Climate and human water use diminish wetland networks supporting continental waterbird migration

Abstract

Migrating waterbirds moving between upper and lower latitudinal breeding and wintering grounds rely on a limited network of endorheic lakes and wetlands when crossing arid continental interiors. Recent drying of global endorheic water stores raises concerns over deteriorating migratory pathways, yet few studies have considered these effects at the scale of continental flyways. Here, we investigate the resiliency of waterbird migration networks across western North America by reconstructing long‐term patterns (1984–2018) of terminal lake and wetland surface water area in 26 endorheic watersheds. Findings were partitioned regionally by snowmelt‐ and monsoon‐driven hydrologies and combined with climate and human water‐use data to determine their importance in predicting surface water trends. Nonlinear patterns of lake and wetland drying were apparent along latitudinal flyway gradients. Pervasive surface water declines were prevalent in northern snowmelt watersheds (lakes −27%, wetlands −47%) while largely stable in monsoonal watersheds to the south (lakes −13%, wetlands +8%). Monsoonal watersheds represented a smaller proportion of total lake and wetland area, but their distribution and frequency of change within highly arid regions of the continental flyway increased their value to migratory waterbirds. Irrigated agriculture and increasing evaporative demands were the most important drivers of surface water declines. Underlying agricultural and wetland relationships however were more complex. Approximately 7% of irrigated lands linked to flood irrigation and water storage practices supported 61% of all wetland inundation in snowmelt watersheds. In monsoonal watersheds, small earthen dams, meant to capture surface runoff for livestock watering, were a major component of wetland resources (67%) that supported networks of isolated wetlands surrounding endorheic lakes. Ecological trends and human impacts identified herein underscore the importance of assessing flyway‐scale change as our model depictions likely reflect new and emerging bottlenecks to continental migration.

Need to Seed? Ecological, Genetic, and Evolutionary Keys to Seed-Based Wetland Restoration

“…Nearby wetlands in relatively intact landscapes can also serve as propagule sources, and seemingly isolated wetlands may be highly connected via bird seed dispersers, non-channelized surface flow, and channelized streamflow (Santamaría, 2002;Nilsson et al, 2010;Soons et al, 2016;Alexander et al, 2018;Leibowitz et al, 2018). However, with landscape fragmentation, historical (often hydrologic) connectivity among wetlands can be severed, and the number of arriving seeds is often too limited and lacking native diversity to support rapid plant community recovery (Galatowitsch and Richardson, 2005;Galatowitsch, 2006;Mazerolle et al, 2006;Kettenring and Galatowitsch, 2011b;Donnelly et al, 2020).…”

“…Hydrology is a defining feature of wetland ecosystems and has an overriding influence on the germination and establishment of native plants, as well as the structure and function of wetlands (Weiher and Keddy, 1995;Cronk and Fennessy, 2001;Doherty et al, 2014;Moor et al, 2017;Daniel et al, 2019;Rosbakh et al, 2020). The hydrology of many wetland systems has been altered via methods such as tile drainage, disconnection of floodplain wetlands through channelization, fragmentation, and increased demands upstream for agriculture and urbanization that reduce inputs to wetland systems (Galatowitsch and van der Valk, 1994;Turner and Lewis, 1996;López-Merino et al, 2011;Downard et al, 2014;Donnelly et al, 2020). Further shifts are occurring with climate change-induced precipitation alterations and increased evaporation rates that affect soil moisture (Walck et al, 2011).…”

Wetland Conservation: Challenges Related to Water Law and Farm Policy

“…Although relatively few farms with irrigated acreage receive conservation payments, due to large-scale conversion of wetlands to agriculture in the west, wetlands created or maintained by inefficient use (e.g., flood irrigation) of agricultural water resources are now the most available wetland type for wetland-dependent wildlife (Donnelly et al 2020). Increased return flows from inefficient flood irrigation also have help sustain aquatic systems in many areas and provide irrigation water for downstream users.…”

“…The U.S. has expended considerable resources in the protection, conservation, and management of wetlands. However, the unsustainable use of water resources, particularly by agriculture, threatens these efforts and has contributed to wetland loss and disruption of wetland functions by altering the volume and timing of surface and/or groundwater inputs (Donnelly et al 2020;Richter et al 2020a). Importantly, the impacts of unsustainable water use are not limited to conservation goals.…”

“…Declines in the Ogallala aquifer of the High Plains are well documented with aquifer depletion in some areas expected within the next few decades (Scanlon et al 2012). These declines strongly affect wetland (Wurtsbaugh et al 2017;Donnelly et al 2020;Starr and McIntyre 2020) and aquatic systems (Perkin et al 2017) as well as the farming communities that rely on this water source (Warziniack and Brown 2019).…”