High Salinity Estuaries Research Articles

Mid- to late Holocene geomorphological and hydrological changes in the south Taihu area of the Yangtze delta plain, China

The Taihu Plain of the Lower Yangtze valley, China was a centre of rice agriculture during the Neolithic period. Reasons for the rapid development of rice cultivation during this period, however, have not been fully understood for this coastal lowland, which is highly sensitive to sea-level change. To improve understanding of the geomorphological and hydrological context for evolution of prehistoric rice agriculture, two sediment cores (DTX4 and DTX10) in the East Tiaoxi River Plain, south Taihu Plain, were collected, and analysed for radiocarbon dating, diatoms, organic carbon and nitrogen stable isotopes (δ13C and δ15N), grain size and lithology. These multiproxy analyses revealed that prior to ca. 7500 cal. yr BP, the East Tiaoxi River Plain was a rapidly aggrading high-salinity estuary (the Palaeo-Taihu Estuary). After ca. 7500 cal. yr BP, low salinity conditions prevailed as a result of strong Yangtze freshwater discharge. Subsequently, seawater penetration occurred and saltmarsh developed between ca. 7000 and 6500 cal. yr BP due to accelerated relative sea-level rise. This transgression event influenced a large area of the Taihu Plain during the Holocene, as shown by multiple sediment records from previous studies. Persistent freshwater marsh (or subaerial land) formed due to dramatic shrinkage/closure of the Palaeo-Taihu Estuary after ca. 5600 cal. yr BP when sea level was relatively stable. We speculate that geomorphological and hydrological changes of the East Tiaoxi River Plain played an important role in agricultural development across the Taihu Plain during the Neolithic period. The closure of the Palaeo-Taihu Estuary and the formation of stable freshwater marsh (or subaerial land) after ca. 5600 cal. yr BP were critical preconditions encouraging the rapid rise of rice productivity in the Liangzhu period (5500–4500 cal. yr BP). This development changed the landscape and river systems, and thus provided adequate freshwater supply to the Taihu Plain.

Distribution of Dissolved, Suspended, and Sedimentary Heavy Metals along a Salinized River Continuum

ABSTRACT Yang, X. and Wang, Z.-L., 2017. Distribution of dissolved, suspended, and sedimentary heavy metals along a salinized river continuum. Attention has been increasingly focused on the geochemical behavior of heavy metals in high-salinity estuaries, but how the salinity gradient affects the behavior of heavy metals in low-salinity rivers is not clear. In this paper, the distribution of Cr, Cu, Co, and Ni were assessed according to the proportions in three phases (dissolved, suspended particle, and surface sediment) along the Jiyunhe River in northern China. Dissolved heavy metals had a significantly positive correlation with salinity (p < 0.01), increasing along a salinity gradient from upstream to the river mouth. Suspended particulate materials were mainly derived from particles like clay rather than algae. With salinity greater than 2‰, suspended heavy metals were released into the water, bringing about an increase in dissolved heavy metal content. High deviations of Cr from conservative mixing be...

Disease ecology of Hematodinium perezi in a high salinity estuary: investigating seasonal trends in environmental detection.

The blue crab Callinectes sapidus has seen a general decline in population levels. One factor influencing mortality is infections by Hematodinium perezi, a dinoflagellate parasite. A 2 yr study was conducted in 2014 and 2015 to monitor H. perezi DNA within the Maryland (USA) coastal bays, comparing seasonal cycles in the abundance of parasite DNA in environmental samples to parasite presence in host blue crabs. A late summer to early fall peak in H. perezi infections in blue crabs was observed, consistent with previous work. Infection intensities matched this trend, showing a slow progression of low intensity infections early in the year, with a peak in moderate and heavy infections occurring between July and September, for both years. It was hypothesized that the peak in water column occurrence would coincide with those months when infection intensities were highest in blue crabs. As the peaks in water column occurrence were in July 2014 and August-September 2015, this is consistent with sporulation being the primary contributor to environmental detection in summer months. An additional peak in environmental detection occurred in both years during the early spring months, the cause of which is currently unknown but may be related to infections in overwintering crabs or alternate hosts. Several new crustacean hosts were identified within this estuary, including grass shrimp Palaemonetes spp. and the sand shrimp Crangon septemspinosa, as well as the mud crab Dyspanopeus sayi. Improved knowledge of this disease system will allow for better management of this important fishery.

Impacts of an abundant introduced ecosystem engineer within mudflats of the southeastern US coast

Invasive ecosystem engineers can have far-reaching effects on systems, especially if they provide structure where none was before. The non-native seaweed Gracilaria vermiculophylla has proliferated on estuarine mudflats throughout the southeastern US, including areas (South Carolina and Georgia) that historically were extremely low in seaweed biomass. Quantitative field surveys across 150 km of high salinity estuaries revealed that the density of the native onuphid polychaete Diopatra cuprea and the aboveground height of its biogenic tubes, which Diopatra decorates with drifting debris and seaweed, positively influenced Gracilaria biomass. The abundance of Gracilaria epifauna, composed primarily of amphipods and small snails, increased with Gracilaria biomass at many locations in our field surveys. To examine whether epifauna were facilitated by Gracilaria we experimentally manipulated Gracilaria biomass in two locations. Consistent with the field surveys, we found that increasing Gracilaria biomass facilitated epifauna, particularly amphipods and snails. Epifaunal densities on Gracilaria were higher than on a biologically-inert structural mimic of Gracilaria (plastic aquarium alga), indicating that epifauna colonize Gracilaria because Gracilaria provisions both physical structure and a biological resource. We also quantified the seaweed’s net rate of productivity and decomposition. Primary production of Gracilaria was variable, but massive in some areas (up to 200 % net biomass increase in 8 weeks). The seaweed rapidly degraded upon burial in silty sediments (79 % loss in mass within 10 days) and thus may represent an important new addition to detrital foodwebs. As a copious, novel source of primary production, detritus, and desirable habitat for epifauna, Gracilaria has the potential to transform southeastern US estuaries.

Outdoor Tank and Pond Spawning of Cobia, Rachycentron canadumin Coastal South Carolina

Research was conducted at the South Carolina Department of Natural Resources Waddell Mariculture Center to evaluate the potential for captive reproduction of cobia, Rachycentron canadumin outdoor tanks and ponds. In May 2001, adult cobia (3 males, 1 female, and 1 suspected female) obtained from a local high salinity estuary were stocked into an outdoor tank (32,000-L) receiving ambient estuary water. Spawning occurred within 2 days after stocking. Over the course of 3 consecutive days, a total of 3.6 million eggs were collected with roughly equal numbers collected during each 24-hour period. Mean fertilization rate was 58.1%. Hatching occurred at approximately 24 hours after initiation of each spawning event. Mean percent hatch was 27.5%. Fish were relocated to a 0.25-ha circular pond 10 days after tank spawning activity ended. One female received pelleted GnRHa before stocking. Eggs were observed 3 days after stocking and at 12 days after hatching, approximately 50,000 larvae were harvested. In May and June 2002, three groups of recently caught adult cobia, each consisting of 3 males and 1 female, were placed in one of three outdoor tanks. Spawning occurred within 2–4 days after stocking of Tanks 1 and 2. During a single spawning event, a total of 2.1 million and 560,000 eggs were collected from Tanks 1 and 2, respectively. Relative batch fecundity of females stocked in Tanks 1 and 2 was estimated to be 79.2 and 20.9 eggs/g, respectively. No fertile eggs were collected from Tank 2. Percent fertilization and hatch of eggs collected from Tank 1 was 3.2% and 1.5%, respectively. No spawning activity of fish stocked in Tank 3 occurred. Findings reveal that naturally conditioned recently caught adult cobia can readily spawn soon after capture and that ponds can be utilized for reproduction of this species in the U.S.

IMPACTS OF URBANIZATION ON NUTRIENT CONCENTRATIONS IN SMALL SOUTHEASTERN COASTAL STREAMS1

ABSTRACT: Coastal watersheds in the southeastern United States are rapidly changing due to population growth and attendant increases in residential development, industry, and tourism related commerce. This research examined spatial and temporal patterns of nutrient concentrations in streams from 10 small watersheds (&lt; 4 km2) that drain into Murrells Inlet (impacted) and North Inlet (pristine), two high salinity estuaries along the South Carolina coast. Monthly grab samples were collected during baseflow during 1999 and analyzed for total and dissolved inorganic and organic forms of nitrogen and phosphorus. Data were grouped into forested wetland creeks (representing predevelopment reference sites), urban creeks, and urban ponds. DON and NH4 concentrations were greater in forested streams than in urban streams. NO3 and TP concentrations were greatest in urban streams. Seasonally, concentrations were highest during summer for TN, NH4, DON, and TP, while NO3 concentrations were greatest during winter. Nutrient ratios clearly highlighted the reduction in organic nitrogen due to coastal development. Multiple regression models to predict instream nutrient concentrations from land use in Murrells Inlet suggest that effects are not significant (small r2). The findings indicate that broad land use/land cover classes cannot be used to predict nutrient concentrations in streams in the very small watersheds in our study areas.

Denitrification in South Carolina (USA) Coastal Plain Aquatic Sediments

AbstractDenitrification rates in aquatic sediments from three sites upland of high salinity estuaries were measured to compare nitrate (NO−3) removal by sediment bacteria. The study sites included two blackwater creeks that drain to coastal inlets (one in an undeveloped coastal forest and the second in a suburban residential development) and drainage pond on a golf course. Two to 20 mmol NO−3 kg−1 soil was added to microcosms and the acetylene block technique was used to estimate denitrification. Nitrate, nitrous oxide (N2O) and ammonium (NH+4) concentrations were monitored over time. The rate and efficiency of denitrification was low at the 2 mmol NO−3 kg−1 addition and increased proportionally with NO−3 added. Across all treatments, the golf course sediment that received consistent N inputs in situ had the most rapid and greatest N2O production, while the salt marsh in the undeveloped area had the least. The NH+4 concentrations remained constant and low (2 mmol N kg−1) except at the undeveloped, forested Oyster Creek (8 mmol NH+4‐N kg−1). In most cases, the majority of NO−3 removal did not occur until 24 to 48 h of incubation, regardless of N2O production. During typical low‐ and no‐flow periods, this time frame may be adequate for slow diffusion of nutrients and removal of NO−3 prior to transport to coastal estuaries or ground water, particularly at the golf course site. However, this time frame may not be adequate during rapid water and nutrient transport due to severe storm events typical of this region.

Epizootiology of the parasitic dinoflagellate Hematodinium sp. in the American blue crab Callinectes sapidus.

Hematodinium sp. is a parasitic dinoflagellate that infects and kills blue crabs Callinectes sapidus. Periodic outbreaks of dinoflagellate infections with subsequent high host mortalities prompted a study of the epizootiology and distribution of the crab pathogen. Hemolymph samples from over 13000 crabs were assessed for infections over 8 yr. Moderate to high prevalences were found at several locations along the Atlantic and Gulf coasts of the United States. In the coastal bays of Maryland and Virginia, prevalence followed a seasonal pattern, with a sharp peak in late autumn. Infections were significantly more prevalent in crabs measuring less than 30 mm carapace width; host sex did not influence prevalence. Prevalences were highest in crabs collected from salinities of 26 to 30%o; no infected crabs were found in salinities below 11%o. Intensity of infection did not vary among crab sizes, molt stages, or sexes. Naturally and experimentally infected crabs died over 35 and 55 d in captivity, with a mean time to death of approximately 13 and 42 d, respectively. Several other crustaceans, including gammaridean amphipods, xanthid (mud) crabs, and the green crab Carcinus maenus, were found with Hematodinium-like infections. Considering its widespread distribution and high pathogenicity, we suggest that Hematodinium sp. represents a significant threat to blue crab populations in high salinity estuaries along the Atlantic and Gulf coasts of the USA.

Assessing the impacts of anthropogenic and physiographic influences on grass shrimp in localized salt-marsh estuaries

The complexity and severity of ecological impacts associated with coastal development demand that resource managers explore new spatial analytical techniques combined with multidisciplinary scientific expertise for proactive coastal zone management. Arising from these environmental concerns and the identified need for adequate databases and integrated models, a long-term study of the impacts of urbanization on localized estuaries of the South eastern United States was initiated in 1990. A goal of this study was to examine the role of Geographic Information Processing (GIP) to integrate data and scientific expertise for the identification, assessment, and modeling of anthropogenic and physiographic relationships within estuaries. This goal is being achieved through the implementation and utilization of a multi-agency Geographic Information System (GIS) and the development and validation of spatially explicit models. This work presents spatial modeling efforts that incorporate land use and land cover characteristics with fisheries data to assess and predict the impacts of anthropogenic and natural influences on key species that inhabit critical estuarine wetlands and streams. A spatial assessment of two small, high-salinity estuaries suggests that upland development adjacent to critical estuarine habitat limits the population size and distribution of adult and larval grass shrimp ( Palaemonetes pugio (Holthuis)). Modeled spatial distributions of adult populations suggest the existence of estuarine ‘deserts’ — wetlands and stream reaches adjacent to commercial and residential land use void of natant fauna. This paper's approach is being developed for coastal resource managers to predict the impact of proposed landscape modifications prior to occurrence of changes.

Distribution of polycyclic aromatic hydrocarbons in oyster (Crassostrea virginica) and surface sediment from two estuaries in South Carolina

The concentration of polycyclic aromatic hydrocarbons (PAHs) was determined in oysters and sediments collected from two high salinity estuaries from the coast of South Carolina. The two estuaries were Murrells Inlet (urban), an estuary receiving urbanized drainage and run-off, and North Inlet (non-urban), receiving drainage from heavily forested terrain and minimal anthropogenic input. A minimum of thirty (30 stations were sampled in Murrells and North Inlets, respectively. A composite oyster sample (n = 30) was analyzed for each station. For sediment, a sample from the top 3-5 cm of the sediment surface from each station was analyzed. In oyster from Murrells Inlet, total PAHs concentrations within the 75 percentile were located in the northern portion of the estuary near marinas, adjacent to residential areas of high population density, near commercial enterprises or run-off from storm drains. Total PAHs within the 25 percentile were located near the mouth of the estuary. These results showed PAHs concentration gradient in the estuary that was highest in narrow creeks, where the urban shore interfaced with tidal creeks and lowest at the mouth of the estuary. In the case for sediment, a similar gradient was observed. In comparing the mean total PAHs of the two inlets, Murrells Inlet had significantly higher (p < 0.01) total PAHs concentrations than North Inlet for oyster and sediment, respectively. In comparing PAHs concentrations among the two matrices in Murrells Inlet, these data showed that the pattern of individual PAHs in oyster and in sediment were different. Oysters tended to accumulate the lower molecular weight and the more water-soluble PAHs compared to PAHs found in sediment. As expected, differences in octanol/water partition coefficient among individual PAHs and the greater persistence of the higher molecular weight PAHs contributed to the accumulation patterns in oyster and sediment.

Trophic relationships and seasonal utilization of salt-marsh creeks by zooplanktivorous fishes

In a high salinity estuary at North Inlet, South Carolina, co-occurrence and possible competition among adults of four dominant zooplanktivorous fishes were minimized by seasonal adjustments in lateral and vertical distributions as well as in dietary preferences. In winter, Atlantic silversides, Menidia menidia, occupied the entire water column while other planktivores were rare or absent from the estuary, and they consumed large prey such as mysid shrimps and fish larvae. An immigration of bay anchovies, Anchoa mitchilli, in the spring resulted in a redistribution of species with Atlantic silversides shifting to the surface waters and bay anchovies dominating the lower half of the water column. Both fishes consumed mostly copepods in the spring, but each favored a different species. There was little similarity in the large prey items consumed by the two fishes. Striped anchovies, Anchoa hepsetus, arrived in mid-summer and were most abundant at the surface while bay anchovies continued to dominate the bottom waters. Atlantic silversides were rare in all summer collections. The diets of the two anchovies were similar, but vertical separation during the period of maximum zooplankton abundance probably minimized competition. Rough silversides, Membras martinica, which were obligate surface dwellers, shared the upper water column with striped anchovies, but the two species had very different diets during their period of co-occurrence. Although seasonal changes in fish diets reflected shifts in zooplankton composition and all fishes consumed a variety of prey types, preferences for some prey taxa and total avoidance of others were indicated. Electivity indices indicated an especially strong selection for fiddler crab megalopae by all fishes in the summer and fall. All fishes, except rough silversides, which fed almost exclusively on copepods and crab zoeae, consumed large prey items when they were available. Fine scale partitioning of the food resources was apparent in the selection of different copepod and insect species by the fishes. Spatial and temporal separation in the distribution and/or dietary preferences of the zooplanktivores fishes probably reduces the potential for resource competition. Given the high abundances and selectivity of the planktivores, significant impacts on some zooplankton populations probably result.

Interactions among Some Dominant Estuarine Nekton Species

Interactions between pairs of numerically dominant species collected at inlet and creek shorezone and channel habitats within a high salinity estuary in northeastern South Carolina were examined using two-way contingency tables and binomial tests. Of the significant species interactions, over 71% were positive and these primarily occurred within shorezone habitats. The strongest positive interactions were between young-of-the-year spot (Leiostomus xanthurus) and blue crab (Callinectes sapidus) juveniles in both shorezone habitats, and between striped killifish (Fundulus majalis), white mullet (Mugil curema), and striped anchovies (Anchoa hepsetus) in the inlet shorezone habitat. One of the most positive species associations in channel habitats was between the bay anchovy (Anchoa mitchilli) and the Atlantic brief squid (Lolliguncula brevis). These positive relationships between species may be explained by one species enhancing the habitat for another, both species responding to similar environmental conditions, cooperative social interactions such as mixed schooling, or the attraction of predators to prey. Negative interactions were found between schools of Atlantic silversides (Menidia menidia) and striped killifish in the inlet shorezone and between schools of Atlantic silversides and bay anchovies in the creek shorezone. Schools of Atlantic silversides may either displace or compete with other common shorezone species. Positive and negative interactions suggest that relationships between some species pairs did not occur randomly within certain habitats and may have contributed to the organization of the estuarine nekton community. Differences in the strengths and direction of interactions of certain species pairs among habitats and seasons were probably related to the differences in the physical characteristics of those habitats and/or changes in the relative abundance of dominant species and life stages over time.

The effects of urbanization on small high salinity estuaries of the southeastern United States

Future development in coastal areas of the southeastern United States (US) will likely result from urbanization (housing and tourist/service related activities) rather than industrialization. In an effort to identify potential impacts associated with urbanization, field studies were conducted in two small, high salinity estuaries of coastal South Carolina. The sites selected for study were Murrells Inlet, an estuary with a history of significant urbanization and North Inlet, a relatively pristine, undisturbed estuary. During field studies conducted in the fall of 1990, a series of 96-h in situ bioassays were undertaken at each of the sites. The species used were the grass shrimp, Palaemonetes pugio, and the mummichog, Fundulus heteroclitus. Water samples were collected at the site during these bioassays and analyzed for polyaromatic hydrocarbons (PAH) residues. Adult oysters, Crassostrea virginica, were also deployed at each of the sites during the in situ bioassays and analyzed for tissue PAH residues. Physicochemical water quality and rainfall were also monitored. Mean waterborne PAH levels were significantly higher at the urbanized Murrells Inlet site than at the more pristine North Inlet. Additionally, oysters deployed at the Murrells Inlet site showed increased PAH levels in comparison to baseline values while those deployed at the North Inlet had PAH levels well below baseline concentrations. No siterelated mortality was observed in the two species used in the bioassays. Fluctuations in salinity, dissolved oxygen, and pH were much less extreme at the urbanized Murrells Inlet site than at North Inlet. The less dynamic physicochemical environment at the Murrells Inlet site may be due in part to urban influences (i.e., jetty construction and bulkheading). Additional work is needed to better define the significance of these observations.

Impact of urbanization on high-salinity estuaries in the southeastern United States

To assess the impact of urbanization on small high-salinity estuaries, studies were initiated which had a broad temporal and spatial base. These studies utilize a geographic information system and a global positioning system technology, as well as new data collection and analytical techniques to characterize the relationship between land-use patterns, nutrient loading, water quality, chemical contaminants, bacteriology, toxicology, hydrodynamics, and primary and secondary production. Thirty monitoring stations at both an urbanized estuary (Murrells Inlet, South Carolina, U.S.A.) and a nearby, similar-sized, relatively pristine estuary (North Inlet, SC) were established. Results indicate the following trends. Polycyclic aromatic hydrocarbon (PAH) levels in seawater and oyster tissue were higher in Murrells Inlet, and the specific PAHs found in higher concentrations in seawater are similar to the PAH composition in urban air. Copper concentrations were higher in Murrells Inlet with the highest concentrations found in oysters located near human habitation. Although total coliform levels in surface waters at both estuaries were not different, faecal coliform levels in Murrells Inlet were generally higher, particularly in oysters. Nitrate and phosphate concentrations were higher in water from Murrells Inlet but, in contrast, ammonium concentrations when significantly different were higher at North Inlet landward stations. The variability in dissolved oxygen was much greater in North Inlet and may be due to the greater marsh/creek drainage in North Inlet. Chlorophyll a values tended to be higher and more variable for North Inlet water samples but no significant differences were observed between the two estuaries during the peak of the growing season. Lower biomass was observed in Murrells Inlet when similar creeks from the two estuaries were sampled by seines.

Bathymetry as an indicator of net circulation in well mixed estuaries 1

In well mixed, high salinity estuaries of the southeastern U.S. the net circulation is mirrored in the bathymetry. Measurements in North Inlet, South Carolina, indicate a net current reversal across the estuary. The cross section bathymetry is usually bimodal with two channels separated by a shallow area. The deeper channel experiences ebb‐directed net flow with ebb‐oriented sand waves as the predominant bedform. In the shallower channel, the net current is flood directed. In well mixed estuaries similar to North Inlet, it may be possible to determine qualitative circulation features from a few lateral and longitudinal bathymetric traces without measurements of current velocity and salinity.