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A review of the ecohydrology of the Sakumo wetland in Ghana

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The Sakumo wetland is an internationally recognized Ramsar site located in a largely urban area and provides essential ecological and social services to wetland community dwellers. Despite its importance, the wetland has over the years been subjected to human interference resulting in considerable risks of deteriorating water quality, biodiversity loss, and drying up of most parts of the wetland. The conversion of land for residential and agricultural uses has significantly altered the hydrological characteristics of the land surface and modified pathways and flow of water into the wetland. Other drivers identified included drainage (mainly as runoff from agricultural farms), anthropogenic pressure (waste discharge) due to infrastructure development associated with urbanization, chemical contamination as a result of industrial and household pollution, and unsustainable fishing practices (overfishing). The purpose of the study was to review some of the physical and chemical properties of the Sakumo wetland on the changing wetland resources with emphasis on water quality. Rapid urbanization, industrialization, and overexploitation of wetland resources were identified as key causative factors affecting the wetland functions. Their effects on the wetland among others include increased nutrient and toxic chemical load which has resulted in reduced wetland surface water quality and decrease in species diversity. pH of the wetland waters was generally alkaline which is characteristic of water bodies influenced by seawater under oxygenated conditions. The increasing trends of electrical conductivity, phosphates, ammonia, nitrate, and nitrite, though small, point to deteriorating water quality in the wetland. The lagoon water was observed to be heavily polluted with nutrients particularly phosphate. The sequence of nutrient in the wetland was found to be in the order of PO4-P > NH3-N > NO3-N > NO2-N. These, if not checked, will result in further deterioration of the wetland function. In order to protect the wetland structure and function, it is recommended that a determination for both surface water and groundwater (quality and quantity) components of the ecological reserve (aquatic ecosystem) as well as the basic human need should be undertaken. In addition, a complete hydrological study of the wetland must be done. This will enable a well-balanced water allocation scheme to all users while still ensuring long-term survival and sustainability of the wetland.
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A review of the ecohydrology of the Sakumo wetland in Ghana
Cynthia Nonterah &Yo n g x i n X u &Shiloh Osae &
Thomas T. Akiti &Samuel B. Dampare
Received: 15 January 2015 /Accepted: 16 September 2015 /Published online: 6 October 2015
#Springer International Publishing Switzerland 2015
Abstract The Sakumo wetland is an internationally
recognized Ramsar site located in a largely urban
area and provides essential ecological and social
services to wetland community dwellers. Despite its
importance, the wetland has over the years been
subjected to human interference resulting in consid-
erable risks of deteriorating water quality, biodiversi-
ty loss, and drying up of most parts of the wetland.
The conversion of land for residential and agricul-
tural uses has significantly altered the hydrological
characteristics of the land surface and modified path-
ways and flow of water into the wetland. Other
drivers identified included drainage (mainly as runoff
from agricultural farms), anthropogenic pressure
(waste discharge) due to infrastructure development
associated with urbanization, chemical contamination
as a result of industrial and household pollution, and
unsustainable fishing practices (overfishing). The pur-
pose of the study was to review some of the phys-
ical and chemical properties of the Sakumo wetland
on the changing wetland resources with emphasis on
water quality. Rapid urbanization, industrialization,
and overexploitation of wetland resources were iden-
tified as key causative factors affecting the wetland
functions. Their effects on the wetland among others
include increased nutrient and toxic chemical load
which has resulted in reduced wetland surface water
quality and decrease in species diversity. pH of the
wetland waters was generally alkaline which is char-
acteristic of water bodies influenced by seawater
under oxygenated conditions. The increasing trends
of electrical conductivity, phosphates, ammonia, ni-
trate, and nitrite, though small, point to deteriorating
water quality in the wetland. The lagoon water was
observed to be heavily polluted with nutrients par-
ticularly phosphate. The sequence of nutrient in the
wetland was found to be in the order of PO
4
-P >
NH
3
-N > NO
3
-N > NO
2
-N. These, if not checked,
will result in further deterioration of the wetland
function. In order to protect the wetland structure
and function, it is recommended that a determination
for both surface water and groundwater (quality and
quantity) components of the ecological reserve
(aquatic ecosystem) as well as the basic human need
should be undertaken. In addition, a complete hydro-
logical study of the wetland must be done. This will
enable a well-balanced water allocation scheme to all
users while still ensuring long-term survival and
sustainability of the wetland.
Keywords Hydrochemical characterization .Sakumo
wetland .Water q uali ty .Shallow groundwater.Stable
isotopes .Ecological water requirements .Wat er qua ntit y
Environ Monit Assess (2015) 187: 671
DOI 10.1007/s10661-015-4872-0
C. Nonterah (*):T. T. Aki ti :S. B. Dampare
Graduate School of Nuclear and Allied Sciences, University of
Ghana, Atomic Campus, Legon, Ghana
e-mail: adwoalaar@gmail.com
C. Nonterah :Y. X u
Department of Earth Sciences, University of the Western Cape, P
Bag X 17, Bellville 7535, South Africa
C. Nonterah :S. Osae
National Nuclear Research Institute, Ghana Atomic Energy
Commission, P.O. Box LG 80, Legon, Ghana
Introduction
The Sakumo wetland is an internationally recognized
Ramsar site located in a largely urban area with a grow-
ing population. The wetland provides essential ecolog-
ical and social economic services to the wetland com-
munities. However, over the years, the wetland has land
use changes that have been influenced by largely due to
human interference. This is due to the conversion of
land for residential and agricultural purposes. The con-
version of land to agricultural and residential uses has
the tendency to significantly alter the hydrological char-
acteristics of the land surface and also modify pathways
and rates of water flow to the wetland. The wetland is
threatened by pollution from domestic and industrial
solid/liquid waste, overexploitation, and urbanization
due to burgeoning human population. Urbanization in
the wetland is a major cause of impairment of water
quality (Anku 2006). This has resulted in short- and
long-term impacts including a decrease long-term deep
and shallow groundwater recharge, lowering of the wa-
ter table which may, in turn, dry up the wetland, and
produce intermittent dry streams during periods of low
flows. These human impacts have negatively impacted
on the wetland drainage processes that have affected the
quality and quantity of wetland water which, in turn,
affects the ecological health and functions of the
wetland.
Despite the significance of the wetland as a unique
habitat in Ghana, very few published studies have fo-
cused on quantifying water inflow and abstraction from
the wetland. Most studies have examined the value of
the wetland from the perspective of fish (Pauly 1976;
Koranteng 1995) or birds (Ntiamoa-Baidu 1991;
Gbogbo and Attuquayefio 2010). Many water quality/
pollution studies (Koranteng 1995; Yawson 2003;Edor
2008; Asmah et al. 2008; Nartey et al. 2011) have
focused on the physicochemical dynamics, nutrient
and pollutant fluxes, and heavy metal contamination.
These studies however did not consider the whole wet-
land catchment but focused on the lagoon. The coverage
of pollution and water quality studies on the lagoon
alone is inadequate for a complete understanding of
the extent of changes within the wetland. Also, few
water pollution studies have employed simple
hydrochemical tools and stable isotopes of O-18 and D
in assessing the quality of the wetland water. Laar et al.
(2011) used stable isotopes of water (δ
18
Oandδ
2
H) to
infer source of waters into the wetland and the effect of
mixing of seawater and wetland water. These methods
often seem to be unable to characterize and differentiate
the origins of the pollutants as well as recommend
appropriate water quality standards needed to meet the
requirements of all users. However, the use of combina-
tion of the stable isotopes of water and the radioactive
isotope, tritium (
3
H), has been known to provide better
understanding of wetland hydrological dynamics. This
is yet to be explored in the Sakumo wetland.
With regard to water-related problems, resource-
directed measures (RDM) can be developed to assess
the environmental flow requirements of the wetland.
The objective of RDM is to ensure the protection of
water resources, in the sense of protecting ecosystem
functioning and maintaining a desired state of health
(integrity or condition). This objective can be met
through various processes, including the setting of the
ecological reserve (the quantity and quality of water
reserved to support ecosystem function). Although rel-
atively new especially in developing countries like
Ghana, RDM studies have been conducted for estuaries,
rivers, forest, and grassland ecosystem (Colvin et al.
2002;Xuetal.2002;Yangetal.2009). A successful
classification scheme of the Sakumo wetland will pro-
vide a balance between protection of the wetland water
resources and socioeconomic development in order to
maximize the welfare of the communities within the
wetland catchment. The findings will also be applicable
to many other wetlands along the coast of Ghana with
similar morphological and land use characteristics,
many of which are subject to increasing pressure from
urbanization.
Questions like: is the wetland a groundwater depen-
dent ecosystem (GDE) or is it rain-fed; is the wetland
losing or gaining water; what are the flow rates suitable
for ensuring an ecologically balance state of the wetland
remain unresolved. The understanding of surface water
and groundwater (quality and quantity) components of
the ecological reserve (aquatic ecosystem) as well as the
basic human need in the wetland will be a prerequisite
for mapping out an allocation scheme to all users (e.g.,
fishing, agriculture, biodiversity, and tourism) while still
ensuring the long-term survival and sustainability of the
wetland.
Study area
Ghana is located in West Africa on the Guinea coast. At
latitudes of 412° N, the climate of Ghana is tropical
671 Page 2 of 14 Environ Monit Assess (2015) 187: 671
and strongly influenced by the West African Monsoon.
Ghanas climate is influenced by three air masses name-
ly the South-West Monsoon, the North-East Trade
Winds (Tropical Continental Air Mass), and the
Equatorial Easterly Winds. The warm but moist South-
West Monsoon which originates from the Atlantic
Ocean and the warm, dry, and dusty Tropical
Continental Air Mass (Harmattan) from the Sahara
Desert approach the tropics from opposite sides of the
equator and flow toward each other into a low-pressure
belt known as the intertropical convergence zone
(ITCZ) (Fig. 1). The pattern of rainfall is closely related
to the movement of the ITCZ (Dickson and Benneh
1995). The Greater Accra Region is divided into eight
districts namely the Accra Metropolitan Area (AMA),
Tema Municipal Area (TMA), Ga East District, Ga West
District, Dangme East District, Dangme West District,
Adenta Municipal, Ashaiman Municipal, Ga South
District, and Ledzekuku-Krowor Municipal. The
Sakumo wetland is located within the TMA area.
The lagoon is connected to the sea by a non-
functional (now permanently open) sluice. The wetland
is periodically inundated especially during the rainy
season. However, large portions of the lagoon dry up
during the dry season, resulting in hyper-saline condi-
tions. However, wetland water quality studies have been
limited to surface water from the wetland which covers
only the lagoon reaches (southern zoneclosest to the
sea, the northern zonethe farthest from the sea, and
the middle zonelying between the two) as shown in
Fig. 3.
Climate
The Sakumo wetland lies within the coastal savannah
vegetation zone with low annual rainfall averaging
800 mm distributed over less than 80 days. The rainfall
pattern of the area is bimodal with the major season
falling between the months of April and mid-July and a
minor rainy season around the month of October
(Fig. 2). The mean monthly temperature ranges from
24.7 °C in August (the coolest) to 28 °C in March (the
hottest) with an annual average of 26.8 °C (Dickson and
Benneh 1995). The nearness of the wetland to the equa-
tor makes daylight hours practically uniform during the
year. Relative humidity is generally high, varying from
65 % in the mid-afternoons to 95 % at night.
Predominant wind direction is from WSW to NNE with
speeds ranging between 8 and 16 km/h. The vegetation
cover of the metropolis is primarily shrub and grassland
with isolated trees that are only denser toward the north-
ern fringes area.
Geology and hydrogeology setting
The coastal zone of Ghana is underlain by a gentle,
mature topography that slopes toward the shore (Muff
and Efa 2006). The country is underlain partly by what
is known as the basement complex which comprises a
wide variety of precambrian igneous and metamorphic
rocks. These crystalline rocks cover about 54 % of the
country (Junner and Bates 1945). The geology of the
Accra coastal environment is made up of various types
Fig. 1 A picture of the structure
of the monsoon and land ITCZ
over Ghana, Africa
Environ Monit Assess (2015) 187: 671 Page 3 of 14 671
of rock. They include unconsolidated sediments, sand-
stones, quartz, and lagoonal sediment. The western part
is predominantly unconsolidated soil, while the eastern
part is more of quartz and little portions of lagoonal
sediment. The central part is mainly sandstone and a
little portion of quartz (Muff and Efa 2006). The geol-
ogy of the Sakumo catchment which is located in the
southeast coastal plains of Accra is mainly underlain by
Dahomeyan (Precambrian) rocks (Fig. 3). The
Dahomeyan formation is one of the oldest formations,
and it consists mainly of metamorphic rocks such as
crystalline gneiss and migmatite, with minor quartz and
biotite schists. The gneiss is generally massive and has
few fractures.
The two main varieties are the silicic and mafic
gneisses, which weather into slightly permeable and
nearly impermeable calcareous clays, respectively. The
generally impervious nature of the weathered zone and
massive crystalline structure of the rocks limit the yields
that can be obtained from hand dug wells or boreholes.
Borehole depths range between 20 and 30 m, with a
success rate of 40 % and yield average 0.30.8 m/l
(Muff and Efa 2006). The source of groundwater for
use is mostly from the shallow aquifer. In most parts of
the Greater Accra Region, the occurrence of groundwa-
ter is mainly due to the existence of linear features as a
result of fracturing, faulting, and weathering as the main
rocks are impermeable (Banoeng-Yakubo et al. 2010).
Depth of groundwater table lies between 5 and 15 m.
Recharge is generally low due to low permeability of
overburden clayey layer (Muff and Efa 2006). Soils
found in the study area are categorized into four main
groups namely drift materials resulting from deposits by
windblown erosion; alluvial and marine mottled clays of
comparatively recent origin derived from underlying
shales; residual clays and gravels derived from weath-
ered quartzites, gneiss and schist rocks; and lateritic
sandy clay soils derived from weathered accraian sand-
stone bedrock formations.
Hydrology
Three principal subdrainage basins have been identified
in the catchment area. The major ones are the
Mamahuma-Onukpawahe (at the western side) and the
Dzorwulu-Gbagbla-Ankonu (situated at the northern
end) subbasins. The eastern and southern subbasins
constitute the minor ones (Fig. 3). The catchment area
has limited groundwater potentials because of the low
rainfall and impermeability of the underlying rocks
(Muff and Efa 2006). The main feeder streams, the
Dzorwulu and Mamahuma, have been rechanneled for
irrigation. The Dzorwulu stream has a dam on it, and
this is situated north of Ashiaman town near Santeo. The
Mamahuma stream also has a dam on its upper catch-
ment. This normally resulted in very little flow of fresh-
water into the lagoon during the dry season. There are
no staff gauges on Sakumo wetland and therefore no
records of water levels. The lagoon reaches its lowest in
the dry season, and seawater flows into the lagoon
Fig. 2 Monthly mean rainfall and temperatures at the Tema meteorological station (19952012). Source: Ghana Meteorological Agency
671 Page 4 of 14 Environ Monit Assess (2015) 187: 671
during high tides. For this reason, the lagoon water is
hyper-saline during the dry season. The lagoon covers
an area of 1 km
2
in the dry season, but the entire flood
plain may be inundated in the wet/rainy season increas-
ing the surface area to about 10 km
2
.
Land use and urbanization
Urbanization is a major cause of loss of coastal wetlands
as it turns to exert significant influences on the structure
and function of wetlands by modifying the hydrological
and sedimentation regimes. In Ghana, settlements with
5000 or more inhabitants are considered urban (GSS
2002). The Sakumo wetland falls between two rapidly
growing cities (Accra and Tema) and has one of the
highest urban growth rates within the coastal zones in
Ghana. Nearly, 60 % of industries in Ghana can be
found along the coast of Accra and Tema (GCLME
2007). From 1984 to 2000, the percentage of persons
living in urban areas in Ghana has risen from 32 to 44 %.
In 1984, the population within the catchment was
114,619. In 1997, the population rose to 250,000; in
2010, the population rose to 402,637 (GSS 2002,2012).
Most of the population of the catchment lives in
suburban areas along the coast. Small urban areas
have also developed to the north and lie mostly
within rural land cleared for agriculture. The wetland
is primarily agriculture. Rice, cassava, and vegetable
farming is undertaken in the northern sections of the
wetland and also along the banks of the rivers which
are the main source of freshwater input into the
wetland. Farmers rely on the rivers to irrigate their
farms. The wetland catchment is also noted for cattle
grazing. Besides population increment, a shift from
farming or crop cultivation to real estate develop-
ment has influenced land cover changes in the catch-
ment. These human activities if not checked could
undermine the wise use of the wetland.
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0
Sesemi
Pantang
Moana
TESHI
Burma Camp
TradeFair
La
Kotoka
International Airport
NUNGUA
Lashibi
TEMA
ASHIAMAN
Misusokope
Santeo
Zenu
Kobekro
Gbetseli
Kakasunanka
Mlitsakpo
Michel Camp
Sebrepor
Ashiyie
OYARIFA
Teiman
Abokobi
Akpomang
Boi
Apenkwa
Adentan
Ashale-Botwe
Ogbojo
MADINA
shongman
rgyCommission
Universityof Ghana
Legon
Mpehuasem
Agirigano
Martey Tsuru
ACHIMOTAPLANTAT ION
FORESTRESE RVE
ofu
Kiseiman
Haatso
FR
Narhman
UniversityFa rm
Okpoi Gonno
Okpegon
0°0'10"E
0°0'10"E
0°1'40"W
0°1'40"W
0°3'30"W
0°3'30"W
0°5'20"W
0°5'20"W
0°7'10"W
0°7'10"W
0°9'0"W
0°9'0"W
0°10'50"W
0°10'50"W
0°12'40"W
0°12'40"W
43'50"N
5°43'50"N
42'0"N
5°42'0"N
40'10"N
5°40'10"N
5°38'20"N
38'20"N
36'30"N
36'30"N
34'40"N
34'40"N
Legend
Road
Contour line
Railway
Water body
Public building
Geology
Phyllite unit
Alluvial
Marble
Metamiccrogabbro
Orthogneiss
Paragneiss
SAKUMO LAGOON
GULF OF GUINEA
KPESHIE LAGOON
MOKWE LAGOON
SONGO LAGOON
02.551.25 Km
Onukpawehe
Mamanhuma
Dzorwulu
Gyorwulu
MAP OF GHANA
Gbagbla-Ankonu
Fig. 3 Geology distribution of the Sakumo wetland, Ghana
Environ Monit Assess (2015) 187: 671 Page 5 of 14 671
Data acquisition
As a starting point, there was a review of the available
literature on the Sakumo wetland. Secondary data were
collected, analyzed, and reviewed. These included rele-
vant academic articles, books, newspapers, magazines,
and reports of previous studies. Major priority issues
considered in selecting publications to be used for the
review were issues of water quality, due to land-based
human activities and also on fishery resources depletion
and loss of marine biodiversity. Limitations of the re-
view lack of quantitative and qualitative assessment of
the major land-based sources. For instance, where data
on pollution concentration are available, data on vol-
umes of discharges are lacking making it difficult to
calculate the actual pollution load. Also, where infor-
mation on types of contaminants is available, no infor-
mation on transport pathways exists. It is also clear that
many of the key sources of pollution are very closely
linked (e.g., sewage and nutrients). Knowledge on in-
teraction and synergies between different land-based
pollutants in the coastal environments is insufficient.
There is an urgent need for a precise qualitative and
quantitative assessment of the significant sources of
land-based pollution in the study area.
Wetland water quality and nutrient concentration
Due to increased urbanization, water quality regimes of
the wetland have become more intensified with storm
water runoff from agriculture and urban lands bringing
excess water, nutrients, and other contaminants to wet-
lands. These discharges have been revealed to carry
large influxes of nutrients, suspended and dissolved
organic matter, contaminants, and other toxic materials
into the wetland resulting in poor water quality status of
the wetland. Amuzu (1997) noted that, in the early
1990s, coastal wetlands with little stress from human
activities (including the Sakumo wetland) maintained
good water quality (Table 1).
This has been attributed to the disappearance of some
fish species and migratory birds from the wetland. High
dissolved oxygen (DO) concentrations in the wetland
waterhavebeenattributedtophotosyntheticactivity,
associated with the high biomass of cyanobacteria and
the intrusion of the seawater at high tide (Biney 1990).
Asmah et al. (2008) reported an increase in DO levels
that is from 98 % in 1997 to about 140 % in 2002 which
they attributed to human activities. Koranteng 1995;
Yawson 2003; Nixon et al. 2007; Asmah et al. 2008)
between the late 1990s and 2000s (Table 2)reported
slightly to moderately alkaline pH of the lagoon water.
Ansa-Asare et al. (2008) reported high NO
3
-N and
PO
4
3
-P at the riverine end of the wetland and also
toward the end of the raining season (Nartey et al.
2011). This is contrary to studies done by Koranteng
1995 and Asmah et al. 2008 which reported high nutrient
concentrations during the dry season. This was attributed
to the processes of evaporation and concentration of
solutes during the dry season. Koranteng (1995)reported
mean total phosphorus concentrations of 0.644 mg/l,
while Asmah et al. (2008) reported a mean of 1.71 mg/l
in 2002. Nartey (2011) reported total phosphorus concen-
trations of 3.62 mg/l which exceeds the EPA maximum
guideline value of 2.0 mg/l. The sequence of order of the
nutrient in the wetland was PO
4
-P > NH
3
-N > NO
3
-N >
NO
2
-N. The distribution of trace metals (such as Fe and
Mn) in the lagoon have been attributed to urbanization
and high exploitation of cultivable lands (Ansa-Asare
et al. 2008;Laaretal.2011). High levels of manganese
in the lagoon for instance have been attributed to waste-
water discharges and leachates from agricultural farm
lands.
Correlation analysis and Piper diagram
The major ion chemistry and compositional relations
among ionic species of a sampled water can reveal the
origin of solutes and processes that generates an ob-
served water composition. Data for the correlation anal-
ysis was extracted from (Laar et al. 2011). From the
matrix plot, strong (r=0.8 to 1.0), moderate (r=0.6 to
0.8), and low (r=0.5 to 0.6) correlation between selected
Tabl e 1 Some selected physiochemical characteristics of coastal
wetlands in Accra (units in mg/l except pH [no units])
Lagoons pH DO BOD PO
4
3
-P NH
3
-N NO
3
-N
Korle 7.1 4.4 98.9 0.86 3.80 0.30
Kpeshie 8.0 7.3 8.1 0.11 0.29 0.48
Mokwe 7.9 6.4 3.2 0.09 0.20 0.30
Sakumo II 8.2 8.0 12.5 0.08 0.15 0.18
Chemu II 8.1 0.5 71.2 0.59 1.30 0.36
Goa 8.1 6.1 6.4 0.04 0.11 0.96
Laloi 7.6 6.6 5.5 0.06 0.20 0.41
WHO 1996 6-9 <0.3 <0.3 <10
Source: Environmental Management Associates (1991)
671 Page 6 of 14 Environ Monit Assess (2015) 187: 671
variables was found out. To know this objective, r
values and correlation probability values were calculat-
ed. To nullify the effect of missing data, pairwise miss-
ing data deletion technique has been adopted. From
Table 3, the surface water samples disclosed a good
correlation between electrical conductivity (EC) and Cl
(r= 0.98) which further indicated that variation in EC
concentration is controlled by Cl
concentration.
Another fairly good correlation also observed between
Na and EC (r=0.93) and Mg and Cl
(r= 0.95), Mn and
Fe (r= 0.90), Mn and NO
2
-N (r= 0.85) confirm a com-
mon primary source which is both domestic effluent/
sewage and/or fertilizer application. The level of signif-
icance is taken at 1 and 5 %, respectively. However, a
perfect positive correlation coefficient was observed
between EC and total dissolved solids (TDS) (r=1),
whereas high positive correlation was observed between
Na
+
and EC (r> 0.90), Na
+
and Cl
(r> 0.90) virtually in
all the different water sources. In the shallow ground-
water (Table 4), high positive correlation coefficient was
observed between Na
+
and EC (r= 0.91), Na and Cl
(r=
0.97), Na and K
+
(r= 0.93), Mg and Na
+
(r= 0.92), Mg
and Cl
(r= 0.95), Mg and HCO
3
(r= 0.95), NO
3
and
NO
2
(r= 0.99), PO
4
3
and NO
2
(r= 0.94), PO
4
3
and
NO
3
(r= 0.95), and SO
4
2
and TDS (r= 0.95). The high
correlation implies that subsurface water chemistry was
mainly controlled by these ions.
The piper diagram (Fig. 4) was prepared in accor-
dance with modifications by Black (1966). Ansa-Asare
et al. 2008; Asmah et al. 2008 the Piper diagram was
used to evaluate differences in major ion chemistry in
both the surface water and groundwater samples. The
Piper diagram shows that the water generally contains
low concentrations of calcium and magnesium compared
to sodium and potassium while chloride is the dominant
anion. Most of the samples plot in the sodium and
chloride regions of the two triangle plots respectively
depicting a NaCl type of water. The predominantly
NaCl water type could be attributed to the near coastal
surface salt nature of the water.
Isotope signature on hydrology
Published studies on distribution of stable isotopes of
18
O and D in the Sakumo wetland are very limited (Laar
et al. 2011) which demonstrated that significant isotopic
differences exist between wetland water and the riverine
waters (Mamahuma, Onukpawahe, and Dzorwulu).
From the stable isotope analysis, δ
18
OandδDvalues
range from 17.96 to 6.22and 3.68 to 0.26for
Tabl e 2 Statistical summary of physicochemical results of surface and subsurface water (n=86) in the Sakumo wetland (unitsin mg/l except
temp [°C] and SEC [μS/cm], pH [no units])
Min. Max. Mean Median Stand. dev. WHO (2004)Seawatervalue
PH 6.6 8.8 7.88 7.92 0.59 6.58.5 NS
Conductivity 9170 43,800 18,819.09 17,060 10392.6 5000
Total dissolved solids 5044 24,090 10,347 9383 5711.26 1000 32,000
Alkalinity as CaCO
3
175 742 298.64 265 152.54 400 NS
Carbonate as CO
3
27.6 96.4 53.2 35.6 37.63 NS
Bicarbonate, HCO
3
236 901 389.64 3223 116.67 142
Chloride as Cl 2680 14,095 6244.18 6055 3548.59 250 19,000
Sodium as Na 1381 5714 3043.73 2561 1395.52 200 10,500
Potassium as K 14.1 28.1 21.13 19.4 5.3 12 390
Calcium as Ca 123 1066 364.82 233 112.2 75 410
Magnesium as Mg 183 1732 504.36 363 253.97 100 1350
Iron as Fe 0.24 8.99 2.06 0.782 1.7 0.3 NS
Manganese as Mn 0.256 2.82 0.95 0.4 0.094 0.1 NS
Ammonium as N 0 5 2.41 2.46 0.96 NS
Nitrite as N 0 0.208 0.07 0.034 0.004 NS
Nitrate as N 0 0.32 0.11 0.059 0.009 10 NS
Orthophosphate as P 0.09 2.53 0.62 0.352 0.389 0.3 NS
Sulfate as SO
4
50.8 893 302.35 289 127.33 200 270
Environ Monit Assess (2015) 187: 671 Page 7 of 14 671
Tab l e 3 Correlation analysis of lagoon (surface) water from the Sakumo wetland
pH EC TDS Turb T.Alk CO
2
3
HCO
3
Cl
F
Na K Ca Mg Fe Mn NH
4
-
N
NO
2
-N NO
3
-
N
PO
4
-
P
SO
4
2
pH
EC 0.743*
TDS 0.743*1.000**
Turb 0.295 0.067 0.067
T.Alk 0.218 0.069 0.069 0.952**
CO
3
2
0.275 0.102 0.102 0.957** 0.930**
HCO
3
0.042 0.011 0.011 0.874** 0.970** 0.846**
Cl
0.717* 0.989** 0.989** 0.004 0.003 0.034 0.087
F
0.199 0.019 0.019 0.981** 0.975** 0.959** 0.921** 0.043
Na 0.578 0.936** 0.936** 0.119 0.129 0.058 0.207 0.965** 0.147
K0.082 0.5 0.501 0.521 0.452 0.37 0.44 0.569 0.446 0.684*
Ca 0.642* 0.486 0.486 0.152 0.239 0.172 0.178 0.483 0.105 0.310 0.085
Mg 0.702* 0.972** 0.972** 0.045 0.011 0.044 0.059 0.956** 0.015 0.907** 0.459 0.328
Fe 0.489 0.398 0.398 0.411 0.295 0.587 0.131 0.38 0.351 0.361 0.133 0.347 0.303
Mn 0.147 0.139 0.139 0.245 0.139 0.469 0.014 0.124 0.219 0.195 0.154 0.016 0.061 0.908**
NH
4
-N 0.245 0.26 0.26 0.487 0.445 0.561 0.313 0.282 0.461 0.321 0.388 0.285 0.377 0.521 0.502
NO
2
-N 0.179 0.062 0.063 0.19 0.087 0.277 0.048 0.101 0.203 0.232 0.247 0.229 0.048 0.412 0.499 0.516
NO
3
-N 0.006 0.117 0.117 0.36 0.292 0.493 0.212 0.126 0.385 0.264 0.212 0.287 0.096 0.54 0.672* 0.41 0.858**
PO
4
-P 0.452 0.044 0.044 0.293 0.069 0.265 0.093 0.05 0.223 0.018 0.055 0.109 0.132 0.374 0.281 0.402 0.618 0.359
SO
4
2
0.257 0.02 0.02 0.015 0.02 0.083 0.111 0.078 0.081 0.169 0.298 0.054 0.081 0.164 0.172 0.436 0.671* 0.35 0.306 1
*Correlation is significant at the 0.05 level (two-tailed)
**Correlation is significant at the 0.01 level (two-tailed)
671 Page 8 of 14 Environ Monit Assess (2015) 187: 671
Tab l e 4 Correlation analysis of groundwater samples from the Sakumo wetland
pH EC TDS Turb T.Alk CO3 HCO3 Cl Na K Ca Mg Fe Mn NH
4
-N NO
2
-N NO
3
-N PO
4
-P SO
4
2
pH 1
EC 0.702
TDS 0.407 0.699
Turb 0.996** 0.678 0.412
T.Alk 0.712 0.838 0.725 0.741
CO3 0.792 0.778 0.773 0.822 0.966**
HCO3 0.219 0.314 0.663 0.179 0.505 0.411
Cl 0.608 0.979** 0.728 0.6 0.888* 0.8 0.48
Na 0.41 0.910* 0.737 0.41 0.841 0.72 0.652 0.971**
K0.387 0.788 0.812 0.41 0.911* 0.827 0.794 0.888* 0.935*
Ca 0.566 0.266 0.664 0.62 0.603 0.771 0.279 0.275 0.2 0.454
Mg 0.544 0.961** 0.547 0.51 0.742 0.617 0.322 0.957* 0.923* 0.746 0.008
Fe 0.595 0.111 0.458 0.565 0.032 0.011 0.862 0.038 0.246 0.399 0.128 0.098
Mn 0.003 0.413 0.834 0.04 0.627 0.6 0.953* 0.548 0.67 0.844 0.536 0.339 0.791
NH
4
-N 0.016 0.517 0.077 0.092 0.018 0.133 0.008 0.469 0.487 0.157 0.634 0.681 0.087 0.105
NO
2
-N 0.197 0.321 0.275 0.11 0.189 0.26 0.557 0.185 0.088 0.263 0.634 0.443 0.603 0.61 0.821
NO
3
-N 0.238 0.33 0.295 0.16 0.161 0.234 0.58 0.194 0.088 0.258 0.619 0.45 0.649 0.63 0.796 0.998**
PO
4
-P 0.499 0.535 0.05 0.42 0.071 0.042 0.535 0.381 0.233 0.086 0.35 0.581 0.686 0.498 0.737 0.944* 0.951*
SO
4
2
0.22 0.459 0.956* 0.23 0.553 0.638 0.688 0.502 0.54 0.68 0.714 0.286 0.611 0.861 0.112 0.465 0.494 0.274
*Correlation is significant at the 0.05 level (two-tailed)
**Correlation is significant at the 0.01 level (two-tailed)
Environ Monit Assess (2015) 187: 671 Page 9 of 14 671
rainwater, 3.42 to 18.30and 0.55 to 3.86for la-
goon water while subsurface water (from the piezome-
ters) ranged from 8.09 to 15.43and 2.01 to 3.45,
respectively (Laar et al. 2011). In addition to the existing
data on stable isotopes of water, six piezometers were
installed and the shallow groundwater analyzed for the
stable isotope composition. The stable isotope compo-
sition of the shallow groundwaters was plotted along
with the surface waters (Fig. 5). Perusal of the
plot showed no difference between the δ
18
Oand
δD concentrations for both surface water and
shallow groundwater. This was attributed to possi-
ble similarity in hydrostratigraphy and climate con-
dition of the catchment.
The effect of evaporation is evident on all the water
types in the area. Isotopic enrichment could be a result
of the interaction between wetland water and seawater
as well as rainfall (Fig. 6) as the waters approached a
seawater value. However, the narrow range in the stable
isotopic composition of the surface water and subsur-
face water is indicative of a fairly homogenized source
of water for the various types of waters.
Piper Diagram
EXPLANATION
Surfacewater
Piezometer water
Fig. 4 Piper diagram
summarizing geochemistry of
surface and subsurface
groundwater (piezometer) from
the Sakumo wetland
Fig. 5 Relationship between δD
vs. VSMOW and δ
18
Ovs.
VSMOW in the different waters
671 Page 10 of 14 Environ Monit Assess (2015) 187: 671
Integration of wetland component for ecological water
requirement study
Globally, there is an increasing desire to conserve or
restore the ecological health and functioning of wetlands
for both biodiversity and human use. To achieve this,
nations which are signatories to the Ramsar convention
are encouraged to develop methods for defining RDM
required to achieve desired ecological objectives. A
study is proposed to clarify the need for an assessment
Fig. 6 A regression line of δD-
δ
18
O of the local meteoric water
line (LMWL) with surface water
from the Sakumo wetland and
theoretical seawater value
Fig. 7 Procedures for the determination of the ecological water requirement (modified from DWA 2010)
Environ Monit Assess (2015) 187: 671 Page 11 of 14 671
of the wetland component of the ecological water re-
quirement (EWR) component of the Sakumo wetland.
A preliminary determination of the surface water (quan-
tity and quality), groundwater component of the wetland
as well as the basic human needs will be drawn out. An
overall assessment of ecological state of the wetland
would be based on the rule-based model developed by
the Directorate of Resource Quality Services for
Estuaries (DWA 2010) but modified for wetlands. The
modified system will use the underlying contemporary
hydrological processes and formative geomorphological
setting as the basis of classification.
An intermediate determination of the wetland com-
ponent for the EWR will be undertaken. The purpose is
to describe the reference conditions and assess the pres-
ent ecological state (PES) of the wetland. Reference
conditions (RCs) and PES for the wetland components
will be evaluated for key ecological drivers (hydrology,
geomorphology, and water quality) and response indi-
cators (vegetation and aquatic invertebrates). This will
inform the definition of the wetland resource units (qual-
ity and quantity) needed to preserve basic human needs
and the ecological reserve (aquatic ecosystem). Based
on the ecological, social, and economic considerations
of the reserve, the wetland will be assigned an ecological
category (EC), ranging from category A (unmodified) to
category F (critically modified) which will effectively
describe the present state of the wetland. The purpose of
the classification system is to recommend an attainable
EC, plus alternative categories where appropriate based
on an understanding of causes of deviations of the PES
from the RC and then set a management class (MC). The
purpose of the MC is to maintain the current EC (if it is
desirable) or improve management in other to increase
to a better/higher EC. A procedure for the determination
of the EWR is illustrated in Fig. 7.
The methods to be used in determining the wetland
component of the ecological water requirement will
include (Table 5):
&An assessment of available geological maps,
hydrogeological maps, topographical maps, and ae-
rial photographs
&An assessment of hydrochemical data, aquifer pa-
rameters, recharge (ecological role), and wetland
vulnerability.
&Population census and population density data will
also be reviewed to give an indicationof the reliance
of wetland catchment communities on groundwater,
which will have an impact on the wetland.
Tabl e 5 Summary of data required for baseline assessment
Component Requirement for baseline study Description of required data
General Description of wetland catchment -Floodplain topography
-Land use practices
-Water uses
-Wastewater discharges
Bathymetry and
sediments
Topographical surveys -Contour maps, location maps, and cross-section plots
-Sediment particle size distribution and total organic
matter content
Water quality -Physical water quality
-General chemistry major ions
-Nutrients
Salinity and temperature profiles
-System variables (pH, turbidity, TDS, DO, etc.)
-Inorganic nutrients
-Toxic substances
Hydrology and
hydrodynamics
Catchment size delineation -Measure river inflow data (gauging stations) at the head of the
wetland
-Measure rainfall data in the catchment (or in a representative
adjacent catchment)
-Hydrological parameters (evaporation rates, radiation rates)
-Flow losses (e.g., abstraction, impoundment) and gains (e.g.,
discharges, transfer schemes)
Fish Species and size composition
of fish community
Documented data from the Center for Africa
Wetland studies
Birds Major bird groups and their
defining features
Documented data from the Center for Africa
Wetland studies
671 Page 12 of 14 Environ Monit Assess (2015) 187: 671
&Land use information such as agricultural activities
that rely on or impact on the wetland will also be
sourced.
&Once-off cross-sectional survey to determine the
geomorphology and hydraulics including surface
flow volumes and the delineation of inundation
zones, saturation, and vegetation zones to be con-
ducted during the dry season;
&Documented data of key habitats, wetland plants,
and aquatic invertebrates, and;
&Assessmentof the anthropogenic impacts and trends
on both water quality and quantity.
Conclusion
Based on this review, it can be concluded that the key
factors affecting the wetland chemistry are domestic
waste, agricultural runoff from farms, and seawater en-
croachment. Source of nutrient to the wetland was also
found to be predominantly from fertilizers introduced by
subsistence farming activities in the wetland. Stable
isotopes of O-18 and deuterium have shown that the
main source of water to the wetland is mostly rain and
seawater. However, there is a gap on information about
catchment behavior in terms of response to rainfall
input, runoff, and storage components of the hydrolog-
ical cycle, and the water balance will provide better
understanding of the overall hydrological processes oc-
curring in the wetland. The following are recommended
for further studies:
(i) What is the rate of groundwater recharge in the
wetland
(ii) What are the flow processes taking place in the
wetland
(iii) What is the wetlandgroundwater interaction
(iv) What are the flow requirements needed to maintain
the basic human needs and the ecological require-
ments of the wetland (quality and quantity)
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... Surface water turbidity is expected to be between 1 to 50 NTU and increases can be caused by the presence of organic matter pollution, other effluents, or run-off with a high suspended matter content (Chapman and Kimstach, 1996). (Nixon et al., 2007;Asmah, Dankwa, Biney & Amankwah, 2008;Nartey et al., 2012;Nonterah, Xu, Osae, Akiti & Dampare, 2015) with the lagoon being hyper-eutrophic at the riverine end and oligotrophic at the seaward end (Ansa-Asare, Mensah & Entsua-Mensah, 2008). These nutrients were suspected to come from domestic waste, agricultural run-offs, etc. Asmah et al. (2008) stated that the current rate of nutrient loading in the lagoon would likely change the structure and function of plankton, benthic and fish communities with time, thereby affecting the whole ecology of the lagoon. ...
... Comparative studies on human activities and nutrients in the Muni and Sakumo II lagoons are common (Nixon et al., 2007;Ansa-Asare et al., 2008;Mensah & Biney, 2008;Tay et al., 2009;Mitchell, Boateng & Couceiro, 2017); all of them describing the Sakumo II Lagoon as polluted. Other studies on heavy metals and nutrients in the Sakumo II Lagoon all point to the pollution of this water body (Biney, 1990;Asmah et al., 2008;Mensah & Biney, 2008;Agbemehia, 2014;Nonterah et al., 2015). Regarding the Muni Lagoon, Tiakor Despite the fact that some of these water bodies have been studied for their ecological status based on benthic macroinvertebrates in the past decade, it is evident that ecological studies in coastal water bodies in Ghana are completely silent on the functional (biological) traits approach. ...
... These two streams have been reported to be polluted as a result of industrial and domestic activities (Tay et al., 2009). Values obtained in this present study however, appear lower than those in previous studies (Tay et al., 2009;Nonterah et al., 2015). Agriculture runoffs from farms along this water body may have also contributed to its high conductivities. ...
Thesis
Full-text available
This study was aimed at assessing the ecological status of six coastal water bodies using abiotic parameters and benthic macroinvertebrates as indicators. Data were collected from June 2016 to August 2017. Physico-chemical parameters were measured in situ while nutrients, heavy metals analyses, sediment organic matter and particle sizes as well as species identification were done in the laboratory. Macroinvertebrates were categorised into five functional groups namely body form, feeding habit, mobility, sexuality and sociability. A total of 45 species were recorded in the six water bodies. The abiotic parameters showed Sakumo II and Fosu lagoons are polluted systems with high conductivity, TDS, nitrate, phosphate and heavy metals concentrations. This was supported by the Bray-Curtis analyses using both taxonomic and functional traits approaches which segregated the two lagoons from the other four water bodies. Pollution tolerant species namely Chironomus sp. and Limnodrilus hoffmeisteri dominated Sakumo II while Melanoides tuberculata and Chironomus sp. were dominant in Fosu. The remaining four water bodies namely Kakum Estuary, Pra Estuary, Benya Lagoon and Muni Lagoon had higher taxonomic and functional richness and diversities than Sakumo II and Fosu. Important abiotic factors that significantly influenced the abundance of macroinvertebrates taxonomic and functional groups were conductivity, salinity, phosphate, nitrate, organic matter, arsenic, copper, chromium, iron, mercury, lead and zinc. The taxonomic and functional traits approaches used in assessing the ecological status of the water bodies in this study produced similar outcomes. In view of the advantages associated with the latter, under situations of limited resources and time, its use should be the preferred option.
... The main drainage network, includes the Onukpawahe, Mamahuma and Dzorwulu rivers. The drainage network catchment is made up of alluvial sediments with marine sand deposits (Nonterah et al. 2015) and has a low relief, with an average elevation of 46 m above mean sea level (Nonterah et al. 2015). ...
... The main drainage network, includes the Onukpawahe, Mamahuma and Dzorwulu rivers. The drainage network catchment is made up of alluvial sediments with marine sand deposits (Nonterah et al. 2015) and has a low relief, with an average elevation of 46 m above mean sea level (Nonterah et al. 2015). ...
... The occurrence of groundwater is mainly due to the existence of linear features due to faulting and weathering as the main rocks are impermeable, whereas the groundwater used in the catchment is mostly sourced from the shallow unconfined Quaternary aquifer (Nonterah et al. 2015). The hydrogeological setting of the Sakumo wetland includes crystalline basement rocks. ...
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... Wetland sustainability is vital for all forms of life, and several studies across the globe have examined the factors contributing to it. In Ghana, most studies on wetlands have focused on water quality and pollution [27][28][29][30], conservation of Ramsar sites [13,31,32], economic value of wetland resources from the perspective of fishing [33], and factors contributing to their ecological damage (land use change, mining, waste disposal, and agriculture) [13]. Although rice farmers are one of the major stakeholders in the utilization of swampy areas, there are no studies on their contribution to the sustainability of swampy wetlands. ...
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Sakumo Lagoon, situated near Accra, is a Ramsar-listed coastal wetland threatened by urban and agricultural waste, being located in an urban area where access to domestic and waste disposal facilities is a major problem. The aim of this study was to assess the pollution status as well as trends, in terms of pollution laoding, in the lagoon. Nutrients, dissolved oxygen, biochemical oxygen demand, suspended solids, temperature, pH and faecal coliforms were monitored on a quaterly basis from 1997–1998 and 2001–2002, covering both wet and dry seasons. Significant increases in the mean concentrations of suspended solids, ammonia-nitrogen, phosphate-phosphorus and biochemical oxygen demand indicated an increase in the level of pollution in the lagoon. Faecal coliform counts were fairly high, exceeding 130 counts 100 ml–1, which is the maximum acceptable count in Ghana for water used for recreation. Results from the study suggested rapid deterioration of the lagoon water quality between 1997 and 2002. Domestic and agricultural discharges into feeder streams were the main sources of pollution, as well as decaying plant material in the lagoon.
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This paper surveys the aquifers and the groundwater resources landscape in Ghana to identify the critical resource issues constraining the development and management of groundwater throughout the country. The research is based on a collation of the recent data on the hydrogeological properties of the different geological terrains in the country. This study finds that there are five main hydrogeological provinces distinguished by their well yields, lithology, and groundwater quality. This latest hydrogeological zonation, which is an improvement over previous works consists of the Birimian Province, the Crystalline Basement Granitoid Complex Province, the Voltaian Province, the Pan African Province, and Coastal Sedimentary Province. The hydrogeological properties of each province are discussed. The most prolific aquifers in the country have been identified among the fractured and weathered zones within the Togo Series, Buem Formation, Birimian and Tarkwaian System rocks. Aquifers of these rock formations also offer groundwater of the best quality for most uses in the country. Hydrochemical data gathered from wells drilled through all the hydrogeological terrains in the country for this study suggest that groundwater hydrochemistry is controlled principally by the weathering of silicate minerals and cation exchange activity. These processes are pervasive throughout the country. In isolated areas, groundwater contamination due to domestic waste discharge and agricultural activities has been noted. Four groundwater types have been identified based on Q-mode hierarchical cluster analysis and conventional graphical methods. In the coastal areas such as the Keta basin, seawater intrusion has been identified as one of the major influences on hydrochemistry of groundwater in the shallow unconfined aquifers. On the basis of the hydrochemistry, groundwater suitability for irrigation purposes is copiously discussed. The aquifer management problems can be posed as follows. There is inadequate knowledge base of the aquifer geometry and safe yield characteristics of most of the aquifers in the country. There is also inadequate information to address the status and trends in groundwater quality for most areas of the country. The following emerging issues have been identified: anthropogenic effects on groundwater quality; salt-water intrusion in coastal aquifers, groundwater depletion or inadequate supplies from groundwater to meet human needs; uncertainties about recharge and sustainability due to increased abstraction; as well as lack of institutional capacity to respond adequately to sustainable groundwater use. Recommendations to ameliorate these problems include the strengthening of institutional capacity for comprehensive national evaluation of groundwater resources, including aquifer delineation and pro-active strategies to reduce groundwater abstraction to safe yield levels and adoption of aquifer protection strategies for overall protection of groundwater quality.
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Forty-two species of waders, comprising 29 Palearctic migrants, eight residents, two partial migrants and three vagrants, were recorded in three years of montly surveys of shorebirds in coastal Ghana. Eleven species occurred in internationally important populations: curlew sandpiper, little stint, sanderling, spotted redshank, grey plover, ringed plover, black-winged stilt, avocet, black-tailed godwit and turnstone. Arrival of migrant waders in coastal Ghana began in August and reached a peak in November/December. Most waders left the Ghana coast in January, leaving only a small proportion which remained until final departure in April. Another peak in numbers was observed during the spring passage in some years for some wader species. The proportion of migrant wader populations oversummering on the Ghana coast varied with species, and from year to year. While the total populations of some species departed, as much as 30% of the populations of others remained on the Ghana sites during the northern summer. The wader numbers recorded in the different sites and the relative importance of the key sites showed annual fluctuations. Two sites, the Keta and Songaw Lagoons, qualified as internationally important wetlands in terms of their total wader numbers and by virtue of the fact that each supported internationally important populations of seven species of waders. Three other sites also supported internationally important populations: Sakumo Lagoon (4 species), Korle Lagoon (3) and Esiama (1). Two sites, Keta and Korle Laggons, face immediate threat of coastal erosion and/or proposed developments involving drainage and land reclamation. The Sakumo and Songaw Lagoons have great potential for development as conservation areas and proposals have beeb submitted to this effect.
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As part of a larger study of demographic change in coastal Ghana, we measured the concentrations of major plant nutrients and phytoplankton chlorophyll in eight coastal lagoons with different land use and human population density. The purpose of our study was to relate human activities to water quality in coastal receiving waters. We also carried out preliminary measurements of stable nitrogen isotopes to quantify the contribution of sewage and fertilizer to fish production in the lagoons. Annual mean concentrations of ammonia, nitrite plus nitrate, dissolved inorganic phosphate (DIP), and water column chlorophyll a varied by factors of over 1400, 15, 315, and 125, respectively, among the eight small coastal lagoons in the Central and Greater Accra Regions of Ghana. Concentrations of ammonia (mean of similar to 1 mmol/L) and phosphate (mean of similar to 60 mu mol/L) in Korle lagoon, near the capital city of Accra, may be the highest yet reported for an estuarine system. In most of the lagoons, nutrient concentrations throughout the study period were much lower than previously reported, perhaps due to analytical problems in earlier measurements. Dissolved inorganic nutrients varied markedly over the year but showed no evidence of a regular seasonal cycle such as commonly observed in temperate coastal systems. Nutrient concentrations did increase sharply and briefly in many lagoons during the wet season. Water column chlorophyll increased greatly during August and September. Since water column inorganic nutrients were very low during July, it is possible that the apparent bloom was stimulated by nutrients brought into the lagoons during coastal upwelling or that the elevated chlorophyll was itself brought into the lagoons from offshore. Human population densities in the watersheds of the lagoons were high and varied widely, from similar to 150 individuals/km(2) to almost 3300 individuals/km(2). Ratios of watershed area to open lagoon area ranged from similar to 30 to almost 2500, much higher than is common in most well-studied estuaries and lagoons in the United States. We found a strong correlation between human population density and mean annual dissolved inorganic nitrogen (DIN) concentrations among the wide range of systems studied. Mean annual DIN concentrations in the Ghana lagoons were higher than found in a number of temperate lagoons with similar population density. The relationship between population density and DIP and chlorophyll was weak. The latter may be due to toxic effects in Korle lagoon and abundant filter feeders in another lagoon. Stable nitrogen isotope ratios in two species of fish, a shrimp, and a crab varied consistently among the lagoons, with higher delta N-15 values indicative of human sewage in lagoons downstream of more densely populated watersheds.
Article
Accelerated urbanization and industrial growth without the provision of adequate infrastructure for waste management in the years after the introduction of the Economic Recovery Programme in 1983 have led to the pollution of surface water sources in the urban settlements of Ghana. Most of the surface waters have high biochemical oxygen demand and low dissolved oxygen levels. In the recent past, however, a National Environmental Action Plan has been formulated for pollution control. Funding has also been obtained to improve sanitation, storm drainage and solid waste management in the major cities of the country. The collection of baseline data on the different components of the environment has also been intensified to enable the setting of environmental standards to control and regulate industrial emissions throughout the country.
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A small coastal lagoon near Tema, Ghana, has been studied from August to December 1971. Data on temperature, salinity and exchange of water with the sea are given for January to December 1971. The extreme hydrographic conditions in the lagoon cause a reduction of the fauna, as compared with a typical "open" lagoon or with the marine shore. The structure of the food web in the lagoon is given. The main part of the animal biomass consists of the gastropod Tympanotonus fuscatus var. radula and the cichlid fish Tilapia melanotheron which feed on bottom deposit and associated microorganisms and are well­ adapted to the rapid changes of salinity that characterize the lagoon. After the rain period (MaY-July) there is a steady increase of marine species, represented mostly by juvenile stages.