CONNECTIVITY OF STREAMS AND WETLANDS TO DOWNSTREAM WATERS: AN INTEGRATED SYSTEMS FRAMEWORK.

Interest in connectivity has increased in the aquatic sciences, partly because of its relevance to the Clean Water Act. This paper has two objectives: (1) provide a framework to understand hydrological, chemical, and biological connectivity, focusing on how headwater streams and wetlands connect to and contribute to rivers; and (2) review methods to quantify hydrological and chemical connectivity. Streams and wetlands affect river structure and function by altering material and biological fluxes to the river; this depends on two factors: (1) functions within streams and wetlands that affect material fluxes; and (2) connectivity (or isolation) from streams and wetlands to rivers that allows (or prevents) material transport between systems. Connectivity can be described in terms of frequency, magnitude, duration, timing, and rate of change. It results from physical characteristics of a system, e.g., climate, soils, geology, topography, and the spatial distribution of aquatic components. Biological connectivity is also affected by traits and behavior of the biota. Connectivity can be altered by human impacts, often in complex ways. Because of variability in these factors, connectivity is not constant but varies over time and space. Connectivity can be quantified with field-based methods, modeling, and remote sensing. Further studies using these methods are needed to classify and quantify connectivity of aquatic ecosystems and to understand how impacts affect connectivity.

Validation of rapid assessment methods to determine streamflow duration classes in the Pacific Northwest, USA.

United States Supreme Court rulings have created uncertainty regarding U.S. Clean Water Act (CWA) authority over certain waters, and established new data and analytical requirements for determining CWA jurisdiction. Thus, rapid assessment methods are needed that can differentiate between ephemeral, intermittent, and perennial streams. We report on the validation of several methods. The first (Interim Method) was developed through best professional judgment (BPJ); an alternative (Revised Method) resulted from statistical analysis. We tested the Interim Method on 178 study reaches in Oregon, and constructed the Revised Method based on statistical analysis of the Oregon data. Next, we evaluated the regional applicability of the methods on 86 study reaches across a variety of hydrologic landscapes in Washington and Idaho. During the second phase, we also compared the Revised Method with a similar approach (Combined Method) based on combined field data from Oregon, Washington, and Idaho. We further compared field-based methods with a GIS-based approach (GIS Method) that used the National Hydrography Dataset and a synthetic stream network. Evaluations of all methods compared results with actual streamflow duration classes. The Revised Method correctly determined known streamflow duration 83.9% of the time, versus 62.3% accuracy of the Interim Method and 43.6% accuracy for the GIS-based approach. The Combined Method did not significantly outperform the Revised Method. Analysis showed biological indicators most accurately discriminate streamflow duration classes. While BPJ established a testable hypothesis, this study illustrates the importance of quantitative field testing of rapid assessment methods. Results support a consistent method applicable across the Pacific Northwest.

Spatial and temporal patterns of dissolved nitrogen and phosphorus in surface waters of a multi-land use basin.

Research on relationships between dissolved nutrients and land-use at the watershed scale is a high priority for protecting surface water quality. We measured dissolved nitrogen (DN) and ortho-phosphorus (P) along 130 km of the Calapooia River (Oregon, USA) and 44 of its sub-basins for 3 years to test for associations with land-use. Nutrient concentrations were analyzed for spatial and seasonal patterns and for relationships with land-use and stream discharge. Ortho-P and DN were higher in lower-elevation sub-basins dominated by poorly drained soils and agricultural production compared with higher-elevation sub-basins dominated by well-drained soils and forests. Eight lower basins had at least one sample period with nitrate-N > 10 mg L(-1). The Calapooia River had lower concentrations of dissolved nutrients compared with lower sub-basins, often by an order of magnitude. Dissolved organic N represented a greater proportion of DN in the upper forested sub-basins. Seasonal nutrient concentrations had strong positive correlations to the percent of a sub-basin that was managed for agriculture in all seasons (p values ≤ 0.019) except summer. Results suggest that agricultural lands are contributing to stream nutrient concentrations. However, poorly drained soils in agricultural areas may also contribute to the strong relationships that we found between dissolved nutrients and agriculture.

Surface water and groundwater nitrogen dynamics in a well drained riparian forest within a poorly drained agricultural landscape.

The effectiveness of riparian zones in mitigating nutrient in ground and surface water depends on the climate, management, and hydrogeomorphology of a site. The purpose of this study was to determine the efficacy of a well drained, mixed-deciduous riparian forest to buffer a river from N originating from a poorly drained grass seed cropping system. The study site was adjacent to the Calapooia River in the Willamette Valley, Oregon. Water was found to move from the rapid drainage of swale surface water. During winter hydrological events, the riparian forest also received river water. Low nitrate (NO3-) concentrations (0.2-0.4 mg NO3- -NL(-1)) in the shallow groundwater of the cropping system were associated with low rates of mineralization and nitrification (33 kg N ha(-1) yr(-1)) and high grass seed crop uptake of N (155 kg N ha(-1) yr(-1)). The riparian forest soil had higher rates of mineralization (117 kg N ha(-1) yr(-1)) that produced quantities of soil N that were within the range of literature values for plant uptake, leading to relatively low concentrations of shallow groundwater NO3 (0.6-1.8 mg NO3- -NL(-1)). The swale that dissected the cropping system and riparian area was found to have the highest rates of denitrification and to contribute dissolved organic C to the river. Given the dynamic nature of the hydrology of the Calapooia River study site, data suggest that the riparian forest plays a role not only in reducing export of NO3- from the cropping system to the river but also in processing nutrients from river water.

Nitrate-nitrogen, land use/land cover, and soil drainage associations at multiple spatial scales.

Managing non-point-source pollution of water requires knowledge of land use/land cover (LULC) influences at altering watershed scales. To gain improved understanding of relationships among LULC, soil drainage, and dissolved nitrate-N dynamics within the Calapooia River Basin in western Oregon, we selected 44 watersheds ranging in size between 3 and 33 km(2) for monthly synoptic sampling of surface water quality between October 2003 and September 2004. Seasonal associations were examined between dissolved nitrate-N and proportion of woody vegetation or poorly drained soils at differing scales (10, 20, 30, 60, 90, 150, 300 m, and entire watershed), which we defined as influence zones (IZs), surrounding stream networks. Correlations between nitrate-N and proportion woody vegetation or poorly drained soil at each IZ were analyzed for differences using the Hotelling-Williams test. We observed negative correlations (r = -0.81 to -0.94) between nitrate-N and proportion of woody vegetation during winter and spring. Poorly drained soils had positive correlations (r = 0.63-0.87) with nitrate-N. Altering the scale of analysis significantly changed correlations between nitrate-N and woody vegetation, with IZs <150 m being stronger than the watershed scale during winter. However, absolute differences in correlation values were small, indicating minimal ecological consequence for significant differences among scales. In contrast, nitrate-N correlations with poorly drained soil were stronger at the watershed scale than the 10- through 90-m IZs during winter and spring, and absolute differences were sufficient to suggest that scale is ecologically important when determining associations between dissolved nitrate-N and poorly drained soils.