Seasonal changes in optical properties of two contrasting tropical freshwater systems

Abstract

We investigated how allochthonous and autochthonous sources of dissolved organic matter (DOM) affected the optical conditions and chemical characteristics of two contrasting tropical freshwater systems (Dom Helvécio-DH and Pampulha Reservoir)

acronyms

“…Our study shows that in addition to providing a source of nutrients, allochthonous inputs to tropical lakes may strongly affect the seasonal dynamics of phytoplankton by reducing of photoinhibition through elevated UV absorption. These results corroborates previous studies that where lake ecosystem metabolism are indirectly controlled by terrestrial material during periods of higher rainfall Brandão et al, 2016). Although additions of allochthonous OM and nutrients both contributed to higher DOC concentrations, divergent effects of these additions were evident in the quality of carbon assessed by optical indices (S 250-450 and S R ).…”

“…Our experiment adds knowledge on how input of terrestrial OM and nutrients, related to water column mixing and rains, influence carbon cycling in tropical lakes Brandão et al, 2016). Even small inputs of allochthonous OM can have much larger effects on the spectral characteristics on the lake CDOM, compared to large production of autochthonous OM.…”

“…Recent studies in this region have shown that the marked seasonality in the inputs of allochthonous material (nutrients and organic matter) during periods of rain (thermal stratification period, summer) plays a key role in the pattern observed for the optical characteristics of lakes, for example the transparency to photosynthetically active radiation (PAR) and ultraviolet (UV) (Gagliardi, 2015;Brandão et al, 2016). Contrary to expectations, greater transparency of these lakes is observed during the rainy season, since the allochthonous material remains trapped in the hypolimnium by temperature difference, until the water mixture (dry season, winter) redistributes it throughout the water column (Reynolds, 2009;Brandão et al, 2016). In this context, higher net phytoplankton production rates occur in the mixing periods, with lower solar radiation incidence and lower transparency .…”

Spatial and temporal dynamics of bacterioplankton community composition in a subtropical dammed karst river of southwestern China

“…Interestingly, the community structures of site C in March and September deviate from their corresponding clusters and appear together in the rainy, hot season cluster. This observation is supported by the fact that water discharge of the Honghua dam results in similar bacterioplankton niches and a higher input of allochthonous organic matter during the rainy, hot season, providing nutrients for bacterioplankton (Brandão, Staehr, & Bezerra‐Neto, ). In addition, unweighted UniFrac and Bray–Curtis analyses revealed an enhanced dissimilarity between communities, suggesting that stratification determines the phylogenetic diversity in each community layer, as previously reported by Ávila et al.…”

“…On the basis of the fact that bacterioplankton community members turn over quickly in response to changing environmental conditions and beta diversity is the variation in species composition among sites in a geographic area (Legendre, Borcard, & Peres-Neto, 2005), we used the unweighted UniFrac and Bray-Curtis distances of beta diversity, independent of changes in alpha diversity, to compare the range of bacterioplankton diversity in spatial-temporal variations ( Figure 5). Highly similar communities (three clusters) are observed at the same sampling time, suggesting that a mixed seasonal environment can facilitate bacterial coexistence (Huang, Dong, Jiang, Wang, & Yang, 2016), as confirmed by Appendix rainy, hot season, providing nutrients for bacterioplankton (Brandão, Staehr, & Bezerra-Neto, 2016). In addition, unweighted UniFrac and Bray-Curtis analyses revealed an enhanced dissimilarity between communities, suggesting that stratification determines the phylogenetic diversity in each community layer, as previously reported by Ávila et al (2017) in two tropical shallow lakes in the Brazilian Atlantic Forest.…”