Effects of urbanization on stream fish biology

Urbanization of watersheds degrades stream systems by introducing pollutants through stormwater runoff and altering natural flow regimes.  Ultimately, physical habitat is greatly altered and stream communities degraded.  While many studies document the loss of species from urbanized watersheds, the organismal,  population and molecular biology of organisms that persist in urban streams has received relatively little attention.  An understanding of how organisms adapt to urban environments is important in developing a complete picture of how humans affect biodiversity, and can helps us identify the biological characteristics that result in  tolerance of human habitat and landscape alteration by select species.

My collaborators (Dr. Gail Gasparich and Dr. Jay Nelson) and I are currently investigating the biology of blacknose dace (Rhinichthys atratulus), a small stream minnow,  across a rural-urban gradient.  The general goals of our investigations are: 1) To quantify the biological response of blacknose dace to watershed urbanization; 2) determine the relative roles of phenotypic plasticity and evolution in the response of dace to urbanization.

To document the biological response of blacknose dace to watershed urbanization we are using comparative field studies involving eight streams arrayed along a rural-urban gradient .

Female (top) and male (bottom) blacknose dace (Rhinichthys atratulus)

The effects of altered flow regimes on a headwater sandhills stream of South Carolina flowing through a protected area (top), and a stream draining an urbanized watershed in the city of Baltimore (bottom).    

With the help of Dr. Martin Roberge we are also documenting changes in the abiotic environment resulting from watershed urbanization in the Baltimore/Washington DC area.

Common garden experiments and investigations of genetic differences among populations are being used to assess the genetic basis of biological differences among populations.  

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Landscape ecologists have primarily focused their attention on terrestrial systems where organisms are viewed as living in a mosaic of habitat patches that have a two-dimensional nature.  In contrast, stream systems are linear networks when viewed at larger spatial scales and many organisms inhabiting streams  are constantly exposed to the unidirectional, downstream forces of flowing water.  Furthermore, many organisms are primarily found only in smaller headwater streams, including many fishes and stream-side salamanders.  How network structure and the unidirectional flow of water in stream systems influences the population dynamics and habitat selection behaviors of headwater species is a growing area of research in landscape ecology.

I am currently working with several collaborators on investigations of population dynamics of headwater stream fish and habitat selection of streamside salamanders in relationship to stream network structure. Dr. Brian Fath and I are currently developing spatially-explicit population models to investigate the potential influences of stream network structure on headwater stream fish population dynamics.  Dr. Don Forester and I are currently investigation habitat selection of streamside salamanders in relationship to stream network structure.

Third-order stream network (blue lines) and unidirectional flow of water (as indicated by arrows) in Baltimore County Maryland.

Results to date

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Larval amphibian trace element toxicology

Many pollutants that enter aquatic systems (e.g., streams, wetlands and stormwater retention ponds) are, or quickly become bound to small sediment particle.  Therefore, these pollutants tend to accumulate in sediments on the bottom of aquatic habitats where benthic organisms can be exposed to them through their feeding and burrowing activities.  Larval frogs and toads, more commonly referred to as tadpoles, may be particular susceptible to pollutant accumulation in sediments of aquatic habitats because of their benthic feeding habits, permeable skin and close associate with the benthos.  In collaboration with Dr. William Hopkins we have developed a bioassay system to investigate the toxicity of aquatic sediments to anuran larvae.

Past projects have investigated the toxicity of sediments from coal combustion waste settling basins.  Currently, we (Dr. Ryan Casey and Dr. Steve Lev) are investigating the toxicity of sediments from stormwater retention ponds.  

Set up of experimental microcosms in the greenhouse at Towson University.  This experiment investigated the toxicological effects of coal ash contaminated sediments on wood frog (Rana sylvatica) tadpoles.

A recently metamorphosed wood frog (Rana sylvatica) that had an axial malformation as a tadpole.  Note the angle of the hind leg joints.

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Wetlands are truly endangered habitats.  Decades of wetland destruction and draining have left us with only a small fraction of the wetland area present at the time of European colonization of North America.  Wetlands referred to as depression wetlands are common features in many North American landscapes, and are particularly threaten because of their relatively small size (i.e., wetland regulations only protect larger wetland areas).  Despite their small size, depression wetlands harbor a great deal of biological diversity.  

A depression wetland just before it dries completely.  This wetland has a shorter hydroperiod, holding water for only three to five months a year.  While it is not occupied by fishes, it is important breeding habitat for several amphibians that don't breed in wetlands with longer hydroperiods.

Aerial view of a depression wetland on the Coastal Plain of South Carolina.  These wetlands are often referred to as Carolina Bays or Delmarva Bays if your in Maryland.

Larry Bryan and I have been investigating the factors that control aquatic vertebrate use of depression wetlands and the potential effects of toxins on wetland associated wildlife.  These investigations have concentrated on the roles of hydroperiod (i.e., the amount of time surface water is present during the annual hydrological cycle) variation and landscape position in controlling variation in assemblage structure among wetlands and bioavailability of pollutant to wildlife.  We have been monitoring fish populations in a number of depression wetlands for the past 10 years and are currently developing models of fish occurrence in depression wetlands and potential toxic effects of Wood Stork foraging in these habitats.

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