Mangrove growth in New Zealand estuaries: the role of nutrient enrichment at sites with contrasting rates of sedimentation

Abstract

Mangrove forest coverage is increasing in the estuaries of the North Island of New Zealand, causing changes in estuarine ecosystem structure and function. Sedimentation and associated nutrient enrichment have been proposed to be factors leading to increases in mangrove cover, but the relative importance of each of these factors is unknown. We conducted a fertilization study in estuaries with different sedimentation histories in order to determine the role of nutrient enrichment in stimulating mangrove growth and forest development. We expected that if mangroves were nutrient-limited, nutrient enrichment would lead to increases in mangrove growth and forest structure and that nutrient enrichment of trees in our site with low sedimentation would give rise to trees and sediments that converged in terms of functional characteristics on control sites in our high sedimentation site. The effects of fertilizing with nitrogen (N) varied among sites and across the intertidal zone, with enhancements in growth, photosynthetic carbon gain, N resorption prior to leaf senescence and the leaf area index of canopies being significantly greater at the high sedimentation sites than at the low sedimentation sites, and in landward dwarf trees compared to seaward fringing trees. Sediment respiration (CO 2 efflux) was higher at the high sedimentation site than at the low one sedimentation site, but it was not significantly affected by fertilization, suggesting that the high sedimentation site supported greater bacterial mineralization of sediment carbon. Nutrient enrichment of the coastal zone has a role in facilitating the expansion of mangroves in estuaries of the North Island of New Zealand, but this effect is secondary to that of sedimentation, which increases habitat area and stimulates growth. In estuaries with high sediment loads, enrichment with N will cause greater mangrove growth and further changes in ecosystem function.

Mangrove forests associated with salt flats: a case study from southeast Brazil

“…Despite the importance of salinity control of the mangrove species distribution, we must consider the importance of many other physico-chemical factors (NICKERSON;THIBODEAU, 1985; FELLER et al, 2003;LOVELOCK et al, 2007), which and are also regulated by tidal flooding. The progressive decrease of structural development towards the transition zone between the forest and the salt flat observed in Guaratiba has also been reported previously for other dry or seasonally dry regions (BALL, 1980;SCHAEFFER-NOVELLI et al, 1990;CINTRON-MOLERO, 1993;SANTOS et al, 1997).…”

Mangroves Response to Climate Change: A Review of Recent Findings on Mangrove Extension and Distribution

“…Both periods coincided with periods of sustained El Niño activity, an atmospheric phenomenon highly influenced by global climate change. Another study from Lovelock et al (2007) showed that, in two other estuaries in New Zealand, fertilization and high sedimentation rate, probably induced by stronger El Niño, favored mangrove area increase. Stokes et al (2010) carried out a study in two embayments of Tauranga Harbour in New Zealand and found that spreading mangroves had become a coastal management issue even under a temperate climate environment.…”

Carbon and Nitrogen Stocks and Below-Ground Allometry in Temperate Mangroves

“…The poor relationship between above and below-ground biomass and C stocks in our study may be associated with a shift in biomass partitioning due to environmental conditions (McKee, 1995;Pezeshki et al, 1997;Naidoo, 2009;Alongi, 2011;Castañeda-Moya et al, 2013). For example, factors such as low sedimentation (Lovelock et al, 2007), high salinity (Saintilan, 1997b;Ball, 1998), extreme weather events (Osland et al, 2014), light limitation (McKee, 1995), and increased water depth or flooding (Ye et al, 2003) have been linked to low above-ground biomass in mangrove. Mangroves have also been shown to allocate more biomass below-ground due to nutrient limitation (McKee, 1995;Naidoo, 2009;Alongi, 2011), low soil redox conditions (Pezeshki et al, 1997), high sulfide concentrations, and permanent flooding (Castañeda-Moya et al, 2013).…”