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	A multi agency project funded by US EPA's STAR Program

Diatom Deformities Reflect Pollution

The nearshore waters of many areas of the Laurentian Great Lakes are examples of ecological instability. Large population and industrial centers on the shores of these originally highly oligotrophic lakes lead to large spatial and temporal gradients in nutrient, conservative ion, and toxic material concentrations. Lake Erie is generally considered the most modified of the Laurentian Great Lakes, and became a focus of concerns about water pollution in the later decades of the twentieth century. The occurrence of morphological abnormalities in birds, fish and invertebrates, particularly in the coastal region of Lake Erie and its tributaries, is well known. Reports of similar effects on benthic diatoms are more rare, but not unknown.

Populations of the diatom genus Tabularia from a coastal site near Cleveland, Ohio, exhibit highly abnormal morphology. The locality of collection is locally known as Whiskey Island (Fig. 1), an area with a legacy of environmental problems. The “island” is actually a peninsula at the mouth of the Cuyahoga River. Its name is derived from a distillery that was built in 1836, and it has been an industrial site, ship graveyard and waste disposal area. It is currently the site of a salt mine, and has recently been developed as a large marina. The collection site is subject to numerous discharges, including industrial contaminants. The Cuyahoga River is particularly notorious because at one time it was so contaminated that it occasionally caught fire. The more obvious ecological problems have now been contained, but the legacy of previous environmental insults remains. There are many causes of morphological abnormalities in diatom frustules, and based on our observations it appears that abnormalities are common in diatom communities that undergo toxic stress, and the abnormalities present near Cleveland are likely related to these factors.

Observations showed an extreme variety of atypical shapes (Fig. 2); frustules were bent, asymmetric, had irregular striae and margins, or any combination of these characters. Abnormalities in diatom valve structure have been noted and reported virtually since the group was first studied. In general, deformities have been associated with pollution or eutrophication. More specific chemical causes include silica limitation and increased salinity in freshwater habitats.
Morphological abnormalities of the diatoms was not originally anticipated to be one of the GLEI indicators, and so to date we have only assessed these site-specific data near Cleveland. However, the presence of benthic diatoms that are atypical (in terms of both distribution and morphology) in the Great Lakes may offer valuable insights into toxic effects. Although the present state of knowledge does not permit firm conclusions concerning the populations described here, investigation of benthic diatom populations in the Great Lakes is a neglected topic that deserves more research attention.