LITERATURE REVIEW ON
RUNOFF WATER QUALITY FROM
BIOSOLIDS APPLICATION
By: Mark Grey, Chuck Henry and Daniel Thompson
Part 7 of the Series:
Environmental Effects of Biosolids Management
Trace Metals: Potential for Movement and Toxicity from Biosolids Application
Effects on Wildlife and Domestic Animals from Biosolids Application
Air Emissions and Ash Resulting from Incineration of Biosolids
Nitrogen Cycle and Nitrate Leaching from Biosolids Application
Microbial Activity, Survival and Transport in Soils Amended with Biosolids
The Fate of Trace Synthetic Organics in Biosolids Applied to Soil
Runoff Water Quality from Biosolids Application
Effects of Organic Residuals on Poplars
Edited by:
Charles L. Henry, Ph.D. and Robert B. Harrison. Ph.D.
University of Washington College of Forest Resources
Seattle, Washington 98195
Prepared for:
Northwest Biosolids Management Association
NBMA Summary—Runoff
RUNOFF WATER QUALITY FROM BIOSOLIDS APPLICATION
INTRODUCTION
The effect of land application of biosolids on runoff water quality has received little indepth examination. This is especially true for forested ecosystems, for which most research in
the past 20 years has focused on the suitability of application techniques, tree growth
response, nitrogen management, and effect on wildlife (Henry, 1994). Few studies exist that
describe the quality of water leaving forested biosolids application sites, either via surface
runoff or via subsurface flow pathways. Whole-watershed studies examining water quality
effects from biosolids application are lacking as well. In agriculture, runoff water quality
research from biosolids application sites is more prevalent but is still limited, with most of
the data focusing on the quality of surface water runoff under different cropping and tillage
techniques in the eastern and southeastern United States.
The limited number of runoff studies may be due to the conservatism built into
guidelines, which often include both a slope restriction and requirements for buffers (EPA,
1995; Ecology, 1994), and which may vary depending upon practice, vegetation, and season.
Also, many application sites are in areas in which rainfall is minimal and little slope exists
(for example, wheat fields in eastern Washington State). Consequently, runoff has not been a
great concern. In recent years, biosolids has been applied to open rangeland in arid regions in
the western United States. Here, too, most of the research has focused on surface water runoff
quality in response to intense storm events (typically simulated).
Despite a general lack of information about how biosolids application affects surface
water quality, it is possible to refer to studies on the use of nitrogen (N) compounds,
primarily urea, for forest fertilization. Much can be learned from studies examining urea
fertilization and the consequences of applying it within forested watersheds (Bisson et al.,
1992). This is particularly true for instances in which steep terrain comprises most of a
forested watershed’s drainage area and where subsurface soil–water flow is thought to be the
dominant pathway for stormwater runoff (Bevin and German, 1982; Luxmoore et al., 1990;
Jardine et al., 1992; Kimmins et al., 1991). While biosolids are more heterogeneous than
urea, the N transformations following application are similar, as are operational issues, such
as the effectiveness of using buffer zones between the application site and streams to protect
water quality. In addition, monitoring strategies used in evaluating the impact of urea on
stream and aquatic resources may be applicable in examining the effects of biosolids
application.
Research on the effect of animal manure application on water quality can also be referred
to when gauging the impact of biosolids application. Manure from cow, poultry, or swine
production more closely resembles the physical and chemical characteristics of biosolids than
do commercial fertilizers like urea, yet the types of manure differ from biosolids in their
overall chemical composition and end use. Manure is used principally on dedicated disposal
sites or on agricultural or forage crops, or it can concentrate at feedlots or dairies (Khaleel et
al., 1980). Biosolids are used primarily as a fertilizer and soil nutrient supplement, and are
2
NBMA Summary—Runoff
rarely applied to land for disposal or concentrated in one area for long periods of time.
Because of the widespread use of manure, the effect of increasing the application rate, pattern
of nutrient release (primarily N and phosphorus [P] species), the quality of the resulting
runoff water, and the surface water runoff response to storm events of varying length and
intensity have been well-documented.
The following is a summary of the content of various literature on the effects of biosolids
application on runoff water. The reviews include studies relating the effect of management
practices (for example, cropping, tilling, and biosolids application rate). In some cases,
studies on the use of manures or chemical fertilizers are include, when pertinent biosolids
studies are lacking. Abstracts of articles that are referenced in this summary are included and
are available for further review by contacting the Northwest Biosolids Management
Association.
WATER QUALITY ISSUES AND COMPOSITION OF BIOSOLIDS
The quality of water leaving a biosolids application site is important for several reasons.
For forested sites, streams that drain application sites may contribute to the public drinking
water supply, either directly through surface water runoff into storage impoundments, or
indirectly through groundwater infiltration. Likewise, water leaving agricultural sites may
reach storage facilities (possibly for human or for livestock consumption), streams or rivers,
or it may infiltrate groundwater. If the water leaving a biosolids application site is high in
some nutrients (primarily P or N), it has the potential to cause eutrophication in the receiving
stream or water. (Eutrophication is the process by which a body of water becomes nutrientrich, which alters biological productivity and potentially changes the composition of living
organisms through a reduction in dissolved oxygen concentration.) It has been suggested that
springtime concentrations of N and P in natural waters that exceed 0.3 mg L-1 N and 0.01 mg
L-1 P may result in excessive algal growth or eutrophication (Vollenwieder, 1968).
Maintaining the quality of water leaving a biosolids application site is vital, therefore, to
protect both public health and aquatic resources.
The concentration of elements in biosolids, particularly nutrient elements, varies
depending on the composition of the incoming wastewater and on the digestion process used.
For example, Sommers (1977) reported that the concentrations of N and P in anaerobic and
aerobic biosolids varied from 0.1 to 17.6 percent for N and from 0.1 to 14.3 percent for P,
with the concentrations falling primarily in the range of 4 to 6 percent and 2 to 4 percent,
respectively. N and P derived from biosolids are a concern because of their potential role in
causing eutrophication. The amounts of mineral, or “available,” N and P vary highly and
depend strongly on the solids handling process used and the environmental conditions
following application. This is especially true when biosolids are dewatered, because NH4 can
leave the solids in the filtrate. Typically, mineral N accounts for 10 to 50 percent of total N,
while mineral P accounts for as much as 70 to 90 percent of total P (Sommers, 1977).
FACTORS AFFECTING RUNOFF WATER QUALITY
3
NBMA Summary—Runoff
Most researchers examining biosolids or animal manure agree that the application
technique (application on the soil surface, versus incorporation into the soil), cropping
strategy (till, in which the soil is tilled and/or disked before cropping, versus no-till), and
application rate strongly influence the quality of water leaving an application site. Other
important variables include the season of application, antecedent soil moisture, duration and
intensity of rainfall, and soil texture. The effect of the slope on runoff quantity and quality
has been scarcely evaluated, and studies have been limited to slopes of less than 15 percent.
Effects of Application Techniques and Cropping Strategy on Runoff Water Quality
The general consensus among researchers is that biosolids application to no-till
agricultural systems is more effective than application to conventional tillage systems in
reducing nutrient and sediment losses via surface runoff (Bruggeman and Mostaghimi, 1993;
Mostaghimi et al., 1992; Deizman et al., 1989; Dunigan and Dick, 1980). Bruggeman and
Mostaghimi (1993) used a rainfall simulator to study the effect of freshly applied dewatered
biosolids (16 percent solids) on infiltration and runoff of sediment and nutrients from
agricultural fields. All plots were planted in winter rye in the fall and sprayed with paraquat a
week before the simulation treatments were initiated. The no-till plots were established on the
killed rye stand; the crop residue was removed from the conventionally tilled plots, which
were then tilled to a depth of 15 to 20 cm and disked. A three-run sequence was used to
simulate different initial moisture conditions. Biosolids were both surface-applied and
incorporated at conventionally tilled plots and only surface-applied on no-till plots at rates of
0, 75, and 150 Kg N ha-1. It was found that the no-till system greatly reduced runoff,
sediment, and nutrient losses compared to the conventionally tilled plots. Surface application
was found to be more effective than incorporation at reducing the amount of runoff and
sediment loss. Incorporating the biosolids was shown to be more effective in limiting nutrient
losses during the third run on the conventionally tilled plots; specifically, concentrations of
PO4–P in runoff water were lowest with incorporation. Peak loadings of nutrients in runoff
appeared during the very wet conditions of the third simulated rainstorm.
Mostaghimi et al. (1992) used a rainfall simulator on experimental field plots to compare
the effect of chemical fertilizers and biosolids application on sediment, N, and P in runoff
from no-till and conventionally tilled plots. Biosolids (16 percent solids) were applied to notill and conventionally tilled plots at rates of 147 kg N ha-1 and 230 kg P ha-1. No-till plots
received only surface application of biosolids, while conventionally tilled plots received both
surface application and incorporation of biosolids. Biosolids application on the no-till plots
had the least amount of NO3-–N leaching and the least amount of sediment in surface runoff,
while chemical fertilizer application on the no-till plots had the least amount of total N and P
in surface runoff. The worst water quality scenarios were observed when either biosolids or
chemical fertilizers were surface-applied on conventionally tilled plots. N losses from the
conventionally tilled plots were minimized when biosolids were incorporated into the soil.
However, incorporating biosolids on conventionally tilled plots resulted in significantly
higher P and sediment loss than on the no-till plots. These findings suggest that, regardless of
the type of amendment (chemical fertilizer or biosolids), a no-till system is more effective
than a conventional tillage system at controlling runoff, sediment, and nutrient losses.
4
NBMA Summary—Runoff
Additionally, the results showed that P yield in runoff was greatest for a conventional tillage
system in which chemical fertilizer was surface-applied or biosolids were incorporated.
Deizman et al. (1989) examined the effect of the biosolids application technique and rate
on the quality of P runoff from no-till and conventionally tilled field plots. They applied
anaerobically digested biosolids (percent solids not given) at P loading rates of 0, 115, and
230 kg P ha-1 to 0.01 ha plots and used 90 mm of simulated rainfall at an intensity of 45 mm
hr-1. Runoff water was collected in concrete gutters directly below the field plots; no buffer
was used between the application border and the gutter. As expected, the no-till system
greatly reduced total runoff and sediment yields. Surface application resulted in higher
concentrations and yields of P, as compared to incorporation. Sediment-bound and total P
yields were less from biosolids-treated plots than control plots because of reduced erosion
and runoff. However, P concentrations in runoff from biosolids-treated plots almost always
exceeded Virginia State regulatory limits for PO43-–P in surface waters (0.01 mg L-1).
Dunigan and Dick (1980) monitored runoff losses from forage plots receiving
commercial fertilizer and biosolids (10 to 15 percent solids) at rates ranging from 150 to 175
kg N ha-1 and 54 to 66 kg P ha-1. The plots had a 5 percent slope. Surface application of
biosolids resulted in higher N and P losses in runoff than from incorporated biosolids plots. N
and P losses for all treatments were less than 1 percent of that added. At all application rates,
surface runoff losses of potassium (K) were approximately equal to or lower than control
values.
Application of liquid biosolids has been examined for its effect on soil water infiltration
rates and on nutrient and sediment loss in surface water runoff. Generally, leaving liquid
biosolids on the surface of agricultural fields to dry is a more effective technique in
controlling nutrient runoff than incorporating liquid biosolids (Kelling et al., 1977; Kladivko
and Nelson, 1979). Kelling et al. (1977) applied liquid digested biosolids at rates ranging
from 3.75 to 60 Mg ha-1 to field plots, and then measured infiltration and runoff at varying
times after application (4, 15, and 26 months). The liquid biosolids were surface-applied and
allowed to dry between applications. Biosolids-treated plots significantly increased soil
moisture and, in some cases, infiltration. For all trials, biosolids application significantly
reduced sediment losses. Surface runoff from biosolids-amended soil contained increased
amounts of inorganic N, whereas sediment and organic N in the runoff were reduced by
biosolids application. The authors reasoned that increased water infiltration and improved
aggregation were the cause of reduced sediment losses. Significantly more dissolved ortho–P
and total P were contained in the runoff waters from biosolids-amended sites than from
control plots for 2 years after application. This was attributed to mineralization of organic P
in the biosolids.
Kladivko and Nelson (1979) determined the effect of varying rates of liquid biosolids
application and incorporation techniques on the amount of sediment, nutrients, and heavy
metals in surface waters during intense rainfall storms. They used soil cores extracted from
the field after biosolids application at rates ranging up to 90 Mg ha-1 and subjected these
cores to rainfall using a simulator. Application techniques included surface application and
incorporation by rototilling or disking. It was found that surface-applied liquid biosolids were
5
NBMA Summary—Runoff
more effective in decreasing sediment and nutrient losses by erosion than either incorporation
technique. Sediment-bound nutrients accounted for most of the total nutrients lost from
treated plots.
Working under the hypothesis that incorporation of surface-applied poultry litter or
inorganic fertilizer by rototilling would improve runoff water quality, Nichols et al. (1994)
instead found that runoff water quality differences were negligible. Moreover, runoff losses
of total Kjeldahl nitrogen (TKN) and total P between manure-only and fertilizer-only plots
were not significantly different. The fertilizer equivalent of 218 kg N ha-1 was used. Giddens
and Barnett (1980) incorporated 11.2 and 22.4 Mg ha-1 of poultry litter into the surface of a
sandy loam soil (fallow field) and monitored fecal coliforms in runoff. It was found that
incorporating poultry litter generally reduced fecal coliforms during the late stages of runoff
events. McLeod and Hegg (1984) applied poultry litter to a fescue pasture, simulated rainfall,
and then monitored weekly runoff. TKN, total P, and chemical oxygen demand (COD)
concentrations in runoff dropped dramatically after each simulated event, and nutrient
concentrations in runoff were not significantly different between manure-treated and control
plots after 7 days of rainfall.
From the studies referenced in this section, it appears that, in general, surface application
without tilling is most effective in reducing both nutrient and sediment losses. Losses appear
to decline with time after application. However, some nutrient losses (for example, P)
continue for a long time (2 years or more), possibly due to continued mineralization.
Effect of Application Rate on Runoff Water Quality
Interest has grown in the past 5 years about the use of biosolids in rangeland. Harris–
Pierce et al. (1995) applied oven-dried biosolids to a rangeland gravelly sandy loam and
sandy loam at rates of 0, 22, and 41 Mg ha-1 in paired plots on slopes of 8 and 15 percent,
respectively. A one-time event of simulated rainfall for 0.5 h at a rate of 100 mm hr-1 was
applied to the plots and the surface runoff was collected for analysis. It was found that
increasing the biosolids application rate from 0 to 41 Mg ha-1 increased sediment, organic N,
NH4+–N, and total P in the runoff. However, concentrations of all measured constituents in
the runoff were less than EPA standards for drinking water. Runoff water quantity was
reduced somewhat in the biosolids-treated plots, but application rate did not affect runoff
yield. The proportion of total rainfall input lost as runoff from control plots ranged from 28 to
65 percent, while that lost from treated plots ranged from 8 to 55 percent.
These results are contrasted with those of Aguilar and Loftin (1992), who recorded runoff
losses of less than 1 percent of rainfall input on semiarid grassland that had received a surface
application of biosolids (6 and 10 to 11 percent slopes). In this study, runoff losses remained
below 1 percent, regardless of total precipitation and storm duration. Time delay between
biosolids application and the onset of rainfall, slope, and soil texture were suggested as
possible reasons for the difference between results. In an area of similar climate near Denver,
Colorado, Tindall et al. (1994) examined surface water runoff and groundwater quality from
sites receiving high rates of biosolids. The sites had been used for biosolids disposal for 18
years, with annual application rates ranging from 408 to 634 Mg ha-1. The biosolids had been
6
NBMA Summary—Runoff
buried or tilled into the soil. Researchers found high levels of nitrates in surface and ground
waters (exceeding drinking water standards) and discovered a strong seasonal pattern of
elevated nitrate in groundwater corresponding to maximum seasonal precipitation.
In a study examining runoff water quality following application of cow manure to millet
and rye grass, Long et al. (1975) found that manure applied on the soil surface (sandy loam
soil) and rototilled in at an N loading rate of 450 kg N ha-1 yr-2 for 3 consecutive years did not
increase surface water biochemical oxygen demand (BOD5) and NO3-–N as compared to
untreated soil. As expected, N concentrations in runoff were greatest when runoff volume
was highest. Couillard and Li (1993) reported increases in nutrient runoff concentrations (N
and P) with increasing cow manure application rates: 0, 150, and 300 kg N ha-1. Edwards and
Daniel (1993) reported that increasing the application rate of poultry litter significantly
increased runoff concentrations of total N, NH3–N, NO3-–N, total P, and dissolved P.
Application rates ranged from 0 to 870 kg N ha-1. The researchers also reported that the mass
of litter transported off the plots via runoff significantly increased with both application rate
and rainfall intensity. At high rainfall intensity, up to 19 percent of total applied N and
7 percent of total applied P were lost in runoff, suggesting that manure losses can be
substantial if followed by intense rainfall events.
Edwards and Daniel (1992) applied a slurry of poultry manure at rates of 0, 220, and 879
kg N ha-1 to fescue grass on a silt loam soil. Increasing the manure application rate
significantly increased runoff concentrations of Kjeldahl N, NH3–N, total P, and dissolved
reactive P. Relationships between runoff nutrient concentration and application rate and mass
loss and application rate were linear over the application rates examined.
Runoff Water Quality from Forests Fertilized with Biosolids
Research on runoff water quality in forested ecosystems has been limited, primarily
because the conservative nature of guidelines that use wide buffers and prevent the use of
biosolids on steep slopes. These site selection and management practices have caused
concern about runoff to be minimal. However, the use of dewatered biosolids has renewed
interest in evaluating runoff water quality in forests. Dewatered biosolids are much more
adhesive than liquid biosolids when applied over forest litter; consequently, slope restrictions
are being questioned. To the authors’ knowledge, no studies have examined runoff water
quality following application of dewatered biosolids to forested sites. The University of
Washington (1986) examined water quality in a treated and control watershed following
application of liquid biosolids at a rate of 45 Mg ha-1. Researchers used a 15-meter buffer
from ephemeral streams draining the watersheds and found no significant difference in
organic or mineral forms of N and P between treated and untreated watersheds.
Kimmins et al. (1991) applied liquid digested biosolids to a 3.58 ha area within the East
Creek watershed in southwestern British Columbia. An extensive network of stream
monitoring was established to determine if biosolids application would impact stream water
quality. Concentrations of total N, NO3-–N, NH3–N, and total P and PO4–P in East Creek and
ephemeral drainages were almost equal to or below pre-biosolids application levels. Stream
data included the evaluation of a 100-year storm that occurred a month after biosolids
7
NBMA Summary—Runoff
application. Fecal coliforms were detected in ephemeral drainage channels during the 100year storm, indicating that subsurface soil–water flow may have occurred, as 30-meter buffers
from streams were used. The researchers found, in general, that fecal coliforms do not persist
beyond 1 month in forest soils and detection in surface water was a storm-induced
phenomena owing to subsurface soil–water flow.
Loch et al. (1995) examined the effect of freshly applied and consolidated biosolids on
surface water runoff quality from small plots on Pinus sp. plantations in Queensland,
Australia. (Consolidated refers to biosolids that are surface-applied and exposed to natural
rainfall for 6 months before monitoring.) The biosolids were aerobically digested and had
been stored for 1 year before application. Researchers applied biosolids at a rate of 90 Mg ha1 to 0.8 x 2.0-meter plots on three different soil series. Plots were replicated twice on each
soil series; all sites were slightly sloping (5 percent). Artificial rainfall was applied at a rate of
150 mm hr-1 for one-half hour and runoff was collected in gutters located directly below the
plots. The rainfall amount and intensity corresponded to a 100-year storm event.
The results from this study found that runoff water quality was generally poor from all of
the treated plots and exceeded Australian regulatory limits. This is not surprising, however,
given the study design. The authors did not use buffers between the plots and collection
points, nor did they examine the effectiveness of various buffer distances between treated
plots and water collection points. Water contacting and moving through biosolids as shown
in this study is essentially biosolids leachate, and would in no way represent the quality of
water moving through an operational application site for which buffers are used.
Concentrations of NO3-–N and NH4+–N were initially high in runoff from freshly applied
biosolids (330 mg L-1 for both ions collected 5 minutes after initiating rainfall), but decreased
rapidly during the rainfall event (16 and 30 mg L-1 for NO3-–N and NH4+–N, respectively, at
30 minutes). Concentrations of NO3-–N and NH4+–N from the consolidated biosolids were
low throughout the rainfall event. In contrast, total P, Cu, and Zn in runoff from both fresh
and consolidated biosolids were relatively high and showed only small decreases during the
rainfall event. Total P concentrations in both treatments ranged from 10.5 to 4.3 mg L-1
between 5 and 30 minutes after initiating rainfall. Cu and Zn concentrations in surface water
runoff ranged from 389 to 78 µg L-1 and 1783 to 203 µg L-1, respectively.
Effect of Urea Application on Stream Water Quality
N has been applied to forest stands since the 1960s; application typically occurs at the
time of crown closure (Nason and Myrold, 1992). Fertilization is most often accomplished by
aerially spraying urea (CO(NH2)2) in pellet form at a rate that ranges from 150 to 25 kg N ha1. Such aerial applications can result in direct deposition in surface water. (One important
advantage biosolids application has, compared to urea application, is that biosolids
application deliberately avoids this potentially harmful activity.) Fertilization efficiency is
often in the range of 10 to 30 percent. In the 1970s, studies were initiated on a watershedscale to better define the effects of urea application on stream water quality. Most studies
monitored streams within treated and untreated watersheds before and immediately after
fertilization, with monitoring continuing typically for more than 1 year. Both automatic and
grab sampling techniques have been used, with the timing of the sampling being most
8
NBMA Summary—Runoff
frequent immediately following urea application. In most cases, no attempts were made to
monitor stream water quality changes in response to rainfall storm events following
application. Results have shown that a pattern of N loss to streams strongly correlated with
the application time and ability to maintain unfertilized stream buffers (Cline, 1973; Moore,
1975). High concentrations of urea N or TKN in stream water have almost always been
associated with direct overhead deposition of urea pellets into streams (Malueg et al., 1972;
Perrin et al., 1984; Meeham et al., 1975; Hetherington, 1984).
A summary of research on the effect of forest fertilization (urea application) on water
quality and aquatic resources in the Douglas-fir region of Oregon and Washington states was
completed by Bisson et al. (1992). As part of the summary, a synthesis of monitoring study
data was completed that showed that forest fertilization causes elevated urea (often measured
as organic N) concentrations over a period of days, elevated NH3–N concentrations over a
period of weeks to a few months, and elevated NO3-–N concentrations for a period of up to 1
year. Peak urea levels have varied between 0.1 and 50 mg L-1, peak NH3–N levels have
varied from 0.1 to 1.4 mg L-1, and peak NO3-–N levels have varied from 0.1 to 4.0 mg L-1.
Total N losses in stream runoff approximately 1 year after urea application ranged from 0.17
to 14.5 percent of the total N applied. The paper suggested that streams draining watersheds
which have been previously fertilized had higher fall season baseline NO3-–N concentrations
than streams draining unfertilized watersheds. The authors concluded that, while forest
fertilization may cause changes in N dynamics of receiving waters, it does not result in water
quality impairment.
Watershed-Level Response to Fertilization
Some researchers have evaluated agricultural or forested watersheds to assess land-use
practices and their effect on water quality. Vighi et al. (1991) studied the P loads (including P
from manure and biosolids) within agricultural and forested watersheds in the agriculturally
productive Po Valley in Italy. They found that streams draining agricultural watersheds
contributed an average of 0.1 kg P ha-1 yr-2, while forested watersheds contributed 0.6 kg P
ha-1 yr-2. The higher P losses in the forested watersheds were attributed to erosion. The
researchers concluded that P losses in the agricultural watersheds were independent of
fertilizer P application rate and were, instead, more directly influenced by slope or
geopedological watershed characteristics. Also in Italy, Caporali et al. (1981) compared an
agricultural watershed (which received both manure and inorganic fertilizer) and a forested
watershed for N losses. Practically all monthly N losses from both watersheds occurred
during the fall and winter months and depended more on total stream flow than on
concentration and land use. Thomas et al. (1992) found, over an 18-year study in Kentucky,
that the parent rock of soils had a greater effect on stream concentrations of NO3-–N and
PO4–P than did agricultural land use. The seven watersheds examined in this study showed
no difference in N and P concentrations over 18 years, except for a portion of one watershed
affected by a small residential development. The interaction of rainfall with surface soil
erosion and the chemical composition of parent material, therefore, cannot be overlooked
when examining the impact of biosolids application on runoff water quality.
9
NBMA Summary—Runoff
SUMMARY
Relatively little work has been completed examining the effect of biosolids application on
runoff water quality; information is particularly lacking for forested watersheds. Fortunately,
there does exist considerable literature exploring the impact on runoff water quality following
the application of urea and animal manure (especially to agricultural systems). Much of this
information can be used as a means of gauging the potential impact of biosolids until
additional, biosolids-specific research has been performed, reviewed, and evaluated.
As with the application of biosolids to other systems, the evidence suggests that
numerous variables exist that must be considered before an effective application resulting in
a minimal risk to a watershed can take place. Generally, it seems clear that application
technique, application rate, seasonal weather changes, soil moisture, and the duration and
intensity of rainfall all may influence the impact of fertilizer (biosolids or other) application.
Application of organic amendments under a no-till system appears to limit sediment, runoff,
and nutrient losses compared to either surface application or incorporation of the amendment
under a conventional tillage system. However, if a conventional tillage system is used, the
results are mixed: surface application seems to minimize P yield in runoff and sedimentation,
while incorporation seems to minimize N losses. Studies suggest that the effect of rainfall
upon nutrient leaching and runoff declines linearly with time.
Studies have indicated that the application of liquid biosolids to a watershed has little to
no impact on stream water quality with respect to N and P levels. Such findings are
particularly encouraging, due to the relatively greater susceptibility to nutrient runoff and
leaching from liquid biosolids compared to dewatered biosolids. It is suggested that the
application of dewatered biosolids will likely have no significant impact on the quality of
water emanating from watersheds. However, it is clear from the lack of peer-reviewed studies
on the subject of runoff water quality that more research needs to be undertaken to further
understand (and subsequently, minimize or eliminate) the potential adverse consequences of
biosolids application.
Reference: Henry, C., and R. Harrison. 1998. Environmental Effects of Biosolids
Management. Trace Metals: Potential for Movement and Toxicity from Biosolids
Application, Effects on Wildlife and Domestic Animals from Biosolids Application, Air
Emissions and Ash Resulting from Incineration of Biosolids, Nitrogen Cycle and Nitrate
Leaching from Biosolids Application, Microbial Activity, Survival and Transport in Soils
Amended with Biosolids, The Fate of Trace Synthetic Organics in Biosolids Applied to
Soil, Runoff Water Quality from Biosolids Application, Effects of Organic Residuals on
Poplars. Northwest Biosolids Management Association.
10