River Basin Export Reduction Optimization Support Tool (RBEROSTv2) Version 2: Demo and Next Steps
Citation:
Detenbeck, N., K. Moffa, S. Clark, S. Anderson, C. Connolly, R. Labiosa, R. Orourke, H. Parker, S. Rego, A. Tatters, M. Ten Brink, AND T. Wolters. River Basin Export Reduction Optimization Support Tool (RBEROSTv2) Version 2: Demo and Next Steps. Presentation to Puget Sound Stakeholders, NA, VT, June 21 - 25, 2024.
Impact/Purpose:
Nutrients are a major source of stress to Puget Sound (PS). Fish and shellfish resources that Tribes in R10 rely upon are impacted by harmful algal blooms (HABs) and hypoxia (oxygen concentrations that are too low to support aquatic life and other designated uses). These issues are increasing in extent and frequency due in part to population growth and climate change over recent decades, which are predicted to continue (Anderson et al. 2008, Anderson et al. 2021, Washington Dept of Ecology 2003). In addition, although some preliminary work has identified transfer of specific cyanotoxins to marine shellfish within PS (Preece et al 2015), the role of cyanobacteria/cyanotoxins in the total biotoxin burden to PS, including fish and shellfish of interest to Tribes, is unknown (Anderson et al. 2021). Through this work, EPA plans to refine our knowledge on the role of nutrients in the prevalence of HABs in PS and evaluate the appropriate mitigations for excess nutrients loading to the Sound. This work addresses top science priorities for WD/R10, including assessing and mitigating HABs, nutrient impacts and mitigation under climate change, and stormwater/low impact development approaches to mitigating multiple pollutants under variable climate conditions.
Description:
• An updated version (2) of EPA’s River Basin Export Reduction Optimization Support Tool (RBEROST) has been developed to provide nutrient management strategies for the Puget Sound Basin. RBEROST is an R-based tool that sets up an optimization problem to determine the least cost solutions for large river basins to meet nutrient (N and/or P) loading targets, with individual practices implemented at the NHDPlusv2 catchment scale. Targets can be identified both for the final downstream water body (e.g., Puget Sound) as well as for intermediate water bodies within the watershed. Source loads from forested lands, scrub and grassland, point sources, developed land, nonsewered populations, atmospheric deposition, farm fertilizer, manure from both confined and unconfined cattle, and springs plus power returns are provided from the USGS 2012 static SPARROW model. EPA has updated information on point source loads and atmospheric deposition. RBEROST considers the options to apply each of 12 types of wastewater treatment plant upgrades, 12 urban stormwater control practices (both green and gray), 15 agricultural conservation practices (plus 3 user-specified), and riparian zone restoration to reduce nutrient loads. RBEROST includes a compilation of costs and efficiencies for each of these practices, as well as default loading targets for Puget Sound subwatersheds, all of which can be adjusted by the user. RBEROST creates three files written in a Mathematical Programming Language (AMPL) to define the optimization problem specified by the user, which the user uploads to the free public Network Enabled Optimization System (NEOS) Server to initiate the optimization process. An RBEROST post-processor ingests the result file returned by NEOS and summarizes least-cost management options overall, with a list of options for individual catchments as well. RBEROST includes an uncertainty module which allows the user to establish margins of safety to improve the probability of meeting loading targets. In Phase II of the project, funded through a Region 10 ROAR proposal, we will update RBEROSTv2 to work with a dynamic version of the SPARROW model for the Puget Sound Basin which will predict seasonal loads over a 20-year span. The dynamic version of RBEROST will be used to evaluate the sensitivity of optimal management strategies to seasonal and interannual variations in weather. The dynamic SPARROW model also will include estimates of loads from terrestrial storage, allowing RBEROST users to consider lags in response to management actions. A second objective of the Region 10 ROAR proposal will evaluate linkages between nutrient loading and the probability of algal blooms, including harmful algal blooms, in Puget Sound. A time series of estimated chlorophyll is being generated for 2015-2022 based on remote sensing (Sentinel 2), and combined with ancillary data on potential modifying factors (salinity, temperature, retention time, turbidity, discharge) to predict probability of HABs events. Predictive models will be tested with historic data on algal community composition as well as newly collected samples.