Use of NASA datasets detailing groundwater depletion and land subsidence allows policy makers to readily assess subbasin scale details on water resources management when in situ data are lacking.ABSTRACT: California's Central Valley aquifer is a critical freshwater resource for the state, providing drinking water to 6.5 million residents and irrigation water for more than half of the nation's produce. Increasing demands have led to a steady decline of aquifer water levels, leading to irreversible compaction and land subsidence. The Sustainable Groundwater Management Act of California (SGMA), instituted in 2014, requires highpriority regions to establish sustainability plans by 2020-2022 that mitigate groundwater depletion and land subsidence. Many regions within the Central Valley lack groundwater monitoring wells or continuous well data, rendering in situ monitoring challenging. When combined with other data, National Aeronautics and Space Administration's Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions provide valuable information about groundwater storage changes at a subbasin scale. Interferometric Synthetic Aperture Radar measurements can map land subsidence, and Global Positioning System can be used to estimate crustal uplift. Yet, all of these measurements have differences in resolution, coverage, discretization, and record length. Here we assess the various datasets that are potentially useful for Central Valley subbasin groundwater monitoring and provide an analysis of gaps and other issues in regard to their suitability for SGMA-related analysis. Finally, we offer the next steps and recommendations on data treatment and integration.

The Arctic and subarctic Pacific Ocean is experiencing rapid change as a result of climate warming and associated feedbacks (Grebmeier et al., 2006;Gregg et al., 2003;Serreze et al., 2007). The northeastern Pacific Ocean and the Bering Sea are characterized as high nutrient, low chlorophyll (HNLC) regions due to limited iron (Fe) inputs. Global satellite-based measurements of primary production suggest a large decrease in the North Pacific region (−9.3%) between the early 1980s and the early 2000s, associated with increasing sea surface temperatures and decreasing terrestrial dust deposition, thus enhancing this region's HNLC status (Gregg et al., 2003). Climate change may impact nutrient cycling by affecting sources and bioavailability of Fe and macronutrients to pelagic phytoplankton (e.g., Aguilar-Islas et al., 2008;Kipp et al., 2018). There also may be changes in the seasonality of nutrient deposition, altering the relevance and impact of different terrestrial nutrient sources.

Industrial activities release aerosols containing toxic metals into the atmosphere, where they are transported far from their sources, impacting ecosystems and human health. Concomitantly, long-range-transported mineral dust aerosols play a role in Earth’s radiative balance and supply micronutrients to iron-limited ecosystems. To evaluate the sources of dust and pollutant aerosols to Alaska following the 2001 phase-out of leaded gasoline in China, we measured Pb-Sr-Nd isotopic compositions of particles collected in 2016 from snow pits across an elevational transect (2180–5240 m-a.s.l) in Denali National Park, USA. We also determined Pb flux and enrichment from 1991–2011 in the Denali ice core (3870 m-a.s.l). Chinese coal-burning and non-ferrous metal smelting account for up to 64% of Pb deposition at our sites, a value consistent across the western Arctic. Pb isotope ratios in the aerosols did not change between 2001 and 2016, despite the ban on lead additives. Emissions estimates demonstrate that industrial activities have more than compensated for the phase-out of leaded gasoline, with China emitting ∼37,000 metric tons year –1 of Pb during 2013–2015, approximately 78% of the Pb from East Asia. The Pb flux to Alaska now equals that measured in southern Greenland during peak pollution from North America.