Biomedical subjects

Alexander D Huryn

Publications and source records attributed to Alexander D Huryn.

4 recordsLinked to original sources

PubMed2006

Urbanization affects stream ecosystem function by altering hydrology, chemistry, and biotic richness.

Catchment urbanization can alter physical, chemical, and biological attributes of stream ecosystems. In particular, changes in land use may affect the dynamics of organic matter decomposition, a measure of ecosystem function. We examined leaf-litter decomposition in 18 tributaries of the St. Johns River, Florida, USA. Land use in all 18 catchments ranged from 0% to 93% urban which translated to 0% to 66% total impervious area (TIA). Using a litter-bag technique, we measured mass loss, fungal biomass, and macroinvertebrate biomass for two leaf species (red maple [Acer rubrum] and sweetgum [Liquidambar styraciflua]). Rates of litter mass loss, which ranged from 0.01 to 0.05 per day for red maple and 0.006 to 0.018 per day for sweetgum, increased with impervious catchment area to levels of approximately 30-40% TIA and then decreased as impervious catchment area exceeded 40% TIA. Fungal biomass was also highest in streams draining catchments with intermediate levels of TIA. Macroinvertebrate biomass ranged from 17 to 354 mg/bag for red maple and from 15 to 399 mg/bag for sweetgum. Snail biomass and snail and total invertebrate richness were strongly related to breakdown rates among streams regardless of leaf species. Land-use and physical, chemical, and biological variables were highly intercorrelated. Principal-components analysis was therefore used to reduce the variables into several orthogonal axes. Using stepwise regression, we found that flow regime, snail biomass, snail and total invertebrate richness, and metal and nutrient content (which varied in a nonlinear manner with impervious surface area) were likely factors affecting litter breakdown rates in these streams.

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PubMed2005

Leaf litter processing and invertebrate assemblages along a pollution gradient in a Maine (USA) headwater stream.

During the autumn of 1997 and 1998, leaf litter processing rates and leaf pack invertebrate assemblages were examined at eight stations along a pollution gradient in Goosefare Brook, a first-order coastal plain stream in southern Maine (USA). There was no significant effect on litter softening rate in 1997, and only the most polluted station showed a decrease in 1998. However, litter loss rates showed decreases in both years. The structure of invertebrate assemblages changed in response to the stresses, showing a decline in EPT richness and an increase in the proportion of collecting taxa. However, total shredder biomass was only weakly affected. Shredder biomass at all stations was dominated by Tipula, and biomass of other shredder taxa showed a serial replacement along the gradient of stress related to their pollution tolerance. Rather than the expected relationship with shredder biomass, litter processing rates were directly related to water and sediment quality. Goosefare Brook demonstrates how variable pollution tolerance of community members enables stress resistance and a consequent preservation of ecosystem function.

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PubMed2003

Impervious surface area as a predictor of the effects of urbanization on stream insect communities in Maine, USA.

The influence of urbanization on stream insect communities was determined by comparing physical, chemical, and biological characteristics of streams draining 20 catchments with varying levels of urban land-cover in Maine (U.S.A). Percent total impervious surface area (PTIA), which was used to quantify urban land-use, ranged from approximately 1-31% among the study catchments. Taxonomic richness of stream insect communities showed an abrupt decline as PTIA increased above 6%. Streams draining catchments with PTIA < 6% had the highest levels of both total insect and EPT (Ephemeroptera + Plecoptera + Trichoptera) taxonomic richness. These streams contained insect communities with a total richness averaging 33 taxa in fall and 31 taxa in spring; EPT richness ranged from an average of 15 taxa in fall and 13 taxa in spring. In contrast, none of the streams draining catchments with 6-27% PTIA had a total richness > 18 taxa or an EPT richness > 6 taxa. Insect communities in streams with PTIA > 6% were characterized by the absence of pollution-intolerant taxa. The distribution of more pollution-tolerant taxa (e.g. Acerpenna (Ephemeroptera); Paracapnia, Allocapnia (Plecoptera); Optioservus, Stenelmis (Coleoptera); Hydropsyche, Cheumatopsvyche (Trichoptera)), however, showed little relation to PTIA. In contrast to the apparent threshold relationship between PTIA and insect taxonomic richness, both habitat quality and water quality tended to decline as linear functions of PTIA. Our results indicate that, in Maine, an abrupt change in stream insect community structure occurs at a PTIA above a threshold of approximately 6% of total catchment area. The measurement of PTIA may provide a valuable tool for predicting thresholds for adverse effects of urbanization on the health of headwater streams in Maine.

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PubMedDate not supplied

Effects of roadway crossings on leaf litter processing and invertebrate assemblages in small streams.

The effects of the Maine Turnpike (Interstate 95) on leaf litter processing were examined in five first- and second-order coastal plain streams in southern Maine, U.S.A. Invertebrate assemblages and red maple leaf softening and loss rates were compared at 53 stations arrayed upstream and downstream of the turnpike. Litter softening rate was not affected by the roadway. Litter loss rate was significantly faster at downstream stations (-0.0024 degree-day(-1)) than at upstream stations or at stations nearest the roadway, which were not different from each other (-0.0022 degree-day(-1)). Litter softening and loss rates were more strongly related to physical and chemical habitat variables than to shredder assemblage characteristics. Significant among-stream differences were observed in most community structural metrics and in biomass of important shredder taxa, but effects of the roadway were rarely consistent among streams. This is attributed in part to habitat variation, which was greater among streams than within streams. This study suggests that while the presence of the Maine Turnpike may influence stream water quality and habitat structure, the relatively subtle effects of roadway runoff and associated habitat modifications on stream ecosystem processes are masked by within- and among-stream variability in litter processing and leaf pack invertebrate assemblage structure.

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