Prepared in cooperation with the Monroe County Department of Health

Phosphorus Loads Entering Long Pond, A Small Embayment 

of Lake Ontario near Rochester, New York 

Reductions in the amount of phosphorus in

discharge from the Spencerport wastewatertreatment plant have decreased phosphorus loads

in Northrup Creek and led to the improvement of

water quality in Long Pond.

Introduction 

Long Pond is one of many small, shallow embayments 

along the southern edge of Lake Ontario (fig. 1). These 

embayments are an important recreational resource and 

wildlife habitat; thus, maintaining their natural state is 

essential to their continued use. In recent decades, Long 

Pond and the adjacent Cranberry Pond have become hypereutrophic (overly enriched with nutrients) (Makarewicz 

and others, 1990) as a result of nitrogen and phosphorus 

transported to those waters by Northrup Creek from sources 

within the drainage basin.

In 1989, the Monroe County Department of Health 

and the Town of Greece, in cooperation with the U.S. Geological Survey (USGS), began a water-quality-monitoring 

program on Northrup Creek near North Greece at a site of a 

gaging station about 5 mi north (downstream) of the Village 

of Spencerport and the Spencerport wastewater-treatment 

plant. The program included the collection of water samples 

from October 1989 through September 1998 for chemical 

analysis and the collection of streamflow data for use in 

calculating phosphorus loads at the site. This fact sheet 

addresses the issue of concentration and loads of phosphorus 

in Northrup Creek, the principal tributary to Long Pond.

Northrup Creek begins just south of the Village of 

Spencerport in Monroe County and flows northward into 

Long Pond. It drains a total of 23.5 mi2

 in the towns of 

Ogden, Parma, and Greece (fig. 1). The drainage basin 

contains agricultural land, housing developments, and 

a small amount of urban land (table 1). 

Table 1. Land use in Northrup Creek Basin, 

Monroe County, N.Y., 1996

[Data from Monroe County Planning Department]

Land-use category Acres

Percentage 

of

drainage basin

Suburban residential (< 1-acre lots) 2,277 15.0

Undeveloped (agricultural) 12,658 83.2

Rural residential (2 to 5-acre lots) 91 .6

Commercial/industrial 180 1.2

TOTAL 15,206 100

U.S. Department of the Interior

U.S. Geological Survey

HILTON

LAKE 

ONTARIO LONG POND

CRANBERRY

POND

Agricultural land

Forest land

Urban, residential

and built-up land

Wetland

Other land uses

Town boundary

City or village boundary

Watershed boundary

EXPLANATION

NEW YORK

Location Map

Monroe

County

77 45' 77 40'

43 10'

43 15'

Northrup Creek near North Greece, N.Y., gaging station

Sewage-treatment plant

Water

Figure 1. Location of principal geographic features of 

Long Pond study area, Monroe County, N.Y.

Base from U.S. Geological Survey

Land Use-Land Cover 1:250,000

0

0 1

1

MILE

KILOMETER

PARMA

C RE E K

N O R T H R U P

BL A C K C R E E K

SPENCERPORT

OGDEN GATES

ROCHESTER

GREECE
Phosphorus in Surface Waters

Two forms of phosphorus are considered in this 

article—total phosphorus, which is a measure of its 

suspended and dissolved states, and orthophosphate, 

a dissolved form that is readily available for biological 

uptake.

Generally, phosphorus (as orthophosphate) is the 

limiting nutrient in freshwater aquatic systems; that is, 

once all the available phosphorus is used, plant growth 

will cease, no matter how much nitrogen is available. 

Many freshwater bodies currently are receiving inputs 

of phosphorus and nitrogen from outside sources, and 

the increasing concentrations of phosphorus allow plants 

to assimilate additional nitrogen until the phosphorus 

is depleted. Thus, if sufficient phosphorus is available, 

accelerated plant growth and algal blooms will result. 

Effects

Phosphorus-induced production of aquatic vegetation in freshwater has several detrimental effects:

• development of algal mats and decaying 

algal clumps that cause odors, discolor the 

water, and interfere with the esthetic quality 

of the pond and its recreational uses;

• extensive growth of rooted aquatic plants, 

which can interfere with aeration of the 

water and with powerboat operation;

• accumulation of dead plants and algae 

on the bottom of the pond where decomposition by microbial processes can deplete 

the oxygen from the water and result in the 

death of desirable fish species;

• clogging of water-treatment-plant filters 

by algae and aquatic plants;

• shading of submerged aquatic vegetation by 

algal blooms, which can reduce or eliminate 

photosynthesis and productivity.

Sources 

Phosphorus, like most other chemical constituents of 

streams, is transported to the stream in runoff from point 

and nonpoint sources. Common nonpoint sources are 

runoff from agricultural areas and urban or residential 

areas, while the primary point source in many watersheds 

is the discharge from sewage-treatment plants. Most of 

the phosphates (phosphorus-based compounds) that 

enter a stream directly are derived from sewage-treatment 

plants. Primary treatment of sewage effluent removes 

only 10 percent of the phosphorus, and secondary treatment removes an additional 20 percent (Smith, 1990). 

Tertiary treatment is required to remove additional 

amounts of phosphorus from the water. The amount of 

additional phosphorus that can be removed depends on 

the success of the type of treatment used, such as biological removal and chemical precipitation.

Atmospheric deposition also can be a substantial 

source of nutrients within a watershed, but the amount that 

enters streams cannot be calculated with certainty because 

other factors, such as the interaction of phosphorus with 

the soil, cannot be quantified.

Phosphorus in Northrup Creek

The primary source of phosphorus in Northrup Creek 

is the Spencerport wastewater-treatment plant. Smaller 

amounts are contributed by agricultural activities within 

the basin, water diverted from the New York State Barge 

Canal, urban runoff, septic systems, and atmospheric 

deposition.

Atmospheric deposition of total phosphorus during 

water years1 1990–98 averaged about 170 pounds per 

square mile, about 24 percent of the phosphorus load 

in the Creek. Discharge from the wastewater-treatment 

plant represented 56 percent of the phosphorus load 

before August 1995 when the Spencerport treatment 

plant began adding iron salts and, as a result, decreased 

the amount of phosphorus in the treatment-plant effluent 

by 85 percent (Monroe County Planning and Development, written commun., 1988). 

Concentrations

Median monthly concentrations of total phosphorus 

and orthophosphate in Northrup Creek are usually 

highest from late spring through early fall (fig. 2) when 

streamflow is low and provides minimal dilution. 

The application of fertilizer during these months also 

can be a contributing factor to concentrations of total 

phosphorus and orthophosphate in water.

Concentrations of chemical constituents in streams 

vary with the volume of streamflow at the time the sample 

is collected. If streamflow variability is not taken into 

consideration when data are tested for trends, it can 

produce misleading results; for example, an apparent 

upward trend in concentration could result from upward 

trends in flow rather than an actual increase in concentration. The concentration variability that results from 

differences in flow can be minimized through statistical 

procedures that produce “flow-adjusted” concentrations 

that then can be tested for trends.

Trend testing of flow-adjusted concentrations 

of orthophosphate in Northrup Creek for water years 

1990–98 indicate an overall downward trend, although 

a short-term variability of direction and magnitude within 

the trend is indicated—an upward trend occurs from 

October 1989 until mid-1992 and in 1994 and 1998

(fig. 3, next page), and a downward trend occurs from 

mid-1992 through September 1993 and during 1995–97. 

1

Water year: the 12-month period from October 1 through 

September 30 of the following year. Thus, the water year ending 

on September 30, 1996, is the 1996 water year.

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

MEDIAN TOTAL PHOSPHORUS

 CONCENTRATION, IN 

MILLIGRAMS PER LITER

MEDIAN ORTHOPHOSPHATE

Figure 2. Median monthly concentrations of phosphorus 

in Northrup Creek, Monroe County, N.Y., water years 

1990-1998. (Location is shown in fig. 1.) 
1990 1991 1992 1993 1994 1995 1996 1997 1998 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

STATISTICAL SMOOTHING

FLOW-ADJUSTED CONCENTRATION 

OF ORTHOPHOSPHATE

OVERALL TREND IN FLOW- ADJUSTED

CONCENTRATION

Figure 3. Overall trend and statistical smoothing of flowadjusted concentrations of orthophosphate in Northrup 

Creek, Monroe County, N.Y., for water years 1990-98. 

The flow-adjusted phosphorus concentrations for the 

periods before and after October 1995, when phosphorus 

controls at the Spencerport wastewater-treatment plant 

were implemented, show no detectable trends for 

either period. The mean flow-adjusted concentrations 

of orthophosphate after October 1995 were about 

30 percent lower than those before; those for total 

phosphorus were about 24 percent lower than

those before.

Loads

Total phosphorus loads at the Northrup Creek 

monitoring site during water years 1990–98 averaged 

8,350 lb/yr (pounds per year), and orthophosphate loads 

averaged 3,430 lb/yr. The months with the largest 

loads of total phosphorus were January and April, which 

generally are the months with the greatest volume of 

streamflow. Orthophosphate loads showed less monthly 

variation, with loads fairly evenly distributed throughout 

the year (fig. 4).

Total phosphorus loads at the Northrup Creek site 

averaged 23.4 lb/d (pounds per day) in the 5 years 

before implementation of the phosphorus-control 

measures and 22.0 lb/d in the 3 years thereafter. 

The corresponding orthophosphate loads averaged 

11.0 lb/d before phosphorus-control measures 

and 6.22 lb/d thereafter. The apparent lack of significant improvement for total phosphorus is a result of 

the considerably higher daily mean streamflow for the 

3 years that followed phosphorus control than those in 

the preceding period. Total phosphorus, which adheres 

to suspended particulate matter, generally shows a 

positive correlation with streamflow; that is, concentration increases as flow increases. Concentration of 

orthophosphate, which is in the dissolved phase, usually 

is less affected by streamflow volume. Thus, the daily 

loads of orthophosphate decreased markedly after 

the implementation of phosphorus controls, despite the 

greater-than-average flows.

Monthly orthophosphate loads showed an overall 

decline of about 8 percent per year for water years 

1990–98, but neither the monthly loads of total phosphorus nor those of orthophosphate show any trends 

for the 5-year period preceding the implementation of 

phosphorus controls nor for the 3-year period thereafter. 

 Phosphorus in Long Pond 

Long Pond has a surface area of about 0.75 mi2

and an average depth of about 7 ft; it is connected to 

Lake Ontario by a narrow channel (fig. 1). 

Phosphorus that is attached to sediment particles 

entering Long Pond from Northrup Creek accumulate 

in the sediments and can be recycled slowly into the 

water column (through chemical reaction) or released 

more rapidly when these sediments are disturbed, such as 

during a storm or flood. The phosphorus stored in bottom 

sediments, therefore, can cause water contamination for 

many years even though sources of phosphorus have 

been identified and controlled.

Annual phosphorus loads in Northrup Creek were 

used to calculate the potential phosphorus loading (an 

estimate of the available phosphorus, in milligrams per 

cubic meter) in Long Pond. The results indicate that 

1990 1991 1992 1993 1994 1995 1996 1997 1998

0

3,000

500

1,000

1,500

2,000

2,500

1

100

2

3

4

5

7

10

20

30

40

50

70

Figure 4. Monthly mean loads of total phosphorus, orthophosphate, and monthly mean streamflow 

for Northrup Creek, water years 1990-98.

ORTHOPHOSPHATE LOAD

TOTAL PHOSPHORUS LOAD

MONTHLY MEAN STREAMFLOW

MONTHLY PHOSPHORUS LOAD, IN POUNDS

STREAMFLOW, IN CUBIC FEET PER SECOND
potential phosphorus underwent a gradual increase 

in water year 1991, then a gradual decrease through 

1995 (when the control measures were implemented), 

followed by larger decreases in water years 1996 

and 1997, and a slight increase in 1998 (fig. 5).

The recent decreases in potential phosphorus in 

Long Pond, indicated by figure 5, result more from the 

high mean flows for water years 1996–98 than from 

the implementation of phosphorus controls. This is because the large flows increased the volume of water in 

Long Pond, thereby diluting the potential phosphorus 

loading (concentration). In addition to the calculation of potential phosphorus loading, measurements 

of phosphorus, chlorophyll, and dissolved oxygen are 

needed to provide a more definitive assessment of the 

improvement in eutrophic conditions in Long Pond and 

Cranberry Pond. Indications of improvement would 

be a decrease in the size and persistence of algal blooms, 

increase in the clarity of water, and a decrease in the 

odor from dead and decaying vegetation.

Conclusions

The effectiveness of wastewater treatment in 

improving the quality of eutrophic water bodies can 

be difficult to assess in the short term. Although an 

improvement in Long Pond is indicated by a decrease 

in the estimates of potential phosphorus loadings 

as calculated from phosphorus inputs from Northrup 

Creek, the estimates do not take into account variables 

that cause resuspension of phosphorus-bearing 

sediments such as wind, turbulence from boat traffic, 

and water-temperature gradients.

The phosphorus loads in Northrup Creek have 

been reduced through improved sewage treatment at the 

Spencerport wastewater-treatment plant, but phosphorus 

remaining in the sediments of the stream channel and in 

Long Pond can be resuspended and recycled for years 

after sources of phosphorus have been identified and 

controlled. The water quality of Long Pond is expected 

to improve, however, as the pond receives decreased 

phosphorus loads from Northrup Creek, the principal 

source of nutrients.

—By Donald A. Sherwood

Selected References

Makarewicz, J.C., Lewis, T.W., Brooks, Anna, and

others, 1990, Chemical analysis and nutrient loading 

of Salmon Creek, Otis Creek, Black Creek, Spencerport 

Sewage Treatment Plant, Precipitation falling in Western 

Monroe County, with a discussion on the trophic status 

of Long Pond and stress stream analysis of Northrup and 

Buttonwood Creeks: Brockport, N.Y., SUNY Brockport, 

unpublished report, 120 p.

Sherwood, D.A., 1997, Water resources of Monroe 

County, New York, water years 1989–93, part 1: U.S. Geological Survey Open-File Report 97-587, 219 p.

______in press, Water Resources of Monroe County, 

New York, water years 1989–93, part 2: U.S. Geological 

Water Resources Investigation Report 99-4084.

Smith, R.L., 1990, 4th ed., Ecology and field biology:

 New York, Harper Collins Publishers, 368 p.

Vollenweider, R.A., 1976, Advances in defining 

critical loading levels for phosphorus in lake eutrophication: 

Memorie dell’Istituto Italiano di idrobiologia 33: 53-83.

Fact Sheet FS-128-99

October 1999

POTENTIAL PHOSPHORUS,

IN MILLIGRAMS PER CUBIC METER

1990 1991 1992 1993 1994 1995 1996 1997 1998 1,000

10,000

1,500

2,000

2,500

3,000

4,000

5,000

6,000

7,000

8,000

9,000

100

1,000

150

200

250

300

400

500

600

700

800

900

TOTAL ANNUAL FLOW IN NORTHRUP CREEK

ANNUAL PHOSPHORUS LOAD IN NORTHRUP CREEK

POTENTIAL PHOSPHORUS LOAD IN LONG POND

Figure 5. Annual phosphorus load and flow in Northrup Creek, 

Monroe County, N.Y., and calculated potential phosphorus load 

in Long Pond, water years 1990-98.

TOTAL ANNUAL FLOW, IN CUBIC FEET PER SECOND

TOTAL PHOSPHORUS LOAD, IN KILOGRAMS