Influence of Size on Fate and Ecological Effects of Kepone in Physical Models.

Three different sizes of marine microcosms were used to study the influence of two features of spatial scale on the chemical fate and ecological effects of the pesticide Kepone. Increasing the size of microcosms reduced the ratio of wall surface area to volume of contained sea water, but increased the number of benthic species due to increasing sample size. Other features of spatial scale, such as water turbulence, water turnover, etc., were held constant. Intact water-column and benthic communities from a north-temperate marine system were coupled together in 9.1-, 35.0-, and 140.O-L containers. Kepone at 20.4 nmol/L was added to these microcosm systems over a 30-d period. A 3 x 2 factorial design was used to discern the effects of size and Kepone. In the absence of Kepone the phytoplankton community exhibited excessive growth relative to the field system for all system sizes. Growth was directly related to the size of microcosms. In addition, the time required to achieve maximum algal biomass was also directly related to size. Release of a growth-stimulating compound(s) from fouling organisms settling on the microcosm walls and size-dependent increases in benthic species provided the best explanation for the observed phytoplankton dynamics. Addition of Kepone indirectly increased phytoplankton densities by reducing through toxic effects, the grazing pressure of zooplankton. Because this effect and mechanism was dependent upon the size of the system, the sensitivity of future perturbation studies may be enhanced by producing similar or related variations in system size. The concentration of Kepone in surficial sediments was also size dependent. Since the average concentrations of Kepone in all water columns were statistically equivalent, these findings were the result of sediment bioturbation coupled with preferential partitioning of Kepone from liquid to the solid, organic phase of sediments. Ecological risk assessments based upon data derived from these systems are therefore dependent upon size. Furthermore, the smaller the size, the greater the underestimate in sediment exposure and the ecological risks of Kepone.

The influence of suburban land use on habitat and biotic integrity of coastal Rhode Island streams.

Watershed land use in suburban areas can affect stream biota through degradation of instream habitat, water quality, and riparian vegetation. By monitoring stream biotic communities in various geographic regions, we can better understand and conserve our watershed ecosystems. The objective of this study was to examine the relationship between watershed land use and the integrity of benthic invertebrate communities in eight streams that were assessed over a 3-year period (2001-2003). Sites were selected from coastal Rhode Island watersheds along a residential land-use gradient (4-59%). Using the rapid bioassessment protocol, we collected biological, physicochemical, habitat, and nutrient data from wadeable stream reaches and compared metrics of structure and integrity. Principal component analyses showed significant negative correlation of indicators for stream physicochemical, habitat, and instream biodiversity with increasing residential land use (RLU) in the watershed. The physicochemical variables that were most responsive to percent RLU were conductivity, instream habitat, nitrate, and dissolved inorganic nitrogen (DIN). The positive correlation of DIN with percent RLU indicated an anthropogenic source of pollution affecting the streams. The biotic composition of the streams shifted from sensitive to insensitive taxa as percent RLU increased; the most responsive biological variables were percent Ephemeroptera, percent Scrapers, percent Insects, and the Hilsenhoff biotic index. These data show the importance of land management and conservation at the watershed scale to sustaining the biotic integrity of coastal stream ecosystems.

Monitoring nekton as a bioindicator in shallow estuarine habitats.

Long-term monitoring of estuarine nekton has many practical and ecological benefits but efforts are hampered by a lack of standardized sampling procedures. This study provides a rationale for monitoring nekton in shallow (< 1 m), temperate, estuarine habitats and addresses some important issues that arise when developing monitoring protocols. Sampling in seagrass and salt marsh habitats is emphasized due to the susceptibility of each habitat to anthropogenic stress and to the abundant and rich nekton assemblages that each habitat supports. Extensive sampling with quantitative enclosure traps that estimate nekton density is suggested. These gears have a high capture efficiency in most habitats and are small enough (e.g., 1 m2) to permit sampling in specific microhabitats. Other aspects of nekton monitoring are discussed, including spatial and temporal sampling considerations, station selection, sample size estimation, and data collection and analysis. Developing and initiating long-term nekton monitoring programs will help evaluate natural and human-induced changes in estuarine nekton over time and advance our understanding of the interactions between nekton and the dynamic estuarine environment.