BasinScale Consequences of Agricultural Land Use

Authors: J P Julian E H Stanley M W Doyle

Publish Date: 2008/09/03

Volume: 11, Issue: 7, Pages: 1091-1105

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Abstract

The emerging spatial scale of interest for fluvial ecosystem studies and applications is the river basin Although much focus has been directed toward habitat availability and nutrient cycling across the fluvial landscape light availability has received considerably less attention and has not been assessed quantitatively at the basinscale despite it being the primary energy source for aquatic ecosystems We developed a basinscale light availability model that couples readily available broad spatial data with easily measured synoptic data using a GIS framework and the principles of hydraulic geometry We used this model to i quantify benthic light availability E bed along a 160km river in central Wisconsin USA ii predict gross primary production GPP along the same river and iii assess the effects of agricultural land use on E bed and GPP Overall E bed decreased in the downstream direction due primarily to increased turbidity and there was considerable local variation caused by changes in topography riparian vegetation and channel orientation These local variations in E bed caused GPP to fluctuate greatly over short distances as much as 21 g C m−2 d−1 over 260 m When summed over the entire channel length presentday postagricultural GPP 635 kg C d−1 was about eight times lower than estimated preagricultural GPP 4992 kg C d−1 Model simulations revealed that agricultural land use can cause an order of magnitude change in GPP reduce or increase intersectional variability in GPP and significantly alter broad spatial trends in GPP Our basinscale benthic light availability model is a tool that researchers can use to investigate relationships between light availability and ecosystem processes at broad spatial scales and also one that practitioners can use for more holistic fluvial ecosystem assessmentsJ P Julian conceived and designed the study performed the research analyzed the data and wrote the manuscript E H Stanley helped design the study assisted with writing and contributed editorial input M W Doyle helped design the study and contributed editorial inputThe project was supported by the National Research Initiative of the USDA Cooperative State Research Education and Extension Service CSREES grant 20043510214793 Steve Powers and Ryan Kroiss assisted with field and laboratory work This manuscript also benefited from the comments of two anonymous reviewers

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