Landscape and Wetland Influences on Headwater Stream Chemistry in the Kenai Lowlands, Alaska

Headwater streams are typically closely connected with the surrounding watershed landscape, making them sensitive to local watershed conditions. Headwater streams of the Kenai Lowlands in Alaska provide important rearing habitat for juvenile salmon and other biota, and understanding the connections between surrounding landscapes and stream conditions will improve management capabilities. We conducted field evaluations of 30 headwater stream sites on the Kenai Lowlands of Alaska, stratified across watersheds and wetland types, and combined these results with GIS analysis of 12 landscape metrics. Flow-weighted slope (FWS), which is an indicator of the combined influence of percentage cover and topographic position of wetlands, was the best predictor of stream chemistry. Our results revealed distinct differences in water chemistry among headwaters that are largely driven by topography and the amount of wetland in the upstream drainage area. Streams with a high FWS (higher gradient, low wetness) had higher dissolved oxygen and dissolved inorganic nitrogen (mostly nitrate-N), and lower temperatures. Lower FWS streams (low gradient, high wetness) had higher dissolved organic carbon, temperatures, and ammonium and lower dissolved oxygen, all of which were consistent with strong connections between wetlands in watershed and headwater streams. The flow-weighted slope metric is a landscape feature that can be easily derived from GIS, and can be used as a spatially explicit approach for predicting landscape connections to headwater streams on the Kenai Lowlands.