Comparison of wrack dynamics between mangrove forests with and without seawalls

Wrack line formation and composition on shores of a large Alpine lake: The role of littoral topography and wave exposure

Wrack lines are a key formation along shorelines that provide organic matter and bring ecological diversity to the local environment. Although wrack line formation has been extensively studied along marine beaches and estuaries, in contrast, knowledge about the environmental variables that promote wrack line formation within inland lakes is widely lacking. In one of the first studies to focus on wrack line formation on lakesides, we analysed the dimensions, volume, elevation and particulate composition of 36 wrack lines across 20 shore sections of a large, oligotrophic Alpine lake with natural water level fluctuations (Lake Constance-Obersee). Using multivariate partial least squares (PLS) regression, we identified the key environmental variables that drive wrack accumulation in lakeside areas. Our results demonstrate that wrack line volume increased with (1) the width of the eulittoral zone as an indicator of the swash conditions (up-rush vs. down-wash), (2) high exposure to wind waves as indicated by the total effective fetch, (3) high exposure to ship waves (catamaran ferry), and (4) the width of the sublittoral zone as an indicator of the availability of source material (Chara spp.) and of the wave energy dissipation rate of the incoming deep water waves. Sediment texture played only a minor role. Wide eulittoral zones and high ship wave exposure favoured high proportions of lake-borne components (Chara remains, mollusc shells), while the reverse was true for land-based components. Anthropogenic wastes were only present in small proportions. We discuss four main factor groups influencing the amount of wrack in marine beaches and on lakeshores considering similarities (waves, breakers, swash, dissipation, relief) and differences (tides vs. annual water level fluctuations) of the two systems, and point out research gaps. We demonstrate that wrack line formation is also important in large inland lakes and can be analysed using basic ideas from relevant marine studies.

Effect of Seawall Embankment Reclamation on the Distribution of Cr, Cu, Pb and Zn Pollution in Invasive Spartina alterniflora and Native Phragmites australis Coastal Saltmarshes of East China

Coastal reclamation by seawall embankments and the spread of invasive C₄ perennial grass Spartina alterniflora have recently become more prevalent in eastern China's coastal wetlands. While trace metals (TMs), carbon, and nitrogen dynamics concerning reclamation have extensively been explored across China's coastal wetlands, to date, the impact of reclamation by coastal embankment and exotic plant invasion on TMs' pollution dynamics in coastal marshes remains largely unexplored. We compared TMs Cr, Cu, Pb, and Zn cumulation in coastal embankment-reclaimed versus unreclaimed S. alterniflora and Phragmites australis saltmarshes in eastern China coastal wetlands. In both S. alterniflora and P. australis marshes, coastal embankment reclamation spurred an increase in Cr, Cu, Pb, and Zn concentrations by 31.66%, 53.85%, 32.14%, 33.96% and by 59.18%, 87.50%, 55.55%, 36.84%, respectively, in both marsh types. Reclamation also reduced plant biomass, soil moisture, and soil salinity in both plants' marshes. Our findings suggest that the impact of coastal embankment reclamation and replacement of native saltmarshes by invasive S. alterniflora had a synergistic effect on TM accumulation in the P. australis marshes, as corroborated by bioaccumulation and translocation factors. Reclamation by coastal embankments and invasive alien plants could significantly impair the physico-chemical properties of native plant saltmarsh and essentially weaken the accumulation of Cr, Cu, Pb, and Zn potential of the coastal saltmarshes. Our findings provide policymakers with an enhanced knowledge of the relationship between reclamation, plant invasiveness, and TM pollution dynamics in coastal wetlands, providing a baseline for attaining future goals and strategies related to the tradeoffs of various wetland reclamation types.