Trends in temporary pool water chemistry and branchiopod communities along a longitudinal climate gradient in the Nebraska Sandhills

Temporary pools are the most abundant insular aquatic habitats in the world and are ideal systems for studying ecological and evolutionary processes; however, they are poorly studied in many regions of the world in favor of larger, permanent systems like lakes and rivers. The Nebraska Sandhills, Nebraska, USA, contains thousands of groundwater-fed lakes and temporary pools, ranging from freshwater to hypersaline-alkaline. Much of the variation in water chemistry is associated with a longitudinal climate gradient where the climate is mesic in the eastern Sandhills and transitions to semiarid in the western Sandhills. Our objective was to conduct a survey of the temporary pools to learn more about their environmental and ecological characteristics and how they differ along the longitudinal climate gradient. We sampled 30 pools from 3 areas along the climate gradient from April to July 2013. Branchiopod crustaceans were used to measure ecological characteristics because they are adapted to live in temporary pools and are sensitive to environmental changes. The frequency and salinity of saline pools increased westward as aridity increased. Salinity was the primary environmental gradient structuring branchiopod communities. Freshwater alpha and gamma diversity declined westward, which may be due to the westward decline in freshwater habitat. The transition from a homogeneous freshwater-dominated landscape in the eastern Sandhills to a heterogeneous landscape consisting of fresh-, low-, and high-salinity waters in the western Sandhills makes this system ideal for studying ecological processes at local and regional scales.