Using existing infrastructure as ground control points to support citizen science coastal UAS monitoring programs

Recent publications have described the ability of citizen scientists to conduct unoccupied aerial system (UAS) flights to collect data for coastal management. Ground control points (GCPs) can be collected to georeference these data, however collecting ground control points require expensive surveying equipment not accessible to citizen scientists. Instead, existing infrastructure can be used as naturally occurring ground control points (NGCPs), although availably of naturally occurring ground control point placement on such infrastructure differs from published best practices of ground control point placement. This study therefore evaluates the achievable accuracy of sites georeferenced with naturally occurring ground control points through an analysis of 20 diverse coastal sites. At most sites naturally occurring ground control points produced horizontal and vertical root mean square errors (RMSE) less than 0.060 m which are similar to those obtained using traditional ground control points. To support future unoccupied aerial system citizen science coastal monitoring programs, an assessment to determine the optimal naturally occurring ground control point quantity and distribution was conducted for six coastal sites. Results revealed that generally at least seven naturally occurring ground control points collected in the broadest distribution across the site will result in a horizontal and vertical root mean square errors less than 0.030 m and 0.075 m respectively. However, the relationship between these placement characteristics and root mean square errors was poor, indicating that georeferencing accuracy using naturally occurring ground control points cannot be optimized solely through ideal quantity and distribution. The results of these studies highlight the value of naturally occurring ground control points to support unoccupied aerial system citizen science coastal monitoring programs, however they also indicate a need for an initial accuracy assessment of sites surveyed with naturally occurring ground control points at the onset of such programs

Maximizing oyster-reef growth supports green infrastructure with accelerating sea-level rise

Within intertidal communities, aerial exposure (emergence during the tidal cycle) generates strong vertical zonation patterns with distinct growth boundaries regulated by physiological and external stressors. Forecasted accelerations in sea-level rise (SLR) will shift the position of these critical boundaries in ways we cannot yet fully predict, but landward migration will be impaired by coastal development, amplifying the importance of foundation species’ ability to maintain their position relative to rising sea levels via vertical growth. Here we show the effects of emergence on vertical oyster-reef growth by determining the conditions at which intertidal reefs thrive and the sharp boundaries where reefs fail, which shift with changes in sea level. We found that oyster reef growth is unimodal relative to emergence, with greatest growth rates occurring between 20–40% exposure, and zero-growth boundaries at 10% and 55% exposures. Notably, along the lower growth boundary (10%), increased rates of SLR would outpace reef accretion, thereby reducing the depth range of substrate suitable for reef maintenance and formation, and exacerbating habitat loss along developed shorelines. Our results identify where, within intertidal areas, constructed or natural oyster reefs will persist and function best as green infrastructure to enhance coastal resiliency under conditions of accelerating SLR

Density-dependent role of an invasive marsh grass, <i>Phragmites australis</i>, on ecosystem service provision

<div><p>Invasive species can positively, neutrally, or negatively affect the provision of ecosystem services. The direction and magnitude of this effect can be a function of the invaders’ density and the service(s) of interest. We assessed the density-dependent effect of an invasive marsh grass, <i>Phragmites australis</i>, on three ecosystem services (plant diversity and community structure, shoreline stabilization, and carbon storage) in two oligohaline marshes within the North Carolina Coastal Reserve and National Estuarine Research Reserve System (NCNERR), USA. Plant species richness was equivalent among low, medium and high <i>Phragmites</i> density plots, and overall plant community composition did not vary significantly by <i>Phragmites</i> density. Shoreline change was most negative (landward retreat) where <i>Phragmites</i> density was highest (-0.40 ± 0.19 m yr^-1 vs. -0.31 ± 0.10 for low density <i>Phragmites</i>) in the high energy marsh of Kitty Hawk Woods Reserve and most positive (soundward advance) where <i>Phragmites</i> density was highest (0.19 ± 0.05 m yr^-1 vs. 0.12 ± 0.07 for low density <i>Phragmites</i>) in the lower energy marsh of Currituck Banks Reserve, although there was no significant effect of <i>Phragmites</i> density on shoreline change. In Currituck Banks, mean soil carbon content was approximately equivalent in cores extracted from low and high <i>Phragmites</i> density plots (23.23 ± 2.0 kg C m^-3 vs. 22.81 ± 3.8). In Kitty Hawk Woods, mean soil carbon content was greater in low <i>Phragmites</i> density plots (36.63 ± 10.22 kg C m^-3) than those with medium (13.99 ± 1.23 kg C m^-3) or high density (21.61 ± 4.53 kg C m^-3), but differences were not significant. These findings suggest an overall neutral density-dependent effect of <i>Phragmites</i> on three ecosystem services within two oligohaline marshes in different environmental settings within a protected reserve system. Moreover, the conceptual framework of this study can broadly inform an ecosystem services-based approach to invasive species management.</p></div

Sampling locations.

<p>A) Location of Currituck Banks and Kitty Hawk Woods Reserves (stars), components of the North Carolina Coastal Reserve and National Estuarine Research Reserve system, in Currituck Sound, North Carolina, USA. B) Location of sampled Low, Medium, and High <i>Phragmites</i> Density sites (stars) within Kitty Hawk Woods Reserve. C) Location of sampled Low and High <i>Phragmites</i> Density sites (stars) within Currituck Banks Reserve—note that no Medium <i>Phragmites</i> density sites were present within Currituck Banks Reserve. All satellite imagery was derived from United States Geological Survey, High Resolution Orthoimagery Dataset.</p

Mean (±SE) normalized total below-ground carbon inventory (g C m^-3).

<p>Below-ground carbon inventory A) at Kitty Hawk Woods and Currituck Banks Reserves, B) between <i>Phragmites</i> Density treatments within Kitty Hawk Woods Reserve, and C) between <i>Phragmites</i> Density treatments within Currituck Banks Reserve. Note that the Medium <i>Phragmites</i> Density treatment was present only in Kitty Hawk Woods Reserve. See text for results of statistical analyses.</p

Mean (±SE) observed plant diversity parameters.

<p>A) Species Richness (<i>d</i>), B) Pielou’s Evenness (<i>J’</i>), C) Simpson’s Diversity (1-<b>D</b>), and D) Shannon Diversity (<i>H’</i>) for Low, Medium, and High <i>Phragmites</i> Density treatments in Currituck Banks Reserve (dark gray shading) and Kitty Hawk Woods Reserve (light gray shading). Note that the Medium <i>Phragmites</i> Density treatment was present only in Kitty Hawk Woods Reserve. See text for results of statistical analyses.</p

Results of Non-Metric Multidimensional Scaling (NMDS) and two-way crossed Analysis of Similarities (ANOSIM) used to evaluate effects of Reserve and <i>Phragmites</i> density on overall emergent vegetation community structure.

<p>2-dimensional stress values denote the degree of mismatch between the predicted values from the regression of the similarity matrix and the distances between samples as displayed by the two-dimensional nMDS plot.</p

Mean (±SE) above-ground biomass (g dry plant material m^-2).

<p>Above-ground biomass A) at Kitty Hawk Woods and Currituck Banks Reserves, B) between <i>Phragmites</i> Density treatments within Kitty Hawk Woods Reserve, and C) between <i>Phragmites</i> Density treatments within Currituck Banks Reserve. Note that the Medium <i>Phragmites</i> Density treatment was present only in Kitty Hawk Woods Reserve. Letters indicate significant differences between levels of a factor. See text for results of statistical analyses.</p

Mean (±SE) shoreline change rate (m yr^-1) as determined in this study (gray shading) and from historical shoreline imagery (white shading).

<p>A) at Kitty Hawk Woods and Currituck Banks Reserves, B) between <i>Phragmites</i> Density treatments within Kitty Hawk Woods Reserve, and C) between <i>Phragmites</i> Density treatments within Currituck Banks Reserve. Note that the Medium <i>Phragmites</i> Density treatment was present only in Kitty Hawk Woods Reserve. Negative values indicate landward retreat and positive values indicate soundward advance. See text for results of statistical analyses.</p

Table1_Using existing infrastructure as ground control points to support citizen science coastal UAS monitoring programs.docx

Recent publications have described the ability of citizen scientists to conduct unoccupied aerial system (UAS) flights to collect data for coastal management. Ground control points (GCPs) can be collected to georeference these data, however collecting ground control points require expensive surveying equipment not accessible to citizen scientists. Instead, existing infrastructure can be used as naturally occurring ground control points (NGCPs), although availably of naturally occurring ground control point placement on such infrastructure differs from published best practices of ground control point placement. This study therefore evaluates the achievable accuracy of sites georeferenced with naturally occurring ground control points through an analysis of 20 diverse coastal sites. At most sites naturally occurring ground control points produced horizontal and vertical root mean square errors (RMSE) less than 0.060 m which are similar to those obtained using traditional ground control points. To support future unoccupied aerial system citizen science coastal monitoring programs, an assessment to determine the optimal naturally occurring ground control point quantity and distribution was conducted for six coastal sites. Results revealed that generally at least seven naturally occurring ground control points collected in the broadest distribution across the site will result in a horizontal and vertical root mean square errors less than 0.030 m and 0.075 m respectively. However, the relationship between these placement characteristics and root mean square errors was poor, indicating that georeferencing accuracy using naturally occurring ground control points cannot be optimized solely through ideal quantity and distribution. The results of these studies highlight the value of naturally occurring ground control points to support unoccupied aerial system citizen science coastal monitoring programs, however they also indicate a need for an initial accuracy assessment of sites surveyed with naturally occurring ground control points at the onset of such programs.</p