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

C E Lovelock; I C Feller; J Ellis; A S; N Hancock; P Nichols; B Sorrell 

2007 

 

 

Article in journal 

Mangrove forest coverage is increasing in teh estuaries of the north Island of New Zealand, causing changes in estuarine ecosystem structure adn 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 mangrvoes were nutrient-limited, nutrient enrichment woud lead to increase in mangrove growth and forest structure and that nutrient enrichment of trees in our site with low seimentation 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, wiht enhancements in growth, photosynthetic carbon gain, N resorption prior to leaf senescence and 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 (CO2 efflux) was higher at teh high sedimentation sites than at the low one sedimentation sites, but it was not signficantly affected by fertilization, suggesting tha the high sedimentation sites upported 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 stimualtes growth. In estuaries with high sediment loads, enrichment with N will cause greater mangrove growth and further changes in ecosystem function. 

 

Biogeophysical--Avicenna marina--Leaf area index--nutrient resorption efficiency--photosynthesis--soil respiration--Waikopua--Whagapoua