Heavy metal removal mechanism of acid mine drainage in wetlands: A critical review

Intercropping, the agricultural practice of cultivating two or more crops in the same space at the same time, is an old and commonly used cropping practice which aims to match efficiently crop demands to the available growth resources and labor. The most common advantage of intercropping is the production of greater yield on a given piece of land by making more efficient use of the available growth resources using a mixture of crops of different rooting ability, canopy structure, height, and nutrient requirements based on the complementary utilization of growth resources by the component crops. Moreover, intercropping improves soil fertility through biological nitrogen fixation with the use of legumes, increases soil conservation through greater ground cover than sole cropping, and provides better lodging resistance for crops susceptible to lodging than when grown in monoculture. Intercrops often reduce pest incidence and improve forage quality by increasing crude protein yield of forage. Intercropping provides insurance against crop failure or against unstable market prices for a given commodity, especially in areas subject to extreme weather conditions such as frost, drought, and flood. Thus, it offers greater financial stability than sole cropping, which makes the system particularly suitable for labor-intensive small farms. Besides, intercropping allows lower inputs through reduced fertilizer and pesticide requirements, thus minimizing environmental impacts of agriculture. However, intercropping has some disadvantages such as the selection of the appropriate crop species and the appropriate sowing densities, including extra work in preparing and planting the seed mixture and also extra work during crop management practices, including harvest. The selection of an appropriate intercropping system for each case is quite complex as the success of intercropping systems depend much on the interactions between the component species, the available management practices, and the environmental conditions. Plant breeding can contribute determinedly to increase of productivity of intercropping systems by investigating and exploiting the genetic variability to intercrop adaptation. This paper provides an overall view and evaluation of annual intercropping, summarizing its main advantages supported by a number of key examples from the literature which point out its great value in the context of sustainable agriculture.

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Annual intercrops: an alternative pathway for sustainable agriculture.

African agriculture is largely traditional--characterized by a large number of smallholdings of no more than one ha per household. Crop production takes place under extremely variable agro-ecological conditions, with annual rainfall ranging from 250 to 750 mm in the Sahel in the northwest and in the semi-arid east and south, to 1500 to 4000 mm in the forest zones in the central west. Farmers often select well-adapted, stable crop varieties, and cropping systems are such that two or more crops are grown in the same field at the same time. These diverse traditional systems enhance natural enemy abundance and generally keep pest numbers at low levels. Pest management practice in traditional agriculture is a built-in process in the overall crop production system rather than a separate well-defined activity. Increased population pressure and the resulting demand for increased crop production in Africa have necessitated agricultural expansion with the concomitant decline in the overall biodiversity. Increases in plant material movement in turn facilitated the accidental introduction of foreign pests. At present about two dozen arthropod pests, both introduced and native, are recognized as one of the major constraints to agricultural production and productivity in Africa. Although yield losses of 0% to 100% have been observed on-station, the economic significance of the majority of pests under farmers' production conditions is not adequately understood. Economic and social constraints have kept pesticide use in Africa the lowest among all the world regions. The bulk of pesticides are applied mostly against pests of commercial crops such as cotton, vegetables, coffee, and cocoa, and to some extent for combating outbreaks of migratory pests such as the locusts. The majority of African farmers still rely on indigenous pest management approaches to manage pest problems, although many government extension programs encourage the use of pesticides. The current pest management research activities carried out by national or international agricultural research programs in Africa focus on classical biological control and host plant resistance breeding. With the exception of classical biological control of the cassava mealybug, research results have not been widely adopted. This could be due to African farmers facing heterogeneous conditions, not needing fixed prescriptions or one ideal variety but a number of options and genotypes to choose from. Indigenous pest management knowledge is site-specific and should be the basis for developing integrated pest management (IPM) techniques. Farmers often lack the biological and ecological information necessary to develop better pest management through experimentation. Formal research should be instrumental in providing the input necessary to facilitate participatory technology development such as that done by Farmer Field Schools, an approach now emerging in different parts of Africa.

Pest management strategies in traditional agriculture: an African perspective.

1 * All correspondence ABSRACT Heavy metals are released into the environment from a wide range of natural and anthropogenic sources. The rate of influx of these heavy metals into the environment exceeds their removal by natural processes. Therefore there is attendance of heavy metals accumulating in the environment. Aquatic ecosystems are normally at the receiving end and usually, with wetlands as intermediaries. The conventional clean up technologies used in the prevention of heavy metal pollution are either inadequate or too expensive for some countries. In the past decades, therefore, research efforts has been directed towards wetlands as an alternative low cost means of removing heavy metals from domestic, commercial, mining and industrial discharge of wastewater. This paper is a comprehensive review of over 200 literature sources. It discusses the potential for heavy metal removal mechanisms by wetlands through reactions involving sedimentation, flocculation, absorption, co-precipitation, cation and anion exchange, complexation, precipitation, oxidation/reduction, microbiological activity and plant uptake.

A review of Heavy Metal Removal Mechanisms in wetlands

Preface.- 1. Microbial Biosorption of Metals - General Introduction.- 2. Potential of Biosorption Technology.- 3. The Mechanism of Metal Cation and Anion Biosorption.- 4. Equilibrium, Kinetic and Dynamic Modelling of Biosorption Processes.- 5. Bacterial Biosorption and Biosorbents.- 6. Fungal Biosorption and Biosorbents.- 7. Algal Biosorption and Biosorbents.- 8. Removal of Rare Earth Elements and Precious Metal Species by Biosorption.- 9. Biosorption and Metal Removal through Living Cells.- 10. Yeast Biosorption and Recycling of Metal Ions by Cell Surface Engineering.- 11. Bacterial surface display of metal-binding sites.- 12. Immobilized Biosorbents for Bioreactors and Commercial Biosorbents.- 13. Magnetically responsive biocomposites for inorganic and organic xenobiotics removal.- Index.

Microbial Biosorption of Metals

Lake George is a shallow equatorial lake in Uganda which, around its fringe, has a wetland designated as a Ramsar site of high international importance. A nearby copper mine has caused serious metal pollution of the surrounding land. Results show that heavy metals from mine waste, particularly copper and cobalt, are entering Kahendero Swamp, part of the Ramsar wetland, and contaminating the lake. In the lake, metals pass along the food chain. The distribution of metals in the wetland and possible modes of transport into the lake are discussed. The consequences of the metal contamination are considered and recommendations for its clean-up, especially in the light of future developments, are made.

Heavy metal contamination of Lake George (Uganda) and its wetlands

The effect of growing cowpeas mixed with either beans or maize on population densities of Megalurothrips sjostedti (Trybom) was investigated. Also investigated was the effect of varying the cropping densities of the host plants on the pest populations.There was a significantly lower population of M. sjostedti in cowpea/maize, bean/maize, and cowpea/bean/maize mixed stands as compared with that in either cowpea/bean stands or monoculture stands of cowpeas and beans. Increasing the cropping densities of the host crops increased the abundance of the pest in non-maize based mixed stands, but this effect was not observed in the maize-based mixed stands.The results indicate that with regard to infestation by M. sjostedti, the practice of mixed cropping beans with cowpeas confers no advantage to either crop with respect to attack by M. sjostedti. On the contrary, combining the two crops attracted infestation levels similar to those attracted by either crop grown in monoculture. But the inclusion of a non-host plant (maize) in the mixture, significantly reduces infestation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1742758400006081

Effect of Mixed Cropping Beans, Cowpeas and Maize on Population Densities of Bean Flower Thrips, Megalurothrips sjostedti (Trybom) (Thripidae)

The paper attempts to assess the current status of books and other resource materials for training tropical entomologists and to suggest ways and means of developing appropriate materials. Attention is drawn to the increasing importance of the study of insects in the tropics and hence the need to train more and more entomologists of all categories and specialization. Noting the fact that most textbooks used at all levels of university teaching mainly concentrate on describing temperate situations, it is suggested that entomologists in the tropics should make special effort to write books that discuss and give examples of situations obtaining in tropical areas. In recognition of the close link existing between theoretical and practical work, writing of clear and detailed manuals and guides to help students in the practical aspects of entomology should also be encouraged. Related to this aspect of training, engineering workshops where equipment necessary for practical exercises or research can be designed and constructed should be developed so as to minimise problems caused by inability to import such equipment. The shortage of insect taxonomists is highlighted and a number of measures to overcome this problem are suggested.

The development of books and other resource materials for training tropical entomologists

The paper acknowledges the need for pesticide usage to boost agricultural production and for disease control in Uganda and elsewhere in Africa. But drawing from some instances of pesticide pollution so far reported in Africa, the paper highlights the need for cautious use of the chemicals in order to avoid further pollution.

Eldad M. Tukahirwa

Papers

Heavy metal contamination of Lake George (Uganda) and its wetlands

Effect of Mixed Cropping Beans, Cowpeas and Maize on Population Densities of Bean Flower Thrips, Megalurothrips sjostedti (Trybom) (Thripidae)

The development of books and other resource materials for training tropical entomologists

Integrated pest management: Options for Uganda