Intertidal foraminifera in the Spartina patens floral zone of the LaHave Estuary, Canada: A baseline for assessing organic pollution remediation

Abstract

The LaHave Estuary is polluted with domestic waste delivered via straight pipes. These are to be replaced with septic tanks. The impact of this remediation on the wider biotic community will need to be assessed. Intertidal foraminifera are ideal for mitigation assessment in the LaHave and comparable estuaries, estuary banks supporting small beds of intertidal vegetation. This paper provides a baseline for future comparisons of the total LaHave intertidal benthic foraminiferal assemblage and presents a method applicable to other estuaries. Regarding the LaHave Estuary, any biotic change must be viewed against the backdrop of other pollutants like mercury near the town of Bridgewater.Four 10 cm3 replicates (push cores) were taken at four sites along the estuary's eastern bank: Miller Point Peace Park (MPPP, near Bridgewater), Dayspring, Upper LaHave and East LaHave. A fifth replicate was tested for %C and %N. To constrain altitude, the replicates were taken immediately inland of a zone of the marsh grass Spartina alterniflora, typically among swirl-patterned (cowlicked) S. patens.The washed replicates were picked clean of foraminifera, 3821 being recovered. Recovery comprised only (in rank order of abundance) Entzia macrescens, Trochammina inflata and Miliammina fusca. The number per replicate ranged from 29 (East LaHave) to 816 (MPPP). Scheffé’s test following ANOVA showed the mean MPPP foraminiferal density to be significantly different from the other sites, which acted as a group. The most upstream assemblage was dominated by E. macrescens, the most downstream by M. fusca.There were no significant correlations between %C, %N and the mean foraminiferal densities of species. The mean population densities per 10 cm3 of E. macrescens differed between sites, (a) MPPP, (b) Dayspring and Upper LaHave, and (c) East LaHave forming non-overlapping subsets that will need to be monitored separately. Trochammina inflata mean population densities were distinct only at East LaHave. Miliammina fusca population densities presented a peculiar pattern, MPPP and East LaHave forming one group, and the intervening Dayspring and Upper LaHave sites forming another. The transformed mean proportions per site of E. macrescens and T. inflata were not significantly correlated with %C or %N, but those of M. fusca were positively correlated with both. It may be that high trace metal concentrations near Bridgewater are affecting foraminiferal distributions and abundances. This must be taken into account when using the benthic foraminiferal assemblage to assess the impact of the organic pollution remediation.