Transport of particulate organic material between salt marsh and estuary

Summary The macrophyte production and the transport of particulate organic matter between march and adjacent estuary have been investigated for a 30 ha salt marsh along the Oosterschelde estuary, The Netherlands.The primary production of macrophytes, measured with Smalley's method, was 837–1030 g dry organic matter.m^–2.year^–1. Measurements of amounts of particulate organic matter transported through one of the main tidal creeks in the salt march resulted in a net import. On average 31% of the material brought in by the flood settled in the marsh. The majority of this material is smaller than 63 m. On the other hand large floating material is exported during storm tides, although the quantity seems to be smaller than that of the suspended material imported.The differences between various marshes with regard to export and import of organic matter are explained in terms of marsh level, primary production, turbulent diffusion, sinking and resuspension of particulate matter and biotic transformations.     

Overwintering waterfowl on Swiss lakes: how are abundance and species richness influenced by trophic status and lake morphology?

During the period 1980–1990 long-term physical, chemical and ecological studies were carried out, to study the changes induced by the building of a storm-surge barrier in the mouth of the Oosterschelde estuary and two large auxiliary compartment dams in the rear ends of the estuary. The storm-surge barrier was constructed in the mouth of Oosterschelde estuary (SW Netherlands) during the period 1979–1986. The barrier allows the tides to enter the estuary freely, and, on the other hand, the barrier guarantees safety for the human population and their properties when a stormflood threatens the area.Oosterschelde estuary is isolated from the river input, the rear ends of the ecosystem were separated from the estuary by sea-walls and the strongly decreased tidal exchange with the North Sea induced sheltered circumstances. The Oosterschelde changed from a turbid estuary into a tidal bay, and yet primary production responses appear to be robust and resilient, and the biological communities showed only quantitative shifts from the dominance of specific species assemblages to other assemblages. In many cases predicted changes in the structure of the biological communities could not be verified owing to the large natural variability mainly caused by physical factors (e.g. temperature).     

Changes in basin geomorphology after implementation of the Oosterschelde estuary project

The completion in 1986/87 of an open storm-surge barrier in the inlet and of secondary dams in the landward parts of the Oosterschelde tidal basin (SW Netherlands) has had and will continue to have a significant impact on geomorphological developments. An analysis of historic data, and of recent detailed bathymetric and morphodynamic process data, indicates that former trends have reversed. At present the Oosterschelde is a sedimentation basin with a degrading intertidal area and silting up of channels. The continuing reduction in intertidal area, the decreasing geomorphological gradients, the increasing fine sediment content of channel deposits, combined with a general reduction in hydrodynamics, imply significant ecological effects.     

Carbon flux between an estuary and the ocean: a case for outwelling

The classical outwelling hypothesis states that small coastal embayments (e.g. estuaries, wetlands) export their excess production to inshore marine waters. In line with this notion, the present study tested whether the Swartkops estuary acts as source or sink for carbon. To this end, concentrations of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and particulate organic carbon (POC) were determined hourly during the first monthly spring and neap tides over one year in the tidal waters entering and leaving the estuary. Each sampling session spanned a full tidal cycle, yielding a total of 936 concentration estimates. Carbon fluxes were calculated by integrating concentrations with water flow rates derived from a hydrodynamic model calibrated for each sampling datum. Over the year, exports to marine waters markedly exceeded imports to the estuary for all carbon species: on the basis of total spring tidal drainage area, 1083 g m^–2 of DIC, 103 g m^–2 of DOC, and 123 g m^–2 of POC left the estuary annually. Total carbon export from the estuary to the ocean amounted to 4755 tonnes, of which 83% was in the inorganic form (DIC). Thus, the bulk of carbon moving in the water column is inorganic - yet, DIC seems to be measured only rarely in most flux studies of this nature. Salt marshes cover extensive areas in this estuary and produce some carbon, particularly DOC, but productivity of the local Spartina species is low (P:B=1.1). Consequently, the bulk of carbon exported from the estuary appears to originate from the highly productive macroinvertebrate and the phytoplankton component and not from the salt marsh plants.     

Changes in the waterbird populations of the Oosterschelde (SW Netherlands) as a result of large-scale coastal engineering works

Between 1982 and 1987, the construction of a storm-surge barrier and two secondary dams in the eastern and northern parts of the Oosterschelde/Krammer-Volkerak area resulted in the loss of 33% of the 170 km² of intertidal area in the estuary. Consequences for non-breeding waterbirds were evaluated on the basis of monthly high-tide counts during five seasons before and three seasons after the construction period.In the entire Oosterschelde/Krammer-Volkerak area, numbers of wintering waders decreased but those of ducks increased. Peak numbers and total number of bird-days changed little, but the seasonal pattern shifted from a midwinter maximum to a peak in autumn.In the Oosterschelde (excluding the Krammer-Volkerak), where 17% of the tidal flats disappeared, species feeding mainly on open water remained stable or increased. Species dependent on intertidal areas for foraging (mainly waders and dabbling ducks) generally decreased. Total density of intertidal foragers decreased slightly. In most intertidal species, the Oosterschelde wintering population showed a stronger decrease, or smaller increase, than was shown during the same period by numbers in Britain and Ireland which were taken as an index of the total W-European winter populations. Changes varied considerably between species, and were correlated with their distribution within the estuary. Species concentrated in the eastern sector, where most habitat loss occurred, declined more than species with a more westerly distribution.Results indicate that intertidal foragers forced to move from the enclosed parts of the estuary were not generally able to settle into the remaining intertidal areas. Both dispersal to adjacent areas (mainly by dabbling ducks) and mortality during severe winter weather (in some wader species) may have contributed to the declines. Populations of intertidal foragers apparently were (and consequently still are) close to carrying capacity, and further changes in capacity, as foreseen from geomorphological changes still under way in the estuary, are likely to be reflected in bird populations.Numbers of waders moulting in the Oosterschelde in late summer declined strongly compared to numbers in other seasons. Increased disturbance due to recreational activities may have played a role during this time of the year.     

Transports of water,particulate and dissolved organic and inorganic matter between a salt marsh and the Ems-Dollard estuary,the Netherlands

Summary Transport processes were studied in a gully between a saltmarsh and an estuary. After storm tides, ebb currents in the gully reached high values. It is concluded that particulate matter (both obganic and inorganic) are imported into the marsh. Coarse organic debris is exported during storm tides, but this amount is low when compared with the primary production on the marsh. Exports are shown for dissolved organic carbon, ammonia, phosphate and silica, while nitrate and possibly nitrite are imported. Therefore, it seems warranted to conclude that the organic matter producedin situ and imported is mineralized in the marsh.     

The freshwater tidal wetland Liberty Island,CA was both a source and sink of inorganic and organic material to the San Francisco Estuary

It is hypothesized that perennial freshwater tidal wetland habitat exports inorganic and organic material needed to support the estuarine food web and to create favorable habitat for aquatic organisms in San Francisco Estuary. It is also hypothesized that most of the material flux in this river-dominated region is controlled by river flow. The production and export of material by Liberty Island were measured and compared using discrete monthly and continuous (15 min) measurements of a suite of inorganic and organic materials and flow between 2004 and 2005. Seasonal material flux was estimated from monthly discrete data for inorganic nutrients, suspended solids and salts, organic carbon and nitrogen and phytoplankton and zooplankton group carbon and chlorophyll a and pheophytin pigment. Estimates of material flux from monthly values were compared with measured daily material flux values for chlorophyll a concentration, salt and suspended solids obtained from continuous measurements (15 min) using YSI water quality sondes. Phytoplankton carbon produced within the wetland was estimated by in situ primary productivity. Most inorganic and organic materials were exported from the wetland on an annual basis, but the magnitude and direction varied seasonally. Dissolved inorganic nutrients such as nitrate, soluble phosphorus, total phosphorus and silica as well as total suspended solids were exported in the summer while total and dissolved organic carbon were exported in the winter. Salts like chloride and bromide were exported in the fall. Chlorophyll a and pheophytin were exported in the fall and associated with diatom and cyanobacteria carbon. Mesozooplankton carbon was dominated by calanoid copepods and exported most of the year except summer. Continuous sampling revealed high hourly and daily variation in chlorophyll a, salt and total suspended solids flux due to high frequency changes in concentration and tidal flow. In fact, tidal flow rather than river discharge was responsible for 90% or more of the material flux of the wetland. These studies indicate that freshwater tidal wetlands can be a source of inorganic and organic material but the export of material is highly variable spatially and temporally, varies most closely with tidal flow and requires high frequency measurements of both tidal flow and material concentration for accurate estimates.     

The transport of microbial biomass and suspended material in a high-marsh creek

The transport of microbial biomass and suspended material in a high-marsh creek was investigated during four 40-h tidal studies throughout the year. Although considerable differences were noted between successive tidal cycles, overall the creek was found to be an exporting system and transported a mean concentration of ATP (-33g), chlorophyll a (-66g), particulate organic carbon (-31kg), total suspended material (-344kg), and fixed suspended material (-195kg) during each tidal cycle. This net outward flux of materials was associated with a net flow of water out of creek, while the net import of aerobic, heterotrophic bacteria (43 x 10(12)) and volatile suspended material (238kg) was generally due to higher mean concentrations of these materials per unit volume of water during the flooding tide. Also the latter generally were associated with increased amounts of suspended material suggesting an association between bacteria and suspended matter.     

Tidal exchange of total mercury and methylmercury between a salt marsh and a Chesapeake Bay sub-estuary

We examined the net exchange of total mercury (THg) and methylmercury (MeHg) between a tidal marsh and its adjacent estuary over a 1-year period from August 2007 to July 2008. Our objectives were to estimate the importance of tidal salt marshes as sources and sinks of mercury within the Chesapeake Bay system, and to examine the hydrologic and biogeochemical controls on mercury fate and transport in tidal marshes. Tidal flows and water chemistry were measured at an established tidal flume at the mouth of the principal tidal creek of a 3-ha marsh section at the Smithsonian Environmental Research Center. Fluxes were estimated by combining continuous tidal flow measurement for the entire study year, with discrete, hourly, flow-weighted measurements of filterable and particulate THg and MeHg, dissolved organic carbon (DOC), and suspended particulate matter (SPM) made over 20 tidal cycles during the year. We found that the marsh was a relatively small net tidal source of MeHg, mainly during the warmer growing season. We also confirmed that the marsh was a substantial source of DOC to the adjacent estuary. DOC was a significant predictor of both filterable THg and MeHg fluxes. However, although the marsh was a source of filterable THg, it was overall a net sink for THg because of particulate trapping. The net per-area annual flux of MeHg from tidal marshes is greater than other MeHg pathways within Chesapeake Bay. The annual load of MeHg from tidal marshes into Chesapeake Bay, however, is likely small relative to fluvial fluxes and efflux from bottom sediment. This study suggests that MeHg production within the tidal marsh has greater consequences for biota inhabiting the marsh than for the efflux of MeHg from the marsh.     

Mussel culture in a changing environment: the effects of a coastal engineering project on mussel culture (Mytilus edulis L.) in the Oosterschelde estuary (SW Netherlands)

To evaluate the effects of a large scale coastal engineering project on the mussel (Mytilus edulis) bottom culture in the Oosterschelde estuary (S.W. Netherlands), mussel growth and production in the period 1980–1990 are studied in relation to food supply and the hydrodynamic conditions. Due to the construction of a storm-surge barrier and two additional dams, the risk that mussels are swept away by high current velocities decreased, resulting in an increase of the area in the Oosterschelde potentially suitable for mussel culture and in food availability now being more important as a limiting factor. For the Oosterschelde, a clear relation between mussel growth, stock sizes, and phytoplankton dynamics has been demonstrated. The meat yield of mussels landed in autumn — which is an index for growth rate — seems to be determined by the phytoplankton production in the preceding summer. In years with dense bivalve stocks, phytoplankton production and meat yields are relatively low. It is concluded that an increase of the mussel biomass cultured can result in a reduction of the primary production and, consequently, in a deterioration of the growing conditions for suspension-feeders in the estuary. This conclusion is supported by model calculations. An expansion of mussel culture in the new Oosterschelde is therefore dissuaded. Apart from primary production and stock sizes, food supply for mussels on culture lots appeared to be controlled by the horizontal advection of phytoplankton between and within the tidal channels. An observed decline in mussel landings from certain areas is attributed to the reduced mixing energy of the estuary in relation to the present distribution of the lots over the estuary. Production figures from the experimental lots, established in 1988 in the newly available areas, demonstrate that the yield of mussels can be enhanced by relaying culture lots towards the areas where the phytoplankton is produced. It is expected that by redistributing the culture lots, without expanding the biomass cultured, the carrying capacity of the Oosterschelde for mussel culture can be maintained.     

Modelling Pb and Cd dynamics in the Seine estuary

The Seine estuary (France) is currently one of the world’s most contaminated estuaries, due in particular to its high cadmium and lead content. Proper understanding of contaminant transfer, transformation and retention mechanisms throughout the estuary and up to the adjacent marine zone require a range of studies involving data collections, experiments, and modeling tool. A multivariable transport model (SiAM-3D) was used to simulate dissolved and particulate transport and it is applied to several calculation grids; a speciation model (MOCO) was used to select key species and obtain a schematic system representation. The coupled model for Cd and Pb was compared with field measurements. The complementary character of various tools (model applied to annual time scale, in situ measurements and experiments) allowed to explore and quantify various hypotheses on the high dissolved cadmium concentrations observed during low river flow. The target is to achieve a compromise between acceptable computing times and adequate result accuracy. Although particle and contaminant behaviour is globally well-reproduced by the coarse grid, calculation errors relating to bayward fluxes and stocks deposited inside the estuary were highlighted after comparison with the fine grid.     

Horizontal biosedimentary gradients across the Sado estuary,W. Portugal

The topography of the Sado estuary, the second largest of Portugal, comprises the outer estuary inside the entrance channel and the inner estuary, on the inward side of which begins the tidal mudflats. The outer estuary subtidal area covers approximately 70 km² and presents a series of longitudinal intertidal sandbanks, separating a northern and a southern channel. A benthic survey was undertaken in the outer estuary during June 1986, in which superficial sediments and macrofauna were sampled at 133 locations. The environmental variables measured in the superficial sediments were the temperature, the granulometric structure, the silt, sand and the gravel content, and the total organic matter content. The primary macrofauna biological variables studied were the species composition, abundance and biomass, calculated on wet, dry and ash-free dry weight. The granulometry and the organic content of superficial sediments agreed with the transient and the residual currents velocity field, simulated in a 2-D hydrodynamic model previously elaborated for the outer estuary. The northern channel superficial sediments showed higher silt and total organic matter content, while the model also suggested lower transient and residual velocities, water flow and shear stress in this channel. The distribution patterns of the subtidal macrofauna were separated into two main groups of species, one comprising taxa essentially settled near the estuarine mouth and the other inwards. Biological primary variables also showed consistent patterns, comparable to other Portuguese estuaries. The major subtidal benthic biotopes were obtained through classification analysis and related to the prevailing hydrophysical and sedimentary conditions in the outer estuary.     

The role of the blue mussel Mytilus edulis in the cycling of nutrients in the Oosterschelde estuary (The Netherlands)

The fluxes of particulate and dissolved material between bivalve beds and the water column in the Oosterschelde estuary have been measured in situ with a Benthic Ecosystem Tunnel. On mussel beds uptake of POC, PON and POP was observed. POC and PON fluxes showed a significant positive correlation, and the average C:N ratio of the fluxes was 9.4. There was a high release of phosphate, nitrate, ammonium and silicate from the mussel bed into the water column. The effluxes of dissolved inorganic nitrogen and phosphate showed a significant correlation, with an average N:P ratio of 16.5. A comparison of the in situ measurements with individual nutrient excretion rates showed that excretion by the mussels contributed 31–85% to the total phosphate flux from the mussel bed. Ammonium excretion by the mussels accounted for 17–94% of the ammonium flux from the mussel bed. The mussels did not excrete silicate or nitrate. Mineralization of biodeposition on the mussel bed was probably the main source of the regenerated nutrients.From the in situ observations net budgets of N, P and Si for the mussel bed were calculated. A comparison between the uptake of particulate organic N and the release of dissolved inorganic N (ammonium + nitrate) showed that little N is retained by the mussel bed, and suggested that denitrification is a minor process in the mussel bed sediment. On average, only 2/3 of the particulate organic P, taken up by the mussel bed, was recycled as phosphate. A net Si uptake was observed during phytoplankton blooms, and a net release dominated during autumn. It is concluded that mussel beds increase the mineralization rate of phytoplankton and affect nutrient ratios in the water column. A comparison of N regeneration by mussels in the central part of the Oosterschelde estuary with model estimates of total N remineralization showed that mussels play a major role in the recycling of nitrogen.     

The influence of vegetation on erosion and accretion in salt marshes of the Oosterschelde,The Netherlands

The total root strength of two plant species (Spartina anglica and Limonium vulgare) is related to salt marsh cliff erosion in the Krabbenkreek (Oosterschelde). A ranking order in cliff stability is predicted on the basis of these root strength calculations. It turns out that the S. anglica root system is more effective in reducing lateral cliff erosion than the root system of L. vulgare. Also the establishment of S. anglica by germination of seeds is studied in relation to the erosion/deposition rates at an accretion site in the Krabbenkreek. The percentage of seeds washed away depends on the mobility of the superficial sediment which increases with decreasing height above N.A.P. (Dutch Ordnance Level). Above 0.90 m + N.A.P. a germination of 20% is measured, but seedlings survive the winter period only in the zone where a patchy vegetation already exists. It is concluded that generative spread of S. anglica in the Krabbenkreek is not very likely under the present hydrodynamic conditions.Nomenclature follows Heukels & van Ooststroom (1977).Acknowledgement: The research presented herein was carried out at the Delta Department, Environmental Division of the Ministry of Transport and Public Works, Middelburg. This work forms part of the research on salt-marsh ecosystems of the Oosterschelde. Assistance with sowing and sampling was given by the Field Survey section of the Environmental Division. Analyses of root weight and root diameter were carried out by the Institute of Soil Fertility in Haren by order of the Environmental Division. I gratefully acknowledge Ir A. de Jager and J. Floris of this institute for putting a special sampling auger at my disposal. G. den Hartog, P. van Vessem and Drs P. M. Schoot of the State University of Utrecht are thanked for their assistance during the study. Special thanks are due to Drs J. M. Roels for this critical editorial review of this paper.     

Mineralization in the Ems-Dollard estuary effects on carbon and oxygen budgets

Summary The Ems estuary is a tidal system, showing typical estuaries characteristics, such as gradients of salinity and suspended matter in the water phase. The tidal amplitude is 2.5–3 m. Tidal flats cover 40% of the total area in the outer part and 75% in the innermost part of the estuary, the Dollard. In the sediment aerobic heterotrophic bacteria are concentrated in the upper 2 cm, the numbers rapidly decreasing with depth.Oxygen production and consumption rates in the sediment, and oxygen consumption in the water are measured, together with environmental parameters and numbers of aerobic heterotrophic bacteria. Using a conversion factor of 12/32, oxygen measurements are translated to organic carbon. Input of organic carbon from external sources (particulate carbon from the river Ems and the North Sea, and organic waste discharge) is calculated for the Dollard. An organic carbon budget for the Dollard, using these calculated figures from one year's measurements, showed that most of the organic carbon entering the systems, originated from external sources.Mineralization was quantitatively more important in the sediment than it was in the water phase. The calculated import and production of organic carbon in the system was larger than the calculated consumption. An explanation for this difference is probably the export of soluble organic carbon, which was not measured, to the adjoining Waddensea, which must be considerable. It was concluded that heterotrophic bacteria must play an important role in carbon fluxes in the Dollard and that studies of growth yield under in situ conditions are necessary for a better understanding of their role in the ecosystem.     

Tidal reduction and its effects on intertidal hard-substrate communities in the Oosterschelde estuary

Developments of intertidal hard-substrate communities in the Oosterschelde estuary were examined in perpendicular transects between high-water line and low-water line in the period 1982–1992. Prior to the beginning of the Oosterschelde estuary works a typology of communities was established and an overall survey of the estuary was carried out. The communities contain flora (algae) as well as fauna. Due to asphalting of dikes in 1986, much of the surface of several communities has been destroyed. The originally well developed communities with large species-richness have not returned. The small reduction in tidal amplitude due to the construction of the storm-surge barrier had a minor effect on the zonation of communities. In the upper part of the intertidal zone the boundaries of the communities moved 0.5–1.0 m downward in the transects along the dike-slopes. At an average inclination of 18° this means a vertical shift of about 15–30 cm. This reflects the reduction of the tidal amplitude: the high-water line shifted ca 22 cm downward. In a number of places sedimentation has caused a reduction in the number of smaller seaweed species in the lower eulittoral zone. At monitoring locations presence of the original communities is rather unchanged. Rare species like Pelvetia canaliculata, Actinia equina and Gelidium pusillum have been able to maintain quite successfully.     

Introductions and developments of oysters in the North Sea area: a review

To replenish the exploited native stocks ofOstrea edulis, imports from almost all European coasts have arrived in the North Sea, particularly in the Dutch Oosterschelde estuary. The American oysterCrassostrea virginica and the Portuguese oysterC. angulata have also been imported into the North Sea several times. However, only the introductions of various genetic strains of the Pacific oysterC. gigas have been of lasting success. Spat from British Columbia (Canada) was first imported to the Oosterschelde in 1964. First spatfalls in this area took place in the warm summers of 1975 and 1976. Further larval outbursts occurred in 1982 and 1989, and good settlements took place on culture plots as well as along the dikes of the Oosterschelde. Since 1977 no more cupped oysters have been imported from overseas. The population maintained itself and was able to spread in a northern direction along the Dutch North Sea coast. In Britain, hatchery-producedC. gigas were transferred to several sites, in the 1970s including the British North Sea coast. Here, occurrence in the wild seems to be rather limited up to now. Into the German Wadden Sea,C. gigas larvae and spat from a Scottish hatchery have been introduced since 1971, as were medium-sized oysters from a variety of European sources in the 1980s. Strong spatfalls on intertidal mussel beds in the northern German Wadden Sea occured in 1991 and 1994. For the introductions ofC. gigas along the west European coasts, precautionary measures to minimize unintentional transfers of associated organisms, as recommended by the ICES Code of Practice in 1994, came too late.     

Oosterschelde estuary (S.W. Netherlands): a self-sustaining ecosystem?

The Oosterschelde estuary has a special position among the Dutch North Sea estuaries. With relatively unpolluted water and high transparency it combines high biotic diversity and high primary and secondary production. Before 1970 a major part of the water of the rivers Rhine and Meuse flowed into the Oosterschelde. The building of a permeable storm-surge barrier (1986) decreased the exchange between Oosterschelde and North Sea. The construction of two additional dams (1987) reduced the very limited fresh water discharge on the estuary even further. The total effect of these changes was a decrease of the nutrient levels in the water column.The estuary is used intensively for culture of mussels and fishery of cockles. Both zoobenthos groups use together up to 60% (in the western part) of the organic food available in the Oosterschelde estuary. The storm-surge barrier resulted in reduced current velocities and increased sedimentation, accompanied by higher transparency, hence accelerating primary production. This phenomenon is counteracted by the lowered nutrient concentrations throughout the year.In the seventies a preliminary carbon budget study indicated that a substantial import of organic carbon was required to sustain the ecosystem. Later studies did not confirm this hypothesis.In the present paper three different methods are presented to answer the question, if internal production suffices to sustain the foodweb. At first a steady state model is applied, secondly, calculations with actually measured process rates are carried out and, finally, a dynamic simulation model is used.The conclusion is drawn that, before the construction of the storm-surge barrier, primary production of organic matter by phytoplankton is much more important than import, although the latter can not be neglected as additional food source for mussels, cockles and zooplankton. The simulation model predicts that this conclusion will not have to be changed in the future. The Oosterschelde will remain largely a self-sustaining ecosystem.     

Urban Metabolism of Paris and Its Region

The article presents the results of a research project aimed at (1) examining the feasibility of material flow analysis (MFA) on a regional and urban scale in France, (2) selecting the most appropriate method, (3) identifying the available data, and (4) calculating the material balance for a specific case. Using the Eurostat method, the study was conducted for the year 2003 and for three regional levels: Paris, Paris and its suburbs, and the entire region. Applying the method on a local scale required two local indicators to be defined in order to take into account the impact of exported wastes on MFA: LEPO, local and exported flows to nature, and DMC_corr, a modified domestic material consumption (DMC) that excludes exported wastes (and imported ones if necessary). As the region extracts, produces, and transforms less material than the country as a whole, its direct material input (DMI) is lower than the national DMI. In all the areas, LEPO exceeds 50% of DMI; in contrast, recycling is very low. The multiscale approach reveals that urban metabolism is strongly impacted by density and the distribution of activities: the dense city center (Paris) exports all of its wastes to the other parts of the region and concentrates food consumption, whereas the agricultural and urban sprawl area consumes high levels of construction materials and fuel. This supports the use of MFA on an urban and regional scale as a basis for material flow management and dematerialization strategies and clearly reveals the important interactions between urban and regional planning and development, and material flows.     

Sedimentation of phosphorus in limnetic and estuarine environments in the River Öre system,northern Sweden

Sedimentation of phosphorus was studied during the spring flood in April and May 1991 in Lake Örträsket and the Öre Estuary, northern Sweden. Lake Örträsket has an area of 7.3 km² and a mean depth of 22 m and is located 100 km from the coast halfways along the course of the River Öre. The river ends in a semi-closed low salinity estuary with an area of ca. 50 km² and a mean depth of 16 m. Sedimentation of phosphorus, iron and organic carbon were measured with sediment traps in Lake Örträsket and in the Öre Estuary. Characterization of particulate phosphorus in river water, sediment trap material and sediments were performed by the sequential extraction procedure proposed by Hieltjes & Lijklema (1980). Apart from being an efficient trap for suspended particles including particulate phosphorus, Lake Örträsket was shown to serve as a source for particulate material during spring 1991. The Öre Estuary, on the other hand, constitutes an efficient trap for the total supply of river-borne phosphorus during the spring flood period. Phosphorus was shown to be closely related to iron in particulate material in both the lake and the estuary. Adsorption of phosphorus on settling inorganic particles seems to be an important process, which is particularly pronounced in the estuary.