Showing papers by "Donald F. Boesch published in 1991"

A brief summary of hypoxia on the northern Gulf of Mexico continental shelf: 1985–1988

Abstract: Abstract Oxygen-deficient conditions occur from April to October on the inner to middle continental shelf of the northern Gulf of Mexico and may cover up to 9500 km2 during mid-summer off the Louisiana coast. Hypoxic bottom waters are found in 5–60 m water depth, 5–60 km offshore and extend up to 20 m above the bottom. Salient forcing functions contributing to hypoxic water formation, maintenance and break-up are presented. Stratification is directly correlated with hypoxia in time and space, suggesting that reaeration of bottom waters is controlled by physical processes that are influenced by regional wind fields, river discharge and continental shelf scale currents. Phytoplankton biomass reaches the bottom waters in the hypoxic zones in large amounts (>5 µg/l), fueling water column and benthic respiration rates, but to a currently unknown degree. Increased nutrient loadings in the two major rivers and changes in the proportion of those nutrients essential to phytoplankton growth have probably changed both the phytoplankton community species composition and community production. It is not yet clear whether the extent and severity of hypoxia on the Louisiana continental shelf have changed as a result of these riverine water quality changes.

Effects of hypoxia on continental shelf benthos: comparisons between the New York Bight and the Northern Gulf of Mexico

Abstract: Abstract Depletion of dissolved oxygen to a point inducing mortality of bottom dwelling organisms (hypoxia) occurs in several continental shelf environments in Europe and North America and may have increased as a result of nutrient overenrichment due to human activities. Hypoxia in coastal waters results from plankton decomposition combined with a density stratification of the water column that hinders the oxygenation of bottom waters. Mass mortalities of benthic organisms have occurred as a result of extensive hypoxia on the inner continental shelves of the New York Bight and the northern Gulf of Mexico off Louisiana and Texas. Extensive hypoxia is rare in the New York Bight, and following catastrophic hypoxia in 1976, recovery of the benthic communities took more than two years. On the Louisiana-Texas shelf, large-scale hypoxia occurs virtually every year and recovery from this disturbance is rapid, because the community is kept in an early successional state by the annually recurring hypoxia.