9 NDSS Case Study

9.1 Overview

This chapter presents a case study applying the CEMPRA framework to two species at risk in British Columbia’s Lower Fraser Valley: Nooksack Dace (Rhinichthys cataractae ssp.) and Salish Sucker (Catostomus sp. cf. catostomus). Both species are listed as Endangered under Canada’s Species at Risk Act (SARA) and occupy distinct ecological niches within the same watershed systems. Nooksack Dace is a riffle specialist, preferring shallow, fast-flowing reaches with cobble substrate, while Salish Sucker is a deep-pool specialist found in slower, deeper habitats with abundant cover.

The environmental stressors evaluated in this case study are derived from upstream spatial stream network (SSN) models that link land use, hydrology, and nutrient loading to in-stream water quality conditions. These models predict dissolved oxygen concentrations under various flow and nutrient scenarios, while climate change projections provide future stream temperature estimates. Physical habitat metrics (percent cobble for Nooksack Dace, deep pool length for Salish Sucker) are drawn from reach-level field surveys.

The purpose of this case study is to demonstrate how CEMPRA can be used to evaluate and compare recovery scenarios for multiple species simultaneously. Nine scenarios (S00–S05b) explore the individual and combined effects of climate warming, flow reduction, nutrient loading, and riparian restoration on habitat quality across the study area. Each scenario modifies the stressor magnitude inputs while holding the stressor-response relationships constant, allowing managers to isolate the relative impact of each threat and assess the potential benefits of restoration actions.

Live instances of the CEMPRA application are available for each species:

9.2 Species-Specific Stressors

Each species is evaluated against a distinct set of environmental stressors:

Stressor	Nooksack Dace	Salish Sucker
Temperature (MWAT)	X	X
August Mean Dissolved Oxygen	X	X
August Minimum Dissolved Oxygen (6-hr)	X	X
Percent Cobble	X
Deep Pool Length		X

9.3 Habitat Capacity

Habitat capacity (maximum potential abundance) is calculated differently for each species:

Nooksack Dace: Reach Length x Wetted Width x Species Index x 1.9 fish/m² x (Percent Riffle / 100)
Salish Sucker: Reach Length x Wetted Width x Species Index x 0.05 fish/m²

9.4 Base Case Model Inputs (S00)

The following files provide the base case inputs for each species. The stressor magnitude workbooks contain present-day stressor values and serve as the reference point (Scenario S00) from which all other scenarios are derived.

9.4.1 Nooksack Dace

9.4.2 Salish Sucker

9.5 Recovery Scenarios

These nine scenarios are run independently for both Nooksack Dace and Salish Sucker. Each scenario modifies specific stressor magnitude values while keeping all other inputs unchanged from the base case.

9.5.1 Base Case

Current conditions. All stressor values reflect observed or modeled present-day measurements:

Temperature: Adjusted MWAT (2001-2020)
Dissolved oxygen: Predicted August mean and 6-hour minimum DO (current conditions)
Physical habitat: Current percent cobble, riffle, and deep pool metrics

This scenario serves as the reference point for all comparisons.

9.5.2 Future Stream Temperature

Projects the effect of climate change on stream temperatures to the mid-century without any mitigation.

Temperature: Replaced with Future MWAT Climate Change Scenario (2061-2080) values
All other stressors: Unchanged from base case

Represents the unmitigated temperature impact of climate change over the next ~40-60 years.

9.5.3 Future Temperature with Riparian Planting

Projects future stream temperatures assuming riparian planting is implemented as a mitigation measure.

Temperature: Replaced with Future MWAT with Riparian Planting values
All other stressors: Unchanged from base case

Quantifies the temperature benefit of riparian restoration under future climate conditions. Comparison with S01 isolates the effect of riparian planting.

9.5.4 Decreased Flows (20% Reduction)

Models how a moderate reduction in stream flows affects dissolved oxygen concentrations.

August Mean DO: Replaced with predicted DO under 20% flow decrease
August Min DO (6-hr): Replaced with predicted DO under 20% flow decrease
All other stressors: Unchanged from base case

Represents a moderate flow reduction scenario (e.g., increased water extraction, moderate drought).

9.5.5 Decreased Flows (60% Reduction)

Models how a severe reduction in stream flows affects dissolved oxygen concentrations.

August Mean DO: Replaced with predicted DO under 60% flow decrease
August Min DO (6-hr): Replaced with predicted DO under 60% flow decrease
All other stressors: Unchanged from base case

Represents a severe flow reduction scenario (e.g., major water extraction, extreme drought). Comparison with S03a shows the sensitivity of DO response to the magnitude of flow reduction.

9.5.6 Increased Nutrients (10% Increase)

Models how a modest increase in nutrient loading affects dissolved oxygen through eutrophication.

August Mean DO: Replaced with predicted DO under 10% nutrient increase
August Min DO (6-hr): Replaced with predicted DO under 10% nutrient increase
All other stressors: Unchanged from base case

Represents a modest nutrient loading increase (e.g., gradual agricultural intensification).

9.5.7 Increased Nutrients (50% Increase)

Models how a substantial increase in nutrient loading affects dissolved oxygen through eutrophication.

August Mean DO: Replaced with predicted DO under 50% nutrient increase
August Min DO (6-hr): Replaced with predicted DO under 50% nutrient increase
All other stressors: Unchanged from base case

Represents a substantial nutrient loading increase. Comparison with S04a shows the sensitivity of DO response to nutrient loading magnitude.

9.5.8 Future Cumulative Effects, No Restoration

Combines multiple stressors to represent a worst-case future scenario without any restoration actions.

Temperature: Replaced with Future MWAT Climate Change Scenario (2061-2080)
August Mean DO: Replaced with predicted DO under combined 60% flow decrease and 50% nutrient increase
August Min DO (6-hr): Replaced with predicted DO under combined 60% flow decrease and 50% nutrient increase
Physical habitat stressors: Unchanged from base case

Represents the compounded effect of climate warming, reduced flows, and increased nutrient loading acting simultaneously without intervention.

9.5.9 Future Cumulative Effects, With Restoration

Combines multiple stressors under a future scenario where restoration actions (riparian planting) are implemented.

Temperature: Replaced with Future MWAT with Riparian Planting values
August Mean DO: Replaced with predicted DO under 60% flow decrease (restoration assumed to eliminate nutrient increase)
August Min DO (6-hr): Replaced with predicted DO under 60% flow decrease (restoration assumed to eliminate nutrient increase)
Physical habitat stressors: Unchanged from base case

Represents a future with climate warming and reduced flows, but where riparian planting mitigates temperature increases and nutrient management eliminates the nutrient loading increase. Comparison with S05a quantifies the benefit of combined restoration actions.

9.6 Scenario Comparison Summary

ID	Scenario	Stressors Modified	Purpose
S00	Base Case	None	Reference point
S01	Future Stream Temp	Temperature	Unmitigated climate warming
S02	Future Temp + Planting	Temperature	Riparian planting mitigation
S03a	Decreased Flows 20%	Aug Mean DO, Aug Min DO	Moderate flow reduction
S03b	Decreased Flows 60%	Aug Mean DO, Aug Min DO	Severe flow reduction
S04a	Increased Nutrients 10%	Aug Mean DO, Aug Min DO	Modest nutrient loading
S04b	Increased Nutrients 50%	Aug Mean DO, Aug Min DO	Substantial nutrient loading
S05a	Future CE No Restoration	Temperature, Aug Mean DO, Aug Min DO	Combined worst-case future
S05b	Future CE With Restoration	Temperature, Aug Mean DO, Aug Min DO	Combined future with restoration

9.7 Data Sources

Temperature projections: Climate Change Scenarios worksheet, Future MWAT CC Scenario (2061-2080)
Riparian planting temperatures: Climate Change Scenarios worksheet, Future MWAT with Riparian Planting
DO predictions under flow/nutrient changes: DO Predictions worksheet in the Critical Reach Master Dataset
Physical habitat metrics: Reach Attributes worksheet (cobble, riffle, deep pool percentages)
Stressor-response relationships: Species-specific workbooks defining dose-response curves

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