LONG-TERM TRENDS IN THE MACROBENTHOS AND WATER-QUALITY OF THE LOWER CHESAPEAKE-BAY (1985-1991)

Long-term trends in macrobenthic communities of the lower Chesapeake B ay, USA, were examined using data collected quarterly (March, June, Se ptember and December) from 1985 to 1991 at 16 stations along a salinit y gradient from tidal freshwater regions of the major tributaries (Jam es, York and Rappahannock rivers) to the polyhaline region of the main -stem of Chesapeake Bay. A non-parametric trend analysis procedure was applied to five parameters characterizing macrobenthic community stru cture: community biomass, species richness, abundance of individuals, proportion of biomass composed of opportunistic species (opportunistic biomass composition) and proportion of biomass composed of equilibriu m species (equilibrium biomass composition). For the parameters tested 36 trends were detected. For community biomass, five trends were sign ificant; all had positive slopes and occurred in the James and York ri vers. For species richness, six trends were significant; all had posit ive slopes with three trends in the James River, two trends in the Yor k River and one trend in the main-stem of Chesapeake Bay. For abundanc e of individuals, 17 trends were detected; all abundance trends were s easonally dependent, had positive slopes and occurred at 12 of the 16 stations. For opportunistic biomass composition, four trends were sign ificant; an had positive slopes with one trend in the lower Rappahanno ck River and three trends in the main-stem of Chesapeake Bay. For equi librium biomass composition four trends were significant; two trends h ad positive slopes (one in the James River and one in the York River) and two trends had negative slopes (one in the Rappahannock River and one in the main-stem of Chesapeake Bay). Trends in the James and York rivers were considered to indicate improving conditions for the bentho s, while trends in the lower Rappahannock River and the main-stem of t he Chesapeake Bay were considered to indicate deteriorating conditions . Deteriorating conditions for the benthos were associated with region s exposed to summer, low dissolved oxygen events. The trends in the in dicators of benthic biological community health were inferentially rel ated to trends observed in water quality conditions in the tributaries and main-stem of Chesapeake Bay. All major water quality and biotic t rends appeared to correspond in an ecologically meaningful manner.