Understanding mangrove regrowth
A problem analysis of the mangrove system of Las Brujas, situated in the Biotopo Monterrico-Hawaii, Guatemala
E.A. van der Weegen (TU Delft - Civil Engineering & Geosciences)
G.I. de Goede (TU Delft - Civil Engineering & Geosciences)
J.J.W. van Heijst (TU Delft - Civil Engineering & Geosciences)
H.E. ten Wolde (TU Delft - Civil Engineering & Geosciences)
R. Bruins (TU Delft - Civil Engineering & Geosciences)
S.A. Taal (TU Delft - Civil Engineering & Geosciences)
A. Blom – Mentor (TU Delft - Civil Engineering & Geosciences)
M. Hrachowitz – Mentor (TU Delft - Civil Engineering & Geosciences)
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Abstract
Situated at the southern coast of Guatemala is the protected nature reserve of Biotopo Monterrico-Hawaii. This biotope contains a mangrove forest consisting of three tree species: the Rhizophora Mangle, Lagunculeria Racemosa and Avicenna Germinans. At the beginning of the 21st century, humaninduced fires destroyed parts of the mangrove forest. After this disturbance, the mangrove forest has shown signs of natural regeneration, although the extent of recovery remains low and spatially restricted. The area of Las Brujas currently shows one of the lowest natural regeneration rates of mangroves within the reserve. This study aimed to identify the main factors limiting mangrove regrowth in Las Brujas.
An extensive literature review was conducted, key stakeholders were interviewed, and field measurements were taken to investigate precipitation data, tidal influence, flow dynamics, ground level, and physical-chemical parameters. Results indicate that visually, the precipitation patterns have been undergoing small changes in the past years. These changes elongate the time during which young mangrove saplings are submerged by water, increasing their risk of drowning. Tidal influence in Las Brujas is minimal. The flow is driven mainly by wind and river discharge. Moreover, flow velocities are low, not exceeding 0.12 m/s, and are stagnated by invasive species. This reduces nutrient, sediment, and propagule transport, and therefore stresses mangrove regrowth. Satellite data reveal no significant changes in ground level, yet sediment flow was observed, indicating that natural heightening of the ground level is possible. A higher ground level could reduce the mortality rate of young saplings by decreasing the risk of drowning. The physical-chemical parameters were within optimal ranges for mangrove growth, suggesting that water quality is not limiting mangrove regeneration during the wet season.
The most critical parameters influencing natural regeneration during the wet season appear to be water depth and flow dynamics. Submergence of saplings for more than 15 days results in high mortality due to oxygen deprivation. In addition, reduced flow conditions limit the dispersal of propagules and restrict nutrient exchange within the water column. To better understand these processes, further hydrological and hydrodynamic investigations during the dry season are recommended.