Was total primary production in the western Wadden Sea stimulated by nitrogen loading?

Borum and Sand-Jensen (1996) described empirical relationships between nitrogen (N) loadings from land and total (benthic + pelagic) primary production rates in shallow coastal marine waters. We applied these relationships to N loadings of the western Wadden Sea system, and compared the production estimates with actually observed primary production rates of autotrophic components (phytoplankton, microphytobenthos, macroalgae and seagrasses) for those years for which field data were available. During the 1980s and early 1990s, primary production values appear in good agreement with those derived from the empirical relationships. During the 1960s and early 1970s, however, these relationships substantially overestimated the total primary production in the western Wadden Sea. Based on ambient nutrient concentrations and the Redfield ratio, production in that period was considered not to be limited by N but by phosphorus (P) during most of the time. It is concluded that primary production is not invariably stimulated by N loading from land. If other factors (i.e. additional nutrient sources, N:P ratios, internal nutrient dynamics and co-limiting effects of nutrients and light) are not taken into account, management regulations that are targeted at diminishing the effects of eutrophication hold the risk of seriously under- or overestimating nutrient reductions that are thought necessary to achieve their goals. Received: 30 November 1998 / Received in revised form: 12 July 1999 / Accepted: 15 July 1999     

Rainwater: Nutrient additions to a hypereutrophic lake

Rainwater was collected near culturally eutrophic Lake Sallie, Minnesota. Rain pH was low, but sulphuric acid did not appear to be the causative agent. Nitrogen varied greatly in single rainfalls. Ammonia was normally more concentrated than nitrate; both fell in sufficient quantitites to enrich surface waters. Atmospheric N loading may stimulate algal production. Rainwater phosphorus was normally less than 40 µg/l and insignificant in contrast to cultural influences. Calculations of rainfall nutrient contributions are given.     

Modelling the influence of nutrient loads on Portuguese estuaries

The effects of implementing Directive 91/271/EEC of 21 May 1991 (Waste Water Treatment Plan Directive) and Directive 91/676/EEC of 12 December (Nitrates Directive) are analysed in 7 Portuguese estuaries (Minho, Lima, Douro, Mondego, Tagus, Sado and Guadiana) and two coastal lagoons (Ria de Aveiro and Ria Formosa), with a modelling approach. MOHID Water Modelling System was used to perform simulations with three nitrogen load scenarios for each system: a reference scenario, a 50% nitrate removal by agriculture scenario and another with a 100% nutrients removal by waste water treatment plants (WWTP). It is shown that the interaction between hydrodynamic and ecological processes is an important feature to study trophic problems in estuaries. Ecological processes such as primary production only occur inside the system if the residence time of water is high enough to enable organismal activity and if the adequate conditions are found (e.g. light, nutrients, temperature). From the model results it is possible to conclude: (i) in systems with short residence time a reduction in nutrient load will only produce a decrease in nutrient transit and will not affect the system’s global ecological status (e.g. Douro Estuary); (ii) in systems with long residence time the effects will range from significant, when primary production is mostly limited by nutrients (e.g. Ria de Aveiro), to non-significant, when primary production in the system is light-limited (e.g. Tagus Estuary).     

武汉东湖不同湖区底泥总磷含量及变化的研究

以武汉东湖为对象,研究了1998.03—1999.02期间不同营养水平湖区底泥中(0—5cm,5—10cm)总磷的含量及季节动态。6个站平均总磷含量为1.15mg/g,同80年代初相比,Ⅰ、Ⅱ站底泥中总磷含量分别增高1.42倍和1.03倍。受污水排放影响较重的0站磷含量高达2.78mg/g,而受污水排放影响较小的Ⅳ、Ⅴ站仅分别为0.52mg/g和0.50mg/g。东湖底泥中磷年平均含量与湖水中磷年平均浓度相关系数极高(r=0.997,n=5,p＜0.02)。通过对不同湖泊的底泥磷含量、水柱磷含量和外源负荷的比较和相关分析可以看出,水柱中磷含量较高,磷负荷较大的湖泊底泥中磷含量也高。可以预测,即使东湖的外源负荷得以控制,巨大的底泥磷内源负荷将会继续对东湖水质构成威胁。     

Effect of dissolved free amino acids (DFAA) on the biomass and production of microphytobenthic communities

Mixed microphytobenthos communities, manipulated in two different ways in the laboratory (semi-natural and sediment-stripped), were examined for their response to dissolved free amino acids (DFAA) and nitrate (NO₃⁻). The semi-natural manipulation involved only the removal of macrofauna; and the sediment-stripped community used microfauna and flora that were separated from natural sediment and re-established on clean sediment, that is, certain indigenous nutrient sources were removed. Using sediment collected on two different occasions, two sets of experiments were made (3 and 4 week), under different light conditions. The response by the communities to the added nitrogen was measured as biomass (Chl a) and primary production. The stimulus from the DFAA addition on microphytobenthos biomass and primary production was similar to or higher than that from NO₃⁻. A conclusively positive effect from the nitrogen additions could be measured only in the sediment-stripped community. Compared to the semi-natural community, the sediment-stripped community responded faster to the added DFAA. When light was limiting, biomass and production by the sediment-stripped community was enhanced by the N additions, in particular by the DFAA addition. Results suggest that an efficient recycling of nitrogen allows generally nitrogen-poor sandy sediments to sustain high microphytobenthos productivity, thereby retaining nitrogen within the system.     

Denitrification efficiency for defining critical loads of carbon in shallow coastal ecosystems

Denitrification efficiency [DE; (N₂ − N/(DIN + N₂ − N) × 100%)] as an indicator of change associated with nutrient over-enrichment was evaluated for 22 shallow coastal ecosystems in Australia. The rate of carbon decomposition (which can be considered a proxy for carbon loading) is an important control on the efficiency with which coastal sediments in depositional mud basins with low water column nitrate concentrations recycle nitrogen as N₂. The relationship between DE and carbon loading is due to changes in carbon and nitrate (NO₃) supply associated with sediment biocomplexity. At the DE optimum (500–1,000 μmol m⁻² h⁻¹), there is an overlap of aerobic and anaerobic respiration zones (caused primarily by the existence of anaerobic micro-niches within the oxic zone, and oxidized burrow structures penetrating into the anaerobic zone), which enhances denitrification by improving both the organic carbon and nitrate supply to denitrifiers. On either side of the DE optimum zone, there is a reduction in denitrification sites as the sediment loses its three-dimensional complexity. At low organic carbon loadings, a thick oxic zone with low macrofauna biomass exists, resulting in limited anoxic sites for denitrification, and at high carbon loadings, there is a thick anoxic zone and a resultant lack of oxygen for nitrification and associated NO₃ production. We propose a trophic scheme for defining critical (sustainable) carbon loading rates and possible thresholds for shallow coastal ecosystems based on the relationship between denitrification efficiency and carbon loading for 17 of the 22 Australian coastal ecosystems. The denitrification efficiency “optimum” occurs between carbon loadings of about 50 and 100 g C m⁻² year⁻¹. Coastal managers can use this simple trophic scheme to classify the current state of their shallow coastal ecosystems and for determining what carbon loading rate is necessary to achieve any future state. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Restoration of shallow lakes by nutrient control and biomanipulation—the successful strategy varies with lake size and climate

Major efforts have been made world-wide to improve the ecological quality of shallow lakes by reducing external nutrient loading. These have often resulted in lower in-lake total phosphorus (TP) and decreased chlorophyll a levels in surface water, reduced phytoplankton biomass and higher Secchi depth. Internal loading delays recovery, but in north temperate lakes a new equilibrium with respect to TP often is reached after <10–15 years. In comparison, the response time to reduced nitrogen (N) loading is typically <5 years. Also increased top-down control may be important. Fish biomass often declines, and the percentage of piscivores, the zooplankton:phytoplankton biomass ratio, the contribution of Daphnia to zooplankton biomass and the cladoceran size all tend to increase. This holds for both small and relatively large lakes, for example, the largest lake in Denmark (40 km²), shallow Lake Arresø, has responded relatively rapidly to a ca. 76% loading reduction arising from nutrient reduction and top-down control. Some lakes, however, have proven resistant to loading reductions. To accelerate recovery several physico-chemical and biological restoration methods have been developed for north temperate lakes and used with varying degrees of success. Biological measures, such as selective removal of planktivorous fish, stocking of piscivorous fish and implantation or protection of submerged plants, often are cheap versus traditional physico-chemical methods and are therefore attractive. However, their long-term effectiveness is uncertain. It is argued that additional measures beyond loading reduction are less cost-efficient and often not needed in very large lakes. Although fewer data are available on tropical lakes these seem to respond to external loading reductions, an example being Lake Paranoá, Brazil (38 km²). However, differences in biological interactions between cold temperate versus warm temperate-subtropical-tropical lakes make transfer of existing biological restoration methods to warm lakes difficult. Warm lakes often have prolonged growth seasons with a higher risk of long-lasting algal blooms and dense floating plant communities, smaller fish, higher aggregation of fish in vegetation (leading to loss of zooplankton refuge), more annual fish cohorts, more omnivorous feeding by fish and less specialist piscivory. The trophic structures of warm lakes vary markedly, depending on precipitation, continental or coastal regions locations, lake age and temperature. Unfortunately, little is known about trophic dynamics and the role of fish in warm lakes. Since many warm lakes suffer from eutrophication, new insights are needed into trophic interactions and potential lake restoration methods, especially since eutrophication is expected to increase in the future owing to economic development and global warming.     

The bacterioplankton of Lake Taihu,China: abundance,biomass, and production

Abundance, biomass and production of pelagic bacteria were examined over one year at monthly sampling intervals across a trophic profile in Meiliang Bay, Lake Taihu. With the lowest density in the open lake, the bacterial abundance showed a clear trend in relation to trophic status. The carbon content per cell was higher in autumn and winter, and the opposite was true for bacterial biomass. Bacterial ³[H]-TdR and ¹⁴[C]-Leu incorporation rates, cell production, turnover times and carbon production varied during the annual cycle at different sites. The ratio of bacterial production to primary production was high, independently of the method used, indicates that the microbial food web in Lake Taihu is an important component of the total food web of the lake and dominated by external inputs. Electronic supplementary material Supplementary material is available for this article at and is accessible for authorized users     

生物操纵理论与技术在富营养化湖泊治理中的应用

近年来,全球范围内湖泊富营养化问题日趋严重。以生物操纵理论为指导,采用水生食物网调控、改善水质、抑制藻类的生物修复方法,为解决这一问题提供了可行的途径。论文综述了生物操纵理论的产生、发展和应用,阐述了富营养化水体生态系统中肉食性鱼类、滤食性鱼类、浮游动物、沉水植物和细菌等的作用,并针对当前生物操纵技术应用中存在的差异性问题,提出了不同湖泊应根据其特性采取不同的组合技术并重点采取相应措施的建议。     

Primary production in papyrus (<Emphasis Type=Italic>Cyperus papyrus</Emphasis> L.) of Rubondo Island,Lake Victoria,Tanzania

Above- and below-ground production and morphological characteristics of papyrus wetlands were measured at monthly intervals from July 2005 to June 2006 at Rubondo Island, Lake Victoria, Tanzania. The average value of live culm biomass (5,789 ± 435 g DW m⁻²) was higher than that of umbel biomass (2,902 ± 327 g DW m⁻²) by 50%. Root to rhizome means biomass value ratio was 1:1.8, rhizome biomass (4,144 ± 452 g DW m⁻²) being higher than roots biomass (2,254 ± 314 g DW m⁻²) by 45%. Direct proportion was observed between shoot density and culm–unit (culms and umbels) biomass. The average value of detritus/litter biomass (1,306 ± 315 g DW m⁻²) was less than total aerial biomass by 86%. The values of biomass are average of 12 sampling months from July 2005 to June 2006.     

Climatic change and its ecological implications at a subantarctic island

Summary Marion Island (47°S, 38°E) has one of the most oceanic climates on earth, with consistently low air temperatures, high precipitation, constantly high humidity, and low incident radiation. Since 1968 mean surface air temperature has increased significantly, by 0.025° C year^–1. This was strongly associated with corresponding changes in sea surface temperature but only weakly, or not at all, with variations in radiation and precipitation. We suggest that changing sealevel (atmospheric and oceanic) circulation patterns in the region underlie all of these changes. Sub-Antarctic terrestrial ecosystems are characterized by being species-poor and having a simple trophic structure. Marion Island is no exception and a scenario is presented of the implications of climatic change for the structure and functioning of its ecosystem. Primary production on the island is high and consequently the vegetation has a large annual requirement for nutrients. There are no macroherbivores and even the insects play only a small role as herbivores, so most of the energy and nutrients incorporated in primary production go through a detritus, rather than grazing, cycle. Ameliorating temperatures and increasing CO₂ levels are expected to increase productivity and nutrient demand even further. However, most of the plant communities occur on soils which have especially low available levels of nutrients and nutrient mineralization from organic reserves is the main bottleneck in nutrient cycling and primary production. Increasing temperatures will not significantly enhance microbially-mediated mineralization rates since soil microbiological processes on the island are strongly limited by waterlogging, rather than by temperature. The island supports large numbers of soil macro-arthropods, which are responsible for most of the nutrient release from peat and litter. The activities of these animals are strongly temperature dependent and increasing temperature will result in enhanced nutrient availability, allowing the potential for increased primary production due to elevated temperature and CO₂ levels to be realized. However, housemice occur on the island and have an important influence on the ecosystem, mainly by feeding on soil invertebrates. The mouse population is strongly temperature-limited and appears to be increasing, possibly as a result of ameliorating temperatures. We suggest that an increasing mouse population, through enhanced predation pressure on soil invertebrates, will decrease overall rates of nutrient cycling and cause imbalances between primary production and decomposition. This, along with more direct effects of mice (e.g. granivory) has important implications for vegetation succession and ecosystem structure and functioning on the island. Some of these are already apparent from comparisons with nearby Prince Edward Island where mice do not occur. Other implications of climatic change for the island are presented which emphasize the very marked influences that invasive organisms have on ecosystem structure and functioning. We suggest that changing sealevel circulation patterns, by allowing opportunities for colonization by new biota, may have an even more important influence on terrestrial sub-Antarctic ecosystems than is suggested merely on the basis of associated changes in temperature or precipitation.     

汤溪水库的富营养化现状研究

为了解汤溪水库的富营养化现状,于2000年丰水期和枯水期对该水库的水质和浮游生物分布进行了调查。结果表明,汤溪水库综合营养状态指数(TLI)在30～50之间,属中营养水平。浮游植物丰度为0.81×10⁶～6.57×10⁶cells·L^-1,丰水期高于枯水期。浮游植物以蓝藻、绿藻和硅藻为主,其优势种主要为水华微囊藻(Microcystis flos-aquae)、颗粒直链藻(Melosira granulata)、极小直链藻(Melosira minmum)和衣藻(Chlamydomonas sp.)等富营养化指示种。浮游动物丰度为43.25～812.2ind.·L^-1,其优势种也多为富营养化指示种,如:螺形龟甲轮虫(Keratella cochlearis)、角突臂尾轮虫(Brachionus angularis)、前节晶囊轮虫(Asplanchna priodonta)和广布中剑水蚤(Mesocyclops leuckarti)。与1984年相比,该水库由硅藻型变为蓝藻型,其营养水平与浮游植物丰度都显著增加。在2000年一次微囊藻水华发生时,水体表层浮游植物丰度高达11.97×10⁶cells·L^-1。     

Benthic shear stress gradient defines three mutually exclusive modes of non-biological internal nutrient loading in shallow lakes

Assessment of the importance of internal nutrient loading is essential for managing and restoring eutrophic shallow lakes. To date, studies of internal loads have tended to focus on one of two abiotic processes, either molecular diffusion or sediment/nutrient entrainment (resuspension). This study presents a new approach to determining the non-biological fluxes of nitrogen (N) and phosphorus (P) from the sediment to the water column of shallow lakes. Three mutually exclusive flux processes: (i) molecular diffusion, (ii) turbulent diffusion (eddy diffusivity) and (iii) wind-induced resuspension of N and P, were related to a gradient of benthic shear stress. A model presented here allowed the durations and magnitudes of different non-biological fluxes to be calculated over time, based on benthic shear stress. Two site-specific critical shear stress thresholds determined which of the three flux processes dominated for any benthic shear stress value. The model was calibrated for a shallow lake and the continuous flux of nutrient from the sediment to the overlying water generated by each process during that period was calculated, enabling the estimation of the relative importance of each of the three flux processes over a one-year period. Wind-induced resuspension dominated the internal nutrient flux, operating for 38% of the time and contributing 0.9 T P year⁻¹ and 10.2 T N year⁻¹ to the internal nutrient load. In contrast, molecular diffusion only contributed 0.01–0.02 T P year⁻¹ and 0.12–0.20 T N year⁻¹ to the water column, while turbulent diffusion provided up to 0.6 T P year⁻¹ and 6.2 T N year⁻¹. Our model suggests that turbulent diffusion is a neglected and potentially important process contributing to internal nutrient loading in shallow lakes, whereas molecular diffusion appears to be relatively unimportant in lakes that experience turbulence at the sediment–water interface. Handling editor: L. Naselli-Flores     

Changes of phytoplankton communities in Lakes Naivasha and Oloidien, examples of degradation and salinization of lakes in the Kenyan Rift Valley

Increasing degradation of the water quality, caused by overuse and salinization, leads to considerable changes of the phytoplankton composition in Kenyan Rift Valley lakes. Exemplarily, the phytoplankton communities and biomasses of deteriorating freshwater Lake Naivasha and salinizing Lake Oloidien were studied between 2001 and 2005, accompanied by physico-chemical measurements (pH, total phosphorus and nitrogen, alkalinity, conductivity). Over the last three decades, the ecology of these two water basins has been subjected to dramatic changes, caused by excessive use of water and catchment area by man. In L. Naivasha a shift in the dominance of coccoid cyanobacteria towards dominance of Chlorophyceae (Botryococcus terribilis) was observed. Lake Oloidien exhibited a shift in the dominance of coccoid Chlorophyceae towards dominance of cyanobacteria (Arthrospira fusiformis, Anabaenopsis elenkinii). Phytoplankton findings and chemical data demonstrate that L. Naivasha has developed towards a eutrophic freshwater lake while L. Oloidien has progressed towards a hypereutrophic alkaline-saline lake. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Padisak