Linking Watershed Drivers and Stream Responses at Various Scales Using Emerging Instream Sensors

Abstract:

Robust inferences of controls on aquatic processes necessitate data that capture temporal variations in multiple solutes that result from drivers acting at different scales. Emerging in situ sensors provide powerful tools to enumerate seasonal to sub-daily variation in water chemistry and flow. We employed a novel suite of such sensors in two coastal plain blackwater streams to collect high resolution data (sub-hourly to sub-daily) on flow, nitrate, soluble reactive phosphorus (SRP), colored dissolved organic matter (CDOM), turbidity, dissolved oxygen, pH, and specific conductance. Together these data are documenting baseline behavior (e.g., nutrient loading, metabolism) in a paired watershed study to isolate forest fertilization effects from natural variation. Baseline data clearly point to natural controls ranging from weather patterns to diurnal processes. Strong relationships between daily concentration and flow (C-Q) exist for most parameters and identify natural enrichment (e.g., CDOM) and dilution (e.g., SRP) processes controlling different solutes. Sub-daily, event-driven C-Q relationships are also evident; these relationships can markedly deviate from those at coarser time scales and often exhibit clear hysteresis. The forms of hysteresis loops vary across solutes, storm characteristics, and antecedent conditions, and can be used to characterize spatial (e.g., vadose vs. groundwater) and temporal (e.g., antecedent watershed wetness) drivers of solute source dynamics. These data provide information across a suite of parameters and at temporal scales otherwise not possible, which together can better elucidate stream responses (water chemistry, metabolism, hydrology) to natural and anthropogenic drivers.