Generalizing Ecological Effects of Shoreline Armoring Across Soft Sediment Environments

Abstract

Despite its widespread use, the ecological effects of shoreline armoring are poorly synthesized and difficult to generalize across soft sediment environments and structure types. We developed a conceptual model that scales predicted ecological effects of shore-parallel armoring based on two axes: engineering purpose of structure (reduce/slow velocities or prevent/ stop flow of waves and currents) and hydrodynamic energy (e.g., tides, currents, waves) of soft sediment environments. We predicted greater ecological impacts for structures intended to stop as opposed to slow water flow and with increasing hydrodynamic energy of the environment. We evaluated our predictions with a literature review of effects of shoreline armoring for six possible ecological responses (habitat distribution, species assemblages, trophic structure, nutrient cycling, productivity, and connectivity). The majority of studies were in low-energy environments (51 of 88), and a preponderance addressed changes in two ecological responses associated with armoring: habitat distribution and species assemblages. Across the 207 armoring effects studied, 71% were significantly negative, 22% were significantly positive, and 7% reported no significant difference. Ecological responses varied with engineering purpose of structures, with a higher frequency of negative responses for structures designed to stop water flow within a given hydrodynamic energy level. Comparisons across the hydrodynamic energy axis were less clear-cut, but negative responses prevailed (>78%) in high-energy environments. These results suggest that generalizations of ecological responses to armoring across a range of environmental contexts are possible and that the proposed conceptual model is useful for generating predictions of the direction and relative ecological impacts of shoreline armoring in soft sediment ecosystems.

Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone

“…First, marsh ecosystems are relatively low energy compared to the open-coast systems where other armoring research has been conducted. Effects of shoreline armoring across soft-sediment environments appears to vary by energy and armoring type, and our work supports the hypothesis that the effects of armoring will be subtler in low energy systems (Dugan et al 2017;Bozek and Burdick 2005). Second, the southeastern US coastline is relatively undeveloped (Crossett et al 2005;Gittman et al 2015).…”

“…In this study, we aimed to evaluate the effect of placing a hard substrate at the upland-marsh ecotone by studying bulkheads that were placed above the high-tide mark adjacent to salt marshes. It is likely that these bulkheads have less of an effect than those placed lower in the tidal profile or in higher energy environments (Dugan et al 2017). However, we hypothesize that they still alter the flow of fresh water and associated nutrients from the upland to the marsh, and impede the movement of animals in both directions.…”

Water Column Turbidity Not Sediment Nutrient Enrichment Moderates Microphytobenthic Primary Production

“…This ultimately can have substantial implications for coastal ecosystems through indirectly facilitating the removal of nutrients in oligotrophic systems or contributing to accelerating water column primary production in eutrophic systems. Consequently, reduced MPB productivity during submergence not only has direct implications on the supply of labile carbon and therefore coastal food webs [6] but can cascade onto reductions in the capacity to moderate pollutants, changes in trophic structure and alterations in nutrient cycling and transformation pathways [10,63,64]. In combination, these changes feedback within the system to modify ecological interaction networks and push ecosystems closer towards tipping points [65][66][67].…”

Impacts of Coastal Land Use and Shoreline Armoring on Estuarine Ecosystems: an Introduction to a Special Issue

“…For example, subestuary comparisons have been applied to studies of SAV (Li et al 2007;Patrick et al 2014), blue crab and bivalve abundance (King et al 2005), polychlorinated biphenyl (PCB) contamination of fish (King et al 2004), bird community diversity (DeLuca et al 2004), and the invasion of wetlands by a non-native form of Phragmites (King et al 2007). The two papers that were not part of the interdisciplinary project (Dugan et al 2017;Gehman et al 2017) were chosen to complement the other papers.…”