The effects of infiltration-based stormwater best management practices on the hydrology and phosphorus budget of a eutrophic urban lake

Figures & data

Figure 1. (A) Location of Como Lake in Saint Paul, MN. (B) The 721 ha watershed includes a regional park and single-family residential neighborhoods. (C) Impervious surface cover varies across the watershed.

Figure 2. Comparison of model (Baseline Scenario) and observed values for lake level (A) and water-column total P (B). Circles are observed values. The horizontal dashed line represents the ordinary high-water level. The vertical dashed line represents the date of stormwater BMP implementation in our simulation.

Table 1. Parameter values used in this model. P_i and P_S values were calibrated for this model; all other values are from Jensen et al. (2006).

Parameter	Value	Unit
Pi	0.3–0.7	mg/L
fd	0.3	unitless
tS	0	unitless
bF	0.000595	1/d
tF	0.08	unitless
bS	0.2	m/d
Ps	55	g/m^2

Figure 3. (A) Lake water column total P in the baseline scenario and in Sensitivity Analyses 1–3. The dashed line represents the date of stormwater BMP implementation in our simulations. The shaded area (2015–2016) is expanded in (B) to better depict representative differences between scenarios.

Table 2. Sensitivity analyses testing effects of central assumptions of model. Model simulation period 2000–2016.

Scenario	Description	Mean lake TP (μg L^−1)	RMSE
Baseline scenario	BMPs implemented in 2006	138.0	214.0
SA1	Infiltrated water returned as groundwater at 30 μg P/L	134.5	207.6
SA2	Unmeasured outflow attributed to evaporation rather than downstream export	144.7	224.6
SA3	Constant runoff TP concentration	139.5	217.9

Table 3. Summary of model scenarios. Mean concentrations and cumulative fluxes are calculated for the 10 yr period following BMP implementation.

Scenario	Scenario description	Effective watershed area (ha)	Turnover time (d)	Percent of water input lost by evaporation	Cumulative external P inputs (kg)	Cumulative downstream P export (kg)	Net P sedimentation (kg)	Mean lake TP (μg L)
Baseline	Existing BMPs	674	192	30.8	5288	1635	3624	145.6
Scenario A	Baseline without BMPs	751	177	28.0	5906	1867	4008	147.8
Scenario B	5 × more watershed area draining into BMP	366	324	49.3	2818	768	2026	136.2
Scenario C	Runoff TP conc. decreased by 50%	751	192	30.8	2686	1416	1249	130.3

Figure 4. Lake water column total P in the baseline scenario and in Scenarios A, B, and C. The dashed line represents the date of stormwater BMP implementation in our simulations. The shaded area (2015–2016) is expanded in (B) to better depict representative differences between scenarios.

Jensen JP, Pedersen AR, Jeppesen E, Søndergaard M. 2006. An empirical model describing the seasonal dynamics of phosphorus in 16 shallow eutrophic lakes after external loading reduction. Limnol Oceanogr. 51(1, part 2):791–800.

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