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Phosphorus is a nutrient important to the growth and reproduction of plants and is considered a pollutant of concern in the Lake Tahoe Region. Nitrogen and phosphorus together support the growth of algae in Lake Tahoe and contribute to the decline in water transparency and adversely affect nearshore aesthetics. Landscape disturbances including impervious surfaces, residential and commercial development, wildfire, and the degradation of stream environment zones (SEZs), can contribute to sediment and nutrient inputs to the lake or its tributaries. Projects such as restoring SEZ and limiting fertilizer use in the Region seek to reduce phosphorous in Lake Tahoe's tributaries. Phosphorous reductions are monitored by partners through the Lake Tahoe Total Maximum Daily Load Program (TMDL).
- Status
- Considerably Better Than Target
- Trend
- Rapid Improvement
- Confidence
- Moderate
- In 2019, TMDL implementors (CalTrans, CLST, Douglas, El Dorado, NDOT, Placer, Washoe) exceeded their load reduction targets for phosphorus by 75 percent greater than the target.
- In 2019, approximately 7,500 miles of streets were swept using high-performance sweepers, 29 non-compliant wood stoves were removed or replaced, and nearly seven miles of pedestrian and bicycle routes were constructed.
- At the September 2020 meeting of the Threshold Update Initiative Stakeholder Working Group, consistent with guidance from the Tahoe Science Advisory Group, the water quality standards related to load reduction were recommended to be removed as threshold standards and retained as Environmental Improvement Program performance measures.
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- Phosphorus is a nutrient important to the growth and reproduction of plants and is considered a pollutant of concern in the Lake Tahoe Region (Lahontan and NDEP, 2010b)
- Nutrient (nitrogen and phosphorus) inputs from anthropogenic sources are considered the primary driver of increasing PPr in temperate lakes (Conley et al., 2009). It is suspected that activities associated with urbanization and watershed disturbance influence Lake Tahoe’s PPr through the release of nutrients and subsequent transport in runoff, or through the atmospheric deposition of nutrients. The nutrient source analysis for the Lake Tahoe TMDL indicates that both urban and non-urban sources of nitrogen and phosphorus are important contributors of nutrients to Lake Tahoe (Lahontan and NDEP, 2010a; Sahoo et al., 2013). Meteorological conditions (e.g., wet vs. dry years) also affect PPr, due to changes in tributary loads of nutrients, and differences in the magnitude of physical processes within the Lake (e.g., deep lake mixing). However, the trend suggests these factors have not substantially influenced the overall trend. The source of nutrients that are driving the increase in PPr is currently unknown.
- Status is evaluated relative to the TMDL target for 2019. Phosphorus load reduction in 2019 exceeded the TMDL target by 75%.
- The 2020 TMDL performance management report finds that phosphorus load reduction has increased from 9.8% of baseline in the 2017 water year to 15.5% of baseline in the 2019 water year. That represents a 63% increase in phosphorus load reduction between 2017 and 2019.
- Evaluation is based on the Lake Clarity Crediting Program (LCCP)
- Evaluation is based on the Lake Clarity Crediting Program (LCCP)
- Evaluation is based on the Lake Clarity Crediting Program (LCCP)
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