Long-term effects of drainage and hay-removal on nutrient dynamics and limitation in the Biebrza mires,Poland

To provide a reference for wetlands elsewhere we analysed soil nutrients and the vegetation of floodplains and fens in the relatively undisturbed Biebrza-valley, Poland. Additionally, by studying sites along a water-table gradient, and by comparing pairs of mown and unmown sites, we aimed with exploring long-term effects of drainage and annual hay-removal on nutrient availabilities and vegetation response. In undrained fens and floodplains, N mineralization went slowly (0–30 kg N ha⁻¹ year⁻¹) but it increased strongly with decreasing water table (up to 120 kg N ha⁻¹ year⁻¹). Soil N, P and K pools were small in the undisturbed mires. Drainage had caused a shift from fen to meadow species and the disappearance of bryophytes. Biomass of vascular plants increased with increasing N mineralization and soil P. Annual hay-removal tended to have reduced N mineralization and soil K pools, but it had increased soil P. Moreover, N concentrations in vascular plants were not affected, but P and K concentrations and therefore N:P and N:K ratios tended to be changed. Annual hay-removal had induced a shift from P to K limitation in the severely drained fen, and from P to N limitation in the floodplain. The low nutrient availabilities and productivity of the undisturbed Biebrza mires illustrate the vulnerability of such mires to eutrophication in Poland and elsewhere. In nutrient-enriched areas, hay removal may prevent productivity increase of the vegetation, but also may severely alter N:P:K stoichiometry, induce K-limitation at drained sites, and alter vegetation structure and composition.     

鄱阳湖湿地两种优势植物叶片C、N、P动态特征

2011年2—6月在鄱阳湖南矶湿地国家级自然保护区逐月测定了灰化苔草(Carex cinerascens)、南荻(Triarrhena lutarioriparia)叶片C、N、P含量及其地上生物量,以阐明鄱阳湖湿地优势植物C、N、P含量及化学计量比动态特征与控制因子,探讨湿地养分利用与限制状况。结果表明：1）两种优势植物叶有机碳含量变化范围分别为365.3—386.6 mg/g和352.6—393.2 mg/g,平均值(?标准差)分别为(375.5?17.4) mg/g和(371.7?12.5) mg/g;叶N含量分别为6.96—17.59 mg/g和5.50—20.68 mg/g,平均值分别为(11.35?1.40) mg/g和(11.54?0.84) mg/g;叶P含量变化范围为0.65—2.14 mg/g和0.57—2.25 mg/g,平均含量为(1.56?0.69) mg/g和(1.55?0.68) mg/g。两种植物C:N、C:P、N:P平均值分别为37.65、413.60、9.62和41.05、410.29、9.57,C、N、P及其化学计量比种间差异不显著(P>0.05)。2）气温与地上生物量是N、P及其化学计量比季节变化的主要控制因子,气温和生物量对两种优势植物叶片氮、磷含量的影响要高于对叶有机碳含量的影响。3）植物C:N、C:P与地上生物量变化趋势基本一致,显示N、P养分利用效率随植物的快速生长而提高;根据两种优势植物及土壤N、P含量与化学计量比来判断,研究区植物更多地受氮限制。     

The mobilisation of phosphorus,organic carbon and ammonium in the initial stage of fen rewetting (a case study from NE Germany)

Currently, more than 10,000 ha of fens have been rewetted to re-establish their function as nutrient sinks in NE Germany. However, field investigations reveal that porewater concentrations of P, dissolved organic carbon (DOC) and ammonium in rewetted fens are orders of magnitude larger than under pristine conditions. Hence, the objective of this study was to investigate the reasons behind enhanced P, organic carbon (OC) and ammonium mobilisation due to rewetting by means of a long-term incubation experiment. Highly, moderately and slightly decomposed peat of a drained fen (polder Zarnekow) was incubated under waterlogged conditions. A time course of concentrations of P, DOC, ammonium, sulphate and other dissolved substances was investigated by means of permanently installed dialysis samplers during 54 weeks of incubation. Simultaneously, the concentrations of these dissolved substances were investigated after rewetting of the field site. Before, and at the end of the incubation study, the amounts of bicarbonate–dithionite (BD) and NaOH soluble P and OC of incubated peat samples were determined by a sequential extraction procedure. The highest mobilisation of P, OC and ammonium occurred in the highly decomposed peat. Final concentrations of P, DOC and ammonium reached about 143 μM, 46 and 1.9 mM, respectively. The initial sulphate concentrations in the rewetting experiment, as well as in the field investigations, were extremely high and ranged between 3 and 13 mM; however, a complete consumption of sulphate was only observed in highly decomposed peat. In conclusion, the reasons for enhanced P, OC and ammonium mobilisation are increased amounts of redox sensitive substances and enhanced availability of decomposable organic matter in the upper highly decomposed peat horizon. These results should be considered in future rewetting management strategies.     

凡口宽叶香蒲湿地植物群落恢复的研究

 调查观测广东韶关凡口铅锌矿宽叶香蒲(Typha latifolia)湿地的水生植物种类、生物多样性、群落结构及生物量,分析湿地基质的理化性质,探索湿地生态恢复的基本特征。研究结果表明：1) 以宽叶香蒲为优势种的湿地生态系统主要植物有98种,隶属44科,86属。次优势种有：芦苇(Phragmites communis)、茳芏(Cyperus malaccensis)。植物群落水平分布从均匀型向群集型分布格局转化,植物群落空间不均匀性增大。2) 随湿地系统的恢复演替进程,表现为土壤肥力（有机质,N,P,K）明     

Effects of Phragmites australis removal on marsh nutrient cycling

In the northeast US removal of exotic and invasive plant species is a common wetland restoration activity and the invasive common reed (Phragmites australis) is often the target of control efforts. We examined effects of reed removal on sediment nutrient pools and denitrification potential in a tidal freshwater marsh on the Connecticut River. In the first year after herbicide application and cutting of a reed stand, porewater ammonium concentrations in the removal area were about 4× higher relative to extant reed or cattail. Denitrification potentials were 50% lower than in a reference stand of reed. Denitrification activity had recovered by the second growing season after reed removal but porewater ammonium continued to accumulate. By the third growing season following reed removal, plant regrowth had occurred over approximately half the experimental plot and porewater ammonium had declined to pre-manipulation levels. Sediment organic content, moisture and porewater phosphate showed no significant response to reed removal over the four-year course of this study. Reed removal allowed regrowth of a more diverse plant community thereby achieving one of the goals of this restoration effort but patterns in ammonium accumulation and denitrification suggest a reduction in the capacity of this site to act as a sink for nitrogen.     

A linked hydrodynamic and water quality model for the Salton Sea

A linked hydrodynamic and water quality model was developed and applied to the Salton Sea. The hydrodynamic component is based on the one-dimensional numerical model, DLM. The water quality model is based on a new conceptual model for nutrient cycling in the Sea, and simulates temperature, total suspended sediment concentration, nutrient concentrations, including and DO concentration and chlorophyll a concentration as functions of depth and time. Existing water temperature data from 1997 were used to verify that the model could accurately represent the onset and breakup of thermal stratification. 1999 is the only year with a near-complete dataset for water quality variables for the Salton Sea. The linked hydrodynamic and water quality model was run for 1999, and by adjustment of rate coefficients and other water quality parameters, a good match with the data was obtained. In this article, the model is fully described and the model results for reductions in external phosphorus load on chlorophyll a distribution are presented. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Shallow lakes,the water framework directive and life. What should it all be about?

The European Water Framework Directive offers an unprecedented opportunity for improvement of ecological quality of both freshwater and marine systems. It has implications for every aspect of how catchments are used by human societies and could potentially mean a step change in how waters and catchments are managed. It must be implemented, however, by official bodies, which seem likely to apply ecologically outdated approaches, used in the past simply to manage water quality, to tackle the very different problem of improving ecological quality. Ecological quality can be characterised by parsimony of available nutrients, characteristic physical and biological structure, strong connectivity among systems and mechanisms of resilience to cope with normal, natural change. The implications of these are that high quality systems in a given location do not have unique lists of species and single formulae for how the biodiversity is constituted. They have considerable inherent variability whilst preserving their fundamental functional characteristics. This appears not to have been recognised by official bodies that seek simple taxonomic indices as measures of quality. To some extent this is a function of the way the Directive has been written, but a slavish adherence to this approach may undermine the spirit of the Directive and result in a failure to bring about the fundamental reform that is needed.     

适应是进化生物学研究的永恒主题

适应是什么?是一个过程(Process),一种状态(State),或是特指某个体的特征(Trait),可指生物现象或是非生物现象。在Rose&Lauder的《Adaptation》一书里,多位在适应进化研究领域里造诣很深的科学家对适应的概念、发展历史、研究适应的方法论和丰富多样的适应过程作了详细的描述。该书共分3部分,14章。     

Portulacaria afra is constrained under extreme soil conditions in the Fish River Reserve, Eastern Cape, South Africa

Restoration of degraded thicket landscapes can be achieved by planting Portulacaria afra (spekboom) cuttings. The factors determining P. afra abundance in thicket types not dominated by P. afra are of interest to restoration practitioners because they could influence restoration protocols using P. afra cuttings in these landscapes. We consequently investigated the relationship between P. afra cover and soil properties, namely pH, EC, organic C, particle size distribution and total content of 26 elements at 78 sites in the Fish River Reserve, Eastern Cape province, South Africa. P. afra cover showed a consistent pattern of constraint at extreme levels (both high and low) of subsoil EC, organic C, sand content, Ca, Zn and Al. The results suggest that P. afra is most competitive in intermediate edaphic environments in the Fish River Reserve. It remains to be investigated in restored landscapes whether P. afra cutting survivorship and growth are greater in such soils.     

A general solution for optimal egg size during external fertilization, extended scope for intermediate optimal egg size and the introduction of Don Ottavio 'tango'

Egg sizes of marine invertebrates vary greatly, both within and between species. Among the proposed causes of this are a trade-off between egg size, egg number and survival probability of offspring, and a selection pressure exerted by sperm limitation during external fertilization. Although larger eggs are indeed a larger target for sperm, producing larger eggs also implies making fewer of them. There has been discussion about whether sperm limitation can (theoretically) and does (in nature) select for larger egg size than under ad libitum sperm. In one specific model, based on a particular fertilization kinetics model and an empirically derived mortality function, the theoretical possibility of a negative shift in optimal egg size with sperm concentration was demonstrated. Here we present a generalized analytical model to explore the effects of survival and fertilization probabilities on optimal egg size. It is demonstrated that incorporating fertilization kinetics greatly increases the scope for intermediate optimal egg size, as opposed to eggs of minimal or maximal size. Second, we present a general analytical qualitative solution to the question whether optimal egg size depends on sperm concentration. It is shown that, under the condition that an intermediate optimal egg size exists, this qualitative outcome of the model (positive, negative or no relation between optimal egg size and sperm limitation) depends on the structure of the fertilization kinetics part of the model. Finally, we evaluate fertilization kinetics models with respect to the general solution, using two previously published kinetics models ('Don Giovanni' and 'Don Ottavio') and a novel alteration of one of them in which sperm concentration covaries with egg concentration (Don Ottavio 'tango'). For all three models the relationship between optimal egg size and sperm concentration is shown to be always negative. This paper thus shows how biologically realistic relationships between egg size on the one hand and survival and fertilization probability on the other hand predict optimal egg size to be intermediate, and that this optimum is in general expected to increase when sperm become more limiting.     

辽东湾芦苇湿地对陆源营养物质净化作用的初步研究

通过廊道系统自净和ｌｙｓｉｍｅｔｅｒ汉滤实验进行了辽东湾芦苇湿地对陆源营养物质净化作用的初步研究,结果表明,营养物质Ｎ、Ｐ和ＣＯＤｃｒ在廊道系统中的自净率为４１．７－６４．７１％,不同深度的土壤－芦苇系统对陆源营养物质Ｎ、Ｐ和ＣＯＤｃｒ的净化率为６０．０％－７５．９２％,Ｎ、Ｐ营养物质经湿地系统地滤后可满足海水水质２类标准,通过收获地上部生物量可使营养物质在陆地和湿地之间形成良性循环,不会造成污染     

退化湿地生态系统恢复的一些理论问题

湿地是陆地和水生生态系统间的过渡带,作为一种重要的自然资源,湿地是野生生物的栖息地,可调控区域内的水分循环和C、N等元素的生物地球化学循环;其生物生产力可为人类提供食物和商品,还能过滤和分解所吸纳的污染物,由于湿地的功能未受到足够的重视。全世界的湿地因大量围垦和干扰而丧失或退化,在退化湿地的恢复过程中,可用自我设计和设计理论、演替理论、入侵理论、河流理论、洪水脉冲理论、边缘效应理论和中度干扰假说等理论作指导,湿地恢复的方法包括：尽可能采用工程与生物措施相结合的方法,恢复湿地的供水连接,利用水文过程加快恢复,控制污染物的流入,修饰湿地的地形或景观,改良湿地土壤,在最佳位置重建湿地的生物群落,减少人类干扰,提高湿地的自我维持能力,建立缓冲带以保护自然的和恢复的湿地,建立湿地稳定性和持续性的评价体系并予以监控。     

酸雨对温州三土羊湿地水体氮营养盐数量的影响

为了解酸雨对温州三垟湿地水体氮营养盐数量的影响,本文测定了三垟湿地水体中不同形态氮的含量,其中氨氮2.90～10.75 mg·L^-1,平均5.38 mg·L^-1、硝态氮0.16～0.44 mg·L^-1,平均0.31 mg ·L^-1;总氮34.04～63.20 mg·L^-1,平均55.75 mg·L^-1和水体的pH值,6.1～6.5,平均6.4;并测算了近两年通过降水输入到三垟湿地和三垟湿地水体中不同形态氮的数量及其占湿地现有水体中各形态氮的比例,其中输入到三垟湿地氨氮、硝态氮和总氮的量分别为2.8～2.86× 10 kg、2.87×10⁴～4.96×10⁴kg和5.35×10⁴～7.82×10⁴ kg,分别占湿地水体现有量的56%～6%、11.21～19.38倍和12%～17%;直接输送到三垟湿地水体各形态氮的数量0.72×10⁴～0.8×10⁴ kg、0.83×10⁴～1.44×10⁴ kg和1.55×10⁴～2.27×10⁴,分别占现有量的16%～19%,3.24～5.63倍和3%～5%.结果表明,酸雨是三垟湿地水体氮污染的主要来源之一,对三垟湿地水体富营养化产生重要影响.     

施肥对潮棕壤钾收支及钾在作物体内分配的影响

通过15年的定位试验,研究了不同施肥制度下土壤K的收支及K在作物体内的分配.结果表明,施K肥处理的大豆籽实和秸秆中K浓度高于不施K肥处理;而施K肥处理的玉米籽实K浓度在各个处理间几乎没有变化.在不施K肥条件下,单一施用N肥或NP配施均可造成K的严重亏缺.保持农业系统养分循环再利用可以缓解K收支赤字,而配合适量K肥的施用可以实现作物高产,平衡土壤中K收支.