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An elevation profile of ghut T10 upslope of Otter Creek, St. John with relevant watershed, vegetation, and road data. Notice the absence of structures and the lone road near the upslope watershed. Also note the moderate slope and small length of ghut T10. (Photo courtesy of U.S. Army Corps of Engineers, 2009)
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Tropical islands such as St. John in the U.S. Virgin Islands are naturally susceptible to terrigenous
(land-based) sediment erosion due to their high-relief slopes, fast weathering rates, and intense precipitation events. Nearshore ecosystems that exist near these islands tend to thrive in static conditions, and are especially stressed by increases...
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Context 1
... Harbor has the largest overall watershed (6.54 km 2 ), while Otter Creek has the smallest (0.9 km 2 ) (Figures 6 & 7 ...
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... one key difference between these two bays is watershed size. Upslope of Coral Harbor is the Ghut T1/2 watershed (largest watershed in Coral Bay, 4.93 km 2 ); whereas Otter Creek's upslope watershed is tiny in comparison (0.09 km 2 ) (Figures 6 & 7; Table 1). This large disparity in watershed size makes a comparison between the two inadequate; although Otter Creek and Coral Harbor are both well-protected embayments fringed with mangroves and have low exposures to storm surges and other wave action. ...
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... Both its waters and hillslopes are under federal protection and the only development exists along the ridgeline of its watershed, a single road 297 meters from the coast ( Figure 6). Thus, the mineralogical distribution of WIF in Otter Creek should indicate a natural pattern of erosion and terrigenous sediment distribution for a watershed of its size in St. John. ...
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... Our objective is to evaluate if low-resolution datasets (463 x 463 m) are accurate on small tropical islands (<1,000 km 2 ). To do this, we use field-collected datasets [4,48,49] on St. John, in the US Virgin Islands. St. John is an ideal test site due to its size (50 km 2 ), wealth of data on land [4,50] and coastal zone [48,49,51,52], and juxtaposition of heavily developed areas and undeveloped forests [4] (Fig 1). ...
... To do this, we use field-collected datasets [4,48,49] on St. John, in the US Virgin Islands. St. John is an ideal test site due to its size (50 km 2 ), wealth of data on land [4,50] and coastal zone [48,49,51,52], and juxtaposition of heavily developed areas and undeveloped forests [4] (Fig 1). ...
... To do this, we use field-collected datasets [4,48,49] on St. John, in the US Virgin Islands. St. John is an ideal test site due to its size (50 km 2 ), wealth of data on land [4,50] and coastal zone [48,49,51,52], and juxtaposition of heavily developed areas and undeveloped forests [4] (Fig 1). ...
The tropics are naturally vulnerable to watershed erosion. This region is rapidly growing (projected to be 50% of the global population by 2050) which exacerbates erosional issues by the subsequent land use change. The issue is particularly of interest on the many (~45,000) small tropical (<5,000 km ² ) islands, and their >115M residents, where ecotourism and sediment intolerant ecosystems such as coral reefs are the main driver of their economies. However, vulnerability to erosion and deposition is poorly quantified in these regions due to the misclassification or exclusion of small islands in coarse global analyses. We use the only vulnerability assessment method that connects watershed erosion and coastal deposition to compare locally sourced, high-resolution datasets (5 x 5 m) to satellite-collected, remotely sensed low-resolution datasets (463 x 463 m). We find that on the island scale (~52 km ² ) the difference in vulnerability calculated by the two methods is minor. On the watershed scale however, low-resolution datasets fail to accurately demonstrate watershed and coastal deposition vulnerability when compared to high-resolution analysis. Specifically, we find that anthropogenic development (roads and buildings) is poorly constrained at a global scale. Structures and roads are difficult to identify in heavily forested regions using satellite algorithms and the rapid, ongoing rate of development aggravates the issue. We recommend that end-users of this method obtain locally sourced anthropogenic development datasets for the best results while using low resolution datasets for the other variables. Fortunately, anthropogenic development data can be easily collected using community-based research or identified using satellite imagery by any level of user. Using high-resolution results, we identify a development trend across St. John and regions that are both high risk and possible targets for future development. Previously published modeled and measured sedimentation rates demonstrate the method is accurate when using low-resolution or high-resolution data but, anthropogenic development, watershed slope, and earthquake probability datasets should be of the highest resolution depending on the region specified.
... We modeled wave height and period using the SWAN wave model and estimated orbital velocities using linear wave theory (Methods). We assumed seabed roughness conservatively 74 from previously measured 45 medium-sized sand grains (0.05 cm diameter), and used the standard specific gravity for aragonite (2.93 g/cm3), which is a common carbonate mineral found in this region 43 and in the deposit (Fig. 4, Table 2, and Supplementary Table S2). We combined these parameters with our modeled results to calculate the non-dimensional critical Shields parameter for both Hurricane Irma Content courtesy of Springer Nature, terms of use apply. ...
... We used standard values for seawater density and viscosity as well as locally observed grain sizes ( Table 2) 45 . For grain density we used aragonite, a mineral dominantly found in Coral Bay 43 (Supplementary Table S2). We used a Nikuradse roughness value proportional to the median sediment grain size (Supplementary Methods) 73 . ...
In 2017, three major hurricanes (Irma, Jose, and Maria) impacted the Northeastern Caribbean within a 2-week span. Hurricane waves can cause physical damage to coastal ecosystems, re-suspend and transport antecedent seafloor sediment, while the associated intense rainfall can yield large influxes of land-derived sediment to the coast (e.g. burial of ecosystems). To understand sedimentation provenance (terrestrial or marine) and changes induced by the hurricanes, we collected bathymetry surveys and sediment samples of Coral Bay, St. John, US Virgin Islands in August 2017, (pre-storms) and repeated it in November 2017 (post-storms). Comparison reveals morphologic seafloor changes and widespread aggradation with an average of ~25 cm of sediment deposited over a 1.28 km2 benthic zone. Despite an annual amount of precipitation between surveys, sediment yield modeling suggests watersheds contributed <0.2% of the total depositional volume. Considering locally established accumulation rates, this multi-hurricane event equates to ~1–3 centuries of deposition. Critical benthic communities (corals, seagrasses) can be partially or fully buried by deposits of this thickness and previous studies demonstrate that prolonged burial of similar organisms often leads to mortality. This study illuminates how storm events can result in major sediment deposition, which can significantly impact seafloor morphology and composition and benthic ecosystems.
... Trends of unsustainable urban sprawl and deforestation at sensitive coastal areas, such as arid steep slopes, increase watersheds' vulnerability to erosion during extreme rainfall episodes (Nemeth and Sladek, 2001;Hernández-Delgado et al., 2012, 2014aRamos-Scharrón et al., 2012;Gellis, 2013;Edmunds and Gray, 2014). Sediment yield and influx from arid coastal watersheds into marine ecosystems vary in response to the watershed's catchment size, slope, land use patterns, and local rainfall volume and intensity (Rogers, 1990;Ramos-Scharrón and MacDonald, 2007;Rodrigues et al., 2013;Browning et al., 2016). In addition, seasonal meteorological and oceanographic forces, which are related to wind, wave and currents, influence local hydronamics, affect sediment distribution along the coastal marine environment (Ogston et al., 2004;Storlazzi et al., 2009). ...
Sedimentation is a critical threat to coral reefs worldwide. Major land use alteration at steep, highly erodible semi-arid islands accelerates the potential of soil erosion, runoff, and sedimentation stress to nearshore coral reefs during extreme rainfall events. The goal of this study was to assess spatio-temporal variation of sedimentation dynamics across nearshore coral reefs as a function of land use patterns, weather and oceanographic dynamics, to identify marine ecosystem conservation strategies. Sediment was collected at a distance gradient from shore at Bahia Tamarindo (BTA) and Punta Soldado (PSO) coral reefs at Culebra Island, Puerto Rico. Sediment texture and composition were analyzed by dry sieving and loss-on-ignition techniques, and were contrasted with environmental variables for the research period (February 2014 to April 2015). Rainfall and oceanographic data were analyzed to address their potential role on affecting sediment distribution with BEST BIO-ENV, RELATE correlation, and linear regression analysis. A significant difference in sedimentation rate was observed by time and distance from shore (PERMANOVA, p < 0.0100), mostly attributed to higher sediment exposure at reef zones closer to shore due to strong relationships with coastal runoff. Sedimentation rate positively correlated with strong rainfall events (Rho = 0.301, p = 0.0400) associated with storms and rainfall intensity exceeding 15 mm/h. At BTA, sediment deposited were mostly composed of sand, suggesting a potential influence of resuspension produced by waves and swells. In contrast, PSO sediments were mostly composed of silt-clay and terrigenous material, mainly attributed to a deforestation event that occurred at adjacent steep sub-watershed during the study period. Spatial and temporal variation of sedimentation pulses and terrigenous sediment input implies that coral reefs exposure to sediment stress is determined by local land use patterns, weather, and oceanographic dynamics. Comprehensive understanding of sediment dynamics and coastal ecosystem interconnectivity is fundamental to implement integrated and adaptive management strategies aimed to promote sustainable development at watershed and island wide-scale to fully mitigate terrigenous sediment impact to marine ecosystems. Furthermore, decision-making processes and policy needs to address sedimentation stress in the context of future climate to reduce land-based threats and strengthen coral reef resilience.
... Extractive industries (e.g., timber extraction, oil production, and mining) and remotely situated infrastructure development, particularly the construction of hydroelectric facilities, are some of the key drivers of extensive road system building in the developing world, as demonstrated in the Lower Paute Basin of Ecuador (Figure 1). Other drivers include infrastructure expansion due to growth in tourism and recreation demand in erosion-vulnerable, and previously un-roaded areas, such as coastal zones (e.g., in Florianópolis, Brazil;Figure 2) and mountain slopes (e.g.Ito, 2011;MacDonald et al., 1997;Brooks et al., 2015;Browning et al., 2016). The opening of international borders (Fox and Vogler, 2005) and the expansion of agricultural frontiers (Fearnside 2001;, common in tropical regions worldwide, further drives road development. ...
Roads are a pervasive form of disturbance with potential to negatively affect ecohydrological processes. Some of the fastest and most rapid growth is occurring in developing countries, particularly in the tropics, where political agendas are often focused on strengthening the economy, improving infrastructure, bolstering national security, achieving self-sufficiency, and increasing citizen well-being, often at the expense of the environment. We review what is known about road impacts on ecohydrological processes, focusing on aquatic systems, both temperate and tropical. We present seven cases that represent the broader trends of road development and impacts in tropical settings. Many of these process dynamics and impacts are not different from those experienced in temperate settings, although the magnitude of impacts in the tropics may be amplified with intense rainfall and lack of best-management practices applied to road construction/maintenance. Impacts of roads in tropical settings may also be unique because of particular organisms or ecosystems effected. We outline a set of best practices to improve road-network management and provide recommendations for adopting an agenda of research and road management in tropical settings. Importantly, we call for incorporation of transdisciplinary approaches to further study of the effects of roads on ecohydrological processes in the tropics. Specific emphasis should also be placed on collaboration with governments and developers that are championing road development to help identify the drivers of road expansion and thresholds of negative impact, as well as methods of sustainable road construction and maintenance.
