Inorganic phytoplankton nutrients in the Wadden Sea areas off Schleswig-Holstein. I. Dissolved inorganic nitrogen

In the summer months of 1984, 1986, 1987 und 1988, several stations off the west coast of Schleswig-Holstein were investigated with regard to the situation of dissolved inorganic nitrogen. An increase in nutrients was observed during the last few years related to a decrease in salinity. This is possibly due to an increased freshwater outflow caused by higher rainfall during recent summers.     

粤东柘林湾无机氮的时空分布特征

2000年5月～2001年5月对粤东柘林湾海域调查结果表明该湾三氮分布呈湾内向湾外递减趋势,湾内以西部海域含量为高。NO₃-N是柘林湾无机氮的主要存在形态,其含量呈冬春季高、夏秋季低的特点。NH₄-N和NO₂-N与盐度的相关性较差,NO₃-N则除秋季外,其余季节与盐度均呈良好的负相关关系,表现保守性行为。     

Nitrogen removal in coastal sediments of the German Wadden Sea

Although sediments of the German Wadden Sea are suspected to eliminate a considerable share of nitrate delivered to the SE North Sea, their denitrification rates have not been systematically assessed. We determined N₂ production rates over seasonal cycles (February 2009–April 2010) at two locations with two sediments types each, the first site (Meldorf Bight) receiving nitrate during all seasons from the Elbe river plume, and a second site on the island of Sylt, where nitrate is depleted during summer months. In sediments from the Sylt site, N₂ production ranged from 15 to 32 μmol N₂ m^?2 h^?1 in the fine sand station and from 7 to 13 μmol N₂ m^?2 h^?1 in the coarse sand station; N₂ production was not detected when nitrate was depleted in May and July of 2009. N₂ production in the Meldorf Bight sediments were consistently detected at higher rates (58–130 μmol N₂ m^?2 h^?1 in the very fine sand station and between 14 and 30 μmol N₂ m^?2 h^?1 in the medium sand station). Analysis of ancillary parameters suggests that major factors controlling N₂ production in coastal sediments of the German Wadden Sea are the nitrate concentrations in the overlying water, the ambient temperature, and the organic matter content of the sediment. Extrapolating our spot measurements to the zone of nitrate availability and sediment types, we estimate an annual nitrogen removal rate around 16 kt N year^?1 for the entire northern sector of the German Wadden Sea area. This corresponds to 14% of the annual Elbe river nitrogen load.     

Bio-availability of phosphorus in sediments of the western Dutch Wadden Sea

The purpose of this study was to make a prognosis of the effects of extended purification of terrestrial waste water, reaching the Wadden Sea by the River Rhine and Lake IJssel, on the phosphate concentration in the western Wadden Sea.The quantities of different phosphorus fractions in intertidal and subtidal sediments of the Marsdiep tidal basin (western Dutch Wadden Sea) were measured. Different methods are applied to determine the amount of phosphorus that can be released from these sediments. The direct bioavailability is determined by inoculating sediment suspensions with a natural mixture of precultured micro-organisms from the sampling area. A second approach is the measurement of the phosphate release under different redox conditions. Sequential extraction of sediment samples with different solvents is also applied. Under the present conditions and compared to the nutrient loads from fresh water (Lake IJssel) and from the North Sea, the phosphorus stored in the sediments of the western Dutch Wadden Sea plays a minor role in the total supply to micro-algae and bacteria. The bulk of the biologically available phosphorus in the sediments originates from the metal-associated fraction. Releasable phosphate may contribute to the local annual primary production to an extent of ca 45 to ca 150 g C m^–2 a^–1. The total amount of phosphorus in the sediment (mainly calcite associated) is twice to 6 times the biologically available amount.     

Germination and anchorage ofEnteromorpha spp. in sediments of the Wadden Sea

Large quantities of filamentous green algae (Enteromorpha spp.) have regularly occurred on muddy and sandy tidal flats in Königshafen, on the island of Sylt (North Sea), since 1979 — covering the sediments in thick mats during the summer months. While spores ofEnteromorpha were encountered in both mud and sand, germling formation was restricted to sand. However, mud snails (Hydrobia ulvae Pennant) were overgrown with smallEnteromorpha filaments in both habitats, about 50% of them at a muddy site and 20% at a sandy one. Filaments, several cm in length and still adhering to the snails, became tangled into clusters. At the sandy site, with abundantArenicola marina L., these clusters slid into the feeding funnels of lugworm burrows; the importance of this secondary anchorage is demonstrated by a field experiment. We suggest that the primary and secondary attachment ofEnteromorpha filaments provided by benthic fauna is an essential step in the development of green algal mats on sedimentary tidal flats.     

Spatial and temporal variations in salt marsh microorganisms of the Wadden Sea

Salt marshes exist at the interface of the marine and the terrestrial system. Shore height differences and associated variations in inundation frequency result in altered abiotic conditions, plant communities, and resource input into the belowground system. These factors result in three unique zones, the upper salt marsh (USM), the lower salt marsh (LSM), and the pioneer zone (PZ). Marine detritus, such as micro‐ and macroalgae, is typically flushed into the PZ daily, with storm surges moving both salt marsh detritus and marine detritus into higher salt marsh zones. Microbial assemblages are essential for the decomposition of organic matter and have been shown to sensitively respond to changes in abiotic conditions such as oxygen supply and salinity. However, temporal and spatial dynamics of microbial communities of Wadden Sea salt marshes received little attention. We investigated the dynamics of soil microbial communities across horizontal (USM, LSM, and PZ), vertical (0–5 and 5–10‐cm sediment depth), and temporal (spring, summer, and autumn) scales in the Wadden Sea salt marsh of the European North Atlantic coast using phospholipid fatty acid (PLFA) analysis. Our results show strong spatial dynamics both among salt marsh zones and between sediment depths, but temporal dynamics to be only minor. Despite varying in space and time, PLFA markers indicated that bacteria generally were the dominant microbial group across salt marsh zones and seasons, however, their dominance was most pronounced in the USM, whereas fungal biomass peaked in the LSM and algal biomass in the PZ. Only algal markers and the stress marker monounsaturated to saturated fatty acid ratio responded to seasonality. Overall, therefore, the results indicate remarkable temporal stability of salt marsh microbial communities despite strong variability in abiotic factors.     

On trends in nutrient concentration in the northern Wadden Sea of Sylt

The mean values on hydrographical parameters in the Wadden Sea of Sylt taken weekly over a period of seven years (1975, 1976 and 1984 to 1988) were compared in order to detect trends in concentrations of nutrients or plankton. An increase in NO₂, NO₃, PO₄ and Si could be found in summer. NH₄ showed a negative trend. Corresponding with the rising nutrient-level, Chlorophyll-a and pH show a positive trend. Salinity decreased significantly. Changes in NH₄ and NO₂ were correlated with rainfall. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)     

Concentrations of nitrogen in sandy sediments of a eutrophic estuarine lagoon

Concentrations of sediment organic nitrogen, dissolved inorganic nitrogen (ammonium, nitrite and nitrate), and dissolved organic nitrogen (DON) in sediments were measured at two sites in a eutrophic estuarine lagoon. One is a shallow aerobic site where macrobenthos are abundant and the other is a deep anaerobic site devoid of macrobenthos. Four species of macrobenthos (Bivalvia: Corbicula japonica, Annelida: Notomastus sp., Neanthes japonica and Oligochaeta sp.) were found in 8 sandy sediment cores collected at a shallow site in three succcessive summers. DON (170–1500 μg atom N l-1) was the major constituent of dissolved nitrogen with 10 times greater concentration than ammonium (55–180 μg atom N l-1) and 1000 times greater than nitrate (0.14–5.9 μg atom N l-1) and nitrite (0.21–1.4 μg atom N l-1). The ammonium content in anaerobic muddy sediments at the deep site (210–350 μg atom N l-1) was higher than in aerobic sandy sediments, whereas DON was higher in aerobic sediments than anaerobic sediments (90–240 μg atom N l-1). In aerobic sediments, depth profiles of DIN were nearly constant whereas DON was mostly highest at the surface. On the other hand, the increase of DON and ammonium was observed where macrobenthos was found. The occurrence of macrobenthos and high content of DON and ammonium content in the layers of sediment may suggest the influence of macrobenthos in the partitioning of nitrogen species through their motion and excretion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparing benthic biogeochemistry at a sandy and a muddy site in the Celtic Sea using a model and observations

Results from a 1D setup of the European Regional Seas Ecosystem Model (ERSEM) biogeochemical model were compared with new observations collected under the UK Shelf Seas Biogeochemistry (SSB) programme to assess model performance and clarify elements of shelf-sea benthic biogeochemistry and carbon cycling. Observations from two contrasting sites (muddy and sandy) in the Celtic Sea in otherwise comparable hydrographic conditions were considered, with the focus on the benthic system. A standard model parameterisation with site-specific light and nutrient adjustments was used, along with modifications to the within-seabed diffusivity to accommodate the modelling of permeable (sandy) sediments. Differences between modelled and observed quantities of organic carbon in the bed were interpreted to suggest that a large part (>90%) of the observed benthic organic carbon is biologically relatively inactive. Evidence on the rate at which this inactive fraction is produced will constitute important information to quantify offshore carbon sequestration. Total oxygen uptake and oxic layer depths were within the range of the measured values. Modelled depth average pore water concentrations of ammonium, phosphate and silicate were typically 5–20% of observed values at the muddy site due to an underestimate of concentrations associated with the deeper sediment layers. Model agreement for these nutrients was better at the sandy site, which had lower pore water concentrations, especially deeper in the sediment. Comparison of pore water nitrate with observations had added uncertainty, as the results from process studies at the sites indicated the dominance of the anammox pathway for nitrogen removal; a pathway that is not included in the model. Macrofaunal biomasses were overestimated, although a model run with increased macrofaunal background mortality rates decreased macrofaunal biomass and improved agreement with observations. The decrease in macrofaunal biomass was compensated by an increase in meiofaunal biomass such that total oxygen demand remained within the observed range. The permeable sediment modification reproduced some of the observed behaviour of oxygen penetration depth at the sandy site. It is suggested that future development in ERSEM benthic modelling should focus on: (1) mixing and degradation rates of benthic organic matter, (2) validation of benthic faunal biomass against large scale spatial datasets, (3) incorporation of anammox in the benthic nitrogen cycle, and (4) further developments to represent permeable sediment processes.     

Mesozooplankton in the northern Wadden Sea of Sylt: Seasonal distribution and environmental parameters

A statistical analysis was performed to determine environmental factors of significant influence on the mesozooplankton in the northern Wadden Sea of Sylt (German Bight) in 1991. The total mesozooplankton (>76 μm) was significantly correlated with water temperature as was the case with the calanoid copepodAcartia sp.;Pseudo- andParacalanus sp. were influenced by the amount of rainfall, whereas the amount of the meroplanktonic larvae of the cirripedia was related to the amount of particulate organic nitrogen in the water. A comparison of the years 1984 and 1991 demonstrates the positive effect of temperature on the copepod speciesAcartia sp. in summer.     

Effects of herbivorous birds on intertidal seagrass beds in the northern Wadden Sea

During autumn migration (September to December), brent geese (Branta b. bernicla) and wigeon (Anas penelope) feed on the seagrass Zostera noltii in the nearshore, upper tidal zone leeward of the island of Sylt (eastern North Sea). To graze on leaves and shoots above the sediment and on rhizomes and roots below, these birds reworked the entire upper 1 cm layer of sediment eight times within this 3-month period. In addition, brent geese excavated pits 3–10 cm deep by trampling in order to feed on below-ground phytomass. About 12% of the seagrass beds became pitted to an average depth of 4.5 cm. Using net exclosures, it was estimated that birds removed 34 g dry weight m^–2 of above-ground and 28 g of below-ground phytomass. This corresponds to 45% of the phytomass in September. Of the overall loss of phytomass from September to December, 63% was caused by birds. Roughly half of the leaves fell off anyway until December and the other half were taken by the birds. Below the ground, phytomass remained almost constant where birds were excluded, while with birds phytomass of rhizomes and roots was halved. In spite of this strong effect, in the next vegetation period the blade density was lower at former exclosure sites compared to the ambient seagrass bed. The underlying process seems to be a self-inhibition of dense overwintering seagrass by mud accretion. Assuming our experimental results can be scaled up to the entire seagrass bed, we hypothesize that in the sheltered upper intertidal zone, seasonal erosion caused by herbivorous geese and ducks is necessary for the persistence of Z. noltii. Received: 7 January 1999 / Received in revised form: 23 August 1999 / Accepted: 25 August 1999     

Long-term changes of intertidal and subtidal sediment compositions in a tidal basin in the northern Wadden Sea (SE North Sea)

Wadden Sea tidal flats are highly dynamic regarding the spatial distribution and the grain size composition of their sediments. From 2003 to 2006 surface sediments have been surveyed in an intertidal and a subtidal area within the tidal inlet Königshafen (south-eastern North Sea, northern Wadden Sea, island of Sylt) with the goal to gain information on short-term development trends in the grain size composition. The average grain size (Mean) becomes finer in the sheltered part of the intertidal survey area whereas a coarsening tendency can be observed in the more exposed part of the intertidal and especially in the subtidal survey area. The trend of the most frequent grain size (first Mode) shows the same spatial distribution pattern but is far less distinct. Thus, the changing Mean must be related to an increase in the deposition of fines in the sheltered part of the intertidal Königshafen as well as a general removal of fine-grained material in the exposed intertidal and subtidal Königshafen. In order to see long-term trends the surveys of 2003–2006 were compared to earlier studies conducted in 1932/1933, 1981 and 1989. A significant depletion of mud can be observed in the entire survey area. It is concluded that primarily changed hydrodynamics that may accompany ongoing climate change are responsible for this. However, the loss of fine-grained sediments is additionally amplified by a reduced vegetation cover and coastal protection measures.     

杭州西湖北里湖沉积物氮磷内源静态释放的季节变化及通量估算

通过采集北里湖不同季节的柱状芯样,在实验室静态模拟沉积物氨氮(NH+4-N)和可溶解性磷酸盐(PO3-4-P)的释放,同时研究了沉积物间隙水中NH+4-N及PO3-4-P的垂直分布特征.结果表明,沉积物间隙水NH+4-N随深度的增加有上升的趋势,PO3-4-P随深度的增加呈先升后降的趋势.氮、磷营养盐在沉积物—水界面均存在浓度梯度,表明存在自间隙水向上覆水扩散的趋势.沉积物NH+4-N在春季、夏季、秋季、冬季的释放速率分别为0.074 mg·m-2· d-1、0.340mg· m-2· d-1、0.087 mg· m-2· d-1、0.0004 mg·m-2·d-1,pO3-4-P的释放速率则分别为0.340 mg·m-2·d-1、0.518 mg·m-2·d-1、0.094 mg·m-2·d-1、-0.037 mg· m-2·d-1.不同采样点表现出明显的季节和空间差异性,释放速率表现为夏季＞春季、秋季＞冬季.根据静态模拟出的不同季节下内源氮、磷释放速率计算,全湖内源氮、磷营养盐的贡献分别为0.0037、0.0057t/a.该研究可为北里湖富营养化及内源污染的治理提供基础数据.     

Regulatory aspects of inorganic nitrogen metabolism in the Rhodospirillaceae

Regulatory aspects of the assimilation of inorganic nitrogen compounds (ammonia, nitrate, nitrogen) were studied in 12 strains belonging to the Rhodospirillaceae. All strains possessed an ammonium transport system, as demonstrated by ¹⁴C-methylammonium uptake. This uptake showed saturation kinetics (K _m between 50–150 M), and was competitively inhibited by ammonium (K _i between 5–18 M). The ammonium transport systems were repressed by ammonium in the growth medium. The nitrogenase activity of all strains was reversibly inhibited by ammonium (switch-off). This effect was not shown under nitrogen starvation conditions with the exception of some strains of Rhodopseudomonas capsulata, the nitrogenase of which was always susceptible to switch-off by ammonium. Assimilation of nitrate was confined to some strains of Rhodopseudomonas capsulata.Abbreviations ATCC American Type culture Collection, Rockville, MD, USA - DSM Deutsche Sammlung von Mikroorganismen, Göttingen, FRG     

Seasonal variability of inorganic and organic nitrogen in the North Sea

This study considers the cycling of nitrogen in the waters of the North Sea, particularly focussing on organic nitrogen. Dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) were measured in the North Sea over a one-year period (autumn 2004–summer 2005). The surface water concentrations of nitrate, ammonium, DON and PON during the present study ranged from <0.1–7.2 μM, <0.1–2.0 μM, 1.9–11.2 μM and 0.3–5.6 μM, respectively, with DON the dominant fraction of total nitrogen at all times. These nutrients concentrations were significantly lower compared to previous studies in the southern North Sea. The seasonal variations showed high mean surface concentrations of nitrate (4.7 ± 0.6 μM) and DON (8.9 ± 0.9 μM), low ammonium (<0.1 μM) and PON (0.8 ± 0.1 μM) in winter, shifting to low nitrate (0.3 ± 0.3 μM) and DON (4.2 ± 1.2 μM) in summer, with high ammonium (0.8 ± 0.4 μM) in autumn and PON (2.5 ± 1.2 μM) in spring. Highest mean surface DON concentration was measured in winter and may be due to resuspension of the organic matter from the bottom sediments. For autumn and spring, phytoplankton DON release was likely to be the most significant source of DON as shown by high concentrations of low molecular weight (LMW) DON and its positive correlation to chlorophyll a. Low total and LMW DON concentrations during summer were likely to be due to the uptake of the LMW DON fraction by phytoplankton and bacteria and the stratification of the water column. DON is therefore shown to be a potentially important source of nitrogen in shelf seas especially after the spring bloom has depleted nitrate to limiting concentrations. Handling editor: L. Naselli-Flores     

High abundance of small zoobenthos around biogenic structures in tidal sediments of the Wadden Sea

On the tidal flats of the island of Sylt (eastern part of the North Sea) the quantity of micro- and meiofauna associated with shoots of seagrass(Zostera noltii), with infaunal bivalves(Macoma balthica), and with tubes and burrows of polychaetes(Pygospio elegans, Pectinaria koreni, Nereis diversicolor, Nereis virens, Arenicola marina) was found to add up to 5 to 33 % of the overall abundance. These structures, taken together, account for 10 to 50 % of the faunal abundance on an average tidal flat at Sylt. The quantitative effect of biogenic structures at the sediment surface (casts and funnels) is small compared to that of tubes and burrows penetrating the anaerobic subsurface layer. In providing stable oxic microenvironments these elite structures frequently bring together more individuals than occur in the entire reducing sediment below surface. Faunal composition of irrigated dwellings of large infauna is different from that of the oxic surface sediment. The common denominator of all elite structures of the subsurface is an oxic halo. Burrows without such a halo are unattractive. There is no evidence that owners of burrows prey on their smaller inmates.     

Temporal and spatial pattern of common tern (Sterna hirundo) foraging in the Wadden Sea

In 1989, 313 foraging flights of common terns in the Wadden Sea were radio-tracked. The feeding trips lasted on average 115 min covering about 30 km per flight. Completely tracked flights had a mean radius of 6.3 km. The terns preferred distinct foraging areas in the Wadden Sea. These were visited at site-specific phases of the tidal cycle resulting in a temporal and spatial pattern of foraging, caused by the site-specific and tide-related fluctuations of food availability.Supported by the Deutsche Forschungsgemeinschaft