Phosphorus inactivation of incoming storm water to reduce algal blooms and improve water clarity in an urban lake

Figures & data

Figure 1. Morses Pond location and watershed in eastern Massachusetts.

Figure 2. Phosphorus inactivation system layout and monitoring stations at Morses Pond, MA.

Table 1. Operational data for the P inactivation system and precipitation record for Morses Pond, MA, 2008–2016.

Year	Applied Alum (L)	Applied Aluminate (L)	Aluminum Mass Applied (kg)	# of Treatment Days	May–June Precipitation (cm)	May–August Precipitation (cm)	Notes
2008	7620	3810	1018	5	15.7	42.3	Testing and adjustment phase, most treatment in July
2009	22868	11049	2998	16	15.0	40.8	Some elevated storm flow untreated
2010	15621	7925	2104	13	15.4	36.8	Additional chemical applied after early July
2011	19050	9430	2531	14	20.3	45.1	Some equipment failures. Additional chemical applied in August in response to bloom
2012	22860	11430	3055	19	17.4	36.5	Equipment problems hampered dosing during treatment
2013	23070	10611	2944	20	34.8	48.5	Very wet June (26.7 cm), unable to treat all storm flows; continued treatment through July
	Polyaluminum chloride (L)
2014	22803		1605	12	13.9	30.0	No treatment after first week of July, first year using polyaluminum chloride
2015	30099		2119	14	15.8	26.7	Leftover chemical used in summer, but little treatment after first week of July
2016	22098		1555	13	11.8	18.4	Only a little over half of the chemical was used by early July, remainder by 15 August

Figure 3. Current housing for pumps, valves, and instrumentation for the P inactivation system at Morses Pond, MA.

Table 2. Statistical characterization of TP in Bogle Brook and Boulder Brook inflows from 2008 to 2016.

	Total phosphorus concentration (mg/L)
Inlet	Mean	Median	Max	Min	n
Bogle Brook	0.128	0.051	1.029	0.013	40
Boulder Brook	0.129	0.065	1.385	0.027	38

Table 3. Phosphorus concentration for pre-treatment, early summer, and late summer periods in 3 zones of Morses Pond, MA, during each year from 2008 to 2016, with observations on algae and plant abundance.

Year	Location	Pre-application TP (mg/L)	Early summer TP (mg/L)	Late summer TP (mg/L)	Algae observations
2008	North basin	0.028	0.018	0.013	Mats observed, some cloudiness
	Transition zone	0.031	0.022	0.014	Some cloudiness, brownish color
	Swimming area	0.021	0.012	0.012	No blooms reported, first year without copper treatment in some time
2009	North basin	0.035	0.040	0.063	Cloudy, some green algae mats
	Transition zone	0.035	0.039	0.045	Cloudy
	Swimming area	0.015	0.010	0.027	Generally clear, no blooms reported
2010	North basin	0.026	0.046	0.053	Cloudy, green algae mats evident
	Transition zone	0.028	0.021	0.032	Brownish color, minimally cloudy
	Swimming area	0.019	0.015	0.043	Generally clear, no blooms until late August (Dolichospermum)
2011	North basin	0.053	0.033	0.130	Cloudy, green algae mats evident
	Transition zone	0.048	0.029	0.095	Slightly brownish
	Swimming area	0.030	0.029	0.060	August bloom (Dolichospermum), dissipated after just a few days without treatment
2012	North basin	0.032	0.024	0.048	Very dense plant growth, associated green algae mats
	Transition zone	0.028	0.037	0.028	Brownish most of summer
	Swimming area	0.020	0.027	0.024	Had bloom in mid-July (Dolichospermum), treated with copper
2013	North basin	0.036	0.047	0.030	Water brownish, little visible algae; first year with newly dredged area within north basin
	Transition zone	No Data	0.078	0.032	Generally elevated turbidity, but much of it is not living algae
	Swimming area	0.024	0.033	0.028	Treatment lowered TP but not to target level; June flushing minimized algae biomass
2014	North basin	0.030	0.022	0.020	Dense plant growths and green algae mats outside dredged area, water fairly clear
	Transition zone	0.021	0.020	0.018	Dense plant growths, but water fairly clear
	Swimming area	0.012	0.013	0.017	Water clear; Secchi to bottom in swimming area, no blooms reported
2015	North basin	0.012	0.017	0.023	Dense plant growths and green algae mats outside dredged area, water fairly clear
	Transition zone	0.008	0.015	0.014	Dense plant growths, but water fairly clear
	Swimming area	0.005	0.005	0.014	Water clear; Secchi to bottom in swimming area, no blooms reported
2016	North basin	0.012	0.009	0.005	Very dense plant growths after mild winter, but water still clear
	Transition zone	0.019	0.016	0.005	Dense plant growths but water clear
	Swimming area	0.014	0.005	0.005	Water clear; Secchi to bottom in swimming area, no blooms reported

Figure 4. Algae biomass in Morses Pond before and after implementation of P inactivation. Each column represents the average summer biomass for the corresponding year, subdivided by major algal group. Algae data are not available for all years. Horizontal threshold lines represent potential and probable recreational impairment levels based on beach operations over many years.

Figure 5. Average TP concentration and Secchi disk transparency over time in Morses Pond, MA. Values represent the summer average for the corresponding year. Pre-treatment and 3 treatment periods are identified based on equipment and chemical changes.

Figure 6. Relationship between average summer TP concentration and Secchi disk transparency before and after P inactivation in Morses Pond, MA. Four periods are represented by different symbols, including pre-treatment (2007 and earlier), early operation (2008–2010), a period of equipment issues (2011–2013), and the period of treatment system improvements (2014–2016).