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Home Water Aquatic Species and Communities

Upper Truckee Marsh

Status and Trend

Interpretation and Commentary

Status: Somewhat Worse Than Target
Trend: Litle or No Change
Confidence: Low

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  • Relevance - Located within the City of South Lake Tahoe, the Upper Truckee Marshis the single largest wetland in the Sierra Nevada, occupying over 1,300 acres (Manley et al. 2000). Development of the Tahoe Keys in the 1960s reduced the area of the wetland to less than half of its former size and more directly channeled the path of the Upper Truckee River to Lake Tahoe (Manley et al. 2000). Despite this development, the marsh is still the largest in the region, and this unique ecosystem provides important habitat for numerous plant, animal, and invertebrate species,including some that depend on the marsh for their entire life cycle (Manley et al. 2009).Extensive sandy beach deposits at the margin of Lake Tahoe support a robust population of the endangered Tahoe yellow cress (Rorippa subumbellata), which is a TRPA listed sensitive plant species (Stanton and Pavlik 2005-2010).Freshwater marshes are one of the most productive ecosystems in the Tahoe Basin, and have been identified in the Tahoe Science Plan (Hymanson and Collopy 2010) as special communities, which are small in extent but have great functional importance (Manley et al. 2009).The Upper Truckee River drains the largest watershed in the Lake Tahoe Basin, and the wetland vegetation in the marsh plays an important role in recycling nutrients, trapping eroding soil, and filtering pollutants (Martin and Chambers 2004). Still, the Upper Truckee River is the single largest source of suspended sediment entering Lake Tahoe (Lahontan and NDEP, 2010). Retention of existing vegetation in the remaining marsh area is important for conservation of wildlife habitat and enhancement of water quality (Manley et al. 2009).
  • Adopted Standard - Provide for the non-degradation of the natural qualities of any plant community that is uncommon to the Basin or of exceptional scientific, ecological, or scenic value. The Threshold Standard shall apply, but not be limited to, 1) deep-water plants of Lake Tahoe, 2) Grass Lake, 3) Osgood Swamp, 4) Hell Hole, 5) Upper Truckee Marsh, 6) Taylor Creek Marsh, 7) Freel Peak Cushion Plant Community, and 8) Pope Marsh.
  • Indicator - The status and trend determination was based on a qualitative assessment of the natural qualities of a plant community. The natural qualities of a plant community include the current plant species assemblage, the health, age, and ecological condition of those plant species, and the condition of the hydrologic regime.
  • Status – The Upper Truckee Marsh is one of the most unique and productive ecosystems in the Lake Tahoe Basin. Its condition depends directly on the proper functioning of the Upper Truckee River and the health of the surrounding watershed. The majority of the marsh is actively managed by the California Tahoe Conservancy (CTC) to maintain and improve the conditions of natural resources, including plant communities. Substantial alteration of the watershed over the past 150 years has caused erosion along the banks of the Upper Truckee River and led to channel incision and increased sediment transport and nutrient loads into Lake Tahoe (Manley et al. 2009). Although increased sediment load from streams contributes to reduced clarity in the Lake, the cumulative effect this has had on the vegetation community in the marsh is not well known. The Upper Truckee River inundates the floodplain less often since being more directly channelized, which deprives the wetland vegetation of needed sediment and nutrients. The incised channel has also lowered groundwater levels and desiccated riparian and meadow vegetation. In addition, heavy grazing in the past may have substantially altered the composition of plant and animal communities within the marsh. These cumulative impacts have compromised the hydrologic integrity of the Upper Truckee River ecosystem and degraded the natural qualities of the marsh (Manley et al. 2000). Because the hydrologic function of the marsh has been degraded, it is thought that the 2006 Threshold Evaluation ranked the status of the Upper Truckee Marsh too high when it described it as being in attainment. Although it is not possible to assess the degree of degradation without quantitative data regarding desired reference conditions or the existing vegetative community, it is evident that the marsh has not achieved its desired condition. Therefore, the status of Upper Truckee Marsh is considered to be “somewhat worse than target.”

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  • Trend The 2006 Threshold Evaluation considered the Upper Truckee Marsh to be in attainment, whereas this evaluation has determined it to be “somewhat worse than target.” The reduced status in this evaluation is based primarily on the location of the Upper Truckee Marsh in the urban core, and its compromised hydrological condition. However, there is no quantitative evidence available indicating there has been any particular decline in the condition of the marsh over the last five years; in fact, many of the management actions implemented by the CTC are expected to improve conditions in the Marsh. Due to the lack of quantitative evidence indicating an improvement or decline in the condition of the Upper Truckee Marsh, the trend was assessed as “little or no change.”
     

  • Confidence – Confidence in the status and trend analysis is “low” because both determinations were based on a qualitative assessment of the hydrological condition, resource management actions, and surrounding land uses, and was not supported by sufficient quantitative data.
  • Human and Environmental Drivers - The Upper Truckee Marsh lies within the largest and most heavily developed watershed in the Basin. A legacy of clear-cutting, heavy grazing, modification and diversion of the Upper Truckee River, and urban development directly within the marsh have shaped the current vegetative community in the Upper Truckee Marsh. Marsh communities are tightly linked with water table attributes and soil water chemistry (Allen-Diaz 1991). Urban runoff and pollution can alter water chemistry and affect vegetation composition. Historical channel and floodplain manipulations lower the water table, and result in a drier marsh that supports a different plant community. Recreational activities can result in soil compaction, stream bank erosion, trampling of plants, disturbance of wildlife, and introduction of invasive species. As with other wetlands, extended drought and climate change pose a threat to the system.
  • Monitoring Approach – The status and trend determinations were based on a qualitative assessment of factors influencing the condition of the site, including historical alterations, on-going hydrologic impacts, sources of recreation-related disturbance, and surrounding land use and management. Vegetation monitoring is performed by the CTC to identify management needs or assess the effectiveness of planned or completed restoration efforts, but it does not yet provide information useful in assessing long-term changes in the natural qualities of the plant community. Monitoring efforts include annual surveys for invasive species, plant community mapping, floodplain biomass monitoring, and monitoring of hydrologic properties that affect plant communities such as ground water levels and river channel capacity. Much of the monitoring data provides baseline conditions for factors that are expected to change after implementation of a large restoration project at the site. This information is expected to better inform future evaluations of the Threshold Standard at the marsh.
  • Monitoring Partners – California Tahoe Conservancy

Links

 
  • Monitoring Plan
  • Conceptual Model

Map

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Map showing location of Upper Truckee Marsh and surrounding area.

Additional Info

References

Additional Information

Last Updated on Tuesday, 02 October 2012 13:26