OMSAP Public Meeting September 1999 Nearfield Hard-bottom Benthic Communities Barbara Hecker Hecker Environmental September 23, 1999 Inflow Outflow Light Concerns Ecological Nutrients Nutrients Contaminants Organic Material Food Chain Community Structure Living Resources Human Health Contaminants Bacteria Viruses Bioaccumulation SEDIMENT Mammals Infauna Piscivorous Fish Zooplankton Phytoplankton Planktivorous Fish EpibenthosHardbottom Demersal Fish Regeneration Detritus Particulate Microbes Dissolved WATER COLUMN Sources Rivers Boundary Nonpoint Effluents Effluents Exchange Gas Exchange N 2, | O 2, CO 2 ATMOSPHERE N, P, Si, O 2, CO 2 Microbes OMSAP Public Meeting September 1999 Hardbottom Benthic CommunitiesOverview n The sea floor in the vicinity of the Massachusetts Bay outfall consists of a series of rock covered topographic highs (drumlins) and sediment covered topographic lows. n Surveys to examine the benthic communities inhabiting these hard-bottom areas were implemented to supplement soft-bottom studies. n Data is used to develop a baseline of the spatial and temporal variability of the benthic communities inhabiting these hard- bottom areas. OMSAP Public Meeting September 1999 Hardbottom Benthic Communities Overview n Surveys are conducted annually at 23 sites using a Benthos Mini Rover ROV equipped with video & still cameras. n Surveys have been conducted during the summer from 1995 to Surveyed 23 sites along 8 transects 10 sites north and 6 sites south of the outfall 2 sites at each of 2 reference locations - NE and SW of outfall (2 sites added in 1996) 1 site at each 2 mid-way reference sites (added in 1997) Diffuser #44 (added in 1997) - will not go online Most of the sites are located on the top of drumlins. OMSAP Public Meeting September 1999 n Collect approximately 20 minutes of video footage and 30 color slides at each waypoint n Video footage is used to develop qualitative data to assess sea floor characteristics: size class of substratum local habitat relief habitat variability within a site abundance of larger recognizable taxa. Hardbottom Benthic Communities Methods OMSAP Public Meeting September 1999 n 35-mm slides used to obtain semi-quantitative data for objective classification of sites relative proportion of taxa - percent composition not density per se since areal coverage varies slides are systematically analyzed for substrate size class degree of sediment drape all taxa were identified and counted algal abundances of Lithothamnion, Asparagopsis, and dulse are estimated in terms of % cover or relative abundance Hardbottom Benthic Communities Methods OMSAP Public Meeting September 1999 n Accuracy of identifications many encrusting forms are only descriptive categories these taxa likely consist of several species. Hardbottom Benthic Communities Methods OMSAP Public Meeting September 1999 n Drumlins tops of usually consist of moderate to high relief mix of boulders and cobbles clean to light sediment dusting (may be heavy) n Drumlins flanks usually consist of low to moderately-low relief cobble pavement with occasional boulders moderate to heavy sediment drape Hardbottom Benthic Communities Results OMSAP Public Meeting September 1999 Hardbottom Benthic Communities Results n Drumlin topography appears to be a major factor in determining composition of benthic communities algae dominate communities inhabiting the top and upper flanks of drumlins invertebrates become more dominant on the flanks of drumlins sediment areas are comparatively depauperate n Spatial heterogeneity of habitat characteristics and biota is highest on the flanks of drumlins and lowest on the top of some drumlins n Spatial heterogeneity of the biotic components exceeds their temporal variability OMSAP Public Meeting September 1999 Benthic CommunitiesResults OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities OMSAP Public Meeting September 1999 Hardbottom Benthic Communities Diffuser 44 OMSAP Public Meeting September 1999 n The structure of the benthic communities in the vicinity of the Massachusetts Bay outfall appears to be controlled by several factors location on the drumlin - concurrent with depth substratum type - size class and hard versus soft local habitat relief amount of sediment drape n A number of areas are spatially heterogeneous in terms of habitat characteristics and biota Hardbottom Benthic Communities Conclusions OMSAP Public Meeting September 1999 n The biota at most of the areas appears to be temporally stable over the 1995 to 1998 time period. n It is hard to dissect differences between temporal and spatial variance. n Some of the variability in the data is related to the generally patchy nature of hard-bottom environments. n As a result of the temporal stability it is very likely that large shifts or changes in the composition of the hard-bottom communities can be detected during discharge monitoring. Hardbottom Benthic Communities Conclusions OMSAP Public Meeting September 1999 n The most likely key-stone species for discharge monitoring is the coralline alga Lithothamnion. It is the most abundant, widely distributed, and predictable taxon encountered and it appears to be sensitive to sediment loading. Hardbottom Benthic Communities Conclusions