Colored dissolved organic matter (CDOM) strongly influences light penetration and biogeochemical processes in inland waters. This study investigates the role of optical control exerted by CDOM on phytoplankton primary production in thirteen urban lakes of Yamoussoukro (C？te d’Ivoire), spanning a wide absorption gradient (a355 = 0.01 - 1.90 m？1). A total of 117 water samples were collected during four monthly campaigns (July-October) with 2 to 3 sampling stations per lake according to lake size and anthropogenic influence. In situ bio-optical measurements, dissolved nutrient analyses, and primary production estimates were combined with nonlinear mixed-effects statistical models accounting for the nested data structure (lake × campaign) and controlling for environmental covariates. The results reveal a significant unimodal relationship between CDOM and primary production (marginal R2 = 0.61; p < 0.01), further supported by a generalized additive mixed model (GAMM; conditional R2 = 0.72). Segmented regression identified a critical optical threshold at a355 ≈ 0.42 m？1 (95% bootstrap CI: 0.31 - 0.53), beyond which light attenuation becomes the dominant limiting factor, leading to a significant decline in productivity. Sensitivity analysis on photosynthetic parameters (±20% to 50%) and independent decoupling tests (constant Kd, direct Chl-a correlation) confirmed that this relationship is not an artefact of the modeling framework. These findings demonstrate that CDOM acts as a nonlinear optical regulator structuring the trophic dynamics of tropical urban lakes and provide a mechanistic framework for their ecological monitoring.
References
[1]
Cole, J.J., Prairie, Y.T., Caraco, N.F., McDowell, W.H., Tranvik, L.J., Striegl, R.G., et al. (2007) Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget. Ecosystems, 10, 172-185. https://doi.org/10.1007/s10021-006-9013-8
[2]
Thrane, J., Hessen, D.O. and Andersen, T. (2014) The Absorption of Light in Lakes: Negative Impact of Dissolved Organic Carbon on Primary Productivity. Ecosystems, 17, 1040-1052. https://doi.org/10.1007/s10021-014-9776-2
[3]
Williamson, C.E., Stemberger, R.S., Morris, D.P., Frost, T.M. and Paulsen, S.G. (1996) Ultraviolet Radiation in North American Lakes: Attenuation Estimates from DOC Measurements and Implications for Plankton Communities. Limnology and Oceanography, 41, 1024-1034. https://doi.org/10.4319/lo.1996.41.5.1024
[4]
Vasconcelos, F.R., Diehl, S., Rodríguez, P., Hedstr？m, P., Karlsson, J. and Bystr？m, P. (2016) Asymmetrical Competition between Aquatic Primary Producers in a Warmer and Browner World. Ecology, 97, 2580-2592. https://doi.org/10.1002/ecy.1487
[5]
Zhang, Y., van Dijk, M.A., Liu, M., Zhu, G. and Qin, B. (2009) The Contribution of Phytoplankton Degradation to Chromophoric Dissolved Organic Matter (CDOM) in Eutrophic Shallow Lakes: Field and Experimental Evidence. Water Research, 43, 4685-4697. https://doi.org/10.1016/j.watres.2009.07.024
[6]
Bushaw, K.L., Zepp, R.G., Tarr, M.A., Schulz-Jander, D., Bourbonniere, R.A., Hodson, R.E., et al. (1996) Photochemical Release of Biologically Available Nitrogen from Aquatic Dissolved Organic Matter. Nature, 381, 404-407. https://doi.org/10.1038/381404a0
[7]
Kosten, S., Huszar, V.L.M., Bécares, E., Costa, L.S., van Donk, E., Hansson, L., et al. (2012) Warmer Climates Boost Cyanobacterial Dominance in Shallow Lakes. Global Change Biology, 18, 118-126. https://doi.org/10.1111/j.1365-2486.2011.02488.x
[8]
Tranvik, L.J., Downing, J.A., Cotner, J.B., Loiselle, S.A., Striegl, R.G., Ballatore, T.J., et al. (2009) Lakes and Reservoirs as Regulators of Carbon Cycling and Climate. Limnology and Oceanography, 54, 2298-2314. https://doi.org/10.4319/lo.2009.54.6_part_2.2298
[9]
Sylla, I., Koffi, M., N’dri, K.M., Bony, K.Y., Assemian, N.E., Konan, K.F., et al. (2019) évaluation de la diversité et de la charge parasitaire des lacs de la ville de Yamoussoukro en C？te d’Ivoire. Journal of Applied Biosciences, 134, 13630-13642. https://doi.org/10.4314/jab.v134i1.2
[10]
Peel, M.C., Finlayson, B.L. and McMahon, T.A. (2007) Updated World Map of the K？ppen-Geiger Climate Classification. Hydrology and Earth System Sciences, 11, 1633-1644. https://doi.org/10.5194/hess-11-1633-2007
[11]
Fick, S.E. and Hijmans, R.J. (2017) Worldclim 2: New 1‐Km Spatial Resolution Climate Surfaces for Global Land Areas. International Journal of Climatology, 37, 4302-4315. https://doi.org/10.1002/joc.5086
[12]
Mopper, K. and Kieber, D.J. (2002) Photochemistry and the Cycling of Carbon, Sulfur, Nitrogen and Phosphorus. In: Hansell, D.A. and Carlson, C.A., Eds., Biogeochemistry of Marine Dissolved Organic Matter, Elsevier, 455-507. https://doi.org/10.1016/b978-012323841-2/50011-7
[13]
Cory, R.M., Ward, C.P., Crump, B.C. and Kling, G.W. (2014) Sunlight Controls Water Column Processing of Carbon in Arctic Fresh Waters. Science, 345, 925-928. https://doi.org/10.1126/science.1253119
[14]
Stedmon, C.A. and Markager, S. (2001) The Optics of Chromophoric Dissolved Organic Matter (CDOM) in the Greenland Sea: An Algorithm for Differentiation between Marine and Terrestrially Derived Organic Matter. Limnology and Oceanography, 46, 2087-2093. https://doi.org/10.4319/lo.2001.46.8.2087
[15]
Helms, J.R., Stubbins, A., Ritchie, J.D., Minor, E.C., Kieber, D.J. and Mopper, K. (2008) Absorption Spectral Slopes and Slope Ratios as Indicators of Molecular Weight, Source, and Photobleaching of Chromophoric Dissolved Organic Matter. Limnology and Oceanography, 53, 955-969. https://doi.org/10.4319/lo.2008.53.3.0955
[16]
Lorenzen, C.J. (1967) Determination of Chlorophyll and Pheo-Pigments: Spectrophotometric Equations. Limnology and Oceanography, 12, 343-346. https://doi.org/10.4319/lo.1967.12.2.0343
[17]
Baird, R.B., Eaton, A.D. and Rice, E.W. (Eds.) (2017) Standard Methods for the Examination of Water and Wastewater. 23rd Edition, American Public Health Association, American Water Works Association, Water Environment Federation.
[18]
Jassby, A.D. and Platt, T. (1976) Mathematical Formulation of the Relationship between Photosynthesis and Light for Phytoplankton. Limnology and Oceanography, 21, 540-547. https://doi.org/10.4319/lo.1976.21.4.0540
[19]
Morel, A. (1988) Optical Modeling of the Upper Ocean in Relation to Its Biogenous Matter Content (Case I Waters). Journal of Geophysical Research: Oceans, 93, 10749-10768. https://doi.org/10.1029/jc093ic09p10749
[20]
Kirk, J.T.O. (2011) Light and Photosynthesis in Aquatic Ecosystems. 3rd Edition, Cambridge University Press. https://doi.org/10.1017/cbo9781139168212
[21]
Talling, J.F. (1971) The Underwater Light Climate as a Controlling Factor in the Production Ecology of Freshwater Phytoplankton. Mitteilungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie, 19, 214-243. https://doi.org/10.1080/05384680.1971.11903932
[22]
Lewis, W.M. (1974) Primary Production in the Plankton Community of a Tropical Lake. Ecological Monographs, 44, 377-409. https://doi.org/10.2307/1942447
[23]
Reynolds, C.S. (2006) The Ecology of Phytoplankton. Cambridge University Press. https://doi.org/10.1017/cbo9780511542145
[24]
Platt, T., Gallegos, C.L. and Harrison, W.G. (1980) Photoinhibition of Photosynthesis in Natural Assemblages of Marine Phytoplankton. Journal of Marine Research, 38, 687-701.
[25]
Behrenfeld, M.J. and Falkowski, P.G. (1997) A Consumer’s Guide to Phytoplankton Primary Productivity Models. Limnology and Oceanography, 42, 1479-1491. https://doi.org/10.4319/lo.1997.42.7.1479
[26]
Strickland, J.D.H. and Parsons, T.R. (1972) A Practical Handbook of Seawater Analysis. 2nd Edition, Fisheries Research Board of Canada.
[27]
Nakagawa, S. and Schielzeth, H. (2012) A General and Simple Method for Obtaining R2 from Generalized Linear Mixed‐Effects Models. Methods in Ecology and Evolution, 4, 133-142. https://doi.org/10.1111/j.2041-210x.2012.00261.x
[28]
Wetzel, R.G. (2001) Limnology: Lake and River Ecosystems. 3rd Edition, Academic Press.
[29]
Seekell, D.A., Lapierre, J., Ask, J., Bergstr？m, A., Deininger, A., Rodríguez, P., et al. (2015) The Influence of Dissolved Organic Carbon on Primary Production in Northern Lakes. Limnology and Oceanography, 60, 1276-1285. https://doi.org/10.1002/lno.10096
[30]
van Nes, E.H. and Scheffer, M. (2007) Slow Recovery from Perturbations as a Generic Indicator of a Nearby Catastrophic Shift. The American Naturalist, 169, 738-747. https://doi.org/10.1086/516845
[31]
Scheffer, M. (2009) Critical Transitions in Nature and Society. Princeton University Press.
