Influence of Hydrological Variables on Macrophytes in a Black Water River Ecosystem

E.D Anwana,F.O Ogbemudia,P.E Sunday,R.E Ita

doi:10.4314/jasem.v25i2.3

Abstract

This study assessed the influence of hydrological variables on macrophytes in a Black Water River ecosystem of Enyong River in Itu and Ibiono Local Government Areas of Akwa Ibom and Cross Rivers States, Nigeria. Four vegetation plots were chosen and in each of the plots, four belt transect were laid. In each transect, macrophyte were systematically sampled in four 10 m × 10 m quadrat at regular intervals. Macrophytes were identified to species level and their frequency and density determined. Water samples were obtained in each quadrat where the macrophytes were sampled and analyzed for their physicochemical properties using standardized methods. Altogether, 10 macrophyte species were encountered. Vossia cuspidata had the highest density (100.00±8.00 st/ha) and frequency values (100 %). Sacciolepis africana had the least density of 7.10±0.45 st/ha while Ludwigia octovalvis, Persicaria senegalensis, andSacciolepis africana had the least frequency of 25 %, respectively. The pH of the water was strongly acidic (5.54±0.03), electrical conductivity was low (20.00±5.77 µs/cm), temperature (29.00±1.10 ºC), Dissolved Oxygen (DO) (9.20±0.12 mg/l) and turbidity (7.10±0.06 NTU) values were high while Biological Oxygen Demand (BOD) (2.00±0.29 mg/l) Total Dissolved Solids (TDS) (10.00±0.29 mg/l) and Total Suspended Solids (TSS) were low (5.00±1.15 mg/l). Water Nutrients followed this decreasing order; chloride (3.55±0.02 mg/l) > nitrate (2.45±0.03 mg/l) > sulphate (2.02±0.06 mg/l) > phosphate (0.08±0.01 mg/l) and sulphide (0.03±0.02 mg/l). Heavy metals also followed this descending order; Pb (0.50±0.03 mg/l) > Zn (0.07±0.02 mg/l) > Cu (0.03±0.02 mg/l). Canonical Correspondence Analysis delineated 11 hydrological variables (temperature, pH, sulphate, turbidity, phosphate, BOD, nitrate, DO, TDS, sulphide and TSS) which exerted great influence on macrophyte distribution. V. cuspidata had affinity to pH and temperature, Sacciolepis africana had affinity to turbidity and BOD, Ludwigia octovalvis and Nymphaea lotus had affinity to sulphate and chloride, respectively, while Ipomoea aquatica and Alternanthera sessils had affinity to phosphate. On the other hand, Persicaria senegalensis, Salvinia molesta, Azolla pinnata and Ceratophyllum demersum had affinities to sulphide, DO, TSS and TDS, respectively. Since hydrological variables regulate macrophyte diversity and distribution, this study calls for consistent, monitoring and management of this ecosystem against future environmental changes.  Keywords: Aquatic plants, Black water, Canonical Correspondence Analysis, Ordination

Highlights

Macrophytes are important components of many aquatic ecosystems
Ludwigia octovalvis (25 %), Persicaria senegalensis (25 %) and Sacciolepis africana (25 %) had the least frequency while Sacciolepis africana had the least density of 7.10±0.45 st/ha
In macrophyte distribution along hydrological gradients are borne by these axes

Summary

Introduction

Macrophytes are important components of many aquatic ecosystems. Their roles in these ecosystems cannot be overlooked as they provide numerous ecological functions such as being primary producers along food chains, providing shelter for periphyton, algae, zooplankton and assisting in nutrient cycling (Hatton-Ellis et al, 2003; Lacoul and Freedman, 2006). Impeding the establishments of pristine macrophyte communities These disturbances are expressed in the form of eutrophication, water pollution, changes in hydrological regime due to dams and channels construction and decline in weeds as a consequence of cutting (Baattrup-Pedersen et al, 2003; Daniel et al, 2005; Hilton et al, 2006 and Catford et al, 2011). The importance of these hydrological variables on macrophytes are strong because they are the major forces responsible for structuring macrophyte communities (De Wilde et al, 2016; Riera et al, 2017). Our aim is to delineate the main hydrological determinants of individual macrophytes of Enyong River in Itu and Ibiono Local Government Areas of Akwa Ibom and Cross Rivers States, Nigeria

Objectives

Methods

Results

Conclusion