Danish Coastal Waters Research Articles

Nucleotide diversity within and between four species of Laminaria (Phaeophyceae) analysed using partial LSU and ITS rDNA sequences and AFLP

In order to estimate the nucleotide diversity of the four kelp species Laminaria digitata, L. hyperborea, L. saccharina and L. faeroensis, three approaches were used. First we sequenced 1320 base pairs (bp) of nuclear-encoded large subunit (LSU) rDNA, which included some of the most variable domains. These sequences discriminated between L. digitata, L. hyperborea and L. saccharina, but L. faeroensis was identical to L. saccharina. A phylogeny inferred based on 672 bp of the nuclear-encoded non-coding internal transcribed spacer regions (ITS1 and ITS2) rDNA, which are more variable than LSU rDNA, likewise failed to resolve a monophyletic L. saccharina with respect to L. faeroensis. Thirdly, we tested the usefulness of the amplified fragment length polymorphism (AFLP) technique to provide a resolved phylogeny for 43 Laminaria specimens. Laminaria digitata and L. hyperborea were resolved as strongly supported monophyletic groups. A third robust clade consisted of L. saccharina plus L. faeroensis. Within this clade, L. faeroensis samples were grouped with bootstrap support of 80%, but the L. saccharina clade was less well supported. The AFLP data in combination with rDNA sequences indicated subspecies status for L. faeroensis. AFLP analyses of different morphotypes of L. digitata and L. saccharina from Danish coastal waters did not reveal any differences. However, L. digitata from the Faroe Islands was genetically distinct from other samples.

Impaired larval development in broods of eelpout (Zoarces viviparus) in Danish coastal waters

Eelpouts (Zoarces viviparus), a viviparous fish, were sampled in Danish coastal waters during October and November 2001 and 2002, in ten different areas, which are receiving effluents from cities and industry to more or minor degree. The presence of gross abnormalities in eelpout broods has been suggested to be a useful biomarker of the impact of hazardous substances on fish reproduction in the marine environment as chronic exposure to various substances has the potential to induce severe developmental defects in fish embryos and larvae. Relatively high frequencies of female eelpouts (20–53) with elevated levels (>5) of larvae with developmental defects in the broods were found in four shallow fjords with effluents from larger cities and industry compared to areas. Deformations like spiral or bend shapes of the spinal axis, cranio-facial defects, eye lesions or loss of eyes were the dominating types. In some of␣the areas with the highest incidences of developmental defects, the adults had significantly enlarged livers, which may also be a possible effect caused by contaminant exposure. In two of the areas, relatively high frequencies of the broods contained larvae, which had died late but without any visible developmental defects. These two areas were affected by severe oxygen depletion prior to sampling time suggesting that examination of broods in the eelpout may include not only impact of hazardous substances but also effect of eutrophication-related problems on fish reproduction in the marine environment.

Long-term changes in area distribution of eelgrass ( Zostera marina) in Danish coastal waters

For five shallow-water eelgrass stands in Denmark, changes in area distribution over the period 1940/50s–1990s were assessed from aerial photographs. In areas where the wasting disease had decimated eelgrass meadows in the 1930s, this included determination of the time scale of recolonization. In addition, we aimed at evaluating whether fluctuations in eelgrass area distribution were related to various natural and human-induced disturbances, namely storm events, ice-cover, water temperature and nutrient loading. We found that populations affected by the wasting disease exhibited a time lag of more than 10 years before substantial recolonization began, probably reflecting long distances to seed-producing populations and extreme climatic events in the period. After the initial time lag, eelgrass area distribution increased rapidly, and a substantial recovery had taken place in the 1960s. All eelgrass populations showed marked inter-annual fluctuations. Declines were often rapid with reductions of about 60% occurring in less than 6 years. Recoveries occurred over similar time scales and documented that recolonization may take place relatively fast when suitable environmental conditions are present. Fluctuations in eelgrass area distribution tended to be larger in enclosed, protected bays as compared to open coasts, probably because enclosed sites are often more eutrophic. Changes in shallow-water eelgrass area distribution did not correlate with the available long-term records of natural and human-induced disturbance parameters. Thus, while deep-water eelgrass populations have declined markedly over the last century in response to eutrophication, long-term changes in shallow-water populations are less equivocal and seem more stochastic.

Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters

A large data set, collected under the national Danish monitoring program, was used to evaluate the importance of photon flux density (PFD), relative wave exposure (REI), littoral slope, and salinity in regulating eelgrass cover at different depth intervals in Danish coastal waters. Average eelgrass cover exhibited a bell-shaped pattern with depth, reflecting that different factors regulate eelgrass cover at shallow- and deep-water sites. The multiple logistic regression analysis was used to identify regulating factors and determine their role in relation to eelgrass cover at different depth intervals. PFD, REI, and salinity were main factors affecting eelgrass cover while littoral slope had no significant effect. Eelgrass cover increased with increasing PFD at water depths of more than 2 m, while cover was in versely related to REI in shallow water. This pattern favored eelgrass cover at intermediate depths where levels of PFD and REI were moderate. Salinity had a minor, but significant, effect on eelgrass cover that is most likely related to the varying costs of osmoregulation with changing salinity. The analysis provided a useful conceptual framework for understanding the factors that regulate eelgrass abundance with depth. Although the regression model was statistically significant and included the factors generally considered most important in regulating eelgrass cover, its explanatory power was low, especially in shallow water. The largest discrepancies between predicted and observed values of cover appeared in cases where no eelgrass occurred despite sufficient light and moderate levels of exposure (almost 50% of all observations). These discrepancies suggest that population losses due to stochastic phenomena, such as extreme wind events, played an important regulating role that is not adequately described by average exposure levels. A more thorough knowledge of the importance of such loss processes and the time scales involved in recovery of seagrass populations after a severe disturbance are necessary if we are to understand the regulation of seagrass distribution in shallow coastal areas more fully.

Estimation of Monthly River Discharge from Danish Catchments

To simulate the nutrient loading of Danish coastal waters, river discharge from unmonitored areas must be assessed. In an attempt to identify the most suitable method, for this purpose eight different versions of the three-parameter monthly water balance model “MWB-3” were tested on data from various Danish catchments for the period 1989-97. The model with the highest R2 and the lowest correlation between the model parameters was chosen for subsequent establishment of regression equations between the model parameters and catchment and climate characteristics. The most important explanatory variables of the regressions are soil properties, potential evapotranspiration, groundwater table depth, percentage of wetland area and catchment slope. Mean R2 was 0.82 for the calibration data subset (62 catchments) and 0.79 for the test data subset (22 catchments). Sensitivity tests indicate that the selected model version is more robust for application in catchments dominated by loamy soils than in catchments dominated by sandy soils. Though the MWB-3 model provides a good basis for determining the water balance of Danish catchments at the regional and national levels, modifications and extensions need to be considered for future studies.

Assessing reference conditions according to the European Water Framework Directive using modelling and analysis of historical data: an example from Randers Fjord, Denmark.

The European Water Framework Directive (WFD) requires the definition of reference conditions, i.e. pristine conditions, for all surface waters. As the present state of Danish coastal waters cannot be referred to as pristine, reference conditions have to be assessed by analysis of historical data or by the use of models. Using Randers Fjord as an example, the aim of this work was i) to demonstrate possibilities and restrictions of assessing reference conditions by historical data and by modelling; and ii) to demonstrate how ecological conditions have changed along with eutrophication. The ample historical data from Randers Fjord allowed us to assess reference conditions with respect to benthic macrophytes and benthic fauna. Models of varying complexity enabled us to assess reference conditions for nutrients, chlorophyll a, Secchi depth, and eelgrass. We conclude that models can be a useful supplement to assess reference conditions, though they are presently restricted by the lack of quantitative links between eutrophication and species composition.

Meristematic oxygen variability in eelgrass (Zostera marina)

We examined the variability in oxygen content of meristematic tissues in eelgrass in order to evaluate its potential role in events of sudden mass mortality within eelgrass beds. Oxygen content within intact eelgrass plants could be described by use of microelectrode techniques at high temporal and spatial resolution in the laboratory and in the field. Under both situations, the meristematic oxygen content was highly variable, ranging from 0 to 200% of air saturation depending on environmental conditions. Changes from steady‐state maximum oxygen content to steady‐state minimum content occurred within 30 min following experimental manipulation. The internal oxygen content exceeded water column oxygen concentration in the light and was intimately coupled to changes in irradiance because of the photosynthetic oxygen release within the leaves. The photosynthetically produced pool of oxygen could, however, not function as an efficient storage to support nighttime respiration. In the dark, oxygen was primarily supplied from the water column via diffusion into leaves, and the meristem quickly turned anoxic if the water column was anoxic. Experimental reduction of oxygen conditions immediately around the basal plant meristem had no major effect on internal oxygen content. High temperatures had a dramatic effect on the internal oxygen balance of eelgrass. Increasing temperature stimulated plant respiration more than photosynthesis, and the meristem went anoxic, even in the light, at water temperatures above 30°C. We hypothesize that low meristematic oxygen content is a key factor in events of seagrass die‐off.

Depth colonization of eelgrass (Zostera marina) and macroalgae as determined by water transparency in Danish coastal waters

We present a comparative analysis of lower depth limits for growth of eelgrass, large brown algae and other macroalgae measured by SCUBA-diving along 162 transects in 27 Danish fjords and coastal waters, coupled to 1,400 data series of water chemistry (especially nitrogen) and Secchi depth transparency collected between March and October. Danish coastal waters are heavily eutrophied and characterized by high particle concentrations, turbid water and lack of macrophyte growth in deep water. Median values are 3.6 m for Secchi depth and median lower-depth limits are 4.0 m for eelgrass, 5.3 m for brown algae and 5.0 m for other macroalgae. Depth limits for growth of eelgrass and macroalgae increase linearly with transparency in the coastal waters. The relationships are highly significant (p<10−6) and transparency accounts for about 60% of the variability of depth limits. Eelgrass extends approximately to half the maximum depth of macroalgae, presumably because of greater respiratory costs to maintain the below-ground rhizomes and roots of eelgrass, which often constitutes half the plant weight. As a reflection of the importance of total nitrogen (TN) in controlling phytoplankton biomass and thus Secchi depth in coastal marine waters, we found that TN could explain 48–73% of the variation in depth limits of eelgrass and macroalgae, according to a multiplicative model (Y=aXb). As with Secchi depth, the relationship to eelgrass showed a lower slope, reflecting the higher respiratory costs of eelgrass. The models show great sensitivity and a profound quantitative response with proportional effects on Secchi depth and depth limits when total-N concentrations are reduced.

Phytoplankton, nutrients, and transparency in Danish coastal waters

We present a comparative analysis of 1400 data series of water chemistry (particularly nitrogen and phosphorus concentrations), phytoplankton biomass as chlorophylla (chla) concentrations, concentrations of suspended matter and Secchi depth transparency collected from the mid-1980s to the mid-1990s from 162 stations in 27 Danish fjords and coastal waters. The results demonstrate that Danish coastal waters were heavily eutrophied and had high particle concentrations and turbid waters. Median values were 5.1 μg chla 1−1, 10.0 mg DW 1−1 of suspended particles, and Secchi depth of 3.6 m. Chlorophyll concentration was strongly linked to the total-nitrogen concentration. The strength of this relationship increased from spring to summer as the concentration of total nitrogen declined. During summer, total nitrogen concentrations accounted for about 60% of the variability in chlorophyll concentrations among the different coastal systems. The relationship between chlorophyll and total phosphorus was more consistant over the year and correlations were much weaker than encountered for total nitrogen. Secchi depth could be predicted with good precision from measurements of chlorophyll and suspended matter. In a multiple stepwise regression model with In-transformed values the two variables accounted for most of the variability in water transparency for the different seasons and the period March–October as a whole (c. 80%). We were able to demonstrate a significant relationship between total nitrogen and Secchi depth, with important implications for management purposes.

Stability of bacterial and viral community compositions in Danish coastal waters as depicted by DNA fingerprinting techniques

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 27:219-232 (2002) - doi:10.3354/ame027219 Stability of bacterial and viral community compositions in Danish coastal waters as depicted by DNA fingerprinting techniques Lasse Riemann*, Mathias Middelboe Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *Present address: Freshwater Biological Laboratory, University of Copenhagen, 51 Helsingørsgade, 3400 Hillerød, Denmark. E-mail: lriemann@vip.cybercity.dk ABSTRACT: Variations in bacterial and viral community compositions were examined over spatial scales ranging from centimeters to kilometers and over temporal scales of days to months in Danish coastal environments by means of denaturing gradient gel electrophoresis (DGGE) and pulsed field gel electrophoresis (PFGE), respectively. Despite several-fold differences in bacterial activity and chlorophyll a, we found only a few differences in microbial community composition among samples from 30 cm intervals in a 3 m vertical profile across a narrow pycnocline during a subsurface coccolithophorid bloom in the southern Kattegat. Likewise, only a few changes in community composition were observed during a 2 mo spring bloom period in the eutrophic Roskilde Fjord. However, more pronounced differences were observed among samples from 5 stations on a transect crossing the Skagerrak-Kattegat front where 2 water masses with different physico-chemical properties meet. The 2 water masses harbored distinct bacterial and viral communities, and a gradual mixing of the microbial communities was observed across the front. Our study indicates stability of microbial community compositions in Danish coastal waters and suggests that changes in microbial abundance and activity were not associated with successions in bacterial and viral communities discernible by the applied DGGE and PFGE protocols. KEY WORDS: Bacteria · Virus · Fingerprinting · Denaturing gradient gel electrophoresis · DGGE · Pulsed field gel electrophoresis · PFGE Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 27, No. 3. Online publication date: April 16, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Competition for inorganic nutrients between phytoplankton and bacterioplankton in nutrient manipulated mesocosms

A manipulative mesocosm experiment in Danish coastal waters tested the effect on plankton biodiversity and function of adding nitrate, phosphate and glucose. A comprehensive set of measurements was made over a 6 d period; these included phytoplankton biomass and production in 3 size fractions (>10, 10-2 and <2 µm), bacterial biomass and production, nitrate and ammonium uptake, and pigment taxonomy. Addition of nitrate and phosphate resulted in increases of biomass and production of all size fractions of phytoplankton. Inorganic nutrients alone had only a minor effect on bacterial abundance and production, with slight increases relative to the control. The largest changes occurred in mesocosms to which glucose was added in excess with nitrate and phosphate. Pigment composition indicated little change in phytoplankton assemblage composition in any treatment. A large increase in bacterial activity in the presence of added glucose had a negative effect on the phytoplankton assemblage and resulted in a decline in phytoplankton biomass. Data on nutrient uptake and size-fractionated carbon fixation suggest that the mechanism of this phyto- plankton suppression was the ability of heterotrophic bacteria to out-compete for available inorganic nutrients, resulting in nutrient limitation of the phytoplankton assemblage.

The use of a LISST-100 laser particle sizer for in-situ estimates of floc size, density and settling velocity

A LISST-100 laser particle sizer was used to measure in-situ particle size spectra (PSS), mean grain size (DM) and volume concentration (VC) of flocculated suspended sediments in Danish coastal waters. DM and VC were found to vary by up to 23% in tens of seconds. Consequently, an averaging period of 1 min for the LISST measurements is proposed. Based on the average values of DM and VC, and when the concentration of total suspended matter (TSM) is known, it is shown how to compute the in-situ mean effective density (Δρ) and mean settling velocity (WS) of suspended flocculated sediments using the LISST. Δρ versus DM, and WS versus DM relationships were found to be in good agreement with published data obtained by use of video systems. This lends credibility to the method used, and also suggests that laser diffraction instruments are capable of measuring DM and VC of flocs quite accurately. This is supported by a selected literature survey. The fractal dimension (Df) of the particles was calculated for different sites and seasons, and variability in the data interpreted in relation to the energy conditions prevailing in the study areas prior to fieldwork.

Optical Properties and Signatures of Chromophoric Dissolved Organic Matter (CDOM) in Danish Coastal Waters

The optical properties of chromophoric dissolved organic matter (CDOM) in Danish estuaries and coastal waters were investigated. A new method for estimating the spectral slope coefficient (S) was examined and found to give a closer fit for the measured absorption (92% reduction in sum of residuals) than the traditional method. The spectral pattern in residuals produced by the new technique enabled the identification of CDOM originating from areas of different land uses/types where S coefficients were similar. S values were found to behave conservatively with respect to salinity in all waters except for the off-shore North Sea region where CDOM from marine sources was suspected to have more influence. The specific absorption coefficient of CDOM did not vary significantly in Danish coastal waters. These waters are of particular interest in bio-optical studies as they allow the study of CDOM across a gradient from estuarine, brackish to near-oceanic environments. The results demonstrate that it is possible to develop regional models for the optical properties of CDOM which would then allow higher precision in remote sensing applications.

Anthropogenic nutrient load of the Baltic Sea

The discharge of nutrients is investigated in relation to their sources and effects in two case studies. The reduction of 47% in the phosphorus load from Denmark to marine areas between 1989 and 1993 has resulted in significantly lower phosphorus concentrations in most Danish coastal waters, and tendency to decrease can be seen in the Belt Sea and Kattegat as well. No general changes in nitrogen concentrations have been observed. This is due to the fact that more than 80% of the nitrogen load in Danish waters originate from diffuse agricultural sources. In the Pomeranian Bight strong nutrient gradients are generated by the mixing of Odra river water and coastal water. The spreading of the river plume could be exactly observed especially in winter, when biological activity is low. In general, different types of distribution, transport and modification patterns can be described. The annual input of nutrients from the catchment area to the Baltic Sea was estimated to be around 1000 kt N and 46 kt P. As a result, winter concentrations of phosphate and nitrate are characterized by positive overall trends in the surface layer in all subregions of the Baltic Proper for the period 1969 to 1993. These trends stem mainly from the strong increase in the 1970ies and early 1980ies. Thereafter, the concentrations of both nutrients fluctuate strongly around a high level. The drastic decrease in fertilizer consumption since the late 1980ies mainly caused by the great economic changes in the countries of the former East Bloc is not yet significantly reflected in decreasing winter concentrations, but first signs already have been found in the decrease in averaged phosphate concentrations in winter, especially in the Arkona and Bornholm Seas.

Ultrastructure of Chrysochromulina ahrengotii sp. nov. (Prymnesiophyceae), a new saddle-shaped species of Chrysochromulina from Danish coastal waters

A new, small, saddle-shaped species of Chrysochromulina with a coiling haptonema is described from Danish coastal waters. The scale cover of C. ahrengotii sp. nov. comprises an inner layer of plate scales and an outer layer of spine-bearing scales. Chrysochromulina ahrengotii bears close morphological resemblance to C. scutellum Eikrem et Moestrup, another species of Chrysochromulina recently described, but differs in details of the scales and in having only one type of spine scale. Details of the flagellar apparatus and some observations on scale formation are reported. The spine scales are formed in T-shaped cisternae of the Golgi apparatus, a very unusual feature somewhat resembling the formation of the flat scales in C. chiton Manton seen by Manton in 1967. The flagellar apparatus is similar to that of other saddle-shaped species such as C. scutellum, C. simplex Estep, Davis, Hargraves et Sieburth, C. apheles Moestrup et Thomsen, and C. acantha Leadbeater et Manton. Chrysochromulina ahrengotii is a fairly common species in Danish waters and appears to be euryhaline, occurring at salinities between 8 and 30 psu. The temperature range at which it occurred was 10° to 23°C.

Characterization of aerosols at a coastal site near Vindeby (Denmark)

Aerosol particle size distributions and aerosol chemical composition were measured with optical particle counters and filter packs, respectively, on an offshore mast in the Danish coastal waters near Vindeby on the island of Lolland. The filter pack samples were analyzed for ions representative of marine and continental aerosol: Na+, Cl−, SO4−−, NO3−, and NH4+. The physical and chemical measurements are complementary, and the information on chemical composition, together with the local meteorological parameters, the synoptic situation, and air mass trajectories, is crucial for interpreting the observed variations in the particle concentrations. Considering these sets of data, four periods can be discerned during the experiment. Further, the aerosol concentrations vary with wind speed, as is expected for marine aerosols, depending strongly on the fetch. In the case of short fetch, the coarse aerosol fraction (diameter &gt;1 μm) and the fine aerosol fraction (0.2–1 μm) decrease with wind speed. Processes like advection, diffusion, and dry deposition cannot explain the strong dependence of the concentrations on wind speed. Apparently, uncertainties in the source strength and origin of aerosol advected across the shore line, as well as processes affecting the aerosol concentrations over land, such as variability in the sources, washout by rain, and other removal and transport mechanisms, have much more influence than the transport and removal over water.

In situ and laboratory growth by a population of blue mussel larvae ( Mytilus edulis L.) from a Danish embayment, Knebel Vig

The aim of this study was to investigate if the growth rate of Mytilus edulis larvae was food limited during the summer period. Populations of M. edulis veliger larvae were investigated during two intensive periods in 1994 and 1995 in the embayment Knebel Vig, Denmark. The abundance of veligers varied from 1.7–40.4 ind. l −1 (1994) and 2.7–99.0 ind. l −1 (1995), generally declining throughout the sampling periods. Exponential disappearance rates for the M. edulis larvae were estimated as 0.06 d −1 and 0.23 d −1 for the two years, presumably caused by predation and settlement. In situ water temperature in the embayment was between 21–23°C both years of investigation. In the laboratory, larvae were fed three different food rations: filtered sea water, natural sea water and natural sea water enriched with added algal culture ( Isochrysis galbana) ad libitum. All laboratory experiments were conducted at 22±1°C. Larval mean±s.e. shell lengths increased at significantly different rates (5% significance level) (Kruskal–Wallis analysis of variance followed by multiple comparisons) of 4.3±0.4 μm d −1 in filtered sea water, 9.1±0.2 μm d −1 in natural sea water, and 13.1±2.8 μm d −1 in enriched sea water, respectively. Under in situ conditions mean±s.e. shell growth rates were estimated as 5.6±0.3 μm d −1 and 7.6±1.3 μm d −1 in 1994 and 1995, respectively, the latter not significantly different from the laboratory growth rate performed with natural sea water. During the sampling periods, the chlorophyll a content of the bay water was 0.5–4.5 μg l −1 (mean 2.8 μg l −1) which is well within the summer range of Danish coastal waters. In order to calculate the specific growth rates of the larvae, a shell length–carbon content regression was carried out with in situ larvae from 1994 giving W(μgC)=3.06×10 −8× L(μm) 2.88 ( L=175–450 μm), where W is individual carbon content and L is shell length. Specific growth rates in situ were 0.062 d −1 in 1994 and 0.064 d −1 in 1995. In the laboratory, the specific growth rates were estimated to be 0.04 d −1, 0.08 d −1 and 0.11 d −1 in filtered, natural and enriched sea water, respectively. The investigations lead us to suggest that growth of M. edulis veligers is commonly limited by food supply in the embayment during the summer.

Standard CZCS Case 1 algorithms in Danish coastal waters

The purpose of the current work was to test the performance of several published CZCS (Coastal Zone Color Scanner) Case 1 algorithms for retrieving pigment concentration and vertical attenuation coefficients in Danish coastal waters. This involves in situ measurements and water samples from the North Sea, the Kattegat, the inner Danish Waters and the Baltic Sea. The entire record of CZCS acquisitions of Danish waters was compared with actual cruise ship data of the Danish National Environmental Research Institute (NERI) 14 days matched exactly but, mainly due to cloud cover, a total of only 38 trustworthy data points were found on seven of these. Vertical attenuation coefficients were estimated from profiles of PAR intensity. Pigment concentrations were determined from spectrophotometric measurements on water samples (chlorophyll- a plus phaeopigment). Correlations between CZCS and in situ estimates were found, but the biases were strong, particularly in the case of pigment concentration. This was as expected because of the extensive amounts of yellow substances present in Danish waters. Therefore, a correction procedure for excluding the yellow substance contribution in pigment concentration retrieval was tested. The results seem promising, but the number of observations is small, and further studies are needed before firm conclusions can be drawn. Nevertheless, it can be stated that trustworthy algorithms for Danish waters for new ocean colour instruments (OCTS, SeaWiFS and MERIS) clearly need to take the absorption by yellow substances into consideration.

The genus Chaetoceros (Bacillariophyceae) in inner Danish coastal waters

The genus Chaetoceros, one of the most important genera of diatoms in the marine plankton, has been investigated from 20 stations in Danish waters during the period 1991–1995. Thirty‐five taxa were identified, 18 of which were brought into culture for further morphological studies. Three taxa are reported for the first time from Danish coastal waters and one new species is proposed, C. impressus. Chaetoceros affinis var. circinalis is raised to species level. Material referred to previously as Chaetoceros sp. B. by Sundström is considered to represent C. pseudobrevis. Twelve taxa found previously in the area by other authors are also described, resulting in a total of 47 descriptions. An artificial key is provided for identifications of all species presently recorded in inner Danish coastal waters.

GIS-based modelling of solute fluxes at the catchment scale: a case study of the agricultural contribution to the riverine nitrogen loading in the Vejle Fjord catchment, Denmark

A model that predicts nitrogen loading is developed and applied on an agricultural catchment draining to a Danish Fjord. Increases in nitrogen loadings of the Danish coastal waters have been recorded and the transformation in the Danish agricultural sector is established to be the main cause. The development in Danish agriculture in the last 40 years has resulted in significant changes in the agricultural production structure which are of major significance to the water quality. Therefore, there is a need for methods which can relate the consequences of changes in the agricultural production structure to the nitrogen loadings of coastal waters. In this study riverine nitrogen loads are modelled by combining spatially distributed data for: (1) non-point source nitrogen leaching; (2) point source nitrogen emissions; (3) soils; and (4) elevation data of the terrain and of the ground water head, with a nitrate decay process. The decay process is expressed as a first-order decay with respect to distance, having two different decay constants according to different flow velocities. N-leaching was partitioned into a component with high velocity (mainly tile drainage) and a component with low velocity (mainly baseflow) based on soil type/flow-path correlations. The nitrogen loading model was implemented into GIS to calculate nitrogen loads for sub-catchments in the Vejle Fjord catchment, Denmark. The two nitrate decay-coefficients were estimated by a trial and error method. Discrepancies between model calculated and measured N-loads vary from −16 to 17%. A source apportionment of the agricultural contribution to the riverine nitrogen loading revealed that livestock production is responsible for about 60% of the total non-point source loading while part time farming contributes with approximately 23% of the total non-point source load. The remainder of the N-loadings originates from plant production and background sources.