Lyngbya majuscula is a bloom-forming toxic marine cyanobacterium. Most research on L. majuscula growth in Moreton Bay has focussed on water column supplies of iron and phosphorus with little consideration of benthic sources and supply. This study investigates the potential for sandy sediments in a shallow, well mixed subtropical embayment (Deception Bay, Moreton Bay, Australia) to supply iron and phosphorus for L. majuscula growth after significant benthic community change following a major flood event. Measurements of benthic oxygen, iron and nutrient fluxes were obtained by incubating intact sediment cores sampled from Deception Bay. Results suggest that post-flood sediment communities are capable of supplying >1300% of daily L. majuscula Fe requirements and up to 9.2% of daily P demands, suggesting that L. majuscula growth in Deception Bay is likely to be P limited. The benthic release of PO43– and FeII only occurred after water column DO became depleted below 3mgL–1. This study suggests that the benthic release of PO43– and FeII could support the initiation and growth of L. majuscula blooms in Deception Bay.
The Vietnamese Mekong Delta (VMD) comprises extensive river and canal networks, both natural and man‐made, and has a history of extensive land use change and development. The delta's wetlands are under considerable ecological stress because of hydrological changes, agricultural and aquaculture development, urban and industrial pollution, climate change, and upstream water resource development. In this paper, we review the current threats and challenges to the conservation and management of the wetlands in the VMD. We recommend that the current water management practices of the Ramsar‐listed Lang Sen Wetland Reserve are changed so that the natural flood regimes are reinstated and the risks to the community from forest fires are managed. Ongoing investment is needed to support further research, set up long‐term monitoring, and to develop hydrodynamic models for the Lang Sen Wetland Reserve so that management and conservation efforts can achieve the specific objectives for the wetland. This approach may be useful for managing other wetlands across the VMD.
Estuaries are productive and dynamic ecosystems that provide a wide range of environmental services to human society, many of which contribute to people's livelihoods and wellbeing. However, many of these coastal ecosystems have become degraded by the impacts of human activity. Such degradation is often manifested in changes to an ecosystem's structure and function. Such changes impact on the resilience of these ecosystems to recover from natural disasters and maintain essential services that human and ecological communities rely upon.In shallow-water estuarine ecosystems, sediment-based processes often play a significant role in ecosystem function, such as the biogeochemical cycling of carbon and nutrients. This thesis examines the importance of benthic community composition on key biogeochemical processes that underpin local phenomena such as blooms of the toxic cyanobacterium Lyngbya majuscula and materials cycling at ecosystem-wide scales.The research presented here shows that changes in benthic community composition have implications for system-wide functions such as biogeochemical cycling.In Deception Bay, 100 % of the seagrass community dominated by Syringodium isoetifolium was lost after a major flood event in January 2011. The loss of S. isoetifolium from Deception Bay was shown to fundamentally change the structure and function of the seagrass meadow from a net heterotrophic seagrass dominated benthic community to a net autotrophic seagrass-microphytobenthic community. Such a change in function has implications for system-wide biogeochemical budgets.This study has quantified a benthic release of Fe(II) from sediments sampled from northern Deception Bay. To our knowledge, this study represents the first documented benthic release of Fe(II) from permeable sandy sediments of a shallow subtropical embayment. The results suggest that sandy sediments that are relatively low in organic carbon are capable of supplying bioavailable Fe at levels significant for the growth of benthic organisms. The results of this research show that the post-flood sediments of northern Deception Bay are capable of supplying >1700 % of the daily Fe demands and up to 10.6 % of daily P requirements for the growth of L. majuscula blooms. This result suggests that the growth of L. majuscula blooms in Deception Bay is likely to be P limited and that future management actions that are targeted towards reducing L. majuscula blooms in Moreton Bay need to include a strategy for reducing P loads to the Bay.
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