HYPORHEIC EXCHANGE IN TEXAS RIVERS: LINKS BETWEEN FLUXES AND INVERTEBRATE RICHNESS AND DIVERSITY

The hyporheic zone is a region of permeable sediments below streams and rivers that affects water quality, habitats, and ecosystem health in and beneath streams and rivers. Sediment permeability and hydraulic gradients control fluxes in the hyporheic zone where water, solutes, and invertebrates move into, out of, and through the hyporheic zone. The hyporheic zone is also an important contributor to whole river metabolism and facilitates nutrient transformations. Despite its importance, relationships between invertebrate community metrics and fluxes in the hyporheic zone are poorly understood.

Using data collected from 2021 to 2022, I quantified relationships between hyporheic fluxes and invertebrate richness and diversity at 49 sites in eight 1^st to 7^th-order rivers in TX. Sites span large precipitation and temperature gradients (east, central, and north TX), diverse geology, and land uses which include rangeland, urban, row-crop agriculture, and forested. Each hyporheic site spanned a riffle where hydraulic gradients and hydraulic conductivity (K) were directly measured at 3-5 shallow wells. Bulk invertebrate samples collected from each well were sorted, counted, and identified to the lowest practical level in the laboratory.

Data analysis and sample processing is incomplete, but preliminary results suggest a weaker relationship between fluxes and invertebrate abundance, and a stronger relationship between K and invertebrate abundance. Measured K at most sites falls in ranges associated with clean or silty sand, but substrates are usually extremely heterogeneous. Sites with relatively high K values (> 0.1 cm/s) or larger grain sizes (gravel and cobble) allow water and nutrients to be transported more easily through the hyporheic zone and have greater invertebrate abundance: per-site abundances ranged from 60 to 14,590 individuals. Fluxes generally increase with increasing K values and therefore are expected to have a similar relationship with invertebrate abundance.

This research is a collaborative effort between Texas State University and the United States Army Corps of Engineers to develop next-generation ecological models for predicting how climate change will affect species abundance and distribution in waterways of the USA.