Over the past 30 plus years, the Arctic has warmed at a rate of 0.6°C per decade. This has resulted in considerable permafrost thaw and alterations of hydrological and biogeochemical processes. Coincident with these changes, recent studies document increases in annual fluxes of inorganic nutrients in larger Arctic rivers. Changing nutrient fluxes in Arctic rivers have been largely attributed to warming‐induced active layer expansion and newly exposed subsurface source areas. However, the ability of Arctic headwater streams to modulate inorganic nutrient patterns manifested in larger rivers remains unresolved. We evaluated environmental conditions, stream ecosystem metabolism, and nutrient uptake in three headwater streams of the Alaskan Arctic to quantify patterns of retention of inorganic nitrogen (N) and phosphorous (P). We observed elevated ambient nitrate‐N (NO3‐N) concentrations in late summer/early fall in two of three experimental stream reaches. We observed detectable increases in uptake as a result of nutrient addition in 88% of PO4‐P additions (
Soil nutrient distribution is heterogeneous in space and time, potentially altering nutrient acquisition by trees and microorganisms. Ecologists have distinguished “hot spots” (HSs) as areas with enhanced and sustained rates of nutrient fluxes relative to the surrounding soil matrix. We evaluated the spatial and temporal patterns in nutrient flux HSs in two mixed-conifer forest soils by repeatedly sampling the soil solution at the same spatial locations (horizontally and vertically) over multiple seasons and years using ion exchange resins incubated in situ. The climate of these forests is Mediterranean, with intense fall rains occurring following summers with little precipitation, and highly variable winter snowfall. Hot spots formed most often for NO3−and Na+. Although nutrient HSs often occurred in the same spatial location multiple times, HSs persisted more often for PO43−NH4+, and NO3−, and were more transient for Ca2+, Mg2+, and Na+. Sampling year (annual precipitation ranged from 558 to 1223 mm) impacted the occurrence of HSs for most nutrients, but season was only significant for PO43−, NH4+, NO3−, and Na+, with HSs forming more often after fall rains than after spring snowmelt. The frequency of HSs significantly decreased with soil depth for all nutrients, forming most commonly immediately below the surficial organic horizon. Although HSs accounted for less than 17% of the sampling volume, they were responsible for 56–88% of PO43−, NH4+, and NO3−resin fluxes. Our results suggest that macronutrient HSs have a disproportional contribution to soil biogeochemical structure, with implications for vegetation nutrient acquisition strategies and biogeochemical models.
- NSF-PAR ID:
- 10485737
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Biogeochemistry
- Volume:
- 167
- Issue:
- 1
- ISSN:
- 1573-515X
- Format(s):
- Medium: X Size: p. 75-95
- Size(s):
- ["p. 75-95"]
- Sponsoring Org:
- National Science Foundation
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