Effects of organic enrichment on estuarine macrofaunal benthos: a comparison of sediment profile imaging and traditional methods

Sediment profile imaging (SPI) is a technique that involves collecting data In the field on sedimentary conditions, particularly vertical variations at and below the s e d i m e n t h a t e r interface SPI approaches were developed nearly 20 yr ago, but have not been widely used in routine pollution monitoring efforts, although their potential for saving time and money is great. The present report is a comparison of SPI and 'traditional' (which involves excising a sediment sample, removing the organisms, and identifying and further processing them in the laboratory) benthic sampling techniques used along an organic enrichment gradient in a temperate coastal lagoon. Twenty-four core samples were taken in summer 1985 along an enrichment gradient mainly resulting from the discharge of sewage effluents, and processed by traditional rnacrofaunal benthic methods. Coincidental with these cores, sediment samples were taken for various physicochemical analyses, and optically clear acrylic box core samples were taken and analyzed in the field for changes in redox potential, dominant benthic taxa and their relative abundances, and sedimentary features. Various univariate and multivariate analyses of the benthic and sedimentary data showed substantial, and expected, changes along the pollution gradient. The changes were similar to those reported from other coastal waters affected by organic wastes: an area nearest the pollution source with lowest taxa numbers (S), abundances (A) and biomass (B); and increased S, A and B with increasing distance from the pollution source. Small near-surface polychaetes (capitellids and Streblospio benedicti) and the amphipod Ampelisca sp, were numerical dominants at all sites, and large, deep-burrowing species (e.g. Asychis elongata) were only found at the least-enriched sites SPI allowed identification of the dominant benthic taxa to useful levels ( e g . 'small near-surface dwelling annelids', 'large deep-burrowing polychaetes'), and location of the apparent color redox potential discontinuity (RPD) layer depth. The RPD ranged from about 1 cm at the site nearest the pollution source to 2 4 cm at the 2 sites farthest away. The SPI data were a s useful a s the traditional data in delimiting the spatial extent of the pollution-impacted benthos. It is suggested that a variety of coring devices presently exist for quickly and efficiently obtaining SPI data, especially in shallow waters.