[1] Over the past 3 decades, nutrient spiraling has become a unifying paradigm for stream biogeochemical research. This paper presents (1) a quantitative synthesis of the nutrient spiraling literature and (2) application of these data to elucidate trends in nutrient spiraling within stream networks. Results are based on 404 individual experiments on ammonium (NH 4 ), nitrate (NO 3 ), and phosphate (PO 4 ) from 52 published studies. Sixty-nine percent of the experiments were performed in first-and second-order streams, and 31% were performed in third-to fifth-order streams. Uptake lengths, S w , of NH 4 (median = 86 m) and PO 4 (median = 96 m) were significantly different (a = 0.05) than NO 3 (median = 236 m). Areal uptake rates of NH 4 (median = 28 mg m À2 min À1 ) were significantly different than NO 3 and PO 4 (median = 15 and 14 mg m À2 min À1 , respectively). There were significant differences among NH 4 , NO 3 , and PO 4 uptake velocity (median = 5, 1, and 2 mm min À1 , respectively). Correlation analysis results were equivocal on the effect of transient storage on nutrient spiraling. Application of these data to a stream network model showed that recycling (defined here as stream length Ä S w ) of NH 4 and NO 3 generally increased with stream order, while PO 4 recycling remained constant along a first-to fifth-order stream gradient. Within this hypothetical stream network, cumulative NH 4 uptake decreased slightly with stream order, while cumulative NO 3 and PO 4 uptake increased with stream order. These data suggest the importance of larger rivers to nutrient spiraling and the need to consider how stream networks affect nutrient flux between terrestrial and marine ecosystems.

We examined the effect of in-channel flow obstructions such as vegetation and coarse woody debris (CWD) on transient storage and nutrient uptake by using experimental channel manipulations. Transient storage and nutrient uptake were measured under existing conditions in a vegetated agricultural stream and a shaded blackwater stream, and measurements were repeated after removal of vegetation and CWD. Removal of vegetation and CWD decreased transient storage area (A s ) by 61% and 43% in the agricultural and blackwater streams, respectively, and decreased the portion of median travel time owing to transient storage (F med ) by 45% and 56%, respectively. Flow baffles were then added to create in-channel transient storage in both streams. Baffles increased A s 227% and 119% for the agricultural and blackwater streams, respectively, and increased F med 309% and 132%, respectively. Ammonium and PO 4 uptake for the blackwater stream, determined by using nutrient addition experiments and expressed as the mass transfer coefficient (V f ), decreased after CWD removal by 88% and 38%, respectively. Ammonium V f in the blackwater stream increased 143-fold after baffles were installed, and PO 4 V f increased from Ϫ1.7 to 53 mm min Ϫ1 . Nutrient uptake rates were not calculated for the agricultural stream because sediment disturbance inadvertently altered the sediment-water column nutrient equilibrium. Results from both streams demonstrate that in-channel transient storage, rather than hyporheic storage, can be a substantial portion of overall transient storage in streams. In-channel transient storage influenced nutrient uptake in a blackwater stream, although these results could not be corroborated with data from the agricultural stream.

Water quality data at 12 sites within an urban, a suburban, and a rural stream were collected contemporaneously during four wet and eight dry periods. The urban stream yielded the highest biochemical oxygen demand (BOD), orthophosphate, total suspended sediment (TSS), and surfactant concentrations, while the most rural stream yielded the highest total organic carbon concentrations. Percent watershed development and percent impervious surface coverage were strongly correlated with BOD (biochemical oxygen demand), orthophosphate, and surfactant concentrations but negatively with total organic carbon. Excessive fecal coliform abundance most frequently occurred in the most urbanized catchments. Fecal coliform bacteria, TSS, turbidity, orthophosphate, total phosphorus, and BOD were significantly higher during rain events compared to nonrain periods. Total rainfall preceding sampling was positively correlated with turbidity, TSS, BOD, total phosphorus, and fecal coliform bacteria concentrations. Turbidity and TSS were positively correlated with phosphorus, fecal coliform bacteria, BOD, and chlorophyll a, which argues for better sedimentation controls under all landscape types.

Carbon (C) standing stocks, C mass balance, and soil C burial in tidal freshwater forested wetlands (TFFW) and TFFW transitioning to low‐salinity marshes along the upper estuary are not typically included in “blue carbon” accounting, but may represent a significant C sink. Results from two salinity transects along the tidal Waccamaw and Savannah rivers of the U.S. Atlantic Coast show that total C standing stocks were 322–1,264 Mg C/ha among all sites, generally shifting to greater soil storage as salinity increased. Carbon mass balance inputs (litterfall, woody growth, herbaceous growth, root growth, and surface accumulation) minus C outputs (surface litter and root decomposition, gaseous C) over a period of up to 11 years were 340–900 g C · m−2 · year−1. Soil C burial was variable (7–337 g C · m−2 · year−1), and lateral C export was estimated as C mass balance minus soil C burial as 267–849 g C · m−2 · year−1. This represents a large amount of C export to support aquatic biogeochemical transformations. Despite reduced C persistence within emergent vegetation, decomposition of organic matter, and higher lateral C export, total C storage increased as forests converted to marsh with salinization. These tidal river wetlands exhibited high N mineralization in salinity‐stressed forested sites and considerable P mineralization in low‐salinity marshes. Large C standing stocks and rates of C sequestration suggest that TFFW and oligohaline marshes are considerably important globally to coastal C dynamics and in facilitating energy transformations in areas of the world in which they occur.