A combined watershed–water quality modeling analysis of the Lake Waco reservoir: II. Watershed and reservoir management options and outcomes

Figures & data

Figure 1 Phosphorus and nitrogen predicted by the SWAT model for the inflows into Lake Waco. The scenarios were determined ad hoc as possible alternative watershed conditions.

Figure 2 Dissolved oxygen values (mg/L) predicted by the CE-Qual-W2 model (baseline) compared with observed data from TIAER. Averages and standard deviation of surface values (at 1 m depth) are shown for Lake Waco reservoir.

Table 1 Summary data for the CE-Qual-W2 scenario simulations. Percentages of simulation days that achieve target values are shown. These target values for the reservoir included (1) chlorophyll-α concentrations <20 μg/L, (2) TP levels <0.05 mg/L, and (3) TN:TP ratio >10. The * indicates a significant different value (P < 0.05) for a scenario as compared with the baseline simulations based on the Mann-Whitney U-test.

	Mean Values and Percentage (%) of Days that Achieve Listed Target Values
	Chl- a (20 μ g/L)		TP (0.05 mg/L)		TN:TP ( > 10)
Scenarios	μ g/L	%	mg/L	%	mg/L	%
Observed	19.9	49.0	0.12	5.9	9.5	35.2
Baseline (Predicted without management)	19.8	58.5	0.13	5.4	6.8	2.9
Phosphorus inactivation treatment (p-inact)	12.3	89.0	0.08	9.5	9.4	24.7
Increased phytoplanktivory (plank)	13.0	81.3	0.11	5.4	6.7	3.1
Removal of all phosphorus and nitrogen for the urban watershed within Waco (urb)	14.1	77.6	0.11	5.4	6.8	3.1
Addition of new wetlands (w2)	15.9	76.1	0.11	5.4	7.0	8.0
Removal of 50% manure from the North Bosque diaries (man)	13.5	80.0	0.09	7.1	7.5	6.7
Conversion of all agricultural land to rangeland (ag-man)	6.9*	100.0	0.03	95.6	8.6	16.8
Reduction in orthophosphorus concentration in the North Bosque by 30% (p-man)	14.1	77.2	0.10	7.4	7.7	8.8
p-man+plank	11.0	92.4	0.08	9.1	9.2	23.4
p-man+plank+man	10.1	98.2	0.07	15.5	9.6	35.7

Figure 3 Chlorophyll-a values (μg/L) predicted by the CE-Qual-W2 model (baseline) compared with observed data from TIAER. Averages and standard deviation of surface values (at 1 m depth) are shown for Lake Waco reservoir.

Figure 4 Total phosphorus values (mg/L) predicted by the CE-Qual-W2 model (baseline) compared with observed data from TIAER. Averages and standard deviation for the TIAER observed data are shown.

Figure 5 Total nitrogen values (mg/L) predicted by the CE-Qual-W2 model (baseline) compared with observed data from TIAER. Averages and standard deviation for the TIAER observed data are shown.

Figure 6 Annual sediment loading (metric tonnes) predicted by the SWAT model for Lake Waco between 2001 and 2004 for baseline and the agricultural land conversion (ag-man) scenario.