Land use/land cover and scale influences on in‐stream nitrogen uptake kinetics

Abstract

[1] Land use/land cover change often leads to increased nutrient loading to streams; however, its influence on stream ecosystem nutrient transport remains poorly understood. Given the deleterious impacts elevated nutrient loading can have on aquatic ecosystems, it is imperative to improve understanding of nutrient retention capacities across stream scales and watershed development gradients. We performed 17 nutrient addition experiments on six streams across the West Fork Gallatin Watershed, Montana, USA, to quantify nitrogen uptake kinetics and retention dynamics across stream sizes (first to fourth order) and along a watershed development gradient. We observed that stream nitrogen (N) uptake kinetics and spiraling parameters varied across streams of different development intensity and scale. In more developed watersheds we observed a fertilization affect. This fertilization affect was evident as increased ash-free dry mass, chlorophyll a, and ambient and maximum uptake rates in developed as compared to undeveloped streams. Ash-free dry mass, chlorophyll a, and the number of structures in a subwatershed were significantly correlated to nutrient spiraling and kinetic parameters, while ambient and average annual N concentrations were not. Additionally, increased maximum uptake capacities in developed streams contributed to low in-stream nutrient concentrations during the growing season, and helped maintain watershed export at low levels during base flow. Our results indicate that land use/land cover change can enhance in-stream uptake of limiting nutrients and highlight the need for improved understanding of the watershed dynamics that control nutrient export across scales and development intensities for mitigation and protection of aquatic ecosystems.Citation: Covino, T., B. McGlynn, and R. McNamara (2012), Land use/land cover and scale influences on in-stream nitrogen uptake kinetics,

DOC:NO3− ratios and NO3− uptake in forested headwater streams

“…Our ambient V f values ranged between 0.05 and 12.65 mm/min and coincide with values reported in earlier studies (0.0001 to 54 mm/min) [e.g., Ensign and Doyle , ; O'Brien et al ., ; Mulholland et al ., ; Hall et al ., ; Hoellein et al ., ]. Our values also agree but fall within the lower range of values reported by other studies using the TASCC method [ Covino et al ., , ; Arce et al ., ; Wollheim et al ., ; Gibson et al ., ] with ambient V f values ranging between 0.10 and 39.4 mm/min. Our ambient areal uptake ( U ) values (0.0012 and 0.912 µg m −2 min −1 ) are within the lower end of earlier studies (0.007–75,000 µg m −2 min −1 ) [e.g., Ensign and Doyle , ; O'Brien et al ., ; Mulholland et al ., ; Hall et al ., ; Rasmussen et al ., ; Sudduth et al ., ] as well as other TASCC studies (2.36–28,920 µg m −2 min −1 ) [ Arce et al ., ; Wollheim et al ., ] .…”

Hydrologic connectivity as a framework for understanding biogeochemical flux through watersheds and along fluvial networks

“…This loading occurs along lateral hydrologic connections via overland flow, GW flow, or subsurface flow through tile drains. As N concentrations in the stream network increase, the efficiency with which the aquatic ecosystem retains N decreases (Covino et al, 2012), and the system becomes leaky with respect to that nutrient Mulholland et al, 2002). The unfortunate result of this progression is that as the system becomes increasingly inefficient it retains a decreasing fraction of an increasing load.…”

Quantifying ambient nitrogen uptake and functional relationships of uptake versus concentration in streams: a comparison of stable isotope, pulse, and plateau approaches

“…The [Br -] was measured using an ion-selective probe at the downstream end of the stream reach and dictated the timing of sample collection. Water samples were collected across the full range of the [Br -] BTC (Covino et al 2012), with more intense sampling occurring when [Br -] began to change rapidly (i.e. leading edge through the rapid decline following the peak).…”