Phytoplankton dynamics within Gulf Stream intrusions on the southeastern United States continental shelf during summer 1981

During July and August 1981 subsurface intrusion of upwelled nutrient-rich Gulf Stream water was the dominant process affecting temporal and spatial changes in phytoplankton biomass and productivity of the southeastern United States continental shelf between 29 and 32°N latitude. Intruded waters in the study area covered as much as 10¹ km including virtually all of the middle and outer shelf and approximately 50% of the inner shelf area.Within 2 weeks following a large intrusion event in late July, middle shelf primary production and Chl a reached 3 to 4 gC m⁻ d⁻¹ and 75 mg m⁻, respectively. At the peak of the bloom 80% of the water column primary production occurred below the surface mixed-layer, and new primary production (i.e., NO₃-supported) exceeded 90% of the total. Chl a-normalized photosynthetic rates were very high as evidenced by high mean assimilation number (15.5 mg C mg Chl a⁻¹ h⁻¹), high mean α (14 mg C mg Chl a⁻¹ Ein⁻¹ m), and no photoinhibition. As a result of the high photosynthetic rates, mean light-utilization index (Ψ) was 2 to 3 times higher than reported for temperature sub-arctic and arctic waters.The results imply a seasonal (June to August) middle shelf production of 150 g C m⁻¹, about 15% higher than previous estimates of annual production on the middle shelf. Intrusions of the scale we observed in 1981 may not occur every summer. However, when such events do occur, they are by far the most important processes controlling summer phytoplankton dynamics of the middle and outer shelf and of the inner shelf in the southern half of the study area.     

Effect of upwelling on phytoplankton productivity of the outer southeastern United States continental shelf

Gulf Stream frontal disturbances cause nutrient-rich waters to frequently upwell and intrude onto the southeastern United States continental shelf between Cape Canaveral, Florida and Cape Hatteras, North Carolina. Phytoplankton response in upwelled waters was determined with three interdisciplinary studies conducted during April 1979 and 1980, and in summer 1978. The results show that when shelf waters are not stratified, upwelling causes productive phytoplankton (diatom) blooms on the outer shelf. Phytoplankton production averages about 2 g C m⁻² d⁻¹ during upwelling events, and ‘new’ production is 50% or more of the total. When shelf waters are stratified, upwelled waters penetrate well onto the shelf as a subsurface intrusion in which phytoplankton production averages about fives times higher than the nutrient-depleted overlying mixed layer. Phytoplankton within the intrusion deplete upwelled NO₃ in about 7 to 10 days, at which point no further net increase in phytoplankton biomass occurs.Current meter records show that upwelling occurs roughly 50% of the time on the outer shelf during November to April (shelf not stratified), and we estimate that seasonal primary production in upwelled waters is 175 g C m⁻² 6 months⁻¹ of which at least 50% is ‘new’ production. More than 90% of outer shelf primary and ‘new’ production occurs during upwelling and thus upwelling is the dominant process affecting primary productivity of the outer shelf. Our seasonal estimates of outer shelf primary and ‘new’ production are, respectively, three and ten times higher than previous estimates that did not account for upwelling.     

Marine sand and gravel production in areas off the northeast coast of the United States

Agencies responsible for issuing permits authorizing excavation of marine sands and gravels have provided information on the amounts of aggregates removed from coastal waters off the New England and Middle Atlantic states. This information is reported herein. Major increases in marine mining are projected. The significance to fisheries of mining marine aggregates is discussed.     

Hydraulic characteristics of a small Coastal Plain stream of the southeastern United States: effects of hydrology and season

Various physical and biological properties affect solute transport patterns in streams. We measured hydraulic characteristics of Payne Creek, a low‐gradient upper Coastal Plain stream, using tracer experiments and parameter estimation with OTIS‐P (one‐dimensional transport with inflow and storage with parameter optimization). The primary objective of this study was to estimate the effects of varying discharge, season, and litter accumulation on hydraulic parameters. Channel area A ranged from 0·081 to 0·371 m² and transient storage area A_s ranged from 0·027 to 0·111 m². Dispersion D ranged from 1·5 to 11·1 m² min⁻¹ and exchange coefficient α ranged from 0·009 to 0·038 min⁻¹. Channel area and dispersion were positively correlated to discharge Q, whereas storage area and exchange coefficient were not. Relative storage size A_s/A ranged from 0·17 to 0·59, and was higher during fall than other seasons under a similar Q. The fraction of median travel time due to transient storage ranged from 8·8 to 34·5% and was significantly correlated with Q through a negative power function. Both metrics indicated that transient storage was a significant component affecting solute transport in Payne Creek, especially during the fall. Comparison between the measured channel area A_c and A suggested that surface storage was dominant in Payne Creek. During fall, accumulation of leaf litter resulted in larger A and A_s and lower velocity and D than during other seasons with similar discharge. Seasonal changes in discharge and organic matter accumulation, and dynamic channel morphology affected the magnitude of transient storage and overall hydraulic characteristics of Payne Creek. Copyright © 2005 John Wiley & Sons, Ltd.     

Distributional change of monthly precipitation due to climate change: comprehensive examination of dataset in southeastern United States

A number of watersheds are selected from the Hydro‐Climate Data Network over southeastern United States to examine possible changes in hydrological time series, e.g. precipitation, introduced by changing climate. Possible changes in monthly precipitation are examined by three different methods to detect second order stationarity, abrupt changes in the variance and smooth changes in quantiles of the time series. An analysis of second order stationarity shows that precipitation in eight of the 56 watersheds display nonstationary behaviour. Change‐point analyses reveal that changes in the long‐term variance of monthly precipitation are only detected for a few sites. As a complementary analysis tool, quantile regression aims to detect potential changes of different percentiles of the monthly precipitation over time. Several sites show diverging trends in the quantiles, which implies that the range and thus variance of the data, is increasing. As distinct change‐points are not identified, this suggests that the effect is small and cumulative. Results are analysed in detail, and possible explanations are provided. This type of thorough analysis provides a basis for understanding the possible redistribution of water cycle. It also provides implications for water resources management and hydrological engineering facility design and planning. Copyright © 2013 John Wiley & Sons, Ltd.     

Wave-forced dynamics in the nearshore river mouths,and swash zones

The role of wave forcing on the main hydro-morphological dynamics evolving in the shallow waters of the nearshore and at river mouths is analyzed. Focus is mainly on the cross-shore dynamics that evolve over mildly sloping barred, dissipative sandy beaches from the storm up to the yearly timescale, at most. Local and non-local mechanisms as well as connections across three main inter-related subsystems of the nearshore – the region of generation and evolution of nearshore bars, river mouths and the swash zone – are analyzed. The beach slope is a major controlling parameter for all nearshore dynamics. A local mechanism that must be properly described for a suitable representation of wave-forced dynamics of all such three subsystems is the proper correlation between orbital velocity and sediment concentration in the bottom boundary layer; while specific dynamics are the wave–current interaction and bar generation at river mouths and the sediment presuspension at the swash zone. Fundamental non-local mechanisms are both infragravity (IG) waves and large-scale horizontal vortices (i.e. with vertical axes), both influencing the hydrodynamics, the sediment transport and the seabed morphology across the whole nearshore. Major connections across the three subsystems are the upriver propagation of IG waves generated by breaking sea waves and swash–swash interactions, the interplay between the swash zone and along-river-flank sediment transport and the evolution of nearshore sandbars. © 2019 John Wiley & Sons, Ltd.     

Mercury in wahoo, Acanthocybium solandri, from offshore waters of the southeastern United States and the Bahamas

Wahoo, Acanthocybium solandri, are predatory oceanic fish that occur and are harvested in all tropical and subtropical oceans. Total mercury concentrations analyzed in dorsal muscle tissue of 208 wahoo from offshore waters of the southeastern United States and the Bahamas ranged from 0.021 to 3.4 mg/kg (wet weight), with a mean of 0.50 mg/kg (± 0.595 SD). Analyses indicated significant positive linear relationships between mercury and length, as well as, age of wahoo. The piscivorous nature, generally high trophic position, fast growth rate, and associated high metabolism of wahoo within tropical offshore pelagic environments may lead to comparatively higher concentrations of mercury over relatively short time periods. Mercury in wahoo, a highly mobile species consisting of one world-wide population, is regionally influenced by large-scale spatial differences in available mercury in selected prey fish species - many of which have been found to contain relatively high concentrations of mercury.     

Geochemical behavior of 210Pb and 210Po in the nearshore waters off western Taiwan

Dissolved and particulate (210)Pb and (210)Po were determined at 15 stations along the coastline off western Taiwan in April 2007. The (210)Pb activities in dissolved and particulate phases fell within a relatively small range of 2.4-5.2 dpm 100 L(-1) and 1.0-3.2 dpm 100 L(-1), respectively. The dissolved and particulate (210)Po activities also fell within a small range of 0.8-3.4 dpm 100 L(-1) and 1.1-2.9 dpm 100 L(-1), respectively. The correlation of the distribution coefficients (K(d)) of (210)Pb and (210)Po with particle concentration in turbid waters are not as evident as in the open ocean. The mass balance calculation shows that the residence times of (210)Pb and (210)Po with respect to particle removal from the nearshore waters ranges from 3 to 15 days and from 14 to 125 days, respectively. The flux of particulate organic carbon was estimated by (210)Po proxy and ranged from 4.8 to 33.7 mmol-C m(-2) d(-1).     

The effects of river discharge and seasonal winds on the shelf off southeastern South America

The Río de la Plata waters form a low salinity tongue that affects the circulation, stratification and the distributions of nutrients and biological species over a wide extent of the adjacent continental shelf. The plume of coastal waters presents a seasonal meridional displacement reaching lower latitudes (28°S) during austral winter and 32°S during summer. Historical data suggests that the wind causes the alongshore shift, with southwesterly (SW) winds forcing the plume to lower latitudes in winter while summer dominant northeasterly (NE) winds force its southward retreat. To establish the connection between wind and outflow variations on the distribution of the coastal waters, we conducted two quasi-synoptic surveys in the region of Plata influence on the continental shelf and slope of southeastern South America, between Mar del Plata, Argentina and the northern coast of Santa Catarina, Brazil. We observed that: (A) SW winds dominating in winter force the northward spreading of the plume to low latitudes even during low river discharge periods; (B) NE winds displace the plume southward and spread the low salinity waters offshore over the entire width of the continental shelf east of the Plata estuary. The southward retreat of the plume in summer leads to a volume decrease of low salinity waters over the shelf. This volume is compensated by an increase of Tropical waters, which dominate the northern shelf. The subsurface transition between Subantarctic and Subtropical Shelf Waters, the Subtropical Shelf Front, and the subsurface water mass distribution, however, present minor seasonal variations. Along shore winds also influence the dynamics and water mass variations along the continental shelf area. In areas under the influence of river discharge, Subtropical Shelf Waters are kept away from the coastal region. When low salinity waters retreat southward, NE winds induce a coastal upwelling system near Santa Marta Cape. In summer, solar radiation promotes the establishment of a strong thermocline that increases buoyancy and further enhances the offshore displacement of low salinity waters under the action of NE winds.     

Diversity and functions of microscopic fungi: a missing component in pelagic food webs

Fungi are a highly complex group of organisms of the kingdom Eumycota (i.e. the true-fungi) and other fungus-like organisms traditionally studied by mycologists, such as slime molds (Myxomycota) and oomycota (Straminopiles or Heterokonts). They constitute a significant proportion of the as yet undiscovered biota that is crucial in ecological processes and human well-being, through at least three main trophic modes: saprophytism, parasitism, or symbiosis. In addition to direct benefit (sources of antibiotics) or adverse effects (agents of disease), fungi can impact many environmental processes, particularly those associated with the decomposition of organic matter. They are present in almost all regions and climates, even under extreme conditions. However, studies have focussed mostly on economically interesting species, and knowledge of their diversity and functions is mainly restricted to soil, rhizosphere, mangrove, and lotic ecosystems. In this study, we review the diversity and potential functions of microscopic fungi in aquatic ecosystems, with focus on the pelagic environments where they often are regarded as allochthonous material, of low ecological significance for food-web processes. Recent environmental 18S rDNA surveys of microbial eukaryotes have (1) unveiled a large reservoir of unexpected fungal diversity in pelagic systems, (2) emphasized their ecological potentials for ecosystem functioning, and (3) opened new perspectives in the context of food-web dynamics. In spite of persisting methodological difficulties, we conclude that a better documentation of the diversity and quantitative and functional importance of fungi will improve our understanding of pelagic processes and biogeochemical cycling.     

Outer planet magnetospheres: influences, interactions and dynamics

The outer solar system is full of surprises, not least in the vicinity of the outer planets and their magnetic fields. Here Caitriona Jackman and Geraint Jones summarize presentations made at an RAS Specialist Discussion Meeting in January 2009.     

The United States and the Mekong Project

The United States has historically been a strong supporter of coordinated, international water resources studies and planning in Southeast Asia's Lower Mekong River Basin. Since 1975, however, the United States has not contributed to the Mekong Project. Nonetheless, the United States may benefit in several ways by supporting the Mekong River Commission. This paper describes a rationale for renewed US participation in the Mekong Project and identifies several Mekong River Commission Secretariat programs to which the United States could contribute.     

A statistical methodology for assessing the long‐term effects of antecedent drought conditions on stream runoff: applications to the Piedmont Province,southeastern United States

A method was developed to investigate the long‐term (months‐to‐years) effects (both magnitude and duration) of antecedent rainfall upon subsequent runoff coefficients (RCs) or runoff/rainfall ratios. The method was applied to a four‐state region (Georgia, South Carolina, North Carolina, and Virginia) within the southeastern Piedmont Province of the United States and incorporated a 59‐year data set of 19 United States Geological Survey stream gages and 57 National Climatic Data Center rain gages. The method was designed to facilitate statistical comparisons [Mann–Whitney rank sum tests] between various groups of normalized runoff coefficients (NRCs) representing 6–36 month periods which differed in terms of antecedent rainfall conditions. The results of this study show that under all subsequent rainfall conditions, with the exception of excess rainfall, a 1‐year period of antecedent drought lowered NRCs for at least 1 year following the drought. The principal finding of this study is that a year‐long drought period within the southeastern Piedmont Province lowers NRCs by ～25% during the following year when rainfall returns to normal. In most cases, RCs are significantly lower during the second year following a drought than they would be when anteceded by normal rainfall; however, the effects of drought wane during this period. This is a statistical and regional method that can be modified to other study areas; however, it cannot be used to predict storm‐event rainfall–runoff relationships for any specific basin. Copyright © 2010 John Wiley & Sons, Ltd.     

Vadose Zone Monitoring: Experiences and Trends in the United States

The vadose zone is the portion of the geologic profile above a perennial aquifer. Inclusion of mandatory vadose zone monitoring techniques as an approach to aquifer protect ion was first proposed under the Resource Conservation and Recovery Act in the United States in 1978 and has since received increasing acceptance at federal and stale levels. The goals of a vadose zone characterization and monitoring effort are to establish background conditions, identify contaminant transport pathways, identify the extent and degree of existing contamination, establish the basis for monitoring network design, measure the parameters needed in a risk assessment, and provide detection of contaminant migration toward ground water resources. The benefits of vadose zone monitoring include early warning of contaminant migration, potential reduction of ground water monitoring efforts, reduction of contaminant spreading and volume, and reduced time and cost of remediation once a contaminant release occurs. Vadose zone characterization and monitoring techniques should be considered as critical hydrologic tools in the prevention of ground water resource degradation.     

Groundwater Governance in the United States: Common Priorities and Challenges

Groundwater is a critical component of the water supply for agriculture, urban areas, industry, and ecosystems, but managing it is a challenge because groundwater is difficult to map, quantify, and evaluate. Until recently, study and assessment of governance of this water resource has been largely neglected. A survey was developed to query state agency officials about the extent and scope of groundwater use, groundwater laws and regulations, and groundwater tools and strategies. Survey responses revealed key findings: states' legal frameworks for groundwater differ widely in recognizing the hydrologic connection between surface water and groundwater, the needs of groundwater‐dependent ecosystems, and the protection of groundwater quality; states reported a range in capacity to enforce groundwater responsibilities; and states have also experienced substantial changes in groundwater governance in the past few decades. Overall, groundwater governance across the United States is fragmented. States nevertheless identified three common priorities for groundwater governance: water quality and contamination, conflicts between users, and declining groundwater levels. This survey represents an initial step in a broader, continuing effort to characterize groundwater governance practices in the United States.