Grantee Research Project Results

2024 Progress Report: Evaluating agricultural management practices benefiting the Monterey Bay: reducing nutrient loads and Harmful Algal Bloom (HAB) events

EPA Grant Number: R840083
Title: Evaluating agricultural management practices benefiting the Monterey Bay: reducing nutrient loads and Harmful Algal Bloom (HAB) events
Investigators: Bowers, Holly , O'Connor, Kevin , Clark, Ross
Institution: San Jose State University , Moss Landing Marine Labs
EPA Project Officer: Ludwig-Monty, Sarah
Project Period: September 1, 2020 through April 28, 2025
Project Period Covered by this Report: September 1, 2023 through August 31,2024
Project Amount: $999,999
RFA: Approaches to Reduce Nutrient Loadings for Harmful Algal Blooms Management (2020) RFA Text | Recipients Lists
Research Category: Harmful Algal Blooms , Water

Objective:

The proposed project will demonstrate the effectiveness of farm runoff treatment systems in reducing nutrient discharges to coastal waterways and provide a blueprint for scaling-up treatment systems within two key agricultural watersheds of the Monterey Bay, CA. In addition, this project will examine the potential link between agricultural nutrient discharges and the growth of harmful algal blooms (HABs).

Progress Summary:

HAB response (laboratory and field): In order to understand nearshore response of HAB species, EBL continued with sample analysis from the twelve transects (8 stations each) by completing full phytoplankton counts, chlorophyll measurements and nutrient panel analyses, (nitrate, ortho phosphate, ammonium, urea, nitrate + nitrite, silicate via the nutrient lab at MLML). Multiple HAB species were identified via microscopy in all twelve transects, and chlorophyll values indicate population fluctuations over time and space. Filters for elemental carbon and nitrogen were prepared and sent to the SLAB lab (University of Hawaii at Manoa). Analyses continued on the samples collected from the Pseudo-nitzschia multiseries mesocosm, including completion of elemental carbon and nitrogen measurements. DNA from all experimental timepoints was extracted and a graduate student empirically worked through developing and validating a standard curve towards quantifying copy numbers per cell over time. All of these data sets are beginning to provide insight from discrete angles into how HAB species in Monterey Bay are utilizing available nutrients from treated and untreated agricultural effluent.

Subwatershed Nutrient loading: Nitrogen loading from the 9 subwatersheds has been calculated for spring and fall growing seasons in 2022 and 2023. Nitrogen concentration and flow results were measured through continuous sampling systems and weekly instantaneous flow and nitrogen grab samples. After completing QA/QC analyses on the continuous nitrate samples collected through the osmotic sampler, these results were deemed unusable due to the high level of biotic activity within the tubing which caused the nitrogen species to change during the sampling period. The weekly grab samples will be used in the watershed nitrogen reduction model. Both the continuous and instantaneous flow measurements are being used in the nitrogen reduction model to get the total discharge coming out of the subwatersheds.

Nitrate reduction of treatment systems: All field work was completed in 2023. Efforts in 2024 focused on nitrate reduction calculations and modeling. Data collected in the nitrate reduction experiments were used to create a watershed sizing tool that will, hopefully, be used to determine the locations and size of new treatment systems to further reduce nutrient loading within the watershed.

Receiving water quality sampling: Three of the four proposed receiving monitoring arrays are functional and quantify hourly nitrate load to the Monterey Bay (Moro Cojo, Gabilan, Old Salinas River). The Pajaro monitoring station was not established due to theft, flooding, and budget constraints, so we will have to rely on our field measurements to quantify nitrate load in this watershed. Technical staff has performed load modeling at the existing arrays that incorporates tidal effects since flow at these stations is heavily influenced by the tides. We will continue to work with the Central Coast Regional Water Quality Control Board and Preservation Inc (agriculture industry monitoring program) to identify how the receiving water monitoring systems can be integrated into regional monitoring programs to document incremental improvements in water quality.

Future Activities:

EBL will complete final analyses for nutrients, elemental carbon and nitrogen, qPCR, and toxins from both mesocosm experiments and the wastewater transects. Rigorous QA/QC pipelines will be applied to produce the final data sets. The development of white papers will be used to visualize individual data sets (e.g. chlorophyll, cell counts, etc.) and facilitate team (EBL + CCWG) discussions for the development of manuscripts.

CCWG will finalize the watershed nitrogen reduction box model and continue working with industry partners to determine how this research can help inform where treatment systems should be placed throughout these subwatersheds.

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Supplemental Keywords:

EPA Region 9, Watersheds, Bioreactors, Treatment Wetlands, HAB Assemblages, modeling, monitoring

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.