Intensification of brown color in surface waters has been observed over several decades in many areas. We examined a 64‐yr daily record (1947–2010) of visual water color, a measure of chromophoric dissolved organic matter (CDOM), in the Mississippi River at Minneapolis, Minnesota. Although no monotonic trends in daily or mean annual color were evident, our analyses revealed trends in seasonal metrics, for example, mean winter...

Longitudinal changes in the structure and function of river ecosystems have long been recognized, yet our understanding of how such patterns shape elemental cycles remains limited. In particular, while benthic fine particulate organic matter (POM, 0.7–1000 μm) may control many stream nutrient cycles, less is known about longitudinal patterns or controls of benthic POM‐associated nutrient uptake. We conducted a survey of benthi...

Radiocarbon natural abundance (Δ 14 C) has emerged as a useful dietary tracer in freshwater ecology for the past decade, yet its applicability for separating aquatic and terrestrial resources has not been examined quantitatively. Here, we report Δ 14 C values of stream invertebrates in different functional feeding groups collected from the upper South Fork Eel River watershed, northern California. We found that algae‐grazing i...

The circumpolar expansion of woody deciduous shrubs in arctic tundra alters key ecosystem properties including carbon balance and hydrology. However, landscape‐scale patterns and drivers of shrub expansion remain poorly understood, inhibiting accurate incorporation of shrub effects into climate models. Here, we use dendroecology to elucidate the role of soil moisture in modifying the relationship between climate and growth for...

Stream and river carbon dioxide emissions are an important component of the global carbon cycle. Methane emissions from streams could also contribute to regional or global greenhouse gas cycling, but there are relatively few data regarding stream and river methane emissions. Furthermore, the available data do not typically include the ebullitive (bubble‐mediated) pathway, instead focusing on emission of dissolved methane by di...

Recent discoveries have altered prevailing paradigms concerning the conditions under which nitrification takes place and the organisms responsible for nitrification in aquatic ecosystems. In Lake Superior, nitrate () concentrations have increased fivefold in the past century. Although previous evidence indicated that most is generated by nitrification within the lake, important questions remain concerning the magnitude and con...

Photodegradation is an important sink for highly toxic methylmercury (MeHg) in aquatic ecosystems. Lakes have been extensively studied for MeHg photodegradation, but much less is known about streams, mainly because of the heterogeneity in sunlight availability along stream reaches and because there has been a lack of tools with which to integrate this longitudinal variability. We utilize odd‐mass anomalies of stable Hg isotope...

Spatial and temporal variations in stable carbon isotope ratios (i.e., δ 13 C) of primary producers are common but poorly understood features of isotopic characterizations of aquatic food webs. I investigated factors that control δ 13 C of algae (concentration and δ 13 C of inorganic carbon, algal fractionation, and growth rates) in riffle habitats across a gradient in stream size and productivity in northern California. There...

We used variation in algal d 13 C between river habitats to study the spatial scale of energy flow through river food webs. We found a strong negative relationship between herbivore d 13 C (which reflects algal d 13 C) and water velocity in three productive Northern California rivers but not in unproductive streams. The contrast among habitats suggests that water velocity affects algal d 13 C most strongly when CO2 availabilit...