NUMERICAL INVESTIGATIONS OF FLUSHING TIME IN SMALL MARINAS

This paper presents the results of 2D and 3D numerical simulations of sea circulation and water mass exchange for a marina with hypothetical dimensions (L/B=2 and L/B=0.5) to calculate the return flow factor. The return flow factor b was analyzed in relation to the marina entrance width, sea current velocity outside the marina (0, 1, 2, and 5 cm/s) and the sea surface level oscillation dynamics. The basic comparative parameter is the e-flushing time, Tf. The intensity of forced circulation is calculated to achieve time Tf of less than 10 days. The impact of the wind field on the e-flushing time for different marina widths was analyzed using a 3D numerical model. The numerical simulation results indicate that the e-flushing time Tf depends on the amplitude of the tidal signal, secondary to the width of the marina inlet, and the smallest amount on the velocity field in the outer region. Conversely, the return flow factor b depends on the width of the marina entrance, less on the tidal signal amplitude, and least on the current velocity outside the marina if currents are ≥ 1 cm/s. Forced circulation of 1 m3/s is only required for the marina with a smaller tidal amplitude (position Dubrovnik) to achieve Tf<10 days. If at the observed location wind is a dominant sea circulation generator, a wider marina entrance will allow faster sea exchange

Tracer and Timescale Methods for Passive and Reactive Transport in Fluid Flows

Geophysical, environmental, and urban fluid flows (i.e., flows developing in oceans, seas, estuaries, rivers, aquifers, reservoirs, etc.) exhibit a wide range of reactive and transport processes. Therefore, identifying key phenomena, understanding their relative importance, and establishing causal relationships between them is no trivial task. Analysis of primitive variables (e.g., velocity components, pressure, temperature, concentration) is not always conducive to the most fruitful interpretations. Examining auxiliary variables introduced for diagnostic purposes is an option worth considering. In this respect, tracer and timescale methods are proving to be very effective. Such methods can help address questions such as, "where does a fluid-born dissolved or particulate substance come from and where will it go?" or, "how fast are the transport and reaction phenomena controlling the appearance and disappearance such substances?" These issues have been dealt with since the 19th century, essentially by means of ad hoc approaches. However, over the past three decades, methods resting on solid theoretical foundations have been developed, which permit the evaluation of tracer concentrations and diagnostic timescales (age, residence/exposure time, etc.) across space and time and using numerical models and field data. This book comprises research and review articles, introducing state-of-the-art diagnostic theories and their applications to domains ranging from shallow human-made reservoirs to lakes, river networks, marine domains, and subsurface flow

Surface waters of the NW Iberian margin: upwelling on the shelf versus outwelling of upwelled waters from the Rías Baixas

A set of hydrographic surveys were carried out in the Ría of Vigo (NW Spain) at 2–4 d intervals during four 2–3 week periods in 1997, covering contrasting seasons. Residual exchange fluxes with the adjacent shelf were estimated with a 2-D, non-steady-state, salinity–temperature weighted box model. Exchange fluxes consist of a steady-state term (dependent on the variability of continental runoff) and a non-steady-state term (dependent on the time changes of density gradients in the embayment). More than 95% of the short-time-scale variability of the exchange fluxes in the middle and outer ría can be explained by the non-steady-state term that, in turns, is correlated (R2>75%) with the offshore Ekman transport. Conversely, 96% of the variability of exchange fluxes in the inner ría rely on the steady-state term. The outer and middle ría are under the direct influence of coastal upwelling, which enhances the positive residual circulation pattern by an order of magnitude: from 10 2 to 10 3 m3s−1. On the contrary, downwelling provokes a reversal of the circulation in the outer ría. The position of the downwelling front along the embayment depends on the relative importance of Ekman transport (Qx, m3s−1km−1) and continental runoff (R, m3s−1). When Qx/ R>7±2 the reversal of the circulation affects the middle ría. Our results are representative for the ‘Rías Baixas’, four large coastal indentations in NW Spain. During the upwelling season (spring and summer), 60% of shelf surface waters off the ‘Rías Baixas’ consist of fresh Eastern North Atlantic Central Water (ENACW) upwelled in situ. The remaining 40% consists of upwelled ENACW that previously enters the rías and it is subsequently outwelled after thermohaline modification. During the downwelling season (autumn and winter), 40% of the warm and salty oceanic subtropic surface water, which piled on the shelf by the predominant southerly winds, enters the rias

Anomalies in the carbonate system of Red Sea coastal habitats

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Baldry, K., Saderne, V., McCorkle, D. C., Churchill, J. H., Agust, S., & Duarte, C. M. Anomalies in the carbonate system of Red Sea coastal habitats. Biogeosciences, 17(2), (2020): 423-439, doi:10.5194/bg-17-423-2020.We use observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) to assess the impact of ecosystem metabolic processes on coastal waters of the eastern Red Sea. A simple, single-end-member mixing model is used to account for the influence of mixing with offshore waters and evaporation–precipitation and to model ecosystem-driven perturbations on the carbonate system chemistry of coral reefs, seagrass meadows and mangrove forests. We find that (1) along-shelf changes in TA and DIC exhibit strong linear relationships that are consistent with basin-scale net calcium carbonate precipitation; (2) ecosystem-driven changes in TA and DIC are larger than offshore variations in >70 % of sampled seagrass meadows and mangrove forests, changes which are influenced by a combination of longer water residence times and community metabolic rates; and (3) the sampled mangrove forests show strong and consistent contributions from both organic respiration and other sedimentary processes (carbonate dissolution and secondary redox processes), while seagrass meadows display more variability in the relative contributions of photosynthesis and other sedimentary processes (carbonate precipitation and oxidative processes). The results of this study highlight the importance of resolving the influences of water residence times, mixing and upstream habitats on mediating the carbonate system and coastal air–sea carbon dioxide fluxes over coastal habitats in the Red Sea.This research has been supported by the King Abdullah University of Science and Technology (KAUST) (grant nos. BAS/1/1071-01-01 and BAS/1/1072-01-01) and the Investment in Science fund at WHOI

A Test Of Educational Methods To Reduce Boating Disturbance To Harbor Seals

Environmental education can affect attitudes and behaviors, but determining the most effective methods for protecting wildlife requires research. This study examined the effect of two modes of environmental education, one passive and one active, on the behaviors of boaters toward harbor seals (Phoca vitulina) at Corkscrew Slough in Redwood City, California, an area where harbor seals haul out and pup. Thirty-one boaters viewed an interpretive sign (passive environmental mode) and 30 experienced a docent talk (active) both designed to educate boaters on protecting harbor seals; 31 boaters received no environmental information (the control), therefore were not exposed to the interpretive sign or the docent talk. I collected data on how these boaters responded to harbor seals in Corkscrew Slough and on the response of harbor seals to the boaters. Data were analyzed with ANOVA and Chi-square to assess differences between treatments. Boaters exposed to signs or docents stayed significantly further from the seals compared to boaters not exposed to any environmental education. However, neither the sign nor the docent reduced the length of time boaters spent traveling through the Slough compared to the control, nor was the number of boaters stopping to observe seals reduced. Harbor seals showed no difference in disturbance responses to boaters, no matter what the mode of education for the boaters. These results suggest signs and docents may change some boater behavior but that managers should not depend solely on these educational approaches to protect sensitive wildlif

Dispersal and coastal geomorphology limit potential for mangrove range expansion under climate change

Latitudinal range limits for mangroves on high-energy, wave-dominated coasts are controlled by geomorphological features and estuarine dynamics. Mangroves reach a southern global range limit along the South African coastline, but the distribution is patchy, with stands occurring in only 16% of the estuaries in the region. Yet, the persistence of forests planted \u3e50 years ago beyond the natural distribution limit suggests that additional estuaries could support mangroves. Understanding regional drivers is necessary to inform global-scale estimates for how this important ecosystem is predicted to respond to climate change. Here, we combine species distribution modelling (MaxEnt), Lagrangian particle tracking using an eddy- and tide-resolving numerical ocean model, and connectivity matrices, to identify suitable mangrove habitats along the South African coastline at present, as well as under the IPCC RCP4.5 and RCP8.5 climate scenarios. Within the current South African distribution range (±900 km), eight more estuaries were identified to be suitable under contemporary conditions. When considering potential range extension (±110 km), an additional 14 suitable estuaries were identified. Connectivity matrices suggest limited long-distance dispersal, stranding mostly at or near the release location, and a decreased probability of connectivity towards the range limit. Under both future climate scenarios, 30% of estuaries currently supporting mangroves are predicted to become unsuitable, while an additional six estuaries beyond the current distribution are predicted to become suitable. However, there is limited connectivity between these new sites and established forests. Synthesis. This study shows that dispersal substantially limits mangrove distribution at the southern African range limit and highlights the importance of including this process in species distribution models. Ultimately, our results provide new insight into mangrove conservation and management at range limits that are not controlled predominantly by temperature, as it has been assumed that mangroves will largely expand to higher latitudes under climate change

Ecological Management Strategies for Impounded Harbours

Long-term physical, chemical and biological monitoring (May 1990 to November 1994) was conducted in order to quantify water and sediment quality changes arising from the impoundment of Sutton Harbour, Plymouth (UK). Spore tracer studies revealed that 95 % water renewal times increased from 45 h to 72 h after impoundment. Semi-diurnal (tidal) salinity variations of circa 5 x10ˉ³ were observed, revealing a mechanism which shunts contaminated estuarine water into the harbour during flood tides. Salinity typically varied from 17 x 10ˉ³ to 34 x 10ˉ³ seasonally, and exhibited strong inverse correlations with total oxidised nitrogen and orthophosphate, demonstrating the riverine source of dissolved nutrients. These varied seasonally in concentration by 2 to 3 orders of magnitude. Impoundment restricted the flux of riverborne nutrients but greater retention of brackish bottom waters produced a stronger concentration gradient, resulting in possible nutrient storage by diffusion into the porewaters. Sewage outfalls and sediments were the main sources of ammonium. Following impoundment, the evidence suggests that a balance between nutrients from reduced external (riverine) fluxes and increased internal (porewater) fluxes has developed. Phytoplankton blooms were regular but short-lived features in summer, and continued after impoundment. Sewage contamination, with faecal coliform bacteria occasionally exceeding 30,000 cfu 100 mtˉ¹, improved unequivocally after impoundment, but stricter controls on internal sources are required. The permanently anoxic harbour sediments, consisting mainly of silt, contained Cd (1.8 µg gˉ¹), Cu (160 µg gˉ¹), Hg (1.2 µg gˉ¹), Pb (200 µg gˉ¹) and Zn (290 µg gˉ¹) in the <63 µm fraction. Sedimentary Cu, Pb and Zn concentrations increased during the monitoring period. The benthic macrofauna consists mainly of polychaete worms, with species diversity decreasing during construction, and then attaining a new, impoverished equilibrium after impoundment. Multivariate analysis revealed changes in community structure involving loss of sensitive taxa and appearance of opportunists. The ecological impact of impoundment was minimal, in that the harbour ecosystem was able to withstand the imposed environmental stresses. The management strategy adopted will ensure that water and sediment quality are maintained in Sutton Harbour; recommendations equally applicable to future harbour impoundment projects.National Rivers Authority South Western Regio