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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.
No reported data for this Indicator
Phosphorus load reduction with the target shown in 2019 in light blue.
- Status
- Insufficient Data to Determine Status or No Target Established
- Trend
- Insufficient Data to Determine Trend
- Confidence
- Not available
- The status of the standard is assessed as "insufficient data" because the monitoring programs assess total phosphorus load, and do not directly quantify dissolved phosphorus load.
- 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.
- 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.
No related projects or programs defined for this indicator.
- The programs and policies of the TMDL are likely to reduce the loading of all forms of phosphorus to the Lake. However, TMDL monitoring only quantifies the reduction of the primary pollutants of concern. In 2019, TMDL implementers (CalTrans, CLST, Douglas, El Dorado, NDOT, Placer, Washoe) exceeded the phosphorus load reduction targets and reduced average nitrogen concentrations in surface runoff by 15.5% from baseline levels. The status of the standard is assessed as "insufficient data" because the monitoring programs assess total P load, and do not directly quantify dissolved phosphorus load.
- The TMDL was adopted in 2011 and the 15.5% reduction was achieved in the last 10 years.
No photos available.
No documents available.