Stream Communities Along a Catchment Land-Use Gradient: Subsidy-Stress Responses to Pastoral Development

When native grassland catchments are converted to pasture, the main effects on stream physicochemistry are usually related to increased nutrient concentrations and fine-sediment input. We predicted that increasing nutrient concentrations would produce a subsidy-stress response (where several ecologi...

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Bibliographic Details
Published in:Environmental management (New York) 2007-02, Vol.39 (2), p.213-225
Main Authors: Niyogi, Dev K, Koren, Mark, Arbuckle, Chris J, Townsend, Colin R
Format: Article
Language:English
Subjects:
Agricultural development
Animals
Catchments
Creeks & streams
Environmental Health
Environmental management
Ephemeroptera
Fresh Water
Freshwater
Geologic Sediments
Grasslands
Invertebrates
Land use
Macroinvertebrates
Nutrient concentrations
Pasture
Physicochemical properties
Plecoptera
Sediments
Species richness
Streambeds
Subsidies
Trichoptera
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Summary:When native grassland catchments are converted to pasture, the main effects on stream physicochemistry are usually related to increased nutrient concentrations and fine-sediment input. We predicted that increasing nutrient concentrations would produce a subsidy-stress response (where several ecological metrics first increase and then decrease at higher concentrations) and that increasing sediment cover of the streambed would produce a linear decline in stream health. We predicted that the net effect of agricultural development, estimated as percentage pastoral land cover, would have a nonlinear subsidy-stress or threshold pattern. In our suite of 21 New Zealand streams, epilithic algal biomass and invertebrate density and biomass were higher in catchments with a higher proportion of pastoral land cover, responding mainly to increased nutrient concentration. Invertebrate species richness had a linear, negative relationship with fine-sediment cover but was unrelated to nutrients or pastoral land cover. In accord with our predictions, several invertebrate stream health metrics (Ephemeroptera-Plecoptera-Trichoptera density and richness, New Zealand Macroinvertebrate Community Index, and percent abundance of noninsect taxa) had nonlinear relationships with pastoral land cover and nutrients. Most invertebrate health metrics usually had linear negative relationships with fine-sediment cover. In this region, stream health, as indicated by macroinvertebrates, primarily followed a subsidy-stress pattern with increasing pastoral development; management of these streams should focus on limiting development beyond the point where negative effects are seen.
ISSN:0364-152X
1432-1009
DOI:10.1007/s00267-005-0310-3