Towards Conservation of Coastal Wetlands: An Assessment of The Ecological Health Status of A Neglected Lagoon In Ghana


 Coastal wetlands are important ecosystems that support biological communities and human populations. Anthropogenic activities have over the years affected these coastal wetlands globally leading to a loss of about 50% of these areas. There have therefore been calls to conserve these wetlands in order to sustain future generations. However, data to support conservation efforts on most of these ecosystems is lacking. The ecological health status of an aquatic system is one indicator that can form the basis of conservation or restoration actions. In Ghana, the Brenu Lagoon in the Central Region has been neglected in terms of ecological health research over the years. This study therefore aimed at assessing the ecological health of the Brenu lagoon using benthic macroinvertebrates. The study showed that the lagoon is hypersaline and moderately polluted with a dominance of two stress-tolerant species – Capitella Capitata and Ampithoe sp. The current state of pollution of the lagoon may be associated with waste disposal and agricultural activities within the catchment of the lagoon. Further studies are required to establish the linkage between these activities and the state of the lagoon on the basis of which remedial actions can be taken.


Introduction
Conservation of coastal wetlands has become a topical issue globally as these ecosystems continue to experience pressure from natural events and anthropogenic activities. Coastal wetlands are fragile ecosystems but play important roles ecologically supporting aquatic and terrestrial life. They are a source of rich natural resources that are often exploited by humans for livelihood and economic development. The exploitation of these resources is often done unsustainably and has resulted in the loss of about 50% of coastal wetlands worldwide, loss of species of ecological importance and degradation of water quality (Davidson, 2014;Lotze et al., 2006). Apart from resource exploitation, wetlands are often treated as wastelands receiving waste from nearby communities and industries. Recognizing the services that coastal wetlands provide, it is important that these ecosystems are protected and conserved. It is now also recognised that biodiversity conservation plays an important role in ensuring sustainable development rather than working against it as it was previously thought to (Niesenbaum, 2019). Consistent with this, the Sustainable Development Goal 14 (SDG) target 5 of the 2030 Agenda for Sustainable Development aims to "by 2020, conserve at least 10 percent of coastal and marine areas, consistent with national and international law and based on the best available scienti c information." However, globally biodiversity conservation is plagued with data insu ciency (Christie et al., 2020). Due to limited resources, biodiversity research is limited both geographically and taxonomically (Christie et al., 2020;Donaldson et al., 2017) and this includes coastal ecosystems such as wetlands. To adequately protect these ecosystems, there is the need to ll the knowledge gaps to inform policy direction and conservation initiatives. This has become particularly critical in developing countries where these coastal ecosystems have become an important source of income and livelihood for many in the face of rapid urbanisation, industrialisation and economic growth in areas.
Ghana, a developing country in West Africa, has a 550km coastline rich with different types of wetland ecosystems made up of ninety-eight (98) lagoons and ten (10) estuaries (Yankson & Obodai, 1998). Five (5)  these lagoons, it is impossible to de ne the extent of loss and degradation these systems have encountered over the years. It is also impossible to determine the potential for the conservation or restoration of these systems.
Brenu lagoon in the Brenu Akyinim community in the Central Region is one of such lagoons that has been poorly studied over the years. A search through literature shows a study on periwinkles (Tympanotonus fuscata) by Aggrey-Fynn (2010) to determine their size distribution, another by Zuh et al. (2019) on black-chinned tilapia Sarotherodon melanotheron to compare size differences with those found in an open lagoon (Narkwa) and Essumang et al. (2007) to determine levels of heavy metals in the both the Tympanotonus fuscata and Sarotherodon melanotheron. Also, Aheto (2004) conducted a study on economic valuation of the Brenu mangrove ecosystem. However, to date, there has not been any health status assessment of the Brenu Lagoon. The health status of an aquatic ecosystem determines the ecosystem services it provides to surrounding biological and human communities. An understanding of this health status, therefore, provides the basis for efforts towards protecting the ecosystem (Costanza et al., 1997).
Benthic macroinvertebrates are the most commonly used bioindicators of water quality (Bonada, Prat, Resh, & Statzner, 2006) and are a cost-effective way of assessing the ecological health of an aquatic ecosystem. They are greatly in uenced by the physical and chemical conditions of the water body. The ecological condition of an aquatic ecosystem is re ected in the benthic community structure (Heino, Muotka, & Paavola, 2003). As compared to chemical assessment methods that show only short-term changes in an aquatic ecosystem, benthic macroinvertebrates provide a better understanding of the changes or uctuations that have occurred within that ecosystem over a period of time (Nkwoji, Ugbana, & Ina-salwany, 2020). Apart from their usefulness as bioindicators, benthic macroinvertebrates play an important role within the ecosystem, providing food for other invertebrates and vertebrates and feeding on organic matter that is deposited within the water column, ensuring an adequate balance of organic matter within the ecosystem (Moulton, Magalhães-Fraga, Brito, & Barbosa, 2010).
The aim of this paper, therefore, is to determine the health status of the Brenu lagoon using benthic macroinvertebrates as an indicator. The results of this study are expected to inform policy towards protecting the resource and also provide relevant stakeholders such as the Non-governmental Organisations (NGO's) with baseline information to initiate actions towards restoration and/or conservation of the lagoon. Study Area: The study was carried out at the Brenu Lagoon (5° 4' 7.8" N; 1° 25' 53.3" W) located in Brenu Akyenim in the Central Region of Ghana, as shown in Fig. 1. The lagoon covers an area of 0.82 km 2 and is bordered by two communities -Brenu Akyenim and Ampenyi-Ayensudo. Five small streams, Obuahu, Asosi, Burabin, Esuaku and Asenche feed into the lagoon, however, most of them dry out during the dry season (Essumang et al. 2007). The lagoon, therefore, experiences hypersaline conditions during the dry season since the main source of dilution is from rainfall (Yankson, 1982). It is closed from the sea by a sandbar which is opened annually by residents of the community to prevent ooding during the rainy season. The sandbar is also removed during the celebration of an annual festival 'Bakatue' to link the lagoon to the sea to allow entry of marine shes into the lagoon (Aggrey-Fynn, 2010). The bottom of the water body is mostly muddy soft, with some areas interspersed by sandy and rocky substratum.
Fishes in the Brenu lagoon mostly include the tilapia, Sarotherodon melanotheron, and other species such as mullets and shrimps (Aheto, 2004). Inhabitants from the neighbouring communities of Brenu Akyenim and Ampenyi-Ayensudo harvest resources from the lagoon for their livelihood, most especially in the dry season, when less farm activities takes place (Zuh et al. 2019). Fishing in the lagoon is mainly done using simple shing gears chie y cast nets and hooks, however, shing is prohibited on Wednesdays (Aheto 2004). There is an indication of over-exploitation of the mollusc Tympanotonus fuscata is (Aggrey-Fynn, 2010). The lagoon is also bordered by strands of mangroves, predominantly Avicennia sp. and small patches of marsh (Zuh et al. 2019). Evidence of mangrove harvesting in the past can be seen along the perimeter of the lagoon, which might have resulted in only patches of the mangrove Avicennia sp. remaining. Also, discharge of domestic sewage, dumping of refuse and agricultural run-offs into lagoon and the adjoining mangroves are major anthropogenic threats the lagoon (Aheto 2004).

Sampling method:
Twelve stations were demarcated across the lagoon. Physico-chemical parameters such as temperature (℃), salinity (ppt), pH, DO (mg/l), conductivity (µS/cm) and TDS (mg/l) were measured using a multi-parametric meter (Eutech PCD 650). Measurements were done in three replicates at all stations. Mean particles sizes (MPS) was determined following Yankson (2000). Organic matter content was determined using the weight loss on ignition method by burning sediments in a furnace at 550°C for 4 hours to burn off the organic matter.
Benthic macroinvertebrates samples were collected from twelve stations as the environmental parameters, using a 15 cm × 15 cm Ekman grab. The samples were screened through a set of sieves (2 mm, 1 mm and 0.5 mm) with the larger meshed sizes stacked above, the smaller ones, preserved in formalin and stained with eosin to aid sorting. Organisms collected were identi ed to the lowest possible taxonomic level using a dissecting microscope with the aid of standard errors were calculated. Analysis of variance (ANOVA) and subsequently Tukey's posthoc test was run to determine spatial variations in environmental parameters. With the benthic macroinvertebrates, frequency of occurrence (F index) described by Guille (1970) was determined as F = pa/P x 100 where pa represents the number of samples a particular species occurred throughout the study period and P is the total number of samples collected throughout the study period. Using this formula, species were classi ed as constant (F ≥ 50 %), common (10 % < F < 49 %) and rare (F < 10 %). Species Data on macroinvertebrates were fourth root transformed to stabilise and normalise the variance prior to determination of species diversity. The similarity in benthic community structure among the stations were determined based on Bray-Curtis similarity index in PRIMER v6 package. Station classi cation was achieved using a complete linkage dendrogram and nonmetric multidimensional scaling. SIMPROF test was determined similarity in benthic community structure among stations.

Results
Variations in environmental factors in the Brenu Lagoon are shown in Table 1. Spatial variations were only observed in temperature and salinity (p < 0.05).
Mean temperature ranged from 30.10 ℃ -32.33 ℃, with St 9 and St 1 being signi cantly higher and lower respectively than most of the other stations.
Salinity was generally high within the lagoon, with mean values ranging between 39.68 ppt to 42.14 ppt. Salinity at St 1 was signi cantly higher than most of the other stations. pH, DO and conductivity showed no signi cant variations spatially. Mean pH within this water body ranged from 8.67-9.37, with St 1 recording a comparatively lower value than the other stations. DO ranged between 5.93 mg/l -6.70 mg/l with relatively low values in stations 11 and 12.
Regarding conductivity, values ranged from 27.14-33.29 µS/cm, with relatively lower values at stations 1, 8 and 11.      Table 4 shows BENTIX scores and classi cations for the various stations in the lagoon. St 6 was of good quality while the rest of the stations were between moderate and poor status. Stations 3, 4, 7, 9, 10 and 12 were of poor quality. The Brenu Lagoon, in totality, was of moderate quality.  Fynn, 2010). The hypersaline nature of this lagoon is an indication of stress for many benthic organisms. This is similar to the situation at the Muni Lagoon, a hypersaline lagoon of up to 165ppt salinity during the dry season, where Gordon (2000) found no benthos during the dry season even though all other environmental parameters within that lagoon were well within acceptable limits (Gordon, Ntiamoa-Baidu, & Ryan, 2000). Interestingly, the overall species diversity of the Brenu lagoon indicated a moderately balanced and stable structure. The species diversity encountered in this lagoon is higher than Fosu (Armah, Ason, Luginaah, & Essandoh, 2012) and Sakumo (Dzakpasu, 2019).
At all sampling stations however, there was a dominance of stress-tolerant species Ampithoe sp. and Capitella capitata indicative of some degree of stress within the entire lagoon system. Nevertheless, there were variations among the stations where 6 stations showed a higher degree of stress than others (Table 4)  On the basis of the pattern observed, it is important to explore other potential stressors or pollutant sources to provide a better understanding of the dynamics of the Brenu Lagoon. As mentioned earlier, two major communities border the lagoon -Brenu Akyenim and Ampenyi-Ayensudo. Agriculture is a source of livelihood for the residents in both communities and these agricultural lands are in close proximity to the lagoon (Fig. 1). Possible runoffs from these lands during rain events potentially drain organic fertilizers, pesticides and other agrochemicals into the lagoon. Again, pockets of waste dumps have been created along the perimeter of the lagoon. These wastes along with their leachates are also discharged into the lagoon, particularly during heavy rain events. Also, several abandoned salt pans can also be found around the lagoon which may contribute to high salinity in the sediments depending on the length of time since abandonment, ooding regime and the drainage of the lagoon (Bouzillé, Kernéis, Bonis, & Touzard, 2001). Consistent with this, the stations that recorded poor BENTIX scores were located closer to areas of human activity as shown in Fig. 1 and several studies have found that these types of anthropogenic activities impact benthic macroinvertebrate community structure (

Conclusion And Recommendations
The Brenu Lagoon is moderately polluted and the most obvious stressor from this study is the hypersaline conditions within this ecosystem. However, the variations in the level of pollution within the stations sampled despite the stability of salinity levels measured indicate the presence of other potential stressors which may be impacting the benthic community structure. Human activities, including waste disposal and agriculture by residents of the communities bordering the lagoon, are potential sources of pollutants that may leak into the water body and impact the stability of the ecosystem.
Despite the current status of the lagoon, there are still opportunities to improve or restore the health of the lagoon if the stressors are identi ed. There is, therefore, the need for further research to establish the linkage between these identi ed anthropogenic activities and the current state of the lagoon. There is the need to investigate pollutants that may be present in the water body, identify the sources of these pollutants and determine the impact of these pollutants on macrofauna within the water body since the community relies on these as a source of protein and livelihood. Availability of data and material (data transparency): All data produced from this study are provided in this manuscript Code availability (software application or custom code): Yes Overall percentage composition of macroinvertebrate species in the Brenu Lagoon Non-metric Multidimentional scaling (nmMDS) of stations based on benthic macroinvertebrates abundance and composition in the Brenu Lagoon