. This article is adapted from portions of PLUARG’s final report to the International Joint Commission.
I D. N.Jeffs ( I ) , f r o m the Ontario Ministrjs o f the Encironmetit, arid J. C. Konrad ( r ) , Wisconsin Department o f iVatural R e sources, served as co-chairmen o f a Task Group which incestigoted land use characteristics i n pilot watersheds.
Additional reading Chesters, G.: Stiefel. R.; Bahr, T.; Robinson, J.; Ostry, R.; Coote, D. R.; Whitt, D. M.,“Pilot Watershed Studies Summary Report,“ PLUARG Task Group C Report, Windsor, Ontario ( I 978). Coote, D. R.; MacDonald, E. M.: Dickenson, W . T.,“Agricultural Watershed Studies in the Canadian Great Lakes Basin, Final Summary Report,” PLUARG Task Group C Report. Windsor. Ontario ( I 978).
R. C. Ostry (1) is head o f t h e TechnimI Support Unit, Water Resources Branch. Ontario Ministrj’ o f the Eririronment. J. B. Robinson (r) is professor o f Encironnienral Biolog).. Unicrrsity o f Guelph ( Onrario). Volume 14, Number 2, February 1980
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