Freshwater marshes as dissolved silica recyclers in an estuarine environment (Schelde estuary, Belgium)

Compared to knowledge about N and P processing in the aquatic continuum of lakes, wetlands and estuaries, knowledge concerning transport and cycling of Si is only fragmentary. Furthermore, Si research in estuaries has mainly been focused on subtidal benthic sediments and uptake and recycling by diatom communities. The biogeochemical cycling of Si in tidal wetlands, which can contain large amounts of Si, has thus far been neglected. We have conducted several whole ecosystem Si mass-balances on a freshwater marsh located in the Schelde estuary (6 tidal cycles, 2 with BSi included). Our measurements show that the freshwater marsh acts as an important source of dissolved Si to the main river (1–18% more export than import, on average 0.114 g m^–2). This export is compensated by import of amorphous silica into the marsh (19–55% more import than export). The marsh was shown to act as silica recycler, resupplying biologically available dissolved Si to the estuarine ecosystem. Extrapolations show that during summer and spring months, when dissolved silica is depleted due to diatom growth, almost half of the total dissolved silica load in the main river channel could result from marsh recycling.     

温带地区表土植硅体对温度的响应

植硅体的现代过程研究是利用植硅体这一指标精准恢复区域古植被、古气候的前提和关键环节,探讨表土植硅体组合的空间分布特征及其对环境因子的响应尤为重要.本研究在东北地区沿着年降水量为600 mm等降水线采集54块表土样品,研究单一温度控制下表土植硅体的空间分布规律,以期寻找对温度比较敏感的植硅体类型.结果表明:54块表土样品...     

The production of phytoliths in China's grasslands: implications to the biogeochemical sequestration of atmospheric CO2

Among the most promising approaches of long‐term atmospheric CO₂ sequestration is terrestrial biogeochemical carbon sequestration. One of the most promising terrestrial biogeochemical carbon sequestration mechanisms is the occlusion of carbon within phytoliths, the silicified features that deposit within plant tissues. Using phytolith content‐biogenic silica content transfer function obtained from our investigation, in combination with published silica content and above‐ground net primary productivity (ANPP) data of China's grasslands, we estimated the production of phytoliths and phytolith‐occluded carbon (PhytOC) in grasslands. The results show that the average above‐ground phytolith production rates of China's grasslands (10.9 10⁶ t yr^?1 or 1.45% of world grasslands) are much lower than those of other grasslands (e.g. North American nonwoody grasslands) mainly because of much lower ANPP. Assuming a median content of PhytOC of 1.5%, the average above‐ground PhytOC production rates of China's grasslands and world grasslands are estimated to be 0.6 10⁶ t CO₂ yr^?1 and 41.4 10⁶ t CO₂ yr^?1, respectively. The management of grasslands to maximize ANPP has the potential to result in considerable quantities of phytoliths and securely bio‐sequestered carbon.     

Monogenean parasites from Clariidae (Teleostei, Siluriformes) in Cameroon: I. Description of two new species of Gyrodactylus from the Nyong basin

The study of gill and skin parasites of three fishes species belonging to the genus Clarias: C. camerunensis, C. jaensis and C. pachynema, from the Nyong basin (Cameroon), revealed the presence of two new Monogenean species of the genus Gyrodactylus Nordmann: G. camerunensis n. sp. and G. nyongensis n. sp. parasite of Clarias camerunensis, C. jaensis and C. pachynema. Gyrodactylus camerunensis n. sp. is clearly distinguished from G. nyongensis n. sp. by the smaller size of the haptor sclerites. These two new species differ also from their closest African relatives of the genus Gyrodactylus, G. rysavyi, G. clarii and G. alberti, by the morphology and size of the haptorail sclerites. Their host specificity was discussed and appeared stenoxenous (mesostenoxenous).     

闽江口潮滩湿地不同植被带土壤及间隙水中硅的分布特征

以闽江口潮滩湿地为研究对象,由岸及海方向对芦苇、短叶茳芏、互花米草(潮沟内)和互花米草(潮沟外)4种湿地土壤生物硅和土壤间隙水氮硅营养盐含量及其随深度变化的特征进行为期1a的季度观测。结果显示:互花米草(外)、短叶茳芏、芦苇和互花米草(内)带湿地土壤生物硅的年均含量依次降低,分别为14.33、10.40、9.98、7.50 mg/g;互花米草(外)、互花米草(内)、短叶茳芏和芦苇带湿地土壤间隙水活性硅酸盐年均含量依次降低,分别为407、359、344、323μmol/L;湿地各植被带土壤及间隙水含硅量均呈现夏秋季节高于冬春季节的趋势。统计分析表明:间隙水活性硅酸盐与土壤生物硅含量、距潮沟的距离之间的正相关性均比较显著(P0.05),温度对土壤中硅含量的影响也有一定的正相关性,说明湿地植被、温度和潮汐作用是影响闽江口湿地硅分布的重要因素。与土著种对比,互花米草入侵在一定程度上改变了闽江口潮滩湿地土壤硅分布的格局。     

Human dental microwear caused by calcium oxalate phytoliths in prehistoric diet of the lower Pecos region,Texas

Recent research demonstrates that silica phytoliths of dietary origin are associated with microwear of human teeth. Previous research has shown that severe enamel microwear and dental wear characterizes Archaic hunter-gatherers in the lower Pecos region of west Texas. Calcium oxalate crystals are especially common in Archaic coprolites. The vast majority are derived from prickly pear and agave, which were the dietary staples in west Texas for 6,000 years. The calcium oxalate phytoliths are harder than enamel. Therefore, calcium oxalate crystals are the most likely source of previously documented dental microwear and wear in the lower Pecos region. Am J Phys Anthropol 107:297–304, 1998. © 1998 Wiley-Liss, Inc.     

Biogenic silica as an estimate of siliceous microfossil abundance in Great Lakes sediments

Biogenic silica concentration (BSi) in sediment cores from the Great Lakes is evaluated as an estimate of siliceous microfossil abundance. A significant linear relationship was found between measured BSi and diatom valve abundance for sediment cores from the Bay of Quinte, Lake Ontario, Lake Erie, Lake Michigan and Lake Superior and between measured BSi and diatom biovolume for Lake Erie, Lake Michigan, and Lake Superior but not for Lake Ontario. Diatom silica predicted from diatom species abundance and an estimated silica content per cell in the Lake Erie cores accounted for 117% and 103% of measured BSi, respectively. By contrast, predicted diatom silica could only account for 28% of measured BSi in the Lake Michigan core and only 25% in the Lake Superior core. A few large diatoms with a large silica content per cell comprised a major portion of predicted diatom silica in all cores. The discrepancy between chemically measured BSi and the silica predicted from diatoms in the Lake Michigan and Lake Superior cores was partially due to the inability of the regression model, used to estimate diatom silica content, to account for different degrees of silicification in the diatom asemblages from the more dissolved silica rich Lake Michigan and Lake Superior.     

Threat of rapid extermination of the lion (Panthera leo leo) in Waza National Park,Northern Cameroon

Lion populations in West and Central Africa are small and fragmented. In areas where park management is weak, threats will likely facilitate the extinction of the lion. Wildlife management requires knowledge of the population estimate. The population of lions in Waza National Park (Waza NP) was assessed by individual identification of members in the population. The population was assessed to comprise of 14–21 adult individual lions. The age structure was skewed towards adults; cubs comprised 22% of all lions identified while the sex ratio was 1 : 3. Two out of four collared lions were lost to illegal, retaliatory killings within 1 year; and probably two more males and one more female were also killed during this period. The lion population appears to have declined during the last 5 years with six lions dying per year, which is at a much higher rate than observed in the previous decades. Human‐livestock pressure has increased tremendously in this period, resulting to frequent human‐lion conflicts. To ensure the survival of the lion in Waza NP and in the entire region, management needs to intensify efforts to mitigate the pressure from humans and their livestock.     

Seasonal variation in the feeding ecology of the grey-cheeked mangabey (Lophocebus albigena) in Cameroon

Seasonal fluctuations in resource abundance often cause primates to change their feeding behavior and ecology. The objective of this study was to examine the response of a largely frugivorous monkey, the grey-cheeked mangabey (Lophocebus albigena), to seasonal variations in fruit abundance. We used 15-min scan sampling to quantify feeding, activity, and habitat use by monkeys between February and December 1998 in the Dja Reserve, Cameroon. L. albigena were found to have omnivorous feeding habits, consuming the fruits, seeds, leaves, and flowers of 132 plant species. Although monkeys fed from many plant species, only five plant species accounted for 45% of all feeding records. The number of feeding observations on a plant species was significantly correlated with its fruit production. L. albigena responded to fruit-lean periods by shifting from a diet dominated by fruit to one dominated by seeds, flowers, and young leaves. This diet shift coincided with greater use of swamp habitat and higher dietary diversity. L. albigena spent the greatest percentage of scan samples feeding and traveling, but activities varied significantly over the day. Individuals spent a significantly higher percentage of scan samples feeding during the fruit-rich season than in the fruit-lean season. Comparing our results to those of studies in Gabon and Uganda, we found that L. albigena differ across regions in the number of plant species they consume and time spent feeding. These differences may be a result of variations in tree diversity or the strength of seasonal fluctuations in resource abundance among sites.     

Diversity and community structure of bats (Chiroptera) in the Centre Region of Cameroon

In this survey, we investigated the diversity and community structure of bats in the Centre Region of Cameroon with respect to their distribution in the different vegetation zones of the region. We mist-netted bats monthly from January 2016 to June 2017 for five nonconsecutive nights per month. Thirty-nine sites were surveyed: 24 in traditional farms, nine in the savannah and six in the forests. A total of 668 bats were captured during 81 nights of capture, covering seven families, 21 genera and 36 species. This included 26 species in traditional farms, 13 species in savannah and 11 species in the forest. Micropteropus pusillus was the most abundant species (30.7%) recorded, followed by Hipposideros ruber (24.9%). The sample efficiency was estimated at 72.1% with fitted species accumulation curves not reaching asymptotes for the three habitat types, suggesting that the survey did not record all the bats present. There was an indication of general increased in abundance of bats during the dry and rainy seasons but it is not significant (Mann–Whitney U: 783.5, p = .195). The rarity index was highest in traditional farms (0.44), followed by savannah (0.38) and then forest (0.33). This preliminary survey provides baseline data on the distribution of bats in the different vegetation types in the Centre Region of Cameroon.     

Home range size and dispersion in the helmeted guineafowl (Numida meleagris galeata Pallas) of the Waza National Park, Cameroon

Field investigations of the home range size and emigration pattern of wild helmeted guineafowl ( Numida meleagris galeata Pallas) from 1992 to 1995 showed that home range size (±95% confidence limits (CL) ) varied with season from 3·6±1·5 km² for the dry seasons to 3·1±1·5 km² for the rainy seasons. Home range size varied depending on whether it was estimated with data for adult males, adult females or young birds, with a higher home range size for young birds, closely followed by adult males. Group size (±95%CL) varied by month, and was highest between March and April (47·0±8·1 birds/group) and lowest in August 9·0±5·1 birds/group). More young birds (±95%CL) (36·8±19·6%) dispersed than adult males (21·1±1·9%) or adult females (13·5±1·8%). There was a highly significant positive correlation between group size and the number of birds emigrating from the group. There was also a significant negative correlation between the weights of birds at tagging and the percentage that emigrated during the first year of study but not later. This is suggested to be linked to the high number of young birds emigrating, since they weigh relatively less than adults. The lack of correlation between body weight and number of birds emigrating a year or later after birds were tagged was thought to be due to the fact that birds tagged while young attained adult weight within a year.     

Diversity and distribution of millipedes (Diplopoda) in the Campo Ma'an National Park,southern Cameroon

Diplopods (millipedes) are one of the important groups of terrestrial Arthropoda in tropical forest ecosystems. Despite their ecological importance, data on millipede populations are still scarce and outdated in Cameroon. The first comparative eco‐faunistic analysis is presented of two local populations of Diplopoda in two lowland rainforests (nearly primary and secondary) during 12 months (2015–2016) at the southern periphery of the Campo Ma'an National Park in southern Cameroon. The millipedes were collected using pitfall trapping and quadrat sampling, their diversity and distribution analyzed with the help of two diversity indexes and two nonparametric estimators. Overall, 27 species in eighteen genera, ten families and four orders were revealed in the two forests, yet each faunule was about equally rich (23 and 22 species in the primary and secondary forest, respectively) and peculiar (five and four species unique, respectively). The Odontopygidae was the most abundant family, which made up to 33% of the total species diversity. The most abundant species in both forests was Aporodesmus gabonicus (26.8% of occurrences). This study shows that despite the similarity in millipede species richness between both habitats, the species composition of all habitats was different. Some species occurred in two habitats whilst others were restricted to only one habitat.     

The regulatory framework for the exploitation of medicinal plants in Cameroon: the case of Prunus africana on Mount Cameroon

Before the beginning of its large scale exploitation by a European pharmaceutical company in 1972, the tree species Prunus africana was known in Cameroon only for traditional uses. The present exploitation may lead to its extinction on Mount Cameroon. This paper explains the destruction of P. africana within the current regulatory framework and recommends stricter compliance with the regulations, which would guarantee survival of this species in the wild. Field observations are also presented.     

Use of a tool-set by Pan troglodytes troglodytes to obtain termites (Macrotermes) in the periphery of the Dja Biosphere Reserve, southeast Cameroon

At the northern periphery of the Dja Biosphere Reserve (southeastern Cameroon) we recorded a new use of a tool-set by Pan troglodytes troglodytes to prey on Macrotermes muelleri, M. renouxi, M. lilljeborgi, and M. nobilis. We recovered 79 puncturing sticks and 47 fishing probes at 17 termite nests between 2002 and 2005. The mean length of the puncturing sticks (n = 77) and fishing probes (n = 45) was 52 cm and 56 cm, respectively, and the mean diameter was 9 mm and 4.5 mm, respectively. Sixty-eight percent of 138 chimpanzee fecal samples contained major soldiers of four Macrotermes species. The chimpanzees in southeastern Cameroon appeared to be selective in their choice of plant material to make their tools. The tools found at our study site resemble those from other sites in this region. However, in southeastern Cameroon only one tool-set type was found, whereas two tool-set types have been reported in Congo. Our study suggests that, along with the different vegetation types and the availability of plant material around termite nests, the nest and gallery structure and foraging behavior of the different Macrotermes spp. at all Central African sites must be investigated before we can attribute differences in tool-use behavior to culture.     

沉积物生源要素对水体生态环境变化的指示意义

受人类活动影响,输入到湖泊、河口中的营养盐剧增,导致水体富营养化、食物链结构改变、底质季节性缺氧等生态环境变化。这些环境变化会在沉积物中留下记录,沉积物中生源要素及其稳定同位素的变化是指示水域古生产力、营养盐水平的有效指标。总结归纳了沉积物中生源要素(碳、氮、磷、硅)指标对水体环境中初级生产力、物质来源、营养盐水平3方面变化的指示作用。沉积物中TOC、TN、δ13C、CaCO3和BSi可以反映水体沉降有机质含量和浮游植物的生长状况,是指示水域初级生产力水平的有效指标。根据不同类型植物来源的有机质中δ13C、δ15N和C/N的差异,可以追踪沉积物中有机质的来源。有效地区分有机质来源对于研究人类活动对水体环境的影响及水体富营养化具有重要的价值。沉积物中TN、δ15 N、TP和非磷灰石磷(NAIP)含量的升高直接反映了陆源输入氮、磷的增加。BSi在指示浮游植物生长状况的同时,还反映了水体溶解硅浓度水平和富营养化状况。水体中的生源物质在沉降和埋藏的过程中,会受到早期成岩作用、水动力搬运等众多因素的作用,使沉积物记录的环境变化信息发生改变,从而干扰其对水体环境演变的重建作用。因此综合分析各生源要素指标反映的环境变化信息及其可能的干扰因素,方能正确地反映水域的环境变化过程。     

Measuring the local community's participation in the management of community forests in Cameroon

Cameroon revised its forestry policy and included the legal concept of community forests, a concept difficult to develop. This study aims to resolve this difficulty by understanding the concept as it is designed by the Cameroon Ministry of Environment and Forestry (MINEF). To this end, two formulae, the second simpler than the first, were developed to measure the percentage of involvement of the local community in the process of implementing a community forest. A questionnaire constructed to assess the importance of the activities in this process provided the coefficients for the first formula. The questionnaire was administered to five groups representing the possible participants in the implementation process. There are statistically significant differences among the mean ratings of importance by the five groups and for the various activities. Despite the latter differences, the numerical difference between the two formulae is negligible. Correlations of the ranking of the importance of the activities predict successful collaboration among MINEF, conservation project officials, and members of non-governmental organizations (NGOs). In contrast, the local communities are less likely to collaborate with the first three groups. There is a gulf between the communities and outside organizations (Ministry, conservation project officials and NGOs). Strategies for facilitating the process of implementing the community forest are suggested.     

Influence of bacteria and salinity on diatom biogenic silica dissolution in estuarine systems

Dissolution of diatom biogenic silica (bSiO₂) in estuaries and its control by water salinity and bacteria were investigated using the river euryhaline species Cyclotella meneghiniana as a model. Laboratory-controlled bioassays conducted at different salinities with an estuarine bacteria inoculum showed a faster dissolution of diatom bSiO₂ at the lowest salinity where bacteria were the most abundant. However in another experiment, salinity increase clearly enhanced the dissolution of cleaned frustules (organic matter free). The presence of active bacteria might therefore predominate on the effect of salinity for freshly lysed diatoms whereas salinity might rather control dissolution of organic-matter-free frustule remains. Incubation of cultivated diatoms at different protease concentrations revealed that high proteolytic activities had little effect on bSiO₂ dissolution at a 1-month scale in spite of an efficient removal of organic matter from the frustules. Altogether it is hypothesized that bacterial colonization increases bSiO₂ dissolution by creating a microenvironment at the diatom surface with high ectoproteolytic activity but also via the release of metabolic byproducts since the presence of organic matter seems generally to facilitate diatom bSiO₂ dissolution.     

The importance of epigeic beetles (Coleoptera) in tropical paddy fields: Example from Cameroon

Abstract

Indicators of diversity (population density, relative number of species, percentage of singletons, evenness) of ground beetles (Carabidae) and rove beetles (Staphylinidae) in rain-fed rice fields were assessed between 1995 and 1999 at Garoua in the Benue valley in North Cameroon. A total of 4369 individuals belonging to 44 species of carabids and 2109 staphylinids in 27 species were caught by means of pitfall traps. Among the carabids, five species: Menigius lucidus var. strigiceps Qued., Chlaeniostenus denticulatus elatus Erichson, Lissauchenius venator (Laferté), Pheropsophus marginatus Dej. and Abacetus crenulatus Dej. in decreasing order, were dominant. In the staphylinid group, the species Paederus sabaeus Erichson was the most common, followed by Stenus ravus Puthz and Stenus (mendicus) senegalensis Bernhauer. Shannon-Weiner and evenness indices varied marginally from year to year. Diversity values remained relatively low ( < 2.8) among each group of beetles, which indicated that paddy fields were moderately populated by this group of polyphagous predators. Features of predacious soil surface-dwelling beetles in West African rice ecosystems are discussed in the light of Integrated Pest Management concepts.     

Impact of the invasive ant Wasmannia auropunctata (Formicidae: Myrmicinae) on local ant diversity in southern Cameroon

The little fire ant, Wasmannia auropunctata Roger, is one of the world's most destructive invasive ants. It has been present in Cameroon for more than four decades, but its impact on local ant diversity is not known. We studied impact of W. auropunctata in three disturbed habitats located in rural and urban areas. We monitored ant diversity in both invaded and noninvaded zones in each area using a combination of three sampling methods: bait, pitfall traps and visual catch in quadrat. We collected 28 species in urban area and 64 in rural area. In invaded zone, W. auropunctata made up 97.72% and 99.96% of all ant fauna and ant species richness decreased to 7 and 2 in urban and rural area, respectively. In accordance with others findings in introduced environments, the presence of W. auropunctata has severely reduced abundance and richness of local ant species in both urban and rural environments in Cameroon. Measures should therefore be put in place to prevent its introduction in natural environment as forest reserves and natural parks.     

A dynamic model for suspended particulate matter (SPM) in rivers

Aim To present a general, process‐based river model for suspended particulate matter (SPM). Location General approach based on processes; data from Europe and Israel. Methods The model has been tested and calibrated using an empirical river model for SPM and validated (blind‐tested) using data from seven European sites. This modelling gives mean monthly SPM concentrations in water for defined river sites. The model is based on processes in the entire upstream river stretch (and not for given river segments) and calculates the transport of SPM from land to water, primary production of SPM (within the upstream river stretch), resuspension, mineralization and retention of SPM in the upstream river stretch (but not bed load of friction materials, such as sand). The catchment area is differentiated into inflow (～ dry land) areas and outflow area (～ wetland areas dominated by relatively fast horizontal SPM‐fluxes). The model is simple to apply in practice as all driving variables may be accessed readily from maps. The driving variables are: latitude, altitude, continentality, catchment area and mean annual precipitation. Results Modelled values have been compared to independent empirical data from sites covering a relatively wide domain (catchment areas from 93 to 5250 km², precipitation from 400 to 660 mm year^?1, altitudes from ?210 to 150 m a.s.l., latitudes from 47 to 59° N and continentalities from 200 to 1000 km from the ocean). When blind‐tested, the model predicts annual SPM‐fluxes well. Conclusion When modelled values are compared to empirical data, the slope is almost perfect (1.03) and the r²‐value is 0.9996. This is good, given the fact that there are several simplifications in the model structure. It must, however, be stressed that there are only seven validation cases and that this model has not been tested for small catchments.