An evaluation of small river restoration using transient river habitat modelling for macrozoobenthos

Figures & data

Figure 1. Location of the study site with an overview of Saxony river systems and Mortelbach within the city of Waldheim showing the four 4 restored river sections (D1, M1, D2, and M2, downstream to upstream) with structural measures such as pools, riffles, and riparian/aquatic vegetation.

Table 1. Fuzzy sets of habitat variables and their descriptions

Habitat variables	Fuzzy sets	Explanation
Mineral substrate	Very low Low Medium High Very high	Mud, silt, loam, clay (<0.063 mm) Sand (0.063–2 mm) Fine to medium-sized gravel (0.2–2 cm) Coarse gravel to hand-sized cobbles (2–20 cm) Stones, boulders, bedrock (>20 cm)
Organic substrate	Very low Low Medium High Very high	No additional cover Micro- and macroalgae Macrophytes, mosses, characeae, living parts of terrestrial plants Coarse and fine particulate organic matter Woody debris, twigs, roots, logs (size > 10 cm)
Water depth	Very low Low Medium High Very high	0.00 m (±0.01 m)−0.08m (±0.07 m) 0.08m (±0.07 m)−0.20 m (±0.1 m) 0.20 m (±0.1 m)−0.50 m (±0.1 m) 0.50 m (±0.1 m)−0.70 m (±0.1 m) > 0.7 m (±0.1 m)
Velocity	Very low Low Medium High Very high	0.00 m/s − 0.10 m/s (±0.1 m/s) 0.10 m/s (±0.1 m/s)−0.30 m/s (±0.1 m/s) 0.30 m/s (±0.1 m/s)−0.50 m/s (±0.1 m/s) 0.50 m/s (±0.1 m/s)−0.70 m/s (±0.1 m/s) > 0.70 m/s (±0.1 m/s)
Temperature	Very low Low Medium High Very high	0 °C − 9 °C (±1 °C) 9 °C (±1 °C)−13 °C (±2 °C) 13 °C (±2 °C)−17 °C (±2 °C) 17 °C (±2 °C)−22 °C (±1 °C) >22 °C (±1 °C)
Habitat suitability	Very low Low Medium High Very high	0.00 (±0.1)−0.20 (±0.1) 0.20 (±0.1)−0.40 (±0.1) 0.40 (±0.1)−0.60 (±0.1) 0.60 (±0.1)−0.80 (±0.1) 0.80 (±0.1)−1.00 (±0.1)

Table 2. Examples of fuzzy rules determining habitat requirement for A. fluviatilis

Rule No.	IF	AND	AND	AND	AND	THEN
	S	C	H	V	T	HS
1	Very low	Very low	Very low	Very low	Very low	Very low
2	Low	Low	Very low	Very low	Very low	Low
3	Low	High	High	Medium	Low	Medium
4	Very high	High	Medium	Medium	Low	High
5	Very high	Low	Medium	Medium	Medium	Very high

S: mineral substrate; C: organic substrate; H: water depth; V: velocity; T: temperature; and HS: habitat suitability.

Figure 2. Spatial distribution of water depth, velocity, and temperature before restoration (a) and afterrestoration (b) at MALF = 0.041 m³/s.

Figure 3. An example of the spatial distribution of velocity vectors showing changes in flow field due to instream structures in Section M1 before restoration (a) and after restoration (b) at MALF = 0.041 m³/s.

Figure 4. Frequency distribution of water depths and velocities before restoration and after restoration at MALF = 0.041 m³/s.

Figure 5. Box plots comparing different habitat suitability index classes for three target taxa with discharge classes at the river site. < MALF: 0.02–0.041 m³/s; MALF–MAF: 0.041–0.1 m³/s; > MAF: 0.1–0.93 m³/s. pre and post denote pre- and post-restoration, respectively.

Figure 6. Habitat areas of Mortelbach with different suitability classes during the study period from spring to summer 2021 for three species of macrozoobenthos with (_post) and without (_pre) restoration measures.

Figure 7. Habitat Suitability Index map for a) A. fluviatilis; b) E. danica; c) G. fossarum at the minimum discharge (0.02 m³/s) on two different days at the current situation (different restoration measures in D1, M1, D2, and M2). The colour represents each habitat suitability index class (grey: 0< HSI ≤0.2; red: 0.2< HSI ≤0.4; yellow: 0.4< HSI ≤0.6; green: 0< HSI ≤ 0.8; blue: 0.8< HSI ≤1).

Figure 8. Habitat Suitability Index map for three target species showing the post-restoration situation in summer at the discharge of 0.85 m³/s. The colour represents each habitat suitability index class (grey: 0< HSI ≤0.2; red: 0.2< HSI ≤0.4; yellow: 0.4< HSI ≤0.6; green: 0< HSI ≤ 0.8; blue: 0.8< HSI ≤1).