Appendix 6: Description of Habitat Pressure Indicators & Relevance to Salmon
Habitat pressure indicators, associated metrics, relevance to salmon habitat, and limitations.
| Indicator | Metric | Description | Rationale | Limitations |
|---|---|---|---|---|
| Total Land Cover Alteration | % watershed area | The percentage of the total watershed area that has been altered by human activity. A sum of forest disturbance, urban land use, agricultural/rural land use, mining development, and other development. | Represents potential changes in cumulative watershed processes, such as hydrologic flows and sediment generation, that can affect spawning and rearing habitats downstream (Poff et al. 2006, in Stalberg et al. 2009). | The data currency and completeness varies for the data sources included in this indicator. Specifically, the land cover classification dataset is current only to 2005 (1996-2005). |
| Mining Development | # of mines | The number of active and past-producing coal, mineral, or aggregate (gravel) mine sites within a watershed. | Mining development can affect or potentially cause the loss of salmon habitat, through the actual footprint of the mine itself, any tailings ponds, other infrastructure development, or indirectly through the disruption of stream beds and input of fine sediment or other contaminants (Meehan 1991, Nelson et al. 1991, Kondolf 1997). | The aggregate mining dataset was last updated in 2004. Data on the actual footprints of mine sites and other infrastructure development is not readily available at the watershed scale. Impacts of mines are therefore assessed in a binary (presence/absence) manner. |
| Impervious Surfaces | % watershed area | The percentage of the total watershed area that is represented by hard, impervious surfaces (e.g. paved). | This indicator reflects the number of built structures (e.g. paved roads, sidewalks, buildings, etc.) that are covered by impervious surfaces (e.g. concrete, asphalt, brick, etc.). Extensive impervious surfaces in a watershed can alter and affect natural hydrologic flow patterns and lead to stream degradation through changes in geomorphology and hydrology, and can also lead to increased nutrient loading and contaminant loads downstream (Rosenau and Angelo 2009). The concentration of impervious surfaces in the built environment and the relative irreversibility of this disturbance means that the impact on habitat quality is typically very high (Schendel et al. 2004; Schindler et al. 2006; Smith et al. 2007; Jokinen et al. 2010; Paul and Meyer 2001 in Nelitz et al. 2011; Cooke et al. 2020. | Patterns of urban/rural development may be overestimated in some Regions (e.g. Central Coast) as the Impervious Surface Coefficients (ISCs) for land types used in this analysis were developed for watersheds in Connecticut (Prisloe et al. 2003) with higher population densities (>500 but <1800 people/square mile). |
| Linear Development | km/km2 | The density of all linear developments within a watershed, including roads, railways, utility corridors, pipelines, power lines, telecom cables, right of ways, etc. | Linear development gives an indication of the overall level of development from resource activities that may affect salmon habitats (WCEL 2011, FLNRORD et al. 2012). | See Road Development |
| Forest Disturbance | % watershed area | The percentage of total watershed area that has been disturbed by logging and burning in the last 60 years. | Logging and other disturbances that reduce forest cover can change watershed hydrology by affecting rainfall interception, transpiration, and snowmelt processes, which may affect salmon habitats through altered peak flows, low flows, and annual water yields (MOF 1995, Smith and Redding 2012). | Datasets may be limited by private land ownership in some Regions, which may result in an underestimate of Forest Disturbance. The temporal cutoff of 60 years may be inappropriate in some cases (e.g. highly developed urban areas, or watersheds with slower regeneration patterns such as snow-dominated biogeoclimatic zones). |
| Equivalent Clearcut Area (ECA) | % watershed area | The percentage of total watershed area that is considered comparable to a clearcut forest. ECA represents the cumulative effect of harvesting and second-growth forests on the hydrological cycle. | A derived metric of forest disturbance, ECA reflects the pressure on salmon habitat mainly from potential increases in peak flow (MOF 2001; Smith and Redding 2012). | Calculating ECA relies on projected tree height data that is not always available in the data sources; if not available, we assume tree height to be zero. Total Land Cover Alteration limitations also apply here due to overlapping data inputs. |
| Riparian Disturbance | % riparian buffer area | The percentage of riparian zone (a 30m buffer zone around all streams, rivers, lakes, and wetlands within a watershed) that has been altered by human activity (forest disturbance, urban land use, agricultural/rural land use, mining development, and other development). | Disturbance to riparian areas can affect salmon habitats by destabilizing stream banks, increasing surface erosion and sedimentation, reducing nutrient and woody debris inputs to water bodies, and increasing stream temperatures if streamside shading is reduced (Meehan 1991, MOF 1995). These impacts have the potential to affect the growth and survival of salmon eggs and juvenile salmon. | The data currency and completeness vary for the data sources included in this indicator. Specifically, the land cover classification dataset is current only to 2005 (1996-2005). |
| Insect and Disease Defoliation | % forest stand killed | The percentage of pine forests that have been killed by insects or disease in each watershed. | Forest defoliation from insects or diseases can reduce precipitation interception, reduce transpiration, and lead to increased soil moisture. The resulting changes to peak flows and groundwater supplies can affect salmon habitats (Bustanul. 2006, EDI 2008 in Nelitz et al. 2011). The hydrological processes in forest stands affected by insects and disease can take 20-60 years to recover (FPB 2007). If salvage logged, these stands will have the same watershed effects as clear cut logging. | The Vegetation Resources Inventory Dead Layer is primarily based on modelled data. In some cases, modelled data is superceded by photo interpretation but overall reliability of dead stand area should be considered low. |
| Road Development | km/km2 | The average density of all roads within a watershed. | Road development can interrupt sub-surface flow, increase peak flows, and interfere with natural patterns of overland water flow in a watershed (Smith and Redding 2012). Road construction can cause significant erosion by exposing large areas of soil to rain and snow, and roads intercept and amplify surface runoff, leading to increased erosion downslope (MOF 1995). These eroded fine sediments can flush into water bodies, affecting salmon spawning habitats by covering redds, reducing oxygenation of incubating eggs, and increasing turbidity which can lead to reduced foraging success of juveniles (Meehan 1991). | Data is an amalgamation of the Digital Roads Atlas (DRA) and Forest Tenure Road segments that occur outside a 30m buffer of all DRA roads. |
| Stream Crossing Density | #/km | The total number of stream crossings per km of the total length of modelled salmon habitat in a watershed. Salmon habitat is defined based on a gradient criterion filtering of the Fish Passage Model (Mount et al. 2011). | Stream crossings can create problems for fish passage by interfering with or blocking access to upstream spawning or rearing habitats, thus decreasing the total amount of available salmon habitat (Harper and Quigley 2000, FLNRO et al. 2012. Stream crossings can also affect water delivery to the stream network, causing increased peak flows, and become a source of fine sediment delivery to streams (MOF 1995; Smith & Redding 2012). | This indicator is based on modelled data determining salmon habitat that is gradient-based, along with the presence of stream crossings which are modelled at the intersection of roads and streams. Stream crossings have not been confirmed nor assessed for actual fish passage. |
| Water Licenses | # of permitted water licenses | The total number of water licences permitted for water withdrawal for domestic, industrial, agricultural, power, and storage uses from points of diversion within a watershed. This indicator is evaluated within watersheds for all salmon CUs. For lake-type sockeye CUs, the number of water licenses is also summed across the full extent of all watersheds in each CU migration ZOI to capture the potential combined effect of water extraction on mainstem water levels along the migration routes of lake-type sockeye. | Heavy allocation and use of both surface and subsurface water for human use can affect salmon habitat by reducing instream flow to levels that could, at critical times of the year, limit physical access to spawning and rearing habitats, or potentially expose redds. Reductions in both surface and subsurface water supply can also lead to increased water temperatures, which can impact salmon at all life stages (Richter et al. 2003 and Hatfield et al. 2003 in Stalberg et al. 2009; Douglas 2006). | Water license data represents water allocation only, not actual water use, as monitoring and compliance of water licences do not occur consistently. Water license data also does not account for temporary water permits obtained for short term use. |
| Waste Water Discharges | # of permitted waste water discharges | The number of permitted waste water management discharge sites within a watershed. | Waste water discharge can impact water quality in salmon habitats through either chemical contamination, which can directly injure or kill aquatic life (US EPA 2008), or excessive nutrient enrichment (eutrophication), which can result in dissolved oxygen depletion in water bodies and suffocate aquatic organisms (Zheng and Paul 2007). | This dataset only identifies permitted waste water discharge sites. Calculating the actual risk and impact to salmon habitats requires data on the volume and nature of waste water discharge. |
References
Stalberg, H.C., Lauzier, R.B., Macisaac, E.A., Porter, M., and Murray, C. 2009. Canada’s Policy for Conservation of Wild Pacific Salmon: Stream, Lake, and Estuarine Habitat Indicators. Canadian Manuscript Report of Fisheries and Aquatic Sciences 2859: xiii + 135 p. Available from https://salmonwatersheds.ca/library/lib_a_680_0711/.