Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 66 Nigerian Journal of Ecology (2016) 15(1):66-81. ©Ecological Society of Nigeria - Jan-June 2016. ISSN: 1116-753X Eutrophication of Dandaru reservoir in Ibadan, Nigeria in relation to land-use and mechanical desilting *Olubode, O.S. and 1 Akpan, P. E. Department of Crop protection and Environmental Biology, University of Ibadan, Ibadan, Oyo State, Nigeria 1 Present Address: Department of Forestry and Environmental Conservation, Ministry of Environment and Natural Resources, Akwa Ibom State, Nigeria *Corresponding Author: bodethanks@yahoo.com (Accepted 5 April 2016) ABSTRACT Eutrophication of water bodies is mainly caused by influx of Nitrogen and phosphorus compounds from land-use. Understanding relationship water reservoirs and farmlands will foster management of ecological resources. This study examined the link between eutrophication and land-use at Dandaru reservoir at Agodi, Ibadan, Oyo State and effect (s) of mechanical clean up on the reservoir. The Vegetation, soil of Lawn (L), bush fallow (BF), vegetable farm (VF) and Agodi Gardens (AG), and water quality of Dandaru reservoir in Ibadan were systematically assessed pre- and post-desilting following standard procedures. Forty 0.25 m 2 quadrats were floristically assessed for Relative importance values (RIV) and Shannon-Weiner index (H`). Three randomly extracted bulked and sub-sampled top soil of each land-use were analysed physiochemically. The reservoir was sampled for phosphate, Organic carbon (TON), nitrate (TN), dissolved oxygen (DO) and pH in three replicates at entry, mid and exit points of the river. Data were analysed using ANOVA at p=0.05. Means statistical differences followed Fisher’s LSD. Fifty one plant species were enumerated pre-desilting consisting of 15, 22, 29 and 11 species in L, BF, VF and AG respectively; 22 plants were enumerated post-silting consisting 10, 10, 8 and 8 species in L, BF, VF and AG respectively. legumes ranged in RIVs from 4.217- 8.397 in BF and VF. Pre-desilting, VF had highest H` (3.334), while AG had lowest (1.988). Post-desilting, Lawn had highest H` (1.956) while VF had lowest (1.679). P, TOC, TN and pH were significantly different in all land-uses with TN (0.81±0.02g/kg) and TOC (7.83±0.05g/kg) in BF. Phosphorus (0.31±0.03g/kg) was high at AG pre-desilting. Post-desilting, TN (32.90±3.37g/kg) and TOC (2.24±0.04g/kg) were significantly high in lawn. Pre-silting, pH and DO were significantly different at all points, lowest at midpoint (6.73±0.04mg/l and 7.89±0.30mg/l respectively); post-silting, pH (7.87±0.00) and DO (9.54±0.0Img/l) increased at midpoint.The legumes in agricultural lands most likely contributed to eutrophication of Dandaru reservoir. However, desilting offered temporary restoration. Cessation of agricultural activities around Dandaru reservoir with its periodic assessment will prevent eutrophication. Keywords: Eutrophication, Dandaru reservoir, desilting, mechanical clean up, agricultural land-use UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 67 INTRODUCTION Land-use is the arrangement, activities and inputs undertaken by people in a certain land cover type to produce, change or maintains it (FAO, 1999). It varies in types and includes activities on the farmland, vegetation types, urbanization type and drainage. Land-use and land management practices have a major impact on natural resources including water, soil, nutrients, plants and animals. Aquatic ecosystems interact with land-use types that surround them, depending on nature and scope of activities (Vitonset, 1997). According to Litke (1999), the impacts of excessive fertilizer use, untreated waste water, effluents and detergents significantly increase nutrient load in lakes and these accelerates eutrophication beyond natural levels bringing about deleterious changes to the natural ecosystem. Eutrophication, defined by OSPAR (2003), as the enrichment of water by nutrients causing an accelerated growth of algae and aquatic plants, produces an undesirable disturbance to the balance of organisms present in the water and the quality of the water. Excessive nutrient loading of aquatic bodies is a most challenging emerging environmental problem in the world (UNEP, 2003, 2009). Agricultural activities involving use of cover crops, especially, nitrogen fixing legumes cause eutrophication in nearby ecosystems (Galloway et al., 1995). Other ecological consequences of eutrophication are presence of excessive planktonic algae and water weeds (macrophytes), low concentration of dissolved oxygen, blockage of sunlight penetration which affects the submerged plants, low water transparency (high turbidity), harmful odours and disruption of ecosystem functions (Rabalais, 2001). Eutrophication is thus, a prioritized emerging environmental issue (UNEP, 2009) resulting from increasing global nitrogen overload of ecosystem from unregulated urban agriculture and human activities, especially in developing nations. Research information on land-use can be used to develop solutions for natural resource management such as management of salinity, siltation and water quality of water bodies used for urban development and other utilitarian purposes. For instance, augmented nutrient inputs to inland waters may result from modifications of land-use of watersheds such as controlled deforestation, agricultural practices, industrial development and urbanization when all variables and their dynamics are known. In the case of eutrophication, when the real cause is identified, various methods of mitigation are proposed (UNEP, 2003), like dredging of accumulated sediments, reduction of erosion into the water body, use of mulch to reduce rainfall eroding the soil surface, stoppage of the use of fertilizers on farms located near the reservoir, banning washing and bathing and/ or agricultural watershed management practices to reduce nutrient. Dandaru reservoir is surrounded by four main land-use types - an extensive open lawn, bush fallow, vegetable farm and Agodi Gardens whose river course empties into the reservoir. The flow of materials into the reservoir from the above sources has become a serious threat to the organisms present in the water body, and its ecosystem services such that the Federal Government included it in desilting projects of Ogun- Oshun River Basin Development Authority. Therefore, studies on the real cause(s) and effects of the eutrophication are needed to prevent re-eutrophication following the planned desilting, of the reservoir and to explore impact and possible sustainability of the co-existence of the agricultural and other land-use types bordering the reservoir. This study was thus carried out to determine the floristic composition and diversity of the various land-use types, identify the floral UNIV ERSIT Y O F IB ADAN L IB RARY http://en.wikipedia.org/wiki/Land_management http://en.wikipedia.org/wiki/Natural_resources http://en.wikipedia.org/wiki/Natural_resources http://en.wikipedia.org/wiki/Water http://en.wikipedia.org/wiki/Soil http://en.wikipedia.org/wiki/Nutrient http://en.wikipedia.org/wiki/Plant http://en.wikipedia.org/wiki/Animal Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 68 species with potential contribution to eutrophication on the reservoir and determine the level of eutrophication of Dandaru reservoir at different points before and after mechanical remediation. MATERIALS AND METHODS Study Area Dandaru reservoir adjoins Agodi Gardens (a public recreation Park) and Oyo State Fisheries Department in Ibadan, Oyo State (Figure 1) on geo-coordinates: N 07 0 24`; E 003 0 53`, and geographical elevation of 211 m above sea level. It is 0.18 km 2 (17.04 ha) in size (Google Earth, 2013). The reservoir is an artificial lake created in the 1960s out of a river basin along Dandaru River opposite Oyo State secretariat complex. In terms of drainage, the river drains water from Bashorun and Agodi areas through the Agodi Gardens down to the lake where it stabilizes before being let into Mokola area of Ibadan city. The Reservoir is surrounded by wetland vegetation and other land-use types - the Agodi Gardens, farm lands (bush fallow and vegetable farms), open lawns and two major roads. The climatic condition of the area in terms of rainfall is a humid tropical area with two peaks of rain in June and September. Figure 1: Locations of land-use types around Dandaru reservoir, Agodi, Ibadan in 2012-2013 (©Google Earth, 2013) Sampling Techniques Floristic assessment was carried out in November, 2012 (before mechanical desilting) and February, 2013 (after mechanical desilting). The herbaceous flora of the four identified land-use types were systematically assessed by laying (0.5 x 0.5 ) m 2 quadrat at 5m intervals along a 50 m UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 69 long transect in each land use. Enumeration and identification of floral species followed Akobundu and Agyakwa (1998) and Johnson, (1997). Data collected were subjected to density and frequency analyses of Kent and Coker (1992) for calculation of Relative Importance values as used by Olubode et al. (2009) where: Relative Important Value (RIV) = RF + RD 2 Where: Density (D) = Abundance of species Number of quadrats laid Frequency (F)= No. of occurrence of species Number of quadrats Relative frequency (RF) = frequency of each species/ total frequency of all species x100 Relative density (RD) = number of individual of species/ total density of all species x100. Species diversity indices were computed for species richness, equitability, and evenness following Hammer and Harper (2012) using the statistical software PAST © 2012, Version 2.02. Muiltivariate ordination and classification were employed for summarization of information contents of the floristic data and phytosociology using Detrended Correspondence analysis (DCA) of Hills (2012) for stand ordination with the DECORANA software; and while Two- Way Indicator Species Analyses for classification with TWINSPAN software. Soil samples were randomly collected at each land-use type from the top (0-15 cm of soil surface) using a soil auger. Soil of each land-use was bulked, separated into three replicates, air-dried, and analysed for physiochemical parameters such as TN, TOC P, K, Ca, Na, pH and soil texture following the standard procedures of A.O.A.C (1984). Assessment of nutrient composition of Dandaru reservoir Water samples (1000 ml) were collected from Dandaru reservoir at three different points (entry, midpoint and exit point) in three replicates using specimen bottles for the determination of the biochemical parameters such as Nitrates, Nitrite, phosphate, dissolved oxygen, pH and turbidity using APHA (1995) procedures. Soil nutrients were assessed by sampling three locations in each land-use type in replicates of three and later bulked before sub-sampling for routing laboratory analyses for physicochemical properties of the soils. The procedure followed the methods of A.O.A.C. (2003). Data Analyses All data sets from soil and water samples were analysed using statistical procedures for completely randomized design for analysis of variance (ANOVA). Where significant, Fischer’s least significance difference was used to separate means at p= 0.05 level of significance. RESULTS Before the mechanical desilting, floristic survey indicated 51 herbaceous plant species in 22 families in the four land-types (Tables 1-4). Fifteen (15) plants with high RIV were documented in the Open lawn (Table 1), with Syndrella nodiflora having the highest RIV (16.087) while Alternanthera sessilis, Centrosenma pubescens, Solenostemon monostachyus and Acalypha ciliata had the lowest RIV (1.375). Leguminous species enumerated at the open lawn were Desmodium scorpirus (3.385) and Centrosenma pubescens (1.375). Twenty two (22) plants were documented in the Bush fallow. The highest RIV was recorded in Oldenladia corymbosa (13.839) while Zea mays, Waltheria indica, Phyllanthus amarus, Laportea aestuans, Solenostemon monostachyus, Setaria UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 70 longiseta and Commelina erecta had the lowest RIV (1.449). Leguminous plants such as Centrosenma pubescens, Schrankia leptocarpa, Calopogonium mucunoides and Desmodium scorpirus were found with moderately high RIV ranging from 4.217 to 8.433 (Table 2). Twenty nine (29) plants species were enumerated in the Vegetable farm with the highest RIV recorded in Syndrella nodiflora (14.071) while lowest was found in Commelina erecta and Spigelia anthelmia (0.997). Leguminous plants such as Desmodium scorpirus, Centrosenma pubescens and Schrankia leptocarpa had moderately high RIV, ranging from 3.7 to 8.397 (Table 3). Agodi Garden had 11 plants, with the highest RIV of 27.887 in Syndrella nodiflora while the lowest RIV was recorded in Musa sapientum, Aspilia africana, Vossia cuspidata and Bambusa bvulgaris (Table 4). The only legume plant found in Agodi Garden with RIV (5.769) was Schrankia leptocarpa. Vegetable farm had the highest species diversity (H’) (3.334) while the lowest species diversity value (1.988) was recorded in Agodi Garden. Similar trends were observed in Equitability index. Agodi Garden however had the highest dominance (0.179) while the lowest dominance (0.054) was recorded in Vegetable farm (Table 5). The inverse was recorded in Evenness indices for Agodi garden (0.664) and vegetable garden (0.623). Table 1: Relative importance values of herbaceous plants occurring in an open lawn around Dandaru reservoir in November, 2012. S \N Names of Species Family RIV 1 Syndrella nodiflora Gaertn Asteraceae 16.087 2 Peperomia pellucida (L.) H.B. & K. Piperaceae 14.713 3 Panicum maximum Jacq. Poaceae 13.968 4 Mitracarpus villosus (Sw.) DC. Rubiaceae 12.599 5 Setaria babata (Lam.) Kunth Commelinaceae 11.219 6 Commelina erecta L. Commelinaceae 6.878 7 Ageratum conyzoides Linn. Asteraceae 5.922 8 Cyathula prostrata (L.) Blume Amaranthaceae 4.972 9 Desmodium scorpirus (Sw.) Desv. Fabaceae 3.385 10 Talinum fruticosum (L.) Juss. Portulacaceae 3.173 11 Laportea aestuans (Linn.) Chew Urticaceae 1.587 12 Alternanthera sessilis (L.) DC. Amaranthaceae 1.375 13 Centrosenma pubescens Benth Fabaceae 1.375 14 Solenostemon monostachyus (P. Beauv.) Brig. Lamiaceae 1.375 15 Acalpha ciliata Forsk. Euphorbiaceae 1.375 UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 71 Table 2: Relative importance values of herbaceous plants occurring in a bush fallow around Dandaru reservoir in November, 2012 S/N Names of species Family RIV 1 Oldenlandia corymbosa Linn. Rubiaceae 13.839 2 Panicum maximum Jacq. Poaceae 12.508 3 Mitracarpus villosus (Sw.) DC. Rubiaceae 8.433 4 Centrosenma pubescens Benth. Fabaceae 8.433 5 Chromolaena odorata (L.) R.M. King & Robinson Asteraceae 6.744 6 Spilanthes filicaulis (Schum. & Thonn.) C.D. Adams Asteraceae 5.481 7 Desmodium scorpiurus (Sw.) Desv. Fabaceae 5.481 8 Ageratum conyzoides Linn. Asteraceae 5.231 9 Schrankia leptocarpa DC Fabaceae 5.008 10 Calopogonum mucunoides Desv. Fabaceae 4.217 11 Mariscus alternifolius Desv. Commelinaceae 4.217 12 Tithonia diversifolia (Hemsl.) A. Gray Asteraceae 3.541 13 Talinum fruticosum (L.) Juss. Portulacaceae 2.528 14 Cissus quadrangularis L. Vitaceae 2.528 15 Zea mays L. Poaceae 1.449 16 Waltheria indica Linn. Sterculiaceae 1.449 17 Phyllanthus amarus Schum. & Thonn. Euphorbiaceae 1.449 18 Laportea aestuans (Linn.) Chew Urticaceae 1.449 19 Solenostemon monostachyus (P. Beauv.) Brig. Lamiaceae 1.449 20 Peperomia pellucida (L.) H.B. & K. Piperaceae 1.449 21 Setaria longiseta P. Beauv. Poaceae 1.449 22 Commelina erecta L. Commelinaceae 1.449 UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 72 Table 3: Relative importance values of herbaceous plants occurring in a Vegetable farm around Dandaru reservoir in November, 2012. S/N Names of species Family RIV 1 Syndrella nodiflora Gaertn Asteraceae 14.071 2 Mitracarpus villosus(Sw.) DC. Rubiaceae 11.234 3 Ageratum conyzoides Linn. Asteraceae 9.365 4 Centrosema pubescens Benth. Fabaceae 8.397 5 Desmodium scorpiurus (Sw.) Desv. Fabaceae 5.674 6 Ipomoea eriocarpa R. Br. Convolvulaceae 5.674 7 Panicum repens Linn. Poaceae 5.674 8 Oldenlandia corymbosa Linn. Rubiaceae 5.583 9 Peperomia pellucida (L.) H.B. & K. Piperaceae 5.583 10 Brachiaria deflexa (Shumach.) Robyns Poaceae 4.613 11 Pentodon pentandrus (Schum. & Thonn.) Vatke Rubiaceae 4.409 12 Telfaria occidentalis Hook. F. Cucurbitaceae 4.165 13 Schrankia leptocarpa D.C. Fabaceae 3.700 14 Tridax procumbens Linn. Asteraceae 3.479 15 Brillantasia lamium (Nees) Benth. Bentham G. Acanthaceae 3.346 16 Ipomoea involucrata P. Beauv. Convolvulaceae 3.168 17 Sida acuta Burm F. Malvaceae 3.168 18 Kylinga erecta Schumach. Cyperaceae 2.881 19 Stachytarpheta cayennensis (L.C. Rich) Schau. Verbenaceae 2.881 20 Mariscus alternifolus Desv. Cyperaceae 2.526 21 Aspilia africana (Pers.) C.D. Adams Asteraceae 2.349 22 Kylinga bulbosa Beauv. Cyperaceae 2.349 23 Euphorbia heterophylla Linn. Euphorbiaceae 2.349 24 Spermacoce octodon (Herper) Lebrun & Stork Rubiaceae 2.172 25 Cyathula prostrata Blume Amaranthaceae 2.172 26 Mariscus longibracteatus Cherm. Cyperaceae 1.706 27 Asystasia gangetica (Linn.) T. Anders Acanthaceae 1.352 28 Commelina erecta L. Commelinaceae 0.997 29 Spigelia anthelmia Linn. Loganiaceae 0.997 Table 4: Relative importance values of herbaceous plants occurring in Agodi garden around Dandaru reservoir in November, 2012. S\N Names of species Family RIV 1 Syndrella nodiflora Gaertn Asteraceae 27.885 2 Paspalum scrobiculatum L. Poaceae 14.423 3 Pupalia lappacea (L.) Juss. Amaranthaceae 12.5 4 Andropogon tectorum Schum. & Thonn. Poaceae 9.615 5 Ageratum conyzoides Linn. Asteraceae 9.615 6 Schrankia Leptocarpa DC. Fabaceae 5.769 7 Mitracarpus villosus (Sw.) DC Rubiaceae 5.654 8 Musa sapientum L. Musaceae 2.885 9 Aspilia africana (Pers.) C.D. Adams Asteraceae 2.885 10 Vossia cuspidata Griff. Poaceae 2.885 11 Bambusa vulgaris Schrad. Ex J.C. Wend Gramineae 2.885 UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 73 Table 5: Diversity of plant species enumerated on four land-use types around Dandaru reservoir in November, 2012 Land-Use Type Diversity Lawn Bush fallow Veg. Farm Agodi garden Taxa_S 15 22 29 11 Individuals 236 148 365 52 Dominance_D 0.1419 0.09386 0.05378 0.179 Simpson_1-D 0.8581 0.9061 0.9462 0.821 Shannon_H 2.133 2.609 3.334 1.988 Evenness_e^H/S 0.5629 0.6472 0.6232 0.6638 After mechanical desilting, 22 herbaceous plant species were enumerated in 9 families from the four land-use types (Tables 6-9). In the open lawn, 10 plant species were, documented with the highest RIV (39.751) recorded for Tridax procumbens while the lowest value (3.253) was recorded in Stachytarpheta cayennensis, Syndrella nodiflora and Tephrosia pedicellata (Table 6). Legumes enumerated with potential contribution to eutrophication were Centrosenma pubesens (6.448) and Desmodium scorpirus (16.622). In the bush fallow there were 10 species (Table 7). Panicum maximum had the highest RIV (31.373), followed by Centrosema pubesens (26.05). Leguminous plant species enumerated were Desmodium scorpirus, Desmodium tortuosum and Calopogonum mucunoides with RIV (5.322). In the vegetable farm, 8 plants species were enumerated of which Panicum maximum also had the highest RIV of 16.729 (Table 8); while the lowest was recorded in Sida acuta, Panicum repens, Calopogonum mucunoides, Corchorus olitorius and Syndrella nodiflora with RIVs (3.396). Legumes in the ecosystem were Calopogonum mucunoides and Centrosema pubesens having relatively high RIVs of 3.396 and 10.063 respectively (Table 8). Agodi Garden had 8 plant species with high RIVs with the highest value (23.044) recorded in Syndrella nodiflora while the lowest value (5.183) was found in Paspalum scrobiculatum and Cynodon dactylon (Table 9). Only Schrankia leptocarpa was the leguminous plant with high RIV of 18.696. In terms of species diversity (Table 10), Agodi Garden had the highest species richness having 0.8347 while other land-use types were relatively high in species richness with values of 0.832 for open Lawn; bush fallow with 0.7943 and 0.7644 for Vegetable farm. Open lawn had the highest value (1.956) for Shannon-Weiner index; while the lowest was recorded in the vegetable farm (1.679). Before mechanical desilting, there were significant differences in P, TOC, TN and pH values at p< 0.05 level of significance across land-use types (Table 11). However, bush fallow had the highest amount of TOC and TN having (0.81 ± 0.02g/kg) and (7.83 ± 0.05g/kg) respectively. Agodi Garden recorded the highest amount of P having (0.31 ± 0.03g/kg) when compared to other locations. The pH was acidic in all the locations with values ranging from 6.23 - 6.73. Textural class for open lawn, bush fallow and vegetable land were all sandy loamy while Agodi garden had a sandy UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 74 texture. Meanwhile, other parameters (Ca, K and Na) were not significantly different in all land-use types. Table 6: Relative importance values of herbaceous plants occurring in an open lawn around Dandaru reservoir in February, 2013 S/N Names of species Family RIV 1 Tridax procumbens Linn. Asteraceae 39.751 2 Panicum maximum Jacq. Poaceae 23.128 3 Desmodium scorpiurus (Sw.) Desv. Fabaceae 16.622 4 Commelina erecta L. Commelinaceae 7.428 5 Centrosenma pubesens Benth. Fabaceae 6.448 6 Cyathula prostrata Blume Amaranthaceae 4.234 7 Cynodon dactylon (Linn.) Pers. Commelinaceae 3.507 8 Stachytarpheta cayennensis (L.C. Rich) Schau. Verbenaceae 3.253 9 Syndrella nodiflora Gaertn Asteraceae 3.253 10 Tephrosia pedicellata Bak. Fabaceae 3.253 Table 7: Relative importance values of herbaceous plants occurring in a bush fallow around Dandaru reservoir in February, 2013 Table 8: Relative importance value of herbaceous plants occurring in a vegetable farm around Dandaru reservoir in February, 2013 S\N Names of species Family RIV 1 Panicum maximum Jacq. Poaceae 16.729 2 Centrosema pubesens Benth. Fabaceae 10.063 3 Tridax procumbens Linn. Asteraceae 6.729 4 Sida acuta Burm. F. Malvaceae 3.396 5 Panicum repens Linn. Poaceae 3.396 6 Calopogonum mucunoides Desv. Fabaceae 3.396 7 Corchorus olitorius L. Tiliaceae 3.396 8 Syndrella nodiflora Gaertn Asteraceae 3.396 S\N Names of species Family RIV 1 Panicum maximum Jacq. Poaceae 31.373 2 Centrosenma pubesens Benth. Fabaceae 26.05 3 Desmodium scorpiurus (Sw.) Desv. Fabaceae 5.322 4 Corchorus olitorius L. Poaceae 5.322 5 Desmodium tortuosum (Sw.) DC. Fabaceae 5.322 6 Stachytarpheta cayennensis (L.C. Rich) Schau. Verbenaceae 5.322 7 Panicum repens Linn. Poaceae 5.322 8 Phyllanthus amarus Schum. & Thonn. Euphorbiaceae 5.322 9 Tridax procumbens Linn. Asteraceae 5.322 10 Calopogonum mucunoides Desv. Fabaceae 5.322 UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 75 Table 9: Relative importance value of herbaceous plants occurring in Agodi garden in February, 2013 S\N Names of species Family RIV 1 Syndrella nodiflora Gaertn Asteraceae 23.044 2 Schrankia leptocarpa DC. Fabaceae 18.696 3 Aspilia busei O. Goffim. & Muschl. Asteraceae 13.172 4 Andropogon gayanus Kunth Poaceae 13.172 5 Ageratum conyzoides Linn. Asteraceae 8.498 6 Aspilia africana (Pers.) C.D. Adams Asteraceae 5.509 7 Paspalum scrobiculatum L. Poaceae 5.183 8 Cynodon dactylon (Linn.) Pers. Commelinaceae 5.183 Table 10: Diversity of plant species enumerated on four land-use types at Dandaru reservoir in February, 2013 Land-use types Diversity Lawn Bush fallow Veg. Farm Agodi garden Taxa_S 10 10 8 8 Individuals 51 29 15 52 Dominance_D 0.168 0.2057 0.2356 0.1653 Simpson_1-D 0.832 0.7943 0.7644 0.8347 Shannon_H 1.956 1.845 1.679 1.925 Evenness_e^H/S 0.7068 0.6328 0.7659 0.8566 The spatial projections of stand relationships revealed that there was a clear difference between one land-use type and another (Figure 2). Axis 1 accounted for 78.6% of the variability, while axis 2 accounted for 55.7%. However, Agodi Garden exhibited two different floristic structures, one of which was similar to a small portion of vegetable farm. There was an undefined group with likely unstable floral species which could result from the low vegetation cover occasioned by mechanical remediation (Figure 3). The maize fallow in classification groups 1, 18 and 11 were high in occurrence of weedy leguminous plants relative to other plant species. The trend was also observed in vegetation groups 4, 2 and 9 (Figure 4). Significant differences were observed in all nutrient parameters except potassium at p< 0.05 before the clean-up. The concentrations were generally higher in the reservoir the cleanup. The soil nutrient levels in the vegetable farm were high, with phosphorus having (0.35± 3.77g/kg). However, the highest amount of TOC and TN were observed in the open lawn as 32.90 ± 3.37g/kg and 2.24 ± 0.04g/kg respectively. The bush fallow was higher in calcium (0.16 ± 0.56g/kg) and sodium (3.19 ± 0.64g/kg) compared to other land-use types. The pH of the soil was acidic for open lawn, bush fallow and vegetable farm while Agodi Garden was alkaline having the lowest amount of nutrients (Table 12). Biochemical properties of water in Dandaru reservoir before clean-up were not significantly different for phosphate, nitrates, nitrite at p>0.05. The highest amount of nutrients was observed in at the entry point as 0.033 ± 0.02mg/l, 0.76 ± 0.02mg/l and 0.46 ± 0.01mg/l respectively. UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 76 However, in all the locations there were significant differences in the DO and pH. The lowest concentration of DO (7.89 ± 0.30mg/l), was obtained at the midpoint, while the highest concentration of DO was recorded at the entry point (19.29 ± 0.25mg/l) (Table 13). The assessment of the level of transparency (Table 12) showed that the midpoint was lowest (0.06 ± 0.03 m) while the entry point had the highest value (0.20 ± 0.02m) indicating that the water at the entry point was far clearer than in the midpoint. The biochemical analyses of water in Dandaru reservoir after the mechanical clean up indicated significant differences in the concentrations of all the parameters at p<0.05 (Table 14). Phosphate significantly increased in all the locations (entry point, midpoint and exit point) when compared to the previous survey having values of (0.081± 0.03 mg/l, 0.054 ± 0.03 mg/l and 0.021± 0.01 mg/l) respectively. However, nitrate and nitrite concentrations were low with values ranging from 0.06 ± 0.03mg/l – 0.44 ± 0.40 mg/l. The entry point had the lowest amount of DO (3.63 ± 0.02 mg/l) while the highest (9.54 ± 0.01mg/l), was recorded in the midpoint. There was no significant difference in pH as all the land use sites were alkaline in all locations. The turbidity (transparency) level of the reservoir was significantly different in all the locations. The entry point had the highest value (0.80 ± 0.37 m). There was an increased turbidity at the midpoint level with value of (0.14 ± 0.15m) compared to the previous value. Figure 2: Relationship between the land use types at Dandaru reservoir in Ibadan based on stand ordination in November, 2012 UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 77 Maize+ fallow legumes Vegetable+ legumes Figure 3: Relationship between land-use types at Dandaru reservoir in Ibadan based on stand ordination in February, 2013 Figure 4: Dendrogram of phytosociology of flora and indicator species of four land-use types in the catchment of Dandaru reservoir, Ibadan in November, 2012 UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 78 Table 11: Nutrient status of soils of four land-use types around the Dandaru reservoir in November, 2012 Locations P (g/kg) TOC (g/kg) TN (g/kg) Ca (g/kg) K (g/kg) Na (g/kg) pH Textural Class Lawn 0.13 ± 0.03 5.70 ± 0.05 0.60 ± 0.03 0.39 ± 0.003 0.08 ± 0.003 0.05 ± 0.004 6.23 ± 0.04 Sandy Loam Bush fallow 0.09 ± 0.02 7.83 ± 0.05 0.81 ± 0.02 0.09 ± 0.001 0.10 ± 0.002 0.05 ± 0.002 6.53 ± 0.11 Sandy Loam Veg. Farm 0.19 ± 0.02 1.07 ± 0.03 0.11 ± 0.02 0.23 ± 0.002 0.07 ± 0.003 0.07 ± 0.002 6.73 ± 0.15 Sandy Loam Agodi garden 0.31 ± 0.03 3.06 ± 0.02 0.32 ± 0.03 0.19 ± 0.002 0.05 ± 0.002 0.06 ± 0.003 6.70 ± 0.07 Sand LSD value 0.08 0.004 0.01 ns ns Ns 0.08 ns= not significant (p> 0.05) Table 12: Nutrient status of soils of four land-use types around the Dandaru reservoir in February, 2013 Table 13: Biochemical properties of water in Dandaru reservoir, Agodi at different locations in November, 2012 Locations Phosphate (Mg/L) Nitrate (Mg/L) Nitrite (Mg/L) (DO) (Mg/L) pH Turbidity (m) Entry point 0.033 ± 0.02 0.76 ± 0.02 0.46 ± 0.01 19.29 ± 0.25 7.31 ± 0.04 0.20 ± 0.02 Mid point 0.013 ± 0.003 0.74 ± 0.003 0.45 ± 0.004 7.89 ± 0.30 6.73 ± 0.04 0.06 ± 0.03 Exit point 0.012 ± 0.004 0.75 ± 0.04 0.45 ± 0.03 14.01 ± 008 7.21 ± 0.13 0.11 ± 0.05 LSD Value ns Ns ns 0.271 0.093 0.01 ns= not significant(p> 0.05) Locations P (g/kg) TOC (g/kg) TN (g/kg) Ca (g/kg) K (g/kg) Na (g/kg) pH Textural class Lawn 0.29 ± 2.06 32.90 ± 3.37 2.24 ± 0.04 0.11 ± 1.12 0.30 ± 0.04 2.50 ± 0.01 6.23 ± 0.36 Sandy loam Bush fallow 0.34 ± 1.07 21.73 ± 0.64 1.92 ± 0.09 0.16 ± 0.56 0.96 ± 0.24 3.19 ± 0.64 6.23 ± 0.27 Sandy loam Veg. Farm 0.35 ± 3.77 21.83 ± 0.59 1.95 ± 0.08 0.12 ± 2.86 0.46 ± 0.28 2.92 ± 0.55 6.63 ± 0.04 Sandy loam Agodi garden 0.26 ± 1.07 6.96 ± 2.42 0.72 ± 0.25 0.07 ± 1.11 0.18 ± 0.01 1.01 ± 0.18 7.29 ± 0.14 Sandy LSD value 1.65 1.29 0.09 1.05 ns 0.32 0.16 ns= not significant (p>0.05) UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 79 Table 14: Biochemical Properties of water in Dandaru reservoir, Agodi at different locations in February, 2013 DISCUSSION AND CONCLUSION The need to produce goods and services and to dispose off the by-products of these activities is an important challenge facing conservation of land resources. The use to which land is usually put sometimes contribute to impoundments, and loss of functions of wetlands and reservoirs located in cities with high concentrations of humans. Of the four land-use types identified in the vicinity of Dandaru reservoir, two which are of core agricultural relevance were found to impact on the water quality of the reservoir based on their floristic composition. The highest species diversity and richness obtained in the vegetable farm during the pre-mechanical remediation was indicative of human interference, especially noting that the farm was yet to be weeded at the time. The results support the studies of Galloway et al., (1995) and Vitousek (1997) which implicated nodulating leguminous plants as contributory factors to eutrophication in lands adjoining water bodies. Eutrophication might have been further caused by fertilizer run-off; erosion of soil particles and other organic matter as reported by Smith et al., (1999). The nutrient status of the soil before the remediation process which showed a high level of TOC and TN in the bush fallow could be due to the intensive cultivation of the land. This agrees with the work of Smith and Schindler (2009) who reported that the amount of nutrients input depend on the types and amount of human activity occurring in the ecosystem. Increased amount of soil nutrients observed in the second phase of the survey could be due to mechanical disturbance occasioned by the mechanical agitation of the water and sediment by the movement of the bull dozer used causing increased mixing of erstwhile settled elements. The high amount of TOC and TN observed in the open lawn during the post-mechanical remediation could be due to organic waste removed from the reservoir which was dumped in close proximity to the lawn. Pre-silting, the pH of the water in the reservoir was acidic in line with descriptions of impacts of eutrophication on pH in which the water becomes acidic as a result of increased activities of micro flora; whereas the reduced amount of nutrients and alkalinic pH post-silting is expected since the metabolic activities of microflora were excluded with their mechanical removal. The results of dissolved oxygen and turbidity follow similar trends. Murphy Locations Phosphate (Mg/L) Nitrate (Mg/L) Nitrite (Mg/L) Dissolved Oxygen (Mg/L) pH Turbidity (m) Entry point 0.081 ± 0.04 0.11 ± 0.06 0.07 ± 0.04 3.63 ± 0.02 7.84 ± 0.10 0.80 ± 0.37 Mid point 0.054 ± 0.04 0.44 ± 0.57 0.27 ± 0.34 9.54 ± 0.01 7.87 ± 0.00 0.14 ± 0.15 Exit point 0.021 ± 0.01 0.12 ± 0.05 0.07 ± 0.03 8.86 ± 0.01 7.78 ± 0.06 0.12 ± 0.22 LSD Value 0.031 0.28 0.16 0.02 Ns 0.01 ns= not significant (p> 0.05) UNIV ERSIT Y O F IB ADAN L IB RARY Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 80 (2002) reported that low concentration of dissolved oxygen was indicative of the decomposition of organic matter by micro- organism leading to oxygen depletion and fish mortality. The post-mechanical remediation which resulted in a high concentration of dissolved oxygen, alkaline pH and low nitrates and nitrites especially at the midpoint is a good approach to the restoration of the ecosystem. The implication of various land-use types in the catchment of Dandaru reservoir was that the anthropogenic activities are linked to eutrophication and impairment of fundamental use and ecosystem function of the Dandaru reservoir in Agodi, Ibadan. Therefore, this study suggests that all forms of agricultural activities around the Dandaru reservoir should be stopped, and future anthropogenic encroachments should be prevented. Also, periodic assessment of the Dandaru reservoir should be carried out to monitor eutrophication status of the reservoir, and to ensure adequate health of the ecosystem. In the future, wastes from the mechanical clean up of reservoirs should not be dumped on the bank of the reservoir to prevent re-infestation of weeds and re- occurrence of euthrophication,. The debris may be processed offsite into compost for peri-urban agricultural purposes. ACKNOWLEDGEMENTS The Director and management of the Department of Inland Fisheries, Oyo State Ministry of Natural Resources; and the Permanent Secretary, Oyo State Ministry of Information, Culture and Tourism are appreciated for permission to conduct the study in and around the Dandaru reservoir and Agodi Gardens, Ibadan. REFERENCES Akobundu, I. O., and Agyakwa, C. W., (1998). A handbook of West African weeds. I.I.T.A., Ibadan 2 nd ed Ibadan: International Institute of Tropical Agriculture. 521pp. AOAC. (1984). Methods of Analysis, Association of Official Analytical Chemists APHA (American Public Health Association) (1995). Standard methods for the examination of water and waste water. 20 th edition. American Public Health Association Inc., New York. 1193pp. fao (1999). IPCC Special Report on Land Use, Land-Use Change and Forestry, 2.2.1.1 land Use Galloway, J. N., Schlesinger, W. H., Levy, C., Michaels, A., and Schnoor, J. L (1995).Nitrogen fixation: anthropogenic enhancement environmental response. Global Biogeochemical cycles 9: 235-252. Gulati, R. D., and Van Dunk, E., (2002). Lakes in the Netherlands, their origin, eutrophication and restoration: State of the art review. Hydrobiologia 478:73- 106. Hammer, O and Harper, D.A.T (2012). Past: Paleontological Statistics software package for Education and Data Analysis. Paleontologia Electronica 4(1): 9pp. http://paleo-electronica. Org/ 2012/ past/issue 101.htm Hill, M.O. (2012). DECORANA and TWINSPAN, for ordination and classification of multivariate species data: a new edition, together with supporting programs, in FORTRAN 77. Institute of Terrestrial Ecology, Huntingdon, Uk.58pp Johnson, D.E., (1997). Weeds of Rice in West Africa. ADRAO/ WARDA, Cote d’Ivore. 312pp Jorgensen, S. E., (2001).The Impact of Eutrophication on Lakes and Reservoirs. Water Quality 3:15-18. Kent, M. and Coker, P., (1992). Vegetation description and analysis: a practical UNIV ERSIT Y O F IB ADAN L IB RARY http://paleo-electronica/ Nigerian J. Ecology 15(1):66-81 Olubode and Akpan. 81 approach. John Wiley and Sons, Chichester.363pp Litke, D.W., (1999). Review of phosphorus control measures in the US and their effects on water quality. National Water Quality Assessment Program: Water-Resources Investigations Report. Report nr 99-4007. Murphy, S. (2002). General information on phosphorus. City of Boulder / USGS Water Quality Monitoring.. Olubode, O.S., Awodoyin, R.O., and Ogunyemi, S. (2011). Floral diversity in the wetlands of Apete river, Eleyele lake and Oba dam in Ibadan, Nigeria: Its implication for biodiversity erosion. West African Journal of Applied Ecology 18: 109-119.. OSPAR, (2003). Strategies of the OSPAR Commission for the protection of the Marine Environment of the North – East Atlantic (Reference number 2003-21) In: OSPAR Convention for the protection of the marine environment of the North East Atlantic: Ministerial Meeting of the OSPAR Commission Bremen: 25 June 2003 Vol. Annex 31 (Ref. B-4.2). Rabalais N. N, (2001), Responses of nekton and demersal and benthic fauna to decreasing oxygen concentrations. In: (eds) Coastal Hypoxia Consequences for Living Resources and Ecosystems. American Geophysical Union, Washington, D.C., pp 115-128. Smith, V. H., Tilman, G.D., and Nekola, J.C., (1999). "Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems". Environmental Pollution 100:179–196. Smith, V. H., and Schindler, D. W., (2009). Eutrophication science: Trends in Ecology and Evolution 24:201-207. UNEP (United Nations Environment Programme) (2003). Planning and Management of Lakes and Reservoirs: An integrated approach to eutrophication., Division of Technology, Industry and Economics UNEP (United Nations Environmental Program) (2009). Towards sustainable production and use of resources: assessing biofuels. ISBN: 978-92-807- 3052-4, Paris, France, 120 p Vitousek, P. M., Aber, J., Howarth, R. W., Likens, G. E., Matson, P. A., and Tilman G. D., (1997). "Human alteration of the global nitrogen cycle: Sources and consequences". Issues in Ecology 1: 1–17. Vitonset, D.M. (1997). Human Domination of Health’s Ecosystems. Science 27: 494-499 Wang, Z.F., Zhang, Q., Lu, Y., and Lv, H.Y., (1996). The effects of nutrients and trace metals on the growth of the red tide organism Prorocentrum micans. Donghai Marine Sciences. 14(3):33–38. UNIV ERSIT Y O F IB ADAN L IB RARY