Introduction

With more people moving from farms and rural areas to urban environments, urban growth is affecting streams and watersheds more than ever.

 As the Puget Sound region becomes more urbanized, streams are becoming more degraded, creating a cascade of ecological degradation. This paper will discuss causes and effects of urbanization on stream health and possible recommendations for improving urban stream health in the Puget Sound region. Two local case studies will be assessed and compared on their stream health, urbanization, and restoration efforts. Because of the complexity of stream health in each stream system, successful rehabilitation must include understanding of the natural functioning stream system and the drivers that degrade the system. Since streams within the Puget Sound lowlands have similar physical and biological environments, they can be compared against each other according to urbanization levels from low disturbance to intensively urbanized watersheds (Booth et al 2004).

Stream health indicators 

Stream health will be described in this review as the primary dependent variable, measured by the 10-metric benthic index of biological integrity (B-IBI) ref. This measurement includes taxa richness within the stream, tolerance of disturbance, dominance, and characteristics of ecological groups. Biological measurements in these studies were taken by collecting benthic invertebrates in each stream during the same time period and comparing against low impact (reference) streams and varying degree of urban impacted streams. Benthic invertebrates are an acceptable indicator of stream health because they are the basic food source for juvenile salmon and other predatory biota, and they are indicators of stable stream hydrology and water quality (Booth et al 2004).

An early study of the relationship between urban development and stream health (Klein, 1979) reported a rapid decline in biological diversity when watershed impervious surfaces exceeded 10%. This relationship, termed the “threshold-of-effect” (TIA), left decision makers believing that keeping TIA below 10% would protect stream health. However, studies and research since has observed streams with poor habitat quality in watersheds below TIAs below 10% (May et al., 1997), demonstrating that the simplified use of TIAs should be used as guides, but not predictors of stream health. A recent study found variation in biological health was high in lower urbanized watersheds, whereas biological variation becomes less variable (uniformly poor) as urbanized watershed increase (Booth et al. 2004). Because stream health has been shown to be a complicated combination of factors, urbanization does not have a direct correlation on stream health. Urbanization is one of many factors influence stream and watershed health.

  

Figure 1. Stream health is more variable in less urbanized environments and becomes uniformly poor in highly urbanized environments (Booth et al. 2004).

Another influencer of stream health was determined to be hydrologic metrics, broken down to stormflow and baseflow patterns over multiple years. These metrics were found to be correlated with urbanization because urbanized streams tend to have more high flow events more often with increasing urban development. Streams with more flashy flows (say what this means here) were found to have lower biota levels, higher erosion, and destabilized channels, therefore having a significant influence on stream health (Booth et al 2004, Konrad and Booth 2002).

B-IBI was found to be correlated with stream flow regimes. Shown in figure —-, B-IBI were higher in less flashy watersheds. When used in combination with TIA, B-IBI was better predicted in studied streams. Streams with more flashy flows were found to be correlated with % urban land cover within a watershed. Thus, urban land cover within a watershed influences the stream health. Urban land cover was not explained in this study, but for this paper, urban land cover will assume land use type (eg. Industrial, commercial, and urban homes). The study inferred that urban land cover may affect biological conditions more than hydrologic conditions.

Local landowner decision making on stream/riparian land use on their property is a large influencer on stream health and is one of the least studied in Washington state. Individual behavior in the Puget Sound watershed has been studied based on mailed questionnaires, interviews, and on-site visits (Schauman, 2000). Local residents were found to place high value on their direct interactions with fish in their stream parcels. During site visits, sites older than 10 years had many backyards with manicured lawns along the stream banks. In sites less than 10 years, most yards contained a riparian buffer with paths leading from the backyard to the stream. All studied residents had a desired connection to their local stream and watershed, but positive desires to fish and stream health was not correlated with positive behavior. The study found that even with local outreach and education efforts, few individuals actually responded by taking action to rehabilitate streams on their property even though many of these residents recognize salmon rehabilitation as a top priority in the region (Booth et al. 2004).

Individual behavior affects both local stream reaches and the greater watershed health. In low impacted areas, streams can be restored to functional health or preserved, but in highly impacted streams, only small improvements to the stream health can be taken because of lack of control of multiple contributing factors influencing stream health. Therefore, private landowner support is crucial to watershed and stream recovery and health (Booth et al 2004).

Seattle watershed case studies

Longfellow Creek in West Seattle has high flash flows and storm water flood events. The Puget Soundkeeper Alliance is using coho salmon as the stream health indicator. Coho were chosen because they spawn during high flow events, when storm water runoff is at its highest, and they are sensitive to urban pollutants. Certain storm water runoff will kill adult coho before they are able to spawn, known as pre-spawn mortality. This is unique to coho salmon, as other salmon do not appear to be as sensitive to pollutants. Even when coho do live to spawn, their eggs are often washed away during flash flow events. 2016 had lower pre-spawn mortality, but those results could be due to above average precipitation in the dry season, possibly lowering pollutant accumulations and concentrations. However, it could also be contributed to restoration efforts in the watershed, which include 1) a one acre natural wetland created to filter runoff by Delridge neighborhood development association, 2) Seattle Public Utilities rebates to homeowners to encourage raingarden installation, and 3) invasive vegetation removal and restoration of riparian cover along the banks of the creek by the nature consortium and other groups.

Figure 2. (Puget Sound Keeper 2016).

 

Another local co-management effort in the Seattle watershed is Thornton Creek, located in North Seattle. Thornton Creek Alliance is a grassroots volunteer group dedicated to preserving and restoring ecological processes within the Thornton Creek watershed. This groups has partnered with local conservation groups and government agencies to provide the best benefits to the whole watershed. Adopt and stream foundation and king conservation district provide free raingardens to qualifying residents within Thornton Creek watershed. The group encourages citizen science to test for water quality, such as E-coli to find pollution point sources, and volunteer work parties restoring riparian vegetation in public parks and lands. Biologists from Northwest Fisheries Science Center are also collecting benthic invertebrates to determine stream health along stream reaches. Seattle Public Utilities is working on restoring Thornton Cr using benthic invertebrates as the health indicator of the stream. Coho salmon are also found with pre-spawning mortality in this stream.

The stream was channelized and dredged in developed areas, leaving no benthic layer to work with (layers of gravel under the stream). The city took on an experimental restoration project and added benthic layers along 1,600 feet along the channel in 2016. These benthic gravels were taken from a relatively healthy local watershed, the Cedar River. The hopes were to re-introduce Thornton Creek with benthic invertebrates and native hyporheic organisms.

Figure 3. Thornton Creek restoration site (Thornton Creek Alliance 2014).

 

Both creeks are in their restoration phase with little information on their current success rates. However, both creeks do appear to be increasing in health. Both stream restoration case studies were compared against each other using 6 rehabilitation goals shown in figure 2.

1. Cluster development and keep as much natural vegetation as possible, leaving riparian buffers intact (Booth et al 2002). This boils down to public policy on development and private landowner decision making.

There is no published information in private landowner decision making along stream reaches, which could lead to further research in the future. Because both streams are in the Seattle watershed, they should have similar public policy.

2. Limit watershed TIA and introduce re-infiltration of storm water (Konrad and Burges, 2001).

 Both streams have volunteer and government efforts to install rain gardens in each watershed.

3. Protect riparian buffers and wetland areas and minimize man-made water crossings (Morley and Karr 2002).

Yes.

4. Get landowners involved in stewardship programs in rehabilitating or maintaining stream health.

Yes.

5. Bring together multiple disciplines in toxicology, hydrology, geology, biology, and ecology, land use, and policy to unify decision making and restoration efforts.

Thornton Creek appears to be doing a better job at coordinated restoration efforts, possibly due to the grass roots volunteer support than Longfellow Creek.

6. Measure stream biota along with physical, chemical, and landscape features to make effective management decisions and policy (Morley and Karr, 2002). 

Thornton creek is doing this.  Longfellow Creek is using coho salmon as an indicator, which are a good indicator of water quality, but because many salmon are hatchery salmon, it is hard to determine if the presence of salmon is indicative to a salmon sustaining stream and overall stream health.

Figure 4. table of 6 rehabilitation goals comparing Thornton Creek and Longfellow Creek.

 

Conclusion

Fully restoring developed watersheds is not feasible in the near future because human influence can’t be completely mitigated in an urban environment. However, stream health is important to ecosystem services, such as fishing economies, clean water, nutrient cycling, etc. restoration efforts should be combined interdisciplinarily, at the holistic watershed approach, tackling as many causes of stream degradation as possible in order to make as much impact as possible. Managing streams needs to include a balance of science, policy, and individual actions (Karr, 2001). Focusing on water quality, stream hydrology, or salmon restoration separately will fall short of successful stream health rehabilitation. Diverse stakeholders, institutions and agencies will need to coordinate efforts to successfully manage stream health in urban environments (Wang, 2001).

 

References

Booth, D. B., Karr, J. R., Schauman, S., Konrad, C. P., Morley, S. A., Larson, M. G., & Burges, S. J. (2004). Reviving urban streams: land use, hydrology, biology, and human behavior. JAWRA Journal of the American Water Resources Association, 40(5), 1351-1364.

Konrad, C. P., & Booth, D. B. (2002). Hydrologic trends associated with urban development for selected streams in the Puget Sound Basin, western Washington (No. 2002-4040).

Konrad, C. P., & Booth, D. B. (2005, September). Hydrologic changes in urban streams and their ecological significance. In American Fisheries Society Symposium (Vol. 47, pp. 157-177).

LeBlanc, R. T., Brown, R. D., & FitzGibbon, J. E. (1997). Modeling the effects of land use change on the water temperature in unregulated urban streams. Journal of Environmental Management, 49(4), 445-469.

Morley, S. A., & Karr, J. R. (2002). Assessing and restoring the health of urban streams in the Puget Sound basin. Conservation Biology, 16(6), 1498-1509.

Puget soundkeeper.  Kerry McGowan  February 21, 2017. https://pugetsoundkeeper.org/wp-content/uploads/2017/02/2016-Salmon-Survey-Report.pdf

https://www.seattletimes.com/seattle-news/environment/thornton-creek-gets-a-makeover-from-the-ground-up/

Schauman, S. (2000). Human behavior in urban riparian corridors. Riparian Ecology and Management in Multi-Land Use Watersheds, PJ Wigington, Jr. and RL Beschta (Editors). American Water Resources Association, Middleburg, Virginia, TPS-00-2, 335-340.

Thornton Creek Alliance, January 24th, 2012. http://www.thornton-creek-alliance.org/