Spatial Variation in Stream Water Quality in Relation to Riparian Buffer Dimensions in a Rural Watershed of Eastern New York State

Northeastern Naturalist, 2007 by Madden, Sean S, Robinson, George R, Arnason, John G

Abstract -

Studies of forested rural watersheds provide estimates of background contamination for comparison with streams and rivers in other settings. We performed a landscape analysis and measured major dissolved ions and benthic macroinvertebrates for a small rural watershed in Albany County, NY, to determine spatial variation in water quality. An estimated 73% of the surface cover is post-agricultural forest, with only 2.3% of the watershed covered by roads and other impervious surfaces. Although water quality was consistently high in most of the creek, we detected three relatively distinct zones separated by impoundments; zonation was most apparent in relative concentrations of major ions, less so with benthic macroinvertebrate community similarity. At ten sample stations, buffer size, measured as upstream land cover and distance to nearest road, did not correlate well with chemical water quality indicators. In particular, we found the highest levels of chloride, indicative of road-salt contamination, in areas of maximum forest buffer. Small feeder creeks that drain nearby roads may function as "leaks" in otherwise well-buffered watersheds with low road densities.

Introduction

Forested, rural watersheds supply much of the drinking water in the northeastern US, and also serve as reference study sites, useful for determining levels and effects of background contaminants, such as atmospheric pollution (e.g., Likens 2004). We studied the rural Ten Mile Creek watershed as a reference study area to examine relationships between riparian vegetation and water quality. In more urbanized regions, high levels of impervious surface cover are associated with degradation of stream water quality, and fine-scale variation can be detected in stream reaches with and without riparian buffers (Groffman et al. 2003, Paul and Meyer 2001, Roy et al. 2005, Walsh et al. 2005). However, even rural watersheds have the potential for spatial variability in water chemistry, in part because land cover in the region derives from a relatively fine-scale mosaic of land- and water-use history (Mladenoff et al. 1993, O'Neill et al. 1988). Rural streams also receive substantial amounts of non-point contamination, via atmospheric deposition, agricultural runoff, and highway deicing agents (Jones et al. 2000, Kaushal et al. 2005). With expanding incursions of urban fringes into rural lands throughout North America (Elvidge et al. 2004), impending land-cover change has prompted renewed interest in the buffering capacity of forest cover, driven by concerns for watershed conservation (Palmer et al. 2004, Theobald 2004).

A common expectation in watersheds of all land-cover types is that riparian buffer width is positively correlated with stream water quality (Castelle et al. 1994, Clausen et al. 2000, Correll 2000, Fischer et al. 2000, Spruill 2000). Riparian zones sequester sediments and non-point source pollutants, slow surface flow, stabilize stream banks, moderate stream temperatures, and serve as important denitrification sites (Correll 2000, Groffman et al. 2003). Low road densities and intact riparian forests are two of the characteristics that make rural watersheds attractive as reference sites, but anticipated landuse change may place greater demands on a reduced buffering capacity.

We tested for spatial variation present in this rural watershed by examining stream water chemistry and benthic macroinvertebrate diversity in comparison to riparian buffer size and surrounding land cover. In the process, we found significantly higher levels of chloride contamination in areas of maximum forest buffer width. In addition, concentrations of major dissolved ions revealed potential contamination not evident from biotic sampling.

Methods

Site description

The headwaters of Ten Mile Creek are located at approximately 600 m in elevation in the Partridge Run Wildlife Management Area of Albany County, NY. The creek flows south into Greene County, where it joins Catskill Creek, a major tributary of the Hudson River. The creek drains a predominately well-forested and post-agricultural watershed (57.7 km^sup 2^) with no current industrial point sources or urban land use. The watershed supports a low population density, but rural Albany County is projected to experience significant population growth and associated suburban development within the next ten years (Capital District Regional Planning Commission 2005). The study area comprises the uppermost 10 km of creek, draining 26.9 km2 of the watershed where most of the creek is bordered by the 75-year-old Edmund Niles Huyck Preserve and Biological Research Station (http://www.huyckpreserve.org/). Within the study area, the creek passes through two impoundments-Lincoln Pond (4 ha) and Lake Myosotis (44 ha)-and the Hamlet of Rensselaerville, which receives drinking water from the latter impoundment.

In the study area, the bedrock geology consists of sandstones, siltstones, and shales of the Lower Hamilton Group. Surficial geology consists of thin (