MULTISCALE INFLUENCES ON PHYSICAL AND CHEMICAL STREAM CONDITIONS ACROSS BLUE RIDGE LANDSCAPES¹

Abstract

Streams integrate biogeochemical processes operating at broad to local spatial scales and long term to short term time scales. Humans have extensively altered those processes in North America, with serious consequences for aquatic ecosystems. We collected data on Upper Tennessee River tributaries in North Carolina to: (1) compare landuse and landscape geomorphology with respect to their ability to explain variation in water quality, sedimentation measures, and large woody debris; (2) determine if landscape change over time contributed significantly to explaining present stream conditions; and (3) assess the importance of spatial scale in examining landuse influences on streams. Stream variables were related to both landuse and landscape geomorphology. Forest cover accounted for the most variation in nearly all models, supporting predictions of nutrient enrichment, thermal pollution, and sedimentation caused by landscape disturbance. Legacy effects from past catchment disturbance were apparent in sedimentation measures. Nitrogen and phosphorus concentrations, as well as stream temperature, were lower where riparian buffers had reforested. Models of stream physicochemistry fit better when predictors were catchment wide rather than more localized (i.e., within 2 km of a site). Cumulative impacts to streams due to changes in landuse must be managed from a watershed perspective with quantitative models that integrate across scales.

Stream temperature prediction in ungauged basins: review of recent approaches and description of a new physics-derived statistical model

“…For example, Tague et al (2007) used the geological aquifer type as a proxy for the presence or absence of groundwater infiltration. Similarly, Hrachowitz et al (2010) and Scott et al (2002) estimated riparian shading based on riparian forest coverage, computed over buffer areas of various widths and lengths around the streams. In the absence of such proxies, the model cannot represent some known processes and must concede some increase in its prediction error (Moore et al, 2013).…”

“…This approach was usually applied to average the land cover characteristics only, particularly forest coverage (e.g. Sponseller et al, 2001;Scott et al, 2002;Macedo et al, 2013;Segura et al, 2014), but also in some cases to average most of the predictor variables, including elevation or slope (Hrachowitz et al, 2010;Imholt et al, 2013). Other authors considered larger portions of the catchments as averaging areas, sometimes extending far beyond the riparian zone.…”

“…While some studies conclude that this area should have a length of about 1-4 km (Isaak et al, 2010;Hrachowitz et al, 2010;Chang and Psaris, 2013;Macedo et al, 2013), others tend to indicate that the catchment scale is the most appropriate one (Sponseller et al, 2001;Scott et al, 2002). Similarly, values between 30 and 200 m are assumed for the width of the riparian buffer affecting stream temperature at a given point (e.g.…”

“…Similarly, values between 30 and 200 m are assumed for the width of the riparian buffer affecting stream temperature at a given point (e.g. Jones et al, 2006;Scott et al, 2002;DeWeber and Wagner, 2014).…”

The importance of land use/land cover data in fish and mussel conservation planning

“…As has been observed for many aquatic systems in the eastern US (Jones et al, 1999;Scott et al, 2002;Singkran and Meixler, 2008), forest cover greatly influenced the aquatic fauna at all spatial scales. Within focal areas (e.g., reach buffer scale), our models indicate that conservation managers should aim at retaining at least 55% forest cover and highly limit agricultural and urban land uses.…”