A newly developed injection method for aluminum treatment in eutrophic lakes: Effects on water quality and phosphorus binding efficiency

Figures & data

Table 1. Background information including morphology and coring locations for lakes Flaten and Långsjön.

	Flaten	Långsjön
Surface area (ha)	63	29
Mean depth (m)	7.4	2.2
Maximum depth (m)	13.6	3.3
Watershed area (ha)	403	243
Residence time (y)	4	0.4
Mean Al dose (g Al/m^2)	61	75
Treatment date (yr)	2000	2006
Core depths (m)	8.4(F3), 11.6(F2), 12.9(F1)	2.0(L1), 2.7(L2), 3.0(L3)

Figure 1. Concentrations (dry weight) of aluminum (Al) and Al-bound P (P_Al) in (a–c) cores F1–F3, respectively, collected from Lake Flaten. Short- and long-dashed lines represent background concentrations for P_Al and Al, respectively.

Table 2. Sediment chemical data and Al:P_Al ratios for lakes Flaten and Långsjön. Al recovered based on only the amount of Al injected in the sediment (only Lake Flaten received partial water application of Al) is shown in parenthesis.

Lake	Core	Al dose (g/m^2)	Al recovered (g/m^2)	Al recovered (%)	PAl (g/m^2)	Al:PAl (g/m^2)
Flaten	F1	70	51.7	74 (98)	5.0	10.4
Flaten	F2	70	29.1	42 (55)	3.3	8.9
Flaten	F3	40	9.0	23 (30)	0.7	12.4
Långsjön	L3	75	71	96	4.7	15.9

Figure 2. (a) Concentrations (dry weight) of aluminum (Al) and Al-bound P (P_Al) in core L3 and (b) P_Al for all 3 cores (L1–L3) collected from Lake Långsjön. Short- and long-dashed vertical lines represent background concentrations for P_Al and Al, respectively (a). The horizontal line indicates separation of the 1968 Al treatment and the more recent treatment (above the line in (a)).

Table 3. Differences in mobile sediment P content pre- and post-treatment. Sediment was collected the year before treatment in both lakes Flaten (1999) and Långsjön (2005).

		Mobile P (mg/g)
Lake	Location	Pre	Post	P-value
Flaten	F1	0.208	0.123	<0.05
	F2	0.203	0.143	<0.05
	F3	0.134	0.055	<0.01
Långsjön	L1	0.210	0.110	<0.05
	L2	0.188	0.147	<0.05
	L3	0.139	0.147	NS

Table 4. Dose, total amount of formed P_Al, and treatment costs for lakes Flaten and Långsjön compared with lakes treated with surface application. An 8.5:1 exchange rate was used to convert Swedish kronor to US dollars (US$).

	Area (ha)	Treated area (ha)	Dose Al (g/m^2)	PAl formed (kg)	Total cost (thousands US$)	Cost per kg PAl formed (US$)
Flaten^a	63	40	61	3660	353	152
Långsjön^b	29	29	75	1450	388	268
Harriet^c	139	45	32	7670	136	18
Cedar^d	70	60	27	1929	218	113
Calhoun^d	180	130	42	10920	241	22
Isles^d	44	26	18	955	109	114

^a Värnhed (2005),

^b Värnhed (2009),

^c Huser (2017), and

^d Huser et al. (2016c).

Table 5. Summer means (Jun–Sep) for water quality and chemistry pre- and post-treatment (1995–2015) in lakes Långsjön and Flaten. Data for year of treatment (2000 for Flaten and 2006 for Långsjön) were not included in the averages.

Lake	Treatment period	TP	Chl-a	Secchi depth	pH
Flaten	Pre	23.3	8.1	3.8	8.5
	Post	8.6	2.9	6.4	8.3
Långsjön	Pre	115	78.6	0.8	8.9
	Post	37.3	21.5	1.5	8.1

Figure 3. Changes in nutrient-related water quality variables (growing season means Jun–Sep) after Al injection treatment in Lake Flaten: (a) TP, (b) Chl-a, and (c) Secchi depth. Dashed and solid lines in the box plots represent means and medians, respectively.

Figure 4. Changes in nutrient-related water quality variables (growing season means Jun–Sep) after Al injection treatment in Lake Långsjön: (a) TP, (b) Chl-a, and (c) Secchi depth. Dashed and solid lines in the box plots represent means and medians, respectively.

Figure 5. Mean growing season pre- and post-treatment concentrations for TP in the bottom waters of lakes (a) Långsjön and (b) Flaten. Dashed and solid lines in the box plots represent means and medians, respectively.

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Värnhed B. 2009. Långsjön – reduction of internal phosphorus loading though aluminum treatment of bottom sediment. Stockholm Vatten report. Swedish.

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