Ariel C. Blanco

Estimation of nearshore groundwater discharge and its potential effects on a fringing coral reef

Radon (²²²Rn) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGD(nearshore)) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGD(nearshore) was 0.39-0.58 m³/s, less than 30% of Todoroki Rivers baseflow discharge. SGD(nearshore) was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGD(nearshore) elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki Rivers baseflow NO₃⁻-N (2-4 mg/L). This increased nearshore Chl-α from 0.5-2 μg/l compared to the typically low Chl-α (< 0.1-0.4 μg/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas.

Mapping of seagrass and other benthic habitats in Bolinao, Pangasinan using Worldview-2 satellite image

The objective of this research is to determine the suitability of Worldview-2 high resolution multispectral data in classifying and mapping benthic habitats, specifically seagrass. Worldview-2 offers an increased number of spectral bands for high-resolution image, from the traditional 4bands to 8 bands. It boasts of the ability to enhance mapping and monitoring of benthic habitats with the addition of the Coastal Band. This was investigated in this research using a Worldview-2 image of Bolinao, Pangasinan acquired on March 2010. The study site, Bolinao, has the highest single concentration of seagrass in the northern part of the Philippines. To achieve more accurate results, geometric, atmospheric and water column corrections were applied to the images. For geometric correction, a Differential Global Positioning System Topcon Hiper Ga model receiver was used to obtain highly accurate ground control points. Atmospheric correction was performed in ENVI using the Fast Line-of-Sight Atmospheric Analysis (FLAASH) model. Three water column correction models were applied and compared in this research, Lyzengas Optical Model, Stumpfs Ratio Model and Simple Radiative Transfer Model. A spectral library was created using in situ reflected spectral radiances on both submerged and emerged vegetation to aid in image classification. Different benthic covers, seagrass, sand, corals and rocks are significantly separable spectrally based on spectral signatures obtained on field using a USB 4000 Fiber Optic Spectrometer. Maximum likelihood supervised classification in ENVI 4.8 is utilized for mapping. Using Worldview 2s coastal, green, yellow and red bands and applying the Simple Radiative Transfer Model produced the highest overall accuracy (88.3%) among the classification results. Using the same bands, Stumpfs Ratio Model produced 87.84% overall accuracy while Lyzengas optical model achieved 75.54%. Morans I spatial autocorrelation was implemented to increase the classification accuracy. Using lag 1 slightly increased Stumpfs Models overall accuracy, from 87.84% to 88.08% while using lags 5 and 10 decreased the overall accuracy with 83.91% and 84.25% respectively.

Reef-scale modeling of coral calcification responses to ocean acidification and sea-level rise

AbstractTo predict coral responses to future environmental changes at the reef scale, the coral polyp model (Nakamura et al. in Coral Reefs 32:779–794, 2013), which reconstructs coral responses to ocean acidification, flow conditions and other factors, was incorporated into a reef-scale three-dimensional hydrodynamic-biogeochemical model. This coupled reef-scale model was compared to observations from the Shiraho fringing reef, Ishigaki Island, Japan, where the model accurately reconstructed spatiotemporal variation in reef hydrodynamic and geochemical parameters. The simulated coral calcification rate exhibited high spatial variation, with lower calcification rates in the nearshore and stagnant water areas due to isolation of the inner reef at low tide, and higher rates on the offshore side of the inner reef flat. When water is stagnant, bottom shear stress is low at night and thus oxygen diffusion rate from ambient water to the inside of the coral polyp limits respiration rate. Thus, calcification decreases because of the link between respiration and calcification. A scenario analysis was conducted using the reef-scale model with several pCO2 and sea-level conditions based on IPCC (Climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change, Cambridge University Press, Cambridge, 2013) scenarios. The simulation indicated that the coral calcification rate decreases with increasing pCO2. On the other hand, sea-level rise increases the calcification rate, particularly in the nearshore and the areas where water is stagnant at low tide under present conditions, as mass exchange, especially oxygen exchange at night, is enhanced between the corals and their ambient seawater due to the reduced stagnant period. When both pCO2 increase and sea-level rise occur concurrently, the calcification rate generally decreases due to the effects of ocean acidification. However, the calcification rate in some inner-reef areas will increase because the positive effects of sea-level rise offset the negative effects of ocean acidification, and total calcification rate will be positive only under the best-case scenario (RCP 2.6).

Remote sensing-based estimation of seagrass percent cover and LAI for above ground carbon sequestration mapping

Seagrasses are distinct flowering plants which thrive underwater. They are part of a complex ecosystem that supports different forms of life. Recent studies found out that coastal wetlands – mangroves, saltmarshes, and seagrass, are far more proficient in sequestering and storing carbon than terrestrial ecosystems. Although seagrasses occupy only 0.2% of the area of the oceans, they sequester approximately 15% of total carbon storage in the ocean. Several remote sensing techniques are available to map and monitor seagrasses but most of them focus only on extent and area coverage. To estimate the carbon sequestration of seagrass beds, aside from extent, other parameters are needed such as leaf area index, percent cover, density, biomass etc., However, there are limits in mapping seagrass parameters using remote sensing. The reflectance measured by sensors is affected by other factors such as water absorption, turbidity, dissolved organic matter, depth and phytoplankton which affects the backscattering of energy. In this study, different remotely sensed datasets and field data were used to measure the parameters needed to estimate the carbon sequestration. Multispectral satellite images such as Sentinel-2 and PlanetScope were utilized to map the distribution and percent cover. High-resolution RGB images obtained by unmanned aerial vehicle (UAV) were also utilized to correlate field data gathered parameters. Field data such as species, percent cover, leaf area index, canopy height and above ground biomass were gathered in situ. Data extracted from different remote sensing technologies were put together to support the estimation of carbon sequestration of seagrass beds.