Quantifying anthropogenic contributions to century-scale groundwater salinity changes, San Joaquin Valley, California, USA

Science of the Total Environment (Elsevier) | June 15th, 2018

Total dissolved solids (TDS) concentrations in groundwater tapped for beneficial uses (drinking water, irrigation, freshwater industrial) have increased on average by abo

Total dissolved solids (TDS) concentrations in groundwater tapped for beneficial uses (drinking water, irrigation, freshwater industrial) have increased on average by about 100 mg/L over the last 100 y ears in the San Joaquin Valley, California (SJV). D uring this period land use in the SJV changed from natural vegetation and dryland agriculture to dominantly irrigated agriculture with growing urban areas. Century-scale salinity trends were evaluated by comparing TDS concentrations and major ion compositions of groundwater from wells sampled in 1910 (Historic) to data from wells sampled in 1993 –2015 (Modern). TDS concentrations in subregions of the SJV, the southern (SSJV), western (WSJV), northeastern (NESJV), and southeastern (SESJV) were calculated using a cell-declustering method. TDS concentrations increased in all regions, with the greatest increases found in the SSJV and SESJV. Evaluation of the Modern data from the NESJV and SESJV found higher TDS concentrations in recently recharged (post-1950) groundwater from shallow (b50 m) wells surrounded predominantly by agricultural land uses, while premodern (pre-1950) groundwater from deeper wells, and recently recharged groundwater from wells surrounded by mainly urban, natural, and mixed land uses had lower TDS concentrations, approaching the TDS concentrations in the Historic groundwater. For the NESJV and SESJV, inverse geochemical modeling with PHREEQC indicated that weathering of primary silicate minerals accounted for the majority o f the increase in TDS concentrations, contributing more than nitrate from fertilizers and sulfate from soil amendments combined. Bicarbonate showed the greatest increase among major ions, resulting from enhanced silicate weathering due to recharge of irrigation water enriched in CO2 during the growing season. The results of this study demonstrate that large anthropogenic changes to the hydrologic regime, like massive development of irrigated agriculture in semi-arid areas like the SJV, can cause large changes in groundwater quality on a regional scale.

Quantifying the Relationship Between Atmospheric River Origin Conditions and Landfall Temperature

American Geophysical Union (AGU) | October 11th, 2022

The temperature of landfalling atmospheric rivers (ARs) has direct implications for regional water resources. Compared to cool ARs, warm ARs can result in more surface ru

The temperature of landfalling atmospheric rivers (ARs) has direct implications for regional water resources. Compared to cool ARs, warm ARs can result in more surface runoff and flooding, less water availability via low snow accumulations and enhanced snowmelt, and greater challenges for storm forecasting and reservoir operations. Based on case studies, ARs with subtropical origin locations and warm origin conditions are assumed to be associated with warmer landfall temperatures—though, to date, this has not yet been demonstrated systematically. We analyze North Pacific ARs that made landfall along the West Coast of North America from 1980 to 2017. We find that ARs originating over the subtropical Pacific Ocean near Hawaii (“Pineapple Express”-type ARs) are indeed 1.5°C warmer and 2 kg/m2 moister in winter than ARs originating elsewhere. We extend this analysis for the full study population of ARs by quantifying AR origin conditions, including the spatial distribution of origin temperature, moisture content, and integrated vapor transport (IVT). We use fixed effects multivariate regression to quantify the relative influence of the origin conditions on landfall temperature. Our regression models show that AR origins with lower latitudes, longer AR lifetimes, and stronger IVT are associated with warmer landfall temperatures and that ARs that start warm generally stay warm. We also find that the phase of the El Niño/Southern Oscillation does not exhibit a consistent relationship with AR landfall temperature. Overall, our results partially affirm—yet also complicate—common assumptions about the role of different origin conditions in landfalling AR temperature.

Rapid emergence of climate change in environmental drivers of marine ecosystems

Nature Portfolio (Springer Nature) | March 7th, 2017

Climate change is expected to modify ecological responses in the ocean, with the potential for important effects on the ecosystem services provided to humankind

Climate change is expected to modify ecological responses in the ocean, with the potential for important effects on the ecosystem services provided to humankind. Here we address the question of how rapidly multiple drivers of marine ecosystem change develop in the future ocean. By analysing an ensemble of models we find that, within the next 15 years, the climate change-driven trends in multiple ecosystem drivers emerge from the background of natural variability in 55% of the ocean and propagate rapidly to encompass 86% of the ocean by 2050 under a ‘business-as-usual’ scenario. However, we also demonstrate that the exposure of marine ecosystems to climate change-induced stress can be drastically reduced via climate mitigation measures; with mitigation, the proportion of ocean susceptible to multiple drivers within the next 15 years is reduced to 34%. Mitigation slows the pace at which multiple drivers emerge, allowing an additional 20 years for adaptation in marine ecological and socio-economic systems alike.

Rapid progression of ocean acidification in the California current system

American Association for the Advancement of Science (AAAS) | June 14th, 2012

Nearshore waters of the California Current System (California CS) already today have a low carbonate saturation state, making them particularly susceptible to o

Nearshore waters of the California Current System (California CS) already today have a low carbonate saturation state, making them particularly susceptible to ocean acidification. Here, we use eddy-resolving model simulations to study the potential development of ocean acidification in this system up to 2050 under the SRES A2 and B1 scenarios. In both scenarios, the saturation state of aragonite Ωaragis projected to drop rapidly, with much of the nearshore regions developing summer-long undersaturation in the top 60 m within the next 30 years. By the year 2050, waters with Ωarag above 1.5 have largely disappeared and more than half of the waters are undersaturated year-round. Habitats along the seafloor become exposed to year-round undersaturation within the next 20 to 30 years. This has potentially major implications for the rich and diverse ecosystem that characterizes the California CS.

Recommendations for a Modeling Framework to Answer Nutrient Management Questions in the Sacramento-San Joaquin Delta

San Francisco Estuary Institute (SFEI) | March 1st, 2016

Management actions in the Delta related to nutrients could cost billions of dollars to implement in the coming decades depending on decisions that will come before the Ce

Management actions in the Delta related to nutrients could cost billions of dollars to implement in the coming decades depending on decisions that will come before the Central Valley Regional Water Quality Control Board (Water Board). The complexity of the Delta ecosystem and the range of questions to be addressed demand that numerical, processed-based water quality modeling be part of Delta management efforts. In light of this fact, the Water Board convened the Modeling Science Workgroup in 2015, and tasked it with advising on the development and use of water quality models as one component of the Water Board’s Nutrient Research Plan. The Charge to the Modeling Science Workgroup (included in Appendix B) was to provide advice to the Water Board on:  · The types of models would be needed to answer the nutrient management questions raised by stakeholders,  · Organizational arrangements to support and maximize the benefits of models, and  · Cost estimates for the modeling task and how such work might be phased over time. 

Recommendations to Address the Expansion of Seawater Intrusion in the Salinas Valley Groundwater Basin

Monterey County Water Resources Agency (MCWRA) | October 12th, 2017

This report provides a discussion of the current knowledge and related background information surrounding seawater intrusion pathways and potential impacts ther

This report provides a discussion of the current knowledge and related background information surrounding seawater intrusion pathways and potential impacts thereof on the Salinas Valley Groundwater Basin. This document also serves as a body of evidence to catalogue the findings used to support the recommendations presented herein. Staff is making six recommendations, with each focused on a component that influences, or could be impacted by, the advancement of seawater intrusion. The recommendations are being presented in an order that builds upon the foundational knowledge laid out in the background section of this report, rather than in an order of priority. Each recommendation can be implemented on its own or in concert with the others, and the relative importance of each will be discussed individually in this report. However, the recommendations have been conceptualized as a comprehensive solution that, along with continued operation of projects that have been constructed for the same purpose, have the strongest potential to ensure success in slowing or halting further seawater intrusion when implemented simultaneously.

Reconstructing the Mediaeval low stands of Mono Lake, Sierra Nevada, California, USA

Holocene (Sage Journals) | December 1st, 2019

Palaeosimulations of Mono Lake covering the past 2 kyr have been conducted using a water balance model forced with tree-ring derived inflow estimates. The results show tw

Palaeosimulations of Mono Lake covering the past 2 kyr have been conducted using a water balance model forced with tree-ring derived inflow estimates. The results show two low stands, during the ninth to tenth and twelfth to thirteenth centuries, that agree well in timing and magnitude with those described by Stine (1987, 1990, 1994) on the basis of geomorphic evidence and relict trees and shrubs exposed on Mono Lake's artificially exposed shorelands. The lake simulation provides independent corroboration of the timing and magnitude of Stine's drought-induced low stands and supports the accuracy of tree-ring-derived estimates of Mediaeval precipitation and runoff reductions in the central Sierra Nevada. Specifically, we estimate that during the two Mediaeval droughts, centennial average precipitation and river runoff in the central Sierra Nevada reached as low as 75% of the twentieth century values, with multidecade averages as low as 60—65%. In both magnitude and duration, these droughts far exceed anything experienced in the region during modern times. An analysis of the spatial patterns of reconstructed drought indices shows that the particular `two drought' Mono Lake low stand signal was focused over central and southern California, indicating the dominant role of boreal winter precipitation deficits. In this respect, the `Great Sierra Nevada droughts' were somewhat distinct from the more general Great Basin/far western Plains pattern of Mediaeval aridity over the western USA.

Regional Monitoring Program (RMP) Small Tributaries Loading Strategy: Modeling and Trends Strategy 2018

San Francisco Estuary Institute (SFEI) | September 3rd, 2018

The Small Tributaries Loading Strategy (STLS) (SFEI, 2009) is a collaboration between the RMP, the Water Board, and Bay Area stormwater programs to address information n

The Small Tributaries Loading Strategy (STLS) (SFEI, 2009) is a collaboration between the RMP, the Water Board, and Bay Area stormwater programs to address information needs associated with improving understanding about the sources, pathways, loads, trends, and management opportunities in relation to watershed-derived pollutants of concern (POCs). Elements contained in this Strategy may be conducted via RMP collaborative efforts, or independently by the Water Board or Bay Area stormwater programs outside of, but in coordination with the RMP. The current priority POCs are mercury (Hg) and polychlorinated biphenyls (PCBs), for which there are identified impairments and cleanup plans in place. The San Francisco Bay Hg and PCBs total maximum daily loads (TMDLs) reports (SFRWQCB, 2006; SFRWQCB, 2007) call for a reduction in tributary loads by 50% and 90%, respectively. In response, from 2010-2015, during the first term of the Municipal Regional Stormwater Permit (MRP 1.0) (SFRWQCB, 2009; 2011), a number of pilot efforts were initiated, focusing mainly on PCBs, to better understand the potential cost-effectiveness for a range of management options and the level of opportunity (the number of polluted sites or the amount of mass associated with polluted sites, property ownership and other factors). During the second term of the MRP (MRP 2.0) (SFRWQCB, 2015), efforts have been made to move from pilot testing to a greater amount of focused implementation. All of these past, current, and future efforts also aim to address (but at a lesser level) multiple benefits for other POCs including current-use pesticides and emerging contaminants, for which there is interest in monitoring the potential for biological impact. These are lower priority at the present, but in the longer term, the STLS Trends Strategy could address these and other POCs in a more focused manner.

Regional Watershed Modeling and Trends Implementation Plan

San Francisco Estuary Institute (SFEI) | July 1st, 2019

Regional Watershed Spreadsheet Model (RWSM) Year 5 Progress Report

San Francisco Estuary Institute (SFEI) | March 1st, 2016

The Regional Watershed Spreadsheet Model (RWSM) is a regional-scale planning tool developed primarily to estimate long-term average annual loads from the small tributari

The Regional Watershed Spreadsheet Model (RWSM) is a regional-scale planning tool developed primarily to estimate long-term average annual loads from the small tributaries surrounding San Francisco Bay, and secondarily to provide supporting information for prioritizing watersheds or areas within watersheds for management actions. The RWSM has been in development since 2010. In previous years, obstacles to calibrating the PCB and Hg models included issues associated with GIS data underlying the Model, a simplistic model structure and parameterization, lack of available empirical data for calibrating concentrations associated with specific land uses and source areas, and the high uncertainty with the empirical calibration dataset. The modeling effort in Years 2014 and 2015 (Year 4 and 5 of the model development) focused on improving the model calibration to attempt to resolve these issues. The major changes included switching from a sediment-based model to a water-based model, elimination of double counting of source areas on top of general land uses, changes in the model calibration approach, and changes to the land use grouping.