Shifting DOC concentration and quality in the freshwater lakes of the Kangerlussuaq region: An experimental assessment of possible mechanisms

Figures & data

Figure 1. Floodplain dust entrained by wind, Kangerlussuaq. Photo credit: Rachel Fowler

Figure 2. Conceptual diagram illustrating potential chemical (photodegradation), biological (bacterial consumption), and physical (flocculation and precipitation) pathways for DOC loss in surface waters. Interactions between dust and solar radiation may lead to DOC loss via photoflocculation, and interactions between solar radiation and bacterial activity could have variable effects. Note that pathways are not exclusive of each other (i.e., DOC loss could occur via multiple pathways)

Table 1. Characteristics of the three study lakes. DOC, pH, and temperature measurements were taken from lake epilimnia in June 2015. Nutrient data are from June–July 2013. a.s.l. = above sea level

Lake	[DOC](mg L^−1)	SUVA254 (L mg C^−1 m^−1)	S275–295 (nm^−1)	pH	Temperature (°C)	DIN (µg L^−1)	TP (µg L^−1)	Maximum Depth (m)	Surface Area (ha)	Elevation (m a.s.l.)
SS2	23.0	1.42	−0.030	8.9	12.0	15	3	12	41	187
SS1381	24.0	1.03	−0.034	8.7	17.6	5	6	21	22	171
SS901	7.3	1.76	−0.024	8.0	8.3	5	4	15	11	399

Figure 3. Study area. SS2, SS1381, and SS901 denote the locations of experimental lakes

Table 2. Mean percent change in DOC concentration and quality metrics for dust addition + light and bacterial activity + light experiments. The dust addition experiment for soil water was incubated in dark conditions only

			[DOC] (% Change)				SUVA254 (% Change)				S275–295 (% Change)
			SS2	SS1381	SS901	Soil Water	SS2	SS1381	SS901	Soil Water	SS2	SS1381	SS901	Soil Water
Dust + light	No-dust Dark		−0.08	−0.91	4.90	−25.88	−14.09	0.44	−5.66	36.21	−20.56	−0.38	−4.08	−3.53
	Dust Dark		0.98	0.39	11.96	−21.59	−0.65	−0.15	−12.25	29.73	−1.53	−0.27	−4.82	−1.66
	No-dust Light		6.47	11.17	33.66	-	−20.19	−14.97	−36.32	-	−20.34	−6.51	−23.70	-
	Dust Light		5.38	12.04	41.31	-	−6.29	−19.16	−37.76	-	−0.81	−7.70	−28.02	-
Bacterial + light	Filtered Dark		2.17	1.19	5.07	-	−1.28	−2.90	−9.13	-	−1.91	−1.02	−4.96	-
	Inoculated Dark		1.81	0.69	10.19	-	−1.91	0.34	−19.63	-	−1.92	1.00	−1.59	-
	Filtered Light		0.13	2.59	9.79	-	−10.73	−11.30	−25.05	-	−11.49	−12.71	−19.86	-
	Inoculated Light		−0.01	1.75	6.17	-	−13.07	−9.46	−16.68	-	−14.31	−9.55	−11.61	-

Table 3. The p values for dust addition + light exposure and bacterial activity + light exposure experiments. Bold values represent a significance level less than 0.05. Nonsignificant (p ≥ 0.10) interaction terms were removed from statistical models. The dust-addition experiment for soil water was incubated in dark conditions only

			[DOC]				SUVA254				S275–295
			SS2	SS1381	SS901	Soil Water	SS2	SS1381	SS901	Soil Water	SS2	SS1381	SS901	Soil Water
Dust + light	Dust		0.985	0.313	0.110	0.230	<0.001	0.329	0.240	0.237	<0.001	0.878	0.111	0.146
	Light		<0.001	<0.001	<0.001	-	<0.001	<0.001	<0.001	-	0.809	0.045	<0.001	-
	Dust × Light		0.076	-	-	-	-	0.017	-	-	-	-	-	-
Bacterial + light	Bacteria		0.670	0.177	0.887	-	0.026	0.009	0.889	-	0.216	0.080	0.122	-
	Light		0.008	0.026	0.401	-	<0.001	<0.001	0.254	-	<0.001	<0.001	0.005	-
	Bacteria × Light		-	-	-	-	-	-	-	-	-	-	-	-

Figure 4. Results of Lake SS2 soil-water exposure to dust addition on SUVA₂₅₄, S_275–295, and [DOC], represented by percent change (n = 3)

Figure 5. Results of SS2, SS1381, and SS901 lake-water exposure to dust addition and light on SUVA₂₅₄, S_275–295, and [DOC], represented by percent change (n = 3)

Figure 6. Results of SS2, SS1381, and SS901 lake-water exposure to bacterial activity and light on SUVA₂₅₄, S_275–295, and [DOC], represented by percent change (n = 3). F = filtered treatments, I = inoculated treatments

Figure 7. S versus a*₃₇₅ for dust + light (A–C) and bacteria + light (D–F) experiments (n = 3)