Ecohydrology of the Eastern Snake River Plain

The Influence of Precipitation, Vegetation and Soil Properties on the Ecohydrology of the Eastern Snake River Plain

Climate change and its impact on precipitation patterns are likely to lead to changes in plant communities (species present and production) and subsequently soil characteristics. Hydroclimatological change in the eastern Snake River Plain could have long-term impacts for aquifer recharge, flowing water, and thus population centers and agricultural industries. Important questions are: How much meteoric water passes through the plant root zone onto groundwater under current and future climate scenarios, and how do our vast desert plant communities adjust to altered hydroclimate.

Using the Protective Cap / Biobarrier Experiment established in 1993, we are looking at the long-term impacts of different plant communities commonly found throughout Idaho (native/sagebrush and crested wheatgrass, an introduced species) subject to different precipitation regimes (doubling of annual precipitation, added in winter or in summer) and to different soil depths. These treatments allow us to investigate how vegetation, precipitation, and soil interact to influence patterns of water infiltration, uptake, and storage. This information will be used to improve a variety of models as well as provide data for these models.

The objectives of this study are as follows: (1) to determine response of vegetation to timing of irrigation and soil depth, and conversely the influence of plant communities and vegetation type on deep soil water infiltration; (2) investigate the microbial communities of plots to assess whether fundamental ecosystem changes to treatments are occurring and could feed back on water flow patterns; and (3) investigate changes in soil carbon pools due to vegetation and precipitation differences. Other biogeochemical and soil physical aspects of plots are also being evaluated, such as stable isotope compositions that can reveal changes in water patterns and plant water use among plots. Ultimately, we hope to determine how plot responses to the treatments feed back on water infiltration, availability, and use.

Accomplishments through 2009
Throughout 2009, tasks that were undertaken included maintenance of the study plots, obtaining permission from INL to resume the long record of water content measurements using a neutron probe, continuation of the irrigation treatments, and collection of soil moisture and plant cover data.

We found that areal cover of plants in the plots have been affected by the treatments, and thus show some surprisingly minor changes in species diversity and changes in cover types. Sagebrush and exotic crested wheatgrass have come to dominate all plots that were planted with native species only. We measured the foliar-crown volume and estimated biomass of sagebrush populations, and detected substantially greater sagebrush presence this way in plots that had deeper soils or supplemental irrigation, particularly where it is added in winter. There were much fewer differences in the carbon isotopic composition and foliar morphological attributes that indicate physiological or plant form adjustments to different water levels. Purosequencing and restriction fragment length polymorphism (RFLP) analyses of soil microbial communities revealed considerable differences among treatments.

Plans for Continuation
We plan to sustain the treatments and soil water content measurements, and resume vegetation cover measurements. We will also be writing proposals to sustain the project after the current project funding is over.

Publications, Theses and Reports

Brandy Janzen finished her M.S. thesis in Dec 2009 on plant community cover changes to 2007, and is submitting manuscripts on the work to journals such as Ecology. Numerous presentations were given on the experiment, at Ecological Society of America, American Geophysical Union, and other meetings.