Relative influence of lake age and watershed land use on trophic state and water quality of artificial lakes in Kansas

Figures & data

Figure 1 Approximate locations of the 44 Kansas study lakes. Open circles = newer lakes/unimpacted watersheds. Black circles = older lakes/unimpacted watersheds. Open triangles = newer lakes/impacted watersheds. Black triangles = older lakes/impacted watersheds.

Table 1 Pearson correlations (R) among physical and water quality features, utilizing the final candidate list of 102 lake/watershed units. Significant (P ⩽ 0.05) correlations are shaded. All data, except watershed land use (portion in cropland or urban land) and lake age, used Log₁₀ transformations to achieve normality. Watershed land use composition used a square-root transformation, while lake age did not require transformation of the data.

	Lake Age	% Cropland/Urban	Surface Area	Mean Depth	Retention Time	TP	Chl-a
Lake Age	1	−0.086	−0.247	−0.005	+0.032	+0.072	−0.006
% Cropland/Urban		1	+0.182	−0.174	−0.265	+0.593	+0.545
Surface Area			1	+0.413	+0.177	−0.051	−0.091
Mean Depth				1	+0.613	−0.563	−0.573
Retention Time					1	−0.540	−0.508
TP						1	+0.819
Chl-a							1

Table 2a Descriptive statistics for lake/watershed group “Newer Artificial Lakes in Unimpacted Watersheds.” N = 11 lake/watershed units.

Parameter	Mean	75th Percentile	Median	25th Percentile
Lake Age (years)	33	49	39	16
Cropland/Urban Land (%)	8.0	12.0	7.0	2.5
Lake Area (ha)	87.3	112.3	55.0	41.5
Mean Depth (m)	3.3	4.0	3.3	2.8
Retention Time (years)	1.08	1.31	1.06	0.89
Total Calcium (mg·L^−1)	34.5	39.8	35.1	32.9
Total Alkalinity (mg·L^−1)	105.0	115.3	101.9	90.4
Total Dissolved Solids (mg·L^−1)	141.5	162.6	137.5	117.6
Non-Algal Turbidity (m^−1)	0.49	0.60	0.49	0.36
Turbidity (NTU)	4.1	4.5	3.4	2.7
Total Phosphorus (μg·L^−1)	22	24	20	19
Total Nitrogen (μg·L^−1)	625	705	588	545
Secchi Disk Depth (cm)	168	201	153	117
Chlorophyll-a (μg·L^−1)	8.7	10.3	7.3	6.0
Blue-Green Algae (cells ·mL^−1)	17,032	20,346	10,969	8,262
Blue-Green Biovolume (ppm)	3.84	2.96	1.79	1.10

Table 2b Descriptive statistics for lake/watershed group “Newer Artificial Lakes in Impacted Watersheds.” N = 11 lake/watershed units.

Parameter	Mean	75th Percentile	Median	25th Percentile
Lake Age (years)	29	35	27	19
Cropland/Urban Land (%)	68.0	76.5	65.0	60.0
Lake Area (ha)	78.5	121.4	48.6	20.8
Mean Depth (m)	2.3	3.0	2.0	1.7
Retention Time (years)	0.75	1.08	0.65	0.28
Total Calcium (mg·L^−1)	42.7	47.1	38.3	28.5
Total Alkalinity (mg·L^−1)	130.6	147.4	125.8	116.9
Total Dissolved Solids (mg·L^−1)	248.2	282.2	211.9	154.6
Non-Algal Turbidity (m^−1)	0.79	1.08	0.68	0.34
Turbidity (NTU)	15.7	20.7	11.5	8.2
Total Phosphorus (μg·L^−1)	232	199	89	61
Total Nitrogen (μg·L^−1)	2,112	2,602	1,326	1,131
Secchi Disk Depth (cm)	59	68	58	46
Chlorophyll-a (μg·L^−1)	77.1	110.1	29.8	24.2
Blue-Green Algae (cells ·mL^−1)	305,423	369,623	62,271	14,372
Blue-Green Biovolume (ppm)	92.83	127.88	25.61	6.03

Table 2c Descriptive statistics for lake/watershed group “Older Artificial Lakes in Unimpacted Watersheds.” N = 11 lake/watershed units.

Parameter	Mean	75th Percentile	Median	25th Percentile
Lake Age (years)	75	77	75	74
Cropland/Urban Land (%)	11.2	17.0	9.0	2.5
Lake Area (ha)	63.6	77.5	58.3	24.5
Mean Depth (m)	3.1	4.0	2.9	2.4
Retention Time (years)	1.28	2.14	1.19	0.56
Total Calcium (mg·L^−1)	37.4	44.5	41.1	28.2
Total Alkalinity (mg·L^−1)	115.4	128.1	110.0	104.0
Total Dissolved Solids (mg·L^−1)	168.0	176.4	167.8	125.4
Non-Algal Turbidity (m^−1)	0.58	0.66	0.53	0.42
Turbidity (NTU)	5.7	7.4	4.0	3.4
Total Phosphorus (μg·L^−1)	27	34	22	19
Total Nitrogen (μg·L^−1)	579	729	622	425
Secchi Disk Depth (cm)	153	173	135	127
Chlorophyll-a (μg·L^−1)	10.4	13.6	8.9	7.4
Blue-Green Algae (cells ·mL^−1)	4,251	6,305	3,590	2,054
Blue-Green Biovolume (ppm)	2.29	2.67	0.85	0.46

Table 2d Descriptive statistics for lake/watershed group “Older Artificial Lakes in Impacted Watersheds.” N = 11 lake/watershed units.

Parameter	Mean	75th Percentile	Median	25th Percentile
Lake Age (years)	77	83	74	72
Cropland/Urban Land (%)	65.6	80.5	61.0	51.0
Lake Area (ha)	51.0	54.6	37.2	30.4
Mean Depth (m)	2.5	3.2	2.4	1.7
Retention Time (years)	1.10	1.08	0.72	0.42
Total Calcium (mg·L^−1)	37.5	40.2	37.9	31.6
Total Alkalinity (mg·L^−1)	130.9	165.0	125.8	97.5
Total Dissolved Solids (mg·L^−1)	220.5	303.2	197.5	151.1
Non-Algal Turbidity (m^−1)	1.04	0.91	0.37	0.04
Turbidity (NTU)	19.5	19.3	12.3	9.3
Total Phosphorus (μg·L^−1)	170	271	105	74
Total Nitrogen (μg·L^−1)	1,477	1,948	1,485	829
Secchi Disk Depth (cm)	67	87	58	53
Chlorophyll-a (μg·L^−1)	58.0	77.3	41.3	27.8
Blue-Green Algae (cells ·mL^−1)	127,815	149,120	87,441	33,027
Blue-Green Biovolume (ppm)	41.43	35.32	23.82	11.15

Table 3 Kruskal-Wallace test results (H) for inter-group comparisons for lake/watershed physical features and general water chemistry parameters. NU = newer artificial lakes in unimpacted watersheds; NX = newer artificial lakes in impacted watersheds; OU = older artificial lakes in unimpacted watersheds; and OX = older artificial lakes in impacted watersheds. Shaded results indicate statistically significant differences between group pairs (P ⩽ 0.05).

	NU-NX	NU-OU	NU-OX	NX-OU	NX-OX	OU-OX
Lake Age (years)	0.28	15.85	15.88	15.83	15.85	0.02
Watershed (% cropland and urban)	15.80	0.04	15.80	15.79	0.07	15.79
Surface Area (ha)	0.13	0.39	1.56	0.03	0.21	0.24
Mean Depth (m)	7.29	0.35	4.04	3.29	0.11	2.11
Retention Time (years)	3.26	0.02	2.38	2.38	0.35	0.79
Total Calcium (mg·L^−1)	0.18	1.32	0.09	0.05	0.00	0.05
Total Alkalinity (mg·L^−1)	4.01	0.91	1.73	1.81	0.04	0.39
Total Dissolved Solids (mg·L^−1)	6.06	0.91	3.75	1.99	0.09	2.28
Non-Algal Turbidity (m^−1)	1.32	1.25	0.13	0.67	0.91	0.48

Table 4 Kruskal-Wallace test results (H) for inter-group comparisons for lake/watershed nutrient and trophic state parameters. NU = newer artificial lakes in unimpacted watersheds; NX = newer artificial lakes in impacted watersheds; OU = older artificial lakes in unimpacted watersheds; and OX = older artificial lakes in impacted watersheds. Shaded results indicate statistically significant differences between group pairs (P ⩽ 0.05).

	NU-NX	NU-OU	NU-OX	NX-OU	NX-OX	OU-OX
Total Phosphorus (μg·L^−1)	14.76	0.91	14.76	14.76	0.09	13.28
Total Nitrogen (μg·L^−1)	14.26	0.13	11.88	14.26	0.13	11.00
Secchi Disk Depth (cm)	15.79	0.09	14.26	14.26	0.48	12.81
Turbidity (NTU)	10.14	2.59	12.81	6.73	0.13	10.14
Chlorophyll-a (μg·L^−1)	15.78	0.91	15.78	14.76	0.02	15.27
Blue-Green Algae (cells ·mL^−1)	4.28	10.14	10.57	13.28	0.05	15.78
Blue-Green Biovolume (ppm)	5.43	1.48	10.14	7.43	0.01	12.34

Figure 2 Percentage of surveyed lakes with a period-of-record trophic state classification of mesotrophic (TSI_Chl-a < 50), lower eutrophic (TSI_Chl-a 50–54.9), eutrophic (TSI_Chl-a 55–59.9), upper eutrophic (TSI_Chl-a 60–63.9), or hypereutrophic (TSI_Chl-a ⩾ 64), versus the percent of watershed land under cultivation.

Figure 3 Box plots depicting period-of-record mean Carlson trophic state index (TSI) scores based on chlorophyll-a versus watershed classes based on the proportion of cropland in the drainage. Whiskers represent the maximum and minimum values, the central box the interquartile range and the median, and the black circle the mean. TSI-to-chlorophyll-a correspondences: 50 = 7.2 μg·L⁻¹, 60 = 20.1 μg·L⁻¹, 70 = 55.7 μg·L⁻¹, and 80 = 154.3 μg·L⁻¹.

Figure 4 Box plots depicting period of record mean Carlson trophic state index (TSI) scores based on total phosphorus versus watershed classes based on the proportion of cropland in the drainage. Whiskers represent the maximum and minimum values, the central box the interquartile range and the median, and the black circle the mean. TSI-to-total phosphorus correspondences: 50 = 24 μg·L⁻¹, 60 = 48 μg·L⁻¹, 70 = 96 μg·L⁻¹, and 80 = 192 μg·L⁻¹.

Figure 5 Box plots depicting period-of-record mean Carlson trophic state index (TSI) scores based on chlorophyll-a versus lake age classes based on the years since dam completion. Whiskers represent the maximum and minimum values, the central box the interquartile range and the median, and the black circle the mean. TSI-to-chlorophyll-a correspondences: 50 = 7.2 μg·L⁻¹, 60 = 20.1 μg·L⁻¹, 70 = 55.7 μg·L⁻¹, and 80 = 154.3 μg·L⁻¹.

Figure 6 Box plots depicting period of record mean Carlson trophic state index (TSI) scores based on total phosphorus versus lake age classes based on the years since dam completion. Whiskers represent the maximum and minimum values, the central box the interquartile range and the median, and the black circle the mean. TSI-to-total phosphorus correspondences: 50 = 24 μg·L⁻¹, 60 = 48 μg·L⁻¹, 70 = 96 μg·L⁻¹, and 80 = 192 μg·L⁻¹.