Abstract:
Littoral zones invasion by macrophytes could facilitate major changes in lake ecosystem especially on the composition of other aquatic assemblages. It has been established that data on environmental interplay influencing macrophytes’ dynamics are needed for effective management of aquatic resources in lakes. However, information on macrophytes composition and other environmental variables required for sustainable management of fish production in Nigeria’s lakes, such as Eleyele Lake (EL), is limited. Therefore, environmental factors, macrophytes diversity and their effects on fish productivity in EL were investigated.
Eleyele Lake was stratified into five zones (mouth Z1, upper Z2, middle Z3, lower Z4 and head Z5) based on the hydrological features. Three sampling points were randomly selected per zone. Water, sediment and macrophyte samples were collected from each sampling points bimonthly covering wet (May-November) and dry (December-April) seasons for 24 months. Fish samples were obtained from fishers’ catches. Water samples were analysed for Temperature (oC), Dissolved Oxygen (DO, mg/L) and Net Primary Productivity (NPP, mgO2/L/day). Organic carbon and silt in sediments were determined following standard methods. Macrophytes and fish samples were counted and identified to species level. Macrophyte species diversity were determined using Simpson’s (1-D) and Shannon-Weiner (H) indexes. Potential Fish Yield (PFY, Kg/ha) was calculated. Environmental Integrity (EI) and Vegetative Quality (VQ) of Macrophytes were evaluated using Aquatic Macrophytes Community Index (AMCI: 7 poorest EI to 70 highest EI) and Floristic Quality Assessment (FQA : 1-19 low VQ, 20-35 high VQ; > 35 natural VQ). Data were analyzed using descriptive statistics, ANOVA and canonical correspondence analysis, at α0.05.
Temperature, DO and NPP ranged from 25.10±1.17 (Z1) to 25.40±1.15 (Z5); 4.25±0.93 (Z2) to 4.65±1.14 (Z5); 0.26±0.13 (Z3) to 0.53±0.21 (Z4), respectively. Temperature was (25.30±1.12, 25.29±1.19) DO (4.07±1.22; 4.51±1.08) and (NPP 0.55±0.31; 0.62±0.03) were for dry and wet seasons, respectively. Organic carbon and silt varied significantly from 4.66±1.61 (Z2) to 5.19±1.37 (Z4) and 18.97±3.92 (Z1) to 21.11±3.59 (Z2), respectively. Organic carbon and silt were 4.96±1.31, 5.02±1.35 and 20.52±4.14, 20.59±3.43 for dry and wet seasons, respectively. Ten families and 14 species of macrophytes were recorded with 7 and 14 species encountered during dry and wet seasons, respectively. Ipomoea aquatica was most dominant (15.4%) while Cyprerus rotundus had the least population (23.3%). A total of 3392 fishes belonging to 7 families and 9 species were recorded. Fish catch recorded in dry season was higher (1830) than wet season (1562). Macrophyte diversity were higher during wet season (1-D=0.90, H=2.4) than dry season (1-D=0.81, H=1.70). Highest and least PFY 536.72 and 367.04 were obtained in dry and wet seasons, respectively. Least AMCI (30) was recorded in Z1 while Z2, Z3 and Z4 had 37, each. Highest and least AMCI were 42 and 33 for dry and wet season, respectively while FQA was 16.05. Macrophyte composition and NPP impacted negatively on PFY with Eigen-value of 98.6%.
Macrophyte composition in Eleyele lake is of low vegetative quality and had resulted in moderately poor environmental integrity. This has negatively impacted the aquatic diversity and fish productivity.
