Characteristics of connectivity between harvested landscapes and fixed-width riparian buffers

Abstract

Fixed-width riparian buffers are a common best management policy enforced in forested landscapes on first and higher order streams. These buffer areas are delineated along stream banks in the field, based on the presence of flowing water. However the presence of ephemeral streams may affect the connectivity of harvested lands to riparian buffers. We sought to understand the influence of ephemeral streams, determined from terrain analysis, on fixed-width riparian buffers. The objectives were to: (1) use LiDAR data and spatially explicit analysis tools to establish the affect of ephemeral streams on buffer efficacy; (2) determine the effect of the location and size of cut-blocks in relation to the presence of a fixed-width riparian buffer; (3) demonstrate that fixed-width riparian buffers are an ineffective management practice for trapping sediments generated in harvested landscapes. The inclusion of high resolution terrain data in the evaluation of riparian buffers: decreased the estimates of the connectivity to harvested lands, the sensitivity of the distribution of cut-blocks on that connectivity and the overall efficacy of fixed-width buffers along first order streams. The inclusion of un-forested ephemeral streams: (i) reduced the area of harvested lands in which flow-paths were directly connected to a riparian buffer and (ii) identified areas within the fixed-width that were isolated from the majority of flow-paths from harvested lands. Finally, the flow-path analysis led to reduced estimates of riparian flow-path length, and the ratio of buffer area to upslope area. It also became evident that when all forested areas were included in the flow-path analysis, watersheds with a fixed-width riparian buffer or cut-to-shore were indistinguishable. Because previous studies on the effectiveness of riparian buffers were based on 1st and higher order streams, the majority of the harvested lands were likely isolated in terms of surface runoff from the riparian buffer area studied. This thesis presents a case study of four watersheds to illustrate that the inclusion of high-resolution terrain data with a topographic flow-path analysis will provide valuable insight on use of fixed-width riparian buffers to mitigate non-point source pollutants from harvested lands.