Ecological regime shifts in salinised wetland systems. II. Factors affecting the dominance of benthic microbial communities

Abstract

This paper is the second in a pair investigating potential mechanisms for ecological regime change in salinising wetlands. The first paper in this series focused on the responses of the salt-tolerant submerged macrophyte community to salinity. In this second paper, we investigated some of the environmental conditions required for initiation and dominance of benthic microbial communities using a combination of experimental and observational data. Two experiments were carried out. One investigated the importance of prior establishment of benthic microbial communities on their ability to maintain prevalence over macrophyte colonisation ('persistence' experiment), while the other investigated hydrology and its effect on sediment perturbation, potential nutrient release and subsequent benthic microbial community establishment ('flooding' experiment). The 'persistence' experiment measured the biomass of benthic microbial communities and emergence of macrophytes from sediments kept either wet or dry for 4 weeks then flooded at a range of salinities. Benthic microbial biomass was similar across all of the salinities tested (15, 45 and 70 ppt), with a slight increase at higher salinities, suggesting that none of these limited benthic microbial community development. Pre-wetting of sediments usually increased benthic microbial community biomass and reduced macrophyte germination, but the latter was attributed to the presence of anoxic sediments rather than the increased benthic microbial community biomass. Germinating macrophytes emerged through benthic microbial communities or dense heterotrophic bacterial blooms, demonstrating that they could become dominant even when another community was already established. Field data supported these results, suggesting that the development of benthic microbial communities is not limited by salinity alone, but includes other factors, such as the water regime. In the 'flooding' experiment, the largest differences in nutrient concentrations ultimately lay between the pre-wet and pre-dry treatments (due to the greater release of nutrients and development of anoxia in the latter) rather than those subjected to fast versus slow flooding. In response to this, highest benthic microbial community biomass was in treatments with pre-wet sediment, corresponding with lower phytoplankton biomass.

Estimation of ecological water requirements based on habitat response to water level in Huanghe River Delta, China

“…The difference of water depths is inferred responsible for a difference in the ri- (1) to (8), then the highest index value in each column is considered as 1, and each value in corresponding column is divided by the highest value, respectively chness and composition of aquatic macrophytes in this study, which is also consistent with the survey work carried out by White et al (2007). This study confirms the previous studies that long-term inundation or permanently flooded conditions may directly reduce species diversity in wetlands and aquatic environments (Fortney et al, 2004;Flinn et al, 2008) or indirectly influence the water regime on competitive interaction (Riis and Hawes, 2002;Sim et al, 2006).…”

Habitat use of an endangered cyprinodontid fish in a saline wetland of the Iberian Peninsula (SW Mediterranean Sea)

“…The conservation of R. cirrhosa meadows by controlling water salinity, since high salinity values prevent R. cirrhosa establishment (Sim et al, 2006), is of special importance. Thus, the maintenance of meso-, or eusaline ponds should be used as a key tool in designing these programmes for the Iberian toothcarp.…”

Biology of the endangered cyprinodontidAphanius iberusin a saline wetland (SE Iberian Peninsula)

“…In confined aquatic systems, collateral effects are known to occur, such as the accumulation of ammonia components, increased vulnerability to disease and pathological changes in gill structure, among others (Wilkie 1997). These effects could be acting on the population studied, aggravated by the decrease approximately 50% in submerged Ruppia spp., which was likely due to increased salinity (Sim et al 2006). These collateral effects could be responsible for the sharp decrease in the relative abundance (CPUEs) and in condition of this population which never recovered the high CPUE values observed during the first spring.…”