Diatom–salinity relationships in wetlands: assessing the influence of salinity variability on the development of inference models

Abstract

Diatoms are among the most widely used indicators of human and climate induced wetland salinity history in the world. This is particularly as a result of the development of diatom-based models for inferring past salinity. These models have primarily been developed from relationships between diatoms and salinity measured at the time of sampling or during the preceding year. Although within site variation in salinity has the potential to reduce the efficacy of such models, its influence has been rarely considered. Hence, diatom-conductivity relationships in eight seasonally monitored wetlands have been investigated. In developing a diatom-conductivity transfer function from these sites, we sought to assess the influence of conductivity variation on diatom inference model performance. Our sites were characterised by variability in conductivity that was not correlated to its range and thus were well suited to an investigation of this type. We found, contrary to expectations, that short-term (seasonal) changes in conductivity which were often dramatic did not result in unduly reduced transfer function performance. By contrast, sites that were more variable in the medium term (5-6 years) tended to have larger model errors. In addition, we identified a secondary ecological gradient in the diatom data which could not be related to any measured variable (including pH, turbidity or nutrient concentrations).

A diatom dataset and diatom-salinity inference model for southeast Australian estuaries and coastal lakes

“…Salinity has previously been found to be the overriding environmental variable influencing Australian diatom communities and diatom-salinity (or -conductivity) relationships have been described (e.g. Hodgson et al 1997;Blinn and Bailey 2001;Gell et al 2002;Philibert et al 2006;Saunders et al 2007;Tibby et al 2007;Taukulis and John 2009). With the exception of Hodgson et al (1997) and Saunders et al (2007), none of these studies were conducted in coastal ecosystems.…”

Quantitative Diatom-Based Reconstruction of Paleoenvironmental Conditions in Florida Bay and Biscayne Bay, U.S.A.

“…Diatom communities occupying the nearshore sites contained many taxa with broad salinity and nutrient tolerances, also observed by Admiral (1984) for most of the epipelic species in the Ems-Dollard Estuary, by Tibby et al (2007) for coastal wetlands in southeast Australia, by Snoeijs (1999) for the Baltic Sea, and by (Chapter 2) for Florida…”

“…The most influential variable was salinity, commonly recognized by many as an important factor controlling the distribution of organisms in estuarine environments (Snoeijs 1994;Underwood 1998;Frankovich et al 2006;Tibby et al 2007). Additionally, nutrient availability, which has been found to structure algal communities in this region Prager and Halley, 1999), also contributes to the small number of indicator species identified for sediment, epiphyton, and plankton, but mostly for the first two habits.…”

“…For example, Admiral and Peletier (1979a), who studied the diatom response to different levels of sulfide, ammonia, salinity, oxygen and light in the Ems-Dollard Estuary of the Netherlands, concluded that no single variable, but rather a combination of them, could best explain the species distribution. Salinity was mentioned in numerous studies conducted in shallow estuaries and lagoons in the past as one of the most important water chemistry variable determining diatom species composition (Snoeijs 1999;Frankovich et al 2006;Tibby et al 2007). Bay is relatively deep and the water turbidity is low, some taxa (e.g., Nitzschia sigma, Licmophora pfannkucheae) originally described as epiphytic or epipelic (Witkowski et al 2000) were identified by ISA as good indicators of planktonic communities, indicating a moderate degree of mixing.…”

“…The majority of the diatom-based paleoenvironmental studies have been conducted in freshwater areas, but in the last few decades they have also been successfully carried out in estuaries and coastal regions to study eutrophication , water circulation (Witak et al 2005), water temperature (De Seve 1999), salinity , and sea level changes (Hamilton and Shennan 2005). Most of these investigations have been done in higher latitudes and only a few have been carried out in subtropical and tropical coastal regions (Fluin et al 2007;Taffs et al 2008) and estuaries (e.g., Zong et al 2006;Sounders et al 2007). …”