Netherlands Journal of Sea Research最新文献

A novel water sampling device which enables vertical profiles of water samples to be obtained within the benthic boundary layer in shelf sea waters is described. A maximum of ten samples spread over 2 m immediately above the seabed can be obtained on each deployment. The design of the sample bottles minimizes disturbances to particle aggregates and positive displacement sampling ensures that the samples are representative of the environment. Suspended-solids profiles sampled in the benthic boundary layer over 15-hour period at a station in the English Channel are presented to demonstrate the utility of the system.

Mercury speciation was determined in samples of surface waters of the North Sea. Seventeen stations were visited including coastal waters off the Thames, Humber, Scheldt, Rhine, Ems, Weser and Elbe estuaries. Mercury concentrations measured in the present study are significantly lower than previous estimates for the North Sea, but they are similar to concentrations recently determined in other coastal environments. Concentrations of total dissolved mercury ranged from 0.9 to 4.8 pM with 0.4 to 1.8 pM as dissolved reactive mercury, representing on average about 30% of the total dissolved mercury. Particulate mercury constituted between 13 and 82% of the total mercury (dissolved and particulate) depending on the distribution of suspended particulate matter, with the highest proportions found near the coasts in the southern North Sea. The mercury content of the seawater particles varied between 116 and 484 ng·g⁻¹ with 6% on average as particulate monomethylmercury. A longitudinal profile was completed in the outer estuary of the Elbe river; mercury concentrations reached 16.4 pM for dissolved mercury and 595 pM for particulate mercury in the low salinity region, indicating that the Elbe estuary is contaminated with mercury. This is similar to the contamination measured recently in the Scheldt estuary. The net input of mercury from the Elbe river to the North Sea was estimated at 0.43 kmol·a⁻¹ for dissolved mercury and 4.24 kmol·a⁻¹ for particulate mercury. The mercury concentrations measured in the Elbe estuary are used to estimate the total mercury input from freshwaters to the North Sea. It is comparable to direct atmospheric inputs to the North Sea.

Long-term fluctuations and trends in the rate of primary production were observed in the middle Adriatic Sea. Variability in the production rate was caused by oceanographic and meteorological factors affecting the advection of the Mediterranean waters in the Adriatic on long-term scale.

Particular attention is given to a sudden and prolonged increase in primary production that started in 1978. This increase is related to the enhanced advection of the Mediterranean waters (richer in nutrients) into the Adriatic. Increased advection of Mediterranean waters to the Adriatic can be attributed to global climatic changes.

Geostatistical methodology was used to analyse the structure and describe the spatial patterns of North Sea herring (Clupea harengus L.), using data from the 1992 ICES (Division IVa) acoustic survey. Three different scales of spatial structures were identified: an unresolved small-scale variability, which accounted for 48% of the total variance, and two structure components, the first being a meso-scale of ≈9 nmi (nautical miles) (≈30%) and the second a large-scale of ≈17 nmi (22%). Geostatistical analysis permitted the determination of spatial density gradients as well as patch sizes (range from 9 to 17 nmi). The use of the truncated data and the robust variogram on the raw data provided additional information for the structure. The utilization of this information in the variographic analysis resulted in better estimations. The best unbiased predictor was used to objectively map the herring population distribution by kriging. The kriging estimates were better with interpolation of a large number of points. Herring tended to aggregate mainly in meso-scale patches with a diameter of 9 nmi and to a lesser extent in large-scale patches of 17 nmi diameter. Environmental factors (depth, salinity and temperature) partly explained the spatial distribution of herring, despite the absence of a trend in the variogram structure. The study demonstrates the existence of spatial correlation and an objective way of optimal mapping of the population. Geostatistics provided additional information on herring spatial organization which is important to understand the behaviour of the species and to study its relationship with the environment.

Closed-circulation, water jacket-insulated laboratory basins (benthic mesocosms) of 1 m² surface area preserved the abundance and species composition of the principal benthic macrofauna of the 350-m-deep Laurentian Trough for periods exceeding a year. Abundance of meiofauna, and bacterial numbers and activity were also sustained. Although the overlying water was permitted to equilibrate with the atmosphere, oxygen penetration depths in the sediment stabilized at about twice the thickness of the in situ aerobic layer, while whole-sediment respiration rates remained within the range observed for freshly obtained sediment cores. Build-up of metabolic by-products in the overlying water was controlled by bi-monthly replacement of a third of the bottom water. The study demonstrated that close observation of organism behaviour and biogeochemical processes within deep coastal sediments can be carried out in laboratory mesocosms.