Seed dispersal in the Amazonian rivers can be estimated using hydrodynamic models.
Seed dispersal plumes of andiroba (Carapa guianensis), a typical species of the várzea forests, during dispersal experiments in the Maracá River. After the releasing of seeds at previously defined sites, their course was monitored. This process was also modeled and simulated by computer models and the differences between the computer simulated dispersion distances and the distances measured in the river were small (5 – 10%), showing that the computational models may be able to estimate the seed dispersal by rivers.
Seed transport by water (hydrochory) is a key mechanism of long-distance dispersal constrained by the attributes of the seed and hydrodynamics. Through hydrodynamic modeling, the authors estimated the maximum distance reached by seed sof C. guianensis during ebb and flood tides along a 27-km stretch of the Maracá River, a tributary of the Amazon River estuary, which is influenced the seasonal changes in hydrological pulse and tidal cycles.
Location of Maracá River, a tributary of the left bank of the Amazon River, where hydrodynamic measurements and seed dispersal experiments were carried out.
The simulations showed that in a tidal cycle (12 hours), the seeds can be dispersed approximately 9 km away in the rainy season and almost 6 km in the dry season. In addition, seed dispersal may occur upstream or downstream depending on the tidal cycle. Seeds were taken at a longer distance in the ebb tide (downstream) than in the full tide (upstream) during the rainy season, when seeds of C. Guianensis are naturally dispersed. The difference between dispersion distance estimated through modeling and the distance measured in the field was very small (0.4 to 1 km), showing that the models are feasible to estimate seed dispersal.
The simulated seed dispersal plumes in (a) the September 2012 ebb tide simulation, (b) the January 2013 ebb tide simulation, (c) the May 2013 ebb tide simulation and (d) the May 2013 flood tide simulation. The two sites marked “SLS- (Up or Down)” show the two locations from which seeds were launched during the seed dispersal simulations. Black and red colours are used to distinguish the positions of the seeds before and after the switching of the tide.
The seeds of C. guianensis were chosen for the experiment because they have a constant buoyancy and because the species is widely distributed along the várzea forests of the Amazonian estuary. Water flux, channel width, depth and river slope data were used to model seed dispersal in SisBaHia (http: //www.sisbahia.c oppe.ufrj.br/), an open access modelling platform developed by one of the authors (PCC Rosman). The results of the modeling were compared with the data obtained from two experiments carried out in the Maracá River. In the first experiment 500 seeds were released during the ebb tide at a point 12 km from the Maracá mouth with the Amazon River and in the second experiment, 500 seeds were released during the flood tide, 2.3 km from the mouth.
The results were published in the journal Freshwater Biology [1] and are the result of the integration among several researchers (AC Cunha, MC Guedes and HFA Cunha from PPGBio / UNIFAP / EMBRAPA, K. Mustin, a Pos-Doc from EMBRAPA / AP, PC Rosman from COPPE / UFRJ and LSL Sternberg of UM / Miami) and multidisciplinary teams involving different expertises such as civil engineering and chemistry, forest engineering, ecology, environmental engineering, environmental sciences, an undergraduate student (EWG Santos) and a post-graduate student of the PPGBIO (ES Santos). The Project had logistical support of EMBRAPA and technical and financial support of CNPq, FINEP and UNIFAP.
[1] Da Cunha, Alan Cavalcanti; Mustin, Karen; Dos Santos, Eldo Silva; Dos Santos, Éwerton Wânderson Gonçalves; Guedes, Marcelino Carneiro; Cunha, Helenilza Ferreira Albuquerque; Rosman, Paulo Cesar Colonna; Sternberg, Leonel da Silveira Lobo (2017). Hydrodynamics and seed dispersal in the lower Amazon. Freshwater Biology, v. 62, p. 1721-1729, 2017. https://onlinelibrary.wiley.com/doi/abs/10.1111/fwb.12982
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