Particulate matter exchange across a Rjord sill

Recent studies have indicated the existence of a considerably higher planktonic biomass in the deep waters of the Saguenay Fjord as compared to corresponding depths in the adjacent St Lawrence Estuary on the other side of a shallow sill. The hypothesis that has been put forward to explain this phenomenon is related to the advection of near surface estuarine waters, at times very rich in particulate matter, over the entrance sill into the deeper waters of the fjord. Mixing processes associated with the development of a density flow, the presence of a hydraulic jump or other mechanisms are assumed to be responsible for the common occurrence of lower density subsurface water within the basin as compared to that penetrating over the sill.The exchange processes between the estuary and the fjord are described and an estimate made of the estuarine water volume that penetrates into the lower layer of the fjord over a semidiurnal tide cycle. From these calculations, the replacement time for the outer basin was estimated to range between one and four days. The biological characteristics of this water were used to establish a budget for particulate matter exchange which showed, in early August, a typical net input of ? 188 t of particulate organic carbon into the deep waters of the fjord over one tide cycle.     

松花江三姓二期整治工程中的GPS工程测量

三姓浅滩是黑龙江水系最著名的浅滩。全文侧重从GPS的优越性方面介绍其在三姓二期整治中水域工程测量中的应用。     

Development of passive sampling devices for bioavailable contaminants of current and emerging concern: Waitemata Harbour case study

Bioavailable contaminant concentrations are an important component in assessing environmental effects as they directly affect ecosystem health. Shellfish contaminant monitoring programmes have traditionally filled this requirement but are being phased out in some jurisdictions. Passive sampling devices (PSDs) have the potential to replace shellfish monitoring; however, there are still knowledge gaps to address before this can occur. This study assessed the suitability of three different PSDs in providing the required information to replace shellfish monitoring. PSDs were deployed at three historic mussel monitoring sites with different levels of urban influence in the Waitemata Harbour, Auckland, New Zealand. Contaminants of interest were urban heavy metals, plus current and emerging organic contaminants. PSDs provided extremely low detection limits and, for some contaminants, very strong correlations to shellfish. PSDs can currently complement shellfish in monitoring, but it is premature to make conclusions as to the suitability of PSDs in replacing shellfish monitoring until more information is available.     

Benthic studies in upper Buzzards Bay,Massachusetts: 2011/12 as compared to 1955

Precise biodiversity mapping that can be compared over decades would greatly inform the discussion of climate change impacts on species richness and shifts in dominant benthic species. Buzzards Bay, Massachusetts, USA, has a long history of field studies documenting benthic community structure. This bioassessment compares 1955 benthic infaunal sampling results with 2011/2012 samples to determine whether there has been a compositional change. I also compared structural components including grain size and near‐bottom temperatures. In addition, benthic temperature rise and fall was logged at 15‐min intervals from May to October of consecutive years. There was an observed difference in the benthic compositional structure, substrate and temperature between the 1955 and 2011/2012 station conditions. The 1955 identification of Buzzards Bay as being nutrient poor and having a reported 20.5 °C benthic temperature maximum has changed. Coastal development has brought increased nutrient inputs, and the 2012 bottom temperature maximum was at least 4 °C greater. These conditions contribute to shifts in benthic species dominance, and the substrate itself has been transformed to shell reefs at the stations where the gastropod Crepidula fornicata proliferated.     

基于河口潮间带底栖微藻群落水平的环境质量状态评价

The feasibility of community-based bioassessment of environmental quality status was studied using microphytobenthos(MPB) in estuarine intertidal ecosystems.The sediment samples of MPB were collected monthly during a 1-year cycle(September 2006–August 2007) at four sampling stations in the Nakdong River Estuary,Korea.Environmental variables,such as salinity,radiation,grain size of sediment,Si(OH)_4(Si),nitrate(NO_3~–),nitrite(NO_2~–),ammonium(NH_4~+) and phosphates(PO_4~(3–)),were measured synchronously for comparison with biotic parameters.The statistical analyses were carried out for assessment the relationship between biotic and environmental parameters.The results showed that:(1) the MPB community structures were significant differences among four sampling stations;(2) spatial variation in the MPB communities were significantly correlated with environmental variables,especially the nutrient NH_4+ in combination with salinity and grain size;(3) three species(Navicula lacustris,Pleurosigma anglulatum and Fragilaria sp.1) were significantly correlated with nutrients and/or Si;and(4) the species richness and diversity were significantly correlated with the grain size.It is suggested that MPB communities may be used as a potentially robust bioindicator for assessing environmental quality status in estuarine intertidal ecosystems.     

Stable isotope analysis of consumer food webs indicates ecosystem recovery following prolonged drought in a subtropical estuarine lake

Assessing changes in food-web structure provides a useful monitoring tool for gauging the resilience of ecosystems in the face of climatic impacts. We consider the ecological resilience of a large estuarine lake (St Lucia Estuary, South Africa) in the wake of an extreme climatic event (prolonged drought). Using carbon and nitrogen stable isotopes, food-web structure was assessed at five sites across the estuary during the winter and spring of 2013. Sampling occurred approximately three years after heavy rains flooded the system and returned it to a relatively diluted state following an almost decade-long drought that decimated food webs in the upper parts of the estuary due to hypersalinity effects. Comparisons of niche width and variance of consumer food webs among sites revealed a general homogenisation of food webs across the entire system, contrasting with the spatial differentiation of food webs documented during the drought phase. Our results indicate that the estuary is able to maintain ecological resilience at the whole-system level in the face of an extreme drought. This is likely facilitated by source pools of species residing in the relatively stable lower estuary, which are able to rapidly recolonise areas denuded by drought in the upper estuary.     

Ingestion rates and grazing impact of the brackwater mussel Brachidontes virgiliae in Lake St Lucia,iSimangaliso Wetland Park,South Africa

Bivalves feed on a combination of phytoplankton and zooplankton and have the potential to impact considerably the planktonic biomass, especially when they occur in high densities, such as in oyster and mussel beds. The brackwater mussel Brachidontes virgiliae is numerically dominant during wet phases within Africa’s largest estuarine lake, St Lucia, in the iSimangaliso Wetland Park on the east coast of South Africa. The ingestion rates and potential grazing impact of this small mussel (maximum shell length = 2.5 cm) were estimated for both the wet and dry seasons using an in situ gut fluorescence technique. Ingestion rates were higher during the wet season (5.78 µg pigment ind.^?1 d^?1) than during the dry season (4.44 µg pigment ind.^?1 d^?1). This might be explained by the increased water temperature and food availability during the wet season. Because of the patchy distribution of mussel populations, there could be higher localised grazing impact near mussel aggregations. Results showed a potential grazing impact of up to 20 times the available phytoplankton biomass at specific sites. These high grazing impacts have the potential to deplete phytoplankton stocks in the lake, especially during wet phases in the northern reaches, where mussel densities are highest. This needs to be factored into ecological models of Lake St Lucia, because the system might function differently during increased flood events.     

Seasonal Variability in Circulation Pattern and Residence Time of Suo-Nada

The development and evolution of the persistent counterclockwise circulation in Suo-Nada have been studied in detail using a three-dimensional numerical model. The realistic circulation has been reproduced from the monthly climatological fields of salinity, temperature along the open boundary, wind, heat flux and buoyancy input from twenty-two major rivers surrounding the basin. The seasonal variation of fresh-water discharge from the rivers proved to be the most important forcing mechanism driving the circulation. The expansion and contraction of coastal low salinity water well corresponded with the development of counterclockwise circulation from spring to summer and dissipation from autumn to winter. The circulation was found to be vertically homogenous and quasi-barotropic. However, confined along the coastal zone is an estuarine flow (i.e., oppositely directed currents in the upper and lower layers) whose horizontal dimension conforms to the period of maximum buoyancy flux from the rivers. This indicates that the flow pattern in Suo-Nada can be separated into two distinct regions where the relative dominance of estuarine circulation plays a significant role. Furthermore, the monthly water exchange capacity for autonomous purification of the basin has been evaluated from the average residence time of conservative material based on the calculated current field. It is demonstrated that the kinetic energy of the basin is directly responsible in promoting water exchange in Suo-Nada. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temporal changes of accretion rates on an estuarine salt marsh during the late Holocene — Reflection of local sea level changes? The Wadden Sea, Denmark

The temporal variability of estuarine sedimentation has been investigated in the northernmost part of the Wadden Sea (Denmark), using an estuarine sedimentary sequence at Ho Havn. The sedimentary sequence appears to have been deposited within the last ∼ 2000 yr based on detailed luminescence dating of the estuarine mud, whose ages range between 225 ± 40 and 2050 ± 300 yr. The age-depth profile reveals that the sedimentation rate has varied considerably in the past. Estuarine sedimentation was very rapid ∼ 1400 yr ago; the ages over almost 1 m of sediment are indistinguishable. After this accretion rate of ∼ 9 mm a^− 1, the rate dropped abruptly to ∼ 0.3 mm a^− 1 some time between 1340 and 970 yr ago. This slow rate of accretion continued until ∼ 350 yr ago, when it accelerated to ∼ 1.3 mm a^− 1. These abrupt changes in the accretion rate are possibly related to local sea level fluctuations, thus the period with low accretion rate most probably reflects a situation with a stable or decreasing relative sea level. The rapid deposition of ∼ 0.9 m of sediment within about one century some 1400 yr ago shows that large amounts of fine-grained sediment were available for deposition in the region at that time, and an increasing relative sea level was most probably responsible for the creation of the accommodation space for sedimentation. Recent studies on mudflats and salt marshes in the region also tend to show high accretion rates, indicating that the coastal lagoons could be less vulnerable and threatened by a future sea level rise than generally believed.