Reports
Poplar Island sediment quality monitoring: April 2009
2010, Wells, D.V., Van Ryswick, S., and Kurtz, N.
File Reports, Coastal and Estuarine Geology, File Report 2010-04
Executive Summary
The Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island, formerly known as the Poplar Island Environmental Restoration Project (PIERP) is an innovative approach to the placement of dredged material through island habitat restoration. The facility was constructed to produce a combination of upland placement in conjunction with the formation of tidal wetlands. This facility is establishing new habitats for a wide range of aquatic and terrestrial wildlife. Depending upon the success of the operation of this facility, similar facilities may be constructed based upon this design. Because this is a prototype facility in the Chesapeake Bay, it is crucial to assure the integrity of the environment of the Chesapeake Bay is not diminished by the placement of dredged material for beneficial use.
In order to assess the impact of the PIERP on the surrounding sedimentary environment, a monitoring program was initiated, beginning with a baseline survey (pre-construction of the facility). This survey established the regional sedimentary background on samples collected at 27 stations in October 1995 and July 1996. The next monitoring samplings were conducted in 2001 and 2002 during which sediments were collected at 12 sites around the completed diked facility. A denser spatial sampling grid (28 sampling stations) was used in the fourth and fifth monitoring events which documented the sedimentary environment before and after Tropical Storm Isabel (September 2003). Since 2003, sampling for monitoring has been conducted each spring using the same 28 sampling sites. This report documents the state of the sedimentary environment adjacent to the PIERP based on samples collect in April 2009.
For the April 2009 samples, all of the metals concentrations of the PIERP samples were low compared to the main Chesapeake Bay, reflecting the coarse nature of the sediment in the exterior environment around the PIERP. The association of metals with grain size conformed well to the associations found in the baseline survey conducted in 1995-96.
With regard to the grain size, there was alteration of the sediment distribution as a result of the construction of the PIERP as observed in the previous post-construction sampling events. The variations in the grain size are attributable to the change in the hydrodynamic regime of the area resulting from the construction of the PIERP. Most notable is the accumulation of fines in the sheltered area east of the PIERP, adjacent to Coaches Island. Increased target metals (metals of concern) were observed at those stations that exhibited finer grain size, potentially due to the change in hydrodynamic conditions, but these increases were expected given the grain size change. Storm action, from Tropical Storm Isabel 2003, altered the grain size distribution by scouring out newly deposited fines in the southeastern portion of Poplar Harbor, and depositing a localized thin veneer of finer sediments from the breach caused by the storm in the northeastern dike of the PIERP. The samples collected in June 2004 exhibited a sediment distribution that was in transition, returning to the pre-Isabel state. The May 2006 sediment pattern was the most consistent with the post-construction, pre-Isabel sampling period (Year 2000 – April 2003) to date. The distribution of sand in April 2007 was similar to the May 2006 sampling; however, it was much coarser. The April 2009 samples are slightly coarser than the 2008 samples.
Nitrogen (N), carbon (C), sulfur (S), and phosphorus (P) concentrations in the PIERP exterior samples are low and within the range found in mainstem Chesapeake Bay samples. The distribution of the N:C ratio shows the pattern of recent deposition within the area protected by the PIERP. The organic matter in the sediment indicated that the study area was relatively quiescent although not to the degree it was during the previous two years.
The target metals were well within the grain size association patterns established with the baseline study (conducted in 1995-96) and the concentrations of the metals continued to be low with respect to the main Bay. These observations continue to support the working hypothesis for the study: “Project conditions will not change the metals behavior in Poplar Harbor when compared to regional background sediments.”
