RAPID: Quantifying the Great Marsh Sedimentation Event 2018

GSTDTAP

项目编号	1832177
	RAPID: Quantifying the Great Marsh Sedimentation Event 2018
	Zoe Hughes
主持机构	Trustees of Boston University
项目开始年	2018
	2018-03-15
项目结束日期	2018-08-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	8000(USD)
国家	美国
语种	英语
英文摘要	An unprecedented event took place on New England marshes between late December 2017 and January 2018 wherein football field-sized patches of marsh were blanketed with 2 to 12 inches of ice-rafted silt and sand. This is hugely significant because these marshes normally gain elevation through sediment accumulation more slowly than local sea level is rising. Because marshes are essentially flat, even a small rise in water level will affect a large area. Ultimately, if the waters remain too deep, marshes will drown and switch to open water, with loss of all ecosystem services and coastal protections they afford. The large amount of sediment that was deposited in January, assuming the marsh grasses can grow through it, will give the areas a boost in elevation, making them more resilient to rising waters. The event occurred when two weeks of extreme cold were followed by higher than normal astronomic tides, combined with a powerful northeast winter storm. During the prolonged cold snap, tidal waters froze to the bottom of creeks and bays, incorporating bottom sediment into the ice, which thickened and trapped more sediment with each successive low tide. When the storm surge occurred, the ice rafts floated up and onto the marsh surface, where they became stranded, eventually melting and leaving the sediment on the marsh. In a normal year, ice-rafting would bring about 5% of the annual inorganic material deposited, but this single storm layer is estimated to be equivalent to 71 years of normal accretion. Such infrequent, high sedimentation ice rafting events may therefore be integral to sustaining marshes in New England (as hurricanes can be to wetlands in the southern US); yet are rarely documented. This project addresses this knowledge gap by mapping the area covered in sediment using aerial photography ground-truthed with measurements of thickness and coverage in the field, to fully quantify the amount of sediment transported onto the marsh and its impact on marsh elevation. In addition to quantifying the importance of winter storm processes to northern marshes, this study will provide insights into marsh restoration strategies, such as artificial elevation building through "thin layer deposition" whereby locally-dredged sediment is sprayed on top of the marsh surface to build new marshes or elevate existing marshes. The January 2018 event sedimentation provides a natural laboratory to study how a Spartina patens-dominated high marsh will respond to artificial sedimentation, and what thickness of sediment the marsh can withstand. The study broadens participation in geoscience research, as it is headed by an early-career woman researcher, and also forms an independent research project for an undergraduate student, who will analyze sediment samples, translate field data into maps, and combine these data with the aerial photography to determine the impact of this event. The primary goal of this study is to assess the extent and volume of the extreme sedimentation event which occurred in January 2018 on the Great Marsh, MA. The researchers will collect measurements of thickness and surface extent of the deposit before the spring grass begins to shoot and obscure its coverage. They will conduct aerial survey mapping to collect ortho-photographs capturing the entire marsh region (~130 km2) at a resolution of 10 cm2 and will use a combination of automated image analysis, manual digitization, and comparison to historical images to map the new ice rafted sediment. Field-based ground-truthing of aerial photos will involve a minimum of eight land to barrier island transects (by foot) across the marsh to map and measure the sediment deposits. Multiple sediment plugs of known volume will be extracted for grain size, organic content and bulk density analysis. Sediment thickness and lateral extent of the deposit, determined from the aerial photographs and field surveys, will allow the researchers to estimate the total volume of sediment deposited during this event, enabling a comparison to known accretion rates. The data collected for this study will provide a record and a baseline for future investigations, including analysis of storm conditions when the ice rafts inundated this marsh, and correlation of vectors of transport to wind direction, water depth and marsh elevation, as well as assessments of grass recovery following the sedimentation event. The work will inform the proposed marsh restoration practice of "thin layer deposition", by determining the thickness of introduced sediment layers that can be tolerated by the marsh ecosystem as aids to accretion under accelerating rates of sea-level rise. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/72368
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Zoe Hughes.RAPID: Quantifying the Great Marsh Sedimentation Event 2018.2018.