Abstract Agricultural development of native grasslands may change stream physico-chemistry in ways that provide both subsidies and stresses to the system. The aims of this study were to determine: (1) which physico-chemical parameters respond most strongly to agricultural development; (2) how biodiversity, community composition, and food-web structure responded to these changes; and (3) to determine the balance between negative and positive impacts of these subsidies and stresses based on the analysis of 18 headwater streams. Developed pasture streams had increased nutrient loading, alterations to streamside vegetation, increased fine sediment composition, and lower moss coverage of streambeds than undeveloped or lightly grazed native grassland catchments (which could not be distinguished from one another). These differences were associated with higher numbers of macroinvertebrate taxa and higher numbers of macroinvertebrates indicating that the net effects of these subsidies and stresses associated with agricultural development were positive within these headwater stream reaches.
Keywords nitrogen; phosphorus; water quality; land use; sediment; QMCI; tussock; pasture
M02055 Received 8 July 2002; accepted 3 February 2003; Published 20 June
2003
New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37:
389-403
0028-8330/03/3702-0389 $7.00 © The Royal Society of New Zealand
2003
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