Benthic Enrichment Research Articles

Mapping of Benthic Enrichment Patterns in Narragansett Bay, Rhode Island

A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats.

Environmental monitoring of caged fish farming in macrotidal environments

Recent years have seen considerable expansion in fish farming using sea cages. These have until recently been located in the sheltered and low current environments of sea lochs and fjords. Significant benthic enrichment is known to occur at these sites, but the effect is highly localized. Fish farm development is now occurring in areas with strong tidal flows. The siting of caged fish farming in macro-tidal environments may reduce the environmental impact of the industry on benthic communities at the farm site. However there exists the potential for accumulation of farm wastes in nearby sedimentary sinks. Additionally the longer residence time of the wastes in the water column has the potential, especially in regions with already high nutrient loadings and/or long flushing times, to lead to stimulation of phytoplankton blooms. Environmental monitoring of such developments therefore needs to consider these addition effects.

Meiofauna and chlorophyll associated with Beggiatoa mats of a natural submarine petroleum seep

Previous studies at the Isla Vista oil seep have suggested that meiofauna, particularly nematodes, might be an important factor in explaining macrofaunal enrichment by making bacterial biomass available to the benthic food web. To explore this possibility, we analyzed meiofaunal abundance and microalgal pigments inside and just outside of bacterial mats at this natural oil seep. The bacterial mats occur where crude oil and natural gas are actively seeping out of the sediment; cores from within the mats contained a great deal of crude oil (up to 50 %). Meiofaunal abundances were the same in and out of the bacterial mats (averaging 1·-9 × 10 6 individuals m -2). However, dramatic changes in community structure were noticed. Harpacticoids made up 19 % of the fauna outside the mats but only 1 % inside. Pigment concentrations were also the same in both sites with phaeophytin dominating chlorophyll (120 compared to 29.8 mg m -2). The variance of both microalgal pigments and meiofauna was much greater inside than outside, suggesting that the bacterial mats are a more heterogeneous environment. Although the effect of crude oil toxicity is not clear, the high abundances of microbial and meiofaunal biomass support the hypothesis of benthic enrichment via microbes and meiofauna.