ECOLOGICAL EFFECTS OF MAJOR STORMS ON COASTAL WATERSHEDS AND COASTAL WATERS - HURRICANE-BOB ON CAPE-COD

Hurricane Bob, a category 3 storm, made landfall on Cape Cod in August 1991, and its effects on watersheds and adjoining estuaries were dete cted in the ongoing studies being caried out as part of the Waquoit Ba y Land Margin Ecosystems Research project. On land, Bob had only minor overall effects on forests; localized wind bursts did snap and break trees in small and widely scattered forest parcels. Wind stripped up t o half the leaves of deciduous trees and many herbaceous plants on the watershed, and most remaining leaves were damaged by salt, so that by the end of Aug, Cape Cod forests were defoliated. Damaged growing tip s of exposed trees were evident for several growing seasons. The salt exposure was followed by a burst of growth and bloom in some plants du ring Sep-Oct. Forest invertebrates were disturbed by the storm. Nests of hornets and wasps, for example, were apparently destroyed and the s urvivors became a serious pest problem: hospital records show a ten-fo ld increase in cases of wasp stings just after Bob. Populations of the se insects did not return to earlier abundance for several years. Bird s and mammals did not appear to have suffered much damage. Leaching of salt to soils released previously-adsorbed soil ammonium. Such loss o f critical nitrogen may be in part responsible for the characteristica lly dwarfed near-shore coastal forests, as well as adds nitrogen to gr oundwater that in turn transports the nitrogen to receiving waters. On the Bay, Bob thoroughly mixed the water column, but the stratificatio n was restored within 1-2 days after passage of the storm. Short recov ery times might be characteristic of shallow bays with short (2-3 d) w ater residence times. Bob opened a new inlet to Waquoit Bay, which rem ains open. The new inlet exerts only minor effects on circulation with in the Bay, but did create localized damage to dune and eelgrass habit ats near the new inlet. The mixing of the water column released major amounts of nutrients that were held within the macroalgal canopy and u pper sediments, into the upper layers, and prompted a short-lived (2-3 d) phytoplankton bloom. Biomass of unattached macroalgae was not affe cted by Bob. Respiration and nitrogen content of the dominant macroalg al species were elevated after passage of the storm, but returned to n ormal rates after several days. Nearly all above-sediment eelgrass bio mass was removed, but returned to previous biomass during the next gro wing season. There was no visible damage to fringing salt marsh habita ts. Damage to aquatic animals appears to have been minimal. A small de crease in water temperature and increased respiration by macroalgae le d to decreased total net ecosystem production and increased net ecosys tem respiration, but the decreases disappeared after 2 d. The effects of Hurricane Bob seemed more intense and protracted on land than on aq uatic ecosystems. Recovery from the various distubances took hours to days in the aquatic system, but months to decades in terrestrial compo nents. Rigid, larger organisms attached or rooted to substrates seem m ost subject to storm-related disturbances.