深圳蛇口渔港沉积物重金属分布及潜在生态风险评价

沉积物重金属污染对水生生态系统具有潜在危害.渔港是海岸带水环境的重要组成部分.对取自深圳蛇口渔港的10个表层沉积物样品中的As、Cd、Cu、Pb和Zn等典型重金属元素进行了分析,探讨了其空间分布;运用地积累指数法(Igeo)和生态危害指数法(RI),评价了表层沉积物中重金属的富集程度和潜在生态风险,初步探讨了其污染来源.结果表明:(1)蛇口渔港海域沉积物重金属Cu的污染十分严重,Zn和Pb污染较严重,其浓度均为港内>港口>港外;(2)渔港内沉积物重金属的富集达重度污染程度,潜在生态危害风险强.其中,又以Cu的富集程度最高,潜在生态危害风险最强;(3)渔港内Cu的污染,可能与电子工业废水的排放,以及渔业特有的防附着生物涂料有关.     

Morphological and statistical analysis of the impact of breakwaters under construction on a sand spit area (Douro River estuary)

The area of Cabedelo sand spit, located at the mouth of Douro River estuary (Porto, Portugal), reduced in recent decades. In order to study its evolution and also the impact of two breakwaters built to fix the river entrance, a dataset from 23 trimestral surveys using differential GPS techniques, conducted between 2001 and 2007, were considered. A time-series analysis and the estimation of relationships between Cabedelo spit area and several hydrodynamic parameters through statistical techniques were performed in order to determine which parameters have more influence in the Cabedelo spit behavior. From the time-series analysis a seasonal tendency is visible, with the lower values occurring in December and the higher values occurring in July. The estimation of a relationship between Cabedelo spit area and several independent variables reached better results when the dataset was divided in Part A (before the beginning of breakwaters construction) and Part B (during the breakwaters construction). An analysis of the morphological evolution of Cabedelo spit shoreline was also performed: (1) a simple analysis of retreat and accretion rates data with a geographical information system and (2) a more exhaustive analysis were performed using Empirical Orthogonal Functions (EOFs). The Cabedelo spit shoreline erosion occurs mostly on the West and North side, and the accretion mostly occurs in the area protected by the South breakwater. During the breakwater’s construction, the Cabedelo spit shoreline presented high retreat rates, with a mean value greater than 100 m. In terms of spatial variance (EOFs analysis), when the dataset was divided in two parts, the first Principal Component (PC) represents 60.10 % and 89.86 % of the mean squared value of the data, for Part A and Part B, respectively. As proved, the breakwaters would tend to stabilize the coastline leading to a higher first PC value after breakwaters construction (Part B).     

Rates of shoreline change along the coast of Bangladesh

Bangladesh, at the confluence of the sediment-laden Ganges and Brahmaputra Rivers, supports an enormous and rapidly growing population (>140 million in 2011), across low-lying alluvial and delta plains that have accumulated over the past few thousand years. It has been identified as one of the most vulnerable places in the world to the impacts of climate change and sea-level rise. Although abundant sediment supply has resulted in accretion on some parts of the coast of Bangladesh, others are experiencing rapid erosion. We report a systematic assessment of rates of shoreline change over a 20-year period from 1989 to 2009, using Landsat satellite images with pixel resolution of 30 m on the ground. A Band ratio approach, using Band-5 divided by Band-2, discriminated the water line on images that were largely cloud-free, adequately registered, and at comparable tidal stages. Rates of shoreline change were calculated for >16,000 transects generated at 50 m intervals along the entire mainland coastline (>1,100 km) and major islands, using the End Point Rate (EPR) method in the Digital Shoreline Analysis System (DSAS) extension in ArcGIS®. Erosion characterises most of the seaward margin of the Sundarbans in western Bangladesh. Retreat rates of up to 20 m/yr are typical, with little evidence that local devastation of the mangrove fringe by Cyclone Sidr in November 2007 had resulted in uncharacteristic long-term rates of retreat where it made landfall. Erosion exceeded accretion in the Barguna Patuakhali coastal zone, most of which eroded at up to 20 m/yr, but with truncation of the southern tip of the Patharghata Upazila at up to 100 m/yr. In Bhola, erosion at rates of up to 120 m/yr were observed along much of the coast, but in the Noakhali Feni coastal zone, similar rates of erosion were balanced by rapid accretion of the main promontory by more than 600 m/yr. Rates of change were more subdued in the Chittagong and Cox’s Bazar coastal zones of southeast Bangladesh. Islands in the Meghna estuary were especially dynamic; Hatiya Island accreted along some of its shoreline by 50 km² between 1989 and 2009, but lost 65 km² through erosion elsewhere, resulting in the island moving south. Similar trends were observed on adjacent islands. The overall area changed relatively little across the entire coastline over the 20-year period with accretion of up to 315 km², countered by erosion of about 307 km².     

Short- and long-term responses of nourishments: Barra-Vagueira coastal stretch,Portugal

Dredged material resulting from deepening and maintenance activities of the Aveiro Harbor inlet channel, northwestern coast of Portugal, has been used to mitigate the erosion trend recorded on nearby beaches (from Barra to Costa Nova Beach) through direct placement of sand by using standard dredge equipment. The disposal activities of dredged material have been undertaken at two main sites: between the south breakwater and the 1st groin of Costa Nova (dumping area 1, DA1) and between the 3rd and the 5th groin of Costa Nova (dumping area 2, DA2).The sand was placed in the nearshore, between the ?2 and ?7 m Chart Datum, CD, contours.In this study, short- and long-term coastal morphologic changes in the sea bottom, in response to several nourishment operations and to the incoming waves, within the dumping area boundaries are investigated based on a data set of hydrographic surveys collected annually, just before and after the nourishments, between 2009 and 2015. Preliminary results describing the main morphologic changes, evolution trends, sediment budget variations, and nourishments performance are discussed using mainly Geographic Information System techniques. Overall, the analysis demonstrates that the short-term losses in the dumping areas (one month of interval) can reach 50% of the nourished volume, revealing a significant movement of the fill material towards offshore. Seasonal variations promoting cross-shore material exchange can also prevail and misrepresent the sediment balances, if the monitoring area is not comprehensive. Furthermore, some bathymetric analysis suggested that longshore transport gradients have moved the fill material from Barra beach to downdrift areas. All the obtained results contribute to the ongoing discussion about the effectiveness of nearshore sand placements especially in context of an energetic environment.     

A bathymetric study to support management plans for La Caimanera coastal lagoon,Gulf of Morrosquillo,Colombia

There are large extensions of coastal lagoons in the Colombian Caribbean. In spite of their renowned environmental and socio-economic importance, these ecosystems have been poorly evaluated. To initiate a process for understanding the biophysical features of the La Caimanera lagoon, bathymetric surveys were conducted on a 25 × 25 m grid approach. Echo sounder and GPS were used to collect the data, which was then analyzed with ArcGIS 9.2 to produce bathymetry maps. A total of 3355 data points indicated an average depth of 1.83 m (SD ± 0.55) with a range of 0.7–5.4 m. Higher and lower values were recorded within the access channel and on the western margin of the lagoon respectively, suggesting that depth distribution was probably related to the interaction of different factors. These factors include the hydrological influence of the entrance channel currents and the micro-catchments of the streams located on the southeast side, along with the possible effects of the survey course selection. Apparently, the dynamic of the streams caused sedimentation on the opposite southwest margin, affecting the environmental quality by siltation and the accumulation of organic matter. Research, monitoring programs, and new management plans are necessary to avoid the deterioration of the ecological goods and services derived from this important local ecosystem.     

Awareness of sea-level response under climate change on the coast of Ghana

In response to climate change, coastal communities are expected to experience increasing coastal impacts of sea-level rise (SLR). Strategies formulated and implemented to curb these impacts can thus be more effective if scientific findings on the response to climate change and SLR impacts on coastal communities are taken into consideration and not based merely on the need for coastal protection due to physical coastal erosion. There is also the need to determine the level of awareness of sea-level rise and responses in coastal communities to improve adaptation planning. This study assesses the impact of future erosion on the coastal land cover of Ghana. This assessment estimates approximately 2.66 km², 2.77 km², and 3.24 km² of coastal settlements, 2.10 km², 2.20 km² and 2.58 km² of lagoons, 1.39 km², 1.46 km² and 1.71 km² of wetlands to be at risk of inundation by the year 2050 based on coastal erosion estimates for the 2.6, 4.5 and 8.5 Representative Concentration Pathways (RCPs) used in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). This study also assesses the level of awareness of respondents to SLR on the coast of Ghana and explores the availability and level of integration of scientific knowledge of SLR into coastal adaptation strategies in Ghana. Assessment of the awareness of SLR responses to the changing climate in Ghana is made through semi-structured interviews at national, municipal/district and coastal community scales. Although settlements may be inundated based on the coastal erosion estimates, coastal dwellers interviewed cherish their proximity to the sea and are determined to maintain their occupancy close to the sea as spatial location influences their source of livelihood (fishing). Respondents lack knowledge/understanding of SLR, as the majority of household interviewees attributed the rise or fall in sea level to God. Respondents from Ngiresia alleged that the ongoing coastal sea defence project in their community has led to increased malaria cases.     

Coastal erosion and shore protection: A brief historical analysis

Since the Neolithic, humans have gathered along coastal plains, where they had to face sea level rise and subsidence without the technology to oppose these processes. When sea level stabilized, approx. 6.000 yr. B.P., coastal colonization was allowed, but where mountain deforestation was carried out river sediment input increased tremendously: settlements were disconnected from the shore and harbour siltation occurred. Shore erosion was a limited process at the time and local solutions were adopted: clay dikes, wood piles, fascinates and rock revetments. Along the Mediterranean, in China and Japan the construction of more complex structures has been documented since the Middle Ages. Further human development, with river bed quarrying, wetland reclamation, dam construction and mountain re-afforestation, favoured a coastal erosion that nowadays threatens most world coasts. From the Venetian “Murazzi” to the recent 114-km-long concrete element defence at the Yellow river delta, shore protection structures evolved following the different needs (protect coastal communication routes, urban and industrial settlements, tourist resorts). Beach nourishment, previously performed with inland quarried materials, is now intensively carried out with marine aggregates. The vernacular solution, left to undeveloped countries, has been recently revaluated by “green engineering”. However, with Sea Level Rise, the debate of whether to defend, accommodate or retreat is open.     

A very unusual ‘groin’, the MV River Princess,Goa, India and its impacts upon tourism

On June 6, 2000, the Merchant Vessel River Princess – dead weight 114,645 tonnes and 261 m in length, grounded on the beach off the Candolim-Sinquerim coast, Goa, India, spilling some 40 tonnes of oil. In the past 10 years it has settled some 10 m into the sea bed and taken in circa 40,000 tonnes of sand. Until the ‘60’s the Goan economy centered on agriculture and fishing with very low key recreation. Over the last three decades it has become heavily reliant upon recreation, with 13 % of GDP arising from this sector. Nine million cubic metres of littoral drift occurs off this beach per annum, with the longshore current broken by rips into a series of circulating cells. The vessel acts as a massive groin so much so that downdrift, erosion of approximately 5 to 10 m/annum (dependent on the monsoon strength) is occurring at the Taj hotel site. Satellite imagery has shown that some 0.13 km² beach loss has occurred since 2001. Downdrift, the beach is circa 20 m wide compared to updrift areas where it exceeds 100 m. Embryo tombola growth has now commenced between shore and ship. In addition to this, the dune system is now seriously out of equilibrium and sand bags, geotextiles etc. are currently in use to combat dune foot erosion. Questionnaires (n?=?111) showed that 37 % of beach users ranked erosion as the top coastal problem. Sixty seven percent of beach users rated scenery as the most important quality of a beach and due to the grounded ship, >60 % rated the scenery as below average, as well as viewing the ship as a source of danger for swimming purposes.     

Temporal analysis of coastal erosion in Turkey: a case study Karasu coastal region

Coastal erosion may be caused by natural causes as well as human factors. Karasu town of the city of Sakarya in Turkey which is a touristic region on the Black Sea coast has been experienced a drastic coastal erosion. In recent years, this erosion reached the threatening dimensions for the structures in the settlement. According to the temporal analyses of Landsat satellite images, the maximum erosion on the coastline was detected 100 m between 1987–2013. The results of the study show that the harbour construct on the Karasu coast has the major impact on this event. The secondary factor is that the amount of the sediment carried by the Sakarya River was decreased in time due to different reasons. To prevent the coastal erosion, a series of offshore breakwaters were planned after the failed application of groins on the coastline. In this study, temporal changes of the coastline are investigated by the Landsat satellite data and land surveys, possible reasons of the erosion are discussed and the solutions are proposed regarding the coastal structures.     

Environmental stresses and intertidal assemblages on hard substrates in the port of Long Beach,California, USA

Nine intertidal stations within the Port of Long Beach, California, USA, were sampled during September and October 1975 using the random point method and the scraping technique. A total of 96,168 individuals belonging to 55 taxa were recorded in the quantitative survey; qualitative scrapings included 136 taxa. The protected outer coast intertidal assemblages were found at all but three stations along the shoreline. The shoreline, being situated in between the more environmentally stressed inner harbor and the less stressed open ocean, supported assemblages characterized by an instability in species composition. The upper midlittoral zone was typically dominated by Chthamalus dalli, C. fissus and Balanus glandula. The lower midlittoral was colonized either by Anthopleura elegantissima-Prionotis lanceolata facies along the outer breakwater or by A. elegantissima-Tetraclita squamosa rubescens facies along the inner breakwater. The mussel bed, which is the characteristic assemblage of the Californian lower midlittoral zone was obscured by the competitors P. lanceolata, T. squamosa rubescens and A. elegantissima, and was thinned out by predators, of which Pisaster ochraceus was the most voracious. Suspension feeders were dominant in the upper midlittoral and producers and grazers in the lower midlittoral. Predators were few in number and restricted to levels below mean lower low water. There was a gradual increase in numbers of intertidal species and individual abundance from level +5 ft (1.5 m) to level +1 ft (0.3 m) and from shoreline to outer breakwater. This may be attributable to the decrease in environmental stresses in the lower water levels and the improvement in water quality from the inner to outer harbor area.     

Ecosystem service value losses from coastal erosion in Europe: historical trends and future projections

Coastal zones experience increased rates of coastal erosion, due to rising sea levels, increased storm surge frequencies, reduced sediment delivery and anthropogenic transformations. Yet, coastal zones host ecosystems that provide associated services which, therefore, may be lost due to coastal erosion. In this paper we assess to what extent past and future coastal erosion patterns lead to losses in land cover types and associated ecosystem service values. Hence, historical (based on CORINE land cover information) and projected (based on Dynamic and Interactive Vulnerability Assessment - DIVA - simulations) coastal erosion patterns are used in combination with a benefits transfer approach. DIVA projections are based on regionalized IPCC scenarios. Relative to the period 1975–2050, a case study is provided for selected European coastal country member states. For historical (1975–2006) coastal erosion trends, we observe territory losses in coastal agricultural, water body and forest & semi-natural areas – total coastal erosion equaling over 4,500 km². Corresponding coastal ecosystem service values decrease from about €22.3 billion per year in 1975 to about €21.6 billion per year in 2006. For future (2006–2050) coastal erosion projections, total territory losses equal between ~3,700 km² and ~5,800 km² – coastal wetland areas being affected most severely. Corresponding coastal ecosystem service values decrease to between €20.1 and €19.4 billion per year by 2050. Hence, we argue that the response strategy of EU member states to deal with coastal erosion and climate change impacts should be based on the economic as well as the ecological importance of their coastal zones.     

Flood-risk mapping for storm surge and tsunami at Cocos Bay (Manzanilla), Trinidad

Cocos Bay is a barrier beach under threat of marine erosion from the high energy environment of the Atlantic Ocean. This barrier beach borders the Ramsar listed Nariva Swamp, and helps maintain its delicate wetland ecosystem, however, ongoing coastal erosion at this beach threatens the longevity of this freshwater wetland. Due to the geographical location of Cocos Bay being exposed to Atlantic generated storm events and the low relief of the study area, there is a potential threat of storm surges breaching the barrier beach. Owing to the geological setting of the region (located in an active seismic province with earthquakes, volcanicity and landslides), there also exists the threat of tsunamis. This paper is a GIS simulation of the area extent of inundation and the affected infrastructure from such events. It utilizes a DEM and land-use to quantifying inundation areas, and the extent of vulnerability of various elements. The low relief of the barrier beach renders the area extremely vulnerable from events that trigger sea level increases. Simulations revealed that as little as a 1 m storm surge has the potential to disrupt the Nariva Swamp and threaten coastal infrastructure while higher storm surges and tsunamis have the potential to decimate the entire area. The flood-risk model generated indicates a very high vulnerability to storm surges, along the entire length of the coastline. These results have implications for future development and sustainable management of this ecologically sensitive area.     

Application to the Port of Sines of a new tool for risk assessment in port navigation

This paper describes a first approach on the risk assessment in port navigation using GUIOMAR, an integrated system for port and coastal engineering modelling developed at the National Civil Engineering Laboratory (LNEC), Portugal, using a GIS software environment. A set of automatic procedures was designed to include a new methodology based on the amplitude of the wave-induced vertical movement of a ship along its trajectory. In this methodology, the risk in port navigation is assessed on the basis of a combination of the probability of exceedance of a pre-set threshold for the ship??s vertical movements and its consequences. To test the new procedures, a set of sea wave records obtained at the Sines wave-buoy from 1988 to 2002 was transferred into Sines Port using two numerical models of sea wave propagation and deformation (SWAN and DREAMS), included in the GUIOMAR system. The numerical model WAMIT was used for estimating the wave-induced ship??s vertical movements inside the port. By applying the new procedures, automatic generation of risk maps was carried out for navigation in the vicinity of the West breakwater of the Port of Sines. The recent developments contribute towards a more versatile and efficient GUIOMAR system, which results in a more adequate tool to support decision-making processes in port and coastal management.     

Restoration and sequestration of carbon and nitrogen in the degraded northern coastal area in Nile Delta,Egypt for climate change mitigation

Most of coastal area in Nile Delta, Egypt, is salt-affected soils and have low carbon (C) and nitrogen (N) inputs as a result of declining vegetation growth and low net primary production. Therefore, this study amid to compare between C and N pools in degraded (uncultivated and salt-affected soil) and restored (cultivated and reclaimed 20 years ago) locations in North Nile Delta. and to examine the impact of cultivation on sequestering C and N pools in this area as one of the most important methods for mitigating climate change impacts. C and N pools increased significantly in surface soil from 2.99 and 0.43 Mgh^?1 in uncultivated sites to 19.26 and 1.66 Mgh^?1 in cultivated ones as salinity was reduced and net primary production was increased due to leaching and reclamation. Particulate (associated with sand) and nonparticulate (associated with clay +silt) soil organic C or N was significantly higher cultivated sites. In addition, nonparticulate organic C or N was lower than particulate part indicating and supporting the strong relationship between organic matter and clay. The sequestration rate (in approximately 1 m profile) was 1.69 and 0.14 Mgh^?1 yr.^?1 C and N pools respectively. Although the cultivation is leading to loss of organic matter in some areas; C and N in this coastal area are partially restored and stored. Therefore, restoration and appropriate management practices will lead to mitigate the negative impacts of climate change in this area.     

Climate change impacts on a large-scale erosion coast of Hai Hau district,Vietnam and the adaptation

Among the effects of global warming, sea level rise (SLR) and severe typhoons pose the greatest threat to the stability of human settlements along coastlines. Therefore, countermeasures must be developed to mitigate the influences of strong typhoons and persistent SLR for coastal protection. This study assesses climate change impacts on coastal erosion, especially in two projected SLR scenarios of RCP2.6 and RCP8.5. The results show that SLR and severe typhoons lead to the increase of coastal erosion, beach lowering and scour. Moreover, as in projected SLR scenarios, average waves in high tide can cause severe soil erosion at inner slopes and lead to dyke failure by 2060. The paper highlights the need for additional countermeasures to protect the coast of Hai Hau district against SLR and severe typhoons. Among the alternatives available for countering these threats, applying soil stabilization and soil improvement combined with geosynthetics are promising strategies for coastal structures. Hybrid structures can be used with earth reinforcement and soil improvement. Additionally, the paper emphasizes the importance of multiple protective adaptations, including geosynthetics and ecological engineering measures against climate change-induced severe erosion on the coast of Hai Hau district.     

As the world warms: rising seas, coastal archaeology, and the erosion of maritime history

The human history of coastal regions around the world has been under assault for decades, from forces that include dam building, coastal modifications, the destruction of wetlands, marine erosion, population growth and rampant development, looting, and other processes. Global warming will exacerbate the destruction of cultural resources in coastal zones through accelerated sea level rise, intensified storm cycles, and related coastal erosion. Although average global sea levels have been rising for ∼20,000 years, they slowed dramatically about 7,000 years ago. Rates of sea level rise now appear to be increasing rapidly due to growing anthropogenic emissions of carbon dioxide and other greenhouse gases. Global warming and rising seas, especially when combined with population growth and the implementation of measures designed to protect endangered coastal properties, threaten the deep maritime history of human migrations, settlement, and adaptations in coastal areas around the world. Ranging in age from the mid-Pleistocene to recent historic times, coastal archaeological sites contain invaluable data on ancient coastal societies, fisheries, and ecosystems. Archaeologists, historians, and other cultural resource managers must do more to anticipate, evaluate, and mitigate the effects of global warming, sea level rise, and coastal erosion on the long history of human maritime cultures.     

Evolution trend analysis of Nearshore seabed in Yangshan Deep-water Port,China

Yangshan Deep-water Port, the largest deep-water port in China, is located in the sea area of the Qiqu Archipelago adjacent to Hangzhou Bay. It goes deep into the ocean and far from the continent, and plays a key role in the economy and shipping of China. The evolution and stability of the seabed in the Yangshan Deep-water Port have potential influences on the security of port engineering. Based on GIS spatial analysis technology and MATLAB numerical analysis software, this study predicted the short-term evolution trend of the Yangshan Port frontier seabed terrain through the establishment of a modified power function model. The research included: (1) a systematic analysis of the characteristics of the terrain evolution before (1960–1997) and after (1998–2008) the construction of Yangshan Port by using terrain data from the study area; (2) based on the historical erosion and deposition characteristics of Yangshan Port, an improved power function model was established and the reliability of the model was validated to simulate the study area’s frontier seabed evolution trend in 2015. The results show that: (1) before the construction of Yangshan Port, the seabed in the study area had a narrower variation in erosion and deposition, with the ratio of erosion and deposition of the stable region, erosion area and deposition area being 53.7 %, 18.3 % and 28.0 % respectively, overall the area showed a relatively stable erosion and deposition character; (2) after the construction of the port, the erosion and deposition variation ranges of the seabed were sharply amplified, obviously due to man-made interference being stronger than natural evolution. The stable region of erosion and deposition was only 22.7 %, erosion area was 53.8 %, and the deposition area was 23.4 %, which showed an erosion intensity that was larger than the deposition intensity; (3) the established improved power function model can be used in the short-term prediction of the Yangshan Port frontier seabed evolution trend with high prediction accuracy. The results can aid in decision making with regard to coastal protection and prospective construction schemes around Yangshan Port.     

Evaluation of geomorphic changes and retreat rates of a coastal pyroclastic cliff in the Campi Flegrei volcanic district,southern Italy

Geomorphic evolution of sea cliffs has significant impact on coastal settlements worldwide, so that evaluation of cliff instability processes, failure factors, and retreat rates involves a growing number of scientists for coastal risk and management purposes. Aerial photogrammetry and lidar are among the most used techniques for topographic characterization and geomorphic monitoring of coastal environments. A crucial role in the combined use of such techniques is the evaluation of different spatial accuracy and co-registration between derived terrain models, so that a robust error analysis is required. In this study, we present a change detection analysis of the Torrefumo coastal cliff, in the Campi Flegrei volcanic area (Southern Italy). Aerial images taken in 1956 and 1974, processed through digital photogrammetry, and an airborne lidar point cloud acquired in 2008 were used to produce Digital Elevation Models of the cliff. The analysis was based on the multi-temporal comparison of these models and included the calculation of volumetric changes and average retreat rates of the cliff face with reference to the 1956–1974 and 1974–2008 time intervals. The spatially variable elevation uncertainty of each Digital Elevation Model was evaluated with a probabilistic approach based on the fuzzy set theory. The results of this study showed significant eroded volumes during the period 1956–1974 and relatively smaller volumes in the 1974–2008 time span, with mean annual retreat rates of 1.2 m/year and 0.17 m/year, respectively. We infer that the significant decrease of erosion characterizing the second period was induced by the sheltering effect at the base of the cliff produced by the construction of a seawall in the early 80’s.     

Size,spatial, and bathymetrical distribution of the ascidian Halocynthia papillosa in Mediterranean coastal bottoms: benthic–pelagic coupling implications

Benthic suspension feeders are abundant in Mediterranean coastal environments, though most of them are threatened due to overexploitation, climate change impacts, and unregulated diving or fishing practices. Little is known about most of the coastal communities in terms of large-scale distribution and realistic benthic–pelagic coupling implications, which are keys to understand and manage those threatened ecosystems. The active suspension feeder Halocynthia papillosa (one of the most common ascidian species of the Mediterranean Sea) was selected as a model organism to help to understand the ecological role in benthic–pelagic coupling processes and its importance as a carbon sink (an essential ecosystem service). The spatial and bathymetrical distribution of this organism has been studied using remotely operated vehicle video transects. The species was distributed throughout the study area, with a maximum density of 4 specimens m^?2. The highest abundances and the biggest sizes were observed on the range of 20–50 m depth. The role as carbon and nitrogen sink of this suspension feeder has been quantified coupling distribution data with existing in situ studies of feeding and respiration. Along the 1.24 ha of the study area, H. papillosa yearly ingested 519.4 g C and 31.4 g N and retained 20.2 g C. As long as the physiological data are known, this new methodology could be very useful in assessing bentho–pelagic links and the capacity of being C and N sinks of a wide range of species. This new approach may be essential for the future management of benthic communities.     

Bed load transport of sediments and morphodynamics in the Topolobampo coastal lagoon system,Mexico

The Topolobampo coastal lagoon system, located on the eastern side of the Gulf of California, is a marine zone of considerable economic importance with vessel traffic, dredging operations and aquaculture development. Despite its relevance as a conservation site, this ecosystem has been poorly studied. Since life in marine substrates is abundant, we investigated the capability of tidal hydrodynamics in the lagoon to erode and to accumulate sediment. We calculated the morphodynamics caused by bed load sediment transport applying a two dimensional non-linear hydrodynamic finite difference model. Bed erosion and accretion patterns of sediment (for specific grain size: 170 μm) were determined from the divergence of sediment transport. After a year of numerical simulation of sediment transport the areas of noticeable changes on the bottom of the lagoon have been revealed. Most of sediment accretion took place in the narrow steeped channel connecting the Topolobampo and Ohuira sections. This area appears characterized by the presence of high tidal velocity gradients. Another finding was that accretion areas were coupled with erosion zones in an alternating form. This outcome suggests that sediment do not travel long distances but is deposited nearby the erosion sites. The results are strong evidence of the influence of tidal hydrodynamics on the sediments distribution in the Topolobampo coastal lagoon system and on the generation of substrates where marine life may find protection.