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Groundwater is the most ubiquitous source of liquid freshwater globally, yet its role in supporting diverse ecosystems is rarely acknowledged 1 , 2 . However, the location and extent of groundwater-dependent ecosystems (GDEs) are unknown in many geographies, and protection measures are lacking 1 , 3 . Here, we map GDEs at high-resolution (roughly 30 m) and find them present on more than one-third of global drylands analysed, including important global biodiversity hotspots 4 . GDEs are more extensive and contiguous in landscapes dominated by pastoralism with lower rates of groundwater depletion, suggesting that many GDEs are likely to have already been lost due to water and land use practices. Nevertheless, 53% of GDEs exist within regions showing declining groundwater trends, which highlights the urgent need to protect GDEs from the threat of groundwater depletion. However, we found that only 21% of GDEs exist on protected lands or in jurisdictions with sustainable groundwater management policies, invoking a call to action to protect these vital ecosystems. Furthermore, we examine the linkage of GDEs with cultural and socio-economic factors in the Greater Sahel region, where GDEs play an essential role in supporting biodiversity and rural livelihoods, to explore other means for protection of GDEs in politically unstable regions. Our GDE map provides critical information for prioritizing and developing policies and protection mechanisms across various local, regional or international scales to safeguard these important ecosystems and the societies dependent on them. Mapping of groundwater-dependent ecosystems, which support biodiversity and rural livelihoods, shows they occur on more than one-third of global drylands analysed, but lack protections to safeguard these critical ecosystems and the societies dependent upon them from groundwater depletion.

This paper examines the significance of knowledge and values for water quality and its governance. Modernist approaches to the governance of water quality in rivers and lakes need to be reconceptualised and overhauled. The problems include: perceiving water only as a physical and chemical liquid, defining quality in narrow terms, rendering water knowledge as invisible, boiling down water values to uses of presumed economic importance and limiting how and by whom objectives are set or actions taken. In addressing the need to reframe water quality governance, and as a counter to the objectification of water quality, we propose a framework that explicitly recognises the significance of knowledge and values relating to water. While our framework could apply to other contexts under the influence of modernist water-management regimes, here we pay particular attention to the relevance of the water knowledge, values and governance of water quality by Indigenous people. In the second half of the paper we address issues related to Indigenous water-quality governance in two countries, Brazil and Australia, showing some of the ways in which, despite enormous obstacles, Indigenous communities re-work governance structures through their engagements with water quality and pay attention to water knowledge and values.

Increased groundwater demand is causing aquifer declines that impact viability of groundwater-dependent ecosystems (GDEs) like springs and phreatophyte communities. To understand which springs and phreatophyte communities may be stressed by groundwater level declines in Oregon and Nevada, we assessed groundwater level trends in nearby monitoring wells. Very few springs and phreatophyte communities were near monitoring wells with adequate data. Less than 1% of >50,000 springs in Nevada and Oregon were within 800 m of analyzed wells, and only 52 springs were near a shallow (<30 m below ground surface) well. Among springs near analyzed wells, 56% in Nevada and 29% in Oregon were near wells with declining groundwater level trends, and percentages were similar among springs that were within 800 m of analyzed shallow wells. Less than 22% of all phreatophyte communities in Nevada and Oregon were near analyzed wells, and only 9.6% were within 800 m of a shallow well. Of phreatophyte communities near analyzed wells, 48% and 57% were near wells with declining trends in Nevada and Oregon, respectively. Differences among GDE types could reflect more groundwater development where phreatophytes exist. Differences between states in proportion of springs near wells with declining trends could be due to more surface water capture in Oregon or increased pressure for groundwater development in Nevada. State-specific policies and administration of groundwater rights and monitoring affect data availability and trends observed in the two states. More groundwater level data are essential for understanding impacts of groundwater withdrawals to GDEs.

Cultivation of highly salt-tolerant plants (i.e., halophytes), may provide a viable alternative to increase productivity compared to conventional salt-sensitive crops, increasing the economic potential of salt-affected lands that comprise ~20% of irrigated lands worldwide. In this study the Agricultural Policy/Environmental eXtender (APEX) model was adapted to simulate growth of the halophyte quinoa, along with salt dynamics in the plant-soil-water system. Model modifications included salt uptake and salt stress functions formulated using greenhouse data. Data from a field site were used to further parameterize and calibrate the model. Initial simulation results were promising, but differences between simulated and observed soil salinity and plant salt values during the growing season in the calibration suggest that additional improvements to salt uptake and soil salinity algorithms are needed. To demonstrate utility of the modified APEX model, six scenarios were run to estimate quinoa biomass production and soil salinity with different irrigation managements and salinities. Simulated annual biomass was sensitive to soil moisture, and root zone salinity increased in all scenarios. Further experiments are needed to improve understanding of crop salt uptake dynamics and stress sensitivities so that future model updates and simulations better represent salt dynamics in plants and soils in agricultural settings.

This study investigated near surface hydrologic processes and plant response over a 1600 m mountain-valley gradient located in the Great Basin of North America (Nevada, U.S.A.) as part of a long-term climate assessment study. The goal was to assess shifts in precipitation, soil water status and associated drainage with elevation and how this influenced evapotranspiration and plant cover/health estimated by a satellite-derived Normalized Difference Vegetation Index (NDVI), all to better understand how water is partitioned in a mountain valley system. Data were acquired during a three-year period from meteorological stations located in five plant communities ranging in elevation from 1756 m (salt desert shrubland zone) to 3355 m (subalpine zone). The analysis also included groundwater depths measured at the Salt Desert Shrub West site, mine water flow near the Pinyon-Juniper West site and drainage estimates using drainage flux meters at the four higher elevation sites. Annual precipitation increased with elevation in a linear fashion (R2 = 0.93, p < 0.001) with an average increase of 2.9 cm for every 100 m in elevation. Reference evapotranspiration (ETref) declined in a highly linear fashion with elevation (R2 = 0.95, p < 0.001) with an average 4.0 cm decline for every 100 m rise in elevation. Drainage occurred only at the Montane West and Subalpine West sites and not at the lower elevations. No drainage occurred after Julian day 160. Growing degree days were found to be negatively associated with the time of peak drainage (R2 = 0.97, p < 0.001), the date drainage first occurred (R2 = 0.90, p < 0.001), drainage duration (R2 = 0.79, p < 0.001) and total drainage volume (R2 = 0.59, p < 0.001). It was estimated that 27% of precipitation at the Montane West site (years 1, 2 and 3) and 66 % at the Subalpine West site (40% without year 1) contributed to drainage at the local site level, indicating possible strong recharge contribution from the higher elevation plant communities. Percent vegetation cover and ETref accounted for 94% of the variation in NDVI and 90% of the variation in ET totals when data from all sites were combined. Such data will be extremely valuable to collect and compare over time to assess shifts associated with potential climate warming and/or basin water diversion.

Transformation of the Khorezm region of Uzbekistan from forested to agricultural landscapes resulted in the formation of hundreds of lakes, the dynamics of which are largely controlled by inputs from irrigation runoff waters. The importance of the ecological and socio-cultural dimensions of one of these lakes, Shurkul, is discussed in order to understand the connection between humans and their environment. Landscape is used as a boundary concept, and we combine quantitative methods of the natural sciences with qualitative methods of the social sciences to assess these dimensions of the lake landscape. In the ecological dimension, Shurkul performs a wide range of ecosystem services from wildlife habitat and foodweb support to the provision of fish, fodder, building material and grazing ground. In the socio-cultural dimension, the lake is part of local ecological knowledge, functions as a prestige object and recreational site, and is rooted in religious beliefs of the population as a symbol of God’s benevolence. The Shurkul landscape may thus create a feeling of environmental connectedness and the desire to act in favor of the natural environment, which could be made use of in environmental education programs.

We investigated the effects on the reservoir food web of a new temperature control device (TCD) on the dam at Shasta Lake, California. We followed a linked modeling approach that used a specialized reservoir water quality model to forecast operation-induced changes in phytoplankton production. A food web-energy transfer model was also applied to propagate predicted changes in phytoplankton up through the food web to the predators and sport fishes of interest. The food web-energy transfer model employed a 10% trophic transfer efficiency through a food web that was mapped using carbon and nitrogen stable isotope analysis. Stable isotope analysis provided an efficient and comprehensive means of estimating the structure of the reservoir's food web with minimal sampling and background data. We used an optimization procedure to estimate the diet proportions of all food web components simultaneously from their isotopic signatures. Some consumers were estimated to be much more sensitive than others to perturbations to phytoplankton supply. The linked modeling approach demonstrated that interdisciplinary efforts enhance the value of information obtained from studies of managed ecosystems. The approach exploited the strengths of engineering and ecological modeling methods to address concerns that neither of the models could have addressed alone: (a) the water quality model could not have addressed quantitatively the possible impacts to fish, and (b) the food web model could not have examined how phytoplankton availability might change due to reservoir operations.

Nevada has the lowest precipitation gauge density in the contiguous United States. Because of this poor gauge coverage, precipitation and runoff must be estimated for most areas with hydrologic models us- ing limited data. Furthermore, regular annual maintenance schedules of the guzzlers that already exist would be minimally impacted by the additional maintenance of the monitoring instru- mentation, which means maintenance expenses of guzzler instrumentation would be much lower than equivalent costs on a standard automated weather station. [...]instrumenting wildlife guzzlers could be a low-cost way to improve the density of climate data availability in remote areas of the western United States.

The economy of the Khorezm Province in Uzbekistan relies on the large-scale agricultural production of cotton. To sustain their staple crop, water from the Amu Darya is diverted for irrigation through canal systems constructed during the early to mid-twentieth century when this region was part of the Soviet Union. These diversions severely reduce river flow to the Aral Sea. The Province has >400 small shallow (<3 m deep) lakes that may have originated because of this intensive irrigation. Sediment cores were collected from 12 lakes to elucidate their origin because this knowledge is critical to understanding water use in Khorezm. Core chronological data indicate that the majority of the lakes investigated are less than 150 years old, which supports a recent origin of the lakes. The thickness of lacustrine sediments in the cores analyzed ranged from 20 to 60 cm in all but two of the lakes, indicating a relatively slow sedimentation rate and a relatively short-term history for the lakes. Hydrologic changes in the lakes are evident from loss on ignition and pollen analyses of a subset of the lake cores. The data indicate that the lakes have transitioned from a dry, saline, arid landscape during pre-lake conditions (low organic carbon content) and low pollen concentrations (in the basal sediments) to the current freshwater lakes (high organic content), with abundant freshwater pollen taxa over the last 50–70 years. Sediments at the base of the cores contain pollen taxa dominated by Chenopodiaceae and Tamarix, indicating that the vegetation growing nearby was tolerant to arid saline conditions. The near surface sediments of the cores are dominated by Typha/Sparganium, which indicate freshwater conditions. Increases in pollen of weeds and crop plants indicate an intensification of agricultural activities since the 1950s in the watersheds of the lakes analyzed. Pesticide profiles of DDT (dichlorodiphenyltrichloroethane) and its degradates and γ-HCH (gamma-hexachlorocyclohexane), which were used during the Soviet era, show peak concentrations in the top 10 cm of some of the cores, where estimated ages of the sediments (1950–1990) are associated with peak pesticide use during the Soviet era. These data indicate that the lakes are relatively young (mostly <150 years old) and that without irrigation and canal inputs from the Amu Darya, the lakes would not exist as freshwater lakes.