Findings and Recommendations

Assessment of Biological Health of Riparian Wetlands, Sonoma Creek Watershed
CD- 98984501-0
March 2004

Findings from Avian and Riparian Inventory

The amount of avian data is too small to draw definitive conclusions. This caveat should be kept in mind when interpreting the data. The following correlations suggest that riparian corridors in the Sonoma Creek watershed composed of a richer shrub layer support higher species diversity in riparian songbird populations. The results also suggest that earlier successional stages within riparian habitat (i.e. minimal canopy/tree cover, tree dbh (diameter at breast height), and high shrub richness) can support a higher diversity of bird species.

• Significant positive correlations were found for bird species diversity and species richness with shrub richness.
• Significant negative correlations were found for species diversity and richness with tree cover, high tree height, high shrub height, and minimum shrub dbh.
• A positive correlation was found between species diversity and minimum tree dbh.

Recommendations from Avian and Riparian Inventory

With only two years of data, it is too early to draw conclusions about the Sonoma Creek watershed's songbird populations. We recommend bird monitoring be continued to enable the development of more specific management recommendations supported by additional years of data.

• At minimum, a subset of the point count transects established in the Sonoma Creek watershed in 2001 and 2002 should be monitored by trained individuals every other year.
• Preferably, existing point count transects should be monitored each year.

We recommend adding additional monitoring methods such as nest searching and mist-netting.

• Utilizing more than one monitoring method will allow for a better understanding of the relationships between bird population health and habitat characteristics, as well as local population trends, thus helping to determine how specific land management practices within the Sonoma Creek watershed are affecting songbird populations and allowing for more specific management recommendations to be developed for landowners in the area.
• By adding the nest searching and/or mist netting methods to the study, we would be able to look at reproductive success and annual survivorship.

The vegetation protocol used in association with the avian data collection is not easy to extrapolate to the entire watershed. It is an intensive protocol that reveals avian dependencies on habitat structure. To better assess riparian conditions watershed-wide, the following approaches should be considered.

• Use aerial photography to map the width of riparian forest canopy. Calculate the mean and variability in riparian width for different classes of adjacent land use. This technique may be limited to the valley floor, because it is difficult to distinguish riparian forest from surrounding trees in the hills.
• For each of 3-5 major land use classes, visit 20-30 riparian sites and use a quick protocol to assess riparian condition for approximately 50 meters on each side of the stream. The protocol should include percent cover of trees, shrubs, and herbaceous plants; presence of invasive species; land use practices under the canopy; presence of roads, trails, and fences; and adjacent land use.

Findings from Aquatic Habitat Inventory

Riparian cover over the stream was generally over 80%. However, by other measures of stream health, Sonoma Creek and its tributaries are in only fair shape. Most tributaries had large sediment loads, very little large woody debris or other instream cover, channel head-cutting, and down-cutting, particularly near confluences with Sonoma Creek. Based on these observations, much of the watershed's stream length appears geomorphically unstable. Since channel instability reduces channel habitat values directly by reducing habitat complexity and indirectly by increasing fine sediment loads, these impacts to channel geomorphology may significantly limit the salmonid population. In addition, channel incision on the main stem appears to have significantly reduced the amount of floodplain and off-channel habitat available for juvenile rearing.

Recommendations from Aquatic Habitat Inventory

Restoration Priorities

• Fish passage barriers are a clear problem on some tributaries. Planned work to assess these and repair the most important barriers is a top priority.
• Installation of logs and boulders, or other methods to increase instream shelter, should be pursued vigorously. However, because the stream appears to be down-cutting, projects need to be designed and located very carefully to ensure the structures are not undermined.
• At the isolated locations where riparian forest canopy is lacking, revegetation efforts are recommended.
• Land use Best Management Practices to reduce sediment inputs to streams are recommended. Until the sediment source analysis (in progess) is completed, it will be unclear how much of the current sediment load is due to current land use practices, and how much of it is from historic "legacy" sources.

Utilizing and Improving Existing Data
The habitat survey has produced a massive, complex data set that can generate much more useful information than we have been able to extract so far. Other available datasets have similarly been under-utilized. For the sake of spending public funds wisely, and of planning restoration intelligently, several questions should be investigated to foster understanding of the issues facing the fishery and to prioritize restoration and management actions that will help its recovery.

• Attempts should be made to fill in data gaps created by un-surveyed reaches. Further efforts at landowner outreach will be necessary to gain access to some of these reaches.
• The dataset lacks important data about many habitat units. In future surveys, all parameters should be measured for all pools.
• Using data from the fish population survey in progress, what habitat conditions are associated with larger numbers of fish, and with fish absence?
• Is it possible to distinguish between, and map, large sheltered pools that are important for rearing versus spawning pools? Is there a watershed-wide pattern in the distribution of the two kinds of pools?

Questions answerable with further analysis of the data from the survey include:

• Are tailout substrates and embeddedness related to salmonid presence/absence?
• How are pool canopy cover and instream shelter correlated? Presumably, low canopy cover would correlate with less woody material instream. However, if streams are incised, they may not be well-correlated. A related question is the relationship between water temperatures and canopy.
• Does the presence of predatory fish such as adult pike minnow correlate with an absence of juvenile salmonids in mainstem pools?
• Are fine sediment substrates and embeddedness correlated? Is only one of these measurements necessary?

Future Studies
Most of the completed and scheduled work in the watershed focuses on the physical structure of habitat. We recommend that the next generation of fisheries studies in the watershed include biological factors affecting each steelhead life stage. For example, in the Napa River watershed, Stillwater Sciences discovered that reduced food supply combined with heightened respiration rates may be limiting for local steelhead populations during periods of summer juvenile rearing. Other limiting factors may include inter-species competition (particularly the effect of introduced species on the viability of the native trout population), other food-web dynamics, and population dynamics affected by the oceanic portion of the life-cycle. Useful biological information could be gained by continued BMI sampling and riparian width and condition assessments, for example.

Rosgen channel typing does not seem to apply neatly to Sonoma Creek watershed's streams, as others have observed about California coast range streams.

• A more in-depth and sub-watershed-specific assessment of geomorphology should be conducted to help determine whether observed dysfunction in the channels is due to historic changes or current issues. This is a critical question for planning restoration and for identifying relevant BMPs.
• If channel incision is a driver of many stream problems, including loss of LWD inputs and in-channel habitat complexity, carefully planned reach-scale restoration actions with the full support of many landowners are needed.

Water quantity appears to be a serious limiting factor.

• To what degree does water extraction in summer and winter affect fish?
• Can observations of pumps and pipes in the streams be correlated with water extraction rates?
• Credible estimates of water inputs, uses, throughflows, and fishery needs are necessary for long-term restoration and maintenance of the aquatic, riparian and valley-floor ecosystems.
• Small, ephemeral tributaries that do not appear on USGS quad maps may provide significant habitat value. During high flow years, conditions may favor spawning in these ephemeral channels (Robert Leidy, USEPA Region IX, pers. comm. 2003). The extent and value of these reaches should be estimated or documented.

The aquatic habitat assessment protocol used does not address water quality.

• The potential exists for unobservable deleterious sub-lethal effects to fish and other aquatic life due to water quality. Water quality assessments-including levels and duration of turbidity, suspended sediment, and pesticides-are needed to address this issue.

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