Importance of Indeginous Macrophytes in Control of Water Hyacinth in the Nyanza Gulf of Lake Victoria, Kenya

Importance of Indeginous Macrophytes in Control of Water Hyacinth in the Nyanza Gulf of Lake Victoria, Kenya.

Item Type Other

Authors Omondi, Reuben; Gichuki, John

Publisher Kenya Marine and Fisheries Research Institute

Download date 26/09/2021 14:23:06

Link to Item http://hdl.handle.net/1834/6909 IMPORTANCE OF INDEGINOUS MACROPHYTES IN CONTROL OF WATER HYACINTH IN THE NYANZA GULF OF LAKE VICTORIA, KENYA

Reuben Omondi and John Gichuki Kenya Marine and Fisheries Research Institute P. O. Box 1881 Kisumu. KENYA

Email: [email protected]

Abstract Observation of macrophytes dynamics in the Nyanza gulf of Lake Victoria is ongoing since the early 1990s. A checklist of the macrophytes and their distribution in the study area is provided. Occurrence of macrophytes before and after the invasion of water hyacinth is highlighted. The dynamics of water hyacinth, control measures employed for its control and macrophyte succession are also mentioned.

Introduction Macrophytes are higher plants that grow in water or wet soils. However, some may endure a period of desiccation. Macrophytes usually occur along the shores of water bodies like dams and lakes and along banks of rivers. The distribution, permanency and quality of the water bodies available for their occupation govern the distribution and ecology of these plants. The most variable environmental factors of basic ecological importance for the aquatic plants are the length of the period during which water is present, whether the habitat is lentic or lotic, the availability of plant nutrients and the quantity and quality of light penetration into water. Factors that influence the establishment of macrophytes include: depth, topography, type of substrate, exposure to currents and/or wind and water turbidity. The distribution of macrophytes is often related to their mode of attachment (Sculthorpe, 1976). In Lake Victoria, the numerous numbers of haplochromines before the introduction of Lates niloticus hindered the establishment of macrophytes in the inshore areas by constantly disturbing the substrate (Witte et al. 1992a). Macrophytes are classified into four groups on the basis of their water requirements, life forms and habitats. Submerged macrophytes occur below the water surface. These have thin finely dissected leaves adapted for rapid exchange of nutrients with water. Floating leafed macrophytes are rooted on the substratum but have their floating leaves confined to the water surface. Free- floating macrophytes are water plants that are not attached and float freely on the surface. Such plants have buoyancy or floating mechanism and their leaves are ecologically adapted to be drifted by water. Lastly, emergent macrophytes are rooted plants with their principal photosynthetic surfaces projecting above the water. Macrophytes are regarded to be the most productive plant communities in the world (Sculthorpe 1976; Penfound 1956; Reddy 1984; Westlake 1963). They are also known to be the cradles of biological diversity, providing water and primary productivity upon which countless species of plants and animals depend for survival (Chapman et al. 2001). Macrophytes act as efficient filters of excessive nutrients from the catchments, which could otherwise lead to eutrophication of water bodies. Although the absorption may not in itself ensure the removal as the plants might re-release them on decomposition, the wet low oxygen soils favour denitrification by bacteria leading to loss of nutrients (Gaudet 1976). Recent studies, in Lake Victoria, have shown that the recent invasion of the lake by water hyacinth resulted in the re-appearance and subsequent increase of some fish species that were earlier on the decline or threatened with extinction (Odongkara 1997; Njiru et al. 2002). The menace of some macrophytes reaches alarming rates especially in the tropical regions where warm water fosters plant growth. The problem is aggravated by the increasing enrichment of water bodies by agricultural inputs and other effluents from the human and industrial wastes. Less than 20 of the 700 species of macrophytes are considered weeds (Triest, 1993). As a consequence of their prolific growth and production, macrophytes often interfere

2 with human utilization of water bodies in a number of ways. Through photosynthesis and respiration and their growth rate, macrophytes may have very significant impacts upon environmental factors such as dissolved oxygen, carbon dioxide and ammonia concentrations, mineral nutrient supplies, pH values, light penetration, current velocity and the rate of siltation. These effects can wield direct or indirect influence on the lives of other aquatic organisms, notably the micro-fauna and flora for which the plants provide support, shelter or food. Water hyacinth invasion in Lake Victoria has recently been blamed on the decimation of certain macrophytes (Omondi and Kusewa, 2006). Materials and methods

Surveys in the lake were carried out aboard MV Utafiti and a canoe in shallow areas, mainly sheltered bays (Fig. 1). Both subjective and quantitative techniques were used for sampling the aquatic plants. The former was carried out in inaccessible while the later was carried out using systematic sampling along transects perpendicular to localities where macrophytic populations were found. Percentage cover was estimated using a 1x1m or larger quadrats depending on the occurrence of different species while densities were determined using a 1x1 m quadrat Plants with diagnostic features such as flowers, fruits, shoots and rhizomes were collected, correctly pressed and labeled with the accurate swamp locality, a brief habitat description and associated taxa. Identifications were carried out using keys by Agnew & Agnew (1994) and Kokwaro & Johns (1998).

Fig. 1. Map showing the Nyanza Gulf of Lake Victoria, Kenya

4 Results and Discussion

A total of 26 families and 39 species were recorded from the different sites surveyed (Table 1). However, the list is expected to be longer considering that a detailed landward survey was not carried out. This more so expected for the families Graminae and Cyperaceae.

Table 1. Distribution of aquatic macrophytes recorded in Lake Victoria, Kenya.

Family/Species Growth habitat Locations

Acanthaceae

Asystasia sp Emergent 7

Amaranthaceae Alternanthera philoxeroides Emergent 7 Araceae Pistia stratiotes Free floating 2, 3, 4, 5, 6, 9, 10 Asteraceae Enydra fluxuans Emergent 1, 6, 10 Sphaeranthus africanus ‘’ 6, 7, 9

Azollaceae Azolla nilotica Free floating 2, 3, 6, 9 Ceratophyllaceae Ceratophyllum demersum Submerged 1, 2, 3, 5, 6, 7, 9

Commelinaceae Commelina benghalensis Emergent 6, 9

C. diffusa ‘’ 2, 4, 7, 9 Floscopa glomerata ‘’ 9 Compositae Melanthera scandens Emergent 2, 3, 4, 5, 7, 8, 9 Convolvulaceae Ipomea aquatica Emergent 1, 2, 3, 4, 5, 6, 7, 9, 10 I. cairica ‘’ 2, 3, 5, 7, 9 Cyperaceae Calyptrocarya angustifolia Emergent 9

Cyperus papyrus ‘’ 1, 2, 3, 4, 5, 6, 7, 9, 10 C. rotundus ‘’ 2 Elegant cyperus ‘’ 7, 8 Gramineae

5 Phragmites australis Emergent 1, 2, 3, 4, 5, 6, 7, 8, 9 Vossia cuspidate Emergent 1, 2, 3, 4, 5, 6, 7, 9, 10 Hydrocharitaceae Vallisneria spiralis Submerged 1, 7, 8, 9 Lemnaceae Lemna sp Free floating 9 Lentibularaceae Utricularia inflexa Emergent 2, 5, 7 Malvaceae Hibiscus diversifolius Emergent 2, 3, 10 H. witteanus ‘’ 2 Najadaceae Najas horrida Submerged 1, 2, 5 Nymphaeaceae Nymphaea lotus Floating leaved 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Onagraceae Ludwigia stolonifera Emergent 1, 2, 5, 6, 7, 9 L. abyssinica ‘’ 2, 3 Papilionoideae Aeschynomene elaphroxylon ‘’ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Polygonaceae Polygonum setosulum Emergent 1, 2, 7, 9, 10 Pontederiaceae Eichhornia crassipes Free floating 1, 2, 3, 4, 5, 6, 7, 9, 10 Potamogetonaceae Potamogeton sweinfurthii Submerged 2, 6, 7, 8 Potamogeton pectinatus ‘’ 2 Tiliaceae Triumfetta sp Emergent 8 Trapaceae Trapa natans Floating leaved 2, 5 Typhaceae Typha domingensis Emergent 1, 2, 3, 4, 5, 6, 7, 9, 10 Vitaceae Cyphostemma adenocaule Emergent 7

Locations: 1 Kibos 2. Nyando 3. Sondu 4. Awach (Kendu) 5. Awach (Asembo) 6. Samunyi 7. Yala 8. Matara 9. Kuja/Migori 10. Lwanda Gembe. All the studied sites except 7, 8 and 9 are found within the Nyanza gulf. The common aquatic in the lake included: I. aquatica, C. papyrus, P. stratiotes, E. crassipes, V. cuspidata, N. lotus, A. elaphroxylon, T. domingensis and P. australis. Macrophytes in Lake Victoria mainly occur in the vicinity of river mouths

6 and in the sheltered bays. River mouths favour the establishment of macrophytes because of sedimentation from rivers. The incoming nutrients from the rivers also stimulate establishment of various plant species. Matara Bay on the other hand had the least number of species. The bay has no river influence besides having rocky shores. Before the invasion of water hyacinth, free floating macrophytes in the lake included: Pistia stratiotes, Azolla spp and Lemna spp. (Omondi and Kusewa, 2006). The former, which originated from Rwanda and Burundi through River Kagera, is believed to have resulted in the decimation of the indigenous species some of which are only sited in the lake during reduced populations of the alien species. Hippo grass, V. cuspidata formed a thin layer at the bank of potamon sections of major affluent rivers before water hyacinth while floating islands consisted of mainly C. papyrus sloughed off from river mouth populations during the rainy seasons. On the establishment in mid 1990s, the weed formed a compact mass, providing a substrate for V. cuspidata a process enhanced by the decaying portions of the weed resulting from the effect of weevils. Presently floating islands in the lake consist mainly of the grass with other emergents C. papyrus and A. elaphroxylon contributing < 5%. Floating leaved plants including N. lotus, C. demersum, N. horida and T. natans have also been affected by water hyacinth through shading and competition for nutrients (LVBC, 2008). Water hyacinth is believed to have been brought under control through biological method and macrophyte succession. Water hyacinth invasion of Lake Victoria was the genesis of the macrophyte succession presently being witnessed. The process has the capacity to alter the diversity of many macrophytes in the lake. First stages of succession start when native littoral, emergents I. aquatica and E. fluctuans invade the water hyacinth mat by creeping into the latter. The taller hippo grass then joins the community and shades off and later dominates the shorter macrophytes while depending on the latter for buoyance and nutrients. Hippo grass cannot survive on water and once the heterotrophic substrate of the dying macrophyte is depleted, end up sinking to the lake bottom.

7 CONCLUSION Water hyacinth invasion was the genesis of macrophytic succession presently being observed in Lake Victoria. Invasion of lake by water hyacinth led to the increase in population of emergent macrophytes, especially Vossia cuspidata and Echinocloa sp along the shores of the lake. These, however, cannot survive in the lake once total decomposition and disintegration of the heterotrophic layer of the floating mats takes place. P. stratiotes and A. pinnata which were the only floating macrophytes were either smothered or pushed land wards. However, with the reduction of water hyacinth in the lake, the populations of these and other macrophytes are expected to grow. Unless environmental degradation around the lake is reduced then re-invasion of water hyacinth is expected.

Acknowledgement The surveys were funded by Lake Victoria Fisheries Research Project (LVFRP) and Lake Victoria Environmental Management Program (LVEMP). We are also grateful to the entire crew of the MV Utafiti which was used during the surveys.

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