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1. Deltas in Arid Environments

   https://doi.org/10.3390/w13121677  

   Day, John; Goodman, Reed; Chen, Zhongyuan; Hunter, Rachael; Giosan, Liviu; Wang, Yanna (June 2021, Water)

   Due to increasing water use, diversion and salinization, along with subsidence and sea-level rise, deltas in arid regions are shrinking worldwide. Some of the most ecologically important arid deltas include the Colorado, Indus, Nile, and Tigris-Euphrates. The primary stressors vary globally, but these deltas are threatened by increased salinization, water storage and diversion, eutrophication, and wetland loss. In order to make these deltas sustainable over time, some water flow, including seasonal flooding, needs to be re-established. Positive impacts have been seen in the Colorado River delta after flows to the delta were increased. In addition to increasing freshwater flow, collaboration among stakeholders and active management are necessary. For the Nile River, cooperation among different nations in the Nile drainage basin is important. River flow into the Tigris-Euphrates River delta has been affected by politics and civil strife in the Middle East, but some flow has been re-allocated to the delta. Studies commissioned for the Indus River delta recommended re-establishment of some monthly water flow to maintain the river channel and to fight saltwater intrusion. However, accelerating climate impacts, socio-political conflicts, and growing populations suggest a dire future for arid deltas. 

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2. Mixed method approach to assess atmospheric nitrogen deposition in arid and semi-arid ecosystems

   https://doi.org/10.1016/j.envpol.2018.04.013  

   Cook, Elizabeth M.; Sponseller, Ryan; Grimm, Nancy B.; Hall, Sharon J. (August 2018, Environmental Pollution)
3. Geoclimatic drivers of diversification in the largest arid and semi‐arid environment of the Neotropics: Perspectives from phylogeography

   https://doi.org/10.1111/mec.17431  

   Guillory, Wilson X; de_Medeiros Magalhães, Felipe; Coelho, Felipe_Eduardo Alves; Bonatelli, Isabel_A S; Palma‐Silva, Clarisse; Moraes, Evandro M; Garda, Adrian Antonio; Burbrink, Frank T; Gehara, Marcelo (July 2024, Molecular Ecology)

   Abstract The South American Dry Diagonal, also called the Diagonal of Open Formations, is a large region of seasonally dry vegetation extending from northeastern Brazil to northern Argentina, comprising the Caatinga, Cerrado, and Chaco subregions. A growing body of phylogeography literature has determined that a complex history of climatic changes coupled with more ancient geological events has produced a diverse and endemic‐rich Dry Diagonal biota. However, the exact drivers are still under investigation, and their relative strengths and effects are controversial. Pleistocene climatic fluctuations structured lineages via vegetation shifts, refugium formation, and corridors between the Amazon and Atlantic forests. In some taxa, older geological events, such as the reconfiguration of the São Francisco River, uplift of the Central Brazilian Plateau, or the Miocene inundation of the Chaco by marine incursions, were more important. Here, we review the Dry Diagonal phylogeography literature, discussing each hypothesized driver of diversification and assessing degree of support. Few studies statistically test these hypotheses, with most support drawn from associating encountered phylogeographic patterns such as population structure with the timing of ancient geoclimatic events. Across statistical studies, most hypotheses are well supported, with the exception of the Pleistocene Arc Hypothesis. However, taxonomic and regional biases persist, such as a proportional overabundance of herpetofauna studies, and the under‐representation of Chaco studies. Overall, both Pleistocene climate change and Neogene geological events shaped the evolution of the Dry Diagonal biota, though the precise effects are regionally and taxonomically varied. We encourage further use of model‐based analyses to test evolutionary scenarios, as well as interdisciplinary collaborations to progress the field beyond its current focus on the traditional set of geoclimatic hypotheses. 

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4. Extreme weather events and transmission losses in arid streams

   https://doi.org/10.1088/1748-9326/ab2949  

   Schreiner-McGraw, Adam; Ajami, Hoori; Vivoni, Enrique R (June 2019, Environmental Research Letters)
5. Phylogenetic diversity and regionalization in the temperate arid zone

   https://doi.org/10.1111/jse.13077  

   Folk, Ryan_A; Maassoumi, Aliasghar_A; Siniscalchi, Carolina_M; Kates, Heather_R; Soltis, Douglas_E; Soltis, Pamela_S; Belitz, Michael_B; Guralnick, Robert_P (May 2024, Journal of Systematics and Evolution)

   Abstract Astragalus(Fabaceae) is astoundingly diverse in temperate, cold arid regions of Earth, positioning this group as a model clade for investigating the distribution of plant diversity in the face of environmental challenges. Here, we identify the spatial distribution of diversity and endemism inAstragalususing species distribution models for 752 species and a phylogenetic tree comprising 847 species. We integrated these to map centers of species richness (SR) and relative phylogenetic diversity (RPD) and used randomization approaches to investigate centers of endemism. We also used clustering methods to identify phylogenetic regionalizations. We then assembled predictor variables of current climate conditions to test environmental factors predicting these phylogenetic diversity results, especially temperature and precipitation seasonality. We find that SR centers are distributed globally at temperate middle latitudes in arid regions, but the Mediterranean Basin is the most important center of RPD. Endemism centers also occur globally, but Iran represents a key endemic area with a concentration of both paleo‐ and neoendemism. Phylogenetic regionalization recovered an east‐west gradient in Eurasia and an amphitropical disjunction across North and South America; American phyloregions are overall most closely related to east and central Asia. SR, RPD, and lineage turnover are driven mostly by precipitation and seasonality, but endemism is driven primarily by diurnal temperature variation. Endemism and regionalization results point to western Asia and especially Iran as a biogeographic gateway between Europe and Asia. RPD and endemism highlight the importance of temperature and drought stress in determining plant diversity and endemism centers. 

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