Scoring: The Central Coast Regional Water Quality Control Board (Water Board) updated the scoring method for assessing the status and trends of waterbodies. The analyses look at all available data, some of it going back to the 1990s. More information on the methods of analysis and results for other areas on the California Central Coast are available at the Water Board website.
Bay Oxygen: The bay oxygen readings were collected by Estuary Program volunteers via kayak using handheld meters by YSI, either the model 85 or the model 2030. For the 2020 report, the Magnitude Exceedance Quotient (MEQ) method was used and included all data going back to 2002. The trend for bay oxygen data was determined by calculating the MEQ analysis using data for all sites, both prior to January 1, 2014 and after that date for comparison. The bay wide trend was Stable (represented by a circle), meaning no real change from before as compared to after January 1, 2014. The overall bay dissolved oxygen condition was Poor (represented by the color orange of the symbol).
Nitrates: The creek nitrate scores for the 2020 report differed greatly from the 2014 report, which is the last time the Estuary Program conducted the analysis. The difference was due to changes in the Water Board method of analysis, rather than a change in nitrate conditions on local creeks. For the 2020 report, the Magnitude Exceedance Quotient (MEQ) method was used and included all data going back to 2001. For the 2014 report, the analysis included five years of data (2008 to 2012) and determined whether a certain percent of the data was above or below the thresholds of 1 mg/L (protective of aquatic life) and 10 mg/L (protective of human health). The Water Board is adopting the MEQ method because it takes into account by how much a reading exceeds the threshold target value and how many of the readings exceed the threshold target value. This revised approach provides better information on the health of a water body.
In determining the trend in nitrate data, it was difficult to distill the status for the entire watershed down to just one symbol. We decided that the best approach would be to represent the watershed nitrate status with the conditions on the sites lowest down (closest to the bay) on our two main creeks, Chorro and Los Osos. Because we lacked adequate data from lower Los Osos Creek due to tidal influence (bay water is pushed up the creek by the tides, making it difficult to measure the nitrates in the freshwater coming downstream), we decided to represent the trend in nitrate data with our most downstream monitoring site on Chorro Creek, which is located at the site known as Twin Bridges. This is where Chorro Creek passes under the South Bay Boulevard bridge. Using the Twin Bridges nitrate data, the results were divided into two groups: data before January 1, 2014 and data after that date. The status was calculated for each group of data, and the readings since the cut-off date have shown some improvement. Thus, the trend went from Very Poor nitrate results to Poor and the indicator symbol was an upward pointing arrow. The symbol has a red square (representing Very Poor conditions of data before January 2014) and an orange triangle (representing Improving but Poor conditions in data since January 2014).
If we had multiple sites on a creek, we combined the data to create a single score for each creek and that score was extrapolated to apply to the entire creek. The exception is Chorro Creek, where the creek was divided into upper, middle, and lower segments based on hydrological characteristics, inputs, and other factors.
Creek Health: The bioassessment data is collected following a detailed technical protocol developed by the state of California. The bioassessment samples are sent to a taxonomy lab for sorting, counting, and identification. The lab provides raw scores (how many of each family or genus was present) as well as metrics calculated with the raw data. One of these metrics is the Southern California Index of Biotic Integrity (IBI) score, and this is the metric that the Estuary Program used for our analysis. We calculated the average of all available data, some going back to the 1990s, and compared it to the scoring criteria for the IBI scores which are as follows: Very Good (80 to 100), Good (60 to 79), Fair (40 to 59), Poor (20 to 39), and Very Poor (0 to 19). The indicator symbol for Creek Health is a circle because the trend has been Stable over time. The color is grey indicating Unknown status, because we lack data from areas that we expect are heavily impacted, specifically lower Los Osos and Warden Creeks.
In creating the map, if we had multiple sites on a creek, we combined the data to create a single score for each creek and that score was extrapolated to apply to the entire creek. The exception is Chorro Creek, where the creek was divided into upper, middle, and lower segments based on hydrological characteristics, inputs, and other factors.