Grantee Research Project Results
2023 Progress Report: Evaluating agricultural management practices benefiting the Monterey Bay: reducing nutrient loads and Harmful Algal Bloom (HAB) events
EPA Grant Number: R840083Title: Evaluating agricultural management practices benefiting the Monterey Bay: reducing nutrient loads and Harmful Algal Bloom (HAB) events
Investigators: Clark, Ross , Bowers, Holly
Current Investigators: Bowers, Holly , O'Connor, Kevin , Clark, Ross
Institution: San Jose State University
Current 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, 2022 through August 31,2023
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 Culture experiments: Data from the two mesocosm experiments are yielding insights into single species HAB response to nutrients derived from agricultural effluent. The A01
(Alexandrium sp.) mesocosm experiment involved spiking Alexandrium into nine 15L bags containing an 85% filtered seawater base. ‘PRE-Bioreactor’ test bags (n=3) utilized 15% agricultural effluent prior to filtration through the Seamist wood chip bioreactor site, and the ‘POST- Bioreactor’ test bags (n=3) utilized effluent
after passing through the bioreactor. Phosphate was adjusted to maintain the same N:P ratio as in the control treatment. These results reflect the typical growth pattern of Alexandrium in pure culture, passing through lag, exponential, and stationary phases within ~12 days. In our experiments, no difference in these patterns was observed in the control (clean river water supplemented with pure nutrients from a media kit), pre- and post-treated agricultural waters which indicates that nutrient availability from agricultural waters can sustain Alexandrium populations.
Figure 1 Cell abundance (via microscopy) and Fv/Fm for Alexandrium (A01) mesocosm experiment
Subwatershed Nutrient loading: Nitrogen loading from the 9 subwatersheds has been calculated for at least two spring and fall growing seasons. Nitrogen concentration and flow results were measured through continuous sampling systems and weekly instantaneous flow and nitrogen grab samples. For many of the subwatersheds, the resulting nitrogen concentration values are similar. Several watersheds however were estimated to have significantly different concentration (Figure 2) dependent on which sampling method was used (i.e. Alisal Slough). These variations in average monthly loading calculations suggest significant fluctuations in concentration exist during the month that can lead to over or under reporting average concentration used to quantify load.
Similarly, average flow calculations were found to differ significantly within some watersheds and average flow calculations were highly dependent upon when the measurements were collected. Within these highly modified watersheds, flow is often driven by farm pumps that cycle on and off depending on local flow conditions. Nitrate concentrations were found to be similar between some sample methods but instantaneous flow measurements can greatly under-represent average flow conditions within the channel.
Nitrate reduction of treatment systems: Field research effort in 2023 has focused on documenting nutrient reduction rates of the various water quality treatment systems. The field team has developed a thorough protocol for sampling within the isolation rings at several sites. The samples collected within the in-situ water over 24 to 48 hr periods will be analyzed to estimate the size and location of new treatment systems to further reduce nutrient loading within the watershed.
Figure 2 Nitrate concentration (blue) and flow values (black and green) from grab samples and continuous monitoring systems. Red values represent nitrate concentration (circle) and flow rate (square) data from industry monitoring program.
HAB response to treatment systems: Receiving water quality sampling: The receiving water monitoring arrays have been installed in the four primary agricultural watersheds discharging to Monterey Bay. Each system (Pajaro, Moro Cojo, Gabilan & Old Salinas River) has been functioning well to quantify hourly nitrate load to Monterey Bay. Technical Staff are investigating statistical methods to fill in data gaps (due to system failure) in continuous monitoring systems. The field team is working with Pajaro Valley Waste Water Treatment facility and the City of Watsonville to relocate the monitoring system to a more secure location, safe from vandalism and flooding. 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 the final analyses for the Pseudo-nitzschia and Alexandrium mesocosm experiments: dissolved organic N and P, CHN (via the SLAB lab in Hawaii), and particulate toxin. We will also complete flask experiments to directly compare HAB species growth and toxin response to pre- and posttreated bioreactor waters to further demonstrate the effects of load reduction that have been well documented.
CCWG will 1) Finalize loading estimates for each subwatershed (waiting on lab data analysis), 2) Complete load reduction estimates from various nitrogen treatment systems and agriculture drainage systems, and 3) populate the watershed loading box model with focus on nitrogen loss estimates.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this projectRelevant Websites:
Moss Landing Marine Laboratories Public Data Portal Exit
Progress and Final Reports:
Original AbstractThe 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.