The potential of benthic iron and phosphorus fluxes to support the growth of a bloom forming toxic cyanobacterium Lyngbya majuscula, Moreton Bay, Australia

Abstract

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.

Anthropogenic influences on ecosystem processes in a tropical estuary: feedback connections and environmental management targets - a case study of Dong Ho Estuary, Kien Giang, Vietnam

“…In view of the nutrient stocks observed in the water column and sediments (section 4.3.4 and 4.3.5), the exchange of nutrients between the benthos and water column was then assessed using core incubations (section 5.3.2). A comparison with other estuarine and marine studies suggests that the benthic nutrient flux rates in Dong Ho estuary were in the highest range in the wet season and in the mid range in the dry season (Jenkins, 2005, Hanington et al, 2016, Burford et al, 2008. In the wet season, NH4 + , NOx fluxes in Dong Ho estuary were similar to those reported for other estuaries and coastal lagoons heavily impacted by anthropogenic activities (Jenkins, 2005, Burford et al, 2008, Pérez-Villalona et al, 2015.…”

“…In the wet season, PO4 3fluxes was taken up by sediments in zone 1 at -0.17 (±0.04) mmol. In general, a comparison with other estuarine and marine studies suggests that the benthic nutrient flux rates in Dong Ho estuary were in the highest range in wet season and in the normal range in dry season (Jenkins, 2005, Hanington et al, 2016, Burford et al, 2008. In wet season, NH4 + , NOx fluxes in Dong Ho estuary were similar to other estuaries and coastal lagoons where are heavily impacted by anthropogenic activities (Jenkins, 2005, Burford et al, 2008, Pérez-Villalona et al, 2015.…”

“…In both cases these ratios suggest that the ecosystem is phosphorous limited rather than nitrogen limited compared to the generally accepted Redfield ratios expected in these ecosystems (Magnien et al, 1992). Whilst a number of studies have suggested that nitrogen is the main limiting nutrient in coastal and marine ecosystems (Nixon, 1995, Alberti, 2008, recent reports have demonstrated that phosphorous may also be the limiting nutrient in some estuaries (Wulff et al, 2011, Hanington et al, 2016. So, compared to Redfield ratios (16:1) Dong Ho estuary (62:1) can be considered as P limited, which, as discussed in the final chapter, has strong implications for water quality management strategies.…”

“…Among the key attributes of coastal estuarine system, the keystone biogeochemical processes demonstrate the vital role in balancing and controlling the availability of nutrients as well as oxygen for the ecosystem (Johnstone, 2012, Hanington et al, 2016. Although measuring biogeochemical processes may require more complicated and higher skill levels, this is increasingly becoming more practical and efficient due to the development of technologies such as sensor networks and data collection networks.…”

“…In this context, the ability of these systems to process the materials they receive from these human activities, and the rate at which these processes might occur are key aspects to understanding the potential future function and sustainability of the system of concern. The exchange of nutrients between the benthos and water column is a central component of this understanding, and has been used widely in many studies to indicate and infer the relative status and performance of marine and estuarine ecosystems (Jenkins, 2005, Pérez-Villalona et al, 2015, Hanington et al, 2016.…”