Regional Water Quality Control Board
North Coast Region
5550 Skylane Blvd.
Santa Rosa, CA
Subject: Inclusion of the Laguna de Santa Rosa on the Clean Water Act Section 303 (d) List of Water Quality Limited Segments – for the invasive hydrophyte Ludwigia – for the next listing cycle.
Currently the Laguna de Santa Rosa is listed on the Clean Water Act Section 303 (d) List of Water Quality Limited Segments as impaired as a result of introduced pollutants: sediment/siltation, elevated temperature, biostimulants Nitrogen and Phosphorus, and lack of Dissolved Oxygen.
Surface water monitoring in the possession of the Regional Board indicates that the levels of biostimulants in the Laguna de Santa Rosa are high and are a significant factor contributing to the deteriorating conditions in the Laguna de Santa Rosa. Wastewater from the Laguna Subregional Treatment Facility, runoff from agricultural operations, and urban runoff have been identified as the sources of elevated nitrogen and phosphorus. The excess of biostimulatory substances (N and P), along with high levels of sediment, are creating the conditions for secondary water quality impairment by supporting the colonization of the Laguna de Santa Rosa by the invasive and nuisance plant species – Ludwigia.
There is significant information in the record, from past monitoring and evidence presented by the Laguna Foundation, to indicate that nuisance aquatic growth of Ludwigia is a serious problem in the Laguna de Santa Rosa – with public health implications for the surrounding neighborhoods. There is evidence that the colonization of the Laguna de Santa Rosa by Ludwigia has spread over the years and presents a mosquito control issue. Control of the Ludwigia by continuous application of pesticides is difficult, expensive, and not effective in the long run. Last year over 5,000 tons of Ludwigia were removed from the Laguna de Santa Rosa. Ludwigia control operations will cost close to $2,000,000 in the next several years.
The Ludwigia control efforts are also compromising water quality standards in the Laguna. Pesticide application with biomass die-off, even with mass removal, leaves behind significant biomass. Eutrophic conditions related to decaying plant matter substantially lowers DO (a listed pollutant) and contributes to the nutrient cycle.
As indicated, the Regional Board has in the record (from previous listing cycles) significant evidence supporting the ongoing existence of the Ludwigia infestation and related nuisance effects where water quality objectives can not be met and beneficial uses can not be protected. In additions there is the ongoing public heath risk presented by this invasive plant as a mosquito and disease vector.
We believe there is sufficient information in the file (prior to February 28, 2007) in the form of monitoring data, data points, history, photos, etc., to support this listing under State Listing Policy – numeric and narrative criteria.
We believe that the effort associated with this listing is justified as it will facilitate progress in finding avenues of control (promoting programs limiting nutrients and sediment inputs) as pesticide control is not all that effective, has definite adverse water quality effects, and can not go on forever.