非点源污染物在沟渠湿地中的累积和植物吸收净化

对有机质和总氮在沟渠湿地底泥中的垂直分布和水平分布的研究表明,40 cm以下深度的芦苇(Phragmites communis)和茭草(Zizania latifolia)湿地底泥对有机质和总氮有显著的持留和累积作用;但表层底泥中含量随季节变化大,最高与最低值相差近2倍以上.有机质和总氮之间有极显著的相关关系,在芦苇和茭草湿地底泥中的相关系数分别为0.9876和0.9335.水体中总氮与NH₄⁺-N和NO₃-N也显著相关,表明总氮的主要成分是有机氮,其矿化作用是无机氮的重要来源.每年秋季芦苇收割以后,可带走氮818 kg·hm^-2和磷103.6 kg·hm^-2,茭草可带走氮131 kg·hm^-2和磷28.9 kg·hm^-2.茭白对氮的吸收能力高,试验表明,利用茭白取代野生植物,既能取得很好的净化效果,又可被农民主动回收,解决植物的二次污染问题.     

Nutrient and microbiological characteristics of fine benthic organic matter in sediment settling ponds

1. Fine benthic organic matter (FBOM, particles <1 mm) was collected eight times in 1995 and 1996 from settling ponds located at the base of five catchments, and assayed for total C, N and P, extractable ammonium, mineralisable N, organic P, labile polysaccharides, denitrification potential, acetylene reduction and respiration rates, and β‐glucosidase and phosphatase activities. The five catchments (10–101 ha in size) are located in the Pacific North‐west of the United States. They contain either old‐growth forests dominated by Douglas‐fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) or stands that were harvested 30 years ago and replanted with Douglas‐fir, with riparian zones dominated by red alder (Alnus rubra), bigleaf and vine maple (Acer macrophyllum; A. circinatum) and understory herbaceous plants. 2. C : N ratios were significantly higher, and mineralisable N, extractable ammonium and labile polysaccharides were all significantly lower, in FBOM from old‐growth catchment sediment than in FBOM from catchments containing harvested stands, showing that the chemical characteristics of FBOM were influenced by forest harvest. C and N concentrations were greatest in sediment from old‐growth catchments, but microbial activities (respiration, denitrification potential, phosphatase and β‐glucosidase) tended to be greater in sediment from the harvested catchments. 3. Levels of certain chemical components of harvested‐catchment FBOM were elevated relative to those found in old growth; specifically, organic and total P, extractable ammonium, mineralisable N and labile polysaccharides, suggesting that stream FBOM from harvested basins is more biodegradable than stream FBOM from old‐growth basins. 4. In addition to effects of past timber harvest on FBOM characteristics, there were also significant seasonal differences in both logged and unlogged catchments in all variables except mineralisable N, labile polysaccharides and acetylene reduction rates. 5. The results indicate that past timber harvest in five river basins influenced both composition of and seasonal fluctuations in fine benthic organic matter (FBOM) collected from stream sediments in settling ponds, suggesting a linkage between forest harvest and stream productivity. 6. Comparisons between seasonal patterns in stream and settling pond sediment FBOM characteristics suggested that the readily decomposable organic matter entering sediments during a storm event are rapidly transported and decomposed during their movement through the catchment basin. It also showed the validity of studying settling pond sediments as a surrogate for mountain stream sediments.     

Palaeolimnology of Neusiedlersee,Austria

Eighteen sediment cores from the Neusiedlersee reed belt were analysed for organic and inorganic carbon, nitrogen, organic and inorganic phosphorus and trace metal content. The depth variation of the distribution patterns of C, P and N in the cores are influenced by: 1. temporal variability of organic matter deposition (e.g. burial of Phragmites litter) 2. the impact of a number of astatic phases in the history of the lake, and 3. early palaeo-ecological changes associated with the alteration of marine to lacustrine environment. At some sites, due to mineralisation, the organic phosphorus compartment in the Pannonian sediments is completely exhausted; accordingly there is a parallel decrease in carbon and nitrogen content in the profiles. These changes in the pattern of the distribution of the nutrients (especially organic phosphorus) can be used to differentiate between the recent and the upper boundary layer of the tertiary sediments. There is no clear trace metal distribution pattern observed in the cores but the Pannonian sediments recorded the lowest levels. In contrast, at some locations surface sediments register a two to three fold increase. The highest C, P, N, values and trace metal concentrations are recorded in the surface sediments deposited after the drying up of the lake a hundred and twenty-two years ago.     

乌梁素海野生芦苇群落生物量及影响因子分析

 对内蒙古乌梁素海湿地野生芦苇(Phragmites australis)生物量的调查基础上,探讨了富营养化湖泊湿地水体的物理化学性质对芦苇生物量的影响。结果表明：1）由于环境因子的影响,芦苇群落生物量变化较大,介于1.73～3.00 kg·m-2之间;地下和地上生物量之比介于1.14～2.19之间;2）芦苇群落生物量受多种因素的影响,其中水深是最主要的限制因子,水上生物量和地上生物量随着水深的增加而增加,而地下与地上生物量的比值则随水深的增加而减少,这主要是由于水深改变了芦苇群落的结构（群落密度）和个体形态(株高和株茎);3）芦苇群落生物量随着水体N浓度增加而增加。芦苇各器官（叶、茎、根状茎和根）的N∶P为7.59～12.21,小于14,这也说明该水体中的N负荷是影响芦苇生长的主要限制因子;4）土壤有机质分解对芦苇生长没有产生毒害作用。     

Long‐term responses of leaf litter decomposition to temperature,litter quality and litter mixing in plateau wetlands

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Performance of Sparganium emersum Rehm. shoots in response to sediment quality

Biomass, dry matter production, nutrient (N, P, K, Ca, Mg) contents and accumulation were studied in Sparganium emersum Rehm. in Southern Bohemia, Czech Republic. The aim was to determine the species' relationship to sediment quality and water flow and to estimate its nutrient uptake from sediments. The plants were sampled from six field sites, and one cultivation experiment was carried out. In the field, dry weight, shoot length and leaf number related to one another, while probably responding to nutrient supply both from water and sediment, while leaf width seemed to be correlated with other environmental factors. In the experiment, all measured growth parameters, except for the number of leaves, reflected sediment quality. The standing stocks of N, P and K reflected best the sediment nutrient contents in the field, both in running and standing water, but the stocks were generally higher in running water. In the experiment, all the measured growth parameters were correlated with sediment nutrient contents, and for N and P they were also with these nutrient contents in the plants. Nutrient removal from the rooting media was substantial for nitrogen. S. emersum was found to grow well in sediments rich both in mineral nutrients and organic matter.     

Changes in the species richness,spatial pattern and species frequency associated with the decline of oak forest

Nomenclature: follows Flora Europea (Tutin et al. 1964–1980). Since the extension of the irrigation system, the water regime of most of the permanent marshes of the Camargue (southern France) have been intensively controlled. Considerable quantities of nutrient rich Rhone water are pumped into these marshes, leading to lower salinities and a higher biomass production and consequently an increasing organic matter concentration of the sediments. Myriophyllum spicatum has become abundant in these permanent marshes since large quantities of freshwater entered these systems. It has displaced Potamogeton pectinatus in several of these marshes. The different factors likely to influence the distribution of P. pectinatus and M. spicatum were investigated experimentally. The impact of Cl^- concentrations between 0 and 6 g l^-1 on the biomass production of both species was tested. P. pectinatus appears to be more salt tolerant than M. spicatum. The influence of sediment quality on the biomass production of both species was investigated using six sediments differing in organic matter concentration. Compared to P. pectinatus, M. spicatum had a lower total biomass production when grown on sediments with low organic matter concentration (2–4% organic matter) and a higher biomass production on sediments with relatively high organic matter concentration (9–13% organic matter).Nitrogen addition to the sediments yielded an increased biomass production of P. pectinatus and M. spicatum. On some sediments M. spicatum needed higher concentrations of nitrogen than P. pectinatus to increase its biomass production.The creation of freshwater marshes by the introduction of irrigation water, resulting in lower salinities and an increase in sediment organic matter concentration, stimulates the biomass production of M. spicatum.As M. spicatum grows less well on poor sediments and at higher salinities it seems to be unable to displace P. pectinatus in more natural systems in the Camargue.     

Influence of submerged macrophytes on sediment composition and near-bed flow in lowland streams

1. Submerged macrophytes have important physical and structural effects on lowland streams. This study investigated the ability of submerged macrophytes to modify the near-bed flow and to retain mineral and organic particles in patches of four common macrophytes in shallow Danish streams during mid-summer. 2. In dense patches of Callitriche cophocarpa and Elodea canadensis, where near-bed velocity was reduced, the sediment surface was markedly raised and enriched with fine particles. In dense patches of Ranunculus peltatus, fine sediments were deposited among rooted shoots in the upstream part of the patches, while erosion and coarse sediments prevailed in the downstream part of the patches because of the strong vortices that formed at the rear and moved up under the trailing canopy. The open canopy of Sparganium emersum, with its streamlined leaves, had little effect on flow and sediment. 3. Patterns of sediment deposition and composition were closely related to the morphology and canopy structure of plant species and the presence of low velocity above the sediment among the rooted shoots. The mineral particles retained probably originate from bed-load, and the enrichment with finer particles within the patches probably results mainly from size-selective processes during erosion and transport of particles rather than during deposition. The mixed sediment composition within patches suggests that the flow-resistant shoots generate an environment conducive to deposition of all transported particles. 4. Fine sediments within macrophyte beds contained high concentrations of organic matter, carbon, nitrogen and phosphorus. The wide scatter in the relationships between mineral grain size and the content of organic matter and nutrients reflects the spatial and temporal complexity of erosion, transport and sedimentation of mineral and organic particles. 5. Enrichment of sediment within macrophyte beds relative to the surrounding substratum ranged from 780 g organic matter m^–2, 30 g N m^–2 and 25 g P m^–2 for the flow-resistant dense canopies af Callitriche cophocarpa to 150 g organic matter m^–2, 6.6 g N m^–2 and 3.4 g P m^–2 for the open canopies of Sparganium emersum. Retention of nutrient-rich particles within the macrophyte beds is probably of limited importance for plant growth in most lowland European streams, because macrophyte growth is rarely nutrient limited.     

Geochemical partitioning and bioavailability of copper to aquatic plants in an artificial oxide-organic sediment

This study investigated the effects of competition between binding substrates (organic matter and iron oxide) and between metals (cadmium and copper), on the partitioning of sedimentary copper and its subsequent bioavailability to an aquatic plant. Organic matter and a synthesized iron oxide, ferrihydrite, were added singly and in combination to a series of sand sediments, which were then dosed with environmentally realistic concentrations of cadmium and copper and planted with rice,Oryza sativa. Organic matter controlled copper partitioning and bioavailability, whereas the synthetic ferrihydrite bound negligible amounts of either metal, even in the absence of organic matter. As organic matter concentrations increased, operationally-defined leachable copper decreased, organic-associated copper increased and the survival of rice plants improved in an approximately linear fashion. At a nominal starting copper concentration of 5.8 μg g dry wt⁻¹, plant survival after four weeks averaged 0–8% in sediments without organic matter, 25% in a sediment containing 0.18% organic matter and 58% in a sediment containing 0.36% organic matter. These results suggest that organic-associated forms of copper are unavailable to plants, and that the operational definition of ‘leachable’ copper (extracted with dilute ammonium acetate) adequately represents the species of copper that is (are) available to plants. Our study using a well-characterized artificial sediment supports the copper fractionation patterns and correlations between copper partitioning and bioavailability reported from the heterogeneous, poorly characterized sediments of natural lake and river sediments.     

Horizontal distribution of carbon and nitrogen and their isotopic compositions in the surface sediment of Lake Biwa

The horizontal distribution of the abundance and isotopic composition of carbon and nitrogen was studied on surface sediment samples (0–15 cm) collected from the entire area of Lake Biwa, the largest freshwater lake in Japan. As water depth increased, a marked increase in organic matter content was observed at the sampling sites, especially in the western North Basin, characterized by a steep slope. In the northwestern North Basin, which has no major inflowing streams, the sediments contained large amounts of organic matter, suggesting the possibility of lateral transportation of sedimented matter from other places by lake currents. The total amounts of carbon and nitrogen in the top-2 cm of sediment of the entire area of Lake Biwa were estimated to be 9.2 × 10⁴ tC and 1.0 × 10⁴ tN. The δ¹⁵N values in the littoral sediment were low and close to those in the inflowing river sediment, suggesting selective sedimentation of allochthonous organic matter onto the littoral area. In the North Basin, vertical profiles of organic matter content and δ¹³C values of the sediments in the littoral area showed a smaller downward decrease than in the profundal area, whereas δ¹⁵N values decreased with sediment depth in both areas. It was suggested that the littoral sediments contained abundant amounts of allochthonous and relatively refractory organic matter. Further, it was suggested that the autochthonous organic matter originated from primary production deposited mainly on the profundal zone and was easily decomposed in early diagenesis after sedimentation. Received: July 30, 1999 / Accepted: December 10, 1999     

The effects of drying on sediment nitrogen content in a Mediterranean intermittent stream: a microcosms study

Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable sediment NO₃ ⁻-N and NH₄ ⁺-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO₃ ⁻-N content of the sediment was enhanced during the first 10 days of sediment drying, whereas NH₄ ⁺-N was lost by 14 days post-drying. During the first 10 days, sediment desiccation seemed to stimulate the net N-mineralization and net nitrification from sediments. Afterwards, the extractable NO₃ ⁻-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter are depleted, and to an increase in NO₃ ⁻-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments would differ depending on desiccation period duration.     

长江口潮滩湿地土壤酶活性的陆向变化以及与环境因子的相关性

研究了长江口崇明东滩潮滩湿地表层沉积物的土壤酶活性和环境因子沿高程的陆向变化及其它们之间的相关性。结果表明,在潮滩湿地表层沉积物中的全磷(TP)、全氮(TN)和有机质(OM)的含量,随着高程的增加,其含量呈上升趋势,而沉积物平均粒径(AGS)和溶解无机磷(DIP)含量逐渐降低。崇明东滩表层沉积物中碱性磷酸酶活性沿高程梯度有增加的趋势,与沉积物平均粒径和溶解无机磷含量呈极显著负相关(p<0.01),与有机质、总氮、总磷含量呈显著正相关(p<0.05),反映出碱性磷酸酶活性受底物和产物并存机制的诱导或抑制。过氧化氢酶活性随高程也有逐渐增大的趋势,其活性与有机质、总氮、总磷呈显著正相关与溶解无机磷和沉积物平均粒径呈负相关(p<0.05),充分反映了随着演替的发展,沉积物的肥力逐渐增高的特点,也反映了沿高程梯度沉积物生物氧化作用逐渐增强。转化酶活性从藻类盐渍带到芦苇(Phragmites australis)带变化并不明显,在海三棱藨草(Scirpus mariqueter)带略高。蛋白酶活性从藻类盐渍带到芦苇带有降低的趋势,蛋白酶活性的高低更决定于有机质中蛋白质的含量而与有机质总量无关,说明蛋白酶可能主要由硅藻产生。     

Evidence for the influence of seagrasses on the benthic nitrogen cycle in a coastal plain estuary near Beaufort,North Carolina (USA)

A study was undertaken to evaluate the interrelationship between the presence of seagrasses, Zostera marina and Halodule wrightii, and the physical and chemical properties of sediments in a coastal plain estuary near Beaufort, North Carolina. In sediments underlying a cover of seagrass, silt-clay, organic matter, exchangeable ammonium, ammonium dissolved in pore waters and total nitrogen were larger than in unvegetated profiles. The magnitude of the physical and chemical properties of sediments varied according to the location of the station in relation to the vegetation, as well as the continuity in the distribution of the seagrass. The largest pools of nitrogen, the finest sediment texture, and the greatest organic matter content were in sediments associated with the mid bed regions of seagrass meadows, intermediate at the edges of the bed and small isolated patches of grass, and least in unvegetated substrate.General conclusions from this study are: 1) once established, seagrasses appear capable of modifying the sediment texture as well as the organic matter and nitrogen content; 2) nitrogen accumulates beneath the vegetation suggesting that vegetated sediments are sinks; however, functional recycling mechanisms seem to be operating as suggested by the larger magnitude of remineralized nitrogen in the vegetated profiles; and 3) the establishment of seagrasses in this geographical region are not necessarily restricted by the sediment properties measured in this study. These data and conclusions are discussed in regard to an application of contemporary theories of ecosystem development to seagrass systems.Contribution Number 82-22-B     

Macronutrients along the sediment profile in a subtropical monsoonal wetland in India

We analyzed 144 composite sediment samples to appraise the seasonal variation in select major nutrients in the bed sediments of Keoladeo National Park (KNP), Bharatpur, a subtropical monsoonal wetland system in India, from September 2003 to July 2005. Total organic carbon (TOC, %) and total nitrogen (TN, %) in the sediments were in the range of 0.61–14.01 and 0.26–0.68, respectively. The total available phosphorus (TAP, %) and total available sulphur (TAS, %) ranged from 0.001 to 0.034 and from 0.001 to 0.012, respectively. While C:N ratio was within a narrow range (1.38–13.56), C:P ratios varied widely (18.81–5995.83). Similar wide variations were seen in C:S ratio (352.2–3929.5) as well as N:P ratio (9.34–56.6). All the parameters except TAS showed depth-wise declines along the sediment profile. In contrast, the pH gradually increased along the depth. Most of the parameters significantly varied across months and sediment layers. A positive correlation (Two-tailed, P < 0.05) existed between TOC and all the nutrients and their ratios except TAP and N:P. TAP was positively correlated with electrical conductivity (EC) and water soluble substances (WSS), suggesting the contribution of phosphate to the dissolved salts. During certain months elements such as P were comparatively low in concentration, in spite of input through agricultural runoff and large scale bird droppings, probably due to its higher uptake by macrophytes growing luxuriantly in the wetland. Organic materials appear to decay at a faster rate during the drier periods as indicated by the fall in TOC and the rise in TN. Principal Component Analysis (PCA) shows that three components contributed to 68.9% of the total variance. The first component that accounted for 26.4% of the total variance reflects the importance of total organic carbon in wetland sediments and the ratio of carbon to other nutrients. The second one accounting for 23.7% of the variance correlated with water soluble substances (EC, WSS and TAS). The third component accounting for 18.7% of the variance reflects the influence of two major nutrients, nitrogen and phosphorus, in sediments those affect the biogeochemical processes in wetlands. Thus, the three PCA components can be characterized as ‘sediment organic carbon and its ratios with other elements’, ‘WSS, TAS’ and ‘the limiting nutrients such as N and P’, respectively.     

Chemical oxygen demand,nitrogen and phosphorus removal by subsurface wetlands with Phragmites vegetation in different models

To improve the removal efficiency of subsurface wetlands vegetated mainly by Phragmites, pilot‐scale gravel‐based wetlands were used to treat sewage characterized by chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) pollution. For Phragmites vegetation, COD, TP and TN removal loads of wetland vegetation with Phragmites australis–Typha angustata–Scirpus validus as main species reached 0.517 g m^?2 d^?1, 0.277 g P m^?2 d^?1 and 0.023 g N m^?2 d^?1. The COD removal loads in pilot‐scale and medium‐scale (260 m² in area) wetlands with Phragmites‐monoculture vegetation were 0.62–0.64 g m^?2 d^?1, while that of P. australis–T. angustata–S. validus wetland reached 0.974 g m^?2 d^?1. Thus, the preferable poly‐culture model for Phragmites wetland vegetation was P. australis, T. angustata, S. validus and Zizania latifolia with stem density ratio of 8:1:5:1. After harvest, nitrogen and phosphorus standing stocks of wetland vegetations ranged only 2.2–9.93 g N m^?2 and 5.39–13.5 g P m^?2, respectively, as both the above ground biomass and the nitrogen and phosphorus contents of the wetland vegetation harvested in late autumn were low.     

Heterotrophic nitrogen fixation in oligotrophic tropical marshes: changes after phosphorus addition

In order to determine the impact of nutrient enrichment on phosphorus (P) limited wetlands, we established experimental P additions in marshes throughout northern Belize. P significantly increased macrophyte primary production, which led to the rapid elimination of cyanobacterial mats. The replacement of cyanobacterial mats by macrophytes constrained autotrophic nitrogen (N) fixation, increased the quantity, and changed the quality of organic matter input to the sediments. We predicted that the activity of sediment heterotrophic N fixers will be impacted by these alterations in carbon input. We used the acetylene reduction technique to measure potential (glucose amended) nitrogenase activity (NA) in sediments from controls and treatment plots that have been P enriched for four years and dominated either by Eleocharis cellulosa, or Typha domingensis for two years. NA in P-enriched plots was 2–3 orders of magnitude higher than NA in controls. NA was positively correlated with the soil reactive P, both total organic and microbial carbon, live root biomass, and total phospholipid fatty acids (PLFA) as an indicator of active microbial biomass. It was negatively correlated with the concentration of ammonium-N. Path analysis revealed that the indirect effect of P on NA through the root biomass was more important than the direct effect of P. NA of the upper sediment layer was consistently higher in Eleocharis than in Typha dominated plots, despite the higher litter input by Typha. We feel that the higher levels of lignin and phenolics occurring in Typha litter, relative to Eleocharis, constrained NA in Typha plots. Handling editor: Luis Mauricio Bini     

潘大水库表层沉积物营养盐污染状况及赋存形态

潘家口-大黑汀水库(简称“潘大水库”)作为“引滦入津工程”的水源地,其水质状况直接关系到受水区饮水安全,是京津冀区域协同发展的重要影响因素.本研究基于2016年7月的调查,分析了沉积物中氮、磷和有机质的含量.结果表明: 潘大水库表层沉积物中总氮(TN)含量在1175.41～2415.67 mg·kg^-1(平均值为1648.71 mg·kg^-1),总磷(TP)含量在1773.25～3471.70 mg·kg^-1(平均值为2790.89 mg·kg^-1),有机质(OM)含量6.0%～25.3%(平均值为12.5%).在空间上,与上游的潘家口水库相比,处于下游的大黑汀水库TN含量与潘家口水库相近,TP含量略高.沉积物中氮主要以有机氮为主,磷主要以无机态的钙磷形态存在,有机质主要来源于外源性物质的输入.污染状况评价结果显示,潘大水库沉积物整体处于有机污染状态,且已达到严重污染的级别,可能会通过沉积物-水界面的营养交换对水环境改善产生潜在影响.     

Influence of quantity and lability of sediment organic matter on the biomass of two isoetids,Littorella uniflora and Echinodorus repens

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO₂ concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO₂ production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants.     

C:N:P Molar Ratios,Sources and 14C Dating of Surficial Sediments from the NW Slope of Cuba

The surficial sediments recovered from 12 sites located near the channel axis of the Florida Straits and the lower slope off NW Cuba were analyzed for total organic carbon (TOC), nitrogen (TN), phosphorus (TP), elemental C:N:P ratios, C and N isotopic values, and ¹⁴C dating. The depth profiles of TOC, TN, and TP (0-18 cm) displayed a downcore trend and a significant variation. The TOC values were low (0.15 to 0.62%; 66 to 516 µmol g^-1). Sites near the island’s lower slope had lower TOC average concentrations (158-333 µmol g^-1) than those closer to the channel axis (averaging 341-516 µmol g^-1; p <0.05). The TN concentrations near the lower slope attained 0.11% (80 µmol g^-1), whereas, towards the channel axis, they decreased to 0.07% (55 µmol g^-1; p<0.05). The C:N ratios ranged from 1.9 to 10.2. The mean molar C:N ratio (5.4) indicated a marine hemipelagic deposition. The TP was lower at sites near the lower slope (38.4 to 50.0 µmol g^-1; 0.12% to 0.16%) than those near the channel axis (50.0 to 66 µmol g^-1; 0.15 to 0.21%). C:P fluctuated from 7.7 to 14.1 in the surficial sediment layer. The bulk organic δ¹³C_org and δ¹⁵N values confirmed pelagic organic sources, and the ¹⁴C dating revealed that the sediments were deposited during the Holocene (1000-5000 yr BP). We suggest that the hydrodynamic conditions in the Straits influence vertical and advective fluxes of particulate organic material trapped in the mixed-layer, which reduces the particulate matter flux to the seabed.     

Concentration of nutrients in selected lakes in the High Tatra Mountains, Slovakia: effect of season and watershed

Concentrations of total phosphorus (TP), inorganic and organic nitrogen, organic matter, and chlorophyll-a were studied in ten mountain lakes at various stages of acidification, trophy, and type of watershed during each July and October from 1987 to 1990. Concentrations of TP and total organic matter were higher in July than in October. Concentrations of NH4₄ ⁺-N decreased and NO₃ ^–-N increased from July to October. The relative composition of total nitrogen (TN) and its concentration were strongly dependent on the type of watershed: the lowest TN concentrations were observed in lakes with forested watersheds, increasing above the timberline and reaching maximum values in acidified lakes with rocky watersheds. In the pool of TN, nitrate was most important in lakes above the timberline (70–86% of TN), and organic nitrogen in forest lakes (> 90% of TN). Lakes with rocky watersheds were characterized by high ratios of TN:TP (> 250 by mass). The concentration of chlorophyll-a varied widely, from 0.01 to 22.6 µg l^–1, without any consistent change between July and October, and were P limited.