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Controls on primary production in Lake Naivasha, a shallow tropical freshwater

机译：浅水热带淡水奈瓦沙湖的初级生产控制

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This study uses Lake Naivasha, Kenya as an example of a shallow tropical freshwater lake. In common with many tropical lakes it experiences fluctuating water-levels which influence its area and productivity, and is currently considered moderately eutrophic.;The light regime experienced by phytoplankton in Lake Naivasha dominates other controls as it determines the potential level of primary production. Photoinhibition reduces productivity by 25% at the surface with maximum productivity at a depth of approximately 0.5m. Light attenuation reduces productivity by 50% at 1m depth with zero productivity at 5m depth. Self-shading causes a 17% loss of productivity under conditions of below average productivity, but a 46% loss when productivity is above average. Hydrological factors form a primary control as the mixing regime determines the light regime. Lake Naivasha is generally well mixed, but where temporary stratification occurs there is nutrient resupply due to sediment anoxia. Without mixing, there is a 75% loss of productivity by cell sedimentation. Low sinking rates, tropical conditions and high nutrient availability favour low Surface Area:Volume species such as Aulacoseira which is the dominant genus. Changing conditions such as increased water-column stability could favour cyanobacteria.;Bottom-up controls were the most important in Lake Naivasha, reducing potential productivity by 50%. Nitrogen was found to be more limiting than phosphorus with an algal preference for ammonium over nitrate. Minor nutrients were not limiting. The main source of allochthonous nutrients was from river inflow with underflow and circulations around the lake. Top-down control by grazing imposes a 15% reduction in productivity with zooplankton preferring large 'production' cells over small 'standing-stock' cells.
机译：这项研究以肯尼亚的奈瓦沙湖为例，是一个浅热带淡水湖。与许多热带湖泊一样，它的水位波动会影响其面积和生产力，目前被认为是中度富营养化的；奈瓦夏湖浮游植物所经历的光照状态决定了初级生产的潜在水平，从而主导了其他控制措施。光抑制使表面的生产率降低了25％，最大深度约为0.5m，生产率最高。光衰减在1m深度处将生产率降低50％，而在5m深度处将生产率降低为零。在低于平均生产率的情况下，自遮蔽会导致生产率损失17％，而当生产率高于平均水平时则会造成46％的损失。当混合状态决定光照状态时，水文因素形成主要控制。奈瓦沙湖通常杂乱无章，但在发生临时分层的地方，由于沉积物缺氧，养分会重新供应。如果不混合，细胞沉降会使生产力损失75％。低下沉率，热带条件和高养分利用率有利于降低表面积：优势种如Aulacoseira。变化的条件（例如增加水柱的稳定性）可能有利于蓝细菌。自下而上的控制是奈瓦夏湖最重要的控制，将潜在生产力降低了50％。发现氮比磷更具限制性，藻类比硝酸盐更偏爱铵。微量营养素没有限制。异源养分的主要来源是河水的流入，湖水的下沉和环流。通过放牧进行自上而下的控制会使浮游动物的生产力降低15％，浮游动物更喜欢大型的“生产”细胞而不是小型的“常备”细胞。

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    Hubble, David S.;

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  • 年度 2000
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  • 正文语种 {"code":"en","name":"English","id":9}
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