Use of Spectral Indices to Identify the Changes in the Vegetation Community Over Time After Restoring a Palustrine Wetland: A Case Study of Spencer Island Regional Park, Everett, WA.

Wetland restoration can be measured over time using community vegetation as an effectiveness indicator of restoration actions. Spencer Island Regional Park is part of the tidal freshwater wetlands along the Snohomish river basin. Those wetlands are part of a complex ecosystems, in which they are included as a salmon corridor. This research analyzes the vegetation community changes over time after restored in 1996 on Spencer Island Regional Park, Everett, Washington State, U.S. I analyzed three spectral indices using segmentation and supervised classification of land cover from 1997 to 2018. I found that in the last 21 years, the areas with emergent palustrine vegetation and forests increased, in contrast to diminishing areas of upland and scrub-shrub classes. Those finds can be interpreted that the community vegetation advanced to higher wetland successional stages as upland areas have been colonized by emergent wetland plant communities. A linear regression model predicted that by 2025, the difference between emergent and upland classes should increase. Empirical evidence is presented that support the integration of spectral indices to identify changes in community vegetation. However, it is recommended for future studies to include spectral indices and spatial information for soil and hydrology to deepen these results.

Urbanization Altered Bacterial and Archaeal Composition in Tidal Freshwater Wetlands Near Washington DC, USA, and Buenos Aires, Argentina

Urban expansion causes coastal wetland loss, and environmental stressors associated with development can lead to wetland degradation and loss of ecosystem services. This study investigated the effect of urbanization on prokaryotic community composition in tidal freshwater wetlands. Sites in an urban, suburban, and rural setting were located near Buenos Aires, Argentina, and Washington D.C., USA. We sampled soil associated with two pairs of functionally similar plant species, and used Illumina sequencing of the 16S rRNA gene to examine changes in prokaryotic communities. Urban stressors included raw sewage inputs, nutrient pollution, and polycyclic aromatic hydrocarbons. Prokaryotic communities changed along the gradient (nested PerMANOVA, Buenos Aires: p = 0.005; Washington D.C.: p = 0.001), but did not differ between plant species within sites. Indicator taxa included Methanobacteria in rural sites, and nitrifying bacteria in urban sites, and we observed a decrease in methanogens and an increase in ammonia-oxidizers from rural to urban sites. Functional profiles in the Buenos Aires communities showed higher abundance of pathways related to nitrification and xenobiotic degradation in the urban site. These results suggest that changes in prokaryotic taxa across the gradient were due to surrounding stressors, and communities in urban and rural wetlands are likely carrying out different functions.

Vegetation Effects on Bacteria and Denitrifier Abundance in the Soils of Two Tidal Freshwater Wetlands in Virginia

This study examined the abundance of bacteria and nirS-type denitrifiers associated with the rhizospheres of three emergent macrophyte species (Juncus effusus, Typha latifolia, and Peltandra virginica) to gain a greater understanding of plant-microbe interactions in wetland soils. Sampling of plant and soil properties was performed during the growing season (June) and following plant senescence (November) at two tidal freshwater wetlands. Quantitative polymerase chain reaction was used to determine the abundance of bacteria (16S rRNA) and nirS-type denitrifier genes from the rhizosphere and rhizoplane of each plant species and from nearby unvegetated soils. For bacteria, there was a positive rhizosphere effect that did not differ significantly across plant species. In contrast, significant differences in the abundance of nirS-type denitrifiers were observed across the plant species. Rhizosphere abundance was ∼2-fold greater in Peltandra virginica and 4-fold greater in Typha latifolia compared to Juncus effusus. For both bacteria and nirS-type denitrifiers, plant effects were greater during the growing season, and abundance was highly correlated with soil pH, moisture, and organic matter content. Overall, these results demonstrate plant effects on the rhizosphere microbial community can be species‐specific and that there is a synergistic relationship between plant species and environmental conditions.