Environmental and structural factors influencing algal communities in small streams and ditches in central Germany

Figures & data

Figure 1. Map of the study and sampling sites.

Table 1. Selected environmental and structural variables and algal data with the corresponding seasonal mean ± SE for ditches (n = 99) and streams (n = 269).

	Spring	Summer	Autumn	Winter	ANOVA (F-values)
Temp, w (°C)	8.5 ± 0.4	15.1 ± 0.2	9.5 ± 0.4	3.5 ± 0.2	100.1*
O2 (mg/L)	10.2 ± 0.1	8.2 ± 0.2	8.4 ± 0.2	10.5 ± 0.2	30.7*
Cond. (µS/cm)	396 ± 8	390 ± 11	397 ± 11	387 ± 15	7.7*
pH	7.83 ± 0.04	7.61 ± 0.04	7.58 ± 0.03	7.53 ± 0.07	8.9*
P-PO4 (mg/L)	0.71 ± 0.05	0.70 ± 0.05	0.58 ± 0.03	0.45 ± 0.03	6.2*
N-NH4 (mg/L)	0.64 ± 0.04	0.74 ± 0.06	0.38 ± 0.02	0.39 ± 0.03	15.7*
N-NO3 (mg/L)	7.99 ± 0.40	6.58 ± 0.51	4.86 ± 0.31	5.47 ± 0.25	10.9*
N-NO2 (mg/L)	0.40 ± 0.02	0.40 ± 0.02	0.57 ± 0.02	0.53 ± 0.02	20.7*
Cl (mg/L)	32.63 ± 1.79	36.52 ± 1.92	35.69 ± 1.77	29.72 ± 1.96	1.0
Depth (cm)	47 ± 4	46 ± 5	44 ± 4	55 ± 5	3.7*
Width (cm)	348 ± 16	330 ± 19	317 ± 20	335 ± 20	2.5*
Vel. (m/s)	0 ± 0	0 ± 0	0 ± 0	0 ± 0	21.9*
Turb. (NTU)	16 ± 1	17 ± 1	17 ± 1	19 ± 1	5.2*
Suspended algae
Total PAP (µg/L)	10.46 ± 0.56	7.39 ± 0.38	5.90 ± 0.61	1.52 ± 0.13	126.0*
Cya (%)	14.14 ± 0.81	14.77 ± 1.04	15.30 ± 1.03	15.19 ± 1.13	58.0*
Gre (%)	29.41 ± 1.82	68.08 ± 1.72	27.11 ± 1.79	27.50 ± 1.75	76.5*
Diat (%)	52.38 ± 1.95	15.00 ± 1.29	51.03 ± 2.11	46.28 ± 2.12	108.7*
Cry (%)	4.07 ± 0.54	2.16 ± 0.55	6.57 ± 0.94	11.02 ± 1.65	1.2
Attached algae
Total PAP (µg/dm^2)	43.98 ± 3.15	35.50 ± 2.68	25.27 ± 1.84	19.58 ± 1.64	189.1*
Cya (%)	17.44 ± 0.68	24.48 ± 0.91	16.60 ± 0.58	14.67 ± 0.70	7.28*
Gre (%)	21.08 ± 0.84	24.35 ± 1.20	21.74 ± 1.30	23.38 ± 1.23	31.17*
Diat (%)	60.41 ± 1.11	49.31 ± 1.40	59.99 ± 1.30	60.40 ± 1.29	31.29*
Cry (%)	1.15 ± 0.22	2.53 ± 0.41	1.74 ± 0.24	1.84 ± 0.29	17.98*

Seasonal comparisons conducted with a one-way ANOVA and the corresponding F-values are presented. Significant differences (p ≤ 0.05) are denoted by *.

Table 2. Mean abundance of suspended and attached algal species counted at all sampling sites in April 2012.

Class	Species	Attached algae	Suspended algae
Bacillariophyceae	Sum	72.9	67.7
Bacillariophyceae	Achnanthes conspicua	21.0	3.6
Bacillariophyceae	Cocconeis pediculus	2.7	30.4
Bacillariophyceae	Fragilaria crotonensis	<2	3.6
Bacillariophyceae	Fragilaria ulna	2.5	1.1
Bacillariophyceae	Navicula hungarica	6.6	<2
Bacillariophyceae	Navicula radiosa	2.1	<2
Bacillariophyceae	Navicula seminulum	2.9	<2
Bacillariophyceae	Nitzschia acicularis	<2	4.4
Bacillariophyceae	Nitzschia gracilis	3.7	–
Bacillariophyceae	Nitzschia palea	10.2	3.7
Bacillariophyceae	Planothidium lanceolatum	9.6	<2
Chlorophyceae	sum	12.9	16.5
Chlorophyceae	Chlorella vulgaris	<2	3.5
Chlorophyceae	Chloromonas sp.	5.0	<2
Chlorophyceae	Coleochaete sp.	2.1	<2
Chrysophyceae	Chrysophyceae	–	2.3
Cyanophyceae	Sum	13.3	10.8
Cyanophyceae	Oscillatoria limnosa	–	5.8
Cyanophyceae	Nodularia spumigena	5.6	–
Cyanophyceae	Oscillatoria rosea	2.7	<2
Cryptophyceae	Sum	0.7	4.0
Motile		17.6	16.6
Benthic		96.7	29.8
Sestonic		23.3	61.5

Species with an abundance <2% in both algal fractions are not shown.

Figure 2. Monthly averaged, log transformed suspended:attached algal ratio calculated. It was calculated with the monthly mean of the suspended photosynthetically active pigments (PAP) above the area sampled for attached algae at all sites and the monthly mean of the attached algae PAP. Displayed are 95% confidence intervals for each monthly mean. The dashed reference line separates the two areas where either the suspended algal fraction (>0) or the attached algal fraction (<0) increases their contribution to the algal community.

Figure 3. Redundancy analysis, showing suspended algal group scores (Diat, diatoms; Gre, green algae; Cry, cryptophytes; Cya, cyanobacteria), plotted relative to the significant environmental and structural variables (p ≤ 0.05, assessed with a Monte Carlo permutation test) and sampling sites. Sampling sites were classified according to season; spring: •, summer: ■, autumn: ▴, winter: x. In suspended algal composition, 39.2% of the variations can be explained by the environmental and structural variables, of which 96.7% is displayed by the first two axes.

Table 3. Explanatory power of the environmental and structural variables (%) from RDA analyses.

	Suspended algae (%)	Attached algae (%)
Agricultural drainage area	0.6	0.6
Canopy cover	–	2.6
Cloud cover	0.8	0.4
Drainage area	1.9	1.2
N-NH4^+	3.0	0.6
N-NO2^−	1.5	n.s.
N-NO3^−	3.2	2.4
O2	1.3	1.3
P-PO4^3−	4.6	0.9
Precipitation	1.0	1.2
Structural classification	0.5	1.4
Sunlight	1.8	7.5
Water temperature	11.5	0.8
Turbidity	1.0	2.1
Velocity	6.5	2.6

–, not included in RDA analysis; n.s., not significant and thus not included in the final RDA (p ≤ 0.05, assessed with a Monte Carlo permutation test).

Table 4. Summary of redundancy analyses (RDA) performed with the suspended and attached algal dataset with and without introducing season as a covariable.

		RDA without covariables				RDA with season as a covariable
		Axis 1	Axis 2	Axis 3	Axis 4	Axis 1	Axis 2	Axis 3	Axis 4
Suspended	Eigenvalue	0.27	0.11	0.01	0	0.03	0	0	0
	Species–environment correlations	0.79	0.52	0.32	0.18	0.47	0.15	0.13	0.07
	Cumulative percentage variance
	of species data	27.1	37.9	39	39.2	6.7	7.6	7.9	8
	of species–environment relation	69.1	96.7	99.6	100	83.4	95.1	99.2	100
	F-ratio of all axes	16.32*				4.32*
Attached	Eigenvalue	0.22	0.02	0.01	0	0.01	0	0	0
	Species–environment correlations	0.55	0.40	0.35	0.18	0.21	0.17	0.14	0.09
	Cumulative percentage variance
	of species data	22.2	24.4	25.5	25.6	2.5	3.1	3.4	3.4
	of species–environment relation	86.6	95.3	99.5	100	73.0	90.3	98.4	100
	F-ratio of all axes	18.02*				7.33*

The results of the Monte Carlo tests for significance (p ≤ 0.05) of all canonical axes are additionally presented if performed. Values denoted by a * indicate significance at p ≤ 0.05.

Figure 4. Abundance of suspended algal groups (Diat, diatoms; Gre, green algae; Cry, cryptophytes; Cya, cyanobacteria) plotted versus significant (p ≤ 0.05) environmental and structural variables (log(x+1) transformed), assessed with a Monte Carlo permutation test. A line-of-fit, estimated by GLM, is plotted for suspended algal groups which are significantly correlated with environmental and structural variables (determined with F-ratio statistics p < 0.05).

Figure 5. Redundancy analysis, showing attached algal group scores (Diat, diatoms; Gre, green algae; Cry, cryptophytes; Cya, cyanobacteria), plotted relative to the significant environmental and structural variables (p ≤ 0.05, assessed with a Monte Carlo permutation test) and sampling sites. Sampling sites were classified according to season; spring: •, summer: ■, autumn: ▴, winter: x. In attached algal composition, 27.4% of the variations can be explained by the environmental and structural variables, of which 95.3% is displayed by the first two axes.

Figure 6. Abundance of attached algal groups (Diat, diatoms; Gre, green algae; Cry, cryptophytes; Cya, cyanobacteria) versus significant (p ≤ 0.05) environmental and structural variables (log(x + 1) transformed), assessed with a Monte Carlo permutation test. A line-of-fit, estimated by GLM, is plotted for attached algal groups which are significantly correlated with environmental and structural variables (determined with F-ratio statistics p < 0.05).