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Soil moisture dynamics and their effect on bioretention performance in Northeast Ohio

Most members of the Watershed Hydrology lab chose to go to GSA this year, and we had a blast sharing our science and enjoying Vancouver and surrounding areas. But now we are sadly missing out on the American Geophysical Union (AGU) meeting going on this week. Fortunately, a small piece of our work will be represented by outstanding summer REU student Sidney Bush. She’s giving a poster on Thursday afternoon in the Moscone West poster hall at H43F-1017. Here’s her abstract:

Soil moisture dynamics and their effect on bioretention performance in Northeast Ohio

Sidney A. Bush1, Anne Jefferson2, Kimberly Jarden2, Lauren E Kinsman-Costello2 and Jennifer Grieser3, (1)University of Virginia Main Campus, Charlottesville, VA, United States, (2)Kent State University Kent Campus, Kent, OH, United States, (3)Cleveland Metroparks, Parma, OH, United States

Urban impervious surfaces lead to increases in stormwater runoff. Green infrastructure, like bioretention cells, is being used to mitigate negative impacts of runoff by disconnecting impervious surfaces from storm water systems and redirecting flow to decentralized treatment areas. While bioretention soil characteristics are carefully designed, little research is available on soil moisture dynamics within the cells and how these might relate to inter-storm variability in performance. Bioretentions have been installed along a residential street in Parma, Ohio to determine the impact of green infrastructure on the West Creek watershed, a 36 km2 subwatershed of the Cuyahoga River. Bioretentions were installed in two phases (Phase I in 2013 and Phase II in 2014); design and vegetation density vary slightly between the two phases. Our research focuses on characterizing soil moisture dynamics of multiple bioretentions and assessing their impact on stormwater runoff at the street scale. Soil moisture measurements were collected in transects for eight bioretentions over the course of one summer. Vegetation indices of canopy height, percent vegetative cover, species richness and NDVI were also measured. A flow meter in the storm drain at the end of the street measured storm sewer discharge. Precipitation was recorded from a meteorological station 2 km from the research site. Soil moisture increased in response to precipitation and decreased to relatively stable conditions within 3 days following a rain event. Phase II bioretentions exhibited greater soil moisture and less vegetation than Phase I bioretentions, though the relationship between soil moisture and vegetative cover is inconclusive for bioretentions constructed in the same phase. Data from five storms suggest that pre-event soil moisture does not control the runoff-to-rainfall ratio, which we use as a measure of bioretention performance. However, discharge data indicate that hydrograph characteristics, such as lag time and peak flow, are altered relative to a control street. This analysis suggests that street-scale implementation of bioretention can reduce the impact of impervious surface on stormflows, but more information is needed to fully understand how soil moisture of the bioretentions affects inter-storm variability in performance.

Sidney’s poster is part of a session on “Water, Energy, and Society in Urban Systems” that Anne nominally helped convened. Check out all of the stimulating morning talks and awesome afternoon posters on Thursday. The rest of us are sorry to be missing it, but if *you* are in San Francisco at AGU this week, don’t miss out on all the great science in the session.

AGU 2013: Transient Storage versus Hyporheic Exchange in Low-gradient Headwater Streams

Abstract season is upon us. I’ll be at AGU, where there looks to be loads of good sessions, including one on “Groundwater-Surface Water Interactions: Physical, biological, and chemical relevance“. Hopefully, my work (abstracted below) will be part of this session.

Transient Storage versus Hyporheic Exchange in Low-gradient Headwater Streams

A.J. Jefferson, S.M. Clinton, M. Osypian

In-channel storage and hyporheic exchange are components of transient storage that exist as a function of geomorphology and which can have contrasting effects on nutrient retention, temperature, and biological communities. In order to evaluate and predict the effects of geomorphic changes on the biogeochemical and ecological functioning of transient storage zones, in-channel storage needs to be quantified separately from hyporheic exchange. In four headwater streams, we used salt injections modeled in OTIS-P to quantify total transient storage fluxes and piezometer measurements to quantify hyporheic fluxes. In the mixed bedrock-alluvial streams, restoration increased both in-channel and hyporheic exchange fluxes, but in-channel transient storage was dominant. In the fully alluvial streams, total transient storage fluxes were ~100 times greater in the stream which had undergone restoration than in one where no restoration had occurred. Conversely, hyporheic fluxes were ~400 times smaller in the restored alluvial stream. Thus, in the restored stream, hyporheic flux was <1% of total transient storage flux, while in the unrestored stream, hyporheic flux accounted for up to 75% of total transient storage fluxes. This difference in the contribution of the hyporheic zone to total transient storage appears to be a function of both channel morphology and bed sediments, primarily the creation of pools and reduction in sediment size that occurred as a result of restoration. These dramatic variations in the magnitude and relative proportions of in-channel and hyporheic fluxes that occur across low-gradient, headwater streams may be an important control on reach-scale biogeochemical and ecosystem functioning.

Watch Anne talk about channel initiation at AGU 2011

I gave two talks at the AGU meeting in San Francisco in December. One talk was in session “EP31G Predictive Understanding of Coupled Interactions Among Water, Life, and Landforms II”, and it was recorded and made available on Vimeo. While all the talks in the session were extremely interesting, if you want to skip to me, go to about 31 minutes and 30 seconds into the video.

EP31G : AGU Fall Meeting 2011 from American Geophysical Union on Vimeo.