SPATIO-TEMPORAL CHANGES IN PHYTOPLANKTON SPECIES DIVERSITY, DISTRIBUTION AND ABUNDANCE IN WATER PANS IN SOCIO-ECOLOGICAL LANDSCAPES OF NAROK COUNTY, KENYA

Abstract

Phytoplankton are aquatic primary producers, and thus, the principal drivers of aquatic food webs that support global fisheries. They are responsible for up to 50% of the global primary production. Phytoplankton growth is influenced by a number of allogenic and autogenic factors, such as temperature, light and nutrients, competition, and predation. This study was conducted between January and July of 2023 to provide a clear representation of the dry and wet seasons, phytoplankton and water quality parameters in waterpans in Narok. Waterpans represent a major source of water that provide ecosystem services supporting livelihoods such as water for domestic use, agriculture, livestock as well as supporting wildlife in this water stressed socio-ecological system. Increased anthropogenic activities are likely to impact on these water bodies. The objectives of the study were: to determine the spatial and temporal variation of physico-chemical parameters of water in waterpans in Narok, to estimate the spatial and temporal variation of phytoplankton species distribution and diversity in waterpans in Narok, to determine the spatial and temporal variation of phytoplankton abundance in waterpans in Narok, to determine the relationship between physico-chemical parameters and phytoplankton abundance in waterpans in Narok and lastly, to assess the influence of land use activities on phytoplankton species diversity and abundance in waterpans in Narok. A total 20 waterpans were identified from Google Earth using GIS techniques. 11 waterpans were sampled purposively from areas where agriculture is mostly practiced, and 9 waterpans were located in areas mostly dominated by pastoralism and wildlife. Temperature, conductivity, pH, and dissolved oxygen (DO), were measured in-situ. Samples for phytoplankton and nutrients (total nitrogen (TN), total phosphorus (TP), alkalinity, hardness, ammonium, nitrate, nitrite, soluble reactive phosphorus (SRP), and silicate and for chlorophyll-a) were taken from two points within each waterpan using a calibrated 20litres water bucket. The chemical parameters were analyzed in the laboratory following APHA standard operating procedures and method of Huber-Pestalozzi as well as publications on East African lakes for identification of phytoplankton. The objectives were analyzed separately where, the variation of physico-chemical parameters was determined by Two-Way MANOVA, phytoplankton species diversity index was generated by PAST software their variation was determined by Two-Way Anova, the variation in phytoplankton abundance was also determined by Two-Way Anova. The relationship between physico-chemical parameters and phytoplankton abundance was determined by Canonical Correspondence Analysis (CCA). The influence of land use activities on phytoplankton species diversity and abundance was determined by One-Way MANOVA. The highest physico-chemical parameters recorded as: temperature 26.20°C, conductivity 761.85uS/cm, dissolved oxygen 9.08mg/L, pH 9.21, total nitrogen 2609.43µgL¯¹, total phosphorus 1331.14µgL¯¹, alkalinity 191.00mgL̄¹, hardness 136.00mgL̄¹, ammonia 516.43µgL¯¹, ammonium 140.82µgL¯, nitrate 93.70µgL¯¹, nitrite 32.94µgL¯¹, soluble reactive phosphorus 183.67µgL¯¹, silicate 41.57mgL¯¹ and chlorophyll-a 176.61µgL¯¹. There was significant spatio-temporal variation in DO(P=0.048), Nitrite(p=0.002), SRP(p=0.003) and Chl-A (p=0.033). The waterpans located in areas mostly influenced by pastoralism recorded the highest phytoplankton taxa of 107 during the wet season as compared to the dry which had the lowest composition in area influenced by pastoralism 90 species. The identified taxa were as follows by species composition: Chlorophytes 35.51% by species, diatoms 27.10%, cyanophytes 14.02%, Zygnematophytes 13.08%, Euglenophytes 8.15% and dinoflagellates 1.87%. Phytoplankton species diversity was higher in area where pastoralism is dominant. The mean index ranged between H=1.6782 (wet) to 1.8531 (dry) and H=1.7562 to 1.7772 between agriculture and pastoralism respectively. Species of Anabaena, Scenedesmus, Nitzschia, Cosmarium, Microcystis, Aphanocapsa and Kirchneriella sp. dominated waterpans during the dry season. During the wet season, species of Chroococcus, Aphanocapsa, Anabaena, Microcystis, Oocystis, Scenedesmus, Tetrahedron, Coelomorn, Nitzchia, Surillella, Diatoma, Cosmarium, Phacus, Coelastrum, Kirchineriella, Aulacoseira and Euglena sp. dominated waterpans. The abundance of phytoplankton in waterpans was highest during the dry season in waterpans located in area influenced by agriculture. During the dry season, phytoplankton abundance ranged from 183×10^5 to 5469×10^5 individuals/L while in the wet season abundance ranged between 213×10^5 to 1833×10^5 individuals/L. Two-Way Anova indicated no significant spatio-temporal variation in phytoplankton abundance. One-Way MANOVA indicated that there was a significant influence of land use activities on phytoplankton abundance (p=0.02) but species diversity was not significant (p=0.788). Canonical Correspondence Analysis (CCA) accounted for 53.33% based on axis 1 and 25.38% on axis 2. There was a relationship between physical-chemical parameters and phytoplankton communities. Land use had a significant influence on phytoplankton abundance but not in diversity. Presence of dinoflagellates Glenodinium pernardii and Glenordinium pulvasistoz may indicate eutrophication of some of the water bodies. Species of Anabaena, Microcystis and Planktolyngbya were present in the waterpans hence should be further investigated for Harmful Agal Blooms (HABs) ) which may lead to production of cyanobacterial toxins hence compromising the quality of the water and posing public health concerns. In general, the waterpans are important reservoirs of aquatic phytoplankton biodiversity. Nature based solutions such as protection of pan embankment by planting grasses and other aquatic vegetation should be undertaken to protect the pans from eutrophication and sediment loading.

Keys Words: Narok, Arid and semi-arid, waterpans, ecosystem services, land use changes, climate variability, phytoplankton, abundance, composition, diversity, water quality,