Effects of hydrogeomorphic region, catchment storage and mature forest on baseflow and snowmelt stream water quality in second‐order Lake Superior Basin tributaries

Abstract

SUMMARY 1. In this study we predict stream sensitivity to non‐point source pollution based on the non‐linear responses of hydrological regimes and associated loadings of non‐point source pollutants to catchment properties. We assessed two hydrologically based thresholds of impairment, one for catchment storage (5–10%) and one for mature forest (<50% versus >60% of catchment in mature forest cover) across two different hydrogeomorphic regions within the Northern Lakes and Forest (NLF) ecoregion: the North Shore [predominantly within the North Shore Highlands Ecological Unit] and the South Shore (predominantly within the Lake Superior Clay Plain Ecological Unit). Water quality samples were collected and analysed during peak snowmelt and baseflow conditions from 24 second‐order streams grouped as follows: three in each region × catchment storage × mature forest class. 2. Water quality was affected by a combination of regional influences, catchment storage and mature forest. Regional differences were significant for suspended solids, phosphorus, nitrogen: phosphorus ratios, dissolved organic carbon (DOC) and alkalinity. Catchment storage was significantly correlated with dissolved silica during the early to mid‐growing season, and with DOC, specific conductance and alkalinity during all seasons. Total nitrogen and dissolved nitrogen were consistently less in low mature forest than in high mature forest catchments. Catchment storage interacted with the influence of mature forest for only two metrics: colour and the soluble inorganic nitrogen : phosphorus ratio. 3. Significant interaction terms (region by mature forest or region by storage) suggest differences in regional sensitivity for conductance, alkalinity, total organic carbon, and colour, as well as possible shifts in thresholds of impact across region or mature forest class. 4. Use of the NLF Ecoregion alone as a basis for setting regional water quality criteria would lead to the misinterpretation of reference condition and assessment of condition. There were pronounced differences in background water quality between the North and South Shore streams, particularly for parameters related to differences in soil parent material and glacial history. A stratified random sampling design for baseflow and snowmelt stream water quality based on both hydrogeomorphic region and catchment attributes improves assessments of both reference condition and differences in regional sensitivity.

Relationship of stream flow regime in the western Lake Superior basin to watershed type characteristics

“…In 1997(second-order streams) and 1998-1999, we randomly selected 24 watersheds in high and low mature forest classes along gradients of watershed storage within each hydrogeomorphic (HGM) region through a random-stratified process (Detenbeck et al, 2003 Table 1). Reaches were selected that had in-stream physical habitat, bank vegetation, and land-use characteristics typical of the stream segment/watershed of interest so that results might apply more broadly than to the specific reach sampled.…”

“…Runoff volume is likely to differ across North and South Shore regions mainly as a function of channel slope, which is generally greater in North Shore streams, rather than as a function of precipitation (with more frequent events in South Shore watersheds) or infiltration rates (highly variable on the South Shore; Detenbeck et al, 2003Detenbeck et al, , 2004. Coefficients of skewness can vary regionally either as a function of degree of skewness in the rainfall-depth frequency distribution, or of total watershed storage.…”

Nutrient Criteria Development With a Linked Modeling System: Methodology Development and Demonstration

“…Rather than modeling every water body in their territory, States and Tribes may choose to apply criteria developed based upon such a reach-specific analysis to all water bodies that are deemed to be sufficiently similar to the reach in question. Such a decision may be based upon results of water body vulnerability classifications such as those developed by Detenbeck et al (2003), as well as related cluster analyses currently being developed by EPA's Office of Research and Development to assess the vulnerability of watersheds of various sizes in EPA's Region 5, which includes Minnesota.…”

A Comparison of Nebraska Reservoir Classes Estimated from Watershed-Based Classification Models and Ecoregions

“…Additionally, previous research has shown that, although ecoregions such as those defined by Omernik, are useful for general ecosystem management and analyses, they do not adequately account for the inherent variations in stream and lake water quality (e.g. Van Sickle and Hughes, 2000;Severn et al, 2001;Winter, 1999;Jenerette et al, 2002;Detenbeck et al, 2003 and2004;Robertson and Saad, 2003).…”