Over the last year, the potential for adverse effects of nutrient loads to San Francisco Bay has become a topic of increasing concern. In recent months, work has commenced to develop a nutrient strategy for the Bay (see Section 4.8). A main goal of the strategy is to develop a well-reasoned and cost-effective program to generate the scientific understanding needed to fully support nutrient management decisions. Among the key objectives outlined in the strategy is quantification of nutrient loads from main potential sources. For urban watershed runoff and riverine inputs, there are currently limited data to support developing such estimates. Developing accurate estimates for regional watershed loads to the Bay requires both acquiring empirical data from representative watersheds (for calibration/validation) and developing models to quantify loads across the region.
The small tributaries loadings strategy was first implemented in 2010 and aims to quantify concentrations and loads of priority pollutants to the Bay from watersheds during wet weather events (see detailed description Task 4.5). Study watersheds have been selected to represent the range of land use and land cover characteristics of the diverse watersheds draining to the Bay. The loads monitoring project is a multi-year effort, studying 4 watersheds for 4 storms in 2011-2012 (3 watersheds monitored by SFEI, one by consultant), and up to 2 additional watersheds in 2012-2013. Empirical data on flow and concentration will be collected and used to compute loads, and to calibrate spreadsheet models to estimate loads across the region. Although nutrients are not the main focus of this study, three nutrient parameters (nitrate, total phosphorous, dissolved orthophosphate) are among the current list of analytes. However, other important nutrient parameters that are needed to create a full picture of nutrient loads to the Bay are not being measured (ammonium, total Kjeldahl nitrogen). At the October RMP Sources, Pathways, and Loadings Workgroup meeting there was general agreement that the current suite of analytes should be augmented to include a full set of nutrient analytes, funds permitting. Adding these nutrient analytes now, when teams are already mobilizing for the other contaminant sampling, is a wise investment, leveraging current funds being invested in this effort.
Applicable RMP Management Questions
- Is there a problem or are there signs of a problem in the Bay? What future nutrient-related impairments are predicted for the Bay?
- Which nutrient sources, pathways, (and transformation processes) contribute most to concern? What is the relative contribution of each loading pathway (POTW, Delta, NPS, etc.) to the Bay overall and the Bay’s key sub-systems, and how do these loads vary seasonally?
Samples will be collected for additional nutrient parameters at the four watersheds being sampled during the 2012-2013 rainy season. The additional analytes to be monitored are ammonium, nitrite and total Kjeldahl nitrogen. The combined suite of nutrient analytes matches the type of information being collected in the USGS monthly Bay surveys, and data may be collected in the near future at some regional POTWs.