Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan.
Faculty of Life and Environmental Sciences, University of Yamanashi, 4-3-11 Takeda, Kofu, 400-8511, Japan.
Sci Rep. 2019 Mar 20;9(1):4932. doi: 10.1038/s41598-019-41427-3.
Since temperature is a key factor affecting photosynthetic and respiration rates, the rates of gross primary production (GPP) and ecosystem respiration (ER) are expected to be lower for rivers at higher latitudes, while the net ecosystem production (NEP) rate likely decrease in rivers at lower latitude due to higher sensitivity of ER to temperature compared with GPP. To examine these possibilities, we estimated the ecosystem metabolism of 30 rivers located from 43.03°N to 32.38°N in Japan during summer using a Bayesian model with hourly changes in dissolved oxygen concentrations. In addition, we examined latitudinal trends of GPP, ER and NEP in a global scale by compiling and analyzing river metabolic data estimated in previous studies. Our analysis showed that both GPP and ER tended to increase with latitude, although these rates were positively related to water temperature in Japanese rivers. Global dataset of GPP and ER also showed increasing trend towards higher latitude. In addition, contrary to our initial expectations, NEP decreased with latitude and most rivers were net heterotrophic at both regional (Japanese rivers) and global scales. These results imply that the latitudinal temperature effect on river metabolism is masked by other factors not examined in this study, such as land use in the watershed, which play pivotal roles in explaining the latitudinal variation of river metabolism.
由于温度是影响光合作用和呼吸作用速率的关键因素，因此预计高纬度地区的河流的总初级生产力（GPP）和生态系统呼吸（ER）速率会较低，而由于 ER 对温度的敏感性高于 GPP，低纬度地区的河流的净生态系统生产（NEP）速率可能会下降。为了检验这些可能性，我们使用贝叶斯模型，根据溶解氧浓度的每小时变化，估算了日本 30 条从北纬 43.03°到 32.38°的河流在夏季的生态系统代谢情况。此外，我们通过汇编和分析以前研究中估算的河流代谢数据，在全球范围内检验了 GPP、ER 和 NEP 的纬度趋势。我们的分析表明，GPP 和 ER 都倾向于随纬度增加而增加，尽管这些速率与日本河流的水温呈正相关。全球 GPP 和 ER 数据集也显示出向高纬度增加的趋势。此外，与我们最初的预期相反，NEP 随纬度降低，在区域（日本河流）和全球范围内，大多数河流都是净异养的。这些结果表明，本研究未考察的其他因素（如流域的土地利用）掩盖了温度对河流代谢的纬度效应，这些因素在解释河流代谢的纬度变化方面起着关键作用。
