Odonate Assemblages of Four Wetland Types Varying in Salinity, Hydroperiod, and Water Chemistry in the Texas Panhandle

Odonates (members of the insect order Odonata: dragonflies and damselflies) are predatory, amphibious invertebrates reliant on freshwater sources for reproduction and development. As a result, these insects are considered an important group of environmental indicators. However, the freshwater sources they rely on are limited in the semi-arid Texas Panhandle, being primarily represented in four forms that differ in source of water, hydroperiod, salinity, and anthropogenic inputs. Rainfall-filled depressional wetlands called playas are the most numerous, with >20,000 playa basins forming a habitat network in Texas. Less-numerous are spring-fed lakes known as salinas. Urban growth and agricultural land use have effectively created two new wetland types: urban “playa lakes” and salinas with severed spring connections that now function hydrologically like playas (although it is unknown if they function ecologically more like playas or like intact salinas). A comprehensive inventory of odonate assemblages across these four wetland types has never been conducted, which constrains our knowledge about these important insects and whether their presence and abundance reflect gradients of hydroperiod, salinity, and anthropogenic inputs to water chemistry. I conducted field surveys in the summers of 2020 and 2021 at 58 wetlands (21 playas, 4 salina springs, 26 urban playa lakes, and 7 former salinas). I assessed adult species presence, conducted vegetation surveys, and collected water samples for analysis back in the lab. Species accumulation curves for each wetland type were constructed to indicate whether sampling had been sufficient to represent species richness. I computed several metrics to characterize each wetland type’s odonate assemblage, including Jaccard and Sørensen indices of beta diversity and Jackknife 1 and 2, Chao, and Bootstrap incidence-based richness estimation methods. Water chemistry variables analyzed included conductivity [μS], water salinity [ppm], pH, total dissolved solids [TDS ppm], nitrate (mg/L NO3-N), nitrite (mg/L NO2-N), sulfate (mg/L SO4), ammonia (mg/L NH3-N), and phosphate (mg/L PO43-). These are known agricultural and urban contaminants of wetland areas and at least some are known to affect aquatic and amphibious animals. A best subset of environmental variables with maximum (rank) correlation with community dissimilarities (BIOENV) analysis was applied to normalized abiotic variables each year to determine which variables produced the highest correlation with assemblage data, thus providing support as to which measured variables structure the assemblage. A multivariate analysis of variance (MANOVA) was used to determine which abiotic variables best explained measured variance across wetland types each summer. Significant MANOVA models were followed by analyses of variance (ANOVA) and Tukey’s tests to determine significant differences in abiotic variables among wetland types. Non-metric multidimensional scaling (NMDS) was used to investigate the influence of wetland type on the distribution of species across sites. Finally, a permutational multivariate analysis of variance (PERMANOVA) was used to determine if odonate assemblages significantly differed by wetland type. A pairwise comparison of all odonate assemblages by wetland type followed to determine which wetland types had significantly different odonate assemblages. Thirty-seven odonate species were detected, with the highest species richness at salina springs (N = 31 species across 2020 and 2021), followed by urban playas (23), former salinas (17), and playas (9). NMDS revealed that the odonate assemblages across all four wetland types were similar. The most speciose odonate assemblages occurred at wetlands with longer hydroperiods. I identified several species (N = 12) that may be tolerant of saline environments and merit further study. Salinas and urban playas hosted the most odonate species and the most unique species, yet these wetlands have few protections; recognizing odonate diversity may elicit greater interest in the protection of regionally unique wetlands. Specific recommendations are made, aimed at landowners or managers of each wetland type.