Influence of Physical Manipulations on Short-Term Salt Marsh Morphodynamics: Examples from the North and Mid-Atlantic Coast, USA

Abstract

Along the mid-and north Atlantic coasts of the USA, over 90 % of salt marshes have been ditched. Ditching was largely abandoned by the mid-twentieth century; however, techniques that create permanent shallow water pools for mosquito control and bird habitat are increasingly being applied to marshes of the USA and elsewhere. Salt marshes in Plum Island Sound, Massachusetts, and Barnegat Bay, New Jersey, were used to examine differences between areas that have been ditched and those altered to increase the density of shallow pools in water table dynamics, salinity, soil and porewater chemistry, as well as short-term sedimentation, accretion, and elevation change rates. We found that the area with plugged ditches, berms, and pools in Plum Island had less drainage, higher salinity and porewater sulfide and ammonium concentrations, and higher soil organic matter than the adjacent ditched area. Despite averaging 8 cm lower in elevation, the Plum Island ditched area had less sediment deposition and was composed of higher elevation plant species than the area with plugged ditches, berms, and shallow pools. Elevation increased in the ditched area at a rate of 3.2 ± 0.5 mm/year, but elevation change was variable in the area with pools. In Barnegat Bay, the marsh area with pools and ditches had less sediment deposition and surface accretion than the ditch-only area, associated, in part, with the higher elevation. An average elevation difference of 4.5 cm was associated with a sixfold difference in mineral sediment deposition. Temporal sediment deposition and surface accretion was important in the ditch-only area but was absent or muted in the area with numerous pools. Elevation increased in both marsh areas at an average rate of 1.8 ± 0.8 mm/year, less than half the long-term average local rate of sea-level rise. Our results illustrate how physical manipulations including changes to tidal hydrology and surface topography interact with elevation to influence short-term biophysical feedbacks.

Salt marsh erosion rates and boundary features in a shallow Bay

“…While this could have affected erosion rates, there is extensive evidence that salt marshes are able to keep peace with sea level rise and maintain their elevation constant with respect to mean sea level thanks to their relatively high accretion rates [e.g., Day et al ., ; Fagherazzi , ; Fagherazzi et al ., ; Kirwan and Murray , ; Kirwan and Megonigal , ; Kirwan et al , , ]. Elsey‐Quirk and Adamowicz [] measured accretion rates of 1.8 ± 0.8 mm/yr in the Bernagat Bay marshes, which partly offset sea level rise. Herein we mainly focus on spatial variations in erosion rate within Barnegat Bay, and a deeper understanding of the role of sea level rise in salt marsh decline is outside the scope of this work, as it might be difficult to infer differential erosional rates induced by sea level variations at a Bay scale.…”

Pond Excavation Reduces Coastal Wetland Carbon Dioxide Assimilation

“…Alterations of the salt marsh caused changes to the physical and chemical soil environment over short time scales (Elsey‐Quirk & Adamowicz, ); ditching lowered water tables, reduced sedimentation, and increased soil aeration, decomposition, and compaction (Elsey‐Quirk & Adamowicz, ). Water table dynamics and topography in the marsh setting influence surface sedimentation, soil development, porewater chemistry, vegetation community, and plant productivity; therefore, altering these systems has had strong impacts to ecosystem structure and function (Elsey‐Quirk & Adamowicz, ). Because of concern with the negative impacts to wildlife, such as fish and water fowl, which utilized ponded areas, grid ditching for mosquito control was phased out in the 1960s (James‐Pirri et al, ; Lathrop et al, ).…”

“…Termed open marsh water management (OMWM), its objective is to reduce mosquito breeding from a given area of marsh while enhancing wildlife habitat (Ferringo & Jobbins, ). This practice has been used extensively in the mid‐Atlantic and in sparse areas of Massachusetts, Connecticut, New York, Florida, and Louisiana (Elsey‐Quirk & Adamowicz, ). The techniques used in OMWM are regionally dependent.…”

“…Mosquitos are a public health concern, as they are vectors for Eastern equine encephalitis and West Nile virus. Efforts to control mosquitos via drainage led to installation of parallel grid ditching in almost 95% of the tidal marshes between Maine and Virginia, mostly dating to the Works Progress Administration of the 1930s (Elsey-Quirk & Adamowicz, 2016;Lathrop et al, 2000;Rochlin et al, 2012). Alterations of the salt marsh caused changes to the physical and chemical soil environment over short time scales (Elsey-Quirk & Adamowicz, 2016); ditching lowered water tables, reduced sedimentation, and increased soil aeration, decomposition, and compaction (Elsey-Quirk & Adamowicz, 2016).…”

“…Efforts to control mosquitos via drainage led to installation of parallel grid ditching in almost 95% of the tidal marshes between Maine and Virginia, mostly dating to the Works Progress Administration of the 1930s (Elsey-Quirk & Adamowicz, 2016;Lathrop et al, 2000;Rochlin et al, 2012). Alterations of the salt marsh caused changes to the physical and chemical soil environment over short time scales (Elsey-Quirk & Adamowicz, 2016); ditching lowered water tables, reduced sedimentation, and increased soil aeration, decomposition, and compaction (Elsey-Quirk & Adamowicz, 2016). Water table dynamics and topography in the marsh setting influence surface sedimentation, soil development, porewater chemistry, vegetation community, and plant productivity; therefore, altering these systems has had strong impacts to ecosystem structure and function (Elsey-Quirk & Adamowicz, 2016).…”