[en] Highlights: • Anadyomene sp. is taking over Thalassia testudinum is Biscayne Bay, USA. • The takeover is not explained by a higher nutrient surge uptake of the seaweed. • Competition for phosphorus may be implicated in the seagrass decline. Apart from direct light effects, we tested whether the takeover of the seagrass Thalassia testudinum by the seaweed Anadyomene sp. in high nutrient areas of Biscayne Bay, Florida, USA, is related to a faster nutrient surge uptake capacity of the seaweed and/or a negative effect on the seagrass uptake rates. Anadyomene sp. and T. testudinum showed a similar ammonium surge uptake capacity, but the seagrass performed better than the seaweed in mixed incubations at high ammonium concentrations. T. testudinum was faster than Anadyomene sp. at taking up pulses of phosphate, but the uptake rates of the seagrass were significantly decreased in the presence of the seaweed. The takeover of T. testudinum by Anadyomene sp. at Biscayne Bay is likely dominated by light and cannot be simply explained by their single or mixed nutrient surge uptake rates, but the phosphate availability and the seagrass uptake inhibition by the seaweed may also play a key role in the process.

[en] Coastal groundwater flow investigations at the Cutler site of the Biscayne Bay south of Miami, Florida, gave rise to the dominating concept of density-driven flow of seawater into coastal aquifers indicated as a saltwater wedge. Within that wedge, convection-type return flow of seawater and a dispersion zone were concluded to be the cause of the Biscayne aquifer ‘seawater wedge.’ This conclusion was merely based on the chloride distribution within the aquifer and on an analytical model concept assuming convection flow within a confined aquifer without taking non-chemical field data into consideration. This concept was later labeled the ‘Henry problem,’ which any numerical variable-density flow program has to be able to simulate to be considered acceptable. Revisiting the summarizing publication with its record of piezometric field data (heads) showed that the so-called seawater wedge was actually caused by discharging deep saline groundwater driven by regional gravitational groundwater flow systems. Density-driven flow of seawater into the aquifer was not found reflected in the head measurements for low and high tide which had been taken contemporaneously with the chloride measurements. These head measurements had not been included in the assumption of a seawater wedge and associated dispersion zone and convection cell. The Biscayne situation emphasizes the need for any chemical interpretation of flow pattern to be backed up by head data as energy indicators of flow fields. At the Biscayne site density-driven flow of seawater did not and does not exist. This conclusion was confirmed by five independent methods. The hydrostatic use of vertical buoyancy forces needs, under hydrodynamic boundary conditions, to be replaced with buoyancy forces along the direction of the pressure potential forces [(grad p)/density] which, in the subsurface, can be pointed in any direction in space.

[en] Few studies have assessed whether patterns of resource partitioning among sympatric marine predators vary between different habitats. This type of data is important for understanding food web functioning as well as for supporting an ecosystem-based fisheries management plan. In this study, we used δ¹³C and δ¹⁵N stable isotope analysis to assess the relative isotopic niche area (i.e., which species has the largest and smallest isotopic niche area within a study site) and core isotopic niche overlap between 299 sharks of 11 co-occurring shark species that vary in size, diet and behavior in three coastal study areas in South Florida. Overall, results show that the relative isotopic niche area and patterns of core isotopic niche overlap between some sympatric shark species varied between sites, suggesting plasticity in resource use and competitive interactions between shark species (e.g., 85% of blacktip shark Carcharhinus limbatus standard ellipse area overlapped with the blacknose shark C. acronotus ellipse in Biscayne Bay, but there was no overlap between these species’ ellipses in nearby Florida Bay). Therefore, patterns of resource use and trophic interactions documented among species from one site may not be applicable to a neighboring location. These findings may have implications for food web models that incorporate trophic data from different areas for a species when local data are unavailable.

No abstract available

[en] Highlights: • Examines past and future groundwater-induced flooding in low-lying coastal area. • Record shows water table rising with sea level, enables future flooding estimation. • Groundwater model integrates rainfall, tidal fluctuations, and sea level rise. • Model projects frequency and intensity of 2060 groundwater-induced flooding. • Sea-level-rise-bellwether area imparts science, social, and policy relevance. Modeling of groundwater levels in a portion of the low-lying coastal Arch Creek basin in northern Miami-Dade County in Southeast Florida USA, which is subject to repetitive flooding, reveals that rain-induced short-term water table rises can be viewed as a primary driver of flooding events under current conditions. Areas below 0.9 m North American Vertical Datum (NAVD) elevation are particularly vulnerable and areas below 1.5 m NAVD are vulnerable to exceptionally large rainfall events. Long-term water table rise is evident in the groundwater data, and the rate appears to be consistent with local rates of sea level rise. Linear extrapolation of long-term observed groundwater levels to 2060 suggest roughly a doubling of the number of days when groundwater levels exceed 0.9 m NAVD and a threefold increase in the number of days when levels exceed 1.5 m NAVD. Projected sea level rise of 0.61 m by 2060 together with increased rainfall lead to a model prediction of frequent groundwater-related flooding in areas < 0.9 m NAVD. However, current simulations do not consider the range of rainfall events that have led to water table elevations > 1.5 m NAVD and widespread flooding of the area in the past. Tidal fluctuations in the water table are predicted to be more pronounced within 600 m of a tidally influenced water control structure that is hydrodynamically connected to Biscayne Bay. The inland influence of tidal fluctuations appears to increase with increased sea level, but the principal driver of high groundwater levels under the 2060 scenario conditions remains groundwater recharge due to rainfall events.

[en] A recent paper by Weyer (Environ Earth Sci 2018, 77:1–16) challenges the widely accepted interpretation of groundwater heads and salinities in the coastal Biscayne aquifer near Miami, Florida, USA. Weyer (2018) suggests that the body of saltwater that underlies fresh groundwater just inland of the coast is not a recirculating wedge of seawater, but results instead from upward migration of deep saline groundwater driven by regional flow. Perhaps more significantly, Weyer (2018) also asserts that established hydrologic theory is fundamentally incorrect with respect to buoyancy. Instead of acting along the direction of gravity (that is, vertically), Weyer (2018) claims, buoyancy acts instead along the direction of the pressure gradient. As a result, Weyer (2018) considers currently available density-dependent groundwater flow and transport modeling codes, and the analyses based on them, to be in error. In this rebuttal, we clarify the inaccuracies in the main points of Weyer’s (2018) paper. First, we explain that Weyer (2018) has misinterpreted observed equivalent freshwater heads in the Biscayne aquifer and that his alternative hypothesis concerning the source of the saltwater does not explain the observed salinities. Then, we review the established theory of buoyancy to identify the problem with Weyer’s (2018) alternative theory. Finally, we present theory and cite successful benchmark simulations to affirm the suitability of currently available codes for modeling density-dependent groundwater flow and transport.

[en] In connection with the dumping problems, measurements were carried out during the years 1966, 1968, 1970, 1972, and 1974 in the Iberian Basin as well as in regions of the northern North Atlantic and the western Mediterranean. Thereby, these radiological measurements refer to the fallout from atomic bomb tests; therefore, show the spreading from the surface into deeper regions of the sea. Anomalies in vertical radioactivity profiles indicate that a model which solely takes into account the physical spreading mechanisms displays the relationships too simply. In the North Sea region - especially with the efficients from fuel reprocessing plants situated on the coasts - radionuclides are introduced into the sea in noticeable amounts. Measurements of the distribution of some of these radionuclides in the North Sea provide a good picture of the transport and spreading processes in this sea area and also clearly show to what degree sea areas which appear to be situated far from each other are connected and which can be influenced by each other. (orig./HP)

[en] The major focus was to understand the function of the seagrass community and to relate this to the impact of energy related activities, most importantly, thermal effluent. In addition, the increased turbidity, current, siltation and heavy metals were factors at the Turkey Point site. We attempted to delineate the effect of heat in the laboratory to determine the upper thermal tolerance of the seagrass. This was shown to be quite close to the combined effect of all the pollutants in the field for Thalassia and the macroalgae. This would indicate that temperature is a very fundamental factor in the growth and survival of the seagrass community

[en] A regional marine model is described which can be used to estimate the exposure of populations as a result of the discharge of radioactive effluents into the coastal waters of northern Europe. The model simulates the dispersion of radionuclides in marine waters, their interaction with marine sediments and the concentration mechanisms occurring in seafoods. A local/regional interface is included whereby releases are assumed to first enter a local marine compartment before widespread dispersion in coastal waters. Depletion mechanisms operate within both the local and regional environments influencing the fraction of radionuclide release which contributes to collective exposure. In general, results of the regional model are expressed as collective intakes of activity from ingestion of marine seafoods. These quantities can be converted into collective doses per unit discharge, given a knowledge of local depletion factors and the dose per unit intake of radionuclides. Results for caesium-137 and plutonium-239 released into United Kingdom coastal waters are discussed. (author)

[en] Highlights: • A range of biota (algae and sea grasses) shows enriched δ¹⁵N close to the coast. • Enriched signals are evident in the particulate and sedimentary organic material. • δ¹⁵N signals are correlated with high inputs of dissolved inorganic matter. • The enriched values support the presence of a sewage related component. • The δ¹⁵N could arise from the local landfill, injected wastewater, or septic systems. - Abstract: Between 2006 and 2007, a study was carried out to determine the relative importance of natural and anthropogenic input of nitrogen into Biscayne Bay (South Florida, USA) using δ¹³C and δ¹⁵N values of algae, seagrasses, and particulate organic material, δ¹⁸O and δ¹⁵N of the NO₃^- and δ¹³C of the dissolved inorganic carbon. The δ¹⁵N values of all components showed a strong east to west gradient approaching more positive values (+7 to +10‰) close to the land-sea interface. The nitrogen could have emanated from the local waste water treatment plant, septic systems within the region, or nitrogen which had been affected by denitrification and leached from the local landfill, wastewater which had been injected into the Floridan aquifer and leaked back to the surface, and/or some other as yet unidentified source. The measured NO₃^- δ¹⁵N and δ¹⁸O values indicated that the dissolved nitrate originated from anthropogenic sources and was fractionated during assimilation