Nutrient delivery to Lake Winnipeg from the Red—Assiniboine River Basin – A binational application of the SPARROW model

Figures & data

Figure 1. Spatial domain of the Red—Assiniboine River Basin (RARB) SPARROW total phosphorus (TP) and total nitrogen (TN) models.

Table 1. Drainage areas and major land coverages for the areal extent of Red—Assiniboine River Basin (RARB) SPARROW models.

Major basin	Drainage area			Forest (%)	Wetland (%)	Agriculture^a (%)	Urban (%)	Open water (%)
	Total (km^2)	Canada (%)	US (%)
Red River	122,730	21.2	78.8	7.8	9.9	74.1	4.5	3.8
Souris River	54,555	64.0	36.0	4.5	3.2	87.5	2.5	2.3
Upper Assiniboine River	42,614	100.0		16.7	3.8	75.2	1.7	2.6
Qu’Appelle River^b	50,900	100.0		11.6	0.3	86.4	0.6	0.8
RARB	219,899	47.1	52.9	8.7	7.0	77.7	3.4	3.2

^a All land used for agricultural production including grassland and pasture.

^b Qu’Appelle included as a point source contribution and in the calculation of yields only.

Figure 2. Major land coverages of the Red—Assiniboine River Basin (RARB) and the locations of calibration sites. Land cover data for Canada circa 2000 is derived from Natural Resources Canada Geobase, and for the US it is from 2001 National Land Cover Data. Red N (nitrogen) circles and orange P (phosphorus) circles show which parameters were sampled from particular water quality stations.

Table 2. Summary of Red—Assiniboine River Basin (RARB) calibration results for total phosphorus (TP) and total nitrogen (TN) SPARROW models. RMSE is root-mean square error.

Variable	Parameter units	Coefficient units	Model coefficient value	90% confidence interval		P value
				Low	High
Total phosphorus model
Sources
Agricultural inputs	kg/yr	Fraction, dimensionless	0.011	0.004	0.017	0.0031
Wastewater treatment plants^a	kg/yr	Fraction, dimensionless	1.000
Forests and wetlands	km^2	kg/km^2/yr	6.016	−0.558	12.032	0.0328
Stream channels (0.03–0.21 m^3/s)	m	kg/km/yr	0.070	−0.009	0.140	0.0402
Qu’Appelle River^b	kg/yr	Fraction	1.000
Land-to-water delivery
Precipitation	mm/yr	mm/yr	0.009	0.006	0.012	< 0.0001
Decay
Reservoir loss	m/yr	m/yr	5.734	−3.027	9.338	0.0289
Model statistics (N = 104)
RMSE		0.489
Adjusted R^2		0.915
Yield R^2		0.815
Total nitrogen model
Sources
Agricultural inputs	kg/yr	Fraction, dimensionless	0.032	0.006	0.047	0.0045
Wastewater treatment plants^a	kg/yr	Fraction, dimensionless	1.000
Atmospheric deposition^c	kg/yr	Fraction, dimensionless	0.032
Qu’Appelle River^bLand-to-water delivery	kg/yr	Fraction	1.000
Precipitation	mm/yr	mm/yr	0.014	0.010	0.016	< 0.0001
Air temperature	C	C	−0.573	−0.719	−0.350	< 0.0001
Decay
Streams (continuous decay)^d	m/d	m/d	0.019	−0.029	0.051	0.39
Reservoir loss^d	m/yr	m/yr	1.809	−1.118	3.445	0.15
Model statistics (N = 75)
RMSE		0.440
Adjusted R^2		0.930
Yield R^2		0.876

^a Wastewater treatment plants, as estimated by population, were directly input into the model.

^b Nutrient loads from the Qu’Appelle River were input into the models as point sources with 76 800 kg/yr of TP and 473 000 kg/yr of TN, both estimated in this study.

^c Atmospheric deposition was highly correlated with agriculture areas and therefore was assumed to be exported at a similar rate as agricultural inputs.

^d Decay terms that were not statistically significant at p ≤ 0.05, but they were still estimated by the model.

Figure 3. Predictability of Red—Assiniboine River Basin SPARROW models for (a) phosphorus (TP) and (b) nitrogen (TN). Predictability is the difference between observed and predicted loads expressed in units of log 2, which represents the number of doublings of the measured loads at each site (i.e. over-predicted – negative values, upward pointing triangles; under-predicted – positive values, downward pointing triangles).

Table 3. Estimated annual loads and yields of total phosphorus (TP) and total nitrogen (TN) from Red—Assiniboine River Basin (RARB) SPARROW models, normalized to 2002. MT is metric tonnes. (Note: loads do not necessarily add up due to rounding.)

Geographic unit	Aggregated (non-decayed) TP load (MT/yr)	Delivered aggregated TP load (MT/yr)	Aggregated TP yield (kg/km^2)	Delivered aggregated TP yield (kg/km^2)	TP delivery fraction^a	Aggregated (non-decayed) TN load (MT/yr)	Delivered Aggregated TN load (MT/yr)	Aggregated TN yield (kg/km^2)	Delivered aggregated TN yield (kg/km^2)	TN delivery fraction^a
Major (river) basin
Red	5,290	4,460	43.1	36.4	0.84	42,900	30,100	350.0	245.0	0.70
Souris	559	171	10.3	3.1	0.31	2,870	840	52.7	15.4	0.29
Upper Assiniboine^b	787	329	16.7	7.0	0.42	6,880	2,340	152.0	51.0	0.34
Province/state
Manitoba	2,190	1,780	36.6	29.8	0.81	18,500	13,300	308.0	221.0	0.72
North Dakota	1,950	1,570	28.1	22.7	0.81	14,600	9,010	210.0	130.0	0.62
Minnesota	1,870	1,450	41.2	31.8	0.77	15,500	10,100	341.0	221.0	0.65
Saskatchewan	546	121	12.5	2.8	0.22	3,820	803	87.5	18.4	0.21
South Dakota	80	42	58.4	30.3	0.52	327	117	238.0	85.1	0.36
Country
Canada	2,730	1,900	26.4	18.4	0.70	22,300	14,100	215.0	136.0	0.63
US	3,900	3,060	33.6	26.3	0.78	30,400	19,200	261.0	165.0	0.63
RARB	6,640	4,970	30.2	22.6	0.75	52,700	33,300	240.0	151.0	0.63

^a Ratio of delivered to non-decayed load.

^b Loads and yields for Upper Assiniboine River Basin include the Qu’Appelle River, included as a point source contribution.

Figure 4. Delivered aggregated yield maps of the Red—Assiniboine Basin River (RARB) by sub-sub-drainage area (SSDA) or Hydrologic Unit Code 8 (HUC8) for (a) phosphorus (TP) and (b) nitrogen (TN).

Figure 5. Delivered aggregated loads (and delivered aggregated yields) to Lake Winnipeg by geographic unit of the Red—Assiniboine River Basin (RARB) for (a) phosphorus (TP) and (b) nitrogen (TN). Loads are subdivided by source and shown as percentages.