Dissolved phosphorus concentrations in Cayuga Lake system and differences from two analytical protocols

Figures & data

Figure 1. Cayuga Lake, the 11 Finger Lakes, and position in New York. Shown are 4 monitored tributaries, USGS gauges, pelagic site, lake source cooling (LSC) discharge, and shelf portion of the lake at its southern end.

Table 1. Specifications for inputs to Cayuga Lake monitored for forms of phosphorus (P); watershed areas, agricultural land use, samples analyzed according to the 2 protocols, and bioavailable fractions for the P forms as analyzed by the standard methods protocol.

				Samples		fBAP^e
Tributary/Input	USGS Gage	Watershed Area (km^2)	Land use Ag^a(%)	E^b	S^d	SRPS	SUPS	PPS	SUPS P (µg/L)^f	SRPS P (µg/L)^f
				02–13^c	2013
Fall Cr.	4234000	330.9	49%	54	97	0.96	0.75	0.13	8.7	10.8
Cayuga Inlet	4233255	240.8	56%	22	72	0.98	0.54	0.06	5.3	4.7
Salmon Cr.	423401815	233.8	68%	31	96	0.99	0.84	0.19	8.5	27.2
Six Mile Cr.	4233300	134.1	22%	56	79	0.99	0.56	0.08	4.8	10.3
LSC				48	48	1.00	0.08	0.14	2.7	8.9

^a Ag = agriculture.

^b number of samples collected and analyzed according to method (USEPA 1978).

^c for years 2002–2013.

^d number of samples collected and analyzed according to S method (Clesceri et al. 1998).

^e f_BAP – fraction of P form bioavailable, as reported by Prestigiacomo et al. (2016).

^f flow-weighted concentrations, from Prestigiacomo et al. (2016).

Table 2. Comparison of selected analytical features for 2 methodologies for measurements of the concentration of phosphorus (P).

	Method
Analytical Step	SM 4500P-E	USEPA 365.3 (1983)
1. Sample volume	50 mL	50 mL
2. Reagent addition	simultaneously, as a “mixed”	sequential additions
	reagent
3. Reagents for color determination	5 N sulfuric acid (50 mL)	11 N sulfuric acid (1 mL)
	antimony potassium tartrate	ammonium molybdate-
	solution (5 mL)	antimonypotassium tartrate
	ammonium molybdate (15 mL)	(4 mL)
	ascorbic acid (30 mL)	ascorbic acid (2 mL)
4. Colorimetric reaction time	read samples within 10–30	read sample within 5 minutes
	minutes of “mixed reagent”	of addition of ascorbic acid
	addition
5. Wavelength	880 nm	660 nm or 880 nm

Figure 2. Time series for the LSC discharge for 3 forms of phosphorus (P) for 2013, according to 2 analytical protocols, standard methods (S) protocol (subscript S), and EPA protocol (subscript E): (a) TP, (b) TDP, and (c) SRP.

Figure 3. Representations of extent of closure of forms of P in the LSC discharge from split samples for the S and E protocols as distributions of ratio values: (a) TP, (b) TDP, (c) PP, (d) SRP, (e) SUP, and (f) the ratio SRP_E:TDP_S.

Figure 4. Lake P patterns and (a) time series of monthly average TDP_S, SRP_S, and SUP_S in the upper waters of Cayuga Lake for the April-October 1999–2006 interval and 2013; vertical bar corresponds to ±1 standard deviation, (b) comparison of TDP, SUP, and SRP concentrations in early April (during turnover) 2013 for deep wake Water and from the S and E protocols and upper lake water from S protocol.

Figure 5. Phosphorus (P) concentration versus stream flow (Q) relationships for Fall Creek that compare results from the 2 analytical protocols: (a) dependencies of TP_S and TP_E on Q, (b) dependencies of SRP_S and SRP_E on Q, and (c) dependencies of TDP_S and SRP_E on Q.

Clesceri LS, Greenberg AE, Eaton AD. 1998. Standard methods for the examination of water and wastewater. Washington (DC): American Public Health Association, American Water Works Association, Water Environment Federation.

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Prestigiacomo AR, Effler SW, Matthews DA, Auer MT, Downer BE, Kuczynski A, Walter MT. 2016. Apportionment of bioavailable phosphorus loads entering Cayuga Lake, New York. J Am Wat Resour Assoc. 52:31–47.

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