Timing and location of sampling

The primary sampling site was location 1 (gaging station USGS 04234000), which is about 6 km upstream from the point where Fall Creek empties into Cayuga Lake. The samples were taken from a bridge just downstream from a low, abandoned dam drained through a notch in the dam. This insured well mixed samples. The stream is incised into the local bedrock just above the control section of the gaging station. These conditions plus the continuous flow measurements make this an excellent location for sampling. Sampling times were based on flow with several samples per day during high flow periods and every 1 to 3 weeks during low flow periods during all seasons.

Other locations were chosen on the basis of human activities in the watershed, size, easy access for sampling and unrestricted flow below the sample location.

More details can be found in the following references:

Porter, Keith S ed. 1975. Nitrogen and phosphorus. Food production, waste and the environment. Chapter 3, pp 61-120. Ann Arbor Science Publishers. Ann Arbor MI 48106

Johnson, Arthur H. 1975. Phosphorus export from the Fall Creek watershed. Ph D thesis. Cornell University Library, Ithaca NY.

Johnson, Arthur H., David R. Bouldin, Edward A. Goyette, and Anne Hedges. 1976. Phosphorus loss by stream transport from a rural watershed: Quantities, processes and sources. J. Environ Quality. 5:148-157

Stream flow

All flow values derived from USGS data, for sites specified below.

Location 1, Sampling site from bridge at intersection of Pleasant Grove Road and Forest Home Drive, about 100 meters upstream from gaging station USGS 04234000, Fall Creek near Ithaca NY. Lat_N 42.45277778, long_W -76.47055556. Records from 1926 through present (June 15, 2007)

Location 16. Virgil Creek at Johnson Street, Freeville. USGS 04233700 Lat_N 42.50583333, long_W -76.35055556. Daily Records 1973-08-01 to1975-10-31.

Location 15. Bridge on rt 366 over Fall Creek in Freeville. Staff Gage USGS 04233648, Lat_N 42.51416667. Long_W -76.34722222. Reading taken when water samples were taken.

Location 6.USGS 042336787. Dryden lake Inlet nr Harford NY Lat_N 42.44694444 Long_W -76.24555556 Daily discharge 1973-09-01 to 1974-11-30.

Sediment / suspended solids

Suspended solids were measured in 200 ml sub-samples after centrifugation at 1500x gravity for 30 minutes in an International Model K centrifuge. If the suspended load was greater than about 50 mg/liter, most of the supernatant was decanted and the sediment was transferred to a tared 50 ml beaker using distilled water. Samples were dried at 105°C and weighed. If suspended load was less than 50 mg/liter, most of the supernatant was decanted and the remaining sediment and solution was separated by filtration through a 1.0 micron Nuclepore filter. The filter with sample was dried in a desiccator charged with desiccant and weighed. A tare weight of filters of 5.5-5.9 mg was determined from weighing several oven-dried filters from each batch.

pH

Determined with Glass electrode- pH meter. Always determined in laboratory, usually within 1 to 3 days of storage but sometimes on samples stored in refrigerator for several days. Equilibration of electrode with samples pH 8 or above was a source of major uncertainty (+/- 0.1) and effects of storage added to this so that in general pH was on the order of +/- 0.2 units with high pH samples. With pH below about 6.5, uncertainties are lower.

Alkalinity

Alkalinity was determined by titration of water sample to endpoint of pH ~ 4.5 with either methyl orange indicator or pH meter, usually determined with in about 1 to 3 days of storage but sometimes on samples stored in refrigerator for several days. Storage was found not to change alkalinity with in range of about +/- 0.1 milliequivalents per liter

References:

American Public Health Association. 1971. Standard Methods for the examination of water and wastewater. 13th ed. 1015 18th Street, N.W., Washington DC.20036

Association of Official Analytical Chemists. 1990. Official Methods of Analysis. 15th ed. Association of Official Analytical Chemist, Inc. 2200 Wilson Boulevard, Arlington VA. 22201. Call no s587.a71, 5th ed 1990 v.1

Cations (calcium, magnesium, potassium, sodium)

During the period 1972 through 1980 a Jarrel Ashe-Perkin Elmer multielement atomic absorption instrument was used for the determination. Post 1980 the determination was with a Jarrell Ashe multielement ICP.

Anions (chloride, nitrate, sulfate) - 1992-1995

These substances were determined with a Dionex 4000i high pressure liquid chromatography unit fitted with a AG4A guard column and AS4A analytical column. Eluent was 1.8 mM Na2CO3 /1.7 mM NaHCO3 with conductivity detector. Samples were filtered through 0.2 micron filter.

Chloride 1972-1992

Except for period 1992 through 1995 Cl was determined with a Buchler Instruments digital chloridometer. This is a dedicated coulometric titrator for determination of Cl.

Nitrate and ammonium

During 1972-1992 NO3 and NH4 were determined by a steam distillation procedure developed for soil extracts. (J.M.Bremner Inorganic forms of nitrogen. In Black,C.A. 1965 ed. Methods of soil analysis part 2. Agronomy 9:1179. American Society of Agronomy. Madison WI). In this procedure the solution is made alkaline with Mg hydroxide which increases pH enough so that the ammonium N is rapidly volatilized by steam distillation. The steam is condensed in a cold water condenser and the condensate and NH4-N are collected in a boric acid buffer and titrated with standard acid. Next Devardas alloy is added and the NO3 and NO2 are converted to NH4 and determined as above. This procedure limits hydrolysis of organic forms of N because the pH is not excessively high and the steam distillation strips the NH4-N in 4 to 5 minutes.

Phosphorus, molybdate reactive phosphorus (MRP), total dissolved phosphorus (TDP) and particulate phosphorus

MRP

All samples were centrifuged at 35,000x gravity for 30 minutes in a Sorvall SS-1 or RC 2-B centrifuge in polypropylene or polycarbonate tubes. Preparation was carried out within a few hours after collection. Johnson et al. (1975) demonstrated that centrifuging is equivalent to filtration through 0.2 micron filters.

Centrifuged samples were routinely analyzed for MRP using the method of Wright (1959) with slight modifications. The procedure entails formation of the heteropoly acid with ammonium molybdate, extraction of the complex into isobutanol to effect about a three-fold concentration, and subsequent reduction to molybdenum blue with stannous chloride. Details of this procedure are given below.

Reagents

1. Isobutanol (2-methyl-l-propanol)

2. HC1, concentrated reagent, sp. gr. 1.18.

3. Molybdate reagent. Dissolve 150 g. (NH4)6MO7O24.4H2O in concentrated HC1 and make to 1 liter with concentrated HCl.

4. Concentrated SnCl2 solution. Dissolve 20 g SnCl.2H2O in 50 ml of concentrated HC1. Store in a brown glass stoppered bottle.

5- Dilute SnCl2 solution. Mix together 1 ml of concentrated SnCl2 solution, 10 ml of concentrated HC1 and 100 ml of absolute ethanol.

Place a 35 ml aliquot of centrifuged sample in a 25 X 100 mm test tube that has a teflon lined, screw cap. Add 2.2 ml of concentrated HC1 and mix. Add 12.8 ml of isobutanol, then 2.2 ml of molybdate reagent. Shake end over end for one minute and allow the phases to separate.

Pipette 7.5 ml of the isobutanol into a suitable container and add 0.5 ml of dilute SnCl2 solution. The SnCl2 solution must be mixed fresh, and is stable for only 10-15 minutes. Mix well and allow color to develop for 30 minutes. The color is stable for at least 20 hours. Measure transmittance at 675 nanometers in a cell with a 5 cm path length, using pure isobutanol as a blank and carrying standards through the procedure. The method is most useful in the range 2-120 microgram P per liter. Addition of HC1 prior to the addition of molybdate reagent is to prevent formation of molybdosilic acid, and the procedure will tolerate Si up to about 50 ppm.

Wright's procedure was compared to an ascorbic acid-molybdenum blue method (Robarge, 1971) which is essentially the single reagent method of Murphy and Riley (1962). The method of Robarge extracts the molybdenum blue complex into isobutanol to concentrate the color. Transmittance is measured at 805 nm using a 5 cm pathlength. A comparison of 21 samples in the range 0-115 microgram P/liter indicated no significant difference between the two methods at the 5 percent level.

The analytical procedure may be expedited somewhat by carrying out Wright's method through the extraction step and storing the isobutanol phase which may then be kept for at least a week prior to reduction and colorimetric analysis. There are slight day to day changes in transmittance upon aging, but if standards used to determine the standard curve have been carried through the storage period, accurate results are obtained. The first few steps are not time consuming if this method is facilitated by the use of automatic pipettes and calibrated test tubes.

TDP ANALYSIS

After centrifugation at 35»000x gravity for 30 minutes, 10 ml aliquots of supernatant were transferred to 15 x 150 mm test tubes and covered. Samples were generally stored at room temperature for one day to three -weeks. Hydrolysis of organic and condensed phosphates was carried out in the same test tubes using the persulfate procedure below.

Reagents

Potassium persulfate solution. Dissolve 17.5 grams of K2 S2 O8 in 500 ml of H2O. To 10 ml of samples and standards add 2.5 ml of potassium persulfate solution. Place covered test tubes in an oven warmed to 95°C for two hours. After cooling, make up to 10 ml with H2O. Subsequent analysis for dissolved phosphate was carried out using the MRP procedure.

REFERENCES FOR MRP/ TDP

Menzel, D. W., and N. Corwin, The measurement of total phosphorus in sea-water based on the liberation of organically bound fractions by persulfate oxidation. Limnol. and Oceanogr., 10(2), 280-282, 1965.

Methods for Chemical Analysis of Wastes, Environmental Protection Agency, 1971.

Murphy, J., and J. P. Riley, A modified single solution method for the determination of phosphate in natural waters. Anal. Chem. Acta. , 27, 31-36, 1962.

Robarge, W. P., Release of Phosphate by Soils and Sediments, M. S. thesis, Cornell University, Ithaca, N. Y,, 1971-

Standard Methods for the Examination of Water and Wastewater, American Waterworks Association, Water Pollution Control Federation, 13th edition, 1971.

Wright, B. C., Investigations of phosphate reaction products in acid soils by the application of solubility criteria, Ph.D. thesis, Cornell University, Ithaca, N. Y., 1959-

Phosphorus in sediment

After weighing, selected sediment samples were analyzed for total P content using the procedure described below. Sediment samples on Nuclepore filters were transferred filter and all to a 50 ml beaker for analysis. Processing of oven dried filters indicated that no phosphorus was present.

Reagents

1. HNO3 Concentrated reagent grade. Specific gravity 1.1+21.

2. HC1. Concentrated reagent grade, sp. gr. l.l8.

3. Mg(NO3)2 solution. Dissolve 102.56 grams of Mg(NO3)2 .6 H2 O in H2 O and make to 1 liter with H 2 O.

Separate sediments into three classes:

1/ 0-10 mg

2/ 10-50 mg

3/ 50-200 mg

Add 1 ml of Mg(NO3)3 solution and 1 ml of HNO3 to each beaker. Evaporate to dryness on a hot plate, then place in a cold muffle furnace.

Gradually raise the temperature to 550° C (2-3 hours) and leave at 550° for one hour. Let cool overnight. Remove from muffle and add:

10 ml concentrated HC1 to 0-10 mg samples

20 ml concentrated HC1 to 10-200 mg samples

Using watch glass covers, heat for 1/2 hour. For 0-10 and 10-50 mg samples, transfer 1 ml aliquot to a 25x200 mm screw top test tube, bring to 36 ml with H20 and analyze using Wright's procedure using 1.2 instead of 2.2 ml of HC1. For 50-200 mg samples, transfer contents of the beaker to a 250 ml volumetric flask and dilute to volume. Analyze by Wright's procedure adding 1.8 instead of 2.2 ml of HC1. Blanks and standards should be carried through the procedure.

Johnson, Arthur H, David .R. Bouldin, Gary W. Hergert. 1975. Some observations concerning preparation and storage of stream samples for dissolved inorganic phosphorus. Water Resources Research. 11:559-562.

Porter, Keith S ed. 1975. Nitrogen and phosphorus. Food production, waste and the environment. Chapter 3, pp 61-120. Ann Arbor Science Publishers. Ann Arbor MI 48106

Determination of watershed areas.

Watershed areas are listed in a supplementary data table. Watershed areas were determined using ArcGIS 9.2 with the hydrologic modeling extension. 10-m resolution digital elevation model (DEM) data were obtained from the Cornell University Geospatial Information Repository (http://cugir.mannlib.cornell.edu/) and mosaicked to form a single, seamless DEM. Elevation "sinks" were identified, and the filled DEMs were used to create flow direction and flow accumulation rasters. Pour points were digitized manually because the sampling location coordinates were not usually perfectly aligned with the stream channels visible on the flow accumulation raster. The hydrologic modeling extension was used to create a watershed raster for each subwatershed, which was then converted to a shapefile in order to calculate watershed area. Area was calculated using the ArcGIS field calculator and the VBA code suggested in the ArcGIS desktop help. Areas were then converted from square meters to square kilometers.