Large Coastal System Research Articles

Chlorophyll-a in Chesapeake Bay based on VIIRS satellite data: Spatiotemporal variability and prediction with machine learning

Chlorophyll-a (Chl-a) concentration indicates the abundance of phytoplankton biomass and its spatiotemporal variations fundamentally modulate the ecosystem dynamics in coastal waters. Compared to conventional low-frequency shipboard measurements at a limited number of sampling locations, satellite data provide a better spatial and temporal coverage allowing for a more synoptic view of Chl-a variabilities in large coastal systems such as Chesapeake Bay. We used Visible Infrared Imaging Radiometer Suite (VIIRS) satellite data from 2011 to 2018 to (1) analyze the Chl-a variability in Chesapeake Bay, (2) examine the robustness of an interpolation method to fill up satellite data gaps, and (3) train a machine-learning-based data-driven model to simulate high-resolution Chl-a variations. The dataset shows clear seasonality with notable spring and summer peaks throughout the bay; this is different from in situ observations at mainstem stations where the water is deep. The seasonality of Chl-a varies in different regions, with maxima concentration occurring in spring for regions near the mouths of major tributaries, winter near the bay entrance, and summer elsewhere. A machine-learning-based data-driven model, together with Data Interpolating Empirical Orthogonal Functions (DINEOF), is applied to simulate the high-resolution Chl-a variations. The DINEOF is used to efficiently estimate the missing records. Driven by external forcing including river discharge, nutrient loadings, solar radiation, wind, and air temperature, the data-driven model shows an overall satisfactory performance in reproducing the spatiotemporal variations of Chl-a, with a bay-wide averaged root mean square error of 1.85 ug/l. By combining DINEOF and machine learning, this study demonstrates the potential of using data-driven model to predict high-resolution spatiotemporal variations of water quality in coastal waters.

Coastal shallow waters explorer imaging spectrometer for aerial remote sensing of shallow waters in UV-VIS-NIR broadband.

Advancements in technology have widened the limits of hyperspectral imaging of remote sensing in mapping shallow water benthic habitats and bathymetry. This paper provides a novel airborne imaging spectrometer for the field. The device, composed of an off-axis two-mirror telescope and an advanced Dyson spectrometer working in the ultraviolet-visible near-infrared region, has been designed, fabricated, and evaluated. It maintained high optical performance, with a pixel spatial resolution better than 0.5 mrad, spectral resolution of 3.5 nm, field of view of 28°, and a high numerical aperture for high SNR in 330-900 nm. The imaging spectrometer will help to obtain a combination of the spectral and textural characteristics of bottom features in shallow waters. These features could result in the ability to map habitats over large coastal systems.

Remote sensing of shallow waters – A 50 year retrospective and future directions

Technical advancements have widened the limits of remote sensing in mapping shallow water benthic habitats and bathymetry over the last decades. On the other hand, the needs of shallow water remote sensing have pushed instrument development. In this manuscript we provide 50-year retrospective of the developments in the field in terms of both instrumentation and methods. We also show that spectral features characteristic of the main benthic groups in shallow water are consistent from the tropics to sub-arctic regions and from salty to freshwaters. The fundamental limiting factor in both benthic mapping and bathymetry is absorption of light by water molecules. However, spectral absorption by water molecules is the key to bathymetry derivation. Variable backscattering by particles and absorption by dissolved organic matter is a confounding factor for all objectives. The combination of using the spectral and textural characteristics of bottom features and our knowledge about these features have now resulted in the ability to map habitats over large coastal systems. This manuscript has shown that optically shallow water remote sensing has reached levels where the satellite derived bathymetry and habitat maps are accepted by different end users (including the International Maritime Organisation) and are routinely used in ecological studies, monitoring and management of coastal environments.

A new species of Monstrilla (Copepoda, Monstrilloida) from the plankton of a large coastal system of the northwestern Caribbean with a key to species.

The genus Monstrilla Dana, 1849 is the most diverse of the copepod order Monstrilloida. Monstrilloid copepods are endoparasites of benthic polychaetes and molluscs; adult individuals are free-living, non-feeding reproductive forms that briefly become part of the zooplankton community, where they are occasionally captured by plankton nets. Monstrilloid copepods are frequently found during routine plankton samplings of coastal and estuarine habitats, but they are rarely found in large numbers. The western sector of the Caribbean Sea is known to harbor a diverse monstrilloid fauna. The analysis of zooplankton samples obtained during nine years from Chetumal Bay, a large embayment of the Mexican Caribbean coast, yielded a male monstrilloid that was found to represent a new species. It is herein described following upgraded standards and compared with its congeners. A key to males and females of the Monstrilla species known from the northwestern Caribbean is also provided.

Seasonal variability of the inorganic carbon system in a large coastal plain estuary

Abstract. Carbonate geochemistry research in large estuarine systems is limited. More work is needed to understand how changes in land-use activity influence watershed export of organic and inorganic carbon, acids, and nutrients to the coastal ocean. To investigate the seasonal variation of the inorganic carbon system in the Delaware Estuary, one of the largest estuaries along the US east coast, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured along the estuary from June 2013 to April 2015. In addition, DIC, TA, and pH were periodically measured from March to October 2015 in the nontidal freshwater Delaware, Schuylkill, and Christina rivers over a range of discharge conditions. There were strong negative relationships between river TA and discharge, suggesting that changes in HCO3− concentrations reflect dilution of weathering products in the drainage basin. The ratio of DIC to TA, an understudied but important property, was high (1.11) during high discharge and low (0.94) during low discharge, reflecting additional DIC input in the form of carbon dioxide (CO2), most likely from terrestrial organic matter decomposition, rather than bicarbonate (HCO3−) inputs due to drainage basin weathering processes. This is also a result of CO2 loss to the atmosphere due to rapid water transit during the wet season. Our data further show that elevated DIC in the Schuylkill River is substantially different than that in the Delaware River. Thus, tributary contributions must be considered when attributing estuarine DIC sources to the internal carbon cycle versus external processes such as drainage basin mineralogy, weathering intensity, and discharge patterns. Long-term records in the Delaware and Schuylkill rivers indicate shifts toward higher alkalinity in estuarine waters over time, as has been found in other estuaries worldwide. Annual DIC input flux to the estuary and export flux to the coastal ocean are estimated to be 15.7 ± 8.2 × 109 mol C yr−1 and 16.5 ± 10.6 × 109 mol C yr−1, respectively, while net DIC production within the estuary including inputs from intertidal marshes is estimated to be 5.1 × 109 mol C yr−1. The small difference between riverine input and export flux suggests that, in the case of the Delaware Estuary and perhaps other large coastal systems with long freshwater residence times, the majority of the DIC produced in the estuary by biological processes is exchanged with the atmosphere rather than exported to the sea.

Coasts, water levels, and climate change: A Great Lakes perspective

The North American Laurentian Great Lakes hold nearly 20 % of the earth’s unfrozen fresh surface water and have a length of coastline, and a coastal population, comparable to frequently-studied marine coasts. The surface water elevations of the Great Lakes, in particular, are an ideal metric for understanding impacts of climate change on large hydrologic systems, and for assessing adaption measures for absorbing those impacts. In light of the importance of the Great Lakes to the North American and global economies, the Great Lakes and the surrounding region also serve as an important benchmark for hydroclimate research, and offer an example of successful adaptive management under changing climate conditions. Here, we communicate some of the important lessons to be learned from the Great Lakes by examining how the coastline, water level, and water budget dynamics of the Great Lakes relate to other large coastal systems, along with implications for water resource management strategies and climate scenario-derived projections of future conditions. This improved understanding fills a critical gap in freshwater and marine global coastal research.

Transient oceanic and tidal contributions to water exchange and residence times in a coastal upwelling system in the NE Atlantic: the Pontevedra Ria, Galicia

An analysis of the intra-annual variability of hydrographic residence times, τ, is presented for the Pontevedra Ria––a large coastal system in NW Spain with a deep, unobstructed connection with the Atlantic Ocean. Ria-offshore water exchange and τ were quantified with an iterative approach to the fraction of freshwater method using 23 quasi-steady state water–salt budgets. Excluding prolonged flushing due to downwelling events at the end of the upwelling season, mean was 6 ± 2 day in the central ria and 2 ± 1 day in the internal ria. The tidal contribution, equal to 10–25% of total water renewal, was quantified for the first time for a Galician ria with the hydrodynamic model estuarine contaminant simulator (ECoS). The relationship between τ and residual freshwater input, Q Z, was atypical, since Q Z played a minor role in water exchange in comparison to periodic upwelling of East North Atlantic Central Water (ENACW) from the continental shelf mainly during spring and summer. During positive upwelling stress, the intrusion of ENACW into the ria produced enhanced flushing and τ<4 day in the central ria and <2 days in the internal ria. Under downwelling favourable conditions, water was retained and τ prolonged to >8 and >5 days, respectively. A quantitative parameterisation of τ with upwelling and Q Z was weakly significant, due to the short-term variability in ria salinity. This paper elucidates problems associated with the use of water budgets to transient coastal systems such as the Pontevedra Ria.