Sediment aluminum:phosphorus binding ratios and internal phosphorus loading characteristics 12 years after aluminum sulfate application to Lake McCarrons, Minnesota

Figures & data

Figure 1. Sediment core station locations in Lake McCarrons, Minnesota.

Table 1. Sediment physical-textural characteristics of the upper 5-cm sediment layer at various stations in Lake McCarrons, Minnesota. Station numbers are generally ordered from west to east (i.e., low to high numbers, 1 = west, 6 = east).

Station	Depth (m)	Longitude	Latitude	Moisture Content (%)	Wet Bulk Density (g/cm^3)	Dry Bulk Density (g/cm^3)	Organic Matter (%)
1	7.6	−93.1164	44.99918	84.8	1.083	0.167	17.6
2	16.8	−93.1145	44.99908	94.1	1.029	0.061	23.6
3	10.4	−93.1122	44.99908	95.3	1.022	0.048	25.2
4	11.0	−93.1134	44.99705	89.5	1.054	0.112	21.0
5	17.4	−93.1118	44.99777	94.8	1.023	0.053	29.2
6	10.7	−93.1098	44.99668	95.1	1.022	0.048	28.6

Figure 2. Vertical variations in sediment aluminum (Al) concentration measured at various stations in 2016. Vertical dashed lines represent background Al concentrations. Arrows denote the general location of added Al.

Table 2. Background-corrected concentrations of added aluminum (Al) and adsorbed aluminum-bound phosphorus (Al-bound P) at various stations in Lake McCarrons, Minnesota. Station numbers are generally ordered from west to east (i.e., low to high numbers, 1 = west, 6 = east). Background-corrected concentrations were calculated by subtraction (i.e., concentration-background concentration, see Fig. 2). ND = not detected. The added Al percentage is based on 77 g/m² added in 2004.

Station	Depth	Added Al		Al-bound P	Al:P binding ratio
	(m)	(g/m^2)	(%)	(g/m^2)	(mass)	(molar)
1	7.6	ND	ND	ND	ND	ND
2	16.8	10.5	14	0.88	12.0	13.7
3	10.4	26.5	34	1.92	13.8	15.8
4	11.0	15.9	21	1.84	8.6	9.9
5	17.4	75.5	98	3.04	24.9	28.5
6	10.7	139.1	181	4.62	30.1	34.6

Figure 3. Vertical variations in sediment moisture content (upper panels), solids content, and wet bulk density (lower panels) for St 2 (left panels), St 5 (middle panels), and St 6 (right panels) in 2016.

Figure 4. Vertical variations in redox-P (i.e., the sum of the loosely-bound P and iron-bound P fractions) and aluminum-bound P concentrations measured at various stations in 2016.

Figure 5. A comparison of relationships between sediment aluminum and aluminum-bound phosphorus (P, upper panels), the molar aluminum:aluminum-bound P (Al:P) binding ratio (middle panels), and the molar P:Al ratio (lower panels) for Lake McCarrons sediments (left) and other lakes (right, Egemose et al. 2013, Huser 2012, Huser et al. 2011, Rydin and Welch 1999, Rydin et al. 2000).

Figure 6. Variations in redox-P (i.e., the sum of the loosely-bound P and iron-bound P fractions) in the surface sediment (upper panels) and predicted (Nürnberg 1988) and measured anaerobic diffusive P flux at various stations in Lake McCarrons.

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