Deborah J. Shafer

A comparison of 28 natural and dredged material salt marshes in Texas with an emphasis on geomorphological variables.

Fourteen dredged material marshes andfourteen natural marshes along the Texas, USA, coastare compared on the basis of 1) edge: area ratios, 2)relative exposure index values, 3) elevation profiles,4) elevation of Spartina alterniflora, 5) soilorganic carbon content, 6) soil silt-clay content, and7) belowground plant biomass. Although edge: areacomparisons cannot detect certain types of differencesin geomorphology, comparisons clearly show thatdredged material marshes, on average, have fewer pondsand flooded depressions than natural marshes. Comparisons of relative exposure index values suggestthat wave protection structures associated with somedredged material marshes may be overbuilt. Elevationprofiles illustrate the potential for structures suchas berms to lead to differences between dredgedmaterial marshes and natural marshes, but they alsoshow the high variability in elevation profiles thatexists among both dredged material and naturalmarshes. S. alternifloraelevations in dredgedmaterial marshes are not significantly different fromthose of natural marshes. Soil organic carbon andsilt-clay content of dredged material marshes are notsignificantly different from those of natural marshes. Although belowground biomass of dredged materialmarshes is significantly lower than that of naturalmarshes, regression analysis suggests that belowgroundbiomass will increase over time. Findings reportedhere suggest several points that should be consideredduring planning and design of dredged material marshesin Texas: 1) if an objective of marsh construction isto mimic natural marsh geomorphology, methods toincrease the amount of unconnected edge need to bedeveloped, 2) methods of effectively summarizinggeomorphic characteristics need further development,and 3) there is some evidence suggesting thatprotective structures may be over-built, and the needfor substantial structural protection should bebalanced against the costs of structures and risk ofsite failure during project design. Lastly, a methodfor increasing the amount of unconnected edge thatinvolves excavation of bay bottom before placement ofdredged material is suggested.

Effects of salinity on survival of the exotic seagrass Zostera japonica subjected to extreme high temperature stress

Abstract Zostera japonica is a non-indigenous seagrass that is expanding along the Pacific Coast of North America. The ecophysiology of this seagrass is poorly studied and management of the species is fragmented. This split-plot mesocosm experiment was designed to evaluate the response of Z. japonica to chronic, extreme temperature and salinity stress to facilitate development of models to predict potential Z. japonica colonization. We collected Z. japonica plants from Padilla Bay, Washington and Yaquina Bay and Coos Bay, Oregon and exposed them to a constant water temperature of 15°C or 35°C at three different salinities (5, 20 and 35). After 7 days exposure, shoot survival ranged between 6% and 42%; after 9 days exposure, only a few plants from the Yaquina Bay population survived. At a ambient temperature (15°C), no differences were detected among the three salinity treatments. However, at a temperature of 35°C, the survival of plants grown at a salinity of 5 was significantly lower than at higher salinities (20 and 35). Although the effect of population was weak, the northern population appeared to be more susceptible to the combined effects of heat stress and low salinity than the southern populations. We suggest that Z. japonica will continue to spread southward along the Pacific coast of North America until it reaches systems that regularly exceed the temperature tolerances of this non-indigenous seagrass.

Predicting dredging-associated effects to coral reefs in Apra Harbor, Guam - Part 1: Sediment exposure modeling

Model studies were conducted to investigate the potential coral reef sediment exposure from dredging associated with proposed development of a deepwater wharf in Apra Harbor, Guam. The Particle Tracking Model (PTM) was applied to quantify the exposure of coral reefs to material suspended by the dredging operations at two alternative sites. Key PTM features include the flexible capability of continuous multiple releases of sediment parcels, control of parcel/substrate interaction, and the ability to efficiently track vast numbers of parcels. This flexibility has facilitated simulating the combined effects of sediment released from clamshell dredging and chiseling within Apra Harbor. Because the rate of material released into the water column by some of the processes is not well understood or known a priori, the modeling approach was to bracket parameters within reasonable ranges to produce a suite of potential results from multiple model runs. Sensitivity analysis to model parameters is used to select the appropriate parameter values for bracketing. Data analysis results include mapping the time series and the maximum values of sedimentation, suspended sediment concentration, and deposition rate. Data were used to quantify various exposure processes that affect coral species in Apra Harbor. The goal of this research is to develop a robust methodology for quantifying and bracketing exposure mechanisms to coral (or other receptors) from dredging operations. These exposure values were utilized in an ecological assessment to predict effects (coral reef impacts) from various dredging scenarios.

The Influence of Breakwaters on Nearshore Sedimentation Patterns in Chesapeake Bay, USA

ABSTRACT Palinkas, C.M.; Barth, N.; Koch, E.W., and Shafer, D.J., 2016. The influence of breakwaters on nearshore sedimentation patterns in Chesapeake Bay, USA. This study describes nearshore Chesapeake Bay sedimentation at sites adjacent to and landward of 24 segmented breakwaters, varying in age (1–19 years) and physical setting. Grain-size and organic-content profiles are examined at the breakwater-protected sites to assess potential changes induced by breakwater installation as well as at the adjacent-exposed sites to establish historical trends. Sedimentation rates at all sites are calculated with 210Pb (half-life 22.3 years). At the breakwater-protected sites, these rates largely reflect preconstruction sedimentation because of the long half-life of 210Pb relative to breakwater ages. Determining the postconstruction sedimentation rate can be more difficult because the signature of breakwater influence in the sedimentological record can be obscured. For example, if the source of sediment is not affected dramatically by construction, down-core profiles may not have obvious changes. The depth of breakwater influence, however, can be interpreted by considering all the sedimentological evidence at a given location, and the postconstruction rates are calculated from this depth. In general, the sedimentological response to breakwater construction is fairly unique for each location but depends on such factors as breakwater age and geometry, shoreline sediment composition, and construction technique.