Guimarais-Bermejo Mayrene O, Merino-Ibarra Martin, Valdespino-Castillo Patricia M, Castillo-Sandoval Fermín S, Ramírez-Zierold Jorge A
Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico.
Unidad Académica de Ecología y Biodiversidad Acuática, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico.
PeerJ. 2018 Jul 17;6:e5205. doi: 10.7717/peerj.5205. eCollection 2018.
Long-term and seasonal changes in production and respiration were surveyed in the Valle de Bravo reservoir, Mexico, in a period during which high water-level fluctuations occurred (2006-2015). We assessed the community metabolism through oxygen dynamics in this monomictic water-body affected by strong diurnal winds. The multiple-year data series allowed relationships with some environmental drivers to be identified, revealing that water level-fluctuations strongly influenced gross primary production and respiratory rates. Production and respiration changed mainly vertically, clearly in relation to light availability. Gross primary production ranged from 0.15 to 1.26 gO m h, respiration rate from -0.13 to -0.83 gO m h and net primary production from -0.36 to 0.66 gO m h within the production layer, which had a mean depth of 5.9 m during the stratification periods and of 6.8 m during the circulations. The greater depth of the mixing layer allowed the consumption of oxygen below the production layer even during the stratifications, when it averaged 10.1 m. Respiration below the production layer ranged from -0.23 to -1.38 gO m h. Vertically integrated metabolic rates (per unit area) showed their greatest variations at the intra-annual scale (stratification-circulation). Gross primary production and Secchi depth decreased as the mean water level decreased between stratification periods. VB is a highly productive ecosystem; its gross primary production averaged 3.60 gC m d during the 10 years sampled, a rate similar to that of hypertrophic systems. About 45% of this production, an annual average net carbon production of 599 g C m year, was exported to the hypolimnion, but on the average 58% of this net production was recycled through respiration below the production layer. Overall, only 19% of the carbon fixed in VB is buried in the sediments. Total ecosystem respiration rates averaged -6.89 gC m d during 2006-2015, doubling the gross production rates. The reservoir as a whole exhibited a net heterotrophic balance continuously during the decade sampled, which means it has likely been a net carbon source, potentially releasing an average of 3.29 gC m d to the atmosphere. These results are in accordance with recent findings that tropical eutrophic aquatic ecosystems can be stronger carbon sources than would be extrapolated from temperate systems, and can help guide future reassessments on the contribution of tropical lakes and reservoirs to carbon cycles at the global scale. Respiration was positively correlated with temperature both for the stratification periods and among the circulations, suggesting that the contribution of C to the atmosphere may increase as the reservoirs and lakes warm up owing to climate change and as their water level is reduced through intensification of their use as water sources.
在墨西哥布拉沃山谷水库水位波动较大的时期（2006 - 2015年），对该水库的生产和呼吸作用的长期及季节性变化进行了调查。我们通过受强烈日风影响的单循环水体中的氧气动态评估了群落代谢。多年的数据序列使我们能够确定与一些环境驱动因素的关系，结果表明水位波动对总初级生产力和呼吸速率有强烈影响。生产和呼吸作用主要在垂直方向上发生变化，这显然与光照可用性有关。在生产层内，总初级生产力范围为0.15至1.26 gO₂ m⁻² h⁻¹，呼吸速率为 -0.13至 -0.83 gO₂ m⁻² h⁻¹，净初级生产力为 -0.36至0.66 gO₂ m⁻² h⁻¹。在分层期，生产层的平均深度为5.9 m，循环期为6.8 m。即使在分层期，混合层较深也使得生产层以下的氧气被消耗，分层期混合层平均深度为10.1 m。生产层以下的呼吸速率范围为 -0.23至 -1.38 gO₂ m⁻² h⁻¹。垂直积分代谢率（单位面积）在年内尺度（分层 - 循环）上变化最大。随着分层期之间平均水位的下降，总初级生产力和透明度深度也随之降低。布拉沃山谷水库是一个生产力很高的生态系统；在采样的10年中，其总初级生产力平均为3.60 gC m⁻² d⁻¹，这一速率与富营养化系统相似。该产量的约45%，即年平均净碳产量为599 g C m⁻² year⁻¹，被输出到温跃层，但平均而言，该净产量的58%通过生产层以下的呼吸作用被再循环。总体而言，布拉沃山谷水库中固定的碳只有19%被埋藏在沉积物中。2006 - 2015年期间，总生态系统呼吸速率平均为 -6.89 gC m⁻² d⁻¹，是总生产力速率的两倍。在采样的十年中，整个水库持续呈现净异养平衡，这意味着它可能一直是一个净碳源，可能平均每天向大气释放3.29 gC m⁻²。这些结果与最近的研究结果一致，即热带富营养化水生生态系统可能比从温带系统推断的更强的碳源，并且可以帮助指导未来对热带湖泊和水库在全球碳循环中贡献的重新评估。无论是在分层期还是在循环期，呼吸作用都与温度呈正相关，这表明由于气候变化，随着水库和湖泊变暖以及由于作为水源的使用强度增加导致水位下降，碳向大气的贡献可能会增加。
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