Table 2. Atmospheric and tributary loading of N, P and SO₄ to Flathead Lake.

Average daily loading of N, P and SO₄ (g ha⁻¹ d⁻¹ ± 1 SD) to Flathead Lake from an atmospheric deposition collector for water years during the period 1982–2004 (excluding 1983 and 1984; NH₄ and SO₄ data unavailable in 1982) and from the tributaries for the same period (excluding 1983, 1984, 2001, 2002; TN, NH₄ and SRP unavailable in 1982; NH₄ unavailable 1992, 1993, 1998–2000). Tributary loads were apportioned relative to the lake surface area for comparison to deposition estimates. Bioavailable-P (BioP) in atmospheric deposition and tributary loads is also shown (see methods). Included are the dissolved inorganic and total molar N:P ratios.

	NH4–N	NO2/3–N	TN	SRP	TP	BioP	SO4	DIN:DIP	TN:TP
	(g ha−1 d−1 ± 1 SD)							(Molar ratio)
Atmospheric
Mean	4.9 ± 2.7	2.7 ± 0.5	9.2 ± 3.5	0.32 ± 0.28	0.8 ± 0.9	0.65 ± 0.71	7.5 ± 1.7	124 ± 126	39 ± 20
Range	1.6–12	1.7–3.6	5.7–18	0.03–0.89	0.2–4.2	0.12–3.2	4.8–12	14–492	8–89
n (years)	17	21	21	21	21	21	19	17	21
Tributaries
Mean	6.3 ± 3.0	40 ± 13	102 ± 69	0.90 ± 0.35	21 ± 20	6.9 ± 3.2		113 ± 25	17 ± 9
Range	3.1–12	25–68	49–330	0.45–1.7	4.4–76	3.8–14		79–154	4–35
n (years)	11	19	18	18	19	19		11	18