Small Estuary Research Articles

Sources and Generation Parameters of the Hydrocarbon Background of Bottom Sediments in Small Estuaries of the Tatar Strait

The paper presents data on the composition of organic matter (OM) in the surface layer of bottom sediments (BS) in two small estuaries in the southwestern part of the Tatar Strait (as of summer of 2014 and 2016). The concentration of hydrocarbons (HC) varied from 0.01 to 2.0 mg/g. The HC content in the uniform silt–psammite sediments (0.55–1.47 mg/g) was higher than the biogenic background level (≈0.1 mg/g). The percentage of HC carbon of total Corg (TOC) in the sediments of Muchke Lake (2.68% on average) was much higher than that in Toki Lake and than the value of ≤1% assumed as an indicator of the absence of a hydrocarbon load. The percentage of autochthonous OM (determined from the chlorophyll a content) in the sediments of weakly flowing Muchke Lake is 41% of TOC, and the value for flowing Toki Lake is 18%. The data obtained in the course of this study are consistent with the molecular composition of the n-alkanes: the OM of Muchke Lake is dominated by that of hydrobiont origin, whereas the OM of Toki Lake consists mostly of terrigenous–humic compounds. The n-alkanes contain much compounds typically produced by bacterial synthesis, which indicates that microorganisms played an important role in forming the hydrocarbon background of sediments in the small estuaries.

Diet of Striped Bass in the Southern Gulf of St. Lawrence (Canada) with Emphasis on the Spring Spawning Aggregation

The southern Gulf of St. Lawrence (sGSL) population of Morone saxatilis (Striped Bass) increased over 50 fold between the mid-1990s and 2013–2015, which led to interest in how their feeding might affect populations of commercially and recreation-ally important species. Information on the feeding habits of Striped Bass in all Canadian waters is scarce; therefore, a large number (n = 2220) of sGSL Striped Bass (19–86 cm fork length [FL]) stomachs were collected seasonally (2013–2015) in the Miramichi Estuary (where almost the entire population of individuals >30 cm FL aggregates during spring) and smaller estuaries that empty into the sGSL (summer only), by means of trap nets and by angling. Striped Bass collected during May–early June fed almost exclusively upon Osmerus mordax (Rainbow Smelt) but also consumed a few juvenile Salmo salar (Atlantic Salmon). Striped Bass collected in trap nets during 5–30 June mainly ate a mix of Alosa pseudoharengus (Alewife) and A. aestivalis (Blueback Herring); those collected by angling consumed aquatic insects and Crangon septemspinosa (Sevenspine Bay Shrimp). Striped Bass collected during July–September (30–45 cm FL) ate C. septemspinosa, Palaemon vulgaris (Common Grass Shrimp), and small estuarine fishes. The autumn sample was too small to be considered representative of the population; nevertheless, these fish (32–73 cm FL) ate juveniles of Microgadus tomcod (Atlantic Tomcod), Urophycis tenuis (White Hake), and Gadus ogac (Greenland Cod). The data collected herein would permit reasonable estimates of prey consumed by the sGSL Striped Bass population during spring and, for fish <45 cm total length, during summer, but estimation of annual prey consumption by the sGSL Striped Bass population requires additional data.

Anatomy of the transgressive depositional system in a sediment-rich tide-dominated estuary: The paleo-Yangtze estuary, China

Sediment-rich tide-dominated estuary is generally considered nonexistent or ephemeral under the stable sea-level condition, given the rapid transition to a deltaic system after massive sediments dumping at the river mouth. The well-preserved transgressive sequence in the Yangtze paleo-valley represents an excellent location to examine the interplay between sediment supply, tide action, and sea-level change. To study the Yangtze paleo-valley geomorphological evolution and facies model, four 60-90-m long cores (YD0901, YD0902, YD0903, and CX03) were obtained. Lithological description, grain-size analysis, XRF core scanning, and AMS 14C dating were carried out. The results show that the Yangtze incised valley evolved from a river channel system (before 14.6 ka), through a tidal river (14.6-13 ka), and a tide-dominated estuary (13-8 ka), to a shallow marine (after 8 ka). The paleo-Yangtze estuary displays inner section dominated by muddy heterolithic deposition and the outer section occupied by mud-rich tidal bars and channels, distinctly differing from the well-down small estuaries with sand predominance. A fining-upward facies succession was produced by migration of mud-rich tidal bars in response to post-glacial sea-level rise. These bars are potentially the predecessor of tidal sand ridges on the East China Sea shelf after they were progressively abandoned during the post-glacial sea-level rise and exposed to tidal and storm-wave reworking. This is the first facies model developed from a sediment-rich tide-dominated estuary. This study provides a best example to study evolution of tide-dominated mega-river systems in response to the post-glacial transgression.

Modelling the Influence of Riverine Inputs on the Circulation and Flushing Times of Small Shallow Estuaries

Simple flushing time calculations for estuarine systems can be used as proxies for eutrophication susceptibility. However, more complex methods are required to better understand entire systems. Understanding of the hydrodynamics driving circulation and flushing times in small, eutrophic, temperate estuaries is less advanced than larger counterparts due to lack of data and difficulties in accurately modelling small-scale systems. This paper uses the microtidal Christchurch Harbour estuary in Southern UK as a case study to elucidate the physical controls on eutrophication susceptibility in small shallow basins. A depth-averaged hydrodynamic model has been configured of the estuary to investigate the physical processes driving circulation with particular emphasis on understanding the impact of riverine inputs to this system. Results indicate circulation control changes from tidally to fluvially driven as riverine inputs increase. Flushing times, calculated using a particle tracking method, indicate that the system can take as long as 132 h to flush when river flow is low, or as short as 12 h when riverine input is exceptionally high. When total river flow into the estuary is less than 30 m3 s−1, tidal flux is the dominant hydrodynamic control, which results in high flushing times during neap tides. Conversely, when riverine input is greater than 30 m3 s−1, the dominant hydrodynamic control is fluvial flux, and flushing times during spring tides are longer than at neaps. The methodology presented here shows that modelling at small spatial scales is possible but highlights the importance of particle tracking methods to determine flushing time variability across a system.

Environmental influences on the recruitment dynamics of juvenile European eels, Anguilla anguilla, in a small estuary of the Tyrrhenian Sea, Sardinia, Italy

Abstract The European eel, Anguilla anguilla, is a catadromous and migratory species of commercial importance. Its complex life cycle results in its exposure to many risk factors, which have resulted in stock declines across all life stages since the 1970s. The temporal recruitment dynamics of juvenile eels (glass eels and elvers) were investigated in a small Mediterranean estuary (Sardinia, Italy). The composition of the population and the monthly and seasonal variations in the abundances of juvenile eels was assessed over 78 sampling events (from February 2017 to February 2018). Furthermore, the effects of abiotic variables on the abundances of glass eels and elvers were investigated using generalized additive models (GAMs). Glass eels had the greatest abundance during the winter months, whereas elvers had the greatest abundance during spring. Modelling revealed that the abundance of glass eels was mostly explained by the combined effects of water temperature (12.3–14.5 °C), tidal coefficient (40–110 cm), moon phase, season, and river mouth condition, whereas the abundance of elvers was associated with water temperature (14–21 °C), dissolved oxygen content (&gt;7 mg/L), and season. These results suggest that the annual recruitment of juvenile eels occurs throughout the year, with clear seasonal migration dynamics. The use of multiple statistical approaches allowed us to identify the importance of several environmental variables in regulating the recruitment dynamics, providing useful information for conserving eel stocks through the restoration of the natural flow regime and the connectivity between freshwater habitats and the sea.

Changes in mangroves at their southernmost African distribution limit

Mangroves in South Africa occur at one of the most southerly locations in the world, which provides a unique opportunity to study their dynamic responses to anthropogenic and natural perturbations. The exposed high-energy South African coastline restricts mangroves to 32 sheltered estuaries of which 18 (56%) are predominantly open to the sea. A large area of mangrove (47% of the country total) occurs in the uMhlathuze Estuary – a novel ecosystem formed by the creation of an artificial mouth. A Drivers-Pressures-State-Impacts-Response (DPSIR) framework was applied to understand factors of change and highlight governance and management responses. The largest mangrove area (440 ha) was lost during the construction of Durban Bay harbour. Mangroves (~7 ha) no longer occur in 10 small KwaZulu-Natal estuaries as a result of catchment and mouth disturbance. In the Eastern Cape, pressures are escalating in the form of harvesting for wood, cattle browsing and changes in mouth condition. Climate related warming and an increase in CO2 are positive conditions for mangroves to expand their distribution to higher latitudes but this will depend on propagule dispersal between estuaries and the availability of suitable habitats. Many of the small estuaries are temporarily closed to the sea for different periods thus limiting recruitment. An increase in the intensity of freshwater floods will scour banks and completely remove mangroves. It is important that these dynamic responses are understood and incorporated into management plans so that mangrove forests can be better protected and conserved.

Spatial and seasonal variations of organic carbon distributions in typical intertidal sediments of China

Intertidal zones are the main sites for land-ocean interaction and play an important role in transporting and accumulating organic carbon (OC). Understanding sources and preservation of sedimentary OC are vital to better evaluate the processes controlling the OC distribution in intertidal zones. In this study, we present bulk parameters of total organic carbon (TOC), δ13Corg, grain size and biomarker contents in surface sediments of 14 typical intertidal zones along China’s coastline during both the wet season (WS) and the dry season (DS). Statistical analysis of our data set showed that TOC and biomarker contents were generally high in small estuaries, intermediate but more variable in large estuaries and low in non-estuaries; and these distribution patterns broadly correlated with sedimentary clay contents. TOC and biomarker contents were generally higher in the WS than the DS reflecting both OC inputs and preservation. A binary mixing model based on δ13Corg and biomarker proxies revealed that large estuaries were characterized by higher terrestrial OC fractions (62–80%) except for the Yellow River Estuary (24%), while lower terrestrial OC fractions occurred in non-estuaries (13–15%). Variable OC contributions were found in small estuaries, with most sites characterized by low terrestrial OC contributions (3–35%), but high terrestrial OC contributions were found at the Qiantang River Estuary site (59%) and the Jiulong River Estuary site (67%). Carbon stocks in Chinese intertidal sediments are comparable with those in marine sediments from shelf areas and the Exclusive Economic Zone (EEZ). This study suggests that intertidal sediments are potentially an important carbon sink.

Small game, estuaries, and nets: New perspectives on Norton culture coastal adaptations from a shell midden in Norton Sound, Alaska

Norton culture (ca. 740 BC–AD 1000) sites are ubiquitous across the western Arctic. Based on artifact and settlement data, it is generally agreed that Norton culture south of Seward Peninsula possessed a mixed marine-focused economy dominated by seasonally available Pacific salmon. However, the few direct studies of Norton subsistence, thus far, have suggested an emphasis on marine mammals rather than salmon. We present the results of a zooarchaeological midden analysis from the large Norton site of Difchahak (49-NOB-005) near Shaktoolik on Norton Sound, Alaska. We argue the faunal remains recovered from this site reflect its local estuarine system. Inhabitants were able to maintain year-round occupation of the region through an expansion of netting technology to non-salmon prey species. The economic focus at Difchahak was on mass capture of several seasonally available taxa, including salmon, mussels, saffron cod, ptarmigan, ducks, geese, and seal. Comparison of these faunal remains to those from Norton culture deposits at the neighboring site of Iyatayet suggests that differences between the localities are largely driven by geographically dependent prey-species distributions, and these two sites may represent complementary parts to a broad logistical foraging system.

КУРОРТНИЙ ПОТЕНЦІАЛ МЕДИЧНОЇ РЕАБІЛІТАЦІЇ: СТРАТЕГІЧНИЙ ПРІОРИТЕТ ДЕРЖАВНИХ ІНВЕСТИЦІЙ

The article, on the basis of the analysis of the current state of sanatorium and resort complex development (on the example of the Odessa oblast), substantiates the priorities of state investment into the development of medical rehabilitation at resorts (in the system of sanatorium and spa treatment). It is established that one of the most promising tourist and recreation centers in the Odessa region is the southwest coast of the Black Sea. In the seaside lane of the Odessa oblast there is a developed network of resort establishments (sanatoriums, sanatoriums-preventive hospitals, houses, boarding houses and recreation centers). To determine the strategic priorities of state investment in the resort sphere of the Odessa oblast, the territories most promising for spa and wellness and recreational development have been allocated, taking into account the rational use of natural healing resources and the potential of the resort and recreational infrastructure of the Odessa oblast. According to the current state of organization of the sanatorium and resort complex and resort-recreational activities in the seaside lane of the Odessa oblast the most attractive for investment are: territories with developed resort and recreational infrastructure: resort «Kuialnyk», resort «Serhiivka», recreation and health improvement zone «Zatoka», resort «Odesa-Center»; areas promising for the development of sanatorium and recreational, recreation and health improvement activities: Sasyksko-Shahanska area - between Lake Shahany and Lake Sasyk along the lagoons of Mali Sasyk and Dzhantshei. On the lands of Tuzlivska, Lymanska, Prymorska settlement councils of Tatarbunarskyi rayon; Kuialnytsko-Tylihulska area - is located between the left bank of the Kuialnytskyi estuary near the village. Krasnosilka along the Black Sea coast to the right bank of the Tylihulskyi estuary within the administrative boundaries of the Lymanskyi rayon of Odesa oblast. Within the area there are also the Small and Large Adzhalytskyi estuaries. It is proved that involvement in the sanatorium and resort industry of investments is the most urgent issue in the aspect of infrastructural development of medical rehabilitation. health resort institutions are the main objects of the resort and recreation infrastructure for the provision of sanatorium and resort, rehabilitation, wellness, tourist and other services. The organization of medical rehabilitation on the basis of health resort institutions provides a competitive advantage and additional investment attractiveness of the resort. It is determined that the investments can be aimed at modernization of existing or creation of new health resorts, organization on the basis of sanatoriums of rehabilitation wards, expansion and development of their medical base, modern high-tech rehabilitation equipment, scientific development of new rehabilitation technologies using natural healing resources, etc. The following prerequisites for the investment attractiveness of the development of the medical rehabilitation system at resorts are defined: the development of medical rehabilitation in health resort institutions is provided with regulatory legal regulation, the organization of medical rehabilitation in sanatoriums is defined at the legislative level; The Ministry of Health of Ukraine has developed the concept of reforming the rehabilitation system in Ukraine: the introduction of the International Classification of Functioning and the training of rehabilitation doctors; the project «Rehabilitation Map of Ukraine» has been launched; the process of inventorying the state of natural healing resources and obtaining the resort status by the respective territories is being implemented. It is emphasized that sanatorium and resort complexes at resorts should be the first investment objects, in particular investments should be directed to the modernization of sanatorium establishments and promotion of brand and rehabilitation services.

Sea-level-rise-induced threats depend on the size of tide-influenced estuaries worldwide

The effects of sea-level rise on the future morphological functioning of estuaries are largely unknown because tidal amplitudes will change due to combined deepening of the estuary mouth and shifting amphidromic points at sea. Fluvial sediment supply is also globally decreasing, which hampers infilling necessary to maintain elevation relative to sea level. Here we model 36 estuaries worldwide with varying sizes, shapes and hydrodynamic characteristics, and find that small shallow estuaries and large deep estuaries respond in opposite ways to sea-level rise. Large estuaries are threatened by sediment starvation and therefore loss of intertidal area, particularly if tidal amplitude decreases at the mouth. In contrast, small estuaries face enhanced flood risks and are more sensitive to tidal amplification on sea-level-rise-induced deepening. Estuary widening can partly mitigate adverse effects. In large estuaries, expanded intertidal areas increase tidal prism and available erodible sediment for adaptation, whereas it slightly reduces tidal amplification in small estuaries. Small shallow estuaries face enhanced flood risk under climate change because of sea-level-rise-induced tidal amplification. In contrast, large deep estuaries are threatened by sediment starvation and therefore a loss of intertidal area. Both cases can potentially be mitigated by estuary widening.

Seasonal distribution of trace metals in suspended particulate and bottom sediments of four microtidal river estuaries, west coast of India

ABSTRACT The seasonal distribution of metals (V, Cr, Co, Cu, Ni, Zn, Pb, Mn, Fe, Al and Ti) in suspended and bottom sediments of four minor estuaries (Terekhol, Chapora, Sal and Talpona rivers) of Goa, India was investigated to understand the metal distribution process in the estuarine region. The highest particulate-metal concentrations were found in low-salinity regions of all the estuaries, in the wet season (e.g. in the Terekhol River, the averages in ppm were Co: 53, Ni: 197, Cu: 208, Zn: 212 and Pb: 65) compared to the dry season averages (Co: 27, Ni: 76, Cu: 105, Zn: 164 and Pb: 13 ppm). The estuarine-mixing diagrams showed non-conservative behaviour in both seasons. The Sal River had the highest particulate-metal concentration (Co: 106, Ni: 300 and Zn: 323 ppm), suggesting an anthropogenic input. The enrichment factor for suspended matter was higher than bottom sediments with extremely high enrichment for Mn (>10). The Geo-accumulation index displayed unpolluted to polluted class for all metals. The study highlights the important role played by small estuaries in seasonal metal release and accumulation along the coastal region.

Physical dynamics of the reef flat, channel, and fore reef areas of a fringing reef embayment: An oceanographic study of Pago Bay, Guam

Long-term observations of oceanographic patterns and processes provide necessary context for integrative ecological studies and for assessing and mitigating anthropogenic impacts to coastal ecosystems. The oceanographic patterns and processes of Pago Bay, Guam, a tropical coral reef system with a small estuary, were observed for one year. An array of 50 sensors including current profilers, temperature and dissolved oxygen loggers, and water quality sensors were deployed throughout Pago Bay from 0–26 m depth. Water flow was primarily driven by wave height in the reef flat and channel. In addition, wind and wave directions that were directly across-shore contributed to faster flow speeds throughout the bay. On the fore reef, wave height was the strongest predictor of current speed, but wind direction had a strong influence on current direction. Flow in the channel and on the reef flat was more tightly tied to environmental factors of wind and waves than flow on the fore reef. Extreme daily temperature variations on the reef flat were observed. In deeper water, cold pulses were observed, indicating that large internal waves may propagate around the slopes of Guam. Cold pulses may deliver nutrients to shallower ecosystems and periodically cool deeper areas of the fore reef. In response to heavy rain events, the estimated backscatter in the channel increased sharply along with significant changes in other water quality parameters. Rain events of this magnitude and associated backscatter increases occur frequently. Along with soil-destabilizing land use practices in the Pago River watershed, the current flow and water quality observations presented here indicate that sedimentation may be a risk for the Pago Bay fore reef coral habitat. The understanding of circulation, thermal environment, and rainstorm impacts in this fringing reef system provides a baseline for understanding the ecology, coral reef resilience, and future oceanographic changes in Pago Bay.

Land‐based and climatic stressors of mangrove cover change in the Auckland Region, New Zealand

Abstract Changes in mangrove forest cover (increases and decreases) have been observed globally as a result of the influence of environmental changes and human impacts. Although mangrove forest increases are globally uncommon, in New Zealand mangroves are increasing in distribution at the expense of other intertidal estuarine habitats. This study quantified the change in mangrove area over a period of 74 years (1940–2014), and investigated the influence of land‐based (e.g. land use conversion in the catchments), climatic, and oceanic factors on the change in temperate mangrove forest cover in the Auckland Region of New Zealand over that period. An improved mapping approach using aerial photographs and Landsat images was applied to quantify changes in tall and dwarf mangrove cover, and to identify the mechanism of change (expansion, gap filling, and loss), across 38 estuaries in the Auckland Region, New Zealand. Mangrove area increased from 2313 ha in 1940 to 10 483 ha in 2014 (on average 3.2% yr−1), with higher rates in small estuaries (&lt;1000 ha) than in large estuaries (&gt;1000 ha). The area of the intertidal mudflat habitat, i.e. potential area for mangrove colonization, has doubled from 14 193 ha in 1974 to 28 764 ha in 2014. The increase in total mangrove area was explained primarily by gap filling followed by expansion. The proportion of expansion‐related increase was predominantly seaward (82%) but mangroves also expanded upstream (16%). Boosted regression tree analysis revealed that catchment forest cover, sea level, and mean annual air temperature explained around 85% of the variation in mangrove area. Periods of catchment forest clearing coincided with gains in mangrove forest area. Dwarf mangroves were more sensitive to changes in sea level, in particular over the past 25 years, when the annual sea‐level rise exceeded the sediment accumulation rates. Catchment land use, especially the clearing of forests, associated with increased sediment supply into estuaries is the strongest driver of mangrove forest gain. Thus, land‐use management is a necessary aspect of the management of New Zealand estuaries to conserve the diversity of estuarine habitats (including mangroves) and the ecosystem services that each habitat provides.

Parameterizing Air‐Water Gas Exchange in the Shallow, Microtidal New River Estuary

AbstractEstuarine CO2 emissions are important components of regional and global carbon budgets, but assessments of this flux are plagued by uncertainties associated with gas transfer velocity (k) parameterization. We combined direct eddy covariance measurements of CO2 flux with waterside pCO2 determinations to generate more reliable k parameterizations for use in small estuaries. When all data were aggregated, k was described well by a linear relationship with wind speed (U10), in a manner consistent with prior open ocean and estuarine k parameterizations. However, k was significantly greater at night and under low wind speed, and nighttime k was best predicted by a parabolic, rather than linear, relationship with U10. We explored the effect of waterside thermal convection but found only a weak correlation between convective scale and k. Hence, while convective forcing may be important at times, it appears that factors besides waterside thermal convection were likely responsible for the bulk of the observed nighttime enhancement in k. Regardless of source, we show that these day‐night differences in k should be accounted for when CO2 emissions are assessed over short time scales or when pCO2 is constant and U10 varies. On the other hand, when temporal variability in pCO2 is large, it exerts greater control over CO2 fluxes than does k parameterization. In these cases, the use of a single k value or a simple linear relationship with U10 is often sufficient. This study provides important guidance for k parameterization in shallow or microtidal estuaries, especially when diel processes are considered.

Revisiting Late Paleocene Lower Wilcox deltas, Gulf of Mexico: River-dominated or mixed-process deltas?

Spatial and temporal changes in physical depositional processes of shallow-marine deltas affect facies distributions, which are critical for reconstructing paleogeography and predicting reservoir heterogeneities. The updated interpretation of the classical ancient ‘river-dominated’ Lower Wilcox delta in the Gulf of Mexico suggests more significant process variations than previously suggested. The dominance of the storm-wave process is indicated by wave-ripple laminae and combined-flow ripple laminae in the fair-weather intervals, and hummocky/swaley cross-stratification and low-angle laminae in the storm beds. However, the relatively simple alternation of fair-weather beds and storm beds is complicated by the presence of: 1) normal and inversely graded siltstone to very fine-grained sandstone beds, suggesting hyperpycnites generated during the river flooding season; 2) mud-dominated heterolithics with delicate mud rhythmites, suggesting tidal modulation between the storm events. The storm-wave generated succession, with preservation of both river-flood and tidal signals during fair-weather condition, represents regressive shoreline to-shelf outbuilding. The wave-dominated delta or shoreface deposits are commonly truncated by fluvial-dominated, tide-influenced distributary channels, then overlain by tidal heterolithics and gradually open-shelf deposits, suggesting the development of small estuaries during transgressive phases of the Wilcox shoreline. The interpreted mixed-process delta is linked to the last growth stage of the Lower Wilcox Group, prior to inundation of the Texas shelf by thick marine mudstones. Its depositional setting was characterized by the widest Lower Wilcox shelf (>50 km) and a weakening sediment supply, resulting in a stronger wave and tide influence, relative to a weak fluvial influence. This work thus provides a well-constrained example of the complex interplay of fluvial, wave, and tidal currents in a process stratigraphy where decreasing river flux and relative sea level rise allowed wave reworking to become the dominant theme, even though the same system has been previously interpreted as a classic river-dominated delta. Many existing interpretations of ancient deltas thought to have mainly been controlled by a single process may need to be revisited and revised to take into account the natural spatial and temporal variability inherent to the shallow marine realm.

Limulus polyphemus (Atlantic Horseshoe Crab) Habitats in a Small Estuary and the Adjacent Inner Continental Shelf: Linkages Across Mid-Atlantic Bight Seascapes

While there are numerous studies of Limulus polyphemus (Atlantic Horseshoe Crab) populations on the East and Gulf coasts of the US, especially for spawning adults in large estuaries such as Delaware Bay, there are fewer efforts relative to small estuaries in the Mid-Atlantic Bight. We determined, for the first time, the pattern of seasonal linkages between the Great Bay–Little Egg Harbor estuaries in southern New Jersey and the adjacent inner continental shelf with multiple gears over multiple years. Adults of both sexes are distributed along the inner continental shelf in all seasons, while large juveniles were most abundant in the fall. The seasonal occurrence of larvae, small juveniles, and spawning adults in high salinity, sandy, natural habitats in these small estuaries was consistent. Our findings suggest that these and other small estuaries may provide the same habitats, predators, prey, and fishery resources as larger estuaries, except at a smaller scale. Thus, small estuaries contribute by enhancing landscape and habitat diversity for this vulnerable species. Further clarification of the importance of estuarine habitats would benefit from an increasing emphasis on juveniles and their subsurface habitats in small and large estuaries.

Benefits and Challenges of UAS Imagery for Eelgrass (Zostera marina) Mapping in Small Estuaries of the Canadian West Coast

Nahirnick, N.K.; Hunter, P.; Costa, M.; Schroeder, S., and Sharma, T., 2019. Benefits and challenges of UAS imagery for eelgrass (Zostera marina) mapping in small estuaries of the Canadian West Coast. Journal of Coastal Research, 35(3), 673–683. Coconut Creek (Florida), ISSN 0749-0208.Seagrasses are a fundamental component of nearshore marine habitats, and as such, concerted effort has been put into developing remote sensing methods to assess the spatial coverage of these important habitats. However, in small coastal bays, traditional aerial or satellite remote sensing can be cost-prohibitive or lack sufficient spatial resolution to detect the small, fringing, and often patchy eelgrass (Zostera marina) meadows. This paper presents a method for collection and processing of unoccupied aerial system (UAS) imagery used to map eelgrass at three small coastal estuaries in the Salish Sea of British Columbia. A low-cost, consumer-grade UAS platform equipped with a GoPro Hero 3+ was used to acquire images with a ground resolution of 2 cm, which were postprocessed using structure-from-motion techniques into georeferenced orthomosaics. A manual classification approach incorporating segmented image objects was used to classify eelgrass on a presence or absence basis, resulting in overall mapping accuracies of 96.3%, 86.5%, and 89.7%, as determined by field validation using kayak videography. The major benefit of this method was fine spatial resolution that allowed for textural discrimination between spectrally similar species. However, eelgrass detection and overall accuracy was found to be highly influenced by the environmental conditions at the time of image acquisition.

Long-term physico-chemical and faunal changes in a small, rural South African estuary

The Palmiet Estuary is a small, rural estuary in the Western Cape that only closes briefly during dry summers. The system was previously surveyed during 1979 to 1980 and we repeated the survey in April 2015 (mouth closed) and September 2015 (mouth open). Salinity, temperature, pH and oxygen saturation were measured, and invertebrate and fish faunas surveyed. Physico-chemical characteristics have undergone little directional change, apart from an apparent increase in pH, possibly as a result of changes in land use and application of fertilisers and pesticides in the catchment. Invertebrate species richness increased from 31 to 40 species, despite lower sampling effort in 2015. Most changes were among rare species, or were readily explained by changes in mouth condition and water chemistry. We also confirmed a substantial range extension of the tropical crab, Varuna litterata, rediscovered the locally endemic amphipod, Quadrivisio aviceps, and reported several new distribution records. Gastropods had virtually disappeared from the system, whereas the previously unreported bivalve, Brachidontes virgilae, had become abundant. Overall, fish diversity dropped from 19 to 11 species, but this can largely be ascribed to differ- ences in sampling frequency, season and mouth state. Comparisons of samples from like months showed the fish assemblage to have remained fairly stable, despite changes in inflowing water chemistry and infection of fish by the pathogenic water mould, Aphanomyces invadans. Bird abundance and diversity increased substantially. No alien invertebrate or fish species were recorded. Accordingly, in marked contrast to other smaller estuaries in the region, the Palmiet Estuary has remains in relatively good condition.

Juvenile fish caging as a tool for assessing microplastics contamination in estuarine fish nursery grounds.

Estuaries serve as nursery grounds for many marine fish species. However, increasing human activities within estuaries and surrounding areas lead to significant habitat quality degradation for the juveniles. In recent years, plastic pollution has become a global environmental issue as plastic debris are found in all aquatic environments with potential adverse impacts on marine biota. Given the important ecological role of estuaries and implications of microplastics (MP) in ecosystems, here we assess the occurrence, number, size, and polymer types of MP ingested by wild and caged juvenile European flounder (Platichthys flesus). We deployed caged fish for 1month at five sites in three estuaries in the eastern English Channel. The Seine estuary, heavily impacted by manmade modifications and one of the most contaminated estuaries in Europe, was compared to two smaller estuaries (Canche and Liane) less impacted by industrial activities. We found that juvenile flounders (7-9cm) were vulnerable to plastic ingestion. Seventy-five percent of caged fish and 58% of wild caught fish had the presence of MP items in their digestive tract. Fibers (69%) dominated in the fish's digestive tract at all sites. An average of 2.04 ± 1.93 MP items were ingested by feral juvenile flounder and 1.67 ± 1.43 by caged juvenile flounder. For the caged fish, the three sites impacted by wastewater treatment plant (Liane, Le Havre harbor, and Rouen) were those with the highest percentage of individuals that has ingested MP items. Most of the isolated items were fibers and blue in color. Polymers identified by micro Raman spectroscopy were polycaprolactam, polyethylene terephthalate, and polyurethane. Although other environmental factors may have affected caged fish condition and mortality, we found no significant correlation with the number of ingested MP. However, the high occurrence of MP ingested by juvenile fish on nursery grounds raises concerns on their potential negative effects for fish recruitment success and population renewal. Finally, this study describes, for the first time, the feasibility of using caged juvenile fish as an assessing tool of MP contamination in estuarine nursery grounds.

SPECIFICITY OF ENGINEERING-ECOLOGICAL SURVEYS IN SMALL TIDAL ESTUARIES OF THE WESTERN SECTOR OF THE RUSSIAN ARCTIC

Field investigations of recent years carried out in the tidal estuaries of the western sector of the Russian Arctic zone using modern hydrometric and analytical equipment made it possible to identify a number of regularities. Analysis of these patterns makes it possible to optimize the complex of engineering and ecological surveys conducted in tidal estuaries. The estuaries of small rivers flowing into the tidal seas of the Arctic Ocean have a very specific hydrological and hydro-chemical regime, characterized by a pronounced short-period variability of many parameters due to both tidal forces and solar radiation. Semidiurnal, diurnal and semi-monthly (spring-neap) cycles are reflected in the specific functioning of aquatic ecosystems. Field-studies of small estuaries of the White and Barents Seas show that the intra-season variability of hydrological and hydro-chemical indicators, formed under the influence of three main factors — tides, solar radiation and synoptic processes, is comparable to their seasonal fluctuations or even surpasses it. Tidal semidiurnal, diurnal and semi-monthly cycles are most clearly expressed in changes in water level, currents, salinity and concentration of soluble conservative impurities, with a significant difference between their river and marine background values. In the fluctuations of the suspended matter and insoluble substances concentration, the dominance of the over-harmonic with a period of 3–4 hours and synoptic disturbances with a period of 6–10 days can be observed. To estimate the short-period variability of the parameters under study, the most optimal variant of engineering-ecological surveys is the 14-day series of observations with different discreteness for the hydrological and hydro-chemical parameters of the water masses in the estuary. Under organizational, technical and financial constraints, it may be permissible to perform two series of daily observations with a discreteness of 1–2 hours during spring and neap tides, separated by a weekly interval. In exceptional cases in the hard-to-reach Arctic regions, 3-time observations can be performed during only the spring tidal cycle: high water, half-tide and low water.