In response to the decline of pelagic fish populations in the early 2000s, the Interagency Ecological Program formed an interagency team to find the causes. The team was called the Pelagic Organism Decline Management, Analysis and Synthesis Team.
The interdisciplinary effort funded a suite of 47 studies to evaluate the likely mechanisms for the decline. In 2010, the team published a comprehensive synthesis of the 47 studies in the report, 2010 Pelagic Organism Decline Work Plan and Synthesis of Results (Baxter et al. 2010.)
The report hypothesized that there had been a regime shift in the Delta ecosystem, stating:
drivers that changed slowly over decades (slow drivers) contributed to the slow erosion of ecological resilience of the system. This made the system more vulnerable to the effects of drivers that changed more rapidly around the time of the POD and/or have greater species specificity.
The report hypothesized that the slow, abiotic drivers of the POD regime shift in order of importance were: 1) Delta outflow, 2) salinity, 3) landscape, 4) temperature, 5) turbidity, 6) nutrients, 7) contaminants, and 8) harvest. The report illustrated the regime shift in this figure:
If there has been a regime shift of the Delta ecosystem, it will take significant, sustained changes in the drivers to shift the ecosystem out of the new regime.
However, the proposed Voluntary Agreement framework has significantly less water than was originally proposed. NRDC’s expert, Doug Obegi, writes:
preliminary analysis shows that the 2022 proposed voluntary agreement would provide an annual average of less than 500,000 acre feet of additional winter-spring outflow compared to the rules in place from 2009 to 2019 (before the Trump Administration gutted environmental protections in the Bay-Delta). That’s less than half of the 1.3 million acre feet of additional outflow included in the State’s 2017 proposed voluntary agreement, and it appears to be about one quarter of the water for the environment that the State Water Resources Control Board has identified in its proposals for and adopted amendments to the Bay-Delta Plan.
The framework also appears to preclude any experimental operations that would cost a large amount of water. The Memorandum of Understanding for the Voluntary Agreement framework states:
The science program will adopt a “safe to fail” experimental approach to maximize learning.
Bathiany, S., Scheffer, M., van Nes, E.H. Williamson, M., Lenton, T. 2018. Abrupt Climate Change in an Oscillating World. Sci Rep 8(5040). https://doi.org/10.1038/s41598-018-23377-4
Baxter, R., Breuer, R., Brown, Conroy, L., Feyrer, F., S. Fong, S., Gehrts, K., Grimaldo, L., Herbold, B., Hrodey, P., Mueller-Solger, A., Sommer, T., and Souza, K. 2010. 2010 Pelagic Organism Decline Work Plan and Synthesis of Results. Interagency Ecological Program.
California Natural Resources Agency et. al. 2022. Memorandum of Understanding Advancing a Term Sheet for the Voluntary Agreements to Update and Implement the Bay-Delta Water Quality Control Plan, and Other Related Actions, March 29, 2022.
Hughes, T., Linares, C., Dakos, V., van de Leemput, I., van Nes, E. 2013. Living dangerously on borrowed time during slow, unrecognized regime shifts. Trends in Ecology & Evolution 28(3): 149-155. https://doi.org/10.1016/j.tree.2012.08.022
Obegi, D. 2022. Honey, the VAs Shrunk the Delta Flows. NRDC expert blog. April 11, 2022.