Comparison of carbon and nitrogen accumulation rate between bog and fen phases in a pristine peatland with the fen-bog transition

Long-term carbon and nitrogen dynamics in peatlands are affected by both vegetation production and decomposition processes. Here, we examined the carbon accumulation rate (CAR), nitrogen accumulation rate (NAR) and δ¹³C, δ¹⁵N of plant residuals in a peat core dated back to ~8500 cal year BP in a temperate peatland in Northeast China. Impacted by the tephra during 1160 and 789 cal year BP and climate change, the peatland changed from a fen dominated by vascular plants to a bog dominated by Sphagnum mosses. We used the Clymo model to quantify peat addition rate and decay constant for acrotelm and catotelm layers during both bog and fen phases. Our studied peatland was dominated by Sphagnum fuscum during the bog phase (789 to −59 cal year BP) and lower accumulation rates in the acrotelm layer was found during this phase, suggesting the dominant role of volcanic eruption in the CAR of the peat core. Both mean CAR and NAR were higher during the bog phase than during the fen phase in our study, consistent with the results of the only one similar study in the literature. Because the input rate of organic matter was considered to be lower during the bog phase, the decomposition process must have been much lower during the bog phase than during the fen phase and potentially controlled CAR and NAR. During the fen phase, CAR was also lower under higher temperature and summer insolation, conditions beneficial for decomposition. δ¹⁵N of Sphagnum hinted that nitrogen fixation had a positive effect on nitrogen accumulation, particular in recent decades. Our study suggested that decomposition is more important for carbon and nitrogen sequestration than production in peatlands in most conditions and if future climate changes or human disturbance increase decomposition rate, carbon sequestration in peatlands will be jeopardized.     

Dynamics of cover, UV-protective pigments, and quantum yield in biological soil crust communities of an undisturbed Mojave Desert shrubland

Biological soil crusts are an integral part of dryland ecosystems. We monitored the cover of lichens and mosses, cyanobacterial biomass, concentrations of UV-protective pigments in both free-living and lichenized cyanobacteria, and quantum yield in the soil lichen species Collema in an undisturbed Mojave Desert shrubland. During our sampling time, the site received historically high and low levels of precipitation, whereas temperatures were close to normal. Lichen cover, dominated by Collema tenax and C. coccophorum, and moss cover, dominated by Syntrichia caninervis, responded to both increases and decreases in precipitation. This finding for Collema spp. at a hot Mojave Desert site is in contrast to a similar study conducted at a cool desert site on the Colorado Plateau in SE Utah, USA, where Collema spp. cover dropped in response to elevated temperatures, but did not respond to changes in rainfall. The concentrations of UV-protective pigments in free-living cyanobacteria at the Mojave Desert site were also strongly and positively related to rainfall received between sampling times (R² values ranged from 0.78 to 0.99). However, pigment levels in the lichenized cyanobacteria showed little correlation with rainfall. Quantum yield in Collema spp. was closely correlated with rainfall. Climate models in this region predict a 3.5–4.0 °C rise in temperature and a 15–20% decline in winter precipitation by 2099. Based on our data, this rise in temperature is unlikely to have a strong effect on the dominant species of the soil crusts. However, the predicted drop in precipitation will likely lead to a decrease in soil lichen and moss cover, and high stress or mortality in soil cyanobacteria as levels of UV-protective pigments decline. In addition, surface-disturbing activities (e.g., recreation, military activities, fire) are rapidly increasing in the Mojave Desert, and these disturbances quickly remove soil lichens and mosses. These stresses combined are likely to lead to shifts in species composition and the local extirpation of some lichen or moss species. As these organisms are critical components of nutrient cycling, soil fertility, and soil stability, such changes are likely to reverberate throughout these ecosystems.     

Phytoplankton and Nutrients in Goat Island Bay,New Zealand

A quantitative study of the phytoplankton and nutrients in Goat Island Bay, northern New Zealand, was carried out at two stations of depths 7 m and 20 m in 1966-69. There were significant differences in the concentrations of the phytoplankton at the two stations, the deeper station having, in general, higher concentrations than the shallower. Low phytoplankton standing crops were found in winter when the increased run-off from the land resulted in lower salinities, higher turbidity, and higher dissolved silicate levels. The spring growth of diatoms was dominated by small diatoms (Cylindrotheca closterium, Leptocylindrus danicus, Nitzschia pseudoseriata, Phaeodactylum tricornutum, and Rhizosolenia delicatula). Occasionally it was dominated by a population of large centric diatoms (Chaetoceros spp., Coscinodiscus spp., Thalassiosira spp.), but these appeared to be found in a separate water mass which entered the bay and displaced the resident water mass. A third water mass entered the bay in spring and was characterised by the coccolithophore Emiliana huxleyi and a lower temperature. During the summer diatoms dominated the phytoplankton population, but were replaced by dinoflagellates for a short period in autumn.     

白江河泥炭地泥炭藓孢子萌发力对排水的响应

排水严重改变泥炭地的环境和生态过程,但对泥炭藓孢子萌发力的影响尚不清楚。在长白山地区白江河泥炭地,分别在优势植物为苔藓的近原始地段和优势植物为小灌木的排水地段,钻取泥炭柱芯为试验材料,逐层测试泥炭理化指标,提取泥炭藓孢子并进行萌发试验,统计孢子数量和萌发力;经过泥炭样品年代测定,建立深度年代关系曲线,研究泥炭藓孢子萌发力对排水的响应和机制。结果表明: 整个柱芯对比,近原始地段平均孢子数略高于排水地段,两地段的平均孢子萌发力无差异,排水地段的泥炭容重、总碳和总氮都显著高于近原始地段。柱芯上部对比,排水(1987年)以后两地段孢子累积速率无显著差异,但近原始地段的平均孢子萌发力(34%)远低于排水地段(72%)。近原始地段的碳氮比与孢子萌发力呈显著正相关;排水地段的总碳、pH和埋藏时间与孢子萌发力呈显著负相关。30年前的泥炭地排水虽对孢子累积影响不大,但通过加速分解而改变了泥炭的理化性质,提升了表层泥炭中孢子萌发力,因此降低孢子库的持久性,可能导致泥炭藓在灾变性干扰后的种群持续更新潜力下降。     

Vegetation dynamics following trampling in rich fen at Sølendet, Central Norway; a 15 year study of recovery

In Sølendet nature reserve in the upper boreal of central Norway, the effects of controlled trampling from 1977 to 1981 were observed in four rich fen localities. The vegetation recovery was monitored on permanent plots on 3–4 occasions during the period 1981–1995. During trampling the vegetation cover was reduced and bare peat increased, particularly in a wet fen expanse locality. Woody species and herbs disappeared or were considerably reduced in cover, while some graminoids (e.g. Carex spp. and Eriophorum angustifolium ) and bryophytes (e.g. Campylium stellatum and Scorpidium cossonii ), appeared to be quite tolerant. Equisetum palustre and Eriophorum angustifolium increased in cover on two tracks. Several bryophytes survived trampling, but Sphagnum warnstorfii was eradicated. Campylium stellatum and Tomentypnum nitens were able to increase after the decrease in S. warnstorfii . The recovery was dependent on which species were present at the outset and which species arrived early. Further development seemed to depend largely on the species' capacity for rapid increase in cover. Eventually, the more vulnerable dominants of the untrampled vegetation (e.g. Thalictrum alpinum, Trichophorum cespitosum and Sphagnum warnstorfii ) increased in abundance. After 15 years the tracks still contained fewer species and had less vegetation cover than the surroundings.     

Mid- and late-Holocene vegetation history,climate and human impact in the forest-steppe ecotone of European Russia: new data and a regional synthesis

Appropriate management of contemporary environments requires knowledge of their long-term history. We use palaeoecological data to explore how contemporary forest-steppe environments have been shaped by climate change and human impacts through the Holocene using the western Mid-Russian Upland as a case-study. Our paper presents new reconstructions of Mid- and Late Holocene climate, vegetation dynamics and local environmental change based on pollen, plant macrofossil and testate amoeba records from a site at Selikhovo (Mid-Russian Upland, Russia). Eutrophic fen vegetation dominated by Phragmites australis developed around 6800 cal year BP and has been resilient to episodes of local burning and variable input of mineral material through the Holocene. New and previously-published data show that the boundary between broadleaf forest and steppe occupied a similar position to present during the period 7000–4800 cal year BP, despite a warmer and drier climate, but shifted to the south following climate cooling and an increase in precipitation from 4800–2500 cal year BP. A subsequent decline in woodland cover was caused by both climate change and human impacts, with human activity becoming increasingly significant over the last two millennia. Prior to major human disturbance (about 1700 cal year BP) the landscape was dominated by mixed broadleaf-pine forests with some spruce covering about 60 % of the study area. Our results emphasize the variability of steppe-forest habitats over long time periods and the need to consider human impacts and climate change when setting targets for habitat conservation.     

Old-field successional dynamics on the Inland Pampa,Argentina

Abstract. The first 10 yr of old-field successional dynamics on the Argentine Inland Pampa were studied on a series of adjacent plots established consecutively between 1978 and 1989. We examined differences in species abundance patterns among plots in order to detect the spatial and temporal variability of succession. Perennial grasses steadily increased in cover and replaced the dominant annual species after 5 yr. Pioneer dicots persisted in older seral stages with 20 — 23 species/plot. Overall, exotic species (mostly the grasses Lolium multiflorum and Cynodon dactylon) contributed much to the plant cover in these communities. Native grasses comprised 45 % of total cover at years 7 — 10 of succession, but occurred with less than 7 species/plot. Substantial variation was found in the successional pathway, which reflected the particular sequence from annual forbs to short-lived and perennial grasses in the various plots. The course of succession was apparently influenced by a 2-yr period of unusually high rainfall. Deyeuxia viridiflavescens, a native perennial grass virtually absent before the wet period, spread over the study area and dominated seral communities for 3 yr, irrespective of plot age. Climatic conditions thus affected the successional turnover of life forms by increasing the rate of colonization by perennial grasses. We further point out the constraints imposed on secondary succession by the life histories of ‘available’ species.     

Structure of major seagrass beds from three coral reef atolls of Lakshadweep, Arabian Sea, India

Detritus-based marine ecosystems such as mangrove and seagrass are of immense ecological importance. Major seagrass meadows from three coral atolls of the Lakshadweep group (Arabian Sea) were studied for their floral components. Seagrass beds were heterogeneous, comprising mainly of Thalassia hemprichii and Cymodocea rotundata, in Agatti and Kavaratti and it was observed to be monospecific (T. hemprichii) in the Kalpeni lagoon. Maximum (0.34 km²) and minimum (0.005 km²) extent of seagrass beds were observed in Kavaratti and Agatti lagoons, respectively. Seagrass weight (dry) of 43.97, 30.88 and 0.74 t were estimated from Kavaratti, Kalpeni, and Agatti, respectively. Maximum biomass occurred from 0–2 m depth, mainly contributed by the aboveground shoots, and was found to be negatively correlated with depth (r=0.71, p<0.05). Sediments were devoid of seed reserves indicating seagrass growth mainly by vegetative propagation. Epiphytes, on an average, contributed 7.5% of the seagrass biomass and were dominated by algae such as Melobesia spp., Microcoleus lyngbyaceus and Ceramium spp. Epiphytic biomass, too, decreased with increasing depth. Associated marine algae were represented by 66 species, dominated by rhodophytes.     

Effect of permanent sea ice cover and different nutrient regimes on the phytoplankton succession of fjords of the Vestfold Hills Oasis, eastern Antarctica

Early season phytoplankton communities in both Omega and TaynayaBays are characterized by diatoms sedimenting out of the overlyingsea ice. Initial nitrate, phosphate and silicate levels arehigh and the bay waters are covered with ice and well mixed.In Taynaya Bay the ice cover is retained throughout the seasonwhile Omega Bay is ice free for 6–8 weeks. After ice breakout in Omega Bay, the phytoplankton community changes from onedominated by diatoms to one dominated by the phytoflagellates,Pyramimonas spp., Cryptomonas sp. and Gymnodinium sp. In TaynayaBay the ice remained and even though phytoflagellates becamemore common, diatoms still dominated. These differences in communitycomposition result from differences in light climate, extentof stratification and nutrient levels.     

Experimental restoration of a fen plant community after peat mining

Question: Which restoration measures (introduction of donor diaspore material, application of straw mulch, alteration of residual peat depths) contribute to the establishment of a fen plant community on minerotrophic surfaces after peat mining? Location: Rivière‐du‐Loup peatland, southern Québec, Canada at 100 m a.s.1. Methods: The effectiveness of introducing fen plants with the application of donor diaspore material was tested. The donor diaspore material, containing seeds, rhizomes, moss fragments, and other plant propagules, was collected from two different types of natural fens. We tested whether the application of straw mulch would increase fen species cover and biodiversity compared to control plots without straw mulch. Terrace levels of different peat depths (15 cm, 40 cm, and 56 cm) were created to test the effects of different environmental site conditions on the success of re‐vegetation. Results: Applying donor seed bank from natural fens was found to significantly increase fen plant cover and richness after the two growing seasons. Straw mulch proved to significantly increase fen plant richness. The intermediate terrace level (40 cm) had the highest fen plant establishment. Compared to reference sites, the low terrace level (15 cm) was richer in base cations, whereas the high terrace level (56 cm) was much drier. Conclusions: The application of donor diaspore material was demonstrated as an effective technique for establishing vascular fen plants. Further re wetting measures are considered necessary at the restoration site to create a fen ecosystem rather than simply restoring some fen species.     

Modeling Northern Peatland Decomposition and Peat Accumulation

To test the hypothesis that long-term peat accumulation is related to contemporary carbon flux dynamics, we present the Peat Decomposition Model (PDM), a new model of long-term peat accumulation. Decomposition rates of the deeper peat are directly related to observable decomposition rates of fresh vegetation litter. Plant root effects (subsurface oxygenation and fresh litter inputs) are included. PDM considers two vegetation types, vascular and nonvascular, with different decomposition rates and aboveground and belowground litter input rates. We used PDM to investigate the sensitivities of peat accumulation in bogs and fens to productivity, root:shoot ratio, tissue decomposability, root and water table depths, and climate. Warmer and wetter conditions are more conducive to peat accumulation. Bogs are more sensitive than fens to climate conditions. Cooler and drier conditions lead to the lowest peat accumulation when productivity is more temperature sensitive than decomposition rates. We also compare peat age–depth profiles to field data. With a very general parameterization, PDM fen and bog age–depth profiles were similar to data from the the most recent 5000 years at three bog cores and a fen core in eastern Canada, but they overestimated accumulation at three other bog cores in that region. The model cannot reliably predict the amount of fen peat remaining from the first few millennia of a peatland's development. This discrepancy may relate to nonanalogue, early postglacial climatic and nutrient conditions for rich-fen peat accumulation and to the fate of this fen peat material, which is overlain by a bog as the peatland evolves, a common hydroseral succession in northern peatlands. Because PDM sensitivity tests point to these possible factors, we conclude that the static model represents a framework that shows a consistent relationship between contemporary productivity and fresh-tissue decomposition rates and observed long-term peat accumulation. Received 19 June 2000; accepted 24 January 2001.     

Spatial and Temporal Variability in Growing-Season Net Ecosystem Carbon Dioxide Exchange at a Large Peatland in Ontario,Canada

We measured net ecosystem exchange of carbon dioxide (CO2) (NEE) during wet and dry summers (2000 and 2001) across a range of plant communities at Mer Bleue, a large peatland near Ottawa, southern Ontario, Canada. Wetland types included ombrotrophic bog hummocks and hollows, mineral-poor fen, and beaver pond margins. NEE was significantly different among the sites in both years, but rates of gross photosynthesis did not vary spatially even though species composition at the sites was variable. Soil respiration rates were very different across sites and dominated interannual variability in summer NEE within sites. During the dry summer of 2001, net CO2 uptake was significantly smaller, and most locations switched from a net sink to a source of CO2 under a range of levels of photosynthetically active radiation (PAR). The wetter areas--poor fen and beaver pond margin--had the largest rates of CO2 uptake and smallest rates of respiratory loss during the dry summer. Communities dominated by ericaceous shrubs (bog sites) maintained similar rates of gross photosynthesis between years; by contrast, the sedge-dominated areas (fen sites) showed signs of early senescence under drought conditions. Water table position was the strongest control on respiration in the drier summer, whereas surface peat temperature explained most of the variability in the wetter summer. Q 10 temperature-respiration quotients averaged 1.6 to 2.2. The ratio between maximum photosynthesis and respiration ranged from 3.7:1 in the poor fen to 1.2:1 at some bog sites; it declined at all sites in the drier summer owing to greater respiration rates relative to photosynthesis in evergreen shrub sites and a change in both processes in sedge sites. Our ability to predict ecosystem responses to changing climate depends on a more complete understanding of the factors that control NEE across a range of peatland plant communities.     

大型热带水库-松涛水库枯水期浮游植物群落特征

松涛水库是一个大型热带水库,分为两个主要水域:番加洋和南丰洋,2003年12月对该水库的这两个水域的浮游植物进行采样,共发现7门65种藻类。松涛水库番加洋库区水体的浮游植物总细胞密度为1.08×10⁶cells·L^-1,主要种类组成为蓝藻(Cyanophyta)-绿藻(Chlorophyta)型。松涛水库南丰洋库区水体的浮游植物群落为细胞密度为1.14×10⁶cells·L^-1,主要种类组成为绿藻(Chlorophyta)-硅藻(diatom)型。松涛水库库区水体总体已为避-富营养,其中富营养型浮游植物指示种类有:铜绿微囊藻(Microcystis aeruginosa Kütz.),针状蓝纤维藻(Dactylococcopsis acicularis),镰形纤维藻(Ankistrodesmus falcatus),小环藻(Cyclotella menighiniana),模糊直链藻(Melosira spp.)等。与亚热带和温带的水库比较,处于热带地区的松涛水库浮游植物,在湖泊区微囊藻等适应高温高光强的种类具有更高的细胞密度。松涛水库河流区最主要的优势种是硅藻门的针杆藻。     

Histosol as an ecologically active constituent of peatland: a case study from Estonia

This study clarifies the area distribution of Estonian peat soils by three factors: main peat soil groups, peat thickness and peat decomposition degree. A digital soil map (1:10,000) and supplementary database were used for summarizing the distribution of peat soils. From the combined database with 859,701 polygons the soil mapping unit code, formula of soil texture (including peat) and formula of epipedon fabric were compiled using the MapInfo software. Peat soils form altogether 10,038 km² or 23.5% of the total Estonian soil cover. From the peat soils the fen soils form 59.0%, bog soils 21.7% and transitional bog soils 14.7%. 45% of peat soils are well, 26% moderately and 29% slightly decomposed, by the peat thickness 13% are very shallow, 21% shallow and 66% thick. The general ecological characterization of peat soils and their mutual relationship with plant cover are given for the main peat soil taxa. The dominant natural ecosystems formed on peatlands are: (1) mixed birch, alder, spruce and pine forests on thin (<100 cm) well decomposed eutrophic fen soils, and (2) a sparse pine forests and hummock-ridge-hollow raised bogs wooded sparsely by pine on thick (>100 cm) slightly decomposed oligotrophic bog soils. The accumulation of organic carbon in peatlands soil cover (0–50 cm) totals 269.4±12.7 Tg and in epipedon layer (as superficial part of soil cover; 0–30 cm) 129.9±5.8 Tg. The former is sequestrated into 543.7 Tg of peat, which forms 22.9% of the total Estonian peat resources (2.37 Pg).     

Spectral feature differences between shrub and grass communities and shrub coverage retri- eval in shrub-encroached grassland in Xianghuang Banner,Nei Mongol,China

Aims Shrub-encroached grassland has become an important vegetation type in China’s arid and semi-arid region. Our study objective is to explore the spectral features of shrub and grass communities, as well as their empirical relationships with shrub coverage. The quantitative estimation of shrub cover based on medium-resolution Landsat satellite imagery provides the practical basis for long term retrieval of large areas of shrub expansion in the grassland region. Methods Linear models and Multiple Endmember Spectral Analysis Model (MESMA) based on medium resolution Landsat satellite imagery were developed to quantify the shrub coverage in a shrub-encroached grassland region in Xianghuang Banner, Nei Mongol using the spectral features and their seasonal differences between the shrub and grass communities. Important findings Compared to Leymus chinensis and Stipa krylovii dominated grass communities, Caragana microphylla community had a higher normalized difference vegetation index (NDVI), modified red edge normalized difference vegetation index (mNDVI₇₀₅), and red edge slope. The red edge position of C. microphylla community shifted to longer wavelengths. The average and the maximum shrub coverage was 13% and 25%, respectively, in the shrub-encroached grassland based on both models. The correlation coefficient of determination (R²) and root mean square error (RMSE) of the linear model was 0.31 and 0.05, respectively. We found that the linear model based on seasonal differences of shrub and grass community was more suitable for retrieving shrub coverage in the study area from medium resolution imagery than the MESMA model that is based on mid-summer images.     

Small rodents, their habitats, and the effects of flooding at Wicken Fen, Cambridgeshire

The habitat preferences of small rodents were studied by live trapping methods at Wicken Fen, Cambridgeshire, a relict area of East Anglian fenland. The study sites were chosen to cover areas of managed fields, dominated by sedge ( Cladium mwiscus ) or by litter (grasses with sedges); the adjacent fen carr "bush growth"; and an area of unmanaged sedge. Clethrionomys glareolus is the commonest rodent species, occurring at relatively high densities, and closely associated with sedge growth. It is ubiquitous in unmanaged sedge but in managed sedge and litter field areas there is a marked preference for the field/fen carr transition where sedge growth is not cut. Thick sedge seems to afford the optimum habitat for this species probably because of the three-dimensional vegetation structure which provides dense ground cover with a natural thatch of dead leaves; this decays only slowly, even in succeeding fen carr. Sedge fields provide a less stable habitat and recolonization of a harvested field by Clethrionomys only began after eight months of sedge regrowth. Micromys minutus are caught only in sedge and litter. Apodemus sylvaticus seem to show no marked habitat preference but there are some data which suggest that high Clethrionomys densities can affect Apodemus distributions locally. Microtus agrestis prefers grassy patches within sedge fields; trap success points tending to be associated with the presence of Calamagrostis canescens. Microtus avoids fen carr and unmanaged sedge and is generally caught more often in litter fields than in sedge fields; however, this preference seems to disappear at the end of the Clethrionomys breeding season. During flooding, Clethrionomys found refuge in the dense sedge and sedge/carr transition habitats; prolonged flooding caused a decline in numbers of Clethrionomys and the elimination of Microtus , while the distribution of Apodemus was apparently unaffected.     

Stand structure and vegetation dynamics of a subalpine wooded fen in Rocky Mountain National Park,Colorado

Abstract. The tree population size structure and relationship between tree diameter and age were examined in a subalpine fen and surrounding Picea-Abies forest in northern Colorado. The fen grades from a sedge fen, through an ecotone, to a treed fen. Tree growth rate varies across the vegetational gradient, with the sedge fen having the slowest growth, and the upland forest having the fastest growth. Differences in growth rate are related to the average size of peat hummocks, with areas containing tall hummocks exhibiting the highest tree growth rates. Size structures display the characteristic reverse-J distribution generally indicative of stable populations, but forest vegetation is expanding into the open regions of the fen, and within the treed fen an increase in Abies lasiocarpa is occurring. These changes are primarily attributed to a positive feedback situation wherein the fen's surface is built up by peat accumulation. Distinct hummocks form first on the open fen but then coalesce to form raised peat islands in the treed fen. This new substrate provides habitat with a comparatively low water table and allows the growth of mesophytic forest vegetation. A pathway for this vegetational development is proposed.     

Fungal and Bacterial Activity in Northern Peatlands

Selective inhibition of substrate-induced respiration with antibiotics cycloheximide and streptomycin sulphate provided insight into eukaryotic versus prokaryotic activities in surface peat soil of three Canadian peatlands. Prokaryotic and eukaryotic communities in peatlands are important in the net sequestration of atmospheric carbon dioxide and therefore play a unique role in global carbon cycling. Selective inhibition techniques were generally successful, with a maximum non-target inhibition of only 17%. Assuming that eukaryotic and prokaryotic activities were dominated by fungi and bacteria respectively, across 3 ecologically and hydrologically diverse and spatially dispersed peatlands, we demonstrated bacterial dominance in a bog and a poor fen both with acidic and primarily Sphagnum derived peat soil and in a near pH neutral wetter rich fen with sedge peat (fungal to bacterial activity ratio = 0.31 to 0.68). These results differ in that in other acidic environments, such as conifer forest soils, fungal to bacterial activity ratios are mostly greater than 1 indicative of fungal dominance.     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.     

Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies ( Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.
2. Mean densities of larvae (range 234–2318 m⁻²) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m⁻²) was always highest at the stable, spring-fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.
3. Annual production was high at the more stable, alkaline site (10.35 gLDW m⁻²) but much lower at the other sites (2.49–3.77 g m⁻²).
4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).
5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).
6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.