**12. Impacts of anthropogenic activities**

#### **12.1 Coastline recession**

The major cause of coastline recession in this region is the wave attack of the clay ridge sediment, because of the absence of longshore current and weak nearshore littoral Guinea current. Tides and waves energy concentrated on the bare surface of the clay ridge, exposing it to direct wave impact because of the absence of the protective force of mangroves. A network of rills is developed on the plain due to wave backwash as it overruns the plain when the tide is high. Subsequent backwash and uprush of currents progressively widened and deepened the rills forming vertical heads U-shaped gullies. The walls of the gullies are terraced and are at the sub-tidal platforms level, becoming wave penetration avenue as the gully rapidly advancing into the coastal plain. The rate of gully head retreats measured the ranged from 5.7 m to 15.8 m annually [17].

Ground surface lowering and coastline recession result from the accumulation of ocean water in the depressions across the coastal plain. The energy uprush and backwash currents of the tides and waves affect the flood pools by increasing the soil water content. This relaxes the coherence of the unconsolidated soil, weakening the soil physicochemical interparticle bonds, thereby exposing the flood pool coastal plain to sheet wash erosion [5]. The coastal plains were eventually destroyed as the depressions gradually widened and deepened until the adjacent ones become incorporated and coalesced into an expanded subtidal platform.

Ebisemiju [17] reported coastline recession in the region (specifically Awoye) by about 3.31 km between 1974 and 1996 with annual rates varying between 31 m to 19 m in 1981. About 487 hectares of the coastline have been claimed into the Atlantic Ocean as a result of coastline recession within a short period of two decades (1973–1991) [17]. This has astronomically led to the loss of about 3000 hectares by 1996, reducing about 62% of the coastal plain and leading to the loss of arable land for animal husbandry and land for settlement in this narrow coastal plain. Presently, about 35 m of arable land is being loss into the Atlantic Ocean annually from this narrow coastal plain of the region.

#### **12.2 Coastal erosion**

Large-scale destruction of mangroves, canals and buildings are some of the direct impacts of erosion disasters in the region. These are evident in the ironwood stakes of abandoned houses found within the nearshore zones and intertidal platforms, indicating previous settlement.

*Climate Change and Anthropogenic Impacts on the Ecosystem of the Transgressive Mud Coastal… DOI: http://dx.doi.org/10.5772/intechopen.105760*

A lot of inhabitants have been forced to abandon their houses and migrated inland to a safe location due to tidal floods and accelerated coastline recession. This makes the people relocate their communities at least once every 4 years. Today, the Awoye community (one of the settlements in the region) was originally about 3 km on the Atlantic Ocean from the present shoreline. Permanent structures could not be erected in the region because of the constant need to dismantle their houses and relocated them to a safer area due to the continuous threat of coastal erosion and tidal floods. Massive breaching of the coastline in one of the communities in the region (Ayetoro) may undoubtedly lead to a catastrophic event that will wipe out the entire community.

#### **12.3 Seismic investigation**

Seismic investigations (which involve explosive charges detonation below the ocean floor) were believed to have induced local subsidence. Ayetoro community claimed that it was Seismic investigations conducted in the area by an oil prospecting company, that generated shock waves which caused extensive damage to the major structures in the town, particularly the King's concrete palace. The claim was a memorandum sent by the community in 1981 to the NNPC (Nigeria National Petroleum Cooperation) but was refuted by the corporation. It is of note that explosion forces like that could result in the consolidation of subsurface sediment and liquefaction of surficial sediment. It could also lead to an increase in water depth and erodibility of sediment. Such activities could induce potential disturbance of the nearshore bottom leading to necessary conditions that promote coastal erosion. Increased water depth within the nearshore zone would enable larger waves to penetrate further inland than otherwise experienced. This would result in coastal erosion and the inundation of inland forests by seawater.

#### **12.4 Oil spillage**

Oil spillage has detrimental effects on both plants and animals. It is reported that oil spillage has caused constant threat to farmlands, crop plants, forest tree species and other vegetations in oil-producing areas in Nigeria [25]. There have been over 4000 oil spills in the Niger-Delta area of Nigeria since 1960. Toxicity of crude oil depends on its physical and chemical composition, the amount of the oil, the plant species and time of application as well as other environmental conditions [26].

Liver damages, infertility, disabilities, blindness, damages to fur and feather of birds and accidental poisoning are some of the direct effects of oil spillage in our ecosystem. It causes alterations in soil microbiological and physiochemical properties and affects soil fertility adversely, thereby having detrimental effects on the aquatic and terrestrial ecosystems.

## **13. Conclusion**

The transgressive mud coastal ecosystem is full of vast resources of minerals, foods, and energy which has witnessed a lot of degradations as a result of several years of anthropogenic pollution (oil exploitations and explorations) and climate change (coastal recession). Meteorological information of the regions shows a

gradual degradation in the past 30 years. Temperature, rainfall and humidity increase annually depict climate change, resulting from uncontrolled exploitation of natural resources is rapidly pushing the region towards ecological disasters.
