Bioassessment IV: Algae
Presiding: J Greenwood, US Environmental Protection Agency; C Lane, US Environmental Protection Agency
NB41A-01 08:30h
Ecological Health Assessment for the Mekong Basin: Primary Productivity and Phytoplankton Composition
A major ecological health assessment project for the entire Mekong Basin was started in 2003, to investigate appropriate bio-indicators for assessing river health. Several indicators were tested at 13 disturbed and undisturbed sites, including main channels and tributaries. Primary productivity and phytoplankton composition were tested for their applicability as ecological health indicators. Primary productivity was estimated using the Dark-Light bottle technique, producing values ranging from less than 10 mg C m-3 h-1 to over 80 mg C m-3 h-1. Phytoplankton composition and density were determined from collected water samples, and a total of 103 species of phytoplankton were found. Diatoms have the highest species diversity (37), contributing approximately 98% by volume of the total phytoplankton density. Neither the primary productivity estimates nor the phytoplankton composition data exhibit unexpected characteristics, which suggests that the sampling sites have not suffered from ecosystem degradation.
NB41A-02 08:45h
Assessing Ecological Health of Large Tropical Rivers in Developing Regions: a Case Study from the Mekong.
Bioassessment tools are being developed to assess the Ecological health of the Lower Mekong River. A multinational team of local specialists has been established working with two international mentors. This approach allows geographical homogeneity of methods, assurance of quality and capacity building. A range of potential indicators were tested in the first year of the program, with benthic and littoral invertebrates, zooplankton and benthic diatoms finally being selected for further development. The first two year's assessments indicate that the health of the Mekong is generally good, with the exception of the Mekong delta, where population density is high and agriculture is most intensive. There is little industry in the Mekong Basin, and as yet no large dams have been constructed. Surveys will be conducted on a three to five year cycle, with different regions in the basin being targeted each year. Development of appropriate metrics to quantify river health is now a priority.
NB41A-03 09:00h
Developing an Eastern Canadian Diatom Index: Preliminary Considerations
Preliminary effort on the development of a Candadian diatom index has generated questions: Is it important to account for cell size? How should rare species be treated? Should those species known to be good indicators have more weight in the analyses? Is chemistry averaged over a certain period of time better than one-time chemistry measurements? What is the seasonal and annual variability in the community structure? Should between-ecoregion or upstream-downstream variability in the parameters used to generate the index be accounted for? We are currently attempting to answer these questions. Preliminary results have allowed to conclude that (1) metrics based on relative cell volume or cell surface did not provide more information than using cell relative abundance, (2) environmental variable metrics gave the best results when expressed as average seasonal conditions and (3) a higher portion of the variance is explained when samples from the spring and the fall are kept separated. An overview of the answer to these questions will be presented as well as recommendations for the development of the index. These investigations are essential to evaluate which metric combination allows to explain the highest percent variance in diatom community structure and therefore provide the most reliable index.
NB41A-04 09:15h
Diatom Assessment of Wetland Condition at Genus, Species, and Subspecies Taxonomic Resolution
This study was conducted to determine if epiphyton-based metrics could be developed using mean autecological values at genus, species, and subspecies taxonomic levels. Epiphytic diatoms from 69 isolated depressional marshes in peninsular Florida were sampled once in either the summers of 1999 or 2000. Soil and water parameters were also sampled. Thirty genera, 148 species, and 26 subspecies were identified. The proportional matrices at each taxonomic level were highly similar. Autecological metrics, based on weighted averages, were developed for pH class, salinity tolerance, N uptake metabolism, oxygen requirements, saprobity level, trophic status, moisture requirement, and pollution tolerance at each taxonomic level. Two additional metrics based on indicator species analysis were also developed. Wetland condition, as determined by summed metric values, was strongly correlated across taxonomic level, and no difference was found when sites were placed into categorical bins based on quartile scoring for each taxonomic level. Specific conductance, soil pH, soil and water total phosphorous, and total Kjeldahl nitrogen were significantly related to site ordination scores at each taxonomic level. This study concludes that indices of biotic integrity, when developed using autecological indices, provide similar qualitative conditional information across taxonomic levels.
NB41A-05 09:30h
Benthic Algal Community Structure and Bioaccumulation of Mercury in a Coastal Watershed
Largemouth bass in the Fish River watershed of coastal Alabama contain relatively high concentrations of mercury, the source of which is unknown. We used benthic microalgal assemblages in effort to describe spatial distribution of mercury in the Fish River and its tributaries. Artificial substrates were deployed for 3-week exposure periods at 13 sites on 4 separate occasions. When analyzed by cold vapor atomic absorption spectroscopy, mercury concentrations in periphyton ranged from 0.066 Μg/g (Pensacola Branch) to 0.493 Μg/g (Barner Branch). Principal Components Analysis indicates that physical and chemical heterogeneity exists throughout the watershed and is correlated with agricultural and urban land use categories. Physical and chemical heterogeneity of stream sites, variability in land use/land cover, and mercury content of periphyton all are reflected in the diatom assemblages which were found to characterize each site. Gomphonema parvulum was cosmopolitan throughout the watershed and therefore deemed suitable for assessment of mercury contamination. However, mercury was not detected in G. parvulum when individual cells of from each site were observed using a Scannning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer.
NB41A-06 09:45h
Diatom Assemblages as Indicators of Solute Levels in Lowland Neotropical Streams, Costa Rica
Previous research in streams draining lowland rainforests of La Selva Biological Station, Costa Rica, has shown that the invertebrate species composition does not differ between solute-poor [soluble reactive phosphorus (SRP) < 10 Μg L-1] versus solute-rich (SRP > 100 Μg L-1) streams that receive groundwater enriched with solutes from geothermal activity. In contrast, algal community analyses shows that solutes play important roles in structuring diatom assemblages in these high- and low-solute streams. Periphyton samples were collected in the wet and dry seasons from epipelic and epilithic substrates in light gaps in streams along a solute gradient. High- solute streams were dominated by taxa associated with high conductivity [i.e., Seminavis sp. and Bacillaria paxillifer (O.F. Müll.) Hendey]. In contrast, cosmopolitan and acidophilic taxa (i.e., Nupela praecipua Reichardt, Navicula longicephala Hustedt, and Frustulia spp.) were most common in low-solute, poorly buffered streams. These results suggest that diatom assemblages in high-solute streams are most likely influenced by a suite of solutes, including phosphorus; low-solute streams have diatom assemblages characteristic of poorly buffered, oligotrophic conditions, and, more importantly, low pH. While these low-solute streams generally have circumneutral pH, diatom response illustrates their poor buffering capacity.