Using hydrogels to enhance water holding capacity and ultimately restoration success in a monsoonally driven dryland system

Background/Question/Methods: Drylands comprise approximately 30-40% of global terrestrial surface area, and are relied upon for multiple historic and modern uses. In the southwestern United States, multiple recent disturbances have degraded landscapes and stimulated positive feedbacks that amplify erosion and ecological community changes, creating a large need for restoration that can mitigate these effects. This degradation, coupled with variable precipitation primarily delivered in discrete monsoon driven events, means the success of vegetative restoration efforts in dryland systems is often low. To try and take advantage of monsoon precipitation pulses, we supplemented seeding and planting restoration efforts with hydrophilic polymers (hydrogels) that hold up to 1000x their weight in water, are biodegradable, and relatively inexpensive. We hypothesized that they would increase the soil water holding capacity, increasing soil moisture and water availability duration in the top few inches of the soil.

In a factorial design, we added two hydrogel concentrations with and without water augmentation to seed and seedling treatments mirrored in two New Mexico field sites (warm-lower elevation and cool-higher elevation). Plots were monitored bi-weekly for 10 weeks, recording germination and establishment of target species and background vegetative cover. The top five centimeters of soil was monitored on hourly intervals.

Results/Conclusions: During preliminary analysis, we found that hydrogel application was correlated with relatively low soil seed bank recruitment, cover, and abundance compared to non-hydrogel treatments. However for targeted species, high variability suggests that hydrogel effect on success is minimal, and further research is needed to examine the interactions between water augmentation and hydrogel on recruitment success. We observed low seedling germination across all treatments, but germination was higher on average at the higher-elevation cool site. Seedling survivorship was much less variable, and higher in the higher-elevation cool site.

Background seed bank recruitment accumulated 57 species from 16 families observed in total. Between sites, we saw a functionally significant difference in alpha diversity, with the lower-elevation warm site accumulating over four times the number of species as the higher-elevation cool site. Hydrogel and watering treatments did not significantly enhance richness at either site, but did have a slight negative affect on abundance (% cover).

Overall, rates of recruitment were low, and targeted seed germination variability was high. Further analysis of rapid recruitment periods in late fall will be carried out. Dryland system complexity and the high variability of success observed suggests that specialized restoration could dramatically improve restoration success.