Tag: Scott Bridgham

Carbon and Nitrogen Mineralization in a Manipulated Northern Hardwood Forest Soil: Do Plants’ Allocation Strategies Help Set the Size and Responsiveness of Soil Organic Matter Pools?

Presenter : Geoffrey Johnson

Mentor : Scott Bridgham

Major : Environmental Science

Poster 31

Plant litter from aboveground and belowground production constitutes a major carbon (C) and nutrient input to forest soils worldwide. Uncertainty in the relative effects of these two biomass allocations on ecosystem structure and function is the impetus for the Detritus Input Removal and Transfer (DIRT) experiment, which incorporates root trenching and leaf litter removal and addition. In this study, we sampled mineral soils from DIRT plots at a temperate hardwood forest in Northwestern Pennsylvania in the 0-10 cm depth for all treatments and additional organic horizon and 10-20 cm profile depths for control (CO) and double litter (DL). This DIRT site was established in 1991. By incubating samples at 35°C and near-optimal moisture content for 56 weeks, we estimated maximum potential respiration and net nitrogen (N) mineralization and used the resulting cumulative values to compare rate constants and pool sizes for 1 and 2 pool exponential models among treatments. Net N mineralization in DL plots was significantly greater than CO (α=0.05) at 10- 20 cm, while the no input (NI) treatment was significantly less than CO and DL (α=0.05) at 0-10 cm. We also provide evidence that the treatment effects will continue to become more significant on longer time-frames. From these results, we suggest soil C and N pools are affected by plant litter allocation ratios on decadal time scales, and the most rapid effects may be outside of the pools in the uppermost mineral soil horizons.

Impacts of Rising Heat and Precipitation on Plant Phenology in Pacific Northwest Prairies

Presenter(s): Benjamin Avis – Environmental Studies

Co presenter(s): Miles Steele, Sean Petitt, Emma Rasmussen, Hunter Mackin

Faculty Mentor(s): Peg Boulay, Scott Bridgham

Oral Session 4CS

Research Area: Environmental Science

This study seeks to understand the anticipated impacts of predicted climate change on the phenology of 12 different prairie grasses and forbs. Three sites have been selected ranging from Southern Oregon to Southern Washington. Our site, Willow Creek, is located in the Southern Willamette Valley and was selected due to its high-quality restored prairie habitat. To address the possible effects of climate change on plant survival rate and vigor, our experimental design approach is to manipulate temperature and precipitation with four treatments (including control) and measure reproductive variables of the planted focal species. Experimental parameters will be consistent with average predictions for temperature and precipitation increase, and the site will be composed of 20 plots with 5 replicants of each treatment. Our team will be responsible for data collection, quality assurance, and analysis of the results. These simulations will predict the likelihood of extinction for focal species within their current range, as well as the effects on phenology and geographic distribution.

The effects of restoration fill elevation on carbon accumulation in Pacific Northwest estuaries

Presenter(s): Emil Sadofsky

Faculty Mentor(s): Scott Bridgham

Oral Session 2 M

Agricultural development has significantly decreased the extent of costal wetlands in the Pacific Northwest. Some previously developed wetlands have been restored, but the effects of restoration on their carbon cycling functions are still unknown. To better understand land use effects on carbon cycling, we compared soil carbon dynamics in restored and reference wetlands in the South Slough estuary in Coos Bay, Oregon. We measured soil carbon content and used radioisotope dating to calculate carbon pools and carbon accumulation rate, and we measured in situ carbon dioxide (CO2) and methane (CH4) emissions in restored and reference wetlands to better understand carbon fluxes. To compare different methods of restoration, the restored sites were originally restored to different elevations. We found that the restored wetlands will have smaller and shallower carbon pools than reference sites. We also found that carbon accumulation will be fastest in the reference marsh. Among the restored marshes, we found that carbon accumulation is fastest in the low elevation marsh and slowest in the high marsh.