4.3 APPLICATION OF THE PROBFLO APPROACH
4.3.4 Step 4: Conceptual model
The development of a conceptual model is a critical step in the risk assessment process as it describes the cause-effect linkages for all the risk components, namely; the sources, stressors, habitats and impacts to endpoints selected for the case study (Wiegers et al., 1998; Ayre and Landis, 2012; Landis, Ayre, et al., 2017). The PROBFLO conceptual model also includes the
consideration of flow and non-flow related variables in a spatial-temporal context to conform to a regional-scale E-flow framework procedure (Poff et al., 2010; O’Brien et al., 2018). This includes: (1) the selection of socio-ecological endpoints that direct the hydrologic foundations for the case study, (2) classifying ecosystem types based on geomorphic, water quality, quantity and ecoregion considerations and, (3) incorporating evidence based flow-ecosystem relationships and flow-ecosystem service relationships, with relevant non-flow variable relationships upon which the assessment is based (O’Brien et al., 2018).
The conceptual models for the case study were constructed through an expert stakeholder workshop after the completion of the literature review. The workshop included hydrologists, geomorphologists, ecologists and ecosystem services scientists. These experts are familiar with the socio-ecological system of the lower Thukela River and eMandeni Stream and were able to generate hypotheses that represent the socio-ecological processes of the system being evaluated, and probable cause and effect relationships of: (1) sources to stressors to (2) multiple receptors in relation to (3) their impacts on the endpoints, selected for the case study (Figure 4.4).
Figure 4.4: Conceptual model of the relevant sources, stressors, habitats and endpoints considered for the lower reach of the Thukela River
Conceptual models that consider all relevant sources, stressors, habitats, effects and impact relationships with spatial and temporal considerations for the assessment included four models namely:
• Macroinvertebrate endpoint model (Figure 4.5).
• Fish endpoint model (Figure 4.6).
• Riparian vegetation endpoint model (Figure 4.7).
• Social endpoint model including sub-component models for natural products, recreation, water abstraction and assimilative capacity of the ecosystem (Figure 4.8).
The models represented here in the format of the BN used in the assessment include exposure relationships with socio-ecological system structure and function variables (green nodes) which contribute to the exposure pathway of the model (yellow nodes). The exposure component of the system is then combined with the effects (pink) component where they contribute to the overall risk to the endpoints of the assessment (blue nodes).
Figure 4.5: Bayesian network of the conceptual model representing the macroinvertebrate endpoint selected for the assessment. Networks include input exposure variables (green nodes), daughter exposure variables (yellow nodes), the effects (pink) variable and endpoints node/variable (blue nodes)
Inv_PhyEnv Zero Low Med High
3.43 17.3 48.5 30.8 64.2 ± 21 Inv_Biotopes Zero Low Med High
49.4 41.4 6.22 2.98 28.2 ± 20
Inv_VD Zero Low Med High
56.1 35.8 6.81 1.36 25.9 ± 19
Inv_Cues Zero Low Med High
23.5 52.0 21.1 3.43 38.6 ± 20 Inv_Subs Zero Low Med High
53.1 40.2 5.05 1.60 26.3 ± 18 Inv_Depth Zero Low Med High
65.0 24.0 10.0 1.0 24.3 ± 19
Inv_Subs_Stones Zero Low Med High
65.0 24.0 10.0 1.00 24.3 ± 19
Inv_Seasonality Zero Low Med High
100 0 0 0 12.5 ± 7.2
Inv_Subs_GSM Zero Low Med High
65.0 24.0 10.0 1.0 24.2 ± 19
Inv_Subs_Veg Zero Low Med High
65.0 24.0 10.0 1.00 24.3 ± 19
Inv_WQ Zero Low Med High
0.98 10.8 60.3 27.9 66.3 ± 17
Inv_SysVar Zero Low Med High
35.7 53.9 9.24 1.12 31.4 ± 18 Inv_SysVar_Turb
Zero Low Med High
65.0 24.0 10.0 1.00 24.3 ± 19 Inv_Nutrients
Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23
Inv_SysVar_O2 Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23 Inv_Access_Long
Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Inv_Eco Zero Low Med High
5.33 27.4 39.6 27.7 59.9 ± 23 Inv_Potential Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Inv_threats Zero Low Med High
3.55 21.1 45.2 30.1 63 ± 21 Inv_Aliens_Comp Zero
Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Inv_Toxicity Zero Low Med High
0 0 100 0 62.5 ± 7.2
Inv_SysVar_Temp Zero
Low Med High
65.0 24.0 10.0 1.0 24.3 ± 19
Inv_Vel Zero Low Med High
65.0 24.0 10.0 1.0 24.2 ± 19
Figure 4.6: Bayesian network of the conceptual model representing the fish endpoint selected for the assessment. Networks include input exposure variables (green nodes), daughter exposure variables (yellow nodes), and the effects (pink) variable and endpoints node/variable (blue nodes)
Figure 4.7: Bayesian network of the conceptual model representing the Riparian vegetation endpoint selected for the assessment. Networks include input exposure variables (green nodes), daughter exposure variables (yellow nodes), and the effects (pink) variable and endpoints node/variable (blue nodes)
Fish_Aliens Zero Low Med High
29.3 52.2 15.2 3.38 35.7 ± 20 Fish_Aliens_Pred Zero Low Med High
21.0 27.6 42.8 8.67 47.3 ± 24
Fish_Biotopes Zero Low Med High
27.2 50.7 19.5 2.52 36.8 ± 20 Fish_Cover Zero Low Med High
14.3 49.7 26.0 10.0 45.4 ± 22 Fish_VD
Zero Low Med High
32.1 40.3 13.7 13.9 39.9 ± 26
Fish_Cover_Struct Zero Low Med High
20.7 50.6 19.7 9.01 41.8 ± 23 Fish_Cover_Veg
Zero Low Med High
20.5 50.2 19.8 9.44 42 ± 23
Fish_Subs Zero Low Med High
65.0 29.1 5.14 0.77 22.9 ± 17
Fish_threats Zero Low Med High
100 0 0 0 12.5 ± 7.2 Fish_PhyEnv
Zero Low Med High
37.5 52.0 5.85 4.62 31.9 ± 20 Fish_Cues
Zero Low Med High
36.6 59.4 3.69 0.28 29.4 ± 16
Fish_WQ Zero Low Med High
24.9 55.3 14.6 5.30 37.6 ± 21
Fish_Nutrients Zero Low Med High
23.3 52.6 19.2 4.85 38.9 ± 21 Fish_SysVar
Zero Low Med High
40.0 46.7 10.2 3.07 31.6 ± 20
Fish_SysVar_O2 Zero Low Med High
66.4 23.5 9.44 0.65 23.6 ± 19 Fish_Subs_GSM
Zero Low Med High
100 0 0 0 12.5 ± 7.2
Fish_Seasonality Zero Low Med High
100 0 0 0 12.5 ± 7.2 Fish_Subs_Bed Zero Low Med High
65.9 23.8 9.33 0.89 23.8 ± 19 Fish_Subs_Rocky
Zero Low Med High
65.7 23.7 9.64 0.89 23.9 ± 19 Fish_Depth Zero Low Med High
28.5 27.4 25.7 18.5 46 ± 28
Fish_Migration Zero Low Med High
11.1 40.5 32.6 15.8 50.8 ± 23
Fish_SysVar_Temp Zero Low Med High
66.4 23.5 9.41 0.64 23.6 ± 19
Fish_SysVar_Turb Zero Low Med High
21.2 51.6 20.0 7.24 40.8 ± 22 Fish_Velocity Zero Low Med High
66.5 23.8 8.95 0.77 23.5 ± 19
Fish_Access_Long Zero Low Med High
10.9 20.9 49.5 18.6 56.5 ± 23
Fish_Access_Lat Zero Low Med High
21.1 50.3 19.3 9.34 41.7 ± 23
Fish_Cover_Depth Zero Low Med High
20.7 50.6 19.7 8.95 41.7 ± 23
Fish_Toxicity Zero Low Med High
23.2 52.9 19.1 4.78 38.9 ± 21
Fish_Eco Zero Low Med High
76.5 21.5 1.04 1.02 19.2 ± 15 Fish_Potential Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23 Fish_Aliens_Comp
Zero Low Med High
32.1 50.8 12.5 4.62 34.9 ± 21
Fish_DTW_Comm Zero Low Med High
38.4 50.2 8.33 3.08 31.5 ± 20 Fish_DTW_Fishermen Zero Low Med High
0 0 100 0 62.5 ± 7.2 Fish_DTW
Zero Low Med High
10.7 75.3 11.5 2.46 38.9 ± 16
Veg_Durat_1in3 Zero Low Med High
65.0 24.0 10.0 1.00 24.2 ± 19
Veg_Regime Zero Low Med High
47.5 42.2 8.92 1.36 28.5 ± 19 Veg_Hflow Zero Low Med High
23.3 67.2 8.49 0.97 34.3 ± 16
Veg_Durat_1in2 Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Veg_Toxicants Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23
Veg_Lflow Zero Low Med High
74.8 18.1 5.93 1.22 20.9 ± 18 Veg_Interfloods Zero Low Med High
12.7 53.4 31.7 2.14 43.3 ± 19
Veg_Mag_1in2 Zero Low Med High
65.0 24.0 10.0 1.0 24.2 ± 19
Veg_1in2 Zero Low Med High
8.32 50.6 37.7 3.34 46.5 ± 18
Veg_GeomZ1 Zero Low Med High
96.8 3.05 0.18 .018 13.4 ± 8.7 Veg_Drybase Zero Low Med High
100 0 0 0 12.5 ± 7.2
Veg_Strperm Zero Low Med High
65.0 24.0 10.0 1.00 24.3 ± 19 Veg_Wetbase
Zero Low Med High
100 0 0 0 12.5 ± 7.2 Veg_Intrafloods
Zero Low Med High
12.0 56.2 29.8 1.99 42.9 ± 18 Veg_Seasonality Zero Low Med High
100 0 0 0 12.5 ± 7.2 Veg_1in5 Zero Low Med High
18.7 58.2 21.6 1.49 39 ± 18
Veg_Mag_Annual Zero Low Med High
65.0 24.0 10.0 1.00 24.3 ± 19 Veg_Annual Zero Low Med High
22.4 57.8 18.3 1.59 37.3 ± 19 Veg_Mag_1in3 Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23
Veg_1in3 Zero Low Med High
33.7 51.8 13.2 1.33 33 ± 19
Veg_Mag_Fresh2 Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Veg_Durat_1in5 Zero Low Med High
65.0 24.0 10.0 1.0 24.3 ± 19 Veg_Mag_1in5 Zero Low Med High
11.1 22.2 55.6 11.1 54.2 ± 22
Veg_Freshet1 Zero Low Med High
14.6 54.7 28.9 1.80 42 ± 19 Veg_Mag_Fresh1
Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23 Veg_Freq_1in5 Zero Low Med High
65.0 24.0 10.0 1.00 24.3 ± 19
Veg_Durat_Fresh1 Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23 Veg_Freq_Fresh1
Zero Low Med High
100 0 0 0 12.5 ± 7.2
Veg_Freq_Fresh2 Zero Low Med High
100 0 0 0 12.5 ± 7.2
Veg_Freshet2 Zero Low Med High
14.2 56.9 27.2 1.76 41.6 ± 18
Veg_Durat_Fresh2 Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23 Veg_Freq_Annual
Zero Low Med High
20.0 50.0 20.0 10.0
42.5 ± 23 Veg_Durat_Annual Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23 Veg_Freq_1in3 Zero Low Med High
65.0 24.0 10.0 1.0 24.3 ± 19
Veg_WQ Zero Low Med High
18.0 44.4 24.4 13.2 45.7 ± 24
Veg_RipHab Zero Low Med High
36.3 52.1 10.3 1.19 31.6 ± 18 Veg_Nutrients Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23
Veg_Geom Zero Low Med High
89.1 8.54 1.26 1.12 16.1 ± 14
Veg_GeomZ2 Zero Low Med High
96.8 3.05 0.18 .018 13.4 ± 8.7 Veg_Freq__1in2 Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Veg_Eco Zero Low Med High
17.7 46.8 26.1 9.49 44.3 ± 23 Veg_Threat
Zero Low Med High
17.9 49.0 27.0 6.06 42.8 ± 21 Veg_Aliens Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23
Veg_Removal Zero Low Med High
20.0 50.0 20.0 10.0 42.5 ± 23
Veg_GeomZ3 Zero Low Med High
96.8 3.05 0.18 .018 13.4 ± 8.7
Veg_Potential Zero Low Med High
10.0 20.0 50.0 20.0 57.5 ± 23
Figure 4.8: Bayesian network of the conceptual model representing the social endpoints selected for the assessment. Networks include input exposure variables (green nodes), daughter exposure variables (yellow nodes), and the effects (pink) variable and endpoints node/variable (blue nodes)