Bald kelp: natural and harvesting-induced frond loss in the South African kelp Ecklonia maxima     

C Elston  LM Price 《African Journal of Marine Science》2015,37(3):373-381

Ecklonia maxima dominates kelp beds on the west coast of southern Africa, and is commercially and ecologically valuable. Some plants lose all their secondary blades (fronds), leaving only the gas-filled bulb and short primary blade at the top of the stipe. These ‘bald’ kelps may persist for months or longer, occupying substratum space but contributing little to productivity. We investigated natural causes of balding in five kelp beds in False Bay, South Africa, and the effect of simulated commercial frond-harvesting on loss of fronds. Densities of sporophytes with and without fronds were measured at the water surface during low tides. Generalised linear modelling analysis showed a significant relationship between balding and site (whether sheltered from or exposed to swell/wind), position in the kelp bed (shoreward or seaward) and total E. maxima density. We conclude that balding is caused mainly by drying of meristematic basal regions of fronds during emersion of kelp heads at low tide. After partial harvesting of fronds, kelp heads floated higher out of the water, but after 95 days frond loss was significantly higher only when fronds were cut too close to the primary blade, possibly because of damage to meristematic tissue. Nevertheless, increased emersion that results from frond-harvesting may increase desiccation and blade loss and we suggest caution in setting harvest limits for this kelp.  相似文献   

多源遥感数据支持下的城市生态状况评价     

王媛  杜明义  杨柳忠  蔡国印  张宁 《测绘通报》2021,(11):16-20

城市生态环境监测具有数据来源广泛、监测要素复杂、服务对象多样等特点,整合可用的资源进行城市生态的综合监测成为目前关注的热点。本文利用高分辨率遥感影像,以及地表覆盖、城市边界等遥感产品,在现有遥感生态指数的基础上,结合黑臭水体指数,构建适合综合评估城市生态状况的集成遥感监测模型,实现对城市生态环境状态的多维度监测。该方法能够较准确客观地反映城市的生态环境质量,理论上补充了基于遥感数据的城市生态环境监测方法,可为城市生态环境监测的信息化建设提供技术支撑。  相似文献   

Historical influences on the current provision of multiple ecosystem services     

《Global Environmental Change》2015

Ecosystem service provision varies temporally in response to natural and human-induced factors, yet research in this field is dominated by analyses that ignore the time-lags and feedbacks that occur within socio-ecological systems. The implications of this have been unstudied, but are central to understanding how service delivery will alter due to future land-use/cover change. Urban areas are expanding faster than any other land-use, making cities ideal study systems for examining such legacy effects. We assess the extent to which present-day provision of a suite of eight ecosystem services, quantified using field-gathered data, is explained by current and historical (stretching back 150 years) landcover. Five services (above-ground carbon density, recreational use, bird species richness, bird density, and a metric of recreation experience quality (continuity with the past) were more strongly determined by past landcover. Time-lags ranged from 20 (bird species richness and density) to over 100 years (above-ground carbon density). Historical landcover, therefore, can have a strong influence on current service provision. By ignoring such time-lags, we risk drawing incorrect conclusions regarding how the distribution and quality of some ecosystem services may alter in response to land-use/cover change. Although such a finding adds to the complexity of predicting future scenarios, ecologists may find that they can link the biodiversity conservation agenda to the preservation of cultural heritage, and that certain courses of action provide win-win outcomes across multiple environmental and cultural goods.  相似文献   

Population variations in the grazing turbinid Lunella smaragda (Mollusca: Gastropoda)     

John R. Walsby 《新西兰海洋与淡水研究杂志》2013,47(2):211-238

The grazing turbinid gastropod Lunella smaragda was sampled regularly over 3.5 y from precise sites of different microtopography and height on the platform shore at Goat Island Beach near Leigh, Northland, New Zealand. Growth is linear for over 3 y, and the year‐classes distinct. The position of the different size‐classes is related to both the shelter afforded by the microtopography, and to the height on the shore. The populations in the mid‐eulittoral turf flats, low eulittoral bare rock areas, and the sublittoral fringe are distinct, and there is a general movement down the shore with age and size. Wave action apparently dislodges the animals from higher areas when they grow to a critical size and transports them to sites lower on the shore, where wave disturbance is less. Field experiments with marked animals and laboratory studies with a wave tank confirm that the wave‐effected distribution is size related. However measurements showed that the ratio of foot attachment area to the shell area presented to the wave does not vary with animal size. The possible benefits of wave dislodgment and wave‐effected distribution are considered.  相似文献   

Chlorophyll production,in response to nutrient additions,by the algae in Lake Taupo water     

E. White  G. W. Payne 《新西兰海洋与淡水研究杂志》2013,47(3):501-507

In batch cultures of Lake Taupo water, phosphorus was the nutrient limiting plant growth from January to June, and nitrogen took over this role from July to December. Chlorophyll production by algae was often stimulated by trace element additions, but it was uncertain whether total cytoplasmic production was also involved.  相似文献   

Oxygen consumption in the epilimnia and hypolimnia of two eutrophic,warm‐monomictic lakes     

S. F. Mitchell  Carolyn W. Burns 《新西兰海洋与淡水研究杂志》2013,47(3):427-441

Oxygen consumption was estimated for two eutrophic New Zealand lakes using a simple 2‐layer model, from estimates of net changes in oxygen, phytoplankton photosynthesis, inflow and outflow, diffusion, eddy diffusion, and changes in the depth of the thermocline. Of the total oxygen consumption, 75–85% occurred in the epilimnia. Epilimetic oxygen consumption per m³ and per m² in Lake Johnson were higher than in Lake Hayes, reflecting known differences in the trophic status of the lakes, but estimates for the hypolimnia of the two lakes were similar. Daily hypolimnetic areal deficits were sensitive to both the depths and time intervals chosen.

In the epilimnia, monthly oxygen production by photosynthesis averaged 1.1 and 1.8 times the initial oxygen content in Lakes Hayes and Johnson respectively. Diffusion appeared to be of similar magnitude to photosynthesis in the isothermal period, but was less important during stratification. Losses to the hypolimnia by eddy diffusion were less than 10% of photosynthesis. Photosynthesis in the hypolimnia contributed 30–40% of the oxygen consumed there and eddy diffusion supplied a further 20%.

In Lake Johnson a 3–5 m stratum of water in the metalimnion became anoxic for 2–3 months each summer while there were still up to 5.2 g.rer³ of oxygen remaining in the hypolimnion. Metalimnetic anoxia is attributed largely to oxygen consumption in situ, resulting from the highly eutrophic state of the lake and intense thermal stratification. Zooplankton respiration accounted for less than 10% of the maximum net decline in metalimnetic oxygen in 1970–71, but was more important in the other 2 years.

Changes in the oxygen content of the hypolimnion indicate that Lake Hayes has become more eutrophic since 1954–55. In Lake Johnson low oxygen concentrations at the autumn overturn (<5 g.m^‐3) represent a threat to the trout population.  相似文献   

Burrowing and burying by the crab Macrophthalmus hirtipes     

Pauline A. Nye 《新西兰海洋与淡水研究杂志》2013,47(2):243-254

Macrophthalmus hirtipes (Jacquinot, 1853) excavates burrows under water in soft, muddy sand that remains waterlogged at low tide. The crabs are immersed for at least 4 h in every tide. The burrows are usually single, blind‐ending, slightly curved passages; their openings do not appear to be deliberately closed by the crabs. Excavation is effected by using one set of walking legs as a scoop while the other set provides sideways traction.

Burrow openings are readily obscured by water movement, so that apparent burrow density does not give a true indication of the number of crabs in an area, but only indicates how many have been active recently; the true density may be found by sieving.

The burrowing activity of M. hirtipes is compared with that of other ocypodid crabs, and the functions of burrows are discussed. A distinction is made between excavating a burrow and rapid burying, because the two behaviours are very different, and must involve different adaptations and selection pressures.  相似文献   

Performing environmental governance     

Morgan Robertson 《Geoforum》2010,41(1):7-10

This essay reflects on issues of researcher positionality within participant observation and action research, and the specific methodological issues surrounding research on neoliberal governance strategies, using my experience at the US Environmental Protection Agency as case material. Although I was initially concerned about participating with the anti-progressive Bush Administration, I attempted to adopt the interests and subjectivity of an environmental bureaucrat. Doing so proved to be an extremely effective way of exploring the multi-vocality and cross-cutting interests constituting the state, which often appears from the outside to be a policy monolith. Participant research among elites in the neoliberal state is an effective way to observe such complexity. It became apparent that, because mainstream economics tends to adopt a totalizing epistemology, both its casual and dogmatic adherents usually do not conceive of a coherent external critique. This often means that researchers of any theoretical background can be quite frank concerning their purposes, background, and interests, even as participants.  相似文献   

Environmental degradation narratives in Madagascar: From colonial hegemonies to humanist revisionism     

Jacques Pollini 《Geoforum》2010,41(5):711-722

It is recurrently argued that political ecologists, by overlooking biophysical realities, misinterpret ecological interactions and underestimate environmental degradation. This article investigates the relevance of these critiques in the case of the Malagasy highlands. It is based on an analysis of three environmental narratives: a narrative developed by European colonists at the beginning of the century; a “modern” narrative developed since the 1980s by combining data from paleobotanists, archeologists and paleontologists; and a narrative developed more recently by political ecologists. I will show that biophysical realities were actually investigated by political ecologists in Madagascar, but that their interpretation differed from those of mainstream ecologists as a result of a different way of defining, characterizing and valuing the environment. With the aim of favoring a more comprehensive understanding of environmental degradation in Madagascar, I will propose to clarify the epistemological framework of political ecology, and to bring an objective nature back into its scope of enquiry. Far from weakening political ecology, this exercise will render the discipline more resistant to the counterattacks it has received, and more powerful for building a future that will answer to both social and environmental challenges.  相似文献   

A Plan to Push Limits? Investigating the ecologically sustainable development dimensions of Melbourne's Central Region sustainable water strategy     

Fiona Miller  Annie Bolitho  Natalie Jamieson  Charlotte Catmur  Anna Hurlimann  Kathryn Bowen 《The Australian geographer》2014,45(1):19-35

Drawing upon theory from the field of urban political ecology, we analyse a major strategic water plan for Melbourne, Australia—the Sustainable water strategy for the Central Region, published in 2006. We assess the extent to which the strategy identified and addressed ecological sustainability in terms of: cultural frames; ecological context; social equity; and engagement processes. We identify that the strategy's framing of water was largely separate from its social and ecological context. This framing resulted in the importance of issues such as environmental flows, social equity and cultural values being diminished, thus avoiding the inevitable confrontation with environmental limits needed to ensure long-term ecological sustainability. Our analysis shows that the discursive dominance of economics limited the response to persuasive scientific arguments for greater ecological consideration in the strategy. Our findings suggest that broadening engagement with the diverse ways in which water is valued is likely to contribute to more equitable and ecologically sustainable water futures.  相似文献