Riparian Buffers:
A Way to Save Our Streams?
Riparian buffers are the complex environments existing directly adjacent to flowing water (Lowerance et al., 1985). These delicate environments can have a large impact on conservation and water quality. In addition to being important habitats for wildlife, riparian buffers can stabilize streambanks, store floodwaters, and remove contaminants from runoff (Wenger, 1999). The last function is of particular interest to Vermont, as high levels of phosphorous contamination has significantly impacted areas of Lake Champlain and solutions including riparian buffer restoration have been shown to reduce phosphorous concentration flowing into the lake (Meals and Hopkins, 2002).
This study examined the upper watershed of Ball Mountain Brook in southern Vermont near the Stratton ski resort in order to study the relationship between types of land cover in the riparian buffer and contaminants in the water, specifically nitrates and phosphorous. It was hypothesized that developed land and open fields would contribute to higher levels of contaminants in water, as opposed to forested land which would have lower, “normal” levels. Common sources of nitrates and phosphorous in river water include agricultural fertilizers, animal waste, septic fields, and leaking sewers, with agricultural areas causing a direct increase in nitrate and phosphorous levels (Wenger, 1999). Impervious surfaces in urban areas have also often been found to have negative effects on stream health (i.e. Sliva and Williams, 2001; Snyder et al., 2005) and lead to higher levels of suspended solids in rivers (Wenger, 1999). The study area also includes the ski trails and base area development of the Stratton ski resort; Wemple et al. found that ski area development in Vermont has led to increased suspended sediment and solute flux at the Stowe resort on Mount Mansfield (2007). Given that developed spaces and open spaces generally lead to lesser stream health, it was expected that riparian zones containing more area of these land cover types would have higher concentrations of nitrates and phosphorous.
Location of the Ball Mountain Brook Watershed
Methodology
1.
Watersheds were generated using ArcHydro tools. The watershed was selected for its location near ski resort development and water quality data availability. NAIP (National Agricultural Imagery Program) imagery from 2014 was clipped to the watershed.
NAIP 2014 (VGCI), EPA STORET
Results
There were no significant relationships found between the type of land cover and nitrate and phosphorous concentrations in the study area. Exploratory regression found that all variables had 0% significance with both of the dependent variables, except for open field cover and phosphate concentration, which had a significance of 15%. A least squares regression was run using these two variables, which found a coefficient of -0.007 and an adjusted R^2 value of -0.02, indicating that the amount of open field cover does not explain much the variation in phosphate concentration.
This is in contrast to the supposed hypothesis and supporting literature, which indicate possible relationships between land cover and contaminants. This could be explained due to limitations in the data and methodology. Only seven riparian zones had data for nitrates and phosphorous, leading to a very small sample size. Water quality sampling points were also not always downstream of the analyzed buffer as well, and therefore did not capture the nature of the discharge of the entire riparian zone. More data about suspended solids would have been useful, as ski area development has been shown to have a significant effect on suspended solid concentrations (Wemple et al., 2007), while increased nitrates and phosphate concentrations are more tied to agricultural land use (Wenger, 1999).
While land cover classification did a good job of identifying large features, such as ski trails or parking lots, there was ample comission of open field and development in the forest category. The grain size was likely too small for the size of the features, which could have led to some of the comission; for example, small patches of light-green forest facing the sun in the imagery were often classified as open field or even developed land cover. The extent size of the land cover classification (the watershed) was appropriate given the size of the buffers, especially before buffers lacking data were excluded. If more water quality data directly in the proximity of Stratton resort were available, then a study with a smaller extent focusing on the resort could be worth conducting.
Lastly, when analyzed through GIS methods water quality may have a better correlation with the land cover of the whole catchment, as opposed to only the land cover contained in riparian buffers (Sliva and Williams, 2001). While Sliva and Williams primarily considered a low-relief, urban area, as opposed to this study's high-relief, rural landscape, it is likely that the buffers used to simulate the riparian zones are not representative of the land cover actually included in each given catchment.
Management Implications
Given the lack of significant results, no specific management strategies can be suggested based on this study. However, previous literature suggests that more in-depth monitoring of the water quality (including suspended solids) in the Ball Mountain Brook watershed is worthwhile, especially in the area of Stratton resort. Riparian buffers have proven to lower pollutant and suspended solid concentrations in surface water in both agricultural areas (Wenger, 1999; Meals and Hopkins, 2001) as well as developed areas with impermeable surfaces (Wenger, 1999; Snyder et al., 2005). The open ski trails, paved parking lots, and residential resort development create conditions that can affect water quality in similar ways and should subsequently be managed using comparable techniques as their agricultural and urban counterparts. Vermont state officials and Stratton ownership could consider taking more measures to protect the health of local streams, although fortunately riparian buffers and minimizing runoff from impervious surfaces are currently included in the Stratton water quality remediation master plan (Therrien and Sky, 2013).
Works Cited
Lowrance, R., Leonard, R., & Sheridan, J. (1985). Managing riparian ecosystems to control nonpoint pollution. Journal of Soil and Water Conservation, 40(1), 87–91.
Meals, D. W., & Hopkins, R. B. (2002). Phosphorus reductions following riparian restoration in two agricultural watersheds in Vermont, USA. Water Science and Technology, 45(9), 51–60.
Sliva, L., & Dudley Williams, D. (2001). Buffer Zone versus Whole Catchment Approaches to Studying Land Use Impact on River Water Quality. Water Research, 35(14), 3462–3472.
Snyder, M. N., Goetz, S. J., & Wright, R. K. (2005). Stream Health Rankings Predicted by Satellite Derived Land Cover Metrics1. JAWRA Journal of the American Water Resources Association, 41(3), 659–677.
Therrien, J. A., & Sky, J. L. (2013, January 11). Stratton Water Quality Remediation Plan Status Update Pursuant to MP Renewal.
Wemple, B., Shanley, J., Denner, J., Ross, D., & Mills, K. (2007). Hydrology and water quality in two mountain basins of the northeastern US: assessing baseline conditions and effects of ski area development. Hydrological Processes, 21(12), 1639–1650.
Wenger, S. (1999). A review of the scientific literature on riparian buffer width, extent and vegetation. Athens, GA: Institute of Ecology, University of Georgia.