Immigration and settlement pattern of Paralichthys dentatus and P. lethostigma in an estuarine nursery ground,North Carolina,U.S.A.

Immigration and settlement pattern of 0-group summer flounder (Paralichthys dentatus) and southern flounder (P. lethostigma) in an estuarine nursery are described. Flounders entering the estuary were transforming larvae. Despite their sympatric occurrence during larval immigration, the two species were found concentrated in different habitats. Sampling along transects within the estuary indicated that newly settled southern flounder were concentrated on tidal flats towards the head of the estuary while greatest numbers of summer flounder were captured on tidal flats in the middle reach of the system. Logistic regression analysis of presence/absence data indicated that salinity affected the distribution of southern flounder while substrate type was an important factor affecting the distribution of summer flounder. Numbers of both species on tidal flats declined in the spring, southern flounder appeared to move upstream to oligohaline riverine habitat and summer flounder appeared to move to high salinity salt marsh habitat. The segregated distribution apparent in juveniles is largely established during the immigration period. Differences in settling behaviour and subsequent movement and/or differential mortality occurring during settlement, appear important in determining the observed distribution of juvenile summer and southern flounder.     

Evaluation of seasonal nutrient dynamics in the oosterschelde (SW Netherlands)

A large set of data obtained from several monitoring programmes covering more than 3 years of registration of environmental parameters in the Oosterschelde estuary were used to evaluate seasonal trends in dissolved nutritive compounds. The deviations from conservative behaviour were calculated. It is concluded that specific estuarine processes rule the distributions of nitrogen compounds within the estuary and that these processes are largely dependent on the input of organic material from the sea. Levels of silica are almost completely governed by fresh water discharges throughout the year, except for the Keeten-Krammer area in spring. Phosphorus concentrations are steady throughout the year with minor influences of exchange with sediment in spring and summer and an influence of the North Sea in spring.     

Daily fecundity of Temora longicornis (Copepoda calanoida) in the Oosterschelde estuary (SW Netherlands)

Daily fecundity of Temora longicornis in the Oosterschelde was estimated in 1986 and 1987 after 24 h incubation of female copepods collected in the estuary. Daily egg production fluctuated between 3 and 25 eggs per female.Egg production rates increased with temperature in the range of 3 to 15°C when algal food was present in excess. Limiting food conditions were found at the end of the phytoplankton spring bloom and occasionally in summer at concentrations of ⩽2 μg chlorophyll·dm⁻³. When chlorophyll maxima were found, predominantly consisting of Phaeocystis, daily fecundity of Temora was suppressed. It could increase, however, in Phaeocystis blooms mixed with diatoms (Rhizosolenia delicatula).Standing stocks of eggs in the springs of 1986 and 1987 were calculated on the basis of the established temperature/fecundity relation and compared with observed numbers, both in the years 1986 and 1987 (estuary provided with a storm-surge barrier in the mouth) and in the years 1983 and 1984 (open estuary).Smaller differences between observed and calculated egg numbers in 1986 and 1987 could be ascribed to possible errors in calculated egg development time and to the different age structure of females in the course of time.Much larger differences were found between the years 1986–1987 and 1983–1984. These are discussed in relation to the following phenomena: sinking of eggs, cannibalism, predation, food quantity and availability, density-dependent effects, hydrodynamical changes of the estuary. Arguments are given for density-dependent factors being responsible for the strongly reduced egg numbers in 1984.     

The distribution of suspended matter in the Dutch coastal zone

Results are presented of suspended matter observations taken at bi-weekly intervals during the period 1975–1983, in a strip 70 km wide along the Dutch coast. The average distribution showed a (weak) minimum zone located north of Noordwijk at a distance of about 30 km from and parallel to the Dutch coast, between the salinity maximum and the coast. Variability was large between different years, seasons and individual cruises. A clear seasonal cycle emerged from the observed suspended-matter patterns: in winter a pronounced minimum existed, while in summer generally a monotonically decreasing concentration was measured, to open-sea values much lower than in winter. This seasonal cycle may be explained by a combination of variation in wind, river discharge and the activity of suspended-matter sources. The Flemish Banks and Channel waters are the main sources supplying suspended matter to the Dutch coastal area. Especially the varying transport through the Strait of Dover, large in winter, small in summer, determines the seasonal variation in the total amount of suspended matter. The existence of a localized turbidity minimum is tied to relatively large discharges from the Rhine and associated steep salinity gradients, also occurring mainly in winter and early spring. A simple model of cross-shore density-driven circulation shows the possible influence of the strong salinity gradients on the sedimentation of suspended matter. Particles with a settling rate comparable to the vertical velocity component of the circulation are forced to move offshore until they reach an area they sink out of the surface layer. The strength of this circulation is determined by the cross-shore density gradient due to the inflow of fresh water from the Rhine-Meuse estuary.     

Dynamics of dissolved silicium and nitrogen-nutrients at low temperature in the Ems-dollard estuary

With salinity and natural fluorescence as conservative tracers to discriminate between fresh water contributions from two different fresh water sources (the river Ems and the river Westerwoldse Aa), deviations from conservative behaviour for silicate, ammonia and nitrate during winter conditions (4–6°C) are reported and discussed. For silicate a net removal from overlying water during transport through the estuary of 15% was found. Nitrification in overlying water (260 μmol·m⁻³·h⁻¹) was the only important process in nitrogen cycling; sediment-water exchange was of no importance during this period.     

A nitrogen budget of the Scheldt hydrographical basin

A nitrogen budget including nitrite, nitrate, ammonium and organic nitrogen is presented for the western Scheldt estuary.The nitrogen entering the estuarine zone is evaluated from measurements of NO₂⁻, NO₃⁻, NH₄⁺ and organic nitrogen concentration at Rupelmonde. These results are part of 10 years survey (1973–1983) of water quality in the Scheldt estuary.The origin of this load in the Scheldt estuary is further investigated by the evaluation of the contribution of domestic, industrial sewages, agriculture and breeding in the nitrogenous load of the upper Scheldt drainage basin. Domestic load is evaluated from the watershed population. Industrial sewages are quantified by use of the evaluation of specific nitrogen spoilage by the various industries as a function of their number of workers. Nitrogen leaching of agricultural soils has been measured by determining the nitrogen concentration in small river draining agricultural areas, upstream any domestic or industrial discharges. Cattle-farming wastes are for the biggest part spread on soils. A fraction however is directly rejected in rivers.Denitrification in the tributaries of the Scheldt is important in the control of nitrate entering the estuarine zone. Its evaluation will be presented.In the estuarine part of the Scheldt (Rupelmonde-Vlissingen), the nitrogenous load is important due to the upstream load and to the sewages of the Antwerp district. These sewages (domestic, industrial, agricultural) have been evaluated as described above for the upper Scheldt basin.The important load carried at that moment by the Scheldt gives rise to an important bacterial activity which results in anaerobic conditions. Denitrification then takes place. This process reduces NO₃⁻ to N₂O and N₂, i.e. eliminates a substantial fraction of the nitrate load in the Scheldt. The importance of this process will be quantified both by measurement of in situ denitrifying activities and by analysis of NO₂⁻ + NO₃⁻ profiles in the river.When reoxidation of the water occurs by reaeration and mixing with well aerated seawater, the total mineral nitrogen has a conservative behaviour as indicated by the (straight) linear relationships between Σ N_min and chlorinity, in spite of the primary production, bacterial activities and sediment influence. This conservative behaviour of Σ N_min is used in this work for evaluating N_min exportation by the Scheldt to the North Sea. The straight line relation extrapolated at low salinity gives a “fictive nitrogen concentration” in fresh water. The product of this “fictive concentration” and the upstream discharge gives an accurate evaluation of the exportation flux of mineral nitrogen to the sea.This work shows the predominant role of denitrification in tributaries of the drainage basin and in the estuary itself as a nitrogen sink which reduces the amount of nitrogen exported by the Scheldt to the North Sea.It is suggested that the pursuit of the present waste water treatment policy, only based on the elimination of the organic load without any tertiary treatment, could result in increasing the nitrogen output into the Belgian-Dutch coastal zones by a factor 2–3.     

Nutrient dynamics in cumberland basin - chignecto bay,a turbid macrotidal estuary in the bay of fundy,canada

The Bay of Fundy is a turbid, high-energy, macrotidal estuary on Canada's east coast. An extensive ecological study of this area has been conducted over the past 5 years. The concentration of nutrients was measured in numerous compartments of this ecosystem on different scales of time and space. While nutrient concentrations in the water column never approached limiting values, concentrations were a complex function of numerous physical and environmental factors. The effects of high concentrations of suspended sediments and the high energy input from the large tidal range on the dynamics of nutrients in this estuary are discussed in detail in an attempt to evaluate sources and sinks of nutrients in the estuary. Due to lack of information on residual water fluxes, estimations of the magnitude and direction of nutrient fluxes in the estuary are only qualitative.     

The effect of deficit irrigation on crop yield and vegetative development of Olea europaea L. (cvs. Frantoio and Leccino)

Water is the most important environmental constrain determining plant growth and fruit yield of olive tree plantations. Although olive trees are resilient to water-limited conditions of Mediterranean-type agroecosystems, crop yields may respond positively to any additional water up to a limit. A field experiment on olive trees was carried out with the aim to present guidelines for efficient management of irrigation scheduling, based on the relationship between plant water status and optimum fruit yield. These relationships were monitored during 2 years by analysing the influence of deficit irrigation strategies on vegetative development and yield parameters on mature modern-trained olive trees of cvs. Frantoio and Leccino. Treatments were: a non-irrigated control (rainfed) and three treatments that received seasonal water amount equivalent to 33, 66 and 100% of ET_C in the period August–September, from the beginning of pit hardening to early fruit veraison. Atmospheric evaporative demand and soil moisture conditions were regularly monitored. Seasonal dynamics of plant water relations varied among treatments, and responded to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. All measurements of tree water status were highly correlated with one another. Differences in yield between treatments indicated that water availability might have affected fruit weight before flowering or during the early stages of fruit growth rather than later in summer season. Results concerning crop yield revealed that irrigation of olive trees from the beginning of pit hardening could be recommended, at least in the experimental conditions of this study and in view of differences between genotypes.     

The effect of deficit irrigation on crop yield and vegetative development of Olea europaea L. (cvs. Frantoio and Leccino)

Water is the most important environmental constrain determining plant growth and fruit yield of olive tree plantations. Although olive trees are resilient to water-limited conditions of Mediterranean-type agroecosystems, crop yields may respond positively to any additional water up to a limit. A field experiment on olive trees was carried out with the aim to present guidelines for efficient management of irrigation scheduling, based on the relationship between plant water status and optimum fruit yield. These relationships were monitored during 2 years by analysing the influence of deficit irrigation strategies on vegetative development and yield parameters on mature modern-trained olive trees of cvs. Frantoio and Leccino. Treatments were: a non-irrigated control (rainfed) and three treatments that received seasonal water amount equivalent to 33, 66 and 100% of ET_C in the period August–September, from the beginning of pit hardening to early fruit veraison. Atmospheric evaporative demand and soil moisture conditions were regularly monitored. Seasonal dynamics of plant water relations varied among treatments, and responded to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. All measurements of tree water status were highly correlated with one another. Differences in yield between treatments indicated that water availability might have affected fruit weight before flowering or during the early stages of fruit growth rather than later in summer season. Results concerning crop yield revealed that irrigation of olive trees from the beginning of pit hardening could be recommended, at least in the experimental conditions of this study and in view of differences between genotypes.     

短期NaCl与Na2CO3胁迫对紫花苜蓿种子萌发可恢复性的影响

探讨短期钠盐胁迫对紫花苜蓿种子萌发特性的影响。试验共设盐分类型、盐分浓度、温度及胁迫时间等4个因子,测定发芽率（势）等指标。结果表明：短期钠盐胁迫解除后,30℃发芽率最低,但温度无持续效应,前期温度仅影响前3天发芽,而不影响后期发芽;Na2CO3具有持久的抑制效应,各个测定指标均低于NaCl;随盐分浓度提高,发芽率逐渐降低,尽管250 mM显著抑制前3天发芽,但第5天该处理有显著恢复性萌发,表明盐分浓度为暂时性抑制效应;胁迫时间与盐分浓度效应类似,随胁迫时间延长,发芽率逐渐下降,30 h抑制前3天萌发,但胁迫解除后有较高的恢复萌发。     

Environmental Interactions between Different Tree Species and Mung Bean (Vigna radiata (L.) Wilczek) in Hedgerow Intercropping Systems in Sri Lanka

Annual crops grown in association with contour hedgerows often show yield reductions. This paper quantifies the variation of above- and below-ground environmental factors in hedgerow intercrops involving six different tree species ( Calliandra calothyrus , Desmodium ransonii , Flemingia c ongesta , Gliricidia sepium , Cassia spectabilis and Tithonia diversifolia ) and thereby shows the effects of tree hedges on mung bean ( Vigna radiata ). Compared to a sole crop of mung bean, most hedgerow intercrops removed greater soil nitrogen, whereas all removed lower soil phosphorus. Mung bean closer to the hedgerows had lower N and P, indicating competitive capture of nutrients by hedges. Most hedgerow intercrops had greater top-soil water because of their shading effect, especially near hedgerows. However, greater absorption by tree root systems decreased subsoil water near hedgerows late in the season. Soil temperature was lower in most hedgerow intercrops than in the control and increased with increasing distance from hedges. During initial stages of mung bean growth, radiation interception of intercrops was greater than that of the control, especially closer to hedgerows. However, after the first month, radiation interception of the sole crop was either equal to or greater than that of hedgerow intercrops. There was significant variation between tree species in all these environmental factors. Gliricidia , which allowed greater mung bean yields, also allowed greater nutrient capture by mung bean, greater top-soil water availability, lower extraction of subsoil water and lower soil temperatures.     

Primary production of phytoplankton in a turbid coastal plain estuary,the Westerschelde (The Netherlands)

An extensive survey was carried out in the Westerschelde estuary in 1989 to estimate phytoplankton primary productivity. High nutrient concentrations year round and very high turbidity resulted in light-limited growth of phytoplankton. This was reflected in a conservative behaviour of silicate and phosphate. The same was true for total inorganic nitrogen. However, in the inner part of the estuary nitrification took place. The calculated annual primary production was 200 – 300 gC·m⁻² at the range 29-20 salinity, 100–150 gC·m⁻² at 18-10 salinity and increased sharply to 900 gC·m⁻² at 2.5 salinity due to freshwater populations. In the inner part of the estuary the vertical mixing zone was frequently larger than 5 times the euphotic zone. The high rates of primary production we measured contrast with generally expected values. This corroborates Grobbelaar's hypothesis that the critical depth can be seriously underestimated. Phytoplankton copes with the turbid conditions by adjusting light-utilization efficiencies.     

Environmental characteristics and distribution of macrobenthos in a mudflat of the west coast of Korea (Yellow Sea)

The spatio-temporal changes of environmental factors and the distribution patterns of macrobenthos were investigated on an intertidal mudflat near Panweol on the west coast of Korea. Temperatures of the surface sediments and salinities of the intertitial water were highest in summer and lowest in winter, while water content of the sediment was lowest in summer and highest in winter. Hourly variations of sediment temperature, water content and interstitial salinity during the daytime depended largely upon both the timing of ebb tide and daylight intensity.Temperature, water content and interstitial salinity showed a marked variation with sediment depth. Temperatures decreased sharply from the surface to 10 or 15 cm depth, and below this depth they were nearly constant, except in summer. Water content and interstitial salinity underwent a rapid decline in this upper layer and began to rise from this depth. From the high tide mark toward the main tidal channel, water content increased but salinity decreased. The sand fraction increased with the decrease of clay content toward the main tidal channel. This tidal flat could be divided into two zones: the “upper intertidal zone” and the “lower intertidal zone”, based on the spatial differences of the water content, interstitial salinity and grain-size composition in the surface sediment.There were three distinct zones of macrobenthos. The upper intertidal zone was dominated by burrowing deposit feeders, such as Ilyoplax dentimerosa, Helice tridens sheni, Cleistostoma dilatatum and Perinereis vancaurica tetradentata. The middle intertidal zone was characterized by other burrowing deposit feeders, such as Ilyoplax pingi, Macrophthalmus japonicus and Periserrula leucophryna. And the lower intertidal zone was dominated by suspension feeders represented by Laonome tridentata and Potamocorbula amurensis. Each zone was named after these characteristic species.Although the species composition of the upper intertidal community was different from that of the middle intertidal, the way of living and the feeding behaviour of the species occurring in these two zones were very similar. But the lower intertidal zone showed a characteristic community structure differing not only in species composition but also in ways of living and feeding of the species. Some sets of environmental factors are considered to explain the zonation. Water content of the sediment and interstitial salinity will be the main factors causing the observed zonation.     

Flocculation and de-flocculation of suspended matter in estuaries

Flocculation and de-flocculation have been observed in estuaries and the processes involved are discussed. Salt flocculation plays a minor role, if any. Flocs are mainly formed by a combination of two groups of processes: those bringing particles together, and those keeping them together. The first group is related to the flow conditions in the water and to organisms that clog particles into faeces or pseudofaeces or attach them to mucus. The second is related to the formation of sticky organic matter by a variety of organisms. Two main types of flocs have been observed: microflocs with a diameter up to 125 μm, and macroflocs with a maximum size of 3–4 mm. Microflocs consist of mineral particles and organic matter. Their formation is strongly related to the origin of the organic matter, to the organisms producing it, and to conditions of (temporary) deposition and resuspension. Mucopolysaccharides, produced by bacteria, algae and higher plants and mobilized from the suspended matter at low salinity, are important in glueing particles together. The microflocs, together with single mineral particles, are the basic building units of macroflocs. Macroflocs are fragile and formed in the water under conditions of viscous flow. Their maximum size is determined by turbulent shear, the size of the smallest turbulent whirls on the Kolmogorov scale being of the same order as the maximum floc size. They are easily destroyed during sampling. In estuaries the microflocs of fluvial origin are broken up by organisms consuming the organic matter in the microflocs, and reflocculated into new microflocs with newly formed organic matter of estuarine origin. The size of the microflocs, as seen under a microscope or determined by size analysis, is likely to be determined mainly by the binding strength of the organic matter in relation to the total mass of the floc and the physical disturbance produced during sampling and size analysis.     

Mixing and flushing of tidal embayments in the western Dutch Wadden Sea part I: Distribution of salinity and calculation of mixing time scales

The distribution of salinity in the western Dutch Wadden Sea is described, mainly on the basis of surveys carried out during 1970 to 1974. Relations are discussed between the salinity distribution and relevant environmental factors such as: fresh water discharge, salinity of the North Sea, the tide, the windfield and the morphology of the area. Flushing time scales of 15 and 31 tidal periods were obtained for fresh water originating from the main sluicing gates near Den Oever and Kornwerderzand, respectively Stationary salinity distributions were used for the calculation of exchange coefficients between compartments of a box model of the area. By means of the box model a series of time scale relevant to the flushing of the area has been calculated and their areal distribution is shown. Distinction has been made between ages and transit times of water originating either from one of the two tidal inlets (sea water) or from one of the two sluicing gates (fresh water). Of the former, the ages in the basin (11.3 and 12.3 T) exceed the transit times (2.7 and 3.0 T) whereas the opposite is found for fresh water (ages 10.6 and 19.8 T, transit times 14.5 and 29.1 T). Turn-over times of the main tidal basins were also calculated, the result being 13.7 T for the Marsdiep basin and 9.0 T for the Vlie basin.     

Behaviour of PCB,pentachlorobenzene, hexachlorobenzene, α-HCH, γ-HCH, β-HCH,dieldrin, endrin and p,p′-DDD in the rhinemeuse estuary and the adjacent coastal area

Organochlorines (pentachlorobenzene, hexachlorobenzene, PCB, α-HCH, γ-HCH, β-HCH, dieldrin, endrin, p,p′-DDD) have been quantitated in water, seston, bottom sediment and interstitial water in samples from the fresh water and estuarine region of the Rhine-Meuse system obtained in 1974, 1976 and 1979.In the estuarine region, the amounts in solution are smaller than in suspension for pentachlorobenzen, hexachlorobenzene and PCB, dissolved concentrations dominating for the hexachlorocyclohexane isomers. In river water, PCB is roughly equally distributed over dissolved and suspended forms while pentachlorobenzene, hexachlorobenzene and the HCHs dominate in solution. Dissolved dieldrin, endrin and p,p′-DDD were below the limits of detection in most river water samples. However dissolved dieldrin and endrin are produced in the upper part of the estuary resulting from local pollution. During estuarine mixing, dissolved concentrations of all compounds were found to be linearly related to salinity (1974 data).Concentration data in seston and sediment in the estuarine region can be explained in terms of mixing of fluviatile and marine derived particles. It is suggested that in particular PCBs are associated specifically with finer particles.Dissolved concentrations in the central part of the Southern Bight are at the very lower end of the range of values reported for various coastal and open ocean areas. Concentrations detected in large volume samples are: penta- and hexachlorobenzene 0.1 ng·1⁻¹; PCB (Aroclor 1254) 0.7 ng·1⁻¹; α-HCH 0.9 ng·1⁻¹; γ-HCH 1.0 ng·1⁻¹; β-HCH 0.04 ng·1⁻¹; dieldrin 0.1 ng·1⁻¹ and endrin and p,p′-DDD < 0.01 ng·1⁻¹.Temperature programmed GLC techniques demonstrate the contribution of lower chlorinated PCB components in the central part of the Bight. This has not been observed in other reports. Adoption of a PCB formulation with a lower degree of chlorination than the usual Aroclor 1254 as the standard for quantitation results in a significant shift of the PCB concentrations from 0.7 (Aroclor 1254 or the equivalent Clophen A50) to 4.1 ng·1⁻¹ (Clophen A30). It is suggested that the lower chlorinated fraction is derived from atmospheric input. River water could not be excluded as a source however.Concentrations in the coastal area are higher than in the central part of the Southern Bight. Analyses of large volume water samples in 1979 are consistent with continuing conservative behaviour in the coastal area. A large fraction of the organochlorine load of the Dutch Wadden Sea is derived from the Rhine-Meuse estuary.     

Breeding for yield, in mixtures of common beans (Phaseolus vulgaris L.) and maize (Zea mays L.)

Summary Despite the growing industrialization, technification and transformation that is happening in the agriculture around the world, and despite that agricultural research has always concentrated its effort on sole crops, multiple cropping systems have historically been important for common bean production in tropical countries. The reasons for this fact, are economical and social, as well as biological. Bean breeders have always been questioned on their work, because the development of new varieties is usually done in sole crop, but the varieties are grown in either systems. This paper addresses a set of questions that are usually presented to the breeders, in light of the evidence obtained from many trials conducted in Brazil and in the U.S.A.: Will the genotypes bred for sole crop conditions, perform well when grown in intercrop; How different should a genotype be, for cultivation in intercropping compared to genotypes developed for sole crop conditions; Is there a need for special breeding programs for intercropping and How could a breeding program focus the question of multiple (associated) cropping?     

Effects of Salinity and Soil–Drying on Radiation Use Efficiency,Water Productivity and Yield of Quinoa (Chenopodium quinoa Willd.)

Drought and salinity reduce crop productivity especially in arid and semi‐arid regions, and finding a crop which produces yield under these adverse conditions is therefore very important. Quinoa (Chenopodium quinoa Willd.) is such a crop. Hence, a study was conducted in field lysimeters to investigate the effect of salinity and soil–drying on radiation use efficiency, yield and water productivity of quinoa. Quinoa was exposed to five salinity levels (0, 10, 20, 30 and 40 dS m^?1) of irrigation water from flower initiation onwards. During the seed‐filling phase the five salinity levels were divided between two levels of irrigation, either full irrigation (FI; 95 % of field capacity) or non‐irrigated progressive drought (PD). The intercepted photosynthetically active radiation was hardly affected by salinity (8 % decrease at 40 dS m^?1) and did not differ significantly between FI and PD. Radiation use efficiency of dry matter was similar between salinity levels and between FI and PD. In line with this, no negative effect of severe salinity and soil–drying on total dry matter could be detected. Salinity levels between 20 and 40 dS m^?1 significantly reduced the seed yield by ca. 33 % compared with 0 dS m^?1 treatment owing to a 15–30 % reduction in seed number per m², whereas the seed yield of PD was 8 % less than FI. Consequently, nitrogen harvested in seed was decreased by salinity although the total N‐uptake was increased. Both salinity and drought increased the water productivity of dry matter. Increasing salinity from 20 to 40 dS m^?1 did not further decrease the seed number per m² and seed yield, which shows that quinoa (cv. Titicaca) acclimated to saline conditions when exposed to salinity levels between 20 and 40 dS m^?1.     

Composition and distribution of dissolved fluorescent substances in the Ems-Dollart estuary

During a 24-months period (October 1978 to October 1980) fluorescence (mF1) was measured in the Ems-Dollart estuary.From the linearity of the inverse relation between fluorescence and salinity it is concluded that the fluorescence mainly originates from the rivers and behaves conservatively. During the summer, there was an increase in fluorescence at high salinity. The possible sources responsible for this increase in the outer part of the estuary are given.To establish the polymeric character of the fluorescent matter, ultrafiltration was done during 5 surveys between February and August 1980. The fraction with a M.W. smaller than 500 showed a high (39 to 76%) contribution to the total fluorescence for all dates. It was concluded that the measure of aggregation of fluorescent material can change during transport in the estuary.     

Suspended-sediment transport in the Dollard estuary

For an analysis of suspended-sediment transport in the Dollard estuary, water samples were taken and current velocities and directions measured on the tidal flats and in the channels. Measurements carried out during fair-weather conditions in summer were compared with measurements carried out during a heavy gale in winter. During the onset of the flood, high suspended-sediment concentrations occurred as a result of resuspension of the top layer of the bottom sediment. Measurements carried out in the channels pointed to sediment transport from the estuary seaward, but inward transport over the flats during fair weather apparently compensates for the outflow during ebb and storms: the result is a net deposition in the order of 1 to 2 mm (up to 8 mm) per year, as previously observed in this area.