Relevance

Pope Marsh occupies roughly 1,500 acres adjacent to the City of South Lake Tahoe, and is managed by U.S. Forest Service Lake Tahoe Basin Management Unit (LTBMU). It was formerly part of the wetland complex at the mouth of the Upper Truckee River, but development of the Tahoe Keys in the 1960s isolated Pope Marsh from the Upper Truckee River and dramatically reduced the size of what was the largest freshwater marsh and meadow complex in the Sierra Nevada (Manley et al. 2000). Pope Marsh is now dependent primarily on rain, snowmelt, and underground flow from Lake Tahoe for its water (Green 1991). Meadows, marshes, and fens have been identified in the Tahoe Science Plan (Manley et al., 2010) as special communities that are small in extent but have great functional importance. Wetland vegetation plays an important role in recycling nutrients, trapping eroding soil, and filtering pollutants (Manley et al. 2000). This filtration capacity is critically important to protect the clarity of Lake Tahoe. Pope Marsh also provides important habitat for numerous species, including waterfowl nesting habitat.

Human and Environmental Drivers

Pope Marsh was irreversibly altered by the development of the Tahoe Keys (Manley et al. 2000).Since then, human activities outside of the marsh (e.g. groundwater pumping, development, and management of lake water levels) impact hydrology within the marsh (Green 1991). The sandy beach deposits that divide Pope Marsh from Lake Tahoe allow for rapid groundwater flow; therefore, the northern portion of Pope Marsh fills and drains in relation to surface elevation of Lake Tahoe. When the level of Lake Tahoe is low, Pope Marsh drains and becomes dry. Based on the presence and depth of peat within Pope Marsh, it is theorized that historically Pope Marsh received water flow in late summer and fall, and sustained saturated conditions throughout the year even when the lake level of Lake Tahoe was lower (before the dam was built). The southern portion of Pope Marsh is less influenced by lake levels, and relies primarily on snowmelt and upland stream flow processes. These anthropogenic stresses on Pope Marsh increase sensitivity to naturally occurring stressors, and likely will initiate gradual changes in the plant community composition of the marsh, which could dramatically change the effectiveness of the marsh as a filter of nutrients and sediments (Green, 1991). In 2011, a high precipitation year, water from Pope Marsh breached the sand berm and flowed into Lake Tahoe. Other human impacts include the introduction of invasive plants, dogs, and some trampling from hiking and bicycling Similar to other wetlands, extended drought and climate change pose a threat to the system. Recent California based climate models predict a nine-degree Fahrenheit increase in temperature by 2100, and more conservative models predict a two- to four-degree Fahrenheit increase in winter and four- to eight- degree Fahrenheit increase in summer (Safford et al., 2012a). Models are more variable for precipitation, but recent models for the Sierra Nevada predict similar to slightly less precipitation. Most models predict drier summer conditions, since more of the precipitation is predicted to come as rain, and snow melt-off will occur earlier in spring (Hayhoe et al. 2004, Dettinger 2005, Safford et al. 2012, Drexler et al. 2013). In the Lake Tahoe Region, these changes appear to be happening at an accelerated pace (Coats 2010). These changes will likely result in decreased stream flow and increased stream temperatures in the summer and fall (Purdy et al. 2014). Climate change may create larger or more frequent flood events if more precipitation comes as rain instead of snow, but will create drier conditions in summer and fall due to lack of slow melting snow pack. Prolonged drought can lower water tables in meadows, increasing the area dominated by drier upland grasses and forbs, and reduce the presence of less resistant and resilient obligate wetland plants (Rejmankova et al. 1999). During the drought of 1988 to 1994, vegetation changes were monitored in Pope Marsh. The results revealed an overall decline in plant production, relative stability in the area dominated by sedge (Carex sp.) and rush (Juncus sp.) communities, and a decline in Rocky Mountain pond-lily (Nuphar lutea subsp. polysepala) and hardstem bulrush (Schoenoplectus acutus) communities. Most species recovered quickly after the drought, but hardstem bulrush did not. An increase in diversity was observed, as forbs such as common mare’s tail (Hippuris vulgaris) and other ruderal terrestrial species established in dry pond margins (Rejmankova et al. 1999).

Transportation Indicators

• Acres of Habitat Restored or Enhanced
• Parcels Inspected for Defensible Space