Precipitation control over inorganic nitrogen import–export budgets across watersheds: a synthesis of long‐term ecological research

Abstract

We investigated long-term and seasonal patterns of N imports and exports, as well as patterns following climate perturbations, across biomes using data from 15 watersheds from nine Long-Term Ecological Research (LTER) sites in North America. Mean dissolved inorganic nitrogen (DIN) import-export budgets (N import via precipitation-N export via stream flow) for common years across all watersheds was highly variable, ranging from a net loss of 0Ð17 š 0Ð09 kg N ha 1 mo 1 to net retention of 0Ð68 š 0Ð08 kg N ha 1 mo 1 . The net retention of DIN decreased (smaller import-export budget) with increasing precipitation, as well as with increasing variation in precipitation during the winter, spring, and fall. Averaged across all seasons, net DIN retention decreased as the coefficient of variation (CV) in precipitation increased across all sites (r 2 D 0Ð48, p D 0Ð005). This trend was made stronger when the disturbed watersheds were withheld from the analysis (r 2 D 0Ð80, p < 0Ð001, n D 11). Thus, DIN exports were either similar to or exceeded imports in the tropical, boreal, and wet coniferous watersheds, whereas imports exceeded exports in temperate deciduous watersheds. In general, forest harvesting, hurricanes, or floods corresponded with periods of increased DIN exports relative to imports. Periods when water throughput within a watershed was likely to be lower (i.e. low snow pack or El Niño years) corresponded with decreased DIN exports relative to imports. These data provide a basis for ranking diverse sites in terms of their ability to retain DIN in the context of changing precipitation regimes likely to occur in the future.

Nitrogen Leaching of Two Forest Ecosystems in a Karst Watershed

“…5). This general pattern is similar to most forested catchments in temperate regions (Kane et al 2008). Low NO 3 − output rates and high N retention during winter months (Judd et al 2007) followed by elevated NO 3 − leaching during snow melt (Ohte et al 2004;Piatek et al 2005) have been reported from other temperate forests.…”

“…Nitrate release from undisturbed forests typically shows seasonal patterns that can be related to climatic and biological processes with seasonal behavior. One such climatic process is snow melt during spring, which promotes high N leaching in most catchments (Kane et al 2008;Ohte et al 2004;Piatek et al 2005). Another process is the N immobilization by microorganisms and its uptake by plants, which follows the pronounced seasonality of temperature and humidity in temperate forests.…”

“…Transport of N through an ecosystem is primarily controlled by hydrology (Kane et al 2008). The dominant runoff process in karstified watersheds is internal runoff (also called "direct runoff"), i.e., water from the vadose zone infiltrates directly into the karst conduits from points breaking the epikarst or through the epikarst (for a detailed description of karst systems, see, e.g., Bakalowicz 2005;Pinault et al 2001).…”

Alder cover drives nitrogen availability in Kenai lowland headwater streams, Alaska

“…Studies examining seasonal changes in stream N concentrations have found that precipitation (Bechtold et al 2003;Stieglitz et al 2003;Kane et al 2008) and precipitation variability (Kane et al 2008) both influence stream N through mobilization of nutrients from watersheds to streams. Watershed area and discharge are also related to increased stream N as larger watersheds experiencing larger flow regimes can more easily transport terrestrial nutrients (Creed and Band 1998;Schaefer et al 2009).…”

Is Biomass Accumulation in Forests an Option to Prevent Climate Change Induced Increases in Nitrate Concentrations in the North German Lowland?

“…We chose somewhat higher values between 0.96 and 0.99, assuming that the N leaching is less pronounced in regions with relatively low rainfall (cf. Chapter 2.1) [68].…”