|Abstract or Summary
- Carter Lake, a freshwater, coastal dune-margin lake,
was sampled at the beginning and end of the summer of 1986
to determine the sediment characteristics and benthic
macroinvertebrate abundance, biomass, variety, and
diversity. The distributions of major benthic habitats were
estimated by snorkeling in June and July, 1986. Water
temperature and dissolved oxygen were measured throughout
the summer of 1986. In July 1987, water temperature,
dissolved oxygen, conductivity, alkalinity and pH were
Thermal stratification was not observed during this
study and the water column warmed gradually between April
and July. Dissolved oxygen remained close to 100%
saturation throughout the study. The water level of Carter
Lake dropped about 2.5 m between May and October, reducing
its surface area by about 40%.
The benthic habitats of Carter Lake were stratified into four major zones: a sandy temporarily submerged
littoral zone; a sandy but permanently submerged littoral
zone; a mid-depth zone where a macrophyte, Nitella. grew;
and a deep zone with soft mud substrate.
The average density of benthic macroinvertebrates was
highest in the shallow permanently submerged zone ( >16000
/ m² in May and October ) and lowest in the deep mud
zone ( 2900 / m² in May and 4700 / m² in October ). In May,
benthic macroinvertebrate biomass was highest in the
shallow zones ( 1.3 - 2.9 g / m² dry weight ); in October
biomass was highest in the mid-depth zone ( 4.4 g/m² dry
weight, excluding crayfish and mussels ).
Fifty-three invertebrate taxa were identified from
Carter Lake, including three euryhaline crustacean species
( Corophium spinicorne. Gnorimosphaeroma oregonensis lutea.
and Acanthomysis awatchensis ) . Corophium spinicorne
dominated the macroinvertebrate communities of the shallow
areas and sphaeriid clams dominated the deep water
community. The mid-depth zone had the most diverse
Two species that were abundant in the temporarily
submerged area, Corophium spinicorne and Juga piicifera.
were found in greater numbers deeper in the lake after the
water level dropped, indicating that these species migrate
in response to changing water level.