Occlusion of the Niger Delta Rivers and creeks by aquatic weeds: Impact on humans and fisheries

Abstract

The term occlusion emanated from Latin word "occlusio" which implies restriction or blockage. The aquatic weeds aside other negative features, obstruct the water ways wherever they are found. Aquatic plants, notably water hyacinth, duck weed, water lettuce and hypha grass have become ubiquitous in the Niger Delta Rivers, Creeks, lakes and reservoirs for nearly three decades. The presence of these sufficive weeds according to previous studies showed they are of grave consequences to man as they hinder economic or social activities such as reduction of capacity of water bodies for fish production, inhibit fishing, hampering on netting and passage of ships, harbors insect pests thereby hosting pathogens. Other problems posed by aquatic plants include impairment of navigation, reduction of water availability to the local communities, prevention of proper functioning of pumps and turbines of power stations where available. The problem is predicted to become greater since there is increased trade across the borders which facilitate spread and growth of weeds. This will be further aggravated with human settlement and its attendant waste generation and intensive use of fertilizers which get washed into the water ways. The nutrient enrichment triggers luxuriant growth of aquatic weeds. The aquatic weeds, spread quickly on the water through movement of boats/ships, water current downstream and flood push, besides agent of dispersion such as birds, wildlife and wind. Various management tools advocated to put the weeds under control include prevention through monitoring and early detection. Other means of Aquatic Plants control include mechanical and biological methods as well as the use of chemicals and more recently the adoption of wide applications in utilization as food for man and feed formulation and as fabric in craft making.

Full text

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International Journal of Fauna and Biological Studies 2022; 9(2): 25-29
E-ISSN 2347-2677
P-ISSN 2394-0522
www.faunajournal.com
IJFBS 2022; 9(2): 25-29
Received: 19-01-2022
Accepted: 21-02-2022
Ogaga A Aghoghovwia
Department of Fisheries and
Aquatic studies/Animal Science,
Niger Delta University,
Wilberforce Island-Bayelsa
State, Nigeria
Bestman Obomunu
Department of Fisheries and
Aquatic studies/Animal Science,
Niger Delta University,
Wilberforce Island-Bayelsa
State, Nigeria
Corresponding Author:
Ogaga A Aghoghovwia
Department of Fisheries and
Aquatic studies/Animal Science,
Niger Delta University,
Wilberforce Island-Bayelsa
State, Nigeria
Occlusion of the Niger Delta Rivers and creeks by
aquatic weeds: Impact on humans and fisheries
Ogaga A Aghoghovwia and Bestman Obomunu
Abstract
The term occlusion emanated from Latin word “occlusio” which implies restriction or blockage. The
aquatic weeds aside other negative features, obstruct the water ways wherever they are found. Aquatic
plants, notably water hyacinth, duck weed, water lettuce and hypha grass have become ubiquitous in the
Niger Delta Rivers, Creeks, lakes and reservoirs for nearly three decades. The presence of these sufficive
weeds according to previous studies showed they are of grave consequences to man as they hinder
economic or social activities such as reduction of capacity of water bodies for fish production, inhibit
fishing, hampering on netting and passage of ships, harbors insect pests thereby hosting pathogens. Other
problems posed by aquatic plants include impairment of navigation, reduction of water availability to the
local communities, prevention of proper functioning of pumps and turbines of power stations where
available. The problem is predicted to become greater since there is increased trade across the borders
which facilitate spread and growth of weeds. This will be further aggravated with human settlement and
its attendant waste generation and intensive use of fertilizers which get washed into the water ways. The
nutrient enrichment triggers luxuriant growth of aquatic weeds. The aquatic weeds, spread quickly on the
water through movement of boats/ships, water current downstream and flood push, besides agent of
dispersion such as birds, wildlife and wind. Various management tools advocated to put the weeds under
control include prevention through monitoring and early detection. Other means of Aquatic Plants control
include mechanical and biological methods as well as the use of chemicals and more recently the
adoption of wide applications in utilization as food for man and feed formulation and as fabric in craft
making.
Keywords: Suffisive aquatic weeds, Occlusio, rivers, creeks pollutants
Introduction
Occlusion in medical sense implies the obstruction or closing of a blood vessel or hollow
organ. The word occlusion emanated from Latin “Occlusio” which means to obstruct, restrain,
shut up or close up. This term however, has been used not only in medicine but also in other
disciplines. For the meteorologist (it refers to cloudy day), to Linguistics (it is the closure of
the vocal tract that produces an oral stop or nasal stop), in Physics (it refers to absorption of a
gas/liquid by metal), in computer (it is the blocking of the view or part of an image by another)
(en.m.wiktionary.org)
Many rivers in the Niger Delta including the Warri, Ethiope, Forcados, and Nun rivers and
their creeks at some points, experiencing what could be described as occlusion imposed by
aquatic weeds (Charudattan et, al., 1999). Aquatic weeds have severely reduced the flow
capacity of rivers, canals (Goldman, 1978; Murphy, 1988 Ndinwa et al., 2012) [7, 20], cause
salinity and alkalinity problems (Kusemiju et al, 1978) [12], serve as habitats for vectors
(Adekulo - John, 1982; Groove et, al., 1995) [3] prevent navigation (Goldman, 1973., Perna and
Burrows, 2005) [7].
This paper identifies some common aquatic plants species; states the problems they posed,
enumerates some of their benefits and explains how they can be managed.
Origin and Distribution of Aquatic Plants
The origin of aquatic plants is still speculative, but it is believed to be from South America
(Cordo et al., 1981) [5]. They have spread virtually to all the continents through ballast water in
ship from South America (Made et al., 2000).
The emergence of aquatic plants in Africa dates back to the end of the HoD nineteenth century
(Tackholm and Drar, 1950) [24], and their massive presence on Nigeria waters became obvious
in the early 1950s (Mitchel et al., 1990) [19].

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International Journal of Fauna and Biological Studies http://www.faunajournal.com
Known for their extremely lavish growth rate, the aquatic
plants have invaded agricultural fields, canals ponds, lakes
and rivers of the Niger Delta region.
Types of aquatic plants
According to (NIFFR, 2013), aquatic weeds can be classified
as follows: Floating, Emergent, submerged, Marginal,
filamentous and Planktonic algae.
Floating aquatic weed: These are aquatic plants that have
their roots below the water surface or both roots and their
vegetable parts floating at the water surface (Lichtenstein,
2017). Examples are: water lettuce (Pistia stratiotoies), water
hyacinth (Eichhornia crassipes) and duck weed (Lemna spp)
Emergent aquatic weeds: These are aquatic plants that have
their roots firmly fixed on soil or substrates in water while
their leaves and vegetative parts extended above the water
surface (Beck, 2019). Examples are Water Lilly (Nymphaea
spp), Myriophyllum, spp, Valliseneria. spp
Submerged aquatic weeds: These consist of plants which are
either rooted or rootless, that grows below the water surface
with both leaves and roots totally covered by water (Beck,
2019). Examples include Hydrilla verticillata, Najas minor
and Caratyphyllum.
Marginal aquatic weeds: These are plants that grow at the
sides of water body often known as shoreline plants
(Lichtenstein,2017) Examples: Typha species and Phargnites.
Filamentous algae: These are aquatic plants with vegetative
parts invisible to the two naked eye or could be interpreted as
plants with no vegetative parts or also called aquatic
microphytes (Beck,2017). These form mats at the periphery of
the water bodies and form scum at the main water body. Some
common examples are: Spirogyra and Pithophora.
Planktonic algae: These are otherwise known as aquatic
microphytes, and have the tendency to multiply rapidly and
form algal bloom in water (Lichtenstein,2019). Examples are:
Microcystis and Anabaena.
Problems posed by aquatic plants
 Hinders Fishing Activities: The overwhelming presence
of the aquatic plants on water bodies has created lot of
problems to fishers (Rockwell,2003). Their massive
physical presence hampers on ability to gain access to
fishing grounds (Uka and Chukwuka, 2011) [25], see
plates A,B,C and D. Fishing gears also entangle the plant
roots, stems and leaves and thereby leading to fish catch
reduction and loss of equipment. Annual loss of fish
resulting from this, is put at 45 million kilogrammes in
Bengal (Gopal and Sharma, 1981) [8].
 Increased Evapotranspiration: Water bodies lose water
to the atmosphere by 3-5 times the normal rate due to
accelerated evapotranspiration. Suton (1983) [23], opined
that the rate of water loss due to evapotranspiration could
be up to 1.8 times that of evaporation from the surface
area.
 Hindrance to Navigation Vessels: Aquatic plants
drastically impede navigation and transportation and by
preventing free movement of navigation vessels
(Goldman, 1978; Perna and Burrows, 2005; De, Groote et
al., 2003) [7].
 Aquatic Plants as Shelter to Variety of Vectors:
Aquatic plants serve as habitat for invertebrates such as
aquatic snails, crustaceans and insects as well as
predators (reptiles and other aquatic wildlives)
(Mitchqell, 1974 [18] cited by Uka and Chukwuka, 2011)
[25]. Majority of these kind of animals cause both human
and animal diseases. These vectors are carriers of
diseases such as malaria, lymphatic filariasis and
schistosomiasis (Pieterse et al., 1990). The consequences
of incidence of diseases, had led to health problems,
disruption of food supply and socio-economic structure
of several people in the riverine communities (Julian and
Wright, 1997; Johnson, 1993) [10].
Other problems include the impediment to water flow, which
in turn increases sedimentation, causing flooding and soil
erosion (Mitchell et al., 1990) the early 1950s (Mitchel et al.,
1990) [19]. It may also lead to drastic change in the physical
and chemical properties of water and the environment (Colon
– Gaud et al., 2004). Aquatic plants incidence is a serious
threat to agricultural production as a result of blockage to
irrigation canals and drainage systems (Uka and Chukwuka,
2011) [25]. More so, they cause reduction in the activity of
electrical power stations thereby jeopardizing the power
supply of the country (Goldman, 1973) [7].
Ways to tackle problems caused by aquatic plats
Several approaches have been propounded by various
scholars on how to drastically reduce the menace of aquatic
plants. This study acknowledges some of the aquatic plants
control methods. These are notably mechanical, biological
and chemical control (NIFFR, 2013). The mechanical control
is usually an effective method, but its success is on a short
run, whilst manpower and machine are engaged to control
their upsurge. The limitation of this method of Aquatic plants
control is that the plant flowers and seeds fall on substrates
and begin the growth process again. As for the herbicides
(chemical method), it is noted to be effective except for the
method of application which is broad spectrum and could
therefore affect non-target aquatic biodiversity including
humans in terms of water use and poisoning.
The biological method appears to be the most effective and
affordable and self-sustaining means of management which
include the use of agent like insects -Neochietina bruchi and
Cyrtobagous salviniae which are natural enemies of aquatic
macro plants such as water hyacinth and ferns respectively
(Charudattan and Chandramohan, 2002) [4]. The reports of
many authors including this study, may have proven many of
the conventional control methods for aquatic plants
ineffective on the long run. This paper is therefore of the view
that the best way to achieve a more robust and result oriented
solution is to involve all stakeholders - the government,
scientists, fisheries officers, fishers and indeed every Nigerian
especially the unemployed. Just as it obtains in Nigeria today
where metal , plastic and paper scraps are gathered from the
environment by some individuals for sales to industries. This
scavenging work is paying off as we speak. The efforts people
put in picking plastics, metals and other wastes from the
environment are sold for by those involved. This has resulted
not only in cleaning the environment, but has positively
influenced their personal earnings. They don’t see the

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International Journal of Fauna and Biological Studies http://www.faunajournal.com
drudgery involved as a problem compared to the financial
gain they derive from the work done. This paper holds the
view that similar model could be adopted to get people
involved in clearing the aquatic weeds off the water ways.
The simple analogy given should be applied to aquatic plants.
This paper is aimed at unveiling the hidden treasures that
abound in them. Below are some of the uses of aquatic plants.
The following pieces of information, shall be of immense
benefit to industrialist, medical practitioners and others.
 Use of Aquatic Plants as Source of Energy: Aquatic
Plants of note, are used as fuel for fish smoking and
domestic energy. In China and India Eichhornia
crassipes is digested directly to produce biogas that serve
as inexpensive energy supply for local communities.
Equally in Nigeria, the stems of Eichhornia crassipes and
Cyperus papyrus are used as fuel for cooking and fish
smoking (Kio and Ola-Adams, 1987) [11]. The utilization
of these weeds as alternative to wood could drastically
reduce felling of trees from our forest for domestic
cooking and thereby aid in reducing desert
encroachments.
 Industrial Use: Aquatic plants have numerous materials
that could meet the needs of creative minds and
revolutionary industry. The materials could fit in
pulp/paper making, production of mats and beddings etc
(UKa and Chukwuka, 2011) [25].
 Aquatic plants as fertilizers: Most aquatic plants are
rich in nitrogen and phosphorus. This makes them first
class option as bio-fertilizers for crops (UKa and
Chukwuka, 2011) [25]. Examples include, Azolla spp a
free floating fern which characteristically fixes nitrogen
in a symbiotic interaction with Cyanobacterium,
Anabaena azollae; a known biofertilizer for rice
production. The use of Azolla sp as biofertilizer in
paddy/fish integrated farming is widely known and
practiced in Asia (Maltby, 1988) [14]. Ratchance (1972)
[22] emphasized the successful use of dried water
hyacinths as a bedding material for cultivating mush
rooms (Volvaria sp). In Nigeria there are a whole lot of
potentials in utilizing water hyacinth, take for instance,
paper pulp, biogas, organic fertilizer production and
sewage treatment (UKa and Chukwuka, 2011) [25].
 Aquatic plants as source of food, fodder and
medicine/pharmacy
Table 1: list of some aquatic weeds and their uses.
Plant species
Part of plant
Uses
Echinocloa stagnina
Seed
Food for fishers in Niger river.
Stalk of the grass
Sugary syrup.
Nymphae lotus (water lily)
Rhizome, floral receptacle and fruits.
Eaten raw or cooked as food spice ingredient of soup.
Ludwingia stolonifera
Leaves
Spice/ingredient of soup.
Eichhornia crassipes
Leaves
As feed in mixture with other grasses.
Polygonum senegalenses
Leaves pounded with hydrated sodium carbonate
Cure rheumatic pain and swellings.
Althermanthera nodiflora
Leaves
Cure stomach disorder
Pistia stratiotes
Leaves
Cure ulcer of mouth and tongue.
Neptuna oleracea
Leaves
Treatment of yellow fever, guinea worm.
Nymphia lotus
Stem and roots.
Fever, urethral discharges.
Nymphia lotus
Flow
Narcotive and sedative.
Aframomum melegueta
Leave
Cure cough.
Sources: Kio and Ola- Adam, 1987., Uka and Chukwuka,2011 [11, 25].
Plate 1: Saccioleois Africana
Plate 2: Pistia stratiotes

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Plate 3: Eichhornia crassipes
Plate 4: ludwigia stolonifera
Other approaches to solved problems caused by aquatic
plant:
 To carry out a study on the aquatic weed relating to why
they are persistent in the aquatic environments (Sousa,
2011).
 To create indigenous or national capacity for enduring
aquatic weeds control.
 To engender collaboration through seeking assistance
from foreign countries that have recorded success in
aquatic plants control.
 To partner regional and sub-regional member countries of
the economic community of West African States
(ECOWAS on integrated aquatic weeds control)
 To identify the prevalence of weed species and the cover.
 Encourage fish feed production using aquatic
macrophytes as replacement for expensive feed
ingredients (Aghoghovwia et al., 2018) [1].
Solving the Problem
 Establish surveillance systems of aquatic weeds in the
country through engagement of the local community.
 Introduction and rearing and release of biological control
agent to use against water hyacinth, water lettuce, water
fern. Examples is the use of some herbivorous fish like
largemouth (Micropterus salmoides) including their
juveniles to feed on the plants (Tate et al., 2003).
 Establish a rearing unit for the biological control agents.
 Conduct public awareness campaign on aquatic weed
problem and method of their control among the rural
population, involving rural communities in the release of
the selected biological control agent.
 Ensure the members of the local community buy into the
project - aquatic weed control. They must be made to
very important citizens Vizavizi their contribution.
 Establish inter country cooperation and exchange of
information on matters related to aquatic weed control.
Conclusion
The pervasive presence of the aquatic plants on surface areas
of many Niger Delta waters interferes directly with the water
use. Put differently, the aquatic macro plants pose nuisance
characteristics to man’s wellbeing. In the wake of the many
other problems or challenges facing Nigeria today (notably,
recession, insecurity, poverty, corruption and likes), the
aquatic weed incidence thus appear to be another
environmental and socio-economic problem. The threat of its
growing trend gives room for concern, while the cost it might
gulp in tackling this ugly trend besides the lack lustre trait or
insincerity on part of leadership, are unequivocally
nightmares. This paper however noted that the detrimental
aquatic plants invasion, presents valuable opportunities that
could be of benefits to the Nigerian state. It is another gray
area of wealth creation. The onus is therefore on all
stakeholders (government, environmentalist, and industrialist)
to make the most use of this problematic weeds, which are at
the moment seem intransigent or too expensive to control.
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