Environmental Science

Hydrogeological setting intensifies the effect of elevated deposition and increases the potential for in-stream N saturation


Authors: Laura S. Craig
Department or Program: BEES
Presented by: Laura Craig
Abstract: In an increasing number of forests, atmospheric inputs of nitrogen (N) have exceeded the capacity of the ecosystem to store or cycle N, resulting in increased leaching of nitrate (NO3-N) to groundwater and streams. It has previously been hypothesized that streams draining N-saturated forests are also likely to become saturated as surface-water NO3-N concentrations increase; however, saturation in both the terrestrial and aquatic components of forested ecosystems has rarely been documented and no direct connection between the two is recognized. The objective of this study was to gain a better understanding of the processes that lead to dramatically elevated NO3-N concentrations in a forested headwater (Sopers Branch) of the Maryland Piedmont, previously shown to be unable to remove appreciable amounts of N. Atmospheric inputs to the Sopers Branch watershed were estimated to be between 3.4 and 5.5 kg N ha-1 yr-1. Elevated NO3-N concentrations in both groundwater (5.8 ± 1.3 mg L-1) and surface-water (1.05 ± 0.08 and 0.67 mg L-1, observed and annual flow-weighted, respectively), along with low soil C:N ratios (12.1) indicate that the forest is N saturated. Groundwater in the Piedmont is susceptible to NO3-N contamination from atmospheric inputs and soil nitrification; I modeled exports associated with both total and baseflow discharge to evaluate the importance of groundwater delivery of NO3-N to the channel. Average annual exports were typical of forests in the Northeast and Mid-Atlantic (2.5 kg ha-1 yr-1), however, baseflow accounted for a disproportionate fraction of exports (0.64 to 0.78). During dry periods, when deep groundwater flowpaths were presumed to be the major source of NO3-N to the channel, export frequently exceeded inputs and observed in-stream concentrations were dramatically elevated. The terrestrial and aquatic components of the Sopers Branch watershed exhibit classic symptoms of N-saturation despite receiving smaller depositional inputs than many northeastern and mid-Atlantic watersheds. Local hydrogeologic factors exacerbated the N-saturation response, particularly during periods of low rainfall, leading to chronically elevated surface-water and groundwater NO3-N concentrations. This is the first un-manipulated forested watershed for which N-saturation has been documented in both terrestrial and aquatic ecosystem components, and I posit that forest streams receiving a similarly large fraction of NO3-N through subsurface flowpaths may be more likely to exhibit symptoms of N saturation in both terrestrial and aquatic components, thereby providing the best opportunity to link N saturation in terrestrial and aquatic systems. We cannot always rely on N processing in less-impacted ecosystems to protect downstream water bodies from the effects of increased N deposition; recognizing the frequency with which both the terrestrial and aquatic ecosystems in a single watershed are N saturated will allow for better quantification of the contribution of undeveloped watersheds to downstream pollution and improved management of impacts to coastal ecosystems.

Tolerance of Sedum species to Various Ratios of Crumb Rubber Amendments in Green Roof Substrate


Authors: Lorelly Solano, Andrew G. Ristvey, John D. Lea-Cox and Steven M. Cohan.
Department or Program: PSLA
Presented by: Lorelly Solano
Abstract: Recently, there has been increased interest in green roofs becoming a part of American cityscapes, primarily to mitigate storm water runoff from impervious surfaces in dense urban areas. Extensive green roofs are functional, increasing stormwater retention by incorporating a thin layer of substrate (approximately 10 cm) with specific roof liners and planted with xerophytic species which are tolerant of large diurnal and seasonal temperature fluctuations. Soon, new city buildings may be required to have systems in place for greater stormwater retention, yet in some cases, city planners will be asked to retrofit extensive green roofs on older structures. The substrates presently used in extensive green roof designs consist primarily of light-weight heat expanded shales, clays and slates. Physical and chemical weathering processes may result in the degradation of substrate particles over time, reducing aeration and increasing the potential for waterlogging, whereby causing reductions in plant health with a consequent increase in maintenance and renovation costs. We therefore seek to investigate the addition of a potentially stable, recycled tire product (crumb rubber) to these substrates, to increase their long-term performance and sustainability. At the same time, crumb rubber would decrease the weight of the substrate and increase the percentage of buildings able for retrofit of extensive green roof systems. However, crumb rubber has been shown to leach quantities of zinc that affect growth of sensitive plants. It is known that the genus Sedum, which is widely used for extensive green roofs, includes one species that can hyperaccumulate zinc. This research studied the growth of three Sedum species in expanded shale substrate with incremental rates of incorporated crumb rubber, the goal being to find the highest ratio of crumb rubber amendment tolerated by several Sedum species.

Local Climate Change Forecasting and its Implications for UM’s Urban Forest


Authors: Stephanie Juchs, Dr. Molly Brown, and Dr. Marla McIntosh
Department or Program: MEES
Presented by: Stephanie Juchs
Abstract: The geographic distributions of plant species are expected to change as a result of global warming. As plant species ranges redistribute independently, new community associations and novel habitats will emerge. Projected trends in temperature, precipitation, and growing degree days and their implications have been used to prepare for the large-scale impacts of climate change. The proposed research will use the Weather Research and Forecast Model (WRF) to investigate its utility for predicting climate change scenarios at the local scale within the Chesapeake Bay Region. Predicted variables from 1990 from the B-W corridor will be compared to the observed climate to test the accuracy at a local scale. If predictions are found to be accurate, the WRF model forecasts for 2050 will be used to predict potential changes to urban forests within this region.

Analysis of Dinoflagellate Species Responses to Temperature Variation


Authors: Letitia Cosbert
Department or Program: CBMG
Presented by: Letitia Cosbert
Abstract: Dinoflagellates are interesting protists that have not been well studied until recently, though they are abundant and essential in aquatic life. These organisms, found in the class Dinophyceae, are unique and share some exceptional characteristics. One unusual characteristic is the abundance of protein coding genes that are found in tandem repeats through out the genome, increasing the size of the genome and raising many questions about the functions of the genes and usefulness (Diaz, et al, 2005). Coupled with this thought is the fact that several dinoflagellates live in extremely different temperature regions and are able to adapt to wide ranges of temperatures. The use of confocal microscopy will be employed to see if adaptation of the dinoflagellates to a variety of temperatures relate to the transcription of variant genes in the genome. This technique will focus specifically on the cytoskeleton structures and consequently the genes associated with it since microtubules and actin are a necessary component to several aspects of the survival and life of all organisms. Secondly, quantitative real time PCR will be used to determine whether alternate genes are being used or if post-transcriptional modifications are occurring. These studies will hopefully reveal many interesting facts about these organisms and lead to better understandings of aquatic environments and possible responses to climate change. Reference: Diaz de la Espina, S.M., Alverca, E., Cuasdrado, A., & franca, S., (2005). Organization of the genome and gene expression in a nuclear environment lacking histones and nucleosomes: the amazing dinoflagellate. European Journal of Cell Biology, 84, 137-149.